Aluminum electrolysis cell low-temperature waste heat flue gas afterburning power generation system and method

Abstract

The invention relates to the technical field of waste heat recycling in the aluminum electrolysis industry, and provides an aluminum electrolysis cell low-temperature waste heat flue gas afterburning power generation system and method.The system comprises a boiler water feeding pump, a heat exchanger, an aluminum electrolysis cell, an afterburning boiler, a water-steam separator, a turbine and a power generator; the heat exchanger is connected with an annular water pipe on the side wall of the aluminum electrolysis cell, the annular water pipe is connected with an afterburning boiler, an air outlet of the afterburning boiler is connected with a water-steam separator, the water-steam separator is connected with a turbine, and the turbine is connected with a generator; a smoke concentration cover is arranged at the smoke outlet end of the aluminum electrolysis cell and connected with the afterburning boiler and the heat exchanger, and the smoke outlet ends of the afterburning boiler and the heat exchanger are connected with the smoke purifier. Flue gas discharged by the aluminum electrolysis cell and waste cathode carbon blocks are used as fuel, the afterburning technology is adopted for enhancing heat energy and converting the heat energy into electric energy, generated energy is used for an aluminum electrolysis cell production system, and therefore the purposes of energy conservation and environment protection are achieved.

Description

Technical Field

[0001] The present application belongs to the technical field of waste heat recovery and utilization in the aluminum electrolysis industry, and more specifically, to a system and method for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum electrolysis cell. Background Art

[0002] With the continuous growth of global energy demand and the improvement of environmental awareness, the waste heat utilization technology of aluminum electrolysis cells has gradually become a research hotspot in the aluminum metallurgical industry. This technology aims to convert the large amount of heat generated during the aluminum electrolysis process into usable energy, such as electricity and heat, through effective waste heat recovery and utilization methods, so as to improve energy utilization efficiency, reduce production costs, and reduce environmental pollution.

[0003] In my country, the aluminum metallurgical industry is an important part of modern industry. Aluminum electrolysis will produce a large amount of low-temperature waste heat flue gas at 135℃-140℃ during production. Currently, only a small amount of waste heat flue gas discharged from the electrolytic cell is used for heating or cooling of the air conditioning system. In the traditional aluminum electrolysis production process, most of the flue gas is still not reasonably recycled and utilized. Direct emission not only causes energy waste, but also aggravates environmental pollution. Therefore, the development of aluminum electrolytic cell waste heat power generation technology to achieve efficient energy conversion and utilization has become an important issue that the current aluminum metallurgical industry needs to solve urgently. Summary of the invention

[0004] In view of the deficiencies of the above-mentioned prior art, the purpose of the embodiments of the present application is to provide a low-temperature waste heat flue gas supplementary combustion power generation system for an aluminum electrolytic cell, which utilizes the flue gas discharged from the aluminum electrolytic cell and the discarded cathode carbon blocks as fuel, adopts supplementary combustion technology to enhance thermal energy and convert it into electrical energy. The generated electricity is used in the aluminum electrolytic cell production system, thereby achieving the purpose of energy saving and environmental protection.

[0005] To achieve the above-mentioned purpose, the technical solution adopted in the present application is: to provide an aluminum electrolytic cell low-temperature waste heat flue gas supplementary combustion power generation system, including: a boiler feed pump, a heat exchanger, an aluminum electrolytic cell, a supplementary combustion boiler, a water vapor separator, a turbine and a generator, the boiler feed pump is connected to the heat exchanger through a first pipe, the heat exchanger is connected to the annular water pipe on the side wall of the aluminum electrolytic cell through a second pipe, the annular water pipe is connected to the supplementary combustion boiler through a third pipe, the air outlet of the supplementary combustion boiler is connected to the water vapor separator through a fourth pipe, the water vapor separator is connected to the turbine through a fifth pipe, and the turbine is connected to the generator; a smoke outlet end of the aluminum electrolytic cell is provided with a smoke concentrating hood, the smoke concentrating hood is connected to the supplementary combustion boiler and the heat exchanger, and the smoke outlet ends of the supplementary combustion boiler and the heat exchanger are connected to a smoke purifier.

[0006] In one embodiment, the water outlet of the turbine is connected to a condenser and a circulating water pump, the condenser and the water vapor separator are connected to a water purifier via an eighth pipeline, and the water outlet of the water purifier is connected to the first pipeline.

[0007] In one embodiment, a water flow regulating valve is provided on the first pipeline, a thermal deaerator is provided on the third pipeline, and a stop valve is provided on the eighth pipeline, and the stop valve is located at the water inlet end of the water purifier.

[0008] In one embodiment, the flue gas concentration hood is connected to the heat exchanger through a sixth pipe, and the flue gas concentration hood is connected to the supplementary combustion boiler through a seventh pipe. The sixth pipe is provided with a first butterfly valve, and the seventh pipe is provided with a second butterfly valve and a fan.

[0009] In one embodiment, a one-way valve is provided on the inlet pipe of the flue gas purifier.

[0010] Another object of the present application is to provide a method for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum reduction cell. Based on the above-mentioned system for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum reduction cell, the method comprises the following steps:

[0011] S1. Low-temperature steam or saturated water is sent to the heat exchanger through the boiler feed water pump for heat exchange. The water temperature is raised to 100°C by the heat exchanger. The low-temperature steam or saturated water is then passed into the annular water pipe to absorb the waste heat lost from the side wall of the aluminum electrolytic cell to raise the water temperature to 135°C-140°C. The low-temperature steam or saturated water is then passed into the supplementary combustion boiler. The water temperature is raised to 420°C medium-temperature high-pressure steam by mixing cathode carbon blocks and supplementary combustion natural gas. The medium-temperature high-pressure steam is then passed into the water-steam separator. Finally, the steam drives the turbine and generator to generate electricity;

[0012] S2. The low-temperature flue gas discharged from the aluminum electrolytic cell is collected by a flue gas collection hood. A part of it enters the heat exchanger for heat exchange, and the other part is introduced into the supplementary combustion boiler as secondary air. The flue gas is finally collected and treated by a flue gas purifier before being discharged.

[0013] S3. The medium-temperature high-pressure water after passing through the turbine becomes condensed water. Under the action of the condenser and the circulating water pump, the condensed water passes through the water purifier and returns to the first pipeline for recycling.

[0014] In one embodiment, the water flow regulating valve on the first pipeline controls the flow rate of low-temperature steam or saturated water to 129 L / h, and the boiler feed pump delivers the low-temperature steam or saturated water to the heat exchanger at a pressure of 1.2-1.5 MPa.

[0015] In one embodiment, the flue gas flow rate entering the heat exchanger is controlled by the first butterfly valve to be 2800 Nm 3 / h, the flue gas flow entering the supplementary combustion boiler is controlled at 20000Nm through the second butterfly valve 3 / h.

[0016] In one embodiment, the fume concentration hood is a sealed structure.

[0017] In one embodiment, the low-temperature steam or saturated water discharged through the annular water pipe first passes through a thermal deaerator to remove oxygen dissolved in the water, and then the low-temperature steam or saturated water passes through the supplementary-fired boiler.

[0018] The beneficial effects of the aluminum electrolysis cell low-temperature waste heat flue gas supplementary combustion power generation system and method provided in the present application are:

[0019] By utilizing the heat of the flue gas discharged from the aluminum electrolysis cell and absorbing the heat lost from the side walls of the aluminum electrolysis cell through the annular water pipe, and then using the heat generated by the waste cathode carbon blocks burned in the supplementary boiler for power generation, the low-temperature waste heat flue gas and the heat lost from the side walls of aluminum electrolysis are effectively utilized, and the waste cathode carbon blocks are efficiently recycled, which has the effect of energy saving and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 A simplified schematic diagram of the connection structure of the low-temperature waste heat flue gas supplementary combustion power generation system for an aluminum electrolysis cell provided in an embodiment of the present application.

[0022] Among them, the reference numerals in the figure are:

[0023] 1. Boiler feed water pump; 2. Heat exchanger; 3. Aluminum electrolytic cell; 4. Supplementary combustion boiler; 5. Water vapor separator; 6. Turbine; 7. Generator; 8. Annular water pipe; 9. Flue gas concentration hood; 10. Fan; 11. Flue gas purifier; 12. Condenser; 13. Circulating water pump; 14. Stop valve; 15. Water purifier; 16. Thermal deaerator; 17. Water flow regulating valve; 18. First butterfly valve; 19. Second butterfly valve; 20. Check valve. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0026] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0027] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0028] like Figure 1 As shown, a low-temperature waste heat flue gas supplementary combustion power generation system for an aluminum electrolytic cell provided in an embodiment of the present application is now described. The low-temperature waste heat flue gas supplementary combustion power generation system for an aluminum electrolytic cell comprises: a boiler feed water pump 1, a heat exchanger 2, an aluminum electrolytic cell 3, a supplementary combustion boiler 4, a water vapor separator 5, a turbine 6 and a generator 7. The boiler feed water pump 1 is connected to the heat exchanger 2 through a first pipe, and the heat exchanger 2 is connected to the annular water pipe 8 on the side wall of the aluminum electrolytic cell 3 through a second pipe. The annular water pipe 8 is a spiral water pipe that absorbs heat from the side wall of the aluminum electrolytic cell 3. The annular water pipe 8 is connected to the supplementary combustion boiler 4 through a third pipe, and the gas outlet of the supplementary combustion boiler 4 is connected to the water vapor separator 5 through a fourth pipe, and the water vapor separator 5 is connected to the turbine 6 through a fifth pipe, and the turbine 6 is connected to the generator 7. Specifically, the first pipeline is also connected to the waste heat boiler. The boiler feed water pump 1 is used to pump the low-temperature steam or saturated water generated by the waste heat boiler into the heat exchanger 2 for heat exchange. After heat exchange, it continues to pass into the annular water pipe 8 on the side wall of the aluminum electrolytic cell 3 for continued heat exchange, and then is heat-exchanged into medium-temperature and high-pressure water vapor through the supplementary combustion boiler 4. Finally, the steam generator 6 and the generator 7 convert the thermal energy into electrical energy.

[0029] Among them, a smoke collecting hood 9 is provided at the smoke outlet end of the aluminum electrolytic cell 3. The smoke collecting hood 9 is a sealed structure that can temporarily store smoke and prevent smoke from escaping into the air; the smoke collecting hood 9 is connected to the supplementary combustion boiler 4 and the heat exchanger 2, and the smoke outlet ends of the supplementary combustion boiler 4 and the heat exchanger 2 are connected to the smoke purifier 11. Among them, a part of the smoke discharged from the smoke collecting hood 9 is passed into the heat exchanger 2, which is beneficial to the heat exchange of the waste heat of the smoke, and the other part is passed into the supplementary combustion boiler 4 as secondary air, so that the cathode carbon blocks in the supplementary combustion boiler 4 are fully burned, and part of the natural gas will be added to the supplementary combustion boiler 4 to make the cathode carbon blocks burn; the heat generated by the combustion of the cathode carbon blocks heats the low-temperature steam or saturated water into medium-temperature and high-pressure water vapor for subsequent power generation; after the heat exchange, the smoke is treated by the smoke purifier 11 and then discharged into the air to avoid pollution.

[0030] In this embodiment, the water outlet of the turbine 6 is connected to a condenser 12 and a circulating water pump 13, and the turbine 6, the generator 7, the condenser 12 and the circulating water pump 13 constitute a condensing turbine generator set; after the medium-temperature and high-pressure steam passes through the turbine 6 for heat exchange, it is cooled and reduced in pressure to become low-temperature steam, and is converted into condensed water through the condenser 12. The condenser 12 and the water vapor separator 5 are connected to a water purifier 15 through an eighth pipeline, and the water outlet of the water purifier 15 is connected to the first pipeline. After the water in the condenser 12 and the water vapor separator 5 is purified by the purifier, it is returned to the first pipeline for recycling.

[0031] In this embodiment, a water flow regulating valve 17 is provided on the first pipeline for controlling the water flow rate; a thermal deaerator 16 is provided on the third pipeline for removing oxygen and other gases dissolved in the water to protect the supplementary burning boiler 4; a stop valve 14 is provided on the eighth pipeline, and the stop valve 14 is located at the water inlet end of the water purifier 15. After the stop valve 14 is closed, the water purifier 15 can be maintained or cleaned, which is convenient for the subsequent regular disassembly and cleaning of the water purifier 15.

[0032] In this embodiment, the smoke concentration hood 9 is connected to the heat exchanger 2 through the sixth pipeline, and the smoke concentration hood 9 is connected to the supplementary combustion boiler 4 through the seventh pipeline. The sixth pipeline is provided with a first butterfly valve 18, and the seventh pipeline is provided with a second butterfly valve 19 and a fan 10. The smoke generated by the aluminum electrolytic cell 3 can be divided into two streams through the sixth pipeline and the seventh pipeline, and the flow of the smoke can be controlled by the first butterfly valve 18 and the second butterfly valve 19. When the fan 10 is in action, the smoke entering the supplementary combustion boiler 4 is used as secondary air.

[0033] In this embodiment, a one-way valve 20 is provided on the inlet pipe of the flue gas purifier 11, so that the flue gas can only be discharged through the flue gas purifier 11, and the outside air cannot enter.

[0034] This embodiment also provides a method for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum electrolysis cell. Based on the above-mentioned system for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum electrolysis cell, the method comprises the following steps:

[0035] S1. The low-temperature steam or saturated water generated by the waste heat boiler is sent to the heat exchanger 2 through the boiler feed water pump 1 and the water flow regulating valve 17 for heat exchange. The water temperature is raised to about 100°C by the heat exchanger 2, and then the low-temperature steam or saturated water is passed into the annular water pipe 8 on the side wall of the aluminum electrolytic cell 3 to absorb the waste heat lost from the side wall of the aluminum electrolytic cell 3 to raise the water temperature to 135°C-140°C. The low-temperature steam or saturated water is then passed into the supplementary combustion boiler 4 after passing through the thermal deaerator 16. The water temperature is raised to medium-temperature and high-pressure steam of about 420°C by mixing cathode carbon blocks and supplementary combustion natural gas in the supplementary combustion boiler 4. The medium-temperature and high-pressure steam at the outlet of the supplementary combustion boiler 4 is passed into the water-steam separator 5, and finally the turbine 6 and the generator 7 are driven by steam to generate electricity;

[0036] S2. The low-temperature flue gas discharged from the aluminum electrolytic cell 3 is collected by the flue gas collection hood 9. A part of the flue gas passes through the first butterfly valve 18 and enters the heat exchanger 2 for heat exchange, and the other part passes through the second butterfly valve 19 and the fan 10 and is passed into the supplementary combustion boiler 4 for use as secondary air. The first butterfly valve 18 and the second butterfly valve 19 are used to control the discharge amount of the flue gas. After passing through the heat exchanger 2 and the supplementary combustion boiler 4, the flue gas is finally collected through the pipeline, and after passing through the one-way valve 20, it is discharged into the flue gas purifier 11 for purification treatment, and finally discharged into the air to achieve environmental protection.

[0037] S3, condenser 12 and circulating water pump 13 are fixed together, and the medium-temperature high-pressure water after passing through turbine 6 becomes low-temperature steam, and the low-temperature steam is converted into condensed water under the action of condenser 12 and circulating water pump 13. The condensed water is purified by water purifier 15 and then returned to the first pipeline for recycling.

[0038] In this embodiment, the water flow regulating valve 17 on the first pipeline controls the flow rate of low-temperature steam or saturated water to 129L / h or within 129L / h, and the boiler feed water pump 1 sends the low-temperature steam or saturated water to the heat exchanger 2 at a pressure of 1.2-1.5Mpa for heat exchange.

[0039] In this embodiment, the flue gas flow rate entering the heat exchanger 2 is controlled by the first butterfly valve 18 to be 2800 Nm 3 / h, the flue gas flow entering the supplementary combustion boiler 4 is controlled at 20000Nm by the second butterfly valve 19. 3 / h.

[0040] In this embodiment, the low-temperature steam or saturated water discharged through the annular water pipe 8 first passes through the thermal deaerator 16 to remove oxygen and other dissolved gases dissolved in the water, and then the low-temperature steam or saturated water passes into the supplementary burning boiler 4 to protect the supplementary burning boiler 4.

[0041] In this embodiment, the supplementary combustion boiler 4 can produce about 31 tons of waste cathode carbon blocks per year by mixing and burning the waste cathode carbon blocks. The heat released by the complete combustion of these waste cathode carbon blocks is in the range of 14-15kw, which is equivalent to generating 6.5×10 4 -6.8×10 4 kwh; to ensure the complete combustion of the cathode carbon block, some natural gas needs to be added to heat the low-temperature and low-pressure water to 420°C 3.82MPa medium-temperature and high-pressure water vapor. The flue gas concentration hood 9 is a sealed structure that can collect flue gas, reduce the emission of harmful substances such as dust, carbon dioxide, sulfur dioxide and nitrogen oxides, and prevent flue gas from directly diffusing into the air to pollute the environment.

[0042] In this embodiment, the temperature of water can be raised to 135°C-140°C by utilizing the flue gas discharged from the aluminum electrolysis cell 3 and the annular water pipe 8 on the side wall of the aluminum electrolysis cell 3 to absorb the heat lost from the side wall; at the same time, the low-temperature waste heat flue gas discharged from the aluminum electrolysis cell 3 is used to provide secondary air to the furnace of the supplementary combustion boiler 4 through the fan 10, thereby strengthening the air disturbance in the furnace and providing sufficient oxygen for the waste cathode carbon blocks, ensuring the full combustion of the waste cathode carbon blocks, and effectively utilizing the low-temperature waste heat flue gas from the aluminum electrolysis cell 3, thereby achieving the purpose of energy saving and environmental protection.

[0043] In this embodiment, the low-temperature and low-pressure water coming out of the annular water pipe 8 of the aluminum electrolytic cell 3 is sent to the supplementary combustion boiler 4 to be mixed with the waste cathode carbon blocks and supplementary combustion of part of the natural gas. The low-temperature and low-pressure water is heated to medium-temperature and high-pressure saturated water vapor for power generation in the aluminum plant, and the waste cathode carbon blocks are efficiently recycled and utilized, thus avoiding the waste of a large amount of waste heat resources.

[0044] In this embodiment, the separated liquid water and condensed water are sent to the water purification device for water quality treatment by using the water vapor separator 5 and the condensing turbine generator 7, and the treated water is then returned to the power generation system for recycling, which effectively reduces the water supply of the waste heat boiler and avoids direct discharge of polluted water to cause environmental pollution.

[0045] In this embodiment, the waste cathode carbon blocks are mixed with the supplementary combustion boiler 4. Taking the 400kA aluminum electrolytic cell 3 as an example, a single cell produces about 31 tons of waste cathode carbon blocks per year. The heat released by complete combustion is about 15kw, which is equivalent to 6.7×10 4 kwh, with good economic and social benefits.

[0046] This embodiment takes a total of 825 sets of 400kA aluminum electrolytic cells 3 of phases 1-3 of an aluminum factory enterprise, and focuses on the flue gas and discarded cathode carbon blocks emitted by the aluminum electrolytic cells 3. By recovering the waste heat of the flue gas of the aluminum electrolytic cells 3, burning the discarded cathode carbon blocks to produce low-temperature steam or saturated water, and then heating and compressing the low-temperature steam or saturated water into medium-temperature steam by supplementary combustion of part of the natural gas, and using steam turbines to generate electricity, the generated electricity is used for electrolytic aluminum industrial production. The efficient resource recovery and utilization of the waste heat of the low-temperature flue gas and discarded cathode carbon blocks of the electrolytic cells is achieved.

[0047] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A low-temperature waste heat flue gas supplementary combustion power generation system for aluminum electrolysis cells, characterized in that: include: A boiler feed pump (1), a heat exchanger (2), an aluminum electrolytic cell (3), a supplementary-fired boiler (4), a water vapor separator (5), a turbine (6) and a generator (7), wherein the boiler feed pump (1) is connected to the heat exchanger (2) via a first pipeline, the heat exchanger (2) is connected to an annular water pipe (8) on the side wall of the aluminum electrolytic cell (3) via a second pipeline, the annular water pipe (8) is connected to the supplementary-fired boiler (4) via a third pipeline, and the outlet gas of the supplementary-fired boiler (4) The outlet is connected to the water vapor separator (5) through a fourth pipe, the water vapor separator (5) is connected to the turbine (6) through a fifth pipe, and the turbine (6) is connected to the generator (7); a smoke collecting hood (9) is provided at the smoke outlet of the aluminum electrolytic cell (3), the smoke collecting hood (9) is connected to the supplementary combustion boiler (4) and the heat exchanger (2), and the smoke outlets of the supplementary combustion boiler (4) and the heat exchanger (2) are connected to a smoke purifier (11).

2. The aluminum electrolysis cell low-temperature waste heat flue gas supplementary combustion power generation system according to claim 1, characterized in that: The water outlet end of the turbine (6) is connected to a condenser (12) and a circulating water pump (13); the condenser (12) and the water vapor separator (5) are connected to a water purifier (15) via an eighth pipeline; the water outlet end of the water purifier (15) is connected to the first pipeline.

3. The aluminum electrolysis cell low-temperature waste heat flue gas supplementary combustion power generation system according to claim 2, characterized in that: The first pipeline is provided with a water flow regulating valve (17), the third pipeline is provided with a thermal deaerator (16), and the eighth pipeline is provided with a stop valve (14), and the stop valve (14) is located at the water inlet end of the water purifier (15).

4. The aluminum electrolysis cell low-temperature waste heat flue gas supplementary combustion power generation system according to claim 3, characterized in that: The smoke concentration hood (9) is connected to the heat exchanger (2) via a sixth pipeline, and the smoke concentration hood (9) is connected to the supplementary combustion boiler (4) via a seventh pipeline. The sixth pipeline is provided with a first butterfly valve (18), and the seventh pipeline is provided with a second butterfly valve (19) and a fan (10).

5. The aluminum electrolysis cell low-temperature waste heat flue gas supplementary combustion power generation system according to claim 4, characterized in that: A one-way valve (20) is provided on the inlet end pipeline of the flue gas purifier (11).

6. A method for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum electrolysis cell, characterized in that: Based on the aluminum electrolysis cell low-temperature waste heat flue gas supplementary combustion power generation system as claimed in claim 5, the method comprises the following steps: S1, low-temperature steam or saturated water is sent to the heat exchanger (2) through the boiler feed water pump (1) for heat exchange, and the water temperature is raised to 100°C by the heat exchanger (2), and then the low-temperature steam or saturated water is passed into the annular water pipe (8), absorbing the waste heat lost from the side wall of the aluminum electrolytic cell (3) to raise the water temperature to 135°C-140°C, and then the low-temperature steam or saturated water is passed into the supplementary combustion boiler (4), and the water temperature is raised to medium-temperature high-pressure steam of 420°C by mixing cathode carbon blocks and supplementary combustion natural gas, and then the medium-temperature high-pressure steam is passed into the water vapor separator (5), and finally the steam drives the turbine (6) and the generator (7) to generate electricity; S2. The low-temperature flue gas discharged from the aluminum electrolytic cell (3) is collected by a flue gas collection hood (9), a part of which enters the heat exchanger (2) for heat exchange, and the other part is introduced into the supplementary combustion boiler (4) as secondary air; the flue gas is finally collected and treated by a flue gas purifier (11) before being discharged; S3. The medium-temperature high-pressure water after passing through the turbine (6) becomes condensed water. Under the action of the condenser (12) and the circulating water pump (13), the condensed water passes through the water purifier (15) and then returns to the first pipeline for recycling.

7. The method for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum electrolysis cell (3) as claimed in claim 6, characterized in that: The water flow regulating valve (17) on the first pipeline controls the flow rate of low-temperature steam or saturated water to 129L / h, and the boiler feed water pump (1) delivers the low-temperature steam or saturated water to the heat exchanger (2) at a pressure of 1.2-1.5Mpa.

8. The method for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum electrolysis cell according to claim 7, characterized in that: The flue gas flow rate entering the heat exchanger (2) is controlled to 2800 Nm by the first butterfly valve (18). 3 / h, the flue gas flow rate entering the supplementary combustion boiler (4) is controlled at 20000Nm by the second butterfly valve (19) 3 / h.

9. The method for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum electrolysis cell (3) as claimed in claim 8, characterized in that: The smoke concentration hood (9) is a sealed structure.

10. The method for power generation by supplementary combustion of low-temperature waste heat flue gas from an aluminum electrolysis cell (3) as claimed in claim 8, characterized in that: The low-temperature steam or saturated water discharged through the annular water pipe (8) first passes through a thermal deaerator (16) to remove oxygen dissolved in the water, and then passes the low-temperature steam or saturated water into the supplementary-fired boiler (4).

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