AU2009351077A1

AU2009351077A1 - Furnace for lead-slag reduction and process for lead-slag reduction

Info

Publication number: AU2009351077A1
Application number: AU2009351077A
Authority: AU
Inventors: Dawei Cui; Zhaolei Deng; Jiang Gui; Qiuan He; Zhijun He; Jimu Jiang; Dong Li; Dongbo Li; Jiamei Liu; Zhifang Lu; Fuyou Sun; Yunfeng Suo; Jianming Wang; Zhongshi Wang; Kejian Wei; Zhenmin Zhang
Original assignee: China ENFI Engineering Corp
Current assignee: China ENFI Engineering Corp
Priority date: 2009-08-14
Filing date: 2009-09-24
Publication date: 2012-03-01
Anticipated expiration: 2029-09-24
Also published as: WO2011017855A1; AU2009351077B2

Abstract

A furnace for lead-slag reduction includes a furnace body (1), bases (4) for supporting the furnace body (1), lances (6) for injecting pulverized coal and electrodes (7). The furnace body (1) includes a hearth, a feed inlet (11), a lead-liquid outlet (12), a slag tap (13), an emptying outlet (18), electrode insertion holes (17) set on top of the furnace body (1), a smoke outlet (14) and lance insertion holes (16) set on the bottom of the furnace body (1). The lances (6) can be inserted into the furnace through the lance insertion holes (16) to inject pulverized coal into the furnace. The electrodes (7) can be inserted into the furnace through the electrode insertion holes (17) to heat materials in the furnace. Furthermore, a process for lead-slag reduction is also described.

Description

FURNACE FOR LEAD SLAG REDUCTION AND PROCESS FOR LEAD SLAG REDUCTION FIELD The present disclosure generally relates to a furnace for lead slag reduction 5 and a process for lead slag reduction, more particularly, to a furnace and a process for lead oxide slag reduction. BACKGROUND Conventional lead bullion smelting processes mainly comprise the QSL process, the SKS process, the Kivcet process, a top-blown immersion bath smelting 10 technology (mainly comprising the Ausmelt process and the ISA process) and the Kaldo process. The QSL process, the top-blown immersion bath smelting technology and the Kaldo process are a one-step lead smelting process. Lead sulfide concentrate is fed into a furnace and smelted by oxidizing to produce a part of lead bullion and a lead oxide slag, and the lead oxide slag is reduction 15 smelted in the furnace to produce lead bullion and a discarded slag. The QSL process and the Kaldo process have been applied in industrial fields, however, a dust rate in a reduction stage is up to 30%-35%, which may cause a large amount of lead to circulate in the system, and economic indicators are poor. A two-stage operation mode in one furnace of the Ausmelt process has been proven to be not 20 successful, and the main problem is that the dust rate in the reduction stage is high. The Kivcet process belongs to a levitation smelting method and is a flash lead smelting method, and besides high dust rate, materials need to be pretreated extremely strictly, so that unit capacity investment is relatively high. In order to solve the above problems, the lead sulfide concentrate is smelted 25 to produce a part of lead bullion and a lead oxide slag, and the lead oxide slag is treated in a blast furnace after cast into ingots. Because a temperature of a flue gas leaving the blast furnace is very low, the dust rate is lower than that in the reduction stage of the above processes. However, during a lead smelting process in the blast furnace, an enthalpy of lead oxide can not be used. Moreover, a slag 30 casting machine is necessary for casting lead oxide slag into the ingots, thus 2 increasing the equipment investment, the power consumption and the installation space. Furthermore, during the reduction process, expensive lump metallurgical coke is needed to use as a reducing agent. Therefore, during the lead smelting process in the blast furnace, the energy consumption and the cost are high. 5 A method and a device for directly reducing a liquid lead oxide slag are described in Chinese Patent Application CN101086038A entitled "method and device for directly lead smelting by bath smelting". In this method, a bottom blown bath reduction furnace is used, oxygen-natural gas or oxygen-coal gas are injected into a reduction furnace from a bottom or bottom side of the reduction 10 furnace using a lance, meanwhile, coke particles are fed into the furnace through a feeding port in a top of the reduction furnace, thus finally producing lead bullion, a flue gas and a discarded slag. This method is substantially the same as the reduction stage of the QSL process, except for different reducing agents. Although the enthalpy utilization problem of the lead oxide slag may be solved, a large 15 amount of heat required by a reduction reaction in the furnace is obtained by burning natural gas or coal gas. Therefore, the required volume of natural gas or coal gas is large, and natural gas and coal gas are relatively expensive, so that the cost is high. In addition, the resulting flue gas volume is large, the dust rate is high, the direct recovery rate of lead is low, the recovery effect is poor, the heat 20 taken away by the high temperature flue gas is large, the energy consumption is increased accordingly, and the construction investment for recycling the waste heat is relatively high. SUMMARY Embodiments of the present disclosure seek to solve at least one of the 25 problems existing in the prior art to at least some extent, or to provide a consumer with a useful commercial choice. Accordingly, an embodiment of the present disclosure is to provide a furnace for lead slag reduction, in which the required amount of pulverized coal is small, the flue gas volume is small, the dust rate is low, the recovery rate of lead is high, 3 the energy consumption is low, the cost is low, and comprehensive economic and technical indicators are excellent. Another embodiment of the present disclosure is to provide a process for lead slag reduction, in which the required amount of pulverized coal is small, the flue 5 gas volume is small, the dust rate is low, the recovery rate of lead is high, the energy consumption is low, the cost is low, and comprehensive economic and technical indicators are excellent. According to a broad aspect of the present disclosure, a furnace for lead slag reduction is provided. The furnace comprises: a furnace body defining a hearth 10 therein and having electrode insertion holes formed in a top of the furnace body, a flue gas outlet formed in the top of the furnace body, a lance insertion hole formed in a bottom of the furnace body, a feeding port, a lead tapping-hole, a slag tapping-hole, and an emptying port; a base for supporting the furnace body; a lance inserted into the lance insertion hole to inject pulverized coal into the 15 hearth; and electrodes inserted into the hearth through the electrode insertion holes to heat materials comprising lead slag contained in the hearth. With the furnace for lead slag reduction according to an embodiment of the present disclosure, pulverized coal is used as a reducing agent, thus reducing the cost. Moreover, by electric cleaning, a content of lead in a discarded slag may be 20 decreased. Meanwhile, a temperature of a melt may be increased by electric heating, and the injected pulverized coal is mainly used as the reducing agent but not used for increasing the temperature of the furnace, thus reducing the used amount of the pulverized coal. Therefore, the amount of the flue gas and the dust may be reduced, the dust rate may be reduced, the direct recovery rate and the 25 total recovery rate of lead may be increased, and the lead content in the discarded slag may be reduced. Because the volume of the flue gas is small, the quantity of the heat taken away by the flue gas may be small, so that investment on a waste heat recovery facility may be reduced, thus reducing the used amount of the pulverized coal and the cost.

4 The feeding port comprises a first feeding port for feeding a molten lead slag into the hearth and a second feeding port for feeding solid materials into the hearth. The solid materials comprise, for example, solid materials comprise a flux and 5 coke particles or lump coal. In addition, the solid materials may also comprise secondary lead materials for reducing the lead in the secondary lead materials. Because the feeding port comprises the first feeding port for feeding the molten lead slag into the hearth therethrough and the second feeding port for feeding the solid materials into the hearth therethrough, the feeding of the molten 10 lead slag and the solid materials may not influence each other, thus facilitating the operation. The furnace body is a horizontal type cylindrical reaction vessel. The furnace body is obliquely supported by the base in a longitudinal direction of the furnace body, and one end of the furnace body in which the lead 15 tapping-hole is formed is lower than the other end of the furnace body. A refractory material layer in the furnace body has a slope in a longitudinal direction of the furnace body, and a thickness of the refractory material layer at the one end of the furnace body is smaller than that of the refractory material layer at the other end of the furnace body. 20 Since the furnace body is obliquely supported by the base and the lead tapping-hole is formed in the lower end of the furnace body, or the refractory material layer in the furnace body has a slope in the longitudinal direction of the furnace body, so that the lead bullion can be more easily discharged from the hearth and the discarded slag content in the lead bullion is lowered. 25 The lead tapping-hole and the slag tapping-hole are formed in two opposite ends of the furnace body respectively. Therefore, the discharging of lead bullion and the discarded slag may not influence each other. Alternatively, the lead tapping-hole and the slag tapping-hole may be formed in the same end of the furnace body.

5 The furnace body is rotatably supported by the base, and the furnace further comprises a driving device for driving the furnace body to rotate around a longitudinal axis thereof. The replacement of the lance may be facilitated by rotating the furnace body. 5 The furnace body further has a secondary tuyere for blasting air into an upper portion of the hearth. By blasting air into the upper portion of the hearth through the secondary tuyere, oxygen in the air may react with carbon monoxide in the flue gas in the upper portion of the hearth to produce carbon dioxide, thus avoiding explosion 10 damage of the downstream device. The furnace body further has a freeboard burner port for inserting a freeboard burner therein and a main burner port for inserting a main burner therein. The materials in the hearth may be auxiliarily heated by the freeboard burner 15 inserted into the furnace through the freeboard burner port, thus rapidly increasing the temperature of the molten lead slag fed into the hearth and consequently promoting the reduction reaction. The main burner inserted into the furnace through the main-burner port is used during the ignition stage of the furnace. 20 The lance has a canular structure and is further used for blasting air and/or nitrogen into the hearth. Through the lance having the canular structure, pulverized coal, air and/or nitrogen can be injected into the hearth simultaneously, the oxygen may react with the pulverized coal to produce carbon monoxide which is used as the reducing agent, and nitrogen is used for cooling 25 the lance and stirring the melt in the hearth, thus promoting the reduction reaction. According to another braod aspect of the present disclosure, a process for lead slag reduction is provided, comprising: feeding a flux and a molten lead slag into a hearth of a furnace for lead slug reduction; heating materials in the hearth 6 using electrodes; injecting pulverized coal into the furnace from a bottom of the furnace; and discharging lead bullion, discarded slag and flue gas from the hearth through a lead tapping-hole, a slag tapping-hole, and a flue gas outlet of the furnace respectively. 5 With the process for lead slag reduction according to an embodiment of the present disclosure, the contents in the hearth is heated by the electrodes, thus reducing the used amount of the pulverized coal. Moreover, by electric cleaning, a content of lead in a discarded slag may be reduced. Therefore, the amount of the flue gas may be reduced, the dust rate may be reduced, the direct recovery rate 10 and the total recovery rate of lead may be increased, and the quantity of the heat taken away by the flue gas may be small, thus saving energy and reducing emissions. The bottom of the hearth is inclined along the longitudinal direction of the furnace body. 15 The same effects may be achieved by inclining the bottom of the hearth along the longitudinal direction of the furnace body and by obliquely supporting the furnace body by the base. For example, the inclining of the bottom of the hearth may be achieved by varying the thickness of the refractory material layer in the furnace body along the longitudinal direction of the furnace body. 20 The process for lead slag reduction according to embodiments of the present disclosure may further comprise feeding a solid reducing agent into the hearth. By feeding the solid reducing agent in conjunction with the heating of the electrodes, the lead slag may be cleaned by electric heating, thus promoting the reduction reaction and further reducing the lead content in the discarded slag. 25 The solid reducing agent may be, for example, coke particles or lump coal. The process for lead slag reduction according to an embodiment of the present disclosure may further comprise blasting air into an upper portion of the hearth. Therefore, carbon monoxide in the flue gas in the upper portion of the 7 hearth may react with oxygen in the air to produce carbon dioxide, thus eliminating the damage to the downstream device. The process for lead slag reduction according to an embodiment of the present disclosure may further comprise recycling waste heat of the flue gas. 5 Therefore, the waste heat in the flue gas may be recycled, thus achieving cyclic economic benefits. The process for lead slag reduction according to an embodiment of the present disclosure may further comprise recycling lead dust in the flue gas. Because a part of lead is discharged with the flue gas in the form of a lead steam or 10 a lead oxide steam and recycled in a subsequent electrical precipitation process, the recovery rate of lead may be further increased. The process for lead slag reduction according to an embodiment of the present disclosure may further comprise blasting air and/or nitrogen together with pulverized coal into the hearth from the bottom of the furnace. 15 Oxygen in the blasted air may react with the pulverized coal to produce carbon monoxide, and nitrogen may be used for cooling the lance and stirring the melt in the hearth, thus further promoting the reduction reaction and increasing the yield of lead. Additional aspects and advantages of the embodiments of the present 20 disclosure will be given in part in the following descriptions, become apparent in part from the following descriptions, or be learned from the practice of the embodiments of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects and advantages of embodiments of the disclosure 25 will become apparent and more readily appreciated from the following descriptions taken in conjunction with the drawings in which: Fig. 1 is a front view of a furnace for lead slag reduction according to an embodiment of the present disclosure; Fig. 2 is a right view of the furnace for lead slag reduction shown in Fig. 1; 8 Fig. 3 is a left view of the furnace for lead slag reduction shown in Fig. 1; Fig. 4 is a top view of a driving device and a support in the furnace for lead slag reduction shown in Fig. 1; Fig. 5 is a front view of a furnace for lead slag reduction according to another 5 embodiment of the present disclosure; Fig. 6 is a flow chart of a process for lead slag reduction according to an embodiment of the present disclosure; and Fig. 7 is a flow chart of a process for lead slag reduction according to another embodiment of the present disclosure. 10 DETAILED DESCRIPTION The embodiments described herein with reference to the drawings are explanatory and illustrative, which are used to generally understand the present disclosure. The embodiments shall not be construed to limit the present disclosure. 15 A furnace for lead slag reduction according to an embodiment of the present disclosure will be described below with reference to Figs. 1-4. As shown in Fig. 1, the furnace for lead slag reduction according to an embodiment of the present disclosure comprises a furnace body 1, a base 4, a lance 6 and electrodes 7. The furnace for lead slag reduction of the present 20 disclosure. may be used for treating a lead slag, for example, a lead oxide slag with a lead content of 25%-45%. It should be noted that the furnace for lead slag reduction according to embodiments of the present disclosure may also be used for treating lead-containing secondary materials and lead oxide minerals, because the electrodes 7 are disposed in the furnace for lead slag reduction. In other 25 words, the furnace for lead slag reduction according to embodiments of the present disclosure may be used for smelting lead, but not be limited to treating the lead slag. As shown in Figs. 1-4, in this example, the furnace body 1 is a horizontal type cylindrical reaction vessel. However, the present disclosure is not limited to this. A 9 hearth is defined inside the furnace body 1, and a lower part of the hearth is formed as a bath. The furnace body 1 is formed with electrode insertion holes 17 formed in a top of the furnace body 1, a flue gas outlet 14 formed in the top of the furnace 5 body 1, a lance insertion hole 16 formed in a bottom of the furnace body 1, a feeding port, a lead tapping-hole 12, a slag tapping-hole 13, and an emptying port 18. The feeding port is used for feeding materials into the hearth. For example, the materials comprise a molten lead slag, a flux (such as quartzite or limestone), a 10 solid reducing agent (such as coke particles or lump coal), or other materials. In a further example, the feeding port comprises a first feeding port 111 and a second feeding port 112. The first feeding port 111 is formed in a top of one end (i.e., a left end in Fig. 1 and Fig. 5) of the furnace body 1 and used for feeding the molten lead slag into the hearth. The second feeding port 112 is substantially 15 formed in a middle of the furnace body 1, for example, between the first feeding port 111 and the electrode insertion holes 17, and used for feeding solid materials such as the flux and the coke particles or lump coal into the hearth. Therefore, the feeding of the molten lead slag and the solid materials may not influence each other. 20 In one example, the furnace body 1 is further formed with a freeboard burner port 20 and a main burner port 19. The freeboard burner port 20 is used for inserting a freeboard burner (not shown) into the hearth therethrough, thus auxiliarily heating materials in the hearth to rapidly increase the temperature of the molten lead slag fed into the hearth, for example, to increase the temperature 25 of the molten lead slag from about 950 0 C-1000 0 C to about 1200 0 C-1250 0 C. As shown in Fig. 1, the freeboard burner port 20 is formed in an end surface of an end of the furnace body 1 adjacent to the first feeding port 111. Because the molten lead slag is fed into the hearth through the first feeding port 111 which is far away from the electrodes 7 inserted into the hearth, the freeboard burner port 30 20 is disposed near the first feeding port 111.

10 The main burner port 19 is used for inserting a main burner (not shown) into the hearth therethrough. The main burner is used for rapidly increasing a temperature in the hearth during the ignition stage of the furnace. As shown in Figs. 1-3, the lead tapping-hole 12 is used for discharging the 5 lead bullion obtained by reducing the lead slag in the hearth from the hearth. The slag tapping-hole 13 is used for discharging a discarded slag from the hearth. The lead tapping-hole 12 is, for example, a siphon lead tapping-hole, and the lead tapping-hole 12 and the slag tapping-hole 13 may be formed in two opposite ends of the furnace body 1 respectively, as shown in Fig. 1. In other words, the lead 10 tapping-hole 12 is formed in one end of the furnace body 1 adjacent to the first feeding port 111, and the slag tapping-hole 13 is formed in the other end of the furnace body 1. Alternatively, according to another embodiment of the present disclosure, as shown in Fig. 5, the lead tapping-hole 12 and the slag tapping-hole 13 are formed in the same end of the furnace body 1. Certainly, whether the lead 15 tapping-hole 12 and the slag tapping-hole 13 are formed in the same end or two opposite ends of the furnace body 1, the slag tapping-hole 13 should be higher than the lead tapping-hole 12 in level. If the furnace body 1 is fixedly supported by the base 4, the emptying port 18 is formed in a bottom of the other end of the furnace body 1. As shown in Fig. 3, if 20 the furnace body 1 is rotatably supported by the base 4 (which will be described below), the emptying port 18 is formed in a bottom of the furnace body 1 when the furnace body 1 rotates to an angle at which the lance 6 may be taken out. Therefore, when the furnace is repaired, lead and the discarded slag in the hearth may be emptied. 25 As shown in Fig. 1 and Fig. 5, the flue gas outlet 14 is formed in the top of the furnace body 1, for example, adjacent to the first feeding port 111, to discharge the flue gas produced in the hearth. The flue gas outlet 14 may be connected to a waste heat boiler (not shown) to recycle waste heat of the flue gas. Lead dust in the flue gas may be recycled by using a dust collecting system.

11 As shown in Figs. 1-2, alternatively, the furnace body 1 is also formed with a secondary tuyere 15, through which air may be blasted into an upper portion of the hearth (i.e., the space above the bath). Oxygen in the air may react with carbon monoxide in the upper portion of the hearth to produce carbon dioxide, thus 5 reducing damage to a downstream apparatus (for example, an electrostatic precipitator). The furnace body 1 is supported by the base 4. In one alternative example, the furnace body 1 is obliquely supported by two bases 4 spaced apart from each other along a longitudinal direction of the furnace body 1, and one end of the 10 furnace body 1 in which the lead tapping-hole 12 is formed is lower than the other end of the furnace body 1. For example, an angle between the axis of the furnace body 1 and the horizontal direction may be in a range of 0.5-5 degrees. Alternatively, the refractory material layer in the furnace body 1 has a slope in the longitudinal direction of the furnace body 1, and the thickness of the refractory 15 material layer at one end of the furnace body 1 in which the lead tapping-hole 12 is formed is smaller than that of the refractory material layer at the other end of the furnace body 1. Therefore, the lead bullion precipitated at the bottom of the hearth may be accumulated at the one end of the furnace body 1, so that the lead bullion may be 20 easily discharged through the lead tapping-hole 12, thus reducing the discarded slag included in the lead bullion and improving the grade of the lead bullion. As shown in Figs. 1-4, in order to rotate the furnace body 1 around its longitudinal axis so as to facilitate the replacement of the lance 6 and the maintenance of the furnace, in one example, the furnace body 1 is rotatably 25 supported by the base 4, and the furnace further comprises a driving device 5 for driving the furnace body 1 to rotate around the longitudinal axis thereof. Accordingly, a rack 3 and a supporting ring 2 are disposed onto the outer peripheral surface of the furnace body 1 along a circumferential direction thereof. Two supporting rings 2 are disposed onto two ends of the furnace body 1 30 respectively. The supporting ring 2 is rotatably supported by the base 4, and the 12 rack 3 is coupled to the driving device 5 and driven by the driving device 5 to rotate the furnace body 1. As shown in Figs. 1-4, each base 4 comprises a base plate 41, a supporting seat 42, a central supporting roll 45 and two lateral supporting rolls 43, 44. Two 5 supporting seats 42 are mounted on two sides of the base plate 41 respectively and inclined towards the furnace body 1. The central supporting roll 45 is mounted on the supporting seat 42. Two lateral supporting rolls 43, 44 are mounted on the supporting seat 42 respectively and disposed above the central supporting roll 45 and at two sides of the central supporting roll 45 respectively. 10 Two lateral supporting rolls 43, 44 are contacted with the central supporting roll 45 and the supporting ring 2 respectively. The driving device 5 may be of any suitable form. For example, as shown in Fig. 4, the driving device 5 comprises a motor 51, a reducer 52 and a gear 53. The gear 53 is engaged with the rack 3 to drive the furnace body 1 to rotate by driving 15 the rack 3. As shown in Figs. 1 and 5, three electrode insertion holes 17 are formed in the top of the furnace body 1 and substantially located in the middle of the furnace body 1 along the longitudinal direction thereof. In Figs. 1 and 5, the three electrode insertion holes 17 are formed near one end of the furnace body 1 in 20 which the slag tapping-hole 13 is formed. The electrodes 7 are inserted into the durance body 1 through the electrode.insertion holes 17 respectively. The electrodes 7 are used to provide heat for maintaining the temperature in the hearth and to provide heat required by the reactions such as the flux melting and the reduction reaction. 25 The lance insertion holes 16 are formed in the bottom of the furnace body 1. The lance 6 is inserted into the lance insertion hole 16 to inject pulverized coal into the hearth, for example, by using compressed air. Alternatively, the lance 6 has a canular structure and is further used for blasting air and/or nitrogen into the hearth. Oxygen in the air may react with pulverized coal to produce carbon 30 monoxide, and carbon monoxide participates in the reduction reaction to reduce 13 the lead in the lead slag. (Certainly, a small part of pulverized coal may also react with oxygen to produce carbon dioxide.) Nitrogen is used for cooling the lance 6 and stirring the molten lead slag in the hearth to promote the reduction reaction. Because the heat for maintaining the temperature in the hearth and the heat 5 required by the reduction reaction are mainly provided by the electrodes 7, the pulverized coal is mainly used as the reducing agent, thus reducing the used amount of the pulverized coal. Therefore, the amount of the flue gas and the dust may be reduced, the dust rate may be reduced, and the direct recovery rate and the total recovery rate of the lead may be increased. Meanwhile, because the 10 amount of the flue gas is reduced, the quantity of heat taken away by the flue gas may be decreased, and the power consumption and the used amount of the pulverized coal may be reduced, thus reducing the cost. Moreover, compared with use of natural gas or coal gas, using pulverized coal as the reducing agent may further reduce the cost. 15 Moreover, because the pulverized coal is mainly used as the reducing agent, most of the pulverized coal paticipitates in the reduction reaction. Therefore, the reduction reaction is fully performed, thus reducing the lead content in the discarded slag. In addition, if the lump coal or coke particles are fed additionally in 20 conjunction with the heating of the electrodes 7, the lead slag may be cleaned by electric heating, thus further reducing the lead content in the discarded slag. The furnace for lead slag reduction according to embodiments of the present disclosure may be connected to a lead smelting furnace such as an oxygen bottom blown lead smelting furnace, so that the lead slag obtained after the lead bullion 25 has been reduced once may be directly fed into the hearth of the furnace body 1, for example, though a chute. Therefore, the lead slag is not needed to be cooled and cast into ingots, the cooling and casting into ingots are necessary for the blast furnace in the prior art. However, it should be noted that the furnace for lead slag reduction according to embodiments of the present disclosure may be used for 30 treating lead oxide minerals and other lead oxide materials without being limited 14 to treating the lead slag, because the electrodes 7 are disposed and the heat for maintaining the temperature in the hearth and required by the reduction reaction are mainly provided by the electrodes 7. A process for lead slag reduction by using the above furnace for lead slag 5 reduction according to embodiments of the present disclosure will be described below with reference to Fig. 6. As shown in Fig. 6, materials such as a molten lead slag and a flux (such as quartzite or limestone) are fed into the hearth in the furnace for lead slug reduction through the first feeding port 111 and the second feeding port 112 10 respectively. The electrodes 7 are energized to provide heat for maintaining the temperature in the hearth and to provide heat required by the reaction, for example, heat required by the flux melting and the reduction reaction. In addition, the interior of the hearth is auxiliarily heated by the freeboard burner to 15 rapidly increase the temperature of the molten lead slag. Meanwhile, the pulverized coal is injected into the hearth from the bottom of the furnace body 1. Most of the injected pulverized coal is used as the reducing agent. The pulverized coal may react with oxygen to produce carbon monoxide, and the carbon monoxide reacts with the lead slag to produce lead and a discarded slag. The lead 20 is precipitated at the bottom of the hearth of the furnace body 1, and the discarded slag is floated on the lead bullion. Then, the lead bullion, the discarded slag and the flue gas are discharged from the hearth through the lead tapping-hole 12, the slag tapping-hole 13, and the flue gas outlet 14 respectively. 25 When the lance 6 needs to be replaced or the furnace needs to be repaired after the furnace is used for a period of time, the furnace may be shut down, the furnace body 1 is rotated by an angle smaller than 90 degrees by the driving device 5, and all the melts in the hearth are emptied through the slag tapping-hole 13, thus facilitating the replacement of the lance 6 and the maintenance of the 15 furnace. If merely the lance 6 needs to be replaced, the furnace body 1 needs to be rotated by 90 degrees without emptying the melts in the hearth. Because the temperature of the discharged flue gas is high, the waste heat of the flue gas is recycled by using a waste heat boiler, thus increasing a heat energy 5 utilization rate and achieving cyclic economic benefits. In addition, because a part of lead is included in the flue gas, finally the lead dust in the flue gas is recycled by using a dust collecting system, thus further increasing the total recovery rate of the lead. Because the heat for maintaining of the temperature in the hearth and 10 required by the reduction reaction are mainly provided by the electrodes 7, the pulverized coal is mainly used as the reducing agent but not used as the fuel for providing heat for maintaining of the temperature in the hearth and required by the reduction reaction, thus reducing the used amount of pulverized coal. Therefore, the amount of the flue gas and the dust may be reduced, the dust rate 15 may be reduced, and the direct recovery rate and the total recovery rate of lead may be increased. Meanwhile, because the amount of the flue gas is small, the quantity of the heat taken away by the flue gas may be small, and the power consumption and the used amount of the pulverized coal may be reduced, thus reducing the cost. Moreover, compared with use of natural gas or coal gas in the 20 prior art, the use of the pulverized coal as the reducing agent may further reduce the cost. A process for lead slag reduction according to another embodiment of the present disclosure will be described below with reference to Fig. 7. As shown in Fig. 7, in addition to the feeding of the molten lead slag and the 25 flux into the furnace for lead slag reduction, a solid reducing agent such as coke particles or lump coal is also fed. By feeding the solid reducing agent into the hearth in conjunction with the heating of the electrodes 7, the lead slag may be cleaned by electric heating, thus further increasing the recovery rate of the lead. In addition, air and nitrogen are blasted together with the pulverized coal 30 into the hearth from the bottom of the furnace. Oxygen in the air may react with 16 pulverized coal to produce carbon monoxide, and the carbon monoxide participates in the reduction reaction to promote the reduction reaction. Nitrogen is used for cooling the lance 6 and stirring the lead slag, thus further promoting the reduction reaction and increasing the recovery rate of lead. 5 Moreover, air is blasted into the upper portion of the hearth through the secondary tuyere 15 near the flue gas outlet 14, so that the carbon monoxide in the flue gas in the upper portion of the hearth may react with oxygen to produce the carbon dioxide, thus eliminating explosion risks of the waste heat boiler and the downstream dust collecting system caused by the carbon monoxide in the flue 10 gas. Other steps of the process for lead slag reduction shown in Fig. 7 may be the same as those of the process shown in Fig. 6, so that detailed descriptions thereof are omitted here. Certainly, the process for lead slag reduction according to embodiments of 15 the present disclosure is not limited to treating the lead slag, and can be used to treat lead oxide minerals and other lead oxide materials. In conclusion, with the furnace and the process for lead slag reduction according to embodiments of the present disclosure, the heat for maintaining the temperature in the hearth and required by the reduction reaction are mainly 20 provided by the electrodes, the pulverized coal is mainly used as the reducing agent, thus reducing the used amount of pulverized coal. Therefore, the amount of the flue gas and the dust may be reduced, the dust rate may be reduced, the direct recovery rate and the total recovery rate of lead may be increased, and the lead content in the discarded slag is low, for example, the lead content in the 25 discarded slag may be lower than 2.5%. Meanwhile, because the amount of the flue gas is reduced, the quantity of the heat taken away by the flue gas may be small, and the power consumption and the pulverized coal amount may be reduced, thus reducing the cost. Moreover, compared with use of natural gas or coal gas in the art, using of the pulverized coal as the reducing agent may further 30 reduce the cost.

17 Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that changes, alternatives, and modifications all falling into the scope of the claims and their equivalents may be made in the embodiments without departing from spirit and principles of the 5 disclosure.

Claims

1. A furnace for lead slag reduction, comprising: a furnace body defining a hearth therein and having electrode insertion holes formed in a top of the furnace body, a flue gas outlet formed in the top of the 5 furnace body, a lance insertion hole formed in a bottom of the furnace body, a feeding port, a lead tapping-hole, a slag tapping-hole, and an emptying port; a base for supporting the furnace body; a lance inserted into the lance insertion hole to inject pulverized coal into the hearth; and 10 electrodes inserted into the hearth through the electrode insertion holes to heat materials comprising lead slag contained in the hearth.

2. The furnace as in claim 1, wherein the feeding port comprises a first feeding port for feeding a molten lead slag into the hearth and a second feeding port for feeding solid materials into the hearth. 15

3. The furnace according to claim 2, wherein the solid materials comprise a flux and coke particles or lump coal.

4. The furnace as in claim 1, wherein the furnace body is a horizontal type cylindrical reaction vessel.

5. The furnace as in claim 4, wherein the furnace body is obliquely supported 20 by the base in a longitudinal direction of the furnace body, and one end of the furnace body in which the lead tapping-hole is formed is lower than the other end of the furnace body.

6. The furnace as in claim 4, wherein a refractory material layer in the furnace body has a slope in a longitudinal direction of the furnace body, and a thickness of 25 the refractory material layer at the one end of the furnace body is smaller than that of the refractory material layer at the other end of the furnace body.

7. The furnace as in claim 1, wherein the lead tapping-hole and the slag tapping-hole are formed in two opposite ends of the furnace body respectively. 19

8. The furnace as in claim 1, wherein the lead tapping-hole and the slag tapping-hole are formed in the same end of the furnace body.

9. The furnace as in claim 1, wherein the furnace body is rotatably supported by the base, and the furnace further comprises a driving device for driving the 5 furnace body to rotate around a longitudinal axis thereof.

10. The furnace as in claim 1, wherein the furnace body further has a secondary tuyere for blasting air into an upper portion of the hearth.

11. The furnace as in claim 1, wherein the furnace body further has a freeboard burner port for inserting a freeboard burner therein and a main burner 10 port for inserting a main burner therein.

12. The furnace as in claim 1, wherein the lance has a canular structure and is further used for blasting air and/or nitrogen into the hearth.

13. A process for lead slag reduction, comprising: feeding a flux and a molten lead slag into a hearth of a furnace for lead slug 15 reduction; heating materials in the hearth using electrodes; injecting pulverized coal into the furnace from a bottom of the furnace; and discharging lead bullion, discarded slag and flue gas from the hearth through a lead tapping-hole, a slag tapping-hole, and a flue gas outlet of the furnace 20 respectively.

14. The process as in claim 13, further comprising: feeding a solid reducing agent into the hearth.

15. The process as in claim 14, wherein the solid reducing agent is coke particles or lump coal. 25

16. The process as in claim 13, further comprising: blasting air into an upper portion of the hearth.

17. The process as in claim 13, further comprising: recycling waste heat of the flue gas. 20

18. The process as in claim 13, further comprising: recycling lead dust in the flue gas.

19. The process as in claim 13, further comprising: blasting air and/or nitrogen together with pulverized coal into the hearth from the bottom of the 5 furnace.

20. The process as in claim 13, further comprising: providing supplementary heat to the hearth using a freeboard burner.