Title of Invention

CONTINUOUS REFINING METHOD AND CONTINUOUS REFINING EQUIPMENT

Abstract

Abstract By setting the piece number of blades 16 of an impeller 10, a relation between a height bO of a base portion and a height bl of a tip portion of the blade 16, a relation between a width d of the blade 16 and a diameter (or width) of a hot metal flow passage, a relation between a maximum depth Z of the hot metal which flows in the hot metal flow passage and a distance hi from an upper end of a tip of the blade 16 to an upper surface of the hot metal, and a relation between a maximum depth Z of the hot metal which flows in the hot metal flow passage and a distance h2 from a lower end of the tip of the blade 16 to a deepest part of a bottom portion of the hot metal flow passage, a refining efficiency is improved while a desiliconization and a desulphurization can be stably performed without unevenness.

Full Text

SPECIFICATION CONTINUOUS REFINING METHOD AND CONTINUOUS REFINING EQUIPMENT Technical Field [0001] The present invention relates to a continuous refining method for continuously refining a hot metal and a continuous refining equipment thereof. Background Art [0002] Generally, a hot metal which is reduced in a blast furnace and tapped contains about 4.3% 4.6% of carbon (c) , about 0.09% -0.13% of phosphorus (P), in addition to about 0.3% - 0.7% silicon (Si) . In order to refine the hot metal to obtain a predetermined steel or the it is necessary to decrease carbon (C) and phosphorus (P) to predetermined concentrations. However, in view of a refining efficiency, before decarburization or dephosphorization, it is desirable to remove silicon (Si) and sulfur (S) to a concentration (for example, silicon (Si) 0.25%) as low as possible. [0003] Moreover, it is desirable to perform a desulfurization treatment at the halfway stage when the hot metal flows through a tap hole trough (which has a highest temperature immediately after a tap hole) from the blast furnace, because the desulfurization treatment is performed by a reduction reaction and is an endothermic reaction. [0004] The desiliconization treatment and the desulfurization treatment in the tap hole trough can be often performed by following three methods. According the first method, a refining agent, being accompanied by carrier gas such as nitrogen, air and the like, is injected into the tap hole trough by a lance. According the second method, the refining agent is made pass a head drop portion (which is arranged at the tap hole trough) after the refining agent is added to the upper surface of the hot metal. In this case, the energy of the fall of the hot metal is used. According to the third method, the refining agent is added at a part which is positioned immediately in front of a tilting portion (tilting runner) arranged at the tap hole trough. In this case, the energy of the fall of the hot metal which flows in sequence of the tap hole trough, the tilting runner and a hot metal ladle is used. [0005] However, the reaction efficiency of the first method is low, and the latent heat of the hot metal is snatched by injection gas so that the temperature of the hot metal is greatly lowered. Moreover, because an equipment related to the pressure sending of the refining agent powder is necessary, the equipment cost is high. According to - the second method, although there is a large merit in practical operation, that is, the slag removal after the treatment can be completed at a blast furnace casting floor. However, the reaction efficiency of the second method is relatively low as compared with the other methods. According to the third method, although the reaction efficiency is relatively high, it is necessary to arrange a free board because foaming of the slag is violent. Due to the foaming, a charge weight of the hot metal into, the hot metal ladle or a torpedo car is significantly reduced, and the productivity is decreased. Moreover, if the slag foams, the slag, together with the hot metal, will flow into the hot metal ladle or the torpedo car. Therefore, an additional slag removing device becomes necessary. [0006] The first and second method where the treatment is performed in the tap hole trough are profitable in view of heat and time, because slag-off in a subsequent process can be omitted. However, the first method and the second method are the processes which only depend on the mixing when continuously flowing through the tap hole trough. Therefore, the reaction efficiencies of the first method and the second method are low. [0007] Referring to PATENT REFERENCE 1, a method for a desulfurization treatment has been disclosed. In this case, a desulfurization agent is added to the hot metal which is housed in a ladle, and an impeller (agitation blade) is immerged in the hot metal and rotated. Thus, the desulfurization is performed. Referring to PATENT REFERENCE 2, a method for a desiliconization treatment has been disclosed. In this case a desiliconization reaction trough (tank) is arranged in a hot metal flow passage of the blast furnace casting floor. A desiliconization agent is added to the hot metal in a desiliconization transportation trough, and the hot metal is agitated by the impeller. Thus, the desiliconization is performed. [0008] Both of the desulfurization treatment and the desiliconization treatment which have been described above are methods where the hot metal is agitated by the impeller so that' the treatment is performed. In the desulfurization treatment, the hot metal is agitated in the state where the hot metal is housed in the ladle. On the other hand, in the desiliconization treatment, the hot metal which continuously flows in the hot metal flow passage of the blast furnace casting floor is agitated. That is different from the desulfurization treatment. Thus, it is relatively easy to perform the desulfurization treatment by evenly agitating the hot metal which is staying, like the desulfurization treatment described in PATENT REFERENCE 1. However, it is difficult to perform the desiliconization treatment or the desulfurization treatment by evenly agitating the hot metal which continuously flows by the impeller like the PATENT REFERENCE 2. In this case, the refining efficiency is low, and it is difficult to steadily perform the desulfurization and the desiliconization without unevenness. These problems occur from the scene. [0009] Moreover, according to the technology disclosed in PATENT REFERENCE 2, in order to increase the reaction efficiency, a desiliconization trough having a relatively big capacity is arranged, and the hot metal is stayed during some time in the desiliconization trough where a complete mixing is supposed so that the hot metal and the refining agent contact each other. However, in this case, the extra desiliconization trough is necessary, and it is not easy to ensure the arrangement space of the desiliconization trough. Moreover, the equipment cost will increase. [0010] According to PATENT REFERENCE 3, an agitation rod having a cylinder shape is arranged at an upstream side of a refining agent blowing-in nozzle and a side-wall side of the refining agent blowing-in nozzle, to guide the flow of the hot metal to the direction of the refining agent blowing-in nozzle. Thus, the contact between the hot metal and the refining agent is improved to increase the reaction efficiency. [0011] In the technology disclosed in PATENT REFERENCE 3, at the spot where the flow of the hot metal and the flow due to the agitation overlap each other, a part of the refining agent is not entrained into the hot metal and flows to the downstream side. Thus, the amount of the refining agent which does not participate in the reaction may increase. [0012] Referring to PATENT REFERENCE 4, a refining method is provided to compulsorily agitate the hot metal and the refining agent in the tilting runner of the blast furnace and entrain the refining agent into the hot metal, so as to perform the refining of the hot metal. As shown in PATENT REFERENCE 4, according to the method where the refining agent (desulfurization agent) is entrained into the hot metal by the agitation of the hot metal, a part of the refining agent (desulfurization agent) is not entrained into the hot metal to flow away. Therefore, there is the case where the refining agent which does participate in the reaction is much and the reaction efficiency is not satisfactory. Particularly, as shown in PATENT REFERENCE 4, the slag is generated in the desulfurization treatment, and gets mixed in a hot metal transfer ladle (for conveying' the hot metal) or the ladle or the like. Thus, a removal of the slag will ■ become necessary "in the subsequent process. Therefore, a loss in heat and that in time may occur. Moreover, according to PATENT REFERENCE 4, because the hot metal is agitated at the same part. the agitated hot metal only strikes on a certain part of the refractory material, so that the refractory member locally wears down. [0013] With reference to PATENT REFERENCE 5, the desulfurization treatment is performed by adding the desulfurization agent to the hot metal which is tapped from the blast furnace. According to this method for performing the desulfurization treatment, after the addition of the desulfurization agent to the hot metal which flows in a hot metal runner, the hot metal where the desulfurization agent has been added is made rapidly flow downward (fall) through a tilting wall so that the desulfurization is performed. [0014] With reference to PATENT REFERENCE 6, similarly to PATENT REFERENCE 5, the desulfurization treatment is performed by adding the desulfurization agent to the hot metal tapped from the blast furnace. According to this method for performing the desulfurization treatment, the hot metal runner in which the hot metal tapped from the blast furnace flows is divided into two parts. After the desulfurization agent is added to the hot metal which flows in the hot metal runner of the one side (upstream side), the hot metal where the desulfurization agent has been added is made fall to the hot metal runner of the other side (downstream side) . Thus, the desulfurization is performed. According to the desulfurization method of PATENT REFERENCE 6, when the hot metal is made fall to the hot metal runner of the downstream side, compressed air is blown .against this hot metal so that the desulfurization agent which has not reacted is drifted to the center of the agitation flow. [0015] As described in PATENT REFERENCE 5 and PATENT REFERENCE 6, according to the method where the desulfurization agent is added to the hot metal and the hot metal (where the desulfurization agent has been added) is made fall to entrain the desulfurization agent into the hot metal, there is the case where the agitation force applied to the hot metal is not sufficient and there is the case where the reaction efficiency is not satisfactory. Moreover, in PATENT REFERENCE 5 and PATENT REFERENCE 6, the conditions about the speed at which the hot metal is made fall and the like are not disclosed. Therefore, even when the method is embodied practically, the sufficient desulfurization cannot be obtained in fact. [0016] With reference to PATENT REFERENCE 7, a preliminary treatment device where a lance for injecting the refining agent (treatment agent) at the upper side of the blast furnace casting floor runner is arranged in the longitudinal direction of the runner. In this preliminary treatment device, the refining treatment is performed by immerging the lance (for injecting the refining agent) in the hot metal to blow the refining agent (together with carrier air) into the hot metal, or by positioning the lance (for injecting the refining agent) at the upper side of the hot metal to blow the refining agent together with carrier air. Moreover, in the preliminary treatment device, the refining agent is blown against or blown into the hot metal, while the lance for injecting the refining agent is moved. [0017] As described in PATENT REFERENCE 7, by moving the lance for injecting the refining agent when the refining of the hot metal is performed, the refractory material of the blast furnace casting floor runner can be restricted from locally wearing down due to the blowing-in of the refining agent. However, according to PATENT REFERENCE 7, although the refractory material can be restricted from wearing down, the moving range of the lance for injecting the refining agent is not prescribed at all. In this case, it is an actual situation that the reaction efficiency is low, [0018] With reference to PATENT REFERENCE 8, a preliminary treatment reaction trough is arranged at the downstream side of a skimmer of the blast furnace casting floor and the desulfurization agent is added to the hot metal in the preliminary treatment reaction trough, to perform the desulfurization treatment of the hot metal. According to the method of PATENT REFERENCE 8, the injection lance is immerged in such a manner that the injection lance faces the downstream side of the hot metal flow direction. The desulfurization is performed, while the desulfurization agent is blown in together with the carrier gas from the lance and while the lance is moved in the width direction of the preliminary treatment reaction trough and in the direction of the hot metal flow direction. [0019] Similarly to PATENT REFERENCE 7, in PATENT REFERENCE 8, because the injection lance is moved when the refining (desulfurization) of the hot metal is performed, the refractory material can be restricted from locally wearing down. However, the moving range of the injection is not prescribed at all. Similar to PATENT REFERENCE 7, there is the case where the reaction efficiency is low. [0020] Furthermore, the methods disclosed in PATENT REFERENCE 7 and PATENT REFERENCE 8 are injection means where the refining agent is blown into the hot metal by using the lance so as to refine the hot metal. According to these means, there is the case where the reaction efficiency is not satisfactory. PATENT REFERENCE 1: JP-B-45-31053 PATENT REFERENCE 2: JP-A-54-137420 PATENT REFERENCE 3: JP-A-62-2 02 011 PATENT REFERENCE 4: JP-A-63-105914 PATENT REFERENCE 5: JP-A-02-250912 PATENT REFERENCE 6: JP-B-50-33010 PATENT REFERENCE 7: JP-A-63-317611 PATENT REFERENCE 8: JP-A-04-052205 Disclosure of the Invention Problems to be Solved by the Invention [0021] In view of the above-described disadvantages, it is a first object of the present invention to provide a continuous refining method by which a refining efficiency is improved and a desiliconization and a desulfurization can be stably performed without unevenness. It is a second object of the present invention to provide a blast furnace casting floor equipment in which an efficiency of a refining treatment such as a desiliconization treatment and a desulfurization treatment and the like can be increased by substantially entraining a refining agent into a hot metal. It is a third object of the present invention to provide a continuous refining method of a blast furnace casting floor and a blast furnace casting floor equipment where a refractory material can be restricted from locally wearing down and the efficiency of the refining treatment can be increased when the refining treatment is performed. It is a fourth object of the present invention to provide a continuous refining method of a blast furnace casting floor where a high reaction efficiency can be obtained by substantially entraining the refining agent (which has been added) into the hot metal. Means for Solving the Problems [0022] In order to achieve the objects of the present invention, according to a first aspect of the present invention, a continuous refining method includes adding a refining agent to a hot metal which flows in a hot metal flow passage of a blast furnace casting floor, and mixing the hot metal with the refining agent by rotating an impeller which is iramerged in the hot metal to continuously refine the hot metal. In this case, a piece number of blades of the impeller which is immerged in the hot metal and rotated is set as three - six, and the blade is set to satisfy following formulas (1) and (2). The impeller is immerged in the hot metal in such a manner that following formulas (3) and (4) are satisfied. bO s bl ... (1) 0.2 0 0 wherein bO represents a height (m) of a base portion of the blade, bl represents a height (m) of a tip portion of the blade, d represents a width (m) of the blade, D represents a maximum width (m) of the hot metal flow passage, Z represents a maximum depth (m) of the hot metal which flows in the hot metal flow passage, hi represents a distance (m) from an upper end of the base portion of the blade to an upper surface of the hot metal, and h2 represents a distance (m) from a lower end of the base portion of the blade to a deepest part of a bottom portion of the hot metal flow passage. [0023] From various aspects, the inventors has verified a method where the refining efficiency in the desiliconization treatment or the desulfurization treatment is improved by evenly agitating the hot metal which flows in the hot metal flow passage of the blast furnace casting floor and the desiliconization and the desulfurization are stably performed without unevenness. [0024] Specifically, the multiple impellers which are respectively provided with different piece numbers of the impellers and different widths of the blade are manufactured, and the impellers are used to perform experiments of the desiliconization treatment and the desulfurization treatment while an immerging degree (a distance hi from an upper end of the base portion of the blade to the upper surface of the hot metal, a distance from a lower end of the base portion of the blade to the deepest part of the bottom portion of the hot metal flow passage) of the impeller to the hot metal is changed. As a result of the experiments, it has been found that the refining efficiency can be improved and the desiliconization treatment and the desulfurization treatment can be stably performed without unevenness even when continuously flowing in the hot metal flow passage, by setting the piece numJoer of the blades of the impeller (which is immerged in the hot metal and rotated) as three - six and setting the blade in such a manner that the formulas (1) and (2) are satisfied and setting the impeller in such a manner that the formulas (3) and (4) are satisfied. [0025] Preferably, the refining agent is a desiliconization agent, and the refining is the desiliconization where the hot metal and the desiliconization agent are mixed with each other to continuously remove silicon in the hot metal. [0026] According to a second aspect of the present invention, a continuous refining method of a blast furnace casting floor includes adding a refining agent to a hot metal which flows in a hot metal flow passage of the blast furnace casting floor, and mixing the hot metal with the refining agent by rotating an impeller which is immerged in the hot metal to continuously refine the hot metal. In this case, a step for making the hot metal fall is arranged in the hot metal flow passage and the impeller is arranged at a downstream side of the step. An adding position at which the refining agent is added is disposed at a downstream side of the impeller, and a position at which a slag generated after the hot metal is agitated by the impeller is removed is disposed at a downstream side of the adding position. The hot metal is refined, after a width of the impeller is set in such a manner that a following formula "(11) is satisfied, the step is set in such a manner that following formulas (12) - (14) are satisfied, the adding position at which the refining agent is added is set in such a manner that a following formula (15) is satisfied, and the position at which the slag is removed is set in such a manner that a following formula (16) is satisfied. 0.3 ^ d/D 0 H/Z > 1 ... (13) e a 30 ... (14) 0 1.2 s R/D s 5 ... (16 ) wherein d represents a width (m) of the impeller, D represents a maximum width (m) of the hot metal flow passage, L represents a distance (m) from the step to the impeller, H represents a height (m) of the step, Z represents a depth (m) of the hot metal, B represents a gradient (deg) of the step, M represents a distance (m) from a center of a rotation shaft of the impeller to the adding position, and R represents a distance (m) from the center of the rotation shaft of the impeller to the position at which the slag is removed. [0027] From various aspects, the inventors have verified a method where the efficiency of the refining treatment is improved by substantially entraining the refining agent into the hot metal. [0028] Specifically, the inventors focuses on the agitation of the hot metal by the impeller and the agitation of the hot metal by making the hot metal fall, and performs the experiments of the desiliconization treatment and the desulfurization treatment by changing the width of the impeller, the position of the step for making the hot metal fall, the height of the step, the gradient (incline angle) of the step, the adding position at which the refining agent is added, and a position at which the slag is removed to the position of the rotation shaft of the impeller. As a result of the experiments, it has been found that the refining agent can be substantially entrained into the hot metal and the efficiency of the refining treatment can be improved, in the case where the width of the impeller satisfies the formula (11), the step satisfies the formulas (12) - (14), the adding position at which the refining agent is added satisfies the formula (15), and the position at which the slag in the hot metal flow passage is removed satisfies the formula (16). [0029] Preferably, the hot metal is refined after setting in such a manner that following formulas (11a) - (16a) are satisfied. 0.55 ^ d/D 0 H/Z s 2.2 ... (13a) e a 45 ... (14a) 0 1.2 s R/D £ 4.4 ... (16a). [0030] According to a third aspect of the present invention, a blast furnace casting floor equipment includes a hot metal flow passage in which a hot metal tapped from a blast furnace flows, an adding device for adding a refining agent to the hot metal which ■ flows in the hot metal flow passage, an agitation device which has an impeller for agitating the hot metal, and a slag draining trough through which a slag on the hot metal generated after an agitation by the agitation device is drained to the external. A different level portion (that is, step portion) for making the hot metal fall is arranged at an upstream side of the hot metal flow passage and the agitation device is arranged in such a manner that the impeller is positioned at a downstream side of the different level portion. The adding device is disposed at a downstream side of the impeller, and the slag draining trough is disposed at a downstream side of the adding device. A width of the impeller is set in such a manner that a following formula (11) is satisfied. The different level portion is set in such a manner that following formulas (12) - (14) are satisfied. A position of the adding device is set in such a manner that a following formula (15) is satisfied. A position of the slag draining trough is set in such a manner that a following formula (16) is satisfied. 0.3s d/D 0 H/Z s 1 ... (13) e > 30 ... (14) 0 1.2 wherein d represents a width (m) of the impeller, D represents a maximum width (m) of the hot metal flow passage, L represents a distance (m.) from the different level portion to the impeller, H represents a height (m) of the different level portion, Z represents a depth (m) of the' hot metal, 9 represents a gradient (deg) of the different level portion, M represents a distance {m) from a center of a rotation shaft of the impeller to the adding device, and R represents a distance (m) from the center of the rotation shaft of the impeller to the slag draining trough. [0031] From various aspects, the inventors have verified a method where the efficiency of the refining treatment is improved by-substantially entraining the refining agent into the hot metal. [0032] Specifically, the inventors focuses on the agitation of the hot metal by the impeller and the agitation of the hot metal by a falling portion, and performs the experiments of the desiliconization treatment and the desulfurization treatment by changing the width of the impeller which is arranged at the agitation device, the position of the different level portion for making the hot metal fall, the height of the different level portion, the gradient (incline angle) of the different level portion, the position of the adding device for adding the refinin'g agent, and a position (to the position of the rotation shaft of the impeller) of the slag draining trough for removing the slag. As a result of the experiments, it has been found that the refining agent can be substantially entrained into the hot metal and the efficiency of the refining treatment can be improved, when the width of the impeller satisfies the formula (11), the different level portion satisfies the formulas (12) - (14), the position of the adding device satisfies the formula (15) , and the position of the slag draining trough satisfies the formula (16). [0033] Preferably, in the blast furnace casting floor equipment, following formulas (11a) ■- (16a) are satisfied. 0.55 0 H/Z s 2.2 ... (13a) e s 45 ... (14a) 0 1.2 s R/D £ 4.4 ... (16a) . [0034] According to a fourth aspect of the present invention, a continuous refining method of a blast furnace casting floor includes adding a refining agent to a hot metal which flows in a hot metal flow passage of the blast furnace casting floor, and mixing the hot metal with the refining agent by rotating an impeller which is immerged in the hot metal to continuously refine the hot metal. The hot metal is made fall from a different level portion which is arranged in the hot metal flow passage, and the impeller is arranged at a downstream side of the different level portion to agitate the hot metal. The impeller is moved in a range of a following formula (12) along the hot metal flow passage when the hot metal is refined. 0 wherein D represents a maximum width (m) of the hot metal flow passage, and L represents a distance (m) from the different level portion to the impeller. [0035] From various aspects, the inventors have verified a method to improve the efficiency of the refining treatment by substantially entraining the refining agent into the hot metal and restrict a refractory material (which is arranged at the hot metal flow passage) from locally wearing down. [0036] Specifically, the inventors have focused on a substantial entrainment of the refining agent into the hot metal by using the agitation functions of both the agitation of the hot metal by the impeller and the agitation of the hot metal by the falling. In this case, the hot metal is made fall from the different level portion (which is arranged in the hot metal flow passage) and the impeller is arranged at the downstream side of the different level portion to agitate the hot metal. Moreover, it is considered by the inventors that the position relation between the impeller and the step is important in utilizing both the agitation of the hot metal by the impeller and the agitation of the hot metal by the falling to the full. Experiments about the efficiency of the refining treatment when the position relation between the impeller and the different level portion is changed are performed. As a result of the experiments, it has been found that the refining efficiency is improved when the position relation between the impeller and the different level portion satisfies the above-described formula. [0037] In order to restrict the refractory material from locally wearing down, it is considered to be effective that the impeller (which agitates the hot metal) is moved in the range between the upstream side and the downstream side without stopping the impeller at a certain position when the refining treatment is performed. In this case, in order to restrict the refractory material from locally wearing down while the efficiency of the refining treatment is improved, the impeller is moved in the range where the above-described formula (0 [0038] A blast furnace casting floor equipment for embodying the above-described method includes a hot metal flow passage in which a hot metal tapped from a blast furnace flows, an adding device for adding a refining agent to the hot metal which flows in the hot-metal flow passage, and an agitation device which has an impeller for agitating the hot metal. A different level portion for making the hot metal fall is arranged at an upstream side of the hot metal flow passage and the agitation device is arranged in such a manner that the impeller is positioned at a downstream side of the different level portion. The agitation device is movable in a range of a following formula (12) along the hot metal flow passage. 0 wherein D represents a maximum width (m) of the hot metal flow passage, and L represents a distance (m) from the different level portion to the impeller. [0039] Thus, the refractory material can be restricted from locally wearing down and the efficiency of the refining treatment can be improved, by moving the impeller in the range where the above-described formula is satisfied. [0040] According to a fifth aspect of the present invention, a continuous refining method of a blast furnace casting floor includes adding a refining agent into a tap hole trough of the blast furnace casting floor, and mixing the hot metal with the refining agent by an impeller to continuously refine the hot metal. A component of a longitudinal direction of the tap hole trough of a swirling flow generated by the impeller is a field which is orthogonal to a flow direction of the hot. metal or opposite to the flow direction of the hot metal, and the refining agent is added at at least one of following positions (i) and (ii). (i) is a position which satisfies a following formula (15b) at an upstream side of the impeller, and (ii) is a position which satisfies a following formula (15) at a downstream side of the impeller. 0 0 wherein D represents a maximum width (m) of a hot metal flow passage, and M represents a distance (m) from a rotation center of the impeller to an adding position Effects of the Invention [0041] According to the continuous refining method of the present invention, the refining efficiency can be improved and the desiliconization and the desulfurization can be stably performed without unevenness. According to the continuous refining method of the present invention, the efficiency of the refining treatment such as the desiliconization treatment and the desulfurization treatment and the like can be increased by substantially entraining the refining agent into the hot metal. According to a blast furnace casting floor equipment of the present invention, the refractory material can be restricted from locally wearing down and the efficiency of the refining treatment can be increased. According to the continuous refining method of the present invention, the reaction efficiency can be improved by substantially entraining the refining agent having been added into the hot metal Brief Description of the Drawings [0042] FIG. 1 is a schematic plan view showing a blast furnace casting floor in a blast furnace equipment according to a first embodiment of the present invention; FIG. 2 is a schematic side view showing the blast furnace casting floor; FIG. 3 is a schematic perspective view showing a hot metal supply passage and an impeller; FIG. 4 is a schematic view showing an immerging state of the impeller; FIGS. 5 (A), (B) and (C) are schematic views showing a shape of a blade of the impeller; FIGS. 6 (A), (B) and (C) are schematic views showing an arrangement of the blades; FIG. 7 is a graph showing a relation between a number of the blades and a desiliconization oxygen efficiency; FIG. 8 is a graph showing a relation between d/D and the desiliconization oxygen efficiency; FIG. 9 is a graph showing a relation between hl/Z and the desiliconization oxygen efficiency; FIG. 10 is a graph showing a relation between h2/'Z and the desiliconization oxygen efficiency; FIG. 11 is a schematic cross sectional view when the impeller is immerged in other tap hole trough; FIG. 12 is a schematic plan view showing a blast furnace casting floor equipment according to a second embodiment of the present invention; FIG. 13 is a schematic cross sectional view showing the blast furnace casting floor equipment; FIG. 14 is a schematic view showing dimensions of the blast furnace casting floor equipment; FIG. 15 is a schematic perspective view showing dimensions of the blast furnace casting floor equipment; FIG. 16 is a schematic cross sectional view when an impeller is immerged in a tap hole trough; FIG. 17 is a graph showing a relation between d/D and a desiliconization oxygen efficiency; FIG. 18 is a graph showing a relation between L/D and the desiliconization oxygen efficiency; FIG. 19 is a graph showing a relation between H/Z and the desiliconization oxygen efficiency; FIG. 20 is a graph showing a relation between a gradient of a^ different level portion and the desiliconization oxygen efficiency; FIG. 21 is a graph showing a relatio-n between M/D and the desiliconization oxygen efficiency; FIG. 22 is a graph showing a relation between R/D and the desiliconization oxygen efficiency; FIG. 23 is a schematic view showing that the tap hole trough is provided with a circle shape and an impeller and an agent feeding lance are arranged at a circle-shaped portion; FIG. 24 is a schematic front view showing an agitation device and an adding device; FIG. 25 is a schematic side view showing the agitation device; FIG. 26 (A) and (B) are schematic cross sectional views when the impeller is immerged in other tap hole trough; FIGS. 27 is a schematic cross sectional view when an impeller is immerged in a tap hole trough according to a third embodiment of the present invention; FIGS. 28 (A) and (B) are schematic views respectively showing a state of a trough refractory wear in the case where the impeller is moved and that in the case where the impeller is not moved; FIG. 29 is a schematic front view showing an agitation device and an adding device; FIG. 30 is a schematic side view showing the agitation device; FIG. 31 is a front cross sectional view showing a refining device according to a fourth embodiment of the present invention; FIG. 32 is a schematic front view showing a blast furnace casting floor where the refining device is arranged; FIG. 33 is a schematic view showing an adding position of a refining agent; FIG. 34 is a graph showing a relation between the adding position of the refining agent and a desiliconization oxygen efficiency; FIGS. 35 (A) and (B) are schematic views showing a flow of a hot metal in a tap hole trough; and FIGS. 36 (I), (II), (III), and (IV) are schematic views showing a relation between an agitation vortex and the proper adding position of the refining agent. Explanation of Reference Numerals [0043] 1 blast furnace casting floor 2 blast furnace 4 tap hole trough 5 slag draining trough 8 different level portion 10 impeller 11 agitation device 12 adding device 16 blade Best Mode for Carrying Out the Invention [0044] (First Embodiment) [0045] A first embodiment of a blast furnace equipment where a continuous refining method of the present invention is suitably used will be described. However, the continuous refining method of the present invention is not only suitably used for this equipment. At first, in the following embodiment, a desiliconization treatment where a desiliconization agent as one of refining agents for refining a hot metal is used is described. However, it is also same in the case where a desulfurization agent is used. That is, the present invention shows an optimal means to increase a reaction rate, by efficiently entraining the refining agent into the hot metal to enlarge an area of reaction interface between the refining agent and the hot metal. Similarly to the desiliconization treatment, even in a desulfurization treatment, it is same that a refining performance is satisfactory and independent of the sort of the refining agent and the composition thereof. [0046] As shown in FIGS. 1-3, a blast furnace casting floor 1 is arranged around a blast furnace 2. The blast furnace casting floor 1 has a tap hole trough 4 (hot metal flow passage) in which the hot metal tapped from the blast furnace 2 flows. The tap hole trough 4 is branched to form a slag draining trough 5 at a halfway portion of the tap hole trough 4. A diving dam 7 is arranged in the vicinity of the downstream side of the branch portion of the tap hole trough 4, to guide in such a manner that a slag 6 of the hot metal flows in the slag draining trough 5. Moreover, a circle-shaped trough 9 which has a substantial circle shape in a plan view thereof is arranged at the downstream side of the branch portion of the tap hole trough 4. Multiple impellers 10 are arranged at the tap hole trough 4. Specifically, a first impeller 10a (agitation blade) is arranged to agitate the hot metal which flows in the circle-shaped trough 9, and a second impeller 10b is arranged between the branch portion and the circle-shaped trough 9. An adding device 12 for adding a refining agent 22 is arranged in the vicinity of the impeller 10a and the impeller 10b. [0047] Therefore, the hot metal tapped from the blast furnace 2 flows in the tap hole trough 4 from the upstream portion of the tap hole trough 4 toward the downstream portion thereof, and the slag 5 on the hot metal is interrupted by the diving dam 7 to flow to the slag draining trough 5. In this case, the hot metal itself, flows toward the circle-shaped trough 9. Thus, the desiliconization treatment of the hot metal which- continuously flows can be performed, by rotating the impeller 10a and the impeller 10b (which are immerged in the hot metal) while the refining agent 22 is added to the hot metal by the adding device 12. As shown in FIG. 4, the tap hole trough 4 has a bottom wall 20, and a side wall 21 which rises from the bottom wall 20. The side wall 21 has a pedestal shape in a cross sectional thereof which gradually protrudes toward the outer side with approaching the upper side from the two end portions of the bottom wall 20. The bottom wall 20 and the side wall 21 are formed by pouring an unshaped refractory material in. [0048] Next, the construction of the impeller 10 used in the continuous refining method will be described in detail. As shown in FIGS. 3 and 4, each of the impeller 10a and the impeller 10b is constructed of a refractory material or the like, and has a rotation shaft 15 (which has a cylinder shape or a rod shape or the like) and multiple blades 16 which are arranged at the tip of the rotation shaft 15. Each of the blades 16 has, for example, a substantial rectangle shape which protrudes from the tip of the rotation shaft 15 toward the outer side of the diameter direction thereof. The height bO of the base portion (that is, joining portion with the rotation shaft 15) of each of the blades 16 is set in such a manner that the height bO is larger than the height bl of the tip portion (protrusion tip portion) of the blade 16. That is, the heights bO and bl of the blade 16 of the impeller 10a, -lOb is set to satisfy the formula (1) [0049] bO a bl ... (1) In other words, as shown in FIGS. 5 (A) - (C), the blade 16 of the impeller' lOa, lOb is constructed in such a manner that the angle 6 between a longitudinal wall 16' of the tip portion of the blade 16 and the lateral wall 16" of the blade 16 is larger than or equal to 90° . As shown in FIG. 5, the shape of the blade 16 of the impeller 10a, 10b can be set as one of a rectangle shape, a trapezoid shape, an arc shape (planed-off shape of the tip portion) and the like in the side view thereof. The piece number of the impeller 10a, 10b can be set as three - six. For example, in this embodiment, as shown in FIGS. 1-5 (C) and FIG. 6 (A), the piece number of the blades 16 can be set as four. The blades 16 are attached to the rotation shaft 15 with an even angle to the rotation shaft 15 in correspondence with the piece number of the blades 16. In the case where the piece number of the blades 16 is four, the blades 16 are attached to the rotation shaft 15 in such a manner that the arrangement angle between the adjacent blades 16 is substantially equal to 90° . [0050] As shown in FIG. 6 (B), in the case where the piece number of the blades 16 is three, the blades 16 are attached to the rotation shaft 15 in such a manner that the arrangement angle between the adjacent blades 16 is substantially equal to 120° . As shown in FIG. 6 (C) , in the case where the piece number of the blades 16 is six, the blades 16 are attached to the rotation shaft 15 in such a manner that the arrangement angle between the adjacent blades 16 is substantially' equal to 60° . As shown in FIG. 4, the width d of the blade 16 is set to satisfy the formula (2), when the width d of the blade 16 is set to be a sum of the protrusion lengths (each of which is a length from the base portion of the blade 16 to the tip portion of the blade 16) of the two blades 16 (which are positioned from each other farthest), that is, be a sum of the protrusion length dl of the one blade 16 (as a criterion) and the protrusion length d2 of the other blade 16 which is positioned farthest from the one blade 16. [0051] 0.2 s d/D £ 0.8 ... (2) wherein D represents the maximum width (m) of the flow passage of the hot metal. Specifically, as shown in FIG. 6 (A) , in the case where the piece number of the blades 16 is four, the width d of the blade 16 is equal to the sum of the protrusion length dl of the first blade 16a and the protrusion length d2 of the third blade 16c. As shown in FIG. 6 (B) , in the case where the piece number of the blades 16 is three, the width d of the blade 16 is equal to the sum of the protrusion length dl of the first blade 16a and the protrusion length d2 of the second blade 16c. [0052] As shown in FIG. 6 (C) , in the case where the piece number of the blades 16 is six, for example, the width d of the blade 16 is equal to the sum of the protrusion length dl of the first blade 16a and the protrusion length d2 of the fourth blade 16d. Thus, the width d of the blade 16 of the impeller 10a, 10b is set to be changed in concordance with the arrangement spot of the impeller 10. The maximum width D (in the formula (2)) of the flow passage of the hot metal is a maxim.um width of the tap hole trough 4 at the contact portion at which the hot metal and the tap hole trough 4 (side wall 21 of the tap hole trough 4) contact each other when the: hot metal is poured in the tap hole trough 4. In other words, the maximum width D of the flow passage of the hot metal is the maximum width of the hot metal flowing in the tap hole trough 4 when the hot metal is made pass the tap hole trough 4. As shown in FIG. 4, in the case where the shape of the tap hole trough 4 is the trapezoid shape in the cross sectional view thereof, the width of the molten metal surface of the hot metal which flows in the tap hole trough 4 becomes the maximum width D of the flow passage of the hot metal. [0053] In the formula (2), in the case where the maximum width D of the flow passage of the hot metal is used, the maxim width in the vicinity of the position (agitation position) at which the impeller 10b is immerged is used for the impeller 10b which is arranged at the linear portion of the tap hole trough 4, and the maxim width in the vicinity of the position (agitation position) at which the impeller 10a is immerged is used for the impeller 10a which is arranged at the circle-shaped trough 9. The impeller is constructed as described above. The continuous desiliconization treatment can be efficiently performed by using the impeller which has the above-described construction. Next, the continuous refining method will be described. [0054] At first, when the hot metal is tapped from a tap hole of the blast furnace 2 to the tap hole trough 4, the refining agent 22 is added (by using the adding device 12) to the hot metal which flows through the tap hole trough 4. In this case, the impeller 10a, 10b having the ^above-described construction is immerged in the hot metal in" such a manner that the impeller 10a, 10b satisfies the formula (3) and the formula (4) and rotated, to mix the hot metal with the refining agent. 0 0 Wherein Z represents a maximum depth (m) of the hot metal which flows in the hot metal flow passage, hi represents a distance (m) from the upper end of the base portion of the blade to the upper surface of the hot metal, and h2 represents a distance (m) from the lower end of the base portion of the blade to the deepest part of the bottom portion of the hot metal flow passage. When the impeller 10 is immerged in the hot metal, the relation formula hl/Z + h2/Z + bO/Z = 1.0 is satisfied. The height bl of the blade 16 is set in such a manner that this formula and the formulas (3) and (4) are satisfied. [0055] The hot metal to which the desiliconization treatment has been performed flows to the downstream side to be put into a torpedo ladle (torpedo car) which is provided to convey the hot metal. Thus, the desiliconization e-fficiency can be increased, and the desiliconization can be stably performed without unevenness. [0056] Next, a first embodiment example and comparison examples will be described. In the embodiment example, the piece number of the blades 16 is set as three - six, and the impeller 10 is manufactured in such a manner that the impeller 10 satisfies the formulas (1) and (2). The desiliconization treatment is performed by using the impeller IQ. In the comparison example, the impeller 10 which does not satisfy the formulas (1) and (2) is manufactured, and this impeller 10 is used to perform the desiliconization treatment. The embodiment condition is shown in the table 1. [0057] Table 1 Tapping amount from blast furnace 2-4 ton/min Desiliconization adding amount 23,3 kg/ton Oxygen [0] concentration in desiliconization agent 19mass% Position of agitation by impeller Linear portion or circle-shaped tank of tap hole trough Rotation speed of impeller 100-200rpm Maximum depth of hot metal 0.3-0.6 m [0058] Silicon (Si) in the hot metal reacts with oxygen (0) in a desiliconization agent 11, and is removed from the hot metal as Si02 according to the reaction formula Si + 20 =Si02 As an index for manifesting whether or not the desiliconization agent 11 added to the hot metal has a efficient contribution to the desiliconizing reaction, a desiliconization oxygen efficiency indicated by the formula (5) is used. The desiliconization oxygen efficiency represents a ratio of the amount of oxygen used in the oxidation of Si in the hot metal to the amount of oxygen in the desiliconization agent 11. [0059] '7o2 =^'^S^°xioc(%)^5r]=[&x -m, wherein 32 is a molecular weight (g/mol) of O2, 28 is a molecular weight (g/mol) of Si, [Si]i represents a concentration (mass%) of Si in the hot metal before desiliconization, [Si]f represents a concentration (mass%) of Si in the hot metal after desiliconization, Wf is a feeding amount (kg/hot metal ton) of the desiliconization agent, and Co is a concentration (mass%) of 0 contained in the desiliconization agent . [0060] Table 2, and FIGS. 7-10 show a summarization of the desiliconization oxygen efficiency when the desiliconization treatment is performed by using the multiple impellers 10. Next, the result shown in Table 2, and FIGS. 7-10 will be described. In this case, 'trough" in the column of the agitation position in table 2 represents the linear portion of the tap hole trough 4, and "circle-shaped reaction trough" in the column of the agitation position in table 2 represents the circle-shaped trough 9. [0061] In the practical operation, the maximum specific consumption of the desiliconization agent which can be added according to a restriction between a hot metal passing speed and a feeding speed of the desiliconization agent is 60kg/ton. In the case where the desiliconization oxygen efficiency is less than 60%, the majority of silicon (Si) after the treatment exceeds 0.25mass% when maximum silicon (Si) in tapping has a high concentration of about 0.7mass%. Therefore, it is necessary to ensure that the desiliconization oxygen efficiency is larger than or equal to 60%. [0062] Table 2 Maxinuiiii depth of hot metal Z (111) Maxiniuni width of hot metal flow passage D (111) Agitation position Number of agitatio n spots Upper surface of hot metal -upper end of blade hi (111) Deepest part of bottom portion of hot metal flow passage - Lower end of blade Ii2 (111) Piece number of blades Width of blade d(iii) Heiglit of base portion of blade bO (ill) Heiglit oftip portion of blade bl (m) Rotation speed/minu te of blade hl/Z h2/Z d/D Tapping Si (%) Si in ladle (%) Feeding amount of desiliconi zatioii agent Wp (k&'() Ox>'geii concent¬ration in desiliconi- zatioii agent Co (%) Desiliconi- zatioji oxygen efficiencv (%) } 1 2 3 4 6 7 8 9 10 11 0.30 ■ 1.3 Trougli 0.05 0.05 3 0.3 0.20 0.20 125 0.167 0.167 0.23 0.65 0.41 23.3 19 61.9 0,30 0.9 Tiougli 0.05 0.10 4 0.4 0.15 0.15 150 0.167 0.333 0.44 0.59 0.28 23.3 19 79.9 0.30 1.2 Tioiigli 0.10 0.05 4 0.6 0.15 0.15 175 0.333 0.167 0.50 0.43 0.17 23.3 19 67.0 0.30 1.0 Trougli 0.05 0.05 4 0.2 0.20 0.20 175 0.167 0.167 0.20 0.49 0.25 23.3 19 61.9 0.3? 1.1 Trougli 0.05 0.05 6 0.3 0.25 0.25 200 0.143 0.143 0.27 0.37 0.12 23.3 19 64.5 0.35 1.1 Trougli 0.10 0.05 6 0.4 0.20 0.20 175 0.286 0.143 0.36 0.61 0.32 23.3 19 74.8 0.35 1.2 Trougli 0.05 0.10 4 0.6 0.20 0.20 175 0.143 0.286 0.50 0.62 0.30 23.3 19 82.5 0.40 0.8 Trougli 0.10 0,10 4 0.3 0.20 0.15 175 0.250 0.250 0.38 0.52 0.22 23.3 19 77.3 0.40 1.0 Trougli 0.15 0.05 4 0.8 0.20 0.20 150 0.375 0.125 0.80 0.55 0.31 23.3 19 61.9 0.60 1.9 Circle-shaped reaction tank 0.03 0.23 4 0.8 0.34 0.30 100 0.050 0.383 0.42 0.59 0.33 23.3 19 67.0 0.60 2.1 Circle-shaped reaction tank 0.15 0.15 4 1,3 0.30 0.30 100 0.250 0.250 0.62 0.50 0.23 23.3 19 69.6 t 12 13 14 0.30 1.1 Trougli 0.05 0.05 2 0.3 0.20 0.20 150 0.167 0.167 0.27 0.44 0.32 23.3 19 30.9 0.30 1.2 Trougli 0.05 0.15 2 0.6 0.15 0.10 150 0.167 0.500 0.50 0.51 0.41 23.3 19 25.8 0.30 0.9 Trough 0.00 0.10 7 0.4 0.20 0.20 175 0.000 0.333 0.44 0.50 0.38 23.3 19 30.9 15 16 17 18 19 20 21 22 0.30 0.9 Trougli 0.00 0.05 4 0.9 0.25 0.25 350 0.000 0.167 1,00 0.52 0,35 23.3 19 43.8 0.30 l.I Trougli 0.05 0.05 4 0.9 0.20 0.20 175 0.167 0.167 0.82 0.54 0.35 23.3 19 49.0 0.35 0.8 Trougli 0.05 0.15 4 0.5 0.20 0,10 175 0.143 0.429 0.63 0.61 0.40 23.3 19 54.1 0.35 0.9 Trougli 0.00 0.15 4 0.5 0.20 0.20 200 0.000 0.429 0.56 0.57 0.39 23.3 19 46.4 0.40 1.0 Trougli 0,15 0.05 4 0.1 0.20 0.20 175 0.375 0.125 0.10 0.64 0.46 23.3 19 46.4 0.40 1,2 Trougli 0.20 0.05 4 0.1 0.20 0.15 175 0.500 0.125 0.08 0.66 0.49 23.3 19 43,8 0.40 1.2 Trougli 0.00 0.20 4 0.5 0.20 0.15 175 0.000 0.500 0.42 0.57 0.39 23.3 19 46.4 0.50 2.0 Circle-shaped reaction tank 0.05 0.30 4 0.5 0.30 , 0.25 100 0.083 0.500 0.25 0.52 0.35 23.3 19 43.8 [0063] Next, the piece number of the blades 16 of the impeller 10 will be described. As shown in table 2 and FIG. 7, when the piece number of the blades 16 is smaller than three so that the piece number of the blades 16 is small, the desiliconization oxygen efficiency is lower than 60% (comparison examples 12 and 13). The reason is considered to be that the capacity (agitation capacity) for entraining the desiliconization agent 11 into the hot metal when the impeller 10 is rotated becomes low because the piece number of the blades 16 is small. On the other hand, when the piece number of the blades 16 is larger than six, the desiliconization oxygen efficiency becomes lower than 60% (comparison example 14) . The reason is considered to be that the slag 6 generated in the desiliconization reaction is easily adhered to the blade 16 so that the slag 6 collects at the blade 16 and touches the blade 16 to be hardened with a dumpling shape when the impeller 10 is rotated because the piece number of the blade 16 is too large. The impeller 10 to which the slag 6 having the dumpling shape is adhered has a weak agitation capacity even when this impeller 10 is rotated. Therefore, the reaction efficiency is deteriorated. [0064] Accordingly, it is desirable that the piece number of the blades 16 is three - six. In this case, the agitation capacity of the blades 16 can be increased, and it is difficult for the slag 6 to collect. Thus, the desiliconization oxygen efficiency which is higher than or equal to 60% can be provided. [0065] Next, the relation between the width of the blade 16 and the maximum width of the hot metal flow passage will be described. As shown in table 2 and FIG. 8, when the relation between the width of the blade 16 and the maximum width of the hot metal flow passage is d/D That means that the immergence width (width d) of the impeller 10 is small as compared with the maximum width of the hot metal flow passage when the impeller 10 is immerged. The reason is considered to be that the agitation force can be only applied to a part of the hot metal which flows in the vicinity of the impeller 10 even when the impeller 10 is rotated so that the sufficient agitation force cannot be applied to the hot metal which is far away from the impeller 10 to flow. [0066] That is, because the hot metal which flows along the side of the side wall 4a which defines the tap hole trough 4 passes through a spot which is far away from the blade 16 of the impeller 10, this hot metal is not agitated so much. The hot metal to which the agitation force is not sufficiently applied flows from the upstream side toward the downstream as is. Thus, the mixing between the hot metal and the desiliconization agent 11 is not sufficiently performed. On the other hand, when the relation between the width of the blade 16 and the maximum width of the hot metal flow passage is d/D > 0.8, the desiliconization oxygen efficiency is lower than 60% (comparison examples 15 and 16). That means that the immergence width (width d) of the impeller 10 is too large as compared with the maximum width of the hot metal flow passage when the impeller 10 is immerged. In this case, the vortex for drawing the desiliconization agent 11 into the hot metal cannot be generated at the surface of the hot metal, even when the impeller 10 is rotated. Conversely, the reaction efficiency is deteriorated. [0067] Therefore, it is desirable that the relation between the width of the blade 16 and the maximum width of the hot metal flow passage is set as defined by the formula (2) where the width d of the blade 16 is not too large and not too small as compared with the diameter or the width of the hot metal flow passage. Thus, the desiliconization oxygen efficiency which is lager than or equal to 60% can be provided. [0068] Next, the maximum depth of the hot metal and the distance from the upper end of the base portion of the blade 16 to the upper surface of the hot metal will be described. As shown in table 2 and FIG. 9, when the upper end of the base portion of the blade 16 and the upper surface of the hot metal are positioned at a same surface, that is, when the relation between the maximum depth of the hot metal and the distance from the upper end of the base portion of the blade 16 to the upper surface of the hot metal is h 1/Z = 0, the desiliconization oxygen efficiency is lower than 60% (comparison examples 14, 15 and 21). [0069] The reason is described hereinafter. In this case, even when the impeller 10 is rotated, the upper end of the base portion of the' blade 16 only rotates the upper surface (bath surface) of the hot metal, that is, the interface between the desiliconization agent 11 and the bath surface of the hot metal. Therefore, the desiliconization agent 11 cannot be sufficiently entrained into the hot metal. On the other hand, when the relation between the maximum depth of the hot metal and the distance from the upper end of the base portion of the blade 16 to the upper surface of the hot metal is hl/Z > 0.4, the desiliconization oxygen efficiency is lower than 60% (comparison example 20). The reason is described hereinafter. In this case, even when the impeller 10 is rotated in such a manner that the blade 16 of the impeller 10 is deeply sunk, the agitation force can be only applied to a part of the hot metal which flows in the vicinity of the impeller 10 so that the sufficient agitation force cannot be applied to the hot metal which flows at the upper side of the blade 16. The hot metal which flows at the upper side of the blade 16 flows from the upstream side toward the downstream side without being sufficiently agitated. Thus, the mixing between the hot metal which flows at the upper side of the blade 16 and the desiliconization agent 11 is not sufficiently performed. [0070] Therefore, it is desirable that the relation between the maximum depth of the hot metal and the distance from the upper end of the base portion of the blade 16 to the upper surface of the hot metal is set as defined by the formula (3) where the impeller 10 is not floated too much and not sunk too much for the hot metal. Thus, the desiliconization oxygen efficiency which is lager than or equal to 60% can be provided. [0071] Next, the distance from the lower end of the base portion of the blade 16 to the deepest portion of the bottom portion of the hot metal flow passage will be described. As shown in table 2 and FIG. 10, the lower end of the tip of the blade 16 is in the state where the lower end contacts the deepest part of the bottom portion of the hot metal flow passage. That is, in the case of h2/Z = 0, the deepest part of the bottom portion of the hot metal flow passage and the blade 16 contact each other so that the operation itself cannot be performed. [0072] On the other hand, the desiliconization oxygen efficiency becomes lower than 60% (comparison examples 13, 21, and 22), when the blade 16 of the impeller 10 is kept apart from the deepest part of the bottom portion of the hot metal flow passage and the relation between the maximum depth of the hot metal and the distance from the lower end of the tip of the blade 16 to the deepest part of the bottom portion of the hot metal flow passage is set as h2/Z > 0.4. The reason is described hereinafter. In this case, because the blade 16 of the impeller 10 is sunk little for the hot metal, the agitation force can be only applied to a part of the hot metal which flows in the vicinity of the impeller 10 and the agitation force cannot be sufficiently applied to the hot metal which flows at the lower side of the blade 16. Thus, the hot metal which flows at the lower side of the blade 16 flows from the upstream side toward the downstream without being sufficiently agitated. The mixing between the hot metal and the desiliconization agent .11 is not adequately performed. [0073] Therefore, it is desirable that the relation between the maximum depth of the hot metal and the distance from the lower end of the tip of the blade 16 to the deepest part of the bottom portion of the hot metal flow passage is set as defined by the formula (4) where the impeller 10 is not floated too much and not sunk too much for the hot metal. Thus, the desiliconization oxygen efficiency which is lager than or equal to 60% can be provided. As described above, the piece number of the blades 16 of the impeller 10 can be set as three - six, and the blade 16 is set to satisfy the formulas (1) and (2). When the desiliconization treatment is performed, this impeller 10 is immerged in the hot metal in such a manner that the formulas (3) and (4) are satisfied, and rotated. Thus, the desiliconization efficiency can be increased, and the desiliconization can be stably performed without unevenness. [0074] Next, a second einbodiment example where the desulfurization treatment is performed by using the impeller 10 similarly to the desiliconization treatment will be described. The embodiment condition is shown in table 3. The embodiment result is shown in table 4. [0075] Table 3 Tapping amount from blast furnace 2-4 ton/min Rotation speed of impeller 100-200rpm Adding amount of desulfurization agent 6,4 kg/ton Maximum depth of hot metal 0.3 -0.6 m Position of agitation by impeller Linear portion of tap hole trough or circle-shaped trough [0077] As an index which manifests whether or not the desulfurization agent (refining agent) added to the hot metal has an efficient contribution to the desulfurization reaction, a desulfurization efficiency shown in the formula (6) is used. [0078] 77, = ^ X100(%), A[5] = [SI - [S]^ ... , „ wherein [Si]i is the concentration (mass%) of S in the hot metal before the desulfurization, and [S]f is the concentration (mass%) of S in the hot metal after the desulfurization. [0079] In the desulfurization treatment, similarly to the desiliconization treatment, the desulfurization efficiency can be increased when the requirement about the piece number of the blades 16 of the impeller 10 is satisfied and the formulas (1) - (4) are satisfied. In the case where the desulfurization efficiency is lower than 50%, an additional desulfurization process may become further necessary so that the productivity will be deteriorated and a heat loss will be caused. Thus, the desulfurization efficiency which is lower than 50% is undesirable in the practical operation. Therefore, it is necessary to ensure that the desulfurization efficiency is higher than or equal to 50%. The present invention is not limited to the above-described embodiment examples. For example, in the above-described embodiment examples, the desiliconization treatment and the desulfurization treatment are performed by agitating the hot metal by the single impeller 10. However, the multiple impellers 10 can be also arranged in the tap hole trough 4 (linear portion of the tap hole trough 4) or the circle-shaped trough 9. [0080] In the above-described embodiment examples, the case where the tap hole trough 4 has the trapezoid shape in the cross sectional view thereof has been described. However, as shown in FIG. 11, the conditions shown in the present invention can be also used without any problem, even when the tap hole trough 4 becomes the substantially arc shape in the cross sectional view thereof due to an erosion accompanying with the flow of the hot metal. [0081] (Second Embodiment) [0082] Next, a blast furnace casting floor equipment according to a second embodiment of the present invention will be described. As shown in FIGS. 12 and 13, the blast furnace casting floor 1 is arranged around the blast furnace 2. The blast furnace casting floor 1 has the tap hole trough 4 in which the hot metal tapped from the blast furnace 2 flows. The tap hole trough 4 is the hot metal flow passage for guiding the hot metal tapped from the blast furnace 2 to a hot metal ladle or the torpedo ladle or the like in which the hot metal is put. The hot metal flows from the left side of FIG. 12 toward the right side of FIG. 12. Therefore, the left side of FIG. 12 is called the upstream side and the right side of FIG. 12 is called the downstream side. The slag draining trough 5 (first slag draining trough 5)^ is branched from the tap hole trough 4 and positioned at the upstream side of the tap hole trough 4. The diving dam 7 (first diving dam 7) is arranged at the downstream side of the branch point of the first slag draining trough 5, to guide in such a manner that the slag 6 which floats on the hot metal flows to the slag draining trough 5. The diving dam, being provided with a rectangle shape or the like, is a dam which has a lower portion apart from the bottom portion of the tap hole trough 4 and an upper portion protruding from the hot metal so as to interrupt the slag which floats on the hot metal and make the hot metal itself pass through the lower side of the' diving dam. [0083] A different level portion 8 which protrudes from the bottom portion of the tap hole trough 4 to the upper side is arranged at the downstream side of the first diving dam 7. The different level portion 8 has a perpendicular portion 8a which stands up at a substantial right angle from a bottom portion 4a (in other word, bottom portion which is near the first diving dam 7) of the upstream side of the tap hole trough 4, and a horizontal portion Bb which horizontally extends from the perpendicular portion 8a toward the downstream side, and a slant portion 8c which slants from the horizontal portion 8b toward the bottom portion 4b of the downstream side of the tap hole trough 4. An agitation device 11 which is provided with the impeller 10 for agitating the hot metal by the rotation is arranged at the downstream side of the different level portion 8. The adding device 12 for adding the refining agent is arranged at the downstream side of the impeller 10. [0084] A second slag draining trough 13 for draining the slag 14 which is generated after the agitation by the impeller 10 branches to be formed at the downstream side of the adding device 12. A second diving dam 18 is arranged at the more downstream side of the tap hole trough 4 than the branch point of the second slag draining trough 13, to guide the slag 14 generated after the agitation by the impeller 10 in such a manner that the slag 14 flows through the second slag draining trough 13. As shown in FIG. 16, the tap hole trough 4 has a bottom wall 20 which constructs the bottom portion 4a and the bottom portion 4b, and a side wall 21 which stands up from the bottom wall 20. The side wall 21 has a pedestal shape in a cross section thereof which gradually protrudes toward the outer side with approaching to the upper side from the two end portions of the bottom wall 20. The bottom wall 20 and the side wall 21 are formed by pouring an unshaped refractory material in. [0085] Next, the different level portion 8, the agitation device 11, the adding device 12, and the second slag draining trough 13 will be described in detail. [0086] The agitation device 11 will be described with reference to FIGS. 24 and 25. As shown in FIGS. 24 and 25, the agitation device 11 is provided with the impeller . 10 for agitating the hot m.etal, a driving member 30 for driving the impeller 10 so that the impeller 10 is rotated, and a lifting/lowering member 31 for lifting and lowering the impeller 10 and the driving member 30. The driving member 30 has a driving motor 32 for driving the impeller 10 so that the impeller 10 is rotated, a first rotation shaft 33 which is an output shaft protruding from the driving motor o Wl 32 to the lower side, a first gear 34 which is attached to the tip f the first rotation shaft 33, a second gear 35 which is meshed ith the first gear 34, and a second rotation shaft 36. The second gear 35 is arranged at the upper end of the second rotation shaft 36, and the shaft core of the second rotation shaft 36 is arranged in the up-down direction. The driving motor 32, the first rotation shaft 33 and the second rotation shaft 36 are mounted at a support member 37. [0087] The second rotation shaft 36 is rotatably supported at the support member 37 by a pair of bearings 38 which are respectively arranged at the upper side and the lower side. A connection member 39 is arranged at the lower side of the second rotation shaft 36, to coaxially connect a rotation shaft 15 (described later) of the impeller 10 with the second rotation shaft 36. The lifting/lowering member 31 has a pair of cylinders 40 (air cylinders with lock). The cylinders 40 are respectively arranged at the two sides of the support member 37, in such a manner that the shaft core of the cylinder 40 faces the up-down direction. The cylinder 40 has a cylinder body 41a which is attached to a frame 41 fixed at a treadle 42. The tip of a rod 40b of the cylinder 40 is connected with the support member 37. The support member 37 can be elevated and lowered via the expansion and contraction of the rod 4 0b. [0088] The impeller 10 has the rotation shaft 15 with the cylinder ^shape or the rod shape, and the multiple blades 16 which are arranged at the tip of the rotation shaft 15. The rotation shaft 15 of the impeller 10 penetrates a hot metal runner cover 43 which is arranged at the upper side of the tap hole trough 4 to cover the tap hole trough 4, and penetrates the treadle 42 which is arranged at the upper side of the hot metal runner cover 43. The upper end of the rotation shaft 15 is connected with the second rotation shaft 36 of the driving member 30 through the connection member 39. Each of the blades 16 of the impeller 10 has the substantial rectangle shape which protrudes from the tip of the rotation shaft 15 toward the diameter-direction outer side. For example, the piece number of the blades 16 of the impeller 10 can be set as four. The blades 16 are attached to the rotation shaft 15 af an interval of an even angle (for example, 90deg) to the rotation shaft 15 in accordance with the piece number of the blade 16. [0089] The width of the impeller 10 is set to satisfy the formula (11) . 0.3s d/D wherein d represents the width (m) of the impeller, and D represents the maximum width (m) of the hot metal flow passage. As shown in FIGS. 14 - 16, the width d of the impeller 10 is calculated by summing the widths (lengths which protrude from the rotation shaft 15) of the blades 16 which face each other and the diameter of the rotation shaft 15 (d= dl + d2 + dl) . That is, the width of the blade 16 and the diameter of the rotation shaft 15 are set in such a manner that the width d of the impeller satisfies the formula (11) . [0090] The maximum width D of the hot metal flow passage' is the maximum width of the tap hole trough 4 at the contact part at which the hot metal and the tap hole trough 4 (side wall 21 of the tap hole trough 4) contact each other when the hot metal flows in the tap hole ^ trough 4. In other words, the maximum width D of the hot metal flow passage is the maximum width of the hot metal flowing in the tap hole trough 4 when the hot metal is made pass through the tap hole trough 4. As shown in FIG. 16, when the tap hole trough 4 has the trapezoid shape in the cross sectional view thereof, the width of the molten metal surface of the hot metal flowing in the tap hole trough 4 becomes the maximum width D of the hot metal flow passage. However, it is desirable that the spot of the tap hole trough 4 where the maximum width D of the hot metal flow passage is used is in the vicinity of the spot (agitation spot) where the impeller 10 is immerged. [0091] By driving the driving motor 32 of the agitation device 11, the second rotation shaft 36 of the agitation device 11 can be driven to rotate. By rotating the second rotation shaft 36, the blade 16 of the impeller 10 can be rotated around the rotation shaft 15 of the impeller 10. Moreover, by lifting and lowering the support member 37 by the lifting/lowering member 31 of the agitation device 11, the attitude of the blade 16 of the impeller 10 can be changed between an immergence attitude (that is, the blade 16 is immerged in the hot metal) and a retreat attitude (that is, the blade 16 is not immerged in the hot metal). When the desiliconization treatment and the desulfurization treatment are performed, the support member 37 is lowered by the lifting/lowering member 31, and the blade 16 of the impeller 10 is provided with the immergence attitude (that is, the blade 16 is immerged). Thereafter, the driving motor 32 is driven to rotate the blade 16 which is immerged in the hot metal. [0092] Next, the different level portion 8 will be described. In this case, the position, the height H and the gradient (slant angle) of the different level portion 8 are set in such a manner that the different level portion 8 satisfies the formulas (12) - (14) . 0 H/Z a 1 ... (13) e s 30 ... (14) wherein L represents the distance (m) from the different level portion to the impeller 10, H represents the height (m) of the different level portion, Z represents the depth (m) of the hot metal, and 6 represents the gradient (deg) of the different level portion. As shown in FIGS. 14 and 15, the distance L from the different -level portion to the impeller 10 is a horizontal -distance from a contact portion T (where the hot metal and the slant portion 8c of the different level portion 8 contact each other) to an orbit K when the blade 16 is rotated. In other words, the distance L from the different level portion to the impeller 10 is a horizontal distance from the contact portion where the hot metal and the slant portion 8c of the different level portion 8 contact each other to the tip portion of the blade 16. [0093] The height H of the different level portion 8 is a distance from the bottom portion 4b of the tap hole trough 4 which is positioned at the more downstream side than the different level portion 8 to the horizontal portion 8b of the different level portion 8. The depth Z of the hot metal represents a depth of the hot metal at the downstream side of the different level portion 8. The depth Z of the hot metal with every tapping is substantially same. 6 in the formula (14) is the gradient of the different level portion 8 to the horizontal bottom surface of the hot metal flow passage. In detail, 9 is a narrow angle between the flat bottom portion 4b of the tap hole trough 4 and the slant portion 8c which stands up from the bottom portion 4b.. [0094] Next, the adding device 12 will be described. As shown in FIG. 24, the adding device 12 is provided with a hopper 45 for storing the refining agent, a cutting 46 for finely cutting the refining agent drained from the lower portion of the hopper 45, and a screw conveyer 47 for conveying the refining agent which has been cut, and an agent feeding lance 17 which -is arranged at a sending-out side (which is also named tip portion) of the refining agent of the screw conveyer 47. [0095] The screw conveyer 47 has a cylinder portion 48 which extends along the tap hole trough 4, and a screw 49 which is arranged in the cylinder portion 4 8 to be coaxial with the shaft core of the cylinder portion 48 and rotatably disposed in the cylinder portion 48. The screw conveyer 47 is constructed in such a manner that the refining agent cut by the cutting 4 6 due to the rotation is conveyed toward the agent feeding lance 17 by the rotation of the screw 49. The agent feeding lance 17, having a shaft core which faces the up-down direction, penetrates the hot metal runner cover 43 and the treadle 42. The upper end of the agent feeding lance 17 is connected with the tip of the screw conveyer 47, and the lower end of the agent feeding lance 17 reaches the upper side of the hot metal. [0096] The adding device 12 is set in such a manner that the position of the adding device 12 satisfies the formula (15). 0 wherein M represents a distance (m) from the rotation shaft center of the impeller 10 to the adding spot. The position of the adding device 12 is a central position of the agent feeding lance 17 which has the cylinder shape. Specifically, M shown in the formula (15) is a horizontal distance from the center (shaft core) of the rotation shaft 15 of the impeller 10 to the center (shaft core) of the agent feeding lance 17. That is, the center position of the agent feeding lance 17 is set to satisfy the formula (15). [0097] The refining agent can be continuously added to the hot metal by the adding device 12. In this case, the screw conveyer 47 is rotated to convey the refining- agent to the agent feeding lance 17, and the refining agent is continuously added to the hot metal via the agent feeding lance 17. [0098] Next, -the second slag draining trough will be described. The position of the slag draining trough (the second slag draining trough 13) is set to satisfy the formula (16). 1.2 s R/D :£ 5 ... (16) wherein R represents a distance (m) from the rotation shaft center of the impeller 10 to the slag draining trough 13. The position of the second slag draining trough 13 is a position of a side wall 13a (upper end of the side wall 13a) of the downstream side at the second slag draining trough 13 which has the rectangle shape in the cross sectional view thereof. R shown in the formula (16) is a horizontal distance from the center of the rotation shaft 15 of the impeller 10 to the side wall 13a (upper end of the side wall 13a) of the downstream side of the second slag draining trough 13. [0099] As described above, in the blast furnace casting floor equipment 1 of the present invention, the width of the impeller 10, the position of the different level portion 8, the height and the gradient of the different level portion 8, the position of the adding device 12, and the position of the second slag draining trough 13 are set based on the formulas (11) - (16). According to the blast furnace casting floor equipment 1, the hot metal tapped from the blast furnace 2 passes the lower side of the diving dam 7 to flow to the downstream side toward ■ the different level portion 8, and the slag 6 flows to the slag-draining trough 5. Thus, the hot metal flowing toward the different level portion 8 passes the horizontal portion 8b of the different level portion 8 to reach the slant portion 8c of the different level portion 8, and flows to the further downstream side along th^ slant portion 8c. [0100] The hot metal having reached the 'slant portion 8c flows along the slant portion 8c. In this case, this hot metal falls toward the bottom portion 4b of the tap hole trough 4 from the different level portion 8 (the horizontal portion 8b) . The hot metal having fallen from the different level portion 8 is agitated because of the falling from the different level portion 8. The hot metal which fell from the different level portion 8 to be agitated reaches the impeller 10 and is mechanically agitated by the impeller 10. Then, the hot metal flows to the more downstream side than the impeller 10. The refining agent (for example, desiliconization agent and desulfurization agent) is added to the hot metal which has reached the vicinity of the adding device 12 . Thus, the desiliconization or/and the desulfurization of the hot metal is performed. [0101] The hot metal to which the desiliconization treatment or/and the desulfurization treatment has been performed passes the downstream side of the second diving dam 18 to flow to the downstream side toward the different level portion 8, and the slag 14 generated due to the agitation of the impeller 10 and the adding of the refining agent flows to the second slag draining trough 13. Next, a third embodiment example will be described. [0102] Hereinafter, the third embodiment example of the present invention and comparison examples are described. In the third embodiment example, the desiliconization treatment and the desulfurization treatment are performed after the width of the impeller, the position of the different level portion, the height and the gradient of the different level portion, the position of the adding device, and the position of the second slag draining trough are beforehand set based on the formulas (11) - (16) . The embodiment condition is shown in table 5. In this case, the tap hole trough 4 which has the trapezoid shape in the cross sectional view thereof before the tapping as shown in FIG. 16 is used. [0103] Table 5 Impeller Number of blades 4 Width of blade: dl 0.1-0.4 m Height of blade: b 0.2 m Diameter of rotation shaft: d2 0.2 m Width of impeller: d 0.1 - 1.0 m Angle of tip portion of blade 90° Agitation position Linear portion (linear trough) or round portion (round trough) of tap hole trough Immergence deptli 0.1m from upper surface of hot metal Rotation speed: n 100 rpm Step Gradient (angle): 6 0-90° Height: H 0- I.5m Distance from impeller: L 0.1 -3.9m Adding device Distance from impeller: M -0.3-1.0 m Slag draining trough Distance from impeller: R 0,5-5m Width of tap hole trough: D 0.8-2.5 m Depth of hot metal: Z 0.35 m [0104] Similarly to the above-described first embodiment, as the index for manifesting whether or not the desiliconization agent added to the hot metal efficiently contributes to the desiliconization reaction, the desiliconization oxygen efficiency r|o2 shown in the formula (5) is used. Moreover, as the index for manifesting whether or not the desulfurization agent (refining agent) added to the hot metal efficiently contributes to the desulfurization reaction, the desulfurization efficiency y\s shown in the formula (6) is used. [0105] ' In the case of the desiliconization agent, the composition of the refining agent includes FeO and/or Fe203. In the case of the desulfurization agent, the composition of the refining agent includes CaO. In this embodiment, 5FeO - 58Fe205 - 21 CaO - 8Si02 (in mass%) is used as the desiliconization agent, and 80CaO - 3Si02 - 3 MgO - 6AI2O3 - 8M. Al (in mass%) is used as the desulfurization agent. In the conventional refining where only a mechanical agitation is performed, the desiliconization oxygen efficiencyTio2 is 30% - 40% when being compared at a same desiliconization agent specific consumption. Considering this, at first, the case where the desiliconization oxygen efficiencyr]o2 is higher than or equal to 50% (which is a high efficiency) is used as a criterion. In this case, silicon (Si) in the tapping is 0.38mass% - 0.42 mass%, and silicon (Si) after the treatment is lower than or equal to 0.25mass%. [0106] Similarly, the desulfurization efficiency is 30% - 40% when being compared at a same desulfurization agent specific consumption. Considering this, at first, the case where the desulfurization efficiency r]s is higher than or equal to 50% (which is a high efficiency) is used as a criterion. In this case, sulfur (S) in the tapping is 0.022mass% - 0.023mass%, and sulfur (S) after the treatment is lower than or equal to 0.010mass%. By setting the criterion of the desiliconization oxygen efficiency r|o2 to be higher than or equal to 50%, the efficiency (shortening of dephosphorization time and improvement of dephosphorization amount) of the dephosphorization treatment performed at the subsequent process of this treatment can be increased. Moreover, in the case where the desulfurization efficiency r}s is lower than 50%, a further additional desulfurization process may become necessary. Thus, the productivity will become low and the heat loss will be caused. Therefore, the desulfurization efficiency Tis which is lower than 50% is not desirable in the practical operation. Accordingly, it is necessary to ensure that the desulfurization efficiency r\s is higher than or equal to 50%. [0107] In the practical operation, there is the case where silicon (Si) of the hot metal tapped from the blast furnace 2 has a relatively high concentration (for example, 0.50 mass%). Even in this case, it is necessary to set the criterion of the desiliconization oxygen efficiency T1O2 to be larger than or equal to 60% so that the concentration of silicon (Si) after the treatment is 0.25mass%. Therefore, in the case where silicon (Si) of the hot metal tapped from the blast furnace 2 has the relatively high concentration, it is desirable to set the criterion of the desiliconization oxygen efficiency r\o2 to be larger than or equal to 60% Moreover, it is desirable to set the desulfurization efficiency r|s to be larger than or equal to 60% to deal with the resulfurization which may occur at the subsequent process. [0108] Table 6, and FIGS. 17 - 22 show a summarization of the desiliconization oxygen efficiency r\o2 and the desulfurization efficiency when the desiliconization treatment and the desulfurization treatment, are performed. Next, the result shown in table 6 and FIGS. 17 - 22 will be described. In this case, the linear trough shown in table 6 represents that the impeller 10 is immerged in the linear portion of the tap hole trough 4 shown in FIG. 12 and the refining agent is added. Moreover, the round trough shown in table 6 represents that the impeller 10 is immerged in the arc portion of the tap hole trough 4 shown in FIG. 23, and the refining agent is added. In the case of the round trough, the maximum width D of the hot metal flow passage is at the arc portion. 0 [0110] Next, the width of the impeller 10 will be described. In the refining treatment in the blast furnace casting floor, it is necessary to continuously add the desiliconization agent or the desulfurization agent to perform the desiliconization treatment or the desulfurization treatment of the hot metal which flows in the tap hole trough 4. In the refining treatment, it is important to substantially entrain the refining agent into the hot metal even when the refining agent is continuously added. If the width d of the impeller 10 is small as compared with the maximum width D of the hot metal flow passage, the agitation vortex generated due to the rotation of the impeller 10 also becomes small (that is, the agitation force is small) so that a part of or majority of the refining agent is not entrained into the hot metal to flow from the upstream side toward the downstream side without contributing to the reaction. Therefore, the reaction efficiency is low. [0111] As shown in table 6 and FIG. 17, when d/D which represents the ratio of the width d of the impeller 10 to the maximum width D of the hot metal flow passage is smaller than 0.3, that is, when the width d of the impeller 10 is small as compared with the maximum width D of the hot metal flow passage, the desiliconization oxygen efficiencyT)o2 becomes smaller than 50% (comparison examples 45 - 47). On the other hand, as shown in table 6 and FIG. 17, in the case of 0.3 large. In this case, the desiliconization oxygen ef f iciencyr)o2 becomes larger than or equal to 50% (embodiment examples 1 - 44) . In the case where the formula (11) is satisfied, the impeller 10 will contact the tap hole trough 4 by virtue of the position of the up-down direction of the impeller 10 to the tap hole trough 4 in the case of d/D « 1. That is, there is the case where the width d of the impeller 10 and the maxim width D of the hot metal flow passage are equal to each other. In this case, the impeller 10 contacts the tap hole trough 4 so that the impeller 10 itself cannot rotate. Thus, the practical operation is unavailable. In the use of the formula (11), it behooves the formula (11) to be satisfied on condition that the impeller 10 can rotate (that is, in the range where the impeller 10 and the tap hole trough 4 do not contact each other). [0112] As shown in FIG. 17, it is greatly desirable to use the condition (that is, the following formula (11a)) under which the desiliconization oxygen efficiencyrioz is larger than or equal to 60% as the condition of the continuous refining method of the blast furnace casting floor. 0.55 £ d/D [0113] Next, the different level portion 8 and the position of the different level portion 8 will be described. The hot metal is made fall by arranging the different level portion 8 at the tap hole trough 4. Thus, a disturbed flow is caused in the hot metal due to the fall. By the generated disturbed flow of the hot metal, the hot metal is agitated so that the effect that the refining agent is entrained into the hot metal can be expected. [0114] That is, although a part of the refining agent added at the more downstream side than the impeller 10 returns toward the slant portion 8c of the different level portion 8 due to the rotation of the impeller 10, the refining agent which has not reacted and returns to the different level portion 8 can be substantially entrained into the hot metal due to the agitation of the different level portion 8. Furthermore, the slant portion 8c of the different level portion 8 functions as a baffle plate to cause a turbulent flow of the hot metal. Thus, the baffle plate effect for entraining the refining agent (which has not reacted and returns) into the hot metal can be also expected. [0115] Thus, by arranging the different level portion 8 to cause the agitation of the hot metal, the effect that the refining agent which has not reacted is entrained into the hot metal can be obtained. Therefore, by combining the agitation by the different level portion 8 and the mechanical agitation by the impeller 10, it can be expectable that the refining agent is substantially entrained into the hot metal. The position relation between the different level portion 8 and the impeller 10 is important in taking advantage of the agitation by the different level portion 8 and the mechanical agitation by the impeller 10. As shown in FIG.' 15 and the formula (12), the position relation between the different level portion 8 and the impeller 10 can be represented by the ratio (L/D) of the distance between the rise of the different level portion 8 and the impeller 10 to the maximum width D of the hot metal flow passage. That is, the lager the value of L/D becomes, the more the different level portion 8 and the impeller 10 are distanced from each other. [0116] As shown in table 6 and FIG. 18, the desiliconization oxygen efficiencyr|o2 becomes lower than 50% (comparison examples 52 - 57) when the value of L/D is larger than 1.5. When the value of L/D is larger than 1.5, the refining agent scarcely returns to the different level portion 8 due to the agitation of the impeller 10 because the different level portion 8 and the impeller 10 are distanced from each other too far. Thus, it is considered that the desiliconization oxygen efficiencyT|o2 becomes low. That is, in the case where the value of L/D is larger than 1.5, the effect that the refining agent is entrained into the hot metal by the agitation of the different level portion 8 is greatly small. Substantially, that is same with the case where the refining agent is entrained into the hot metal only by the agitation of the impeller 10. [0117] The case of L/D = 0 means that the position of the different level portion 8 is same with that of the impeller 10. However, in this case, the impeller 10 itself cannot be rotated so that the practical operation cannot be performed. Therefore, 0 Moreover, as shown in FIG. 18, it is greatly desirable to use the condition (that is, the following formula (12a)) under which-the desiliconization oxygen efficiencyr|o2 is larger than or equal to 60% as the condition of the continuous refining method of the blast furnace casting floor. 0 [0118] Next, the height of the different level portion 8 will be described. With the height H of the different level portion 8 increasing, the fall energy of the hot metal which falls becomes large. When the fall energy becomes large, the disturbance of the hot metal can be increased so that the effect for entraining the refining agent into the hot metal becomes large. Accordingly, the reaction efficiency becomes high. [0119] As shown in table 6 and FIG. 19, in the case where the height H of the different level portion 8 is relatively large as compared with the depth Z of the hot metal, that is, in the case where the value of H/Z is larger than 1, the desiliconization oxygen efficiencyrio2 becomes larger than or equal to 50% (embodiment examples 1 - 44) . Conversely, as shown in table 6 and FIG. 19, in the case where the height H of the different level portion 8 is relatively small as compared with the depth Z of the hot metal, that is, in the case where the value of H/Z is smaller than 1, the desiliconization oxygen- iciencyrioa becomes smaller than 50% (comparison examples 48 - 50). In this case, it is desirable that the upper limit value of H/Z, that is, the height H of the different level portion 8 is determined by the equipment restriction. For example, as shown in FIG. 19, even when the value of H/Z is equal to 4.0, the desiliconization oxygen efficiency rio2 is larger than or equal to 50% while there is no problem in the equipment restriction. [0120] As shown in FIG. 19, it is greatly desirable to use the condition (that is, the following formula (13a)) under which the desiliconization oxygen efficiencyiio2 is larger than or equal to 60% as the condition of the continuous refining method of the blast furnace casting floor. H/Z s 2.2 ... (13a) [0121] Next, the gradient of the different level portion 8 will be described. The larger the gradient 6 of the different level portion 8 becomes, the larger the effect that the refining agent is entrained into the hot metal becomes (that is, the reaction efficiency becomes high) . As shown in table 6 and FIG. 20, in the case where the gradient 6 of the different level portion 8 is larger than 30deg, the desiliconization oxygen efficiency r\o2 becomes larger than or equal to 50% (embodiment examples 1 - 44) . Conversely, as shown in table 6 and FIG. 20, in the case where the gradient 6 of the different level portion 8 is smaller than 30deg, the desiliconization oxygen efficiency rio2 becomes smaller than 50% (comparison examples 51 and 52). However, the desiliconization oxygen efficiencyrjoa is larger than or equal to 50% even when the gradient 6 of the different level portion 8 is equal to 90deg which is the maximum value. [0122] Moreover, as shown in FIG. 20, it is greatly desirable to use the condition (that is, the following formula (14a)) under which the desiliconization oxygen efficiencyrjo; is larger than or equal to 60% as the condition of the continuous refining method of the blast furnace casting floor. e > 45 ... (14a) [0123] Next, the position of the adding device 12 will be described. It can be considered that the position of the adding device 12 (that is, the position of the agent feeding lance 17 of the adding device 12) is arranged at the upstream side or the downstream side to the position of the impeller 10 which mechanically agitates the hot metal (that is, there are two patterns about the position of the agent feeding lance 17) . In the case where the agent feeding lance 17 of the adding device 12 is positioned at the upstream side of the impeller 10, the amount of the refining agent which is not entrained into the hot metal and flows to the downstream side is large. [0124] In the case where the position of the agent feeding lance 17 is set at the more downstream side than the position of the impeller 10, the refining agent goes against the flow of the hot metal to become easy to flow toward the side of the different level portion 8, due to the rotation of the impeller 10. Thus, the amount of the refining agent which is scarcely entrained into the hot metal to flow to the downstream side is small. As shown in table 6 and FIG. 21, in the case of M/D^ 0 . 8, it can be ensured that the desiliconization oxygen : is larger than or equal to 50% (embodiment examples 1-44) . M/D represents the position of the agent feeding lance 17 to the position of the impeller 10. As shown in table 6 and FIG. 12, when the value of M/D is larger than 0.8, the impeller 10 and the agent feeding lance 17 are distanced from each other so much that the refining agent cannot be entrained into the hot metal by the agitation. In this case, it is considered that the desiliconization oxygen efficiency-]o2 is smaller than 50% (comparison examples 58-60) [0125] Because the case where the value of M/D is smaller than or equal to 0 means that the position of the agent feeding lance 17 is at the more upstream side than the impeller 10, 0 As shown in FIG. 21, it is greatly desirable to use the condition (that is, the following formula (15a)) under which the desiliconization oxygen efficiency T1O2 is larger than or equal to 60% as the condition of the continuous refining method of the blast furnace casting floor. 0 [0126] Next, the position of the second slag draining trough 13 will be described. If the second slag draining trough 13 is arranged in the vicinity of the position at which the impeller 10 is arranged, the hot metal will be m.ixed in the slag 14 to which the agitation treatment has been performed. Thus, the slag 14 may flows toward the second slag draining trough 13 in such a state where the slag 14 and the hot metal are'not separated from each other and the hot metal is mixed in the slag 14. Therefore, not only iron loss is caused, but also the property of the slag 14 varies because the hot metal is mixed in the slag 14. [0127] If the slag ladle is charged with the slag 4 (which property has varied) after the slag 14 passes the second slag draining trough 13, the wear (damage) of the refractory material which is arranged at the slag ladle will become fierce so that the life duration of the slag ladle may be shortened. On the other hand, if the second slag draining trough 13 is arranged at a position which is far distanced from the position at which the impeller 10 is disposed, the liquid slag 14 will become solid before the slag 14 is drained to the second slag draining trough 13. Thus, the slag 14 generated due to the refining agent which has been initially added piles in the vicinity of the impeller 10, so that a hindrance to the operation may be caused. [0128] As shown in table 6 and FIG. 22, in the case of R/D> 5 . 0 (which represents the position of the second slag draining trough 13 to the position of the impeller 10) , the impeller 10 and the second slag draining trough 13 are distanced from each other too far. Therefore, although the desiliconization oxygen efficiency r|o2 is larger than or equal to 50%, the temperature from the generation of the slag 14 to the draining of the slag 14 is lowered by 200°C and up (in FIG. 22 and table 6, the degree of the temperature drop of the slag is represented by AT S which is a surface temperature drop amount) . Thus, the liquid slag 14 becomes solid to be difficult to flow (comparison 63). Moreover, in the case of R/D second slag draining trough 13 are near each other so much that the hot metal is mixed in the slag 14. Therefore, although the desiliconization oxygen efficiency 1102 is larger than or equal to 50%, the iron ingredient contained in the slag 14 increases (comparison example 61, 62) [0129] As shown in FIG. 22, in the case of R/D 20%) . In the practical operation, when the amount of M. Fe contained in the slag 14 is smaller than or equal to 20% and the surface temperature drop amount ATs of the slag 14 is lower than 200°C , the operation condition becomes acceptable. That is, it is greatly desirable to use the following formula (16a) as the condition of the continuous refining method of the blast furnace casting floor. 1.2 [0130] As described above, in the blast furnace casting floor 1, the refining treatment is performed after the width of the impeller, the position of the different level portion, the height and the gradient of the different level portion, the position of the adding device and the position of the second slag draining trough are beforehand determined based on the formulas (11) - (16) . Thus, the efficiency of the refining treatment can be increased. The blast furnace casting floor of the present invention is not limited to the above-described embodiments. For example, in the case where the refining agent is powder type, the cutting 46 can be omitted. Moreover, the conveying member for conveying the refining agent from the hopper 45 to the agent feeding lance 17 can be ^not constructed of the screw conveyer 47. For example, the conveying member can be constructed to convey the reefing agent by the air pressure. [0131] In the above-described embodiments, the case where the tap hole trough 4 has the trapezoid shape in the cross sectional view thereof is described. However, as shown in FIG. 26 (B) , even when the tap hole trough 4 varies to have the substantial arc shape in the cross sectional view thereof due to the erosion because of the flow of the hot metal, the condition shown in the present invention can be used without problem. Furthermore, as shown in FIG. 26 (A), even when the tap hole trough 4 has the substantial rectangle shape in the cross sectional view thereof, the condition shown in the present invention can be used without problem. That is, when the width of the impeller, the position of the different level portion, the height and the gradient of the different level portion, the position of the adding device and the position of the second slag draining trough are set to satisfy the formulas (11) - (16) or (11a) - (16a), the efficiency of the refining treatment such as the desiliconization treatment, the desulfurization treatment and the like can be improved. [0132] (Third Embodiment) [0133] Next, the blast furnace casting floor equipment according to a third embodiment of the present invention will be described. Because the blast furnace casting floor equipment according to the third embodiment is substantially same with what is shown in FIGS. 12 - 14 of the second embodiment, only the different part will be described hereinafter. [0134] According to the blast furnace casting floor equipment of the third embodiment, the tap hole trough 4 has a heat insulation member 60, a rear member 61 which is arranged at an inner side of the heat insulation member 60 and constructed of brick or the like, and a refractory member 62 which is arranged at an inner side of the rear member 61, as shown in FIG. 27. The refractory member 62 is formed by pouring a unshaped refractory material to the inner side of the rear member 61, and includes a bottom wall 20 (which constructs the bottom portion 4a and the bottom portion 4b) and a side wall 21 which rises from the two end portions of the bottom wall 20. In this embodiment, the refractory member 62 has a trapezoid shape which gradually protrudes to the outer side with the side wall 21 rising from the two end portions of the bottom wall 20. [0135] The maximum width D of the hot metal flow passage is . the maximum width of the refractory member 62 at the contact part where the hot metal and the side wall 21 of the refractory member 62 contact each other when the hot metal flows in the tap hole trough 4. In other words, the maximum width D of the hot metal flow passage is the maximum width of the hot metal flowing in the tap hole trough 4 when the hot metal is made pass through the tap hole trough 4. As shown in FIG. 5, when the refractory member 62 has the trapezoid shape in the cross sectional view thereof, the width of the molten metal surface of the hot metal flowing in the tap hole trough 4 becomes the maximum width D of the hot metal flow passage. Next, the agitation device 11 and the adding device 12 will be described in detail. [0136] The agitation device 11 will be described with reference to FIGS. 29 and 30. As shown in FIGS. 29 and 30, the agitation device 11 has the impeller 10, and a moving member 50 which is provided to move the driving member 30 and the lifting/lowering member 31. [0137] The moving member 50 has a frame 41 (for supporting the impeller 10, the driving member 30, the lifting/lowering member 31 and the like), and rolling wheels 51 which are rotatably supported by the frame 41 and roll on the cover 43 of the tap hole trough 4. The frame 41 has a base portion 52 which extends along the tap hole trough 4. A foot portion 53 which extends downwards from the base portion 52 is arranged at the base portion 52. The foot portion 53 reaches the vicinity of the treadle 42 via (through) a second opening portion 26. The rolling wheel 51 which is rotatable is arranged at the tip (lower end) of the foot portion 53 in such a manner that the rolling wheel 51 is movable along the tap hole trough 4. In this case, an orbit (for example, rail) at which the rolling wheel 51 travels is arranged at the treadle 42, in such a manner that the rolling wheel 51 can linearly move on the treadle 42 along the tap hole trough 4. [0138] According to the adding device 12 of the third embodiment, it is capable to rotate one or all of the rolling wheels 51 and move the agitation device 11 (that is, the impeller 10) in the range which satisfies the formula (12). However, it is desirable to arrange an electric-powered motor for rotating the rolling wheel 51 at the frame 41. In this case, the rolling wheel 51 is automiatically rotated by the driving of the electric-powered motor. [0139] The adding device 12 (that is, the hopper 45, the cutting 46, the screw conveyer 47 and the agent feeding lance 17) is supported by the frame 41 (the base portion 52) of the agitation device 11. Thus, the adding device 12 can move together with the agitation device 11. Specifically, in the case where the desiliconization treatment and the desulfurization treatment are performed, the agent feeding lance 17 of the adding device 12 also moves at the same time when the impeller 10 of the agitation device 11 moves. [0140] Next, the continuous refining method of the blast furnace casting floor of the present invention will be described. According to the continuous refining method of the blast furnace casting floor, the different level portion 8 is arranged in the tap hole trough 4 and the hot metal falls from the different level portion 8. The impeller 10 is positioned at the downstream side of the different level portion 8 to agitate the hot metal, and is moved along the tap hole trough 4 in such a manner that the formula (12) is satisfied. [0141] As shown in FIG. 28 (A), in the refining treatment, when the impeller 10 is rotated in the state where the position of the impeller 10 is fixed, the hot metal agitated by the impeller 10 strikes on the same part (spot) of the refractory material, so that the part on which the hot metal often strikes may locally wear down. On the other hand, as shown in FIG. 28 (B) , in the refining treatment, when the impeller 10 is ■ rotated in such a manner that the position of the impeller 10 is not fixed and the impeller 10 is moved along the tap hole trough 4, the hot metal agitated by the impeller 10 strikes on the different parts (spots) of the refractory material. Therefore, it is capable that the refractory material evenly wears, so that the life duration of the tap hole trough 4 can be elongated. [0142]' According to the present invention, the impeller 10 is moved along the tap hole trough 4 in such a manner that the formula (12) is satisfied, in order to improve the refining efficiency as described above while the refractory material is restricted from locally wearing down. The moving of the impeller 10 can be performed by moving the agitation device 11 along the longitudinal direction of the tap hole trough 4. For example, the impeller 10 can be moved in the range defined by the formula (12) by a predetermined pitch every time the tapping amount having been tapped becomes a predetermined amount, or be continuously moved in the range defined by the formula (12) to be independent of the tapping amount having been tapped. Next, a fourth embodiment example will be described. [0143] The fourth embodiment example of the present invention where the desulfurization treatment or the desiliconization treatment is performed by moving the impeller 10 based on the formula (12) and comparison examples will be described. The embodiment condition is shown in table 7. [0144] Table 7 Tapping amount from blast frtmace 3.0-3.2t/min Hot metal Tapping fSi] 0.38 - 0.42 mass% Tapping fS] 0.022 - 0.023 mass% Temperature 1486-1517°C Desiliconization agent Composition of agent 5FeO-58Fe203-21CaO-8Si02 (in mass%) Specific consumption of agent 22.6 - 24.0 kg/tp Desulfurization agent Composition of agent 80CaO-3SiO2-3MgO-6A12O3-8M.Al (in mass%) Specific consumption of agent 6.3 - 6.5 kg/tp Agitation device (Impeller) Number of blades 4 Width of blade: dl 0.16m Height of blade: b 0.18m Diameter of rotation shaft: d2 0.18m Width of impeller: d 0.5 m Angle of tip portion of blade 90° Agitation position Linear portion (linear trough) of tap hole trough Immergence depth 0.1 m from upper surface of hot metal Rotation speed 100 rpm Step Gradient (angle): 6 60° Height: H Llm Distance from impeller: L 0.25-L25m or 3.25-4.25 m Adding device Distance from impeller: M 0.6 m (Lower side of blade) Slag draining trough Distance from impeller: R 3.3 m Largest width of hot metal flow passage: D 0,9 m Depth of hot metal: Z 0.35 m [0145] Similarly to the first embodiment, as the index for manifesting whether or not the desiliconization agent added to the hot metal efficiently contributes to the desiliconization reaction, the desiliconization oxygen efficiency 1^02 shown in the formula (5) is used. Moreover, as the index for manifesting whether or not the desulfurization agent (refining agent) added to the hot metal efficiently contributes to the desulfurization reaction, the desulfurization efficiency r)s shown in the formula (6) is used. [014 6] Moreover, it is used as a criterion that a maximum wearing amount S of the refractory material after the tapping is finished is smaller than 200mm. The maximum wearing amount S of the refractory material which is set to be smaller than 200miti is obtained from the past practical operation. When the maximum wearing amount S is larger than 200mm, the tap hole trough 4 will come to the end of the life duration thereof even when only a part of the tap hole trough 4 has the maximum wearing amount S. If the tap hole trough 4 comes to the end of the life duration thereof, a major work is to be performed. For example, pouring of the refractory material is to be performed to the whole of the tap hole trough 4 to replace the refractory material of the whole of the tap hole trough 4 (in following description, the replacement of the refractory material is also named pouring-work-after). Table 8 shows a summarization of the embodiment example and the comparison examples. According to the first embodiment example, in the desiliconization treatment, the impeller 10 is continuously moved in the range where the formula (12) is satisfied. In the second -ninth embodiment examples, every time the hot metal having been tapped is putted in the hot metal ladle at the downstream side (for example, every one ladles, five ladles, ten ladles or fifty ladles or the like), the desiliconization treatment is performed while the impeller 10 is moved in the range where the formula (12) is satisfied. According to the tenth embodiment example, in the desulfurization treatment, every time the hot metal having been tapped is putted in the hot metal ladle at the downstream side (for example, every five ladles) , the impeller 10 is moved in the range where the formula (12) is satisfied. The capacity of the one ladle is 90ton, for example. In this case, the agitation position shown in table 8 represents a distance L from the different level portion 8 to the impeller 10 when the impeller 10 is moved. In the column of the agitation position shown in table 8, for example, according to the first embodiment example, the impeller 10 is continuously reciprocatingly moved in the range of L = 0.25 L = 0.25 to 1.25 (L/D = 0. 28 to 1.39). According to the second embodiment example, every time the hot metal having been tapped is putted in the one ladle (the amount of the tapped hot metal is 90ton) , the impeller 10 is moved in units of 0.05 to 0.5m in the range of L = 0.25 to 0.25 (L/D = 0. 28 to 1.39) . [0149] The wastage degree shown in table. 8 represents a ratio of the maximum wearing amount S of the refractory material (after a one-hundred-ladle treatment is performed) to the thickness (thickness of 350mm at the contact portion J at which the molten metal surface of the hot metal and the refractory material contact each other) of the initial (after the pouring process) refractory material. It is greatly undesirable that the wastage degree is larger than 57%, because the control value of the maximum wearing amount S is set to be smaller than 200mm. The desiliconization oxygen efficiency rio2 and the desulfurization efficiency r|s shown in table 8 are the average value after the hundred-ladle treatment is performed. As shown in table 8, in the refining treatment, in the case where the impeller 10 is moved in the range which satisfies the formula (12), the desiliconization oxygen efficiency r)o2 and the desulfurization efficiency r\s can become larger than 50% and the maximum wearing amount S of the refractory material after the hot metal with the amount of one hundred of ladles is tapped is smaller than 200mm. In all of the cases, the wastage amount is smaller than 57% (embodiment examples 1-10) . [0150] On the other hand, in the case where the refining treatment is performed in such a manner that the impeller 10 is fixed in the range which satisfies the formula (12), the maximum wearing amount S of the refractory material after the tapping is larger than or equal to 200mm although the desiliconization oxygen efficiency rio2 and the desulfurization efficiency i-js can become larger than or equal to 50%. The wastage amount greatly exceeds 57% (comparison examples 11 and 13). Moreover, in the case where the refining treatment is performed in such a manner that the impeller 10 is fixed in the range which does not satisfy the formula (12), the desiliconization oxygen efficiency r|o2 and the desulfurization efficiency r\s are smaller than 50% and the maximum wearing amount S of the refractory material after the tapping also becomes larger than or equal to 200mm. The wastage amount greatly exceeds 57% (comparison example 12) . [0151] As described above, when the hot metal is refined, the impeller 10 is moved along the hot metal flow passage in such a manner that the formula (12) is satisfied. Thus, the refractory material can be restricted from locally wearing down, and the efficiency of the refining treatment can be improved. [0152] (Fourth Embodiment) [0153] Next, the blast furnace casting floor equipment according to a fourth embodiment of the present invention will be described. The blast furnace casting floor (at which the refining device is arranged) of the blast furnace casting floor equipment of the fourth embodiment is shown in FIG. 32 which is a schematic plan view. The basic part of the blast furnace casting floor equipment of the fourth embodiment is substantially same with that shown in FIGS. 12-14 of the second embodiment, and the description of the basic part is omitted. Here, the suitable arrangement position of the agent feeding lance 17 in the continuous refining of the hot metal which is performed in the blast furnace casting floor 1, that is, the suitable adding position of the refining agent to the hot metal will be described. [0154] FIG. 31 is a front cross sectional view of a refining device 100 which is used for consideration. The adding device 12 is constructed of the hopper 45, the cutting 46, a transferring pipe 80 and the agent feeding lance 17. The hopper 45 is fixed at a trestle 81 which is fixed at the upper surface of the base portion 52. The transferring pipe 80 connects the cutting 46 with the agent feeding lance 17, to quantitatively transfer the refining agent from the cutting 4 6 to the agent feeding lance 17. The transferring pipe 80 can be constructed of a resin tube which has a low friction coefficient and can be easily deformed. The transference of the refining agent from the cutting 46 to the agent feeding lance 17 via the transferring pipe 80 is performed by using a head drop between the cutting 4 6 and the agent feeding lance 17. The hopper 45 is attached to the trestle 81 and arranged at a sufficiently high position. [0155] The base portion 52 is formed in such a manner that the agent feeding lance 17 can be fixed at an arbitrary position. The position of an adding port 75 of the agent feeding lance 17 can be changed from the vicinity of the rotation shaft 15 to the vicinity of the side wall of the tap hole trough 4, and can be changed from the vicinity of the rotation shaft 15 to the upstream side edge and the downstream side edge of the base portion 52. Next, a fifth embodiment example will be described. [0156] The refining treatment of the hot metal is performed by arranging the agent feeding lance 17 respectively at various positions at the base portion 52, and the suitable position of the adding of the refining agent in the continuous refining of the hot metal performed in the blast furnace casting floor 1 is considered. Table 9 shows a summarization of the refining device 100 and the blast furnace casting floor 1 which are used in the consideration. Table 10 shows a relation between the condition of the desiliconization treatment performed by using 5Fe - SSFeaOs-21CaO-8Si02 (in mass%) which is the desiliconization agent as the refining agent, and the result of the desiliconization treatment. FIG. 33 is a view which shows the adding position of the refining agent in table 10 by a relation between the adding position and the impeller 10. FIG. 34 is a graph which shows a relation between the adding position of the refining agent in table 10 and the desiliconization oxygen efficiency r)o2- [0157] The conditions of the agitation device 11 in table 10 are determined before the suitable position of the adding of the refining agent is considered, and are the agitation conditions under which the vortex of the hot metal generated by the impeller 10 broadens to the whole width direction of the tap hole trough 4. In table 10, the ratio (d/D) of the diameter d of the impeller 10 to the width D of the tap hole trough 4 is 0.56 and the rotation speed of the impellar is lOOrpm. However, the inventors performs a great number of experiments in the range of the rotation speed 80rpm - 200rpm by using the impeller having the diameter which satisfies■0.3 s d/D hole trough 4 in all of the experiments. [0158] In this case, the width D of the tap hole trough in table 10 is the maximum width of the hot metal flowing in the tap hole trough 4, as shown in FIG. 27 of the above-described third embodiment. Moreover, the distance M from the center of the rotation shaft of the impeller 10 to the adding position is a horizontal distance from the center (shaft core) of the rotation shaft 15 of the impeller 10 to the center (shaft core) of the agent feeding lance 17. [0161] In table 10, the content percentage of silicon of the hot metal tapped from the blast furnace is determined from the specimen picked at the position PI in FIG. 32, and the content percentage of silicon of the hot metal after the desiliconization treatment is determined from the specimen picked at the position P2 in FIG. 32. [0162] Similarly to the first embodiment, the desiliconization oxygen efficiencyr|o2 shown in the formula (5) is used as the index which manifests whether or not the desiliconization agent added to the hot metal efficiently contributes to the desiliconization reaction, and the desulfurization efficiency T]S shown in the formula (6) is used as the index which manifests whether or not the desulfurization agent (refining agent) added to the hot metal efficiently contributes to the desulfurization reaction. [0163] Mover, the synthesized appraisement of the desiliconization treatment in table 10 is set as good ("circle") when the desiliconization oxygen efficiencyrioa (Which is used as a boundary) is higher than or equal to 50%, and set as no-good ("cross") when the desiliconization oxygen efficiencyr)o2 is lower than 50%. In the conventional refining method where only the mechanical agitation is provided, the desiliconization oxygen efficiency r|o2 is 30% - 40% when compared at a same specific consumption of the desiliconization agent. In view of that, at first, the case where the desiliconization oxygen efficiency rio2 becomes larger than or equal to 50% (which is a high efficiency) is used as- the criterion. In this- case, silicon in the tapping is 0.38 - 0.42 mas5%, and silicon after the treatment is smaller than or equal to 0.25 mass%. By setting the criterion of the desiliconization oxygen efficiency r]o2 to be larger than or equal to 50%, the efficiency (shortening of dephosphorization time and improvement of dephosphorization amount) of the dephosphorization treatment which will be performed at the subsequent process can be improved. [0164] As shown in table 10 and FIG. 33 in which the organized result of the desiliconization treatment is shown, the desiliconization oxygen efficiency rio2 becomes larger than or equal to 50% in the following case. This case is that the component of the longitudinal direction (left-right direction (X direction) in FIG. 33) of the tap hole trough of the swirling flow generated by the impeller 10 is at the upper side of the hot metal of the field (at the upper side of the rotation shaft 15 in FIG. 33) which is orthogonal to the flow direction of the hot metal or is opposite to the flow direction of the hot metal, and the horizontal distance M from the rotation center of the impeller 10 to the adding position (center of the adding port 29 of the agent feeding lance 17) satisfies 0 As shown in FIG. 35 (A) , the agitation vortex generated by the rotation of the impeller 10 is inclined to the downstream side due to the flow of the hot metal, and the downstream side is provided with a condition beneficial to entrainment. Therefore, the difference between the range of the distance M (where the satisfactory desiliconization treatment can be performed) from, the rotation center of the impeller to the adding position at the upstream side and that at the downstream side is caused. [0165] In the case where the desiliconization agent is added outside the above-described range at the upstream side, the ratio of the desiliconization agent which is never entrained into the agitation vortex and flows toward the downstream side while floating at the hot metal is large. Moreover, in this case, even when the desiliconization agent is entrained into the agitation vortex, it is easy for the desiliconization agent to escape away from the agitation vortex (when floating up) at the spot where the hot metal flow and the agitatioji flow overlap each other. Accordingly, the desiliconization agent will flow toward the downstream side, without sufficiently contacting the hot metal. Similarly, in the case where the desiliconization agent is added outside the above-described range at the downstream side, the ratio of the desiliconization agent which flows toward the downstream side (while floating at the hot metal) without contributing to the desiliconization reaction is large. As -shown in FIGS. 35 (A) and (B) , in the flow of the hot metal around the impeller 10 which is rotated, a flow which faces the upstream side (to be opposite to the flow of the hot metal) is generated from the downstream side of the impeller 10. If the desiliconization agent is made accompany this flow which flows toward -.the.' upstream side, the period during which the desiliconization agent contributes to the reaction can become long by a time from the adding of the desiliconization agent to 1/4 - 1/2 rotation of the impeller. 10, to be beneficial to the reaction efficiency. Therefore, if the value of the distance M from the rotation center of the impeller 10 to the adding position is same, it is preferable to add the desiliconization agent at the downstream side. [0166] In the present invention, the optimum range of the adding of the desiliconization agent is prescribed to be 0 FIGS. 36 (I)- (IV) are views which show the finding as the relation between the agitation vortex and the adding position of the refining agent. In the above-described embodiments, the impeller 10 having a cross shape (that is, the impeller 10 has four blades) is used, and the whole of the impellers 10 is immerged in the hot metal. Stop at an arbitrary depth at the lifting/lowering position 11 is available. If the condition for generating the agitation vortex at the whole of the width D of the tap hole trough can be provided, the shape, the rotation speed, and the like of the impeller 10 are not limited. [0167] The refining device 100 can be constructed in such a manner that the agent feeding lance 17 is free movable in the X direction and the Y direction (as shown in FIG. 32) in the vicinity of the agitation position. Moreover, the constructions of the refining device 100 and the blast furnace casting floor 1, and' the whole construction, shape, dimension, number, material and the like can be suitably changed based on the purpose of the present invention. In the above-described embodiments, the desiliconization treatment where the desiliconization agent is used as one of the refining agents for refining the hot metal is described. However, the case where the desulfurization agent is used is same. That is, the present invention shows an optimum means for increasing the reaction rate by efficiently entraining the refining agent into the hot metal to enlarge the interface area of the reaction between the refining agent and the hot metal. Similarly to the desiliconization treatment, in the desulfurization treatment, the refining performance is high and is independent of the sort and the composition of the refining agent. Possibility of Use in Industry [0168] The present invention can be suitably used in a method for continuously refining the hot metal tapped from the blast furnace, for example. Claims 1. A continuous refining method, comprising: adding a refining agent to a hot metal which flows in a hot metal flow passage of a blast furnace casting floor; and mixing the hot metal with the refining agent by rotating an impeller which is immerged in the hot metal to continuously refine the hot metal, characterized in that: a piece number of blades of the impeller which is immerged in the hot metal and rotated is set as 3 - 6, and the blade is set to satisfy following formulas (1) and (2); and the impeller is immerged in the hot metal in such a manner that following formulas (3) and (4) are satisfied, bO & bl ... (1) 0.2s d/D s 0.8 ... (2) 0 0 wherein bO represents a height (m) of a base portion of the blade, bl represents a height (m) of a tip portion of the blade, d represents a width (m) of the blade, D represents a maximum width (m) of the hot metal flow passage, Z represents a maximum depth (m) of the hot metal which flows in the hot metal flow passage, hi represents a distance (m) from an upper end of the base portion of the blade to an upper surface of the hot metal, and h2 represents a distance (m) from a lower end of the base portion of the blade to a deepest part of a bottom portion of the hot metal flow passage. 2. The continuous refining method according to claim 1, wherein the refining agent is a desiliconization agent, and the refining is a desiliconization where the hot metal and the desiliconization agent are mixed with each other to continuously remove silicon in the hot metal. 3. A continuous refining method of a blast furnace casting floor, the continuous refining method comprising: adding a refining agent to a hot metal which flows in a hot metal flow passage of the blast furnace casting floor; and mixing the hot metal with the refining agent by rotating an impeller which is immerged in the hot metal to continuously refine the hot metal, characterized in that: a step for making the hot metal fall is arranged in the hot metal flow passage and the impeller is arranged at a downstream side of the step; an adding position at which the refining agent is added is disposed at a downstream side of the impeller, and a position at which a slag generated after the hot metal is agitated by the impeller is removed is disposed at a downstream side of the adding position; and the hot metal is refined after a width of the impeller is set in such a manner that a following formula (11) is satisfied, the step is set in such a manner that following formulas (12) - (14) are satisfied, the adding position at which the refining agent is added is set in such a manner that- a following formula (15) is satisfied, and the position at which the slag is removed is set in such a manner that a following formula (16) is satisfied, 0.3 0 H/Z s: 1 ... (13) 6 ^ 30 ... (14) 0 1.2s R/D £ 5 ... (16) wherein d represents a width (m) of the impeller, D represents a maximum width (m) of the hot metal flow passage, L represents a distance (m) from the step to the impeller, H represents a height (m) of the step, Z represents a depth (m) of the hot metal, 6 represents a gradient (deg) of the step, M represents a distance (m) from a center of a rotation shaft of the impeller to the adding position, and R represents a distance (m) from the center of the rotation shaft of the impeller to the position at which the slag is removed. 4. The continuous refining method according to claim 3, wherein the hot metal is refined after setting in such a manner that, following formulas (11a) - (16a) are satisfied, 0.55 0 H/Z > 2.2 ... (13a) e > 45 ... (14a) 0 1.-2 5. A blast furnace casting floor equipment, comprising: a hot metal flow passage in which a hot metal tapped from a blast furnace flows; an adding device for adding a refining agent to the hot metal which flows in the hot metal flow passage; an agitation device which has an impeller for agitating the hot metal; and a slag draining trough through which a slag on the hot metal generated after an agitation by the agitation device is drained to the external, characterized in that: a different level portion for making the hot metal fall is arranged at an upstream side of the hot metal flow passage and the agitation device is arranged in such a manner that the impeller is positioned at a downstream side of the different level portion; the adding device is disposed at a downstream side of the impeller, and the slag draining trough is disposed at a downstream side of the adding device; a width of the impeller is set in such a manner that a following formula (11) is satisfied; the different level portion is set in such a manner that following formulas (12) - (14) are satisfied; a position of the adding device is set in such a manner that a following formula (15) is satisfied; and a position of the slag draining trough is set in such a manner that a following formula (16) is, satisfied, 0.3 0 H/Z > 1 ... (13) e a 30 ... (14) 0 1.2s R/D £ 5 ... (16) wherein d represents a width (m) of the impeller, D represents a maximum width (m) of the hot metal flow passage, L represents a distance (m) from the different level portion to the impeller, H represents a height (m) of the different level portion, Z represents a depth (m) of the hot metal, 9 represents a gradient (deg) of the different level portion, M represents a distance (m) from a center of a rotation shaft of the impeller to the adding device, and R represents a distance (m) from the center of the rotation shaft of the impeller to the slag draining trough. 6. The blast furnace casting floor equipment according to claim 5, wherein following formulas (11a) - (15a) are satisfied, ■ 0.55 s d/D 0 H/Z a 2.2 ... (13a) e s: 45 ... (14a) 0 1.2 s R/D s 4.4 .... (16a) 7. A continuous refining method of a blast furnace casting .floor, the continuous refining method comprising: adding a refining agent to a hot metal which flows in a hot metal flow passage of the blast furnace casting floor; and mixing the hot metal with the refining agent by rotating an impeller which is immerged in the hot metal to continuously refine the hot metal, characterized in that: the hot metal is made fall from a different level portion which is arranged in the hot metal flow passage, and the impeller is arranged at a downstream side of the different level portion to agitate the hot metal; and the impeller is moved in a range of a following formula (12) along the hot metal flow passage when the hot metal is refining, 0 wherein D represents a maximum width (m) of the hot metal flow passage, and L represents a distance (m) from the different level portion to the impeller. 8. A blast furnace casting floor equipment, comprising: a hot metal flow passage in which a hot metal tapped from a blast furnace flows; an adding device for adding a refining agent to the hot metal which flows in the hot metal flow passage; and an agitation device which has an impeller for agitating the hot metal, characterized in that: a different level portion for making the hot metal fall is arranged at an upstream side of the hot metal flow passage and the agitation device is arranged in such a manner that the impeller is positioned at a. downstream side of the different level portion; and the agitation device is movable in a range of a following formula (12) along the hot metal flow passage, 0 wherein D represents a maximum width (m) of the hot metal flow passage, and L represents a distance (m) from the different level portion to the impeller. 9. A continuous refining method of a blast furnace casting floor, the continuous refining method comprising: adding a refining agent into a tap hole trough of the blast furnace casting floor; and mixing the hot metal with the refining agent by an impeller to continuously refine the hot metal, characterized in that a component of a longitudinal direction of the tap hole trough of a swirling flow generated by the impeller is a field which is orthogonal to a flow direction of the hot metal or opposite to the flow direction of the hot metal, and the refining agent is added at least one of following positions (i) and (ii), (i) a position which satisfies a following formula (15b) at an upstream side of the impeller, (ii) a position which satisfies a following formula (15) at a downstream side of the impeller, 0 0 wherein D represents a maximum width (m) of a hot metal flow passage, and M represents a distance (m) from a rotation center of

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2837-chenp-2008 drawings.pdf

2837-chenp-2008 form-1.pdf

2837-chenp-2008 form-18.pdf

2837-chenp-2008 form-3.pdf

2837-chenp-2008 form-5.pdf

2837-chenp-2008 pct.pdf