Magnesium electrolysis waste heat cascade recovery system and method based on wet heat exchange

Abstract

The invention provides a magnesium electrolysis waste heat cascade recovery system and method based on wet heat exchange. The system comprises a medium supply part, a magnesium electrolytic cell and a waste heat absorber, a cell shell outer lining is arranged on a shell of the magnesium electrolytic cell, a heat exchanger is arranged in a cell cavity of the magnesium electrolytic cell, and a chlorine cover of the magnesium electrolytic cell is sleeved with a heat exchange sleeve; the medium supply part is communicated with a medium inlet of the heat exchange sleeve and a medium inlet of the heat exchanger and conveys air mixed with water mist to the heat exchange sleeve and the heat exchanger, and the medium supply part is communicated with a medium inlet of the tank shell outer lining and conveys normal-temperature air to the tank shell outer lining; a medium outlet of the heat exchange sleeve, a medium outlet of the heat exchanger and a medium outlet of the tank shell outer lining are all communicated with a heat exchange coil pipe of the waste heat absorber; according to the system, the waste heat recovery rate is increased, a blind area of waste heat recovery is avoided, waste heat of different heat energy grades can be recovered, and the multi-grade energy consumption requirement of a plant area steam pipe network can be met; meanwhile, the size of the heat exchange equipment can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conservation in non-ferrous metal metallurgy, and particularly relates to a magnesium electrolysis waste heat cascade recovery system and method based on wet heat exchange. Background Art

[0002] A large amount of waste heat is generated during the production of metallic magnesium in a magnesium electrolysis cell. Reasonably recovering and utilizing these waste heat resources can significantly reduce energy consumption, reduce carbon emissions, and improve economic benefits. Magnesium electrolysis production is mainly achieved by electrolyzing molten magnesium chloride (MgCl2), and the electrolysis temperature is usually above 655–680°C. The waste heat mainly comes from:

[0003] First, heat dissipation from the electrolysis cell body: The high-temperature electrolysis cell dissipates heat to the environment through radiation, convection, and conduction. The outer surface temperature of the electrolysis cell is usually between 50 and 120°C.

[0004] Second, waste heat of electrolysis gases: High-temperature gases such as chlorine (Cl2) and a small amount of CO2, CO, etc. generated during the electrolysis process. The temperature of these electrolysis gases can reach 300–500°C.

[0005] Third, heat from the cooling system: The electrolysis cell needs to maintain a stable temperature through a water-cooling or air-cooling system. The heat carried away by the cooling medium constitutes waste heat resources. Among them, the temperature of the cooling water after water cooling can be as high as 80°C, and the temperature of the cooling air after air cooling is generally around 300°C.

[0006] As can be seen above, the waste heat recovery of the magnesium electrolysis cell has great potential, which is mainly manifested in:

[0007] First, wide temperature range: The waste heat temperature has a large span, and the waste heat carried by high-temperature gases (300–500°C) and medium-low temperature cooling water (50–90°C) can be utilized.

[0008] Second, large calorific value estimation: The waste heat per hour of a single magnesium electrolysis cell can reach 300–500 kW.

[0009] Third, high energy value: If the recovery rate is calculated at 50%, the annual waste heat power generation of a factory with an annual output of 10,000 tons of magnesium can reach several million kilowatt-hours, or replace a large amount of coal / gas for heating.

[0010] For the traditional waste heat recovery system of multi-pole magnesium electrolysis cells, conventional air-cooled heat exchangers or water-cooled heat exchangers are often used, which have the following technical defects:

[0011] 1. Conventional heat exchangers have the defects of low heat transfer efficiency and insufficient waste heat recovery rate (usually <40%);

[0012] 2. It is difficult to implement hierarchical heat exchange for different temperature zones of the electrolysis cell (such as: 200–300°C gas phase zone, 50–120°C cell body surface);

[0013] 3. The recovered heat energy has a single grade and cannot meet the multi-grade energy consumption requirements of the plant steam pipe network;

[0014] 4. The specific heat capacity of the heat exchange medium on the air side of the conventional air-cooled heat exchanger is low, resulting in a large volume of the heat exchange equipment. Summary of the Invention

[0015] In view of this, the present invention aims to propose a magnesium electrolysis waste heat cascade recovery system and method based on wet heat exchange to solve the problems in the prior art that the traditional multi-stage magnesium electrolysis cell waste heat recovery system is difficult to carry out hierarchical heat exchange for different temperature zones of the electrolysis cell, the waste heat recovery rate is relatively low, and the equipment volume is relatively large.

[0016] To achieve the above object, the technical solution of the present invention is realized as follows:

[0017] A magnesium electrolysis cell waste heat cascade recovery system based on wet heat exchange includes a medium supply unit, a magnesium electrolysis cell, and a waste heat absorber. The outer shell of the magnesium electrolysis cell is provided with a cell shell outer lining. A heat exchanger is arranged in the cell cavity of the magnesium electrolysis cell, and a heat exchange sleeve is sleeved outside the chlorine hood of the magnesium electrolysis cell; the medium supply unit is communicated with the medium inlet of the heat exchange sleeve and the medium inlet of the heat exchanger to convey air mixed with water mist to the heat exchange sleeve and the heat exchanger, and the medium supply unit is communicated with the medium inlet of the cell shell outer lining to convey normal-temperature air to the cell shell outer lining; the medium outlets of the heat exchange sleeve, the heat exchanger, and the cell shell outer lining are all communicated with the heat exchange coil of the waste heat absorber.

[0018] Further, the medium supply unit includes a chlorine hood fan, a heat exchanger fan, and a cell shell fan. The air outlet of the chlorine hood fan is communicated with the medium inlet of the heat exchange sleeve, and a first atomizing nozzle is arranged at the air outlet of the chlorine hood fan; the air outlet of the heat exchanger fan is communicated with the medium inlet of the heat exchanger, and a second atomizing nozzle is arranged at the air outlet of the heat exchanger fan; the air outlet of the cell shell fan is communicated with the medium inlet of the cell shell outer lining.

[0019] Further, the system includes a waste heat spray tower and a hot water pump. The heat exchange coil outlet of the waste heat absorber is communicated with the inner cavity of the waste heat spray tower. A pure water nozzle is arranged at the top of the waste heat spray tower. The liquid suction side of the hot water pump is communicated with the bottom of the waste heat spray tower, and the liquid discharge side of the hot water pump is communicated with the inner cavity of the waste heat absorber.

[0020] Further, along the vertical direction from bottom to top, the inner cavity of the waste heat absorber is sequentially divided into a low-temperature zone, a medium-temperature zone, and a high-temperature zone. A low-temperature coil is arranged in the low-temperature zone, a medium-temperature coil is arranged in the medium-temperature zone, and a high-temperature coil is arranged in the high-temperature zone. The low-temperature coil, the medium-temperature coil, and the high-temperature coil are independent heat exchange coil structures from each other.

[0021] Further, the medium outlet of the heat exchange sleeve is communicated with the high-temperature coiled pipe, the medium outlet of the heat exchanger is communicated with the medium-temperature coiled pipe, and the medium outlet of the outer lining of the tank shell is communicated with the low-temperature coiled pipe.

[0022] Further, the outlets of the low-temperature coiled pipe, the medium-temperature coiled pipe, and the high-temperature coiled pipe are all communicated with the inner cavity of the waste heat spray tower and are arranged in sequence in the vertical direction from bottom to top.

[0023] Further, the outlet of the low-temperature coiled pipe is communicated with the bottom of the waste heat spray tower, and the outlet of the low-temperature coiled pipe is lower than the liquid level of the bottom of the waste heat spray tower.

[0024] Further, the waste heat spray tower is provided with an induced draft fan, and the air suction side of the induced draft fan is communicated with the inner cavity of the waste heat spray tower.

[0025] Further, the waste heat absorber is provided with a temperature monitor and a liquid level monitor for monitoring the water temperature and water level in the inner cavity of the waste heat absorber; a steam outlet is arranged at the top of the waste heat absorber.

[0026] A method for cascaded recovery of waste heat from magnesium electrolysis based on wet heat exchange is used for the cascaded waste heat recovery system of magnesium electrolysis cell based on wet heat exchange described above; the method includes: S1. Start the medium supply part; S2. Heat the heat exchange sleeve and the heat exchanger through air mixed with water mist, and heat the outer lining of the tank shell through normal temperature air; S3. Send the medium after heat exchange in step S2 to the waste heat absorber to exchange heat with the water in the inner cavity of the waste heat absorber and produce waste heat steam.

[0027] Compared with the prior art, the cascaded waste heat recovery system and method for magnesium electrolysis based on wet heat exchange of the present invention have the following advantages:

[0028] The cascaded waste heat recovery system and method for magnesium electrolysis based on wet heat exchange of the present invention, by setting a medium supply part, perform regional waste heat recovery on the waste heat at three different positions (with completely different temperature states) of the magnesium electrolysis cell, which is not only beneficial to improving the waste heat recovery rate, avoiding blind areas in waste heat recovery, but also can recover waste heat with different heat energy grades, and can meet the multi-grade energy consumption requirements of the plant steam pipe network.

[0029] Meanwhile, for the electrolytic gas temperature and the heat exchanger medium outlet temperature that are relatively high, the medium supply section conveys air mixed with water mist to the heat exchange sleeve and the heat exchanger. While the gaseous components conduct conventional heat exchange (sensible heat), the water mist can absorb more heat in the form of phase change (latent heat of phase change) through the evaporation of the droplets upon heating. On the one hand, it improves the heat absorption capacity and heat exchange efficiency for the first-stage waste heat and the second-stage waste heat, contributing to the improvement of the waste heat recovery rate. On the other hand, due to the synergy of the latent heat effect and the sensible heat effect of phase change, it can significantly increase the equivalent specific heat capacity of the medium, enabling the heat exchange equipment to recover more waste heat under the same volume, thus contributing to the reduction of the volume of the heat exchange equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention. In the drawings:

[0031] Figure 1 It is a schematic diagram of a magnesium electrolysis waste heat cascade recovery system based on wet heat exchange according to an embodiment of the invention.

[0032] DESCRIPTION OF THE REFERENCE NUMERALS

[0033] 11. Chlorine hood fan; 12. Heat exchanger fan; 13. Tank shell fan; 21. First atomizing nozzle; 22. Second atomizing nozzle; 3. Magnesium electrolysis cell; 31. Outer lining of the tank shell; 32. Heat exchanger; 33. Chlorine hood; 34. Heat exchange sleeve; 35. Chlorine outlet; 4. Waste heat absorber; 41. Low-temperature coil; 42. Medium-temperature coil; 43. High-temperature coil; 44. Temperature monitor; 45. Liquid level monitor; 46. Low-temperature area; 47. Medium-temperature area; 48. High-temperature area; 5. Waste heat spray tower; 51. Pure water nozzle; 52. Hot water pump; 53. Induced draft fan. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Hereinafter, the inventive concepts of the present disclosure will be described using the terms that those skilled in the art would typically use to convey the substance of their work to other skilled artisans in the art. However, these inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0035] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other. The red dashed boxes in the drawings are only for distinguishing different waste heat temperature regions in the waste heat absorber 4 and are not structural lines, so as to facilitate the intuitive understanding of the temperature region distribution in the waste heat absorber 4.

[0036] The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0037] In order to solve the problems existing in the traditional multi-pole magnesium electrolysis cell waste heat recovery system in the prior art, such as the difficulty in grading heat exchange for different temperature zones of the electrolysis cell, the relatively low waste heat recovery rate, and the relatively large equipment volume, this embodiment proposes a magnesium electrolysis waste heat cascade recovery system based on wet heat exchange, as shown in the attached Figure 1 As shown, the system includes a medium supply unit, a magnesium electrolysis cell 3, and a waste heat absorber 4. The outer shell of the magnesium electrolysis cell 3 is provided with an outer lining 31 of the cell shell, a heat exchanger 32 is arranged in the cell cavity of the magnesium electrolysis cell 3, and a heat exchange sleeve 34 is sleeved outside the chlorine hood 33 of the magnesium electrolysis cell 3; the medium supply unit is communicated with the medium inlet of the heat exchange sleeve 34 and the medium inlet of the heat exchanger 32 to convey air mixed with water mist to the heat exchange sleeve 34 and the heat exchanger 32, and the medium supply unit is communicated with the medium inlet of the outer lining 31 of the cell shell to convey normal temperature air to the outer lining 31 of the cell shell; the medium outlets of the heat exchange sleeve 34, the heat exchanger 32, and the outer lining 31 of the cell shell are all communicated with the heat exchange coil of the waste heat absorber 4 for heat exchange of the water in the inner cavity (i.e., "shell side") of the waste heat absorber 4.

[0038] It should be noted that in the scheme introduction of this application, the term "medium" refers to the substance used for recovering the waste heat of the magnesium electrolysis cell. Correspondingly, the "medium inlet" and "medium outlet" also refer to the flow pipeline structures of the corresponding substances. The chlorine hood 33 has a pipeline structure for the magnesium electrolysis cell 3 to convey electrolysis gases such as chlorine outwards. Correspondingly, one end of the chlorine hood 33 away from the magnesium electrolysis cell 3 has a chlorine outlet 35.

[0039] Among them, for the magnesium electrolysis cell 3, in the normal operating state, the temperature of the electrolysis gas in the chlorine hood 33 is often 300-500 °C, which is regarded as the first-level waste heat in this application; the medium outlet temperature of the conventional air-cooled heat exchanger 32 is often 200-300 °C, which is regarded as the second-level waste heat in this application; the temperature at the outer shell and the outer lining 31 of the cell shell of the magnesium electrolysis cell 3 is often 50-120 °C, which is regarded as the third-level waste heat in this application.

[0040] Therefore, in this application, by setting the medium supply unit, waste heat recovery in different regions is carried out for the three places of waste heat at different positions (with completely different temperature states) of the magnesium electrolysis cell 3, which is not only beneficial to improving the waste heat recovery rate, avoiding blind areas in waste heat recovery, but also capable of recovering waste heat with different heat energy grades, and can meet the multi-grade energy consumption requirements of the plant steam pipe network.

[0041] Meanwhile, for the electrolytic gas temperature and the medium outlet temperature of the heat exchanger 32 which are relatively high, the medium supply unit conveys air mixed with water mist to the heat exchange sleeve 34 and the heat exchanger 32. While the gaseous components conduct conventional heat exchange (sensible heat), the water mist can absorb more heat in the form of phase change (latent heat of phase change) through the evaporation of the droplets when heated. On the one hand, it improves the heat absorption capacity and heat exchange efficiency for the first-stage waste heat and the second-stage waste heat, contributing to improving the waste heat recovery rate. On the other hand, due to the synergy of the latent heat effect and the sensible heat effect of phase change, it can significantly increase the equivalent specific heat capacity of the medium, enabling the heat exchange equipment to recover more waste heat under the same volume, thus helping to reduce the volume of the heat exchange equipment.

[0042] The medium supply unit includes a chlorine hood blower 11, a heat exchanger blower 12, and a tank shell blower 13. The air outlet of the chlorine hood blower 11 is communicated with the medium inlet of the heat exchange sleeve 34, and a first atomizing nozzle 21 is arranged at the air outlet of the chlorine hood blower 11 for spraying water mist onto the air sent to the heat exchange sleeve 34; the air outlet of the heat exchanger blower 12 is communicated with the medium inlet of the heat exchanger 32, and a second atomizing nozzle 22 is arranged at the air outlet of the heat exchanger blower 12 for spraying water mist onto the air sent to the heat exchanger 32; the air outlet of the tank shell blower 13 is communicated with the medium inlet of the tank shell outer lining 31 for conveying normal-temperature air to the tank shell outer lining 31.

[0043] For the air mixed with water mist, the content of droplets in each cubic meter of air is greater than 200 g, so that sufficient latent heat can be provided during the heat recovery of the first-stage waste heat and the second-stage waste heat, enhancing the heat absorption capacity of the medium. It should be noted that the "droplets" in this application refer to tiny liquid water droplets suspended in the air, rather than gaseous water vapor.

[0044] For the recovery of the first-stage waste heat, the heat exchange sleeve 34 is a heat exchanger made of nickel-based alloy, which has the advantages of high temperature resistance and chlorine corrosion resistance. After the waste heat recovery process, the electrolytic gas temperature is reduced from 300 - 500 °C to 60 - 80 °C, and the medium forms an air-steam mixture with a temperature of 200 - 3°C.

[0045] For the recovery of the second-stage waste heat, the heat exchanger 32 is a coil-type heat exchanger made of stainless steel. After the waste heat recovery process, the medium forms an air-steam mixture with a temperature of 200 - 250 °C.

[0046] For the recovery of the third - level waste heat, the outer lining 31 of the tank shell is a heat - exchange jacket made of carbon steel. After the waste - heat recovery process, the medium forms air with a temperature of 80 - 100 °C. Of course, since air inevitably has a certain humidity, this air can essentially be regarded as an air - water vapor mixture. However, for the purpose of differentiating from the first - level and second - level waste - heat recovery, this application suggests regarding it as conventional air rather than an air - water vapor mixture.

[0047] In the vertical direction from bottom to top, the inner cavity of the waste - heat absorber 4 is successively divided into a low - temperature zone 46, a medium - temperature zone 47, and a high - temperature zone 48. A low - temperature coil 41 is arranged in the low - temperature zone 46, a medium - temperature coil 42 is arranged in the medium - temperature zone 47, and a high - temperature coil 43 is arranged in the high - temperature zone 48. The low - temperature coil 41, the medium - temperature coil 42, and the high - temperature coil 43 are independent heat - exchange coil structures.

[0048] The medium outlet of the heat - exchange sleeve 34 is communicated with the high - temperature coil 43, the medium outlet of the heat exchanger 32 is communicated with the medium - temperature coil 42, and the medium outlet of the outer lining 31 of the tank shell is communicated with the low - temperature coil 41.

[0049] Due to the property of water that "hot water rises and cold water sinks", for the water in the inner cavity of the waste - heat absorber 4, the water temperature in the upper layer is lower than that in the lower layer, resulting in a certain water - temperature gradient in the vertical direction of the waste - heat absorber 4. Based on this, this application places the low - temperature coil 4 with the lowest temperature at the bottommost layer of the waste - heat absorber 4, and the high - temperature coil 43 with the highest temperature at the topmost layer of the waste - heat absorber 4. The medium - temperature gradient in each heat - exchange coil is consistent with the water - temperature gradient, enabling effective heat exchange between each heat - exchange coil and the water body corresponding to its height, so that the water in the waste - heat absorber 4 can conduct multi - gradient heat exchange, which helps to improve the waste - heat recovery capacity of the waste - heat absorber 4 and thus improve the waste - heat recovery rate of the entire system.

[0050] In addition, the low - temperature coil 41, the medium - temperature coil 42, and the high - temperature coil 43 are all made of copper pipes, which can provide good heat - exchange effects. The waste - heat absorber 4 is provided with a temperature monitor 44 and a liquid - level monitor 45 for monitoring the water temperature and water level in the inner cavity of the waste - heat absorber 4.

[0051] A steam outlet is arranged at the top of the waste - heat absorber 4. After the water in the inner cavity of the waste - heat absorber 4 exchanges heat with the medium in the heat - exchange coil, waste - heat steam is formed and transported to the steam pipe network through the steam outlet.

[0052] Considering that the media entering the medium - temperature coil 42 and the high - temperature coil 43 are both air - water vapor mixtures, as the medium - temperature coil 42 and the high - temperature coil 43 exchange heat with the water in the waste - heat absorber 4, liquid water is inevitably separated out during the cooling process of the air - water vapor mixture, thus affecting the discharge.

[0053] Based on this, in order to simultaneously achieve full recovery of waste heat and recovery of this part of the liquid water, the system includes a waste heat spray tower 5 and a hot water pump 52. The outlet of the heat exchange coil of the waste heat absorber 4 is communicated with the inner cavity of the waste heat spray tower 5. A pure water spray head 51 is arranged at the top of the waste heat spray tower 5. The liquid suction side of the hot water pump 52 is communicated with the bottom of the waste heat spray tower 5. The liquid discharge side of the hot water pump 52 is communicated with the inner cavity of the waste heat absorber 4.

[0054] Thus, through the setting of the waste heat spray tower 5, after the medium in the heat exchange coil of the waste heat absorber 4 is heat-exchanged, it is sent into the waste heat spray tower 5. The medium contacts and exchanges heat with the spray water (at normal temperature state). A part of the waste heat and liquid water carried by the medium can be absorbed by the spray water and then fall into the bottom of the tower. Then, under the action of the hot water pump 52, it is sent into the inner cavity of the waste heat absorber 4. On the one hand, it realizes further recovery of the residual waste heat in the medium, which helps to improve the waste heat recovery rate. On the other hand, the liquid water carried by the medium can also enter the spray water, separating from the gaseous substances in the medium. While realizing the recovery and utilization of this part of the liquid water, it is also convenient to separately process and discharge the gaseous substances in the medium.

[0055] In addition, the settings of the waste heat spray tower 5 and the hot water pump 52 can also be regarded as the water supply component (or make-up water component) of the waste heat absorber 4 to ensure that there is enough water in the waste heat absorber 4. At the same time, the waste heat recovery function provided by the waste heat spray tower 5 also provides a preheating effect for the water inlet of the waste heat absorber 4.

[0056] Correspondingly, in this application, if the heat exchange between the medium provided by the medium supply part and the magnesium electrolytic cell 3 is regarded as the primary waste heat absorption process, then the heat exchange process in the waste heat absorber 4 can be regarded as the secondary waste heat recovery process, and the spraying process in the waste heat spray tower 5 can be regarded as the tertiary waste heat recovery process. Thus, through multi-stage waste heat recovery, this application can effectively improve the waste heat recovery rate.

[0057] The outlets of the low-temperature coil 41, the medium-temperature coil 42, and the high-temperature coil 43 are all communicated with the inner cavity of the waste heat spray tower 5 and are arranged in sequence in the vertical direction from bottom to top.

[0058] Thus, the relatively low-temperature spray water will first contact the medium delivered by the high-temperature coil 43. Due to the significant temperature difference between the two, the heat exchange efficiency is high, enabling the spray water to fully preheat and recover the medium delivered by the high-temperature coil 43. Subsequently, the spray water contacts the medium delivered by the medium-temperature coil 42. There is a certain temperature difference between the two, and there is a certain heat exchange efficiency, enabling the spray water to also recover a certain amount of waste heat from the medium delivered by the medium-temperature coil 42.

[0059] For the medium delivered from the outlet of the low-temperature coil 41, its temperature is relatively low. Instead of using the spraying method to exchange heat for the medium delivered from the outlet of the low-temperature coil 41, it is preferably to connect the outlet of the low-temperature coil 41 to the bottom of the waste heat spray tower 5, and the outlet of the low-temperature coil 41 is lower than the liquid level of the bottom of the waste heat spray tower 5, so as to ensure that the medium delivered from the outlet of the low-temperature coil 41 can fully contact the water in the bottom of the tower. Compared with the heat exchange by the spraying method, the contact area and contact time between the medium and water are increased, and the waste heat of the medium delivered from the outlet of the low-temperature coil 41 is recovered as much as possible.

[0060] The waste heat spray tower 5 is provided with an induced draft fan 53. The suction side of the induced draft fan 53 is communicated with the inner cavity of the waste heat spray tower 5. Thus, after the medium delivered by each heat exchange coil is preheated and recovered, the waste heat spray tower 5 can use the induced draft fan 53 to discharge the gaseous substances in the medium from the waste heat spray tower 5, so as to facilitate the subsequent process to separately treat and discharge the gaseous substances in the medium.

[0061] On the basis of the system, the present application further proposes a method for cascaded recovery of magnesium electrolysis waste heat based on wet heat exchange, including:

[0062] S1. Start the medium supply unit;

[0063] Specifically, start the chlorine hood fan 11, the heat exchanger fan 12, the tank shell fan 13, the first atomizing nozzle 21, and the second atomizing nozzle 22; among them, by adjusting the first atomizing nozzle 21 and the second atomizing nozzle 22, control the droplet content carried in each cubic meter of air entering the heat exchange sleeve 34 and the heat exchanger 32 to be greater than 200 g.

[0064] S2. Exchange heat for the heat exchange sleeve 34 and the heat exchanger 32 through the air mixed with water mist, and exchange heat for the outer lining 31 of the tank shell through normal temperature air;

[0065] Among them, for the heat exchange conditions in each area, they have been introduced above and will not be elaborated here.

[0066] S3. Send the medium after heat exchange in step S2 to the waste heat absorber 4 to exchange heat with the water in the inner cavity of the waste heat absorber 4 and produce waste heat steam.

[0067] Among them, by regulating the operating state of the waste heat absorber 4, steam with a pressure of 0.3 - 1.0 MPa can be produced.

[0068] Through multiple tests and verifications in the present application: the total waste heat recovery rate of the system is increased to 78.3% (the waste heat recovery system of the multi-stage magnesium electrolysis cell is 42.1%), the steam production thermal efficiency reaches 91.5%, the comprehensive energy consumption of the electrolysis process is reduced by 15.6 kWh / t (Mg), and the floor area of the equipment is reduced by 35%.

[0069] Meanwhile, a magnesium electrolysis waste heat cascade recovery system and method based on wet heat exchange proposed in this application, by setting atomizing nozzles to convey air mixed with water mist to the heat exchange sleeve 34 and the heat exchanger 32, constructs a wet air enhanced heat transfer system, and cooperates with a three-stage waste heat cascade recovery framework to achieve efficient recovery of electrolysis waste heat and co-production of multi-grade steam. The system can increase the comprehensive utilization rate of waste heat to more than 78%, and the thermal efficiency of steam output exceeds 90%, significantly reducing the comprehensive energy consumption of magnesium smelting.

[0070] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A waste heat cascade recovery system for a magnesium electrolysis cell based on wet heat exchange, characterized in that, The system includes a medium supply unit, a magnesium electrolysis cell (3), and a waste heat absorber (4). The outer shell of the magnesium electrolysis cell (3) is provided with an outer lining of the cell shell (31). A heat exchanger (32) is arranged in the cavity of the magnesium electrolysis cell (3). A heat exchange sleeve (34) is sleeved outside the chlorine hood (33) of the magnesium electrolysis cell (3). The medium supply unit is communicated with the medium inlet of the heat exchange sleeve (34) and the medium inlet of the heat exchanger (32), and conveys air mixed with water mist to the heat exchange sleeve (34) and the heat exchanger (32). The medium supply unit is communicated with the medium inlet of the outer lining of the cell shell (31) and conveys normal temperature air to the outer lining of the cell shell (31). The medium outlets of the heat exchange sleeve (34), the heat exchanger (32), and the outer lining of the cell shell (31) are all communicated with the heat exchange coil of the waste heat absorber (4).

2. The waste heat cascade recovery system for a magnesium electrolysis cell based on wet heat exchange according to claim 1, wherein The medium supply unit includes a chlorine hood fan (11), a heat exchanger fan (12), and a cell shell fan (13). The air outlet of the chlorine hood fan (11) is communicated with the medium inlet of the heat exchange sleeve (34), and a first atomizing nozzle (21) is arranged at the air outlet of the chlorine hood fan (11). The air outlet of the heat exchanger fan (12) is communicated with the medium inlet of the heat exchanger (32), and a second atomizing nozzle (22) is arranged at the air outlet of the heat exchanger fan (12). The air outlet of the cell shell fan (13) is communicated with the medium inlet of the outer lining of the cell shell (31).

3. A waste heat cascade recovery system for a magnesium electrolytic cell based on wet heat exchange according to claim 1, characterized in that The system includes a waste heat spray tower (5) and a hot water pump (52). The outlet of the heat exchange coil of the waste heat absorber (4) is communicated with the inner cavity of the waste heat spray tower (5). A pure water nozzle (51) is arranged at the top of the waste heat spray tower (5). The liquid suction side of the hot water pump (52) is communicated with the bottom of the waste heat spray tower (5), and the liquid discharge side of the hot water pump (52) is communicated with the inner cavity of the waste heat absorber (4).

4. A cascade heat recovery system for the waste heat of a magnesium electrolysis cell based on wet heat exchange according to claim 3, characterized in that, In the vertical direction from bottom to top, the inner cavity of the waste heat absorber (4) is successively divided into a low temperature zone (46), a medium temperature zone (47), and a high temperature zone (48). A low temperature coil (41) is arranged in the low temperature zone (46), a medium temperature coil (42) is arranged in the medium temperature zone (47), and a high temperature coil (43) is arranged in the high temperature zone (48). The low temperature coil (41), the medium temperature coil (42), and the high temperature coil (43) are independent heat exchange coil structures from each other.

5. A waste heat cascade recovery system for a magnesium electrolysis cell based on wet heat exchange according to claim 4, characterized in that, The medium outlet of the heat exchange sleeve (34) is communicated with the high temperature coil (43), the medium outlet of the heat exchanger (32) is communicated with the medium temperature coil (42), and the medium outlet of the outer lining of the cell shell (31) is communicated with the low temperature coil (41).

6. A waste heat cascade recovery system for a magnesium electrolysis cell based on wet heat exchange according to claim 4, characterized in that, The outlets of the low temperature coil (41), the medium temperature coil (42), and the high temperature coil (43) are all communicated with the inner cavity of the waste heat spray tower (5) and are arranged successively in the vertical direction from bottom to top.

7. A waste heat cascade recovery system for a magnesium electrolytic cell based on wet heat exchange according to claim 6, characterized in that, The outlet of the low temperature coil (41) is communicated with the bottom of the waste heat spray tower (5), and the outlet of the low temperature coil (41) is lower than the liquid level of the bottom of the waste heat spray tower (5).

8. A waste heat cascade recovery system for a magnesium electrolysis cell based on wet heat exchange according to claim 3, characterized in that The waste heat spray tower (5) is provided with an induced draft fan (53), and the air suction side of the induced draft fan (53) is communicated with the inner cavity of the waste heat spray tower (5).

9. The waste heat cascade recovery system for a magnesium electrolytic cell based on wet heat exchange according to claim 1, characterized in that, The waste heat absorber (4) is provided with a temperature monitor (44) and a liquid level monitor (45) for monitoring the water temperature and water level in the inner cavity of the waste heat absorber (4); a steam outlet is arranged at the top of the waste heat absorber (4).

10. A method for cascaded recovery of waste heat from magnesium electrolysis based on wet heat exchange, characterized in that, The method is used for a magnesium electrolytic cell waste heat cascade recovery system based on wet heat exchange according to any one of claims 1-9; the method comprises: S1. Start the medium supply part; S2. Exchange heat for the heat exchange sleeve (34) and the heat exchanger (32) through air mixed with water mist, and exchange heat for the outer lining of the cell shell (31) through normal temperature air; S3. Send the medium after heat exchange in step S2 to the waste heat absorber (4) to exchange heat with the water in the inner cavity of the waste heat absorber (4) and produce waste heat steam.

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