|Title of Invention||
PYROMETALLURGICAL REACTOR COOLING ELEMENT AND ITS MANUFACTURE
|Abstract||This invention relates to a method of manufacturing by continuous casting a pyrometallurgical reactor cooling element with flow channels. In order to enhance heat transfer capability, the wall surface area of the flow channel, which is traditionally round or oval in cross-section, is increased without increasing the diameter or length of the flow channel. The invention also relates to the element fabricated by this method.|
TWEPATENTS ACT, 1S70
(39 of 1970)
(Section-10, rule 13)
PYROMETALLURGICAL REACTOR COOLING ELEMENT AND ITS MANUFACTURE
of Riihitontuntie 7, FIN-02200 Espoo, Finland a Finnish Public Limited Company
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:-
PYROMETALLURGICAL REACTOR COOLING ELEMENT AND ITS MANUFACTURE
The present invention relates to a method of manufacturing a .cooling 5 element for pyrometallurgical reactors, said element having at least one flow channel, and where the manufacture of the element is made by continuous casting, i.e. slip casting. In order to enhance the heat transfer capability of the element, the wall surface area of the cooling channel wall is increased with respect to its round or oval shape on cross-section without increasing 10 the diameter or length of the flow channel. The invention also relates to the element manufactured by this method.
The refractory of reactors in pyrometallurgical processes is protected by water-cooled cooling elements so that, as a result of cooling, the heat
15 coming to the refractory surface is transferred via the cooling element to water, whereby the wear of the lining is significantly reduced compared with a reactor which is not cooled. Reduced wear is caused by the effect of cooling, which brings about forming of so called autogenic lining, which fixes to the surface of a heat resistant lining and which is formed from slag and
20 other substances precipitated from the molten phases.
Conventionally cooling elements are manufactured in two ways: primarily, elements can be manufactured by sand casting, where cooling pipes made of a highly thermal conductive material such as copper are set in a
25 sand-formed mould, and are cooled with air or water during the casting around the pipes. The element cast around the pipes is also of highly thermal conductive material, preferably copper. This kind of manufacturing method is described in e.g. GB patent no. 1386645. One problem with this method is the uneven attachment of the piping acting as cooling channel to
30 the cast material surrounding it because some of the pipes may be completely free of the element cast around it and part of the pipe may be completely melted and thus damaged. If no metallic bond is formed between
completely melted and thus damaged. If no metallic bond is formed between the cooling pipe and the rest of the cast element around it, heat transfer will not be efficient. Again if the piping melts completely, that will prevent the flow of cooling water. The casting properties of the cast material can be 5 improved, for example, by mixing phosphorus with the copper to improve the metallic bond formed between the piping and the cast material, but in that case, the heat transfer properties (thermal conductivity) of the copper are significantly weakened by even a small addition. One advantage of this method worth mentioning is the comparatively low manufacturing cost and 10 independence from dimensions.
Another method of manufacture is used, whereby glass tubing in the shape of a channel is set into the cooling element mould, which is broken after casting to form a channel inside the element.
US patent 4,382,585 describes another, much used method of manufacturing cooling elements, according to which the element is manufactured for example from rolled copper plate by machining the necessary channels into it. The advantage of an element manufactured this
20 way, is its dense, strong structure and good heat transfer from the element to a cooling medium such as water. Its disadvantages are dimensional limitations (size) and high cost.
A well-known method in the prior art has been to manufacture a cooling 25 element for a pyrometallurgical reactor by casting a hollow profile as continuous casting i.e. slip casting through a mandrel. The element is manufactured of a highly thermal conductive metal such as copper. The advantage of this method is a dense cast structure, good surface quality and the cast cooling channel gives good heat transfer from the element to the 30 cooling medium, so that no effects impeding heat transfer occur, rather the heat coming from the reactor to the cooling element is transferred without
any excess heat transfer resistance directly to the surface of the channel and onwards to the cooling water. The cross-section of the cooling channel is generally round or oval and the mandrel has a smooth surface. This type of cooling channel is mentioned in US patent 5,772,955. , „, 5
In order to improve the heat transfer capability of a cooling element it is however preferable to increase the heat transfer surface area of the element. As demonstrated by the explanation below, according to the present invention this occurs by increasing the wall surface area of the flow
10 channel without enlarging the diameter or adding length. The wall surface area of the cooling element flow channel is increased by forming grooves in the channel wall during casting or by machining grooves or threads in the channel after casting so that the cross-section of the channel remains essentially round or oval. As a result, with the same amount of heat, a
15 smaller difference in temperature is needed between the water and the flow channel wall and an even lower cooling element temperature. The invention also relates to cooling elements manufactured by this method. The essential features of the invention will become apparent in the attached patent claims.
20 The ability of a cooling element to receive heat can be presented by means of the following formula:
Q = ax Ax AT, where Q = amount of heat being transferred [W] 25 a = heat transfer coefficient between flow channel wall and water [W/Km2] A = heat transfer surface area [m2] AT = difference in temperature between flow channel wall and water [K]
Heat transfer coefficient a can be determined theoretically from the formula 30 Nu=aD/λ
X = thermal conductivity of water [W/mK]
D = hydraulic diameter [m]
Or Nu = 0.023 x Re*0.8Pr*0A, where 5 Re = wOp/t] w = speed [mis]
D - hydraulic diameter of channel [ml p = density of water [kg/m3] TJ - dynamic viscosity 10 Pr - Prandtl number [ ]
Thus, according to the above, it is possible to influence the amount of heat transferred in a cooling element by influencing the difference in temperature, the heat transfer coefficient or the heat transfer surface area.
The difference in temperature between the wall and the tube is limited by the fact that water boils at 100 °C, when the heat transfer properties at normal pressure become significantly worse due to boiling. In practice, it is more advantageous to operate at the lowest possible flow channel wall
The heat transfer coefficient can be influenced largely by changing the flow speed, i.e. by affecting the Reynolds number. This is limited however by the increased loss in pressure in the tubing as the flow rate increases, which 25 raises the costs of pumping the cooling water and pump investment costs also grow considerably after a certain limit is exceeded.
In a conventional solution, the heat transfer surface area can be influenced
either by increasing the diameter cf the cooling channel and/or its length.
30 The cooling channel diameter cannot be increased unrestrictedly in such a
way as to be still economically viable, since an increase in channel diameter
increases the amount of water required to achieve a certain flow rate and furthermore, the energy requirement for pumping. On the other hand, the channel diameter is limited by the physical size of the cooling element, which for reasons of minimizing investment costs, is preferably made as small and 5 light as possible. Another limitation on length is the physical size of the cooling element itself, i.e. the quantity of cooling channel that will fit in a given area.
When it is desired to increase the heat transfer surface of the cooling
10 element presented herein, it is done by changing the wall shape of the slip
cast cooling element flow channel to achieve a greater heat transfer surface
area, calculated per flow channel length unit, with the same flow
cross-section (same rate is achieved with the same amount of water). This
increase in surface area is achieved, for example, by the following means:
15 At least one flow channel, essentially round in cross-section, is formed in
the slip-cast cooling element during casting, and threads are machined
into the flow channel after casting.
At least one flow channel, essentially round in cross-section, is formed in
the cast cooling element during slip casting, and rifle-like grooves are
20 machined into the flow channel after casting. The grooves are
advantageously made by using a so-called expanding mandrel, which is
drawn through the flow channel. Grooving can be made to e.g. a hole
closed at one end, in which case the mandrel is drawn outwards. A hole
made in the channel, which is open at both ends, is made either by
25 pushing or drawing a purpose-designed tool through the channel.
The most advantageous increase in surface area is obtained by forming,
during casting, one or several grooved, preferably straight-grooved, flow
channels in the cooling element, using a purpose-designed, grooved
casting mandrel. Despite the grooving, the shape of the flow channel is
30 still essentially round or oval in cross-section. Using this method will
avoid mechanical machining stages after casting.
In all the methods described above, it is evident that, should there be channel parts in the flow channel transverse with regard to the casting direction, these parts are made mechanically by machining, for instance by 5 drilling, and the openings not belonging to the channel are plugged.
The benefit of the method to increase heat transfer surface area described in this invention was compared with a method of the prior art with the aid of the example given here. In connection with the example there are some
10 diagrams to illustrate the invention, in which
Figure 1 shows a principle drawing of the cooling element used in the tests, Figure 2 shows a cross-sectional profile of the test cooling element, Figures 3a -3d indicate the temperature inside the element at different measuring points as a function of melt temperature,
15 Figure 4 presents the heat transfer coefficient calculated from the measurements taken as a function of the melt, and
Figure 5 presents the differences in temperature of the cooling water and the channel wall at different cooling levels for normalized cooling elements.
The cooling elements relating to the present invention were tested in practical tests, where said elements A,B,C and D were immersed in about 1cm deep molten lead from the bottom surface. Cooling element A had a conventional smooth-surfaced channel, and this element was used for
25 comparative measurements. The amount of cooling water and the temperatures both before feeding the water into the cooling element and afterwards were carefully measured in the tests. The temperature of the molten lead and the temperatures inside the cooling element itself were also carefully measured at seven different measuring points.
Figure 1 shows the cooling element 1 used in the tests, and the flow channel 2 inside it. The dimensions of the cooling element were as follows: height 300 mm, width 400 mm and thickness 75 mm. The cooling tube or flow channel was situated inside the element as in Figure 1, so that the centre of 5 the horizontal part of the tube in the figure was 87 mm from the bottom of the element and each vertical piece was 50 mm from the edge of the plate. The horizontal part of the tube is made by drilling, and one end of the horizontal opening is plugged (not shown in detail). Figure 1 also shows the location of temperature measuring points T1 - T7. Figure 2 presents the surface shape 10 of the cooling channels and Table 1 contains the dimensions of the test cooling element channels and the calculated heat transfer surfaces per metre as well as the relative heat transfer surfaces.
Figures 3a - 3d demonstrate that the temperatures of cooling elements B, C and D were lower at all cooling water flow rates than the reference measurements taken from cooling element A. However, since the flow 20 cross-sections of the said test pieces had to be made with different dimensions for technical manufacturing reasons, the efficiency of the heat transfer cannot be compared directly from the results in Figures 3a - 3d. Therefore the test results were normalized as follows:
25 Stationary heat transfer between two points can be written:
Q = Sxλx(T1-T2), where
Q = amount of heat transferred between the points [W] S = shape factor (dependent on the geometry) [m]
λ= thermal conductivity of the medium [W/mK] T1 = temperature of point 1 [K] T2 = temperature of point 2 [K]
5 Applying the above equation to the test results, the following quantities are obtained:
Q = measured thermal power transferred to cooling water λ= thermal conductivity of copper [W/mK] T1= temperature at base of element as calculated from tests [K]
10 T2 = temperature of water channel wall as calculated from tests [K]
S = shape factor for a finite cylinder buried in a semi-infinite member (length L, diameter D) shape factor can be determined according to the equation S = 2πL/ln(4z/D) whenZ>1.5D, z = depth of immersion measured from the centre line of the cylinder [m].
The heat transfer coefficients determined in the above way are presented in Figure 4. According to multivariate analysis a very good correlation is obtained between the heat transfer coefficient and the water flow rate as well as the amount of heat transferred to the water. The regression equation heat
20 transfer coefficients for each cooling element are presented in Table 2.
Thus a [W/m2K] = c + a x v [m/s] + b x Q [kW].
To make the results comparable, the cross-sectional areas of the flow
channels were normalized so that the amount of water flow corresponds to
the same flow rate. The flow channel dimensions and heat transfer surface
30 areas normalized according to the flow amount and rate are presented in
Table 3. Using the dimensions given in Table 3 for cases A", B", C"and D" and the heat transfer coefficients determined as above, the temperature difference of the wall and water for normalized cases regarding the flow amount were calculated as a function of water flow rate for 5 ,, 10, 2Cband 30 5 kW heat amounts with the equation ΔT=Q/(axA)
The results are shown in Figure 5. The figure shows that all the cooling elements manufactured according to this invention achieve a certain amount of heat transfer with a smaller temperature difference betweervthe water and the cooling channel wall, which illustrates the effectiveness of the method.
15 For example, at a cooling power of 30kW and water flow rate of 3 m/s, the temperature difference between the wall and water in different cases is:
When the results are compared with the heat transfer surfaces, it is found that the temperature difference between the wall and the water needed to transfer the same amount of heat is inversely proportional to the relative heat transfer surface. This means that the changes in surface area
25 described in this invention can significantly influence the efficiency of heat transfer.
1. A method to manufacture a pyrometallurgical reactor cooling element, said element being slip-cast manufactured of a highly thermal conductive metal and having at least one cooling water flow channel, characterized in that, the cooling water flow channel, essentially round or oval in cross-section is formed in the cooling element during casting by means of a grooved mandrel, said flow channel comprised of a plurality of straight channel parts, at least one channel parts being transverse to the other channel parts and the wall surface area of the flow channel inside the cooling element is subsequently increased after casting, without increasing the diameter or length of the flow channel by machining threads or rifle-like grooves on the inner surface of each of the flow channel parts.
2. A method according to claim 1, characterized in that the rifle-like grooves are made by means of an expanding mandrel.
3. A method according to claim 1, characterized in that the highly thermal conductive metal is copper.
4. A pyrometallurgical reactor cooling element, slip-cast manufactured of highly thermal conductive metal and having at least one cooling water flow channel, characterized in that the wall surface area of the flow channel is increased, without enlarging the diameter of the flow channel or adding to the length.
5. A cooling element according to claim 4, characterized in that the flow channel, essentially round or oval in cross-section, is formed by means of a grooved mandrel.
6. A cooling element according to claim 5, characterized in that the grooves of the flow channel, essentially round or. oval in cross-section, are straight-grooved.
7. A cooling element according to claim 4, characterized in that the flow channel, essentially round in cross-section, is formed by means of a mandrel and that threads are machined into the flow channel after casting.
8. A cooling element according to claim 4, characterized in that the flow channel, essentially round in cross-section, is formed by means of a mandrel and that rifle-like grooves are machined into the flow channel after casting.
9. A cooling element according to claim 8, characterized int hat the rifle-like grooves made by means of an expanding mandrel.
10. A cooling element according to claim 4, characterized in that the element is made of copper.
Dated this 18th day of June 2001.
in-pct-2001-00738-mum-petition under rule 123(14-8-2001).pdf
in-pct-2001-00738-mum-petition under rule 123(30-1-2002).pdf
in-pct-2001-00738-mum-petition under rule 124(30-1-2002).pdf
in-pct-2001-00738-mum-petition under rule 138(10-10-2003).pdf
in-pct-2001-00738-mum-power of attorney(19-6-2001).pdf
|Indian Patent Application Number||IN/PCT/2001/00738/MUM|
|PG Journal Number||13/2008|
|Date of Filing||19-Jun-2001|
|Name of Patentee||OUTOKUMPU OYJ|
|Applicant Address||RIIHITONTUNTIE 7, FIN-02200 ESPOO,|
|PCT International Classification Number||F27D1/12, F28F1/40, B22D11/00|
|PCT International Application Number||PCT/FI99/01029|
|PCT International Filing date||1999-12-14|