|Title of Invention||
"METHOD OF REFINING HIGH-CARBON METAL MELT"
|Abstract||The invention relates to a method of refining a highcarbon metal melt, comprising charging the high—carbon metal melt into a refining vessel and blowing through the melt, an oxygencontaining gas through tuyures located in the refining vessel under the melt. The oxygen-containing gas in an amount ensuring the supply of SO-100% of the oxygen necessary to obtain a predetermined degree of refining is blown during the process of charging the refining vessel with the melt.|
|Full Text||The invention relates to metallurgy, in particular to methods of refining a high-carbon metal melt, for example iron melt (hot metal), when steel or a semiproduct for its production is being produced
The method most similar in respect to engineering essence to the instant method is a method for refining high-carbon melt, for example, hot metal, in a converter with bottom blowing, the method including charging a melt into a converter and blowing it with oxygen-containing gas (see Y.A Kudrin. Steel Metallurgy. Moscow: Metallurgia. 1981. pp. 234-240). Wherein, the volume of the inner space of the converter is 0.5-0.9 ml. which is 3-6 times more that the volume of a metal bath. The duration of the blowing with an intensity of feeding oxygen of about 3 m tonfmin is 15-20 min. the duration of the melting from tapping to tapping is about 40 min.
A drawback of the known method is the large capital expenditures that are related to the large volume of the converter, the high productivity of the gas-exhaust and gas-purification devices and the oxygen feeding svstem. the large dimensions of the plant building. All of this is a consequence of the fact that high productivity of the process is achieved by reducing the duration of blowing the melt to 15-20 minutes (0,3-0.5 the duration of the melting cycle), even in the case where the capacity of the converter is very large (to 350 tons). The highly intensive oxygen blowing of the melt (3-5 in tonmin). necessary in that case, is accompanied by vigorous boiling of the bath A converter with a large volume is required in order to avoid the ejection of metal and slag. Highly productive gas-discharge and gas-purification devices and a large expensive plant building are also necessary.
- 1A -
The technical effect achieved upon use of the present invention is a reduction of the capita] expenditures spent on carrying out the process of refining a high-carbon metal melt, for example, hot metal, and, as a result, a reduction of the cost of the obtained product.
This is achieved in a known method comprising charging a high-carbon metal melt into a refining vessel and blowing an oxygen-containing gas through tuyures located in the refining vessel under the melt, in that in accordance with the invention, the oxygen-containing gas in an amount ensuring the supply of 80-100% of the oxygen necessary to obtain a predetermined degree of refining is blown in the process of filling the refining vessel with the melt.
Wherein, iron-carbon melt may be used as the high-carbon metal melt.
After filling the refining vessel with the melt within the limits of 0.5-0.9 of its height, it is advisable to reduce the oxygen flow rate in the oxygen-containing gas to a value equal to 0.3-0.5 of its initial value.
It is desirable to use at least two refining vessels, feeding them in turn to be filled with high-carbon metal melt to ensure continuous refining of the melt.
A ladle may be used as the refining vessel
Reduction of the capital expenditures on carrying out the process and of the cost of the produced metal is effected in the first place as a result of the fact that in the proposed process the same productivity (determined by the productivity of the hot metal melting unit) is obtained at a lower intensity of feeding oxygen. This is due to the fact that when the invention is implemented short-time oxygen blowing of the melt in the converter is replaced with more lengthy blowing -during the whole period of charging the hot metal from the hot metal melting unit into the refining vessel
A liquid-phase reduction unit "Romelt," for example, may be used as this hot metal melting unit, and ladles, alternately placed under the stream of hot metal, with tuyeres located under the melt, for example, with "false stopper" type devices - as the refining vessels.
3 With the productivity of the liquid-phase reduction unit (Romelt) equal to, for example,
1 ton/min, a 50 ton ladle will be filled with hot metal in the course of 50 minutes. If all that time (instead of 15-20 minutes in the converter) is used for refining the hot metal, then the intensity of feeding oxygen, and consequently the productivity of the gas-outlet path and gas purification, may be 2-3 times lower than in the converter They may be combined with the gas-outlet system and the gas purification of the Romelt unit.
In addition to the general reduction of the intensity of blowing, a reduction of the volume of the refining vessel (as compared with the converter) and related thereto reduction of the capital expenditures and cost of the metal will occur as a result of the fact that in the final part of filling the ladle with metal, the oxygen flow rate is additionally reduced. The volume of free space in the ladle at the beginning of the filling is sufficiently large to prevent ejection's. Therefore it is possible to a certain degree to not limit the intensity of feeding the oxygen into the ladle. In the final part of filling the ladle with metal, the volume of free space above the level of the bath is reduced, and the danger of ejections increases. Therefore the oxygen flow rate at this stage is, in accordance with the invention, reduced
Incomplete refining of the hot metal in this stage is compensated either by some increase of the refining (as compared with that necessary in order to produce a predetermined steel) in the first stage of filling the ladle or by additionally refining the metal after the ladle is filled.
Thus, as a result of carrying out the invention, there is no longer the necessity of providing large-volume converters, highly-productive gas-outlet and gas purification devices and large buildings for their arrangement and servicing. If converters are already present at the plant, the implementation of the invention may increase their productivity (as a result of the preliminary partial refining of the hot metal in the ladle), ensure the full volume of production while one of the converters is being repaired, etc
4 The range of values of the amount of oxygen blown in the process of filling the refining
vessel with the melt within the range of 80-100% of the total amount of oxygen necessary in
order to obtain the predetermined degree of melt refining is explained by the laws of oxidation of
the carbon of the metal. With values less than 80%, a sufficient degree of refining the hot metal
will not be ensured in the course of charging it into the refining vessel. This results in
excessively large expenditures on additional refining of the metal after finishing the charge - in
the already filled vessel
This range is established in direct proportion to the predetermined content of carbon in the metal after oxygen blowing and to the height of the ladle'. This is related to the fact that at a high final content of carbon it is easier to compensate a reduction of the degree of refining a metal in the final stage of filling a ladle by increasing it in the first stage of filling. Wherein, sometimes it is possible to increase the fraction of oxygen, fed during the filling of the ladle, to 100%. The height of the ladle has an effect on the probability of ejections during the blowing, and therefore when the height is large, the fraction of the oxygen injected during the filling of the ladle may be increased.
The range of values of the height of filling the ladle within the limits of 0.5-0.9 of its height, at which the consumption of the fed oxygen being fed is reduced, is explained by the laws of oxidation of the impurities of the semiproduct. The value of that height of filling the ladle characterizes the reserve of the reliability of the process of blowing from the point of view of preventing ejections with maximum use of the possibilities of blowing tuyeres. At values of the aforesaid height less than 0.5 the height of the ladle, the possibilities of the blowing tuyeres will be used to an insufficient degree, the necessary degree of refining the hot metal during the charging will not be ensured, refining in an already filled ladle will have to be continued for too long a time, heat losses increase. At values of the aforesaid height greater than 0.9 the height of the ladle, the probability of the ejection of metal and slag when the upper portion of the ladle is
5 filled increases to an inadmissible value. The aforesaid range is established in direct proportion
to the height of the vessel
The range of values of the degree of reduction of the oxygen flow rate within the limits of 0.3-0.5 of the initial value is explained by the laws of chemical interaction of oxygen with impurities of the melt. At values less than 0.3 the supply of the required volume of oxygen necessary for the predetermined oxidation of the impurities of the melt in the process of filling the ladle will not be ensured; refining in an already filled ladle will have to be continued for too long a time, heat losses will increase. At values greater than 0.5, the probability of ejections of metal and slag during the final stage of refining increases.
The aforesaid range is established in direct relationship to the height of the ladle and in reverse relationship to the selected height of filling the ladle at which the oxygen flow rate is reduced.
An analysis of scientific and patent literature shows that the distinctive features of the present method do not coincide with the features of known technical solutions. A conclusion is made on the basis of this that the present technical solution conforms with the "inventive level" criterion.
An embodiment of the method is presented below which does not exclude other embodiments within the limits of the set of claims.
The method of refining high-carbon melt when steel is to be obtained therefrom is carried out in the following manner. Hot metal for producing steel, obtained in a "Romelt" type liquid-phase reduction unit, comprises 4% carbon, 0.15% silicon, 0.2% manganese and 0.035% phosphorus. In order to obtain steel having a predetermined composition, the metal prior to deoxidation (prior to termination of the refining) should comprise: 0.05% carbon, 0.05% silicon, 0.1% manganese and 0.01% phosphorus.
6 The hot metal is tapped from the unit with a mass flow of 1 ton/min into a refining ladle
having a capacity of 50 tons. The ladle is filled in 50 minutes, after which the following ladle is
placed under the stream.
If necessary, scrap (own waste) in an amount of 10-15% is preliminarily loaded into each ladle. The scrap is heated by supplying natural gas and oxygen through one or more "false stopper" type tuyeres provided in the ladle. In the process of filling the ladle with hot metal, oxygen-containing gas is entered therein through these tuyeres in an amount ensuring the supply of 80-100% of the oxygen which is necessary to obtain the predetermined degree of refining,. Wherein slag-forming materials may also be entered into the ladle.
The oxygen flow rate for oxidation of a predetermined amount of hot metal impurities Q, m3/ton, is determined according to the equation:
where and are the stoichiometric coefficients of oxygen and the oxidized impurity in the oxide;
is the atomic weight of the impurity is the percent (absolute) of the oxidized impurity In the example under consideration, with the predetermined practically complete oxidation of the impurities the value of
is equal to:
In order to take the additional oxygen flow rate for oxidation of the combustible components of the oxygen-containing gas, oxidation of iron and incomplete use of oxygen into
7 account, the value of should be multiplied by the factor where is an empirical
coefficient equal to 0.01-0.7, dimensionless. The value of is selected in direct relationship on
the content of oxygen in the oxygen-containing gas and on the content of carbon and hydrogen
therein: (at.%C) + 2x(at.%H).
In the example under consideration (when the metal is being blown with oxygen with the
addition of 8% CH4 as a protective gas) a = 0.45. Consequently, the oxygen flow rate that is
necessary to produce the predetermined steel is
The oxygen consumption q per minute (flow rate) is determined according to the equation
where g is the mass flow of the melt fed into the ladle, ton/min.
In the example under consideration, the oxygen flow rate per minute that is necessary for almost complete refining of the hot metal in the course of tapping into the ladle is q = 1 x 53.5 = 53.5 m3/min. But the oxygen flow rate should be reduced in the final stage of filling the ladle in order to prevent ejections. In order to compensate the incomplete refining of the hot metal in this case, an additional amount of oxygen should be fed into the ladle after the latter is filled. Variants of carrying out the method are shown in the table below with different technological parameters (for the conditions of the example under consideration: g = 1 ton/min, capacity of the ladle - 50 tons, the composition of the hot metal and metal after oxygen blowing [before deoxidation]) are indicated on page 5. It is accepted that the oxygen flow rate in the second stage of filling the ladle changes in a linear manner from
As is evident from the table, the first embodiment of carrying out the method is unacceptable, since due to the too early and strong reduction of the oxygen flow rate during the filling of the ladle, additional refining of the metal in the already filled ladle is required for a
8 period which is too long. The loss of heat whereby is greatly increased. The fifth embodiment
of the method is unacceptable too, since due to the too late and insufficient reduction of the
oxygen flow rate at the end of filling the ladle, the probability of ejections of metal and slag from
the ladle inadmissibly grows.
In the optimum embodiments 2-4, additional refining of the metal may be earried out without a great deal of difficulty, and the probability of ejections is not great.
During the smelting of steel with an increased content of carbon, the additional refining of the metal with oxygen may be excluded, entering all of the necessary oxygen while the ladle is being filled. For this, it is necessary to provide for some "over-refining" of the melt at the beginning of filling the ladle by increasing the initial oxygen flow rate as compared with that necessary. For example, in order to obtain a content of 1% carbon instead of
0.05% in the metal under the conditions of the preceding example prior to deoxidation, = 29 m3/ton, m3/min are respectively required.
In the initial stage of filling the ladle, the blowing should be carried out with a per minute oxygen flow rate in an oxygen-containing gas equal to 53.5 m /min. After filling the ladle to 0.7 of its height, the oxygen flow rate should be reduced to 15.2 m /min (0.3 of the initial flow rate). The total oxygen flow rate for the whole period of filling a 50 ton ladle will be: 0.7x50x53.5 + 0.3x50x15.2 = 2100 m3 or 42 m3/ton (100% of the whole amount of oxygen necessary to refine the hot metal to 1 % carbon).
The calculated values of oxygen flow rate indicated in the table and in the text are corrected in the course of a real process, taking the determined continuous weighing of the real consumption of the hot metal charged into the ladle (g) and the results of an express analysis of a sample of the metal into account. After being filled, the ladle is moved to the point of additional refining and of finishing the metal. Wherein, blowing may be continued (with oxygen-
9 containing or neutral gas depending on the used technology) or it may be terminated if it is not
The slag is removed from the ladle by one of the known methods: by drawing off or with a pumping siphon or by reladling. Reladling may be combined with additional refining of the metal with the proposed method.
Use of the proposed method makes it possible to reduce capital expenditures on organizing the refining of hot metal into steel by 25-75%.
Embodiments of carrying out 3 the method
Parameters 1 2 4 5
1. Height of ladle, m 2.4 53.5 2.4 2.6 3.0 3.0
2. Initial oxygen flow rate (necessary per minute oxygen flow rate for predetermined practically complete refining of pig iron in course of production), q*i, m3/min 53.5 53.5 53.5 53.5
3. Ratio of height of filling the ladle prior to the beginning of the final rcduclion of flow rate of oxygen being fed to the total height of the ladle 0,4 0.5 0.7 0.4 0.9 0.95
4. Ratio of flnal oxygen flow rate (at end of filling the ladle) to the initial, q*2/ q*/ 0.2 0.3 0.5 0.6
5. Final oxygen flow rate, q*2, m'Vmin 10.7 16.05 21.4 0.428 26.75 0.535 32.1
6 Same, per 1 ton of metal in ladle, m7ton min 0.214 0.321 0.642
7. Probability of emissions low low low low high
S- Average oxygen flow rate at final stage of filling the ladle (with gradual reduction of oxygen flow rate) ^v,,,,,^,,., - (q*, + q*})/2, m'Vmin 32.1 34.775 37.45 40.13 42.S
9. Amount of oxygen entered for the whole period of filling the ladle, m 20 53.5-30 32.1-2033 2553.5125 34,745-2207 35 53.5-15 37,45=2434 45 53.5-5 40.13-260S 47.5 53.5-2.5 42.8-2648
10. Same, % of whole amount of oxygen necessary for refining iron 76 82.5 91 97,5 99
11. Necessary time for additional feeding of oxygen through tuyeres after filling the ladle, min (2675-2033): 10.7-60 (2675-2207): 16 05-29.2 (2675-2434): :21.4=11.4 (2675-2608): :26.75=2.5 (2675-2648): :32.1-0.84
1. A method of refining a high—carbon metal melt, comprising charging the high-carbon metal melt into a refining vessel and blowing through the melt, an oxygen-containing gas through tuyures located in the refining vessel under the melt, characterized in that the oxygen—containing gas in an amount ensuring the supply of 80-10055 of the oxygen necessary to obtain a predetermined degree of refining is blown during the process of charging the refining vessel with the melt.
2. A method as claimed in claim 1, wherein iron-carbon melt is used as the high—carbon metal melt.
3. A method as claimed in any one of claims 1, 2, wherein after filling the refining vessel with the melt within the limits of 0.5-0.9 of its height, the oxygen flow rate in the oxygen-containing gas is reduced to a value equal to 0.3-0.5 of its initial value.
4. A method as claimed in any one of claims 1-3, wherein at least two refining vessels are used, which are fed in turn to be filled with high-carbon metal melt to ensure continuous refining of the melt.
5. A method as claimed in any one of claims 1-4, wherein a ladle may be used as the refining vessel.
The invention relates to a method of refining a highcarbon metal melt, comprising charging the high—carbon metal melt into a refining vessel and blowing through the melt, an oxygencontaining gas through tuyures located in the refining vessel under the melt. The oxygen-containing gas in an amount ensuring the supply of SO-100% of the oxygen necessary to obtain a predetermined degree of refining is blown during the process of charging the refining vessel with the melt.
|Indian Patent Application Number||00161/CAL/2000|
|PG Journal Number||17/2007|
|Date of Filing||16-Mar-2000|
|Name of Patentee||MOSKOVSKY GOSUDARSTVENNY INSTITUT STALI I SPLAVOV (TEKHNOLOGICHESKY UNIVERSITET)|
|Applicant Address||FEDERATION, MOSCOW, LENINSKY PROSPEKT.D.4.|
|PCT International Classification Number||C 21 C 7/10|
|PCT International Application Number||N/A|
|PCT International Filing date|