A device for recycling waste heat from an electrolytic cell and a method for controlling the same

Abstract

The present invention discloses a device for recycling and utilizing electrolytic cell waste heat and a recovery control method, belonging to the technical field of waste heat recovery from aluminum electrolytic cells. The recycling and utilization device includes a heat exchange module, a first heat exchanger, a flue gas heat exchanger, a second heat exchanger, and a utilization component. The heat exchange module is provided with a sidewall heat exchange channel, the first heat exchanger has a first heat exchange channel and a second heat exchange channel; the flue gas heat exchanger has a flue gas channel and a flue gas heat exchange channel, the second heat exchanger has a third heat exchange channel and a fourth heat exchange channel, the third heat exchange channel is connected to the flue gas heat exchange channel to form a second heat exchange circuit for the circulation of a second heat exchange medium, and the utilization component is provided with a utilization channel, the fourth heat exchange channel, the second heat exchange channel, and the utilization channel are connected in sequence to form a third utilization circuit for the circulation of the third heat exchange medium. The present invention recovers the waste heat of the electrolytic cell in stages, thereby improving the heat recovery efficiency; the heat recovery of the sidewall and flue gas of the electrolytic cell is achieved separately, further improving the heat recovery efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste heat recovery and utilization of aluminum electrolytic cells, and particularly relates to a waste heat recovery and utilization device and a recovery control method for an electrolytic cell. Background Art

[0002] Aluminum reduction cells are the primary equipment for electrolytic aluminum production. They consist of a shell and a conductive cathode lining built into the shell. As the raw materials undergo electrolysis within the molten bath, heat is transferred to the sides of the cell. This process also produces high-temperature flue gas. According to statistics, my country's electrolytic aluminum industry emitted approximately 426 million tons of carbon dioxide in 2020, accounting for 64% of the total emissions from the non-ferrous metals industry. Currently, the average AC power consumption per ton of molten aluminum produced in the electrolytic aluminum industry is approximately 13,500 kWh, with actual energy utilization rates of only 45%-50%. Calculations indicate that heat lost to the sides of the cell and flue gas accounts for approximately 60% of total energy consumption, leaving a significant amount of waste heat to be recovered and utilized.

[0003] Patent publication number CN102134727B2 discloses collecting the side waste heat of the electrolytic cell and the waste heat of the flue gas into a collector A, and then using the heat to preheat the alumina powder, the raw material for electrolytic aluminum, through a primary heat exchanger A, and then comprehensively utilized through a secondary heat exchanger B. This waste heat recovery device has low waste heat recovery efficiency. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an electrolytic cell waste heat recovery device and a recovery control method, which have high waste heat recovery efficiency.

[0005] A technical solution of the present invention is to provide a device for recovering and utilizing waste heat from an electrolytic cell, comprising:

[0006] The heat exchange module is provided with a side wall heat exchange channel;

[0007] A first heat exchanger having a first heat exchange channel and a second heat exchange channel, wherein the first heat exchange channel is connected to the side wall heat exchange channel to form a first heat exchange circuit for circulating a first heat exchange medium;

[0008] A flue gas heat exchanger having a flue gas channel for the flow of flue gas from the electrolytic cell and a flue gas heat exchange channel;

[0009] The second heat exchanger has a third heat exchange channel and a fourth heat exchange channel. The third heat exchange channel is connected to the flue gas heat exchange channel to form a second heat exchange circuit for the second heat exchange medium to flow.

[0010] The utilization component is provided with a utilization channel, and the fourth heat exchange channel, the second heat exchange channel and the utilization channel are connected in sequence to form a third utilization circuit for the circulation of the third heat exchange medium.

[0011] In some embodiments, the first heat exchange circuit includes a first heat exchange tube connected between the output end of the side wall heat exchange channel and the input end of the first heat exchange channel, and the recycling device includes a first on-off valve and a storage tank connected in series, and the first on-off valve and the storage tank are connected to the first heat exchange tube in parallel.

[0012] In some embodiments, the recycling device comprises:

[0013] a first temperature sensor, configured to detect the temperature of the first heat exchange medium at the input end of the first heat exchange channel;

[0014] A controller is electrically connected to the first temperature sensor and the first on-off valve.

[0015] In some embodiments, the first heat exchange circuit includes a second heat exchange tube and a second on-off valve for controlling the opening and closing of the second heat exchange tube, wherein the second heat exchange tube is connected between the output end of the first heat exchange channel and the input end of the side wall heat exchange channel; the second heat exchange circuit includes a fourth on-off valve for controlling the opening and closing of the third heat exchange channel;

[0016] The recycling device includes a third on-off valve connected to the input end of the flue gas heat exchange channel. The flue gas heat exchange channel and the third on-off valve are connected to the second heat exchange tube in parallel. The input end of the flue gas heat exchange channel is close to the output end of the first heat exchange channel.

[0017] In some embodiments, the recycling device includes a second temperature sensor for detecting the temperature of the first heat exchange medium or the second heat exchange medium flowing through the output end of the flue gas heat exchange channel;

[0018] The fourth on-off valve, the second temperature sensor, the third on-off valve, and the second on-off valve are all electrically connected to the controller.

[0019] In some embodiments, the utilization component includes an expander, a condenser and a power mechanism connected in series to the output end of the second heat exchange channel, the power mechanism is connected to the fourth heat exchange channel, and the gas channel of the expander, the condensation channel of the condenser and the power channel of the power mechanism connected in series form the utilization channel, and the third heat exchange medium is an organic working fluid.

[0020] In some embodiments, the recycling device further includes a connecting valve connected in series to the second heat exchange channel and the fourth heat exchange channel, and a bypass valve connected in parallel to the second heat exchange channel and the connecting valve.

[0021] In some embodiments, the recycling device includes a compressor for compressing air, the compressor is connected to the expander, and the compressor is provided with a waste heat recovery channel connected to the first heat exchange channel.

[0022] Another technical solution of the present invention is to provide a method for controlling the recovery of waste heat from the electrolytic cell, comprising the following steps:

[0023] According to the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel, obtaining an absolute value ΔT1 of the difference between the temperature T1 and the first set temperature;

[0024] When the absolute value △T1 of the difference is greater than the first target value, the first on-off valve is controlled to open so that the first heat exchange medium enters the storage tank; when the absolute value △T1 of the difference is less than the first target value, the first on-off valve is controlled to close so that the first heat exchange medium flows in the first heat exchange circuit, and the first target value is a set value.

[0025] Another technical solution of the present invention is to provide a method for controlling the recovery of waste heat from an electrolytic cell, characterized in that it comprises the following steps:

[0026] Obtaining a difference ΔT2 between the temperature T1 and the temperature T2 according to the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel and the temperature T2 of the first heat exchange medium or the second heat exchange medium at the output end of the flue gas heat exchange channel;

[0027] When the difference ΔT2 is less than the second target value, the third on-off valve is opened, and the second on-off valve and the fourth on-off valve are closed, so that the flue gas heat exchange channel of the flue gas heat exchanger is connected to the first heat exchange channel of the first heat exchanger;

[0028] When the difference ΔT2 is not less than a second target value, the second on-off valve and the fourth on-off valve are opened, and the third on-off valve is closed to conduct the second heat exchange circuit. The second target value is a set value.

[0029] The beneficial effects of the present invention include at least:

[0030] The recycling and utilization device provided by the present invention includes a heat exchange module, a first heat exchanger, a flue gas heat exchanger, a second heat exchanger and a utilization component. The heat exchange module is provided with a side wall heat exchange channel. The first heat exchange medium exchanges heat with the side wall of the electrolytic cell when in the side wall heat exchange channel. The first heat exchanger has a first heat exchange channel and a second heat exchange channel. The first heat exchange channel is connected with the side wall heat exchange channel of the heat exchange module to form a first heat exchange circuit for the first heat exchange medium to circulate; the flue gas heat exchanger has a flue gas channel and a flue gas heat exchange channel for the flue gas of the electrolytic cell to circulate, the second heat exchanger has a third heat exchange channel and a fourth heat exchange channel, the third heat exchange channel is connected with the flue gas heat exchange channel to form a second heat exchange circuit for the second heat exchange medium to circulate, the utilization component is provided with a utilization channel, the fourth heat exchange channel, the second heat exchange channel and the utilization channel are connected in sequence to form a third utilization circuit for the third heat exchange medium to circulate. The first heat exchange circuit is used for circulating the first heat exchange medium, which can exchange heat with the wall of the electrolytic cell. When the first heat exchange medium circulates in the first heat exchange channel, it exchanges heat with the third heat exchange medium in the second heat exchange channel, and the heat of the first heat exchange medium is transferred to the third heat exchange medium. The second heat exchange circuit is used for circulating the second heat exchange medium, which can exchange heat with the flue gas of the electrolytic cell in the flue gas channel in the flue gas heat exchange channel, so that the flue gas transfers heat to the second heat exchange medium in the second heat exchange circuit, and when the second heat exchange medium circulates in the third heat exchange channel, it exchanges heat with the fourth heat exchange channel. The third heat exchange medium in the electrolytic cell is heat exchanged, and the second heat exchange medium transfers heat to the third heat exchange medium. In this way, the second heat exchange medium and the first heat exchange medium respectively transfer the waste heat of the side wall of the electrolytic cell and the flue gas to the third heat exchange medium, and the third heat exchange medium is heated in stages, thereby improving the heat recovery efficiency; the heat recovery of the side wall of the electrolytic cell and the flue gas is respectively realized by the first heat exchange loop and the second heat exchange loop, which has high flexibility and is not affected by the different heat of the side wall of the electrolytic cell and the flue gas. It can match the side wall of the electrolytic cell and the flue gas at different temperatures, thereby further improving the heat recovery efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of an electrolytic cell waste heat recovery and utilization device according to Example 1 is shown;

[0032] Figure 2 for Figure 1 Schematic diagram of the structure in which the compressor is connected in parallel with the first heat exchange channel of the first heat exchanger.

[0033] Figure 3 A process step diagram of a method for controlling recovery of electrolytic cell waste heat according to a second embodiment is shown.

[0034] Figure 4 A process step diagram of the electrolytic cell waste heat recovery control method of embodiment 3 is shown.

[0035] Description of reference numerals:

[0036] 101-heat exchange module, 102-first heat exchanger, 103-second heat exchanger, 104-flue gas heat exchanger, 105-first on-off valve, 106-second on-off valve, 107-third on-off valve, 108-fourth on-off valve, 109-storage tank, 110-expander, 111-condenser, 112-cooling tower, 113-power mechanism, 114-first heat exchange pipe, 115-second heat exchange pipe, 116-connecting valve, 117-bypass valve, 118-compressor, 119-gas storage tank, 120-dryer, 121-filter, 122-dust collector, 123-fan, 124-power pump.

[0037] 100-first heat exchange circuit, 200-second heat exchange circuit, 300-third utilization circuit. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to which this application belongs to understand this application more clearly, the technical solution of this application is described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0039] Example 1

[0040] An embodiment of the present invention provides a device for recovering and utilizing waste heat from an electrolytic cell, which can recover and utilize waste heat from the side walls of the electrolytic cell and flue gas, and the waste heat recovery from the side walls of the electrolytic cell and flue gas is flexible and efficient.

[0041] Please combine Figure 1 as well as Figure 2 The embodiment of the present invention provides a recycling device including a heat exchange module 101, a first heat exchanger 102, a flue gas heat exchanger 104, a second heat exchanger 103 and a utilization component. The heat exchange module 101 is provided with a side wall heat exchange channel. The first heat exchange medium exchanges heat with the side wall of the electrolytic cell in the side wall heat exchange channel. The first heat exchanger 102 has a first heat exchange channel and a second heat exchange channel. The first heat exchange channel is connected to the side wall heat exchange channel of the heat exchange module 101 to form a first heat exchange loop 100 for the first heat exchange medium to circulate; the flue gas heat exchanger 104 has a flue gas channel and a flue gas heat exchange channel for the flue gas of the electrolytic cell to circulate. The second heat exchanger 103 has a third heat exchange channel and a fourth heat exchange channel. The third heat exchange channel is connected to the flue gas heat exchange channel to form a second heat exchange loop 200 for the second heat exchange medium to circulate. The utilization component is provided with a utilization channel. The fourth heat exchange channel, the second heat exchange channel and the utilization channel are connected in sequence to form a third utilization loop 300 for the third heat exchange medium to circulate.

[0042] The heat exchange module 101 can be equipped with an S-shaped heat pipe, which forms a sidewall heat exchange channel. The panel that connects the heat exchange module 101 to the sidewall of the electrolytic cell can be made of metal, such as copper or carbon steel, to transfer waste heat from the sidewall of the electrolytic cell to the first heat exchange medium through heat conduction. The first heat exchange medium can be thermal oil or an organic working fluid. Multiple heat exchange modules 101 can be provided, and multiple heat exchange modules 101 are connected in parallel in the first heat exchange circuit 100. More structures of the heat exchange module 101 can be referred to the existing disclosures and are not limited by this invention.

[0043] The flue gas heat exchanger 104 is used to exchange the flue gas of the aluminum electrolytic cell. Considering that the flue gas contains corrosive components such as sulfur dioxide and hydrogen fluoride, as well as heat exchange efficiency, service life and economy, the flue gas heat exchanger 104 can be selected from a composite phase change type, a heat pipe type and a fin type flue gas heat exchanger 104. More details about the flue gas heat exchanger 104 can be disclosed in the prior art, and this application is not limited thereto. The second heat exchange medium circulating in the second heat exchange loop 200 can be selected from water, thermal oil and other media, and this application is not limited thereto. The first heat exchanger 102 and the second heat exchanger 103 are also both prior art, for example, a water-organic working fluid heat exchanger, a thermal oil-organic working fluid heat exchanger, etc., which can be selected from the prior art as needed, and more details will not be repeated here. Of course, the third heat exchange medium can be water, organic oil and organic working fluid, and there is no limitation here.

[0044] The first heat exchange loop 100 is used for circulating a first heat exchange medium, which can exchange heat with the cell wall of the electrolytic cell. The heat of the cell wall of the electrolytic cell is transferred to the first heat exchange medium circulating in the first heat exchange loop 100. When the first heat exchange medium circulates in the first heat exchange channel, it exchanges heat with the third heat exchange medium in the second heat exchange channel, and the heat of the first heat exchange medium is transferred to the third heat exchange medium. The second heat exchange loop 200 is used for circulating a second heat exchange medium, which can exchange heat with the flue gas of the electrolytic cell in the flue gas channel in the flue gas heat exchange channel, so that the flue gas transfers heat to the second heat exchange medium in the second heat exchange loop 200. When the second heat exchange medium circulates in the third heat exchange channel, it exchanges heat with the third heat exchange medium in the fourth heat exchange channel, and the second heat exchange medium transfers heat to the third heat exchange medium. The second heat exchange medium and the first heat exchange medium transfer the waste heat of the side wall of the electrolytic cell and the flue gas to the third heat exchange medium respectively, and heat the third heat exchange medium in stages, thereby improving the heat utilization efficiency. Generally speaking, the temperature of the flue gas is lower than the side wall temperature of the electrolytic cell. Taking the 400KA electrolytic aluminum production area as an example, the flue gas volume of a single electrolytic cell is 7000m3(N) / h, and the flue gas temperature generally varies from 90 to 120°C with the seasons. The side wall window temperature of the electrolytic cell is approximately 260 to 320°C. The heat recovery of the side wall of the electrolytic cell and the flue gas is separately realized by the first heat exchange loop 100 and the second heat exchange loop 200, which has high flexibility and is not affected by the different heat of the side wall of the electrolytic cell and the flue gas. It can match the side wall of the electrolytic cell and the flue gas at different temperatures, thereby further improving the energy utilization efficiency.

[0045] In order to further improve the stability of the recycling device, please combine Figure 1 In some embodiments, the first heat exchange circuit 100 includes a first heat exchange pipe 114, which is located between the heat exchange module 101 and the first heat exchanger 102. The first heat exchange pipe 114 is connected to the input end of the first heat exchange channel and the output end of the side wall heat exchange channel. The recycling device includes a first on-off valve 105 and a storage tank 109 connected in series. The first on-off valve 105 and the storage tank 109 are connected in parallel to the first heat exchange pipe 114. When the heat exchange load of the heat exchange module 101 becomes higher or the first heat exchanger 102 is lowered, the heat exchanger 102 is heated. When the load of the third utilization loop 300 decreases, the first on-off valve 105 opens, allowing the first heat exchange medium to store heat in the storage tank 109. When the heat exchange load of the heat exchange module 101 decreases or the load of the third utilization loop 300 increases, the first on-off valve 105 opens, supplying the heat in the storage tank 109 to the first heat exchange loop 100. This ensures that the heat load fluctuations of the aluminum electrolytic cell and the load fluctuations of the third utilization loop 300 are matched, thereby improving the operational stability of the recycling device. In certain embodiments, the input end of the storage tank 109 is connected to the output end of the first heat exchange tube 114, and the output end of the storage tank 109 is connected to the input end of the first heat exchange tube 114.

[0046] In order to achieve automatic adjustment of the recycling device, in some embodiments, the recycling device includes a first temperature sensor and a controller, wherein the first temperature sensor is used to detect the temperature of the first heat exchange medium at the input end of the first heat exchange channel to determine whether the heat exchange load of the heat exchange module 101 is too large or too small. The controller is electrically connected to the first temperature sensor and the first on-off valve 105. When the heat exchange load of the heat exchange module 101 is too small, that is, when the difference △T1 between the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel and the first set temperature is less than the first target value (set value), the controller controls the first on-off valve 105 to open, and the first heat exchange medium in the storage tank 109 enters the first heat exchange loop 100 with heat to compensate for the small heat exchange load. 3. The problem of instability of the utilization loop 300; when the heat exchange load of the heat exchange module 101 is too large, that is, when the difference △T1 between the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel and the first set temperature is greater than the second target value (set value), the controller controls the first on-off valve 105 to open, and heat enters the storage tank 109 along with a part of the first heat exchange medium to exchange heat with the first heat exchange medium in the storage tank 109, and then enters the first heat exchange loop 100 after the temperature is lowered, thereby realizing the storage of heat in the storage tank 109; when the heat exchange load of the heat exchange module 101 is neither too large nor too small, that is, when the difference △T1 is in the range from the first target value to the second target value, the controller controls the first on-off valve 105 to close, and the first heat exchange medium circulates in the first heat exchange loop 100.

[0047] In order to further improve the waste heat recovery efficiency and reduce heat loss, please combine Figure 1In some embodiments, the first heat exchange circuit 100 includes a second heat exchange tube 115 and a second on-off valve 106. The second heat exchange tube 115 is connected between the output end of the first heat exchange channel and the input end of the side wall heat exchange channel. The second on-off valve 106 controls the opening and closing of the second heat exchange tube 115. The second heat exchange circuit 200 includes a fourth on-off valve 108 for controlling the opening and closing of the third heat exchange channel. The recycling device includes a third on-off valve 107 connected to the input end of the flue gas heat exchange channel. The flue gas heat exchange channel and the third on-off valve 107 are connected in parallel to the second heat exchange tube 115. The input end of the flue gas heat exchange channel is close to the output end of the first heat exchange channel. When the flue gas waste heat is close to the side wall waste heat of the electrolytic cell, recovering the flue gas waste heat and the side wall waste heat of the electrolytic cell separately will cause heat loss due to the excessively long pipeline. At this time, the flue gas waste heat recovered by the flue gas heat exchanger 104 can be transferred to the third heat exchange medium through the first heat exchange medium. At this time, the third on-off valve 107 can be opened, the second on-off valve 106 and the fourth on-off valve 108 can be closed, and the second heat exchange loop 200 is disconnected. The flue gas heat exchange channel of the flue gas heat exchanger 104, the side wall heat exchange channel of the heat exchange module 101 and the first heat exchange channel of the first heat exchanger 102 form a circulation loop. The first heat exchanger 102 is used to simultaneously recover the flue gas waste heat and the side wall waste heat, eliminating the second heat exchanger 103 and reducing heat energy loss. In this case, the first heat exchange medium and the second heat exchange medium can be the same heat exchange medium, such as heat transfer oil. In this way, when the first heat exchange circuit 100 and the second heat exchange circuit 200 are switched to operating separately and the flue gas heat exchanger 104 is connected in series to the first heat exchange circuit 100, there will be no pollution problem caused by switching the heat exchange medium of the flue gas heat exchange channel of the flue gas heat exchanger 104; in other embodiments, if the first heat exchange medium and the second heat exchange medium are different, the flue gas heat exchanger 104 is also provided with an energy-saving heat exchange channel for the circulation of the first heat exchange medium, and the energy-saving heat exchange channel and the third opening and closing valve 107 are connected to the second heat exchange pipe 115.

[0048] In order to achieve automatic control to reduce losses, in some embodiments, the recycling device includes a second temperature sensor for detecting the temperature of the first heat exchange medium or the second heat exchange medium flowing through the output end of the flue gas heat exchange channel; Figure 1The fourth on-off valve 108 , the second temperature sensor, the third on-off valve 107 and the second on-off valve 106 are all electrically connected to the controller. The controller obtains the difference ΔT2 between the temperature T1 and the temperature T2 based on the temperature T2 of the first heat exchange medium or the second heat exchange medium at the output end of the flue gas heat exchange channel and the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel detected by the second temperature sensor; when the flue gas waste heat is close to the side wall waste heat of the electrolytic cell, that is, the difference ΔT2 is less than the third target value (set value), the third on-off valve 107 is opened, and the second on-off valve 106 and the fourth on-off valve 108 are closed to make the flue gas heat exchange channel of the flue gas heat exchanger 104 and the first heat exchange channel of the first heat exchanger 102 conductive; when the difference ΔT2 is not less than the third target value (set value), that is, the difference between the flue gas waste heat and the side wall waste heat of the electrolytic cell is large, the second on-off valve 106 and the fourth on-off valve 108 are opened, and the third on-off valve 107 is closed to make the second heat exchange circuit 200 conductive, and the flue gas waste heat and the side wall waste heat of the electrolytic cell are separately recovered to match the electrolytic aluminum process.

[0049] During automatic control, the first on-off valve 105 , the second on-off valve 106 , the third on-off valve 107 and the fourth on-off valve 108 are all electrically controlled valves, such as solenoid valves, which are opened or closed under the control of the controller to achieve conduction or closure of the passage.

[0050] In some embodiments, the utilization component includes an expander 110, a condenser 111 and a power mechanism 113 connected in series at the output end of the second heat exchange channel. The power mechanism 113 is connected to the fourth heat exchange channel. The gas channel of the expander 110, the condensation channel of the condenser and the power channel of the power mechanism 113 form a utilization channel. The third heat exchange medium is an organic working fluid. The organic working fluid can be selected from mono- or di-elementary organic working fluids such as difluoromethane (R32), R123 (molecular formula is CF3CHCl2), pentafluoropropane (R245), etc. These organic working fluids are low-temperature working fluids. Under the action of low-temperature waste heat such as flue gas waste heat and side wall waste heat of the electrolytic cell, the low-temperature working fluid can exist in gaseous form. The expander 110 is a machine that uses the principle of outputting mechanical work to reduce the gas temperature when the compressed gas expands and depressurizes to obtain cooling capacity. The gaseous third heat exchange medium can be depressurized and cooled in the expander 110 to be converted into Mechanical work is utilized, and the third heat exchange medium after cooling can be transformed from gas to liquid in the condenser 111, and actively circulates in the third utilization loop 300 under the action of the power mechanism 113, such as an organic working fluid pump, and the liquid third heat exchange medium performs heat exchange in the second heat exchanger 103 and the first heat exchanger 102. In order to improve the condensation effect of the condenser 111, the condenser 111 can be equipped with a cooling tower 112. The condenser 111 and the cooling tower 112 are both existing technologies. For more details, please refer to the existing technology disclosure, which will not be elaborated in the present invention.

[0051] In some embodiments, combined Figure 1 The recycling device also includes a connecting valve 116 and a bypass valve 117. The connecting valve 116 is connected in series between the second heat exchange channel and the third heat exchange channel, and the bypass valve 117 is connected in parallel to the second heat exchange channel and the connecting valve 116. When the connecting valve 116 is open and the bypass valve 117 is closed, the flue gas waste heat and the side wall waste heat of the electrolytic cell are recycled and reused in a graded manner. When the connecting valve 116 is closed and the bypass valve 117 is open, only the flue gas waste heat can be utilized to accommodate more operating conditions. The bypass valve 117 and the connecting valve 116 can both be electrically controlled valves, and both the bypass valve 117 and the connecting valve 116 are electrically connected to the controller.

[0052] In some embodiments, please continue to combine Figure 1 The recycling device also includes a compressor 118 for compressing air. Compressor 118 is connected to expander 110 and is equipped with a waste heat recovery channel connected in parallel to the first heat exchange channel. Specifically, compressor 118 and expander 110 are connected via a coupling. Under the action of a low-melting-point third heat exchange medium, expander 110 converts the pressure energy of steam into mechanical energy and transmits it to compressor 118. Compressor 118 can use this mechanical energy to produce compressed air for use in the electrolytic aluminum industry. For example, it can be used for daily operations such as shelling cylinders in aluminum electrolytic cells, conveying alumina, lifting aluminum ladles, casting, and workshop purging. Waste heat is used to generate electricity and then used to produce compressed air by compressor 118. Compressor 118 can only convert 10-30% of electrical energy into compressed air. Compared with this, the solution of the present application directly uses waste heat to produce compressed air, which is more efficient. Connecting the waste heat recovery channel of compressor 118 in parallel with the first heat exchange channel can recycle the heat. Compressor 118 can be a screw compressor 118 or a turbine compressor 118. The type of compressor 118 is not limited in this embodiment. In other embodiments, the recycling device can also be a fan 123 or a dynamic pump. Fan 123 or dynamic pump 124 is connected to expander 110 via a coupling to convert waste heat into other forms of mechanical energy such as wind energy. In other embodiments, the recycling device also includes an air storage tank 119, a dryer 120, a filter 121, and a dust collector 122, which are sequentially connected to compressor 118. Dust collector 122 is used to connect to the user end.

[0053] Taking the first heat exchange medium as heat transfer oil, the second heat exchange medium as heat transfer oil, and the third heat exchange medium as R32 as an example, the recycling process of the recycling device of this embodiment is as follows:

[0054] The first on-off valve and the third on-off valve are closed, the second on-off valve and the fourth on-off valve are opened, the high-temperature flue gas flows through the flue gas channel in the flue gas heat exchanger 104, the heat transfer oil circulates in the second heat exchange loop 200, the 20°C heat transfer oil exchanges heat with the high-temperature flue gas in the flue gas heat exchange channel, the heat transfer oil is heated to 75-85°C by the high-temperature flue gas, and the heat transfer oil brings heat to the third heat transfer channel of the second heat exchanger 103; the side wall of the electrolytic cell exchanges heat with the heat transfer oil in the side wall heat transfer channel of the heat exchange module 101, and the heat transfer oil is heated to 160-220°C, and the heat transfer oil circulates in the first heat exchange loop 100, bringing heat to the first heat transfer channel of the first heat exchanger 102; the third utilization loop 300 R32 exchanges heat with water in the third heat exchange channel in the fourth heat exchange channel of the second heat exchanger 103, and then runs to the second heat exchange channel of the first heat exchanger 102 to exchange heat with the heat transfer oil in the first heat exchange channel. At this time, the waste heat of the flue gas and the waste heat of the side wall of the electrolytic cell are concentrated in R32. At this time, R32 is in a gaseous state. Under the action of the power mechanism 113, it continues to run to the expander 110, doing work on the expander 110. The pressure of R32 is reduced, and under the action of the condensing tower, it forms a liquid state and continues to circulate and recover heat; the expander 110 works and transmits mechanical energy to the compressor 118 to produce 0.4-0.7Mpa compressed air, thereby realizing the preparation of compressed air using the waste heat of the aluminum electrolytic cell, and effectively reducing the energy consumption of electrolytic aluminum.

[0055] When the absolute value △T1 of the difference between the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel and the first set temperature is greater than the first target value, the first on-off valve 105 is controlled to open, and the first heat exchange medium is heated by the waste heat of the side wall of the electrolytic cell from the side wall heat exchange channel of the heat exchange module 101, enters the first heat exchange channel in one way, enters the storage tank 109 in the other way and flows out of the storage tank 109, and finally enters the first heat exchange channel. The first heat exchange medium heats the third heat exchange medium in the second heat exchange channel in the first heat exchange channel, and finally flows back to the side wall heat exchange channel of the heat exchange module 101.

[0056] When the difference ΔT2 between the temperature T1 of the heat transfer oil at the input end of the first heat exchange channel and the temperature T2 of the heat transfer oil at the output end of the flue gas heat exchange channel is less than the second target value, the third on-off valve 107 is opened, and the second on-off valve 106 and the fourth on-off valve 108 are closed. The heat transfer oil first enters the flue gas heat exchange channel of the flue gas heat exchanger 104 to be heated by the flue gas, then enters the side wall heat exchange channel of the heat exchange module 101, is heated by the side wall of the electrolytic cell, then enters the first heat exchange channel in the first heat exchanger 102 to heat R32, and then returns to the flue gas heat exchange channel of the flue gas heat exchanger 104, completing a cycle.

[0057] The recycling device of this embodiment has at least the following advantages:

[0058] 1. In view of the heat difference between the side of the aluminum electrolysis cell and the waste heat of the flue gas, a first heat exchange loop 100, a second heat exchange loop 200 and a third utilization loop 300 are set. The second heat exchange loop 200 and the first heat exchange loop 100 perform staged heating on the organic working fluid in the third utilization loop 300. The system has a simple and flexible structure and high thermal efficiency, effectively realizing the efficient recovery of waste heat from the aluminum electrolysis cell.

[0059] 2. Using the waste heat of flue gas generated during the aluminum electrolysis process and the heat dissipated from the side walls of the electrolytic cell as heat sources, an organic Rankine cycle working system is established using the first heat exchanger 102, the second heat exchanger 103, the expander 110, the condenser 111 and the compressor 118 to convert the waste heat from the electrolytic aluminum production into compressed air, thereby saving the power consumption of the air compressor in the electrolytic aluminum production workshop and improving the power utilization efficiency of the electrolytic aluminum.

[0060] Example 2

[0061] Based on the same technical concept as Example 1, an embodiment of the present invention provides a method for controlling the recovery of waste heat from an electrolytic cell based on Example 1, which controls the on or off of the passage where the storage tank 109 is located, meets the heat exchange requirements for stabilizing the first heat exchange circuit 100, and ensures the stability of the recycling device.

[0062] Combine Figure 3 , the recycling control method comprises the following steps:

[0063] S21 . Obtain, based on the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel, an absolute value ΔT1 of the difference between the temperature T1 and the first set temperature.

[0064] The temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel can be obtained by the first temperature sensor. The first set temperature is a set value. The first set temperature can be determined based on historical data of aluminum electrolysis. The first set temperature can be the average value of the first heat exchange medium in the first heat exchange channel running for a period of time, such as three months or six months. Of course, it can also be determined as needed, and this embodiment does not limit it. When the absolute value of the difference ΔT1 is too large, it means that the heat load of the heat exchange module 101 is too large or too small. Specifically, when the temperature T1 is greater than the first set temperature, the heat load of the heat exchange module 101 is too large. When the temperature T1 is less than the first set temperature, the heat load of the heat exchange module 101 is too small. At this time, the operating temperature of the first heat exchange circuit 100 fluctuates greatly, which will affect the stable operation of the third utilization circuit 300.

[0065] S22. When the absolute value of the difference △T1 is greater than the first target value, the first on-off valve 105 is controlled to open so that the first heat exchange medium enters the storage tank 109; when the absolute value of the difference △T1 is less than the first target value, the first on-off valve 105 is controlled to close so that the first heat exchange medium flows through the first heat exchange circuit 100, and the first target value is the set value.

[0066] When the absolute value of the difference △T1 is greater than the first target value, the first target value is the set value, for example 50°C, and the heat load of the heat exchange module 101 is too large or too small. At this time, it is necessary to open the first on-off valve 105, the storage tank 109 and connect the first heat exchange pipe 114 to stabilize the heat of the first heat exchange circuit 100.

[0067] The control method of this embodiment is applied to the recycling device of the above-mentioned embodiment 1. Specifically, the control method is stored in the controller in the form of a computer program. The controller obtains the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel, and obtains the absolute value △T1 of the difference between the temperature T1 and the first set temperature based on the temperature T1. Then, based on program judgment, according to the comparison result of the absolute value of the difference △T1 and the first target value, a corresponding control instruction is issued to the first on-off valve 105 to activate the first on-off valve 105 to realize the conduction or closing of the passage where the storage tank 109 is located.

[0068] In summary, the control method provided in the embodiment of the present application cooperates with the aforementioned recycling device to control the conduction or closing of the passage where the storage tank 109 is located, meet the heat exchange requirements of the first heat exchange circuit 100, and ensure the stability of the recycling device.

[0069] Example 3

[0070] Based on the same technical concept as Example 1, the embodiment of the present invention provides a method for controlling the recovery of waste heat from an electrolytic cell based on Example 1, connecting the flue gas heat exchanger 104 in series to the first heat exchange loop 100 or the second heat exchange loop 200, thereby improving the heat energy recovery rate.

[0071] Combine Figure 4 , the recycling control method comprises the following steps:

[0072] S31, obtaining a difference ΔT2 between the temperature T1 and the temperature T2 of the first heat exchange medium at the input end of the first heat exchange channel and the temperature T2 of the first heat exchange medium or the second heat exchange medium at the output end of the flue gas heat exchange channel;

[0073] The first temperature sensor can be used to obtain the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel, and the second temperature sensor can be used to obtain the temperature T2 of the first or second heat exchange medium at the output end of the flue gas heat exchange channel. The difference between the two can then be calculated. When the flue gas temperature differs significantly from the sidewall temperature of the electrolytic cell, staged recovery can improve the heat recovery rate. When the flue gas temperature and the sidewall temperature of the electrolytic cell are similar, separate recovery can be performed. However, long pipelines increase energy consumption. In this case, the second heat exchanger 103 can be connected in series to the first heat exchange loop 100 to reduce energy consumption during the recovery process.

[0074] S32. When the difference △T2 is less than the second target value, the third on-off valve 107 is opened, and the second on-off valve 106 and the fourth on-off valve 108 are closed to connect the flue gas heat exchange channel of the flue gas heat exchanger 104 with the first heat exchange channel of the first heat exchanger 102; when the difference △T2 is not less than the second target value, the second on-off valve 106 and the fourth on-off valve 108 are opened, and the third on-off valve 107 is closed to connect the second heat exchange circuit 200. The second target value is the set value.

[0075] The second target value is a set value, for example, 50°C, or other values, which are not limited by the present invention. When the difference ΔT2 is less than the second target value, it indicates that the difference between temperature T1 and temperature T2 is not large. In this case, it is not necessary to separately recover the flue gas waste heat and the waste heat from the side walls of the electrolytic cell. The flue gas heat exchanger 104 can be connected in series to the first heat exchange loop 100. When the difference ΔT2 is greater than the second target value, it indicates that the difference between temperature T1 and temperature T2 is large. It is necessary to connect both the first heat exchange loop 100 and the second heat exchange loop 200 to separately recover the flue gas waste heat and the waste heat from the side walls of the electrolytic cell to match the process and improve the heat recovery rate.

[0076] The control method of this embodiment is applied to the recycling device of the above-mentioned embodiment 1. Specifically, the control method is stored in the controller in the form of a computer program. The controller obtains the difference △T2 between the temperature T1 and the temperature T2 based on the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel and the temperature T2 of the first heat exchange medium or the second heat exchange medium at the output end of the flue gas heat exchange channel. Then, based on program judgment, according to the comparison result of the difference △T2 with the second target value, corresponding control instructions are issued to the second on-off valve 106, the third on-off valve 107 and the fourth on-off valve 108 to activate the second on-off valve 106, the third on-off valve 107 and the fourth on-off valve 108 to realize the conduction or closing of the second heat exchange circuit 200.

[0077] In summary, the control method provided in the embodiment of the present application is combined with the aforementioned recycling device to connect the flue gas heat exchanger 104 in series to the first heat exchange loop 100 or the second heat exchange loop 200, thereby improving the heat energy recovery rate.

[0078] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0079] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A device for recovering and utilizing waste heat from an electrolytic cell, characterized in that: include: The heat exchange module is provided with a side wall heat exchange channel; a first heat exchanger having a first heat exchange channel and a second heat exchange channel, wherein the first heat exchange channel is connected to the side wall heat exchange channel to form a first heat exchange circuit for circulating a first heat exchange medium, and the first heat exchange circuit includes a first heat exchange tube connected between an output end of the side wall heat exchange channel and an input end of the first heat exchange channel; A flue gas heat exchanger having a flue gas channel for the flow of flue gas from the electrolytic cell and a flue gas heat exchange channel; The second heat exchanger has a third heat exchange channel and a fourth heat exchange channel. The third heat exchange channel is connected to the flue gas heat exchange channel to form a second heat exchange circuit for the second heat exchange medium to flow. The utilization component is provided with a utilization channel, wherein the fourth heat exchange channel, the second heat exchange channel and the utilization channel are sequentially connected to form a third utilization circuit for circulating a third heat exchange medium; a first on-off valve and a storage tank, wherein the first on-off valve and the storage tank are connected in series, and the first on-off valve and the storage tank are connected in parallel to the first heat exchange pipe; a first temperature sensor, configured to detect the temperature of the first heat exchange medium at the input end of the first heat exchange channel; A controller is electrically connected to the first temperature sensor and the first on-off valve.

2. The electrolytic cell waste heat recovery and utilization device according to claim 1, characterized in that: The first heat exchange circuit includes a second heat exchange tube and a second on-off valve for controlling the opening and closing of the second heat exchange tube, wherein the second heat exchange tube is connected between the output end of the first heat exchange channel and the input end of the side wall heat exchange channel; the second heat exchange circuit includes a fourth on-off valve for controlling the opening and closing of the third heat exchange channel; The recycling device includes a third on-off valve connected to the input end of the flue gas heat exchange channel. The flue gas heat exchange channel and the third on-off valve are connected to the second heat exchange tube in parallel. The input end of the flue gas heat exchange channel is close to the output end of the first heat exchange channel.

3. The electrolytic cell waste heat recovery and utilization device according to claim 2, characterized in that: The recycling device includes a second temperature sensor for detecting the temperature of the first heat exchange medium or the second heat exchange medium flowing through the output end of the flue gas heat exchange channel; The fourth on-off valve, the second temperature sensor, the third on-off valve, and the second on-off valve are all electrically connected to the controller.

4. The electrolytic cell waste heat recovery and utilization device according to claim 3, characterized in that: The utilization component includes an expander, a condenser and a power mechanism connected in series to the output end of the second heat exchange channel. The power mechanism is connected to the fourth heat exchange channel. The gas channel of the expander, the condensation channel of the condenser and the power channel of the power mechanism connected in series form the utilization channel. The third heat exchange medium is an organic working fluid.

5. The electrolytic cell waste heat recovery and utilization device according to claim 4, characterized in that: The recycling device further includes a connecting valve connected in series between the second heat exchange channel and the fourth heat exchange channel, and a bypass valve connected in parallel to the second heat exchange channel and the connecting valve.

6. The electrolytic cell waste heat recovery and utilization device according to claim 4, characterized in that: The recycling device includes a compressor for compressing air, the compressor is connected to the expander, and the compressor is provided with a waste heat recovery channel connected to the first heat exchange channel.

7. A recovery control method for an electrolytic cell waste heat recovery device according to any one of claims 1 to 6, characterized in that: The steps include: According to the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel, obtaining an absolute value ΔT1 of the difference between the temperature T1 and the first set temperature; When the absolute value △T1 of the difference is greater than the first target value, the first on-off valve is controlled to open so that the first heat exchange medium enters the storage tank; when the absolute value △T1 of the difference is less than the first target value, the first on-off valve is controlled to close so that the first heat exchange medium flows in the first heat exchange circuit, and the first target value is a set value.

8. A recovery control method for an electrolytic cell waste heat recovery device according to any one of claims 3 to 6, characterized in that: The steps include: Obtaining a difference ΔT2 between the temperature T1 and the temperature T2 according to the temperature T1 of the first heat exchange medium at the input end of the first heat exchange channel and the temperature T2 of the first heat exchange medium or the second heat exchange medium at the output end of the flue gas heat exchange channel; When the difference ΔT2 is less than the second target value, the third on-off valve is opened, and the second on-off valve and the fourth on-off valve are closed, so that the flue gas heat exchange channel of the flue gas heat exchanger is connected to the first heat exchange channel of the first heat exchanger; When the difference ΔT2 is not less than a second target value, the second on-off valve and the fourth on-off valve are opened, and the third on-off valve is closed to conduct the second heat exchange circuit. The second target value is a set value.

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