An electrochemical regulation and phase change temperature control synergistic corrosion prevention low-temperature waste heat utilization system

Abstract

The application discloses a low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control and cooperative corrosion prevention. The system comprises a waste heat recovery device and a heat exchange module arranged along the flow direction of flue gas in a tail flue. The heat exchange module comprises a heat exchanger A and a heat exchanger B. The heat exchanger A is internally provided with phase change medium, and is connected with the waste heat recovery device. The heat exchanger A and the heat exchanger B are communicated. The phase change medium in the heat exchanger A is used for condensing flue gas to form phase change medium steam, and flows back to the heat exchanger B. The heat exchanger B is used for condensing the phase change medium steam to form liquid phase change medium, and flows back to the heat exchanger A. The heat exchanger A is provided with an electrochemical corrosion prevention module. The application realizes heat exchange through the phase change medium, so that the temperature of the wall surface of the heat exchanger is higher than the dew point temperature, and low-temperature dew point corrosion is avoided. The electrochemical corrosion prevention module is arranged on the heat exchanger A, the potential information of a heat exchange element A in the heat exchanger A is regulated and controlled through the electrochemical corrosion prevention module, and the corrosion of the heat exchanger A is reduced.

Description

Technical Field

[0001] This invention belongs to the field of corrosion prevention and control technology for power plant boiler tail section, specifically involving a low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for corrosion prevention. Background Technology

[0002] With the continuous development of industrial production, energy demand continues to grow, while the requirements for environmental protection and sustainable development are becoming increasingly stringent. As an important component of traditional energy supply, the transformation of coal-fired power generating units into basic, guaranteed, and system-regulating power sources, as well as the implementation of deep peak shaving, are key steps in achieving my country's clean and green energy transition.

[0003] In power plant boilers, fuel combustion produces flue gas. Some of the sulfur in this flue gas, specifically sulfur dioxide, is further oxidized to SO3 within the furnace. SO3 then combines with water vapor in the flue gas to form sulfuric acid vapor. The dew point of sulfuric acid vapor is influenced by many factors, generally ranging from 90 to 120°C. If the temperature of the heated surface is lower than the dew point temperature of the sulfuric acid vapor, the sulfuric acid vapor will condense on the heat exchange surface, causing corrosion. However, since the waste heat from the low-temperature flue gas of coal-fired boilers is used to heat feedwater, the greatest risk to the heat exchanger is sulfuric acid dew point corrosion. To avoid dew point corrosion, the temperature of the economizer's heated surfaces must be kept above the dew point temperature. Based on this, the flue gas temperature of low-temperature economizers in coal-fired boilers is often controlled at 160–150℃. However, to recover more waste heat, heat exchangers that recover waste heat in the corrosion zone are required. Their operating parameters are: inlet flue gas temperature of 110–120℃, outlet flue gas temperature of 70–80℃; assumed acid dew point temperature of 90–100℃; and external water supply inlet temperature of 20–50℃. Since the tube wall temperature of the heat exchanger is between the water temperature and the flue gas temperature, under the above conditions, the wall temperature of most of the heated surfaces of the waste heat recovery heat exchanger will be lower than the dew point temperature. At this time, sulfuric acid vapor will condense into a sulfuric acid-containing liquid on the heated surfaces, causing low-temperature corrosion. Therefore, the heated surfaces are highly susceptible to dew point corrosion, which is difficult to control. Developing corrosion-resistant heat exchangers is costly and difficult, increasing the economic costs of power plant boiler operation.

[0004] In summary, existing methods for deep utilization of boiler flue gas waste heat cannot effectively solve the problems of dew point corrosion and the high cost and difficulty in developing corrosion-resistant heat exchangers. Therefore, this invention provides a low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for synergistic corrosion prevention. Summary of the Invention

[0005] To address the issues of dew point corrosion in existing boiler flue gas waste heat utilization processes and the high development costs and difficulties of developing corrosion-resistant heat exchangers, this invention aims to provide a low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for synergistic corrosion prevention. Using water as the phase change medium, the phase change medium in heat exchange element A of heat exchange tube A exchanges heat with the flue gas, condensing to form phase change medium vapor, which then flows back to heat exchanger B. Heat exchange element B31 in heat exchanger B condenses the phase change medium vapor into a liquid phase change medium, which also flows back to heat exchanger A, forming a recycling system. Through phase change medium heat exchange, the temperature of the heat exchanger wall is kept above the dew point temperature, preventing low-temperature dew point corrosion. An electrochemical corrosion prevention module is installed on heat exchanger A, which regulates the potential information of heat exchange element A within heat exchanger A to reduce corrosion.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0007] This invention provides a low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for corrosion prevention, including a waste heat recovery unit and a heat exchange module arranged along the flue gas flow direction of the tail flue.

[0008] The heat exchange module includes heat exchanger A and heat exchanger B. Heat exchanger A contains a phase change medium. The inlet of heat exchanger A is connected to the outlet of the waste heat recovery unit. Heat exchanger A and heat exchanger B are interconnected. The phase change medium in heat exchanger A is used to condense the flue gas into phase change medium vapor, which flows back to heat exchanger B. Heat exchanger B is used to condense the phase change medium vapor into liquid phase change medium, which flows back to heat exchanger A. A compressor is provided between the outlet of heat exchanger A and the inlet of heat exchanger B. The compressor is used to regulate the pressure of the phase change medium vapor. Through the heat exchange of the phase change medium in heat exchanger A and heat exchanger B, the inner wall temperature of heat exchanger A is made higher than the dew point temperature, reducing the corrosion of heat exchanger A.

[0009] The heat exchanger A is equipped with an electrochemical anti-corrosion module. The heat exchanger A (2) is equipped with a heat exchange element A. The potential information of the heat exchange element A is regulated by the electrochemical anti-corrosion module to reduce the corrosion of the heat exchanger A.

[0010] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for corrosion prevention, the heat exchange element A contains a phase change medium, the compressor is used to regulate the pressure of the phase change medium vapor in the heat exchange element A, a gas-liquid separator is provided above the heat exchange element A, the gas-liquid separator is connected to the outlet of the heat exchange element A, the outlet of the gas-liquid separator is connected to the compressor, and the gas-liquid separator includes multiple corrugated plates stacked sequentially along the vertical direction of the heat exchange element A.

[0011] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control with corrosion prevention, a liquid storage tank is provided below the heat exchanger A. The liquid storage tank is connected to the inlet of the heat exchange element A. An overflow port is provided on the side wall of the gas-liquid separator. The liquid storage tank is connected to the overflow port through a downcomer. A power transmission mechanism is provided on the downcomer.

[0012] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for synergistic corrosion prevention, the electrochemical corrosion prevention module includes an acid collection tank and an active metal. The acid collection tank is used to collect sulfuric acid and is located at the bottom of heat exchange element A, with the lower end of heat exchange element A in contact with sulfuric acid. The active metal is located inside the acid collection tank, and the active metal and heat exchange element A are connected by a wire. The active metal regulates the potential information of heat exchange element A to reduce corrosion of heat exchanger A.

[0013] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for corrosion prevention, the acid collection tank is equipped with an acid guide pipe, one end of which extends out of the outer wall of heat exchanger A and is connected to an acid collection tank.

[0014] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for corrosion prevention, the gas-liquid separator is equipped with a level detector, a temperature detector A, and a pressure detector. The level detector, temperature detector A, and power transmission mechanism are all signal-connected. The level detector is used to detect the liquid level in the gas-liquid separator and to regulate the liquid level and temperature of the gas-liquid separator. The pressure detector is signal-connected to the compressor and is used to detect the pressure inside the heat exchanger A and to regulate the pressure of the phase change medium vapor inside the heat exchanger A.

[0015] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control with corrosion prevention, a diversion pipe is provided between the inlet of the waste heat recovery unit and the inlet of heat exchanger A. Along the flow direction of heat exchanger A, a temperature detector B is provided in front of the connection end between heat exchanger A and the diversion pipe. The temperature detector B is used to detect the temperature of the flue gas at the inlet of heat exchanger A and to adjust the flue gas flow rate in the diversion pipe to control the temperature of the flue gas at the inlet of heat exchanger A.

[0016] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control with corrosion prevention, temperature detector A is also connected to a diversion pipe. Temperature detector A is used to detect the temperature inside the gas-liquid separator and adjust the flue gas flow rate in the diversion pipe to regulate the temperature of the gas-liquid separator.

[0017] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control with corrosion prevention, heat exchanger B is equipped with heat exchange element B. The inlet of heat exchange element B is connected to the external water supply inlet, and the outlet of heat exchange element B is connected to the waste heat recovery unit. After the external water supply condenses the phase change medium vapor, it is heated by the waste heat recovery unit and then returned to other heat exchange equipment. Heat exchanger B is connected to the liquid storage tank through a return pipe, and the inlet of heat exchanger B is connected to the outlet of the gas-liquid separator.

[0018] Furthermore, in the aforementioned low-temperature waste heat utilization system that combines electrochemical regulation with phase change temperature control for synergistic corrosion prevention, the phase change medium is water.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention uses water as the phase change medium. The phase change medium in heat exchange element A of heat exchange tube A exchanges heat with flue gas and condenses to form phase change medium vapor, raising the temperature of the liquid phase change medium from 50-70℃ to 70-80℃. This vapor then flows back to heat exchanger B. Heat exchange element B in heat exchanger B condenses the vapor, lowering its temperature from 70-120℃ to a liquid state of 50-70℃, forming a liquid phase change medium that also flows back to heat exchanger A, creating a recycling system. Through heat exchange with the phase change medium, the temperature of the heat exchanger wall is kept above the dew point temperature, preventing low-temperature dew point corrosion. An electrochemical anti-corrosion module is installed on heat exchanger A to regulate the potential information of heat exchange element A within heat exchanger A, reducing corrosion of heat exchanger A.

[0021] 2. This invention employs an electrochemical method, including a sacrificial material method. An electrochemical corrosion prevention is achieved by connecting an active metal and heat exchange element A through a wire to form a circuit. When the active metal is corroded, electrons are generated and transferred to the protected heat exchange element A, keeping the potential of heat exchange element A in a low corrosion rate potential region. This prevents the loss of electrons from the heat exchange element A, thus preventing corrosion of the heat exchange element A and improving the corrosion prevention effect.

[0022] 3. This invention uses water as the phase change medium and maintains the vacuum in the heat exchange tube to control the operating temperature of the phase change medium at around 110°C, so that the temperature of the heat exchanger wall is close to or higher than the dew point temperature, thus avoiding the occurrence of low-temperature dew point corrosion.

[0023] 4. This invention uses MVR technology to compress the phase change medium, which increases the temperature of the phase change medium and also improves the heat exchange efficiency between the phase change medium and the heat exchanger.

[0024] 5. The waste heat recovery device of this invention makes deep utilization of waste heat from flue gas, improves boiler efficiency, and deeply purifies flue gas through heat exchange tube A, making it possible to capture and reduce CO2. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the low-temperature waste heat utilization system of the present invention;

[0026] Explanation of reference numerals in the attached figures:

[0027] 1. Waste heat recovery unit; 2. Heat exchanger A; 21. Heat exchange element A; 3. Heat exchanger B; 31. Heat exchange element B; 4. Compressor; 5. Gas-liquid separator; 51. Corrugated plate; 6. Overflow port; 7. Liquid storage tank; 8. Downcomer; 81. Power transmission mechanism; 9. Acid collection tank; 91. Acid guide pipe; 10. Acid collection vessel; 11. Liquid level detector; 12. Temperature detector A; 13. Pressure detector; 14. Diverter pipe; 141. Temperature detector B; 15. External water supply equipment; 16. Air preheater; 17. Desulfurization tower; 18. Other heat exchange equipment. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] This invention addresses the problems of dew point corrosion and the high development cost and difficulty of developing corrosion-resistant heat exchangers in the deep utilization of waste heat from boiler flue gas. It provides a low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for synergistic corrosion prevention. The system includes a waste heat recovery unit 1 and a heat exchange module arranged along the flue gas flow direction at the tail end of the flue. The heat exchange module includes heat exchanger A2 and heat exchanger B3. Heat exchanger A2 contains a phase change medium. The inlet of heat exchanger A2 is connected to the outlet of waste heat recovery unit 1. Heat exchanger A2 and heat exchanger B3 are connected. The phase change medium in heat exchanger A2 is used to condense the flue gas to form phase change medium vapor, which then flows back to heat exchanger B3. B3 is used to condense the phase change medium vapor into a liquid phase change medium, which is then returned to heat exchanger A2. A compressor 4 is provided between the outlet of heat exchanger A2 and the inlet of heat exchanger B3. The compressor 4 is a mechanical vapor recompressor (MVR) used to regulate the pressure of the phase change medium vapor. Through heat exchange between the phase change medium in heat exchanger A2 and heat exchanger B3, the inner wall temperature of heat exchanger A2 is made higher than the dew point temperature, thus reducing the corrosion of heat exchanger A2. An electrochemical anti-corrosion module is provided on heat exchanger A2, and a heat exchange element A21 is provided inside heat exchanger A2. The potential information of heat exchange element A21 is controlled by the electrochemical anti-corrosion module to reduce the corrosion of heat exchanger A2.

[0031] In this invention, external water supply within heat exchange element B31 in heat exchanger B3 exchanges heat with phase change medium steam, causing the phase change medium steam to cool from 70-120℃ to a liquid state of 50-70℃. The liquid phase change medium then flows back into heat exchanger A2. Within heat exchange tube A, heat exchange element A21 exchanges heat with flue gas, causing the liquid phase change medium to heat up from 50-70℃ to 70-80℃, forming phase change medium steam, which then flows back into heat exchanger B3. This reduces the flue gas temperature from 100-120℃ to 60-90℃, creating a recycling system. Through phase change medium heat exchange, the temperature of the heat exchanger wall is kept above the dew point temperature, preventing low-temperature dew point corrosion. An electrochemical anti-corrosion module is installed on heat exchanger A2. Through electrochemical methods, including sacrificial material methods, the potential information of heat exchange element A21 within heat exchanger A2 is controlled, reducing corrosion of heat exchanger A2. After the liquid phase change medium in heat exchange element A21 inside heat exchange tube A exchanges heat with the flue gas, it forms phase change medium vapor. The vapor is compressed by compressor 4 (MVR) and then transported to heat exchange element A21 inside heat exchanger A2. The use of MVR technology to compress the phase change medium increases the temperature of the phase change medium and also improves the heat exchange efficiency between the phase change medium and the heat exchanger.

[0032] The following specific examples will provide further explanation.

[0033] A low-temperature waste heat utilization system combining electrochemical regulation and phase change temperature control for corrosion prevention includes a waste heat recovery unit 1 and a heat exchange module arranged along the flue gas flow direction at the tail end of the flue. The heat exchange module includes heat exchanger A2 and heat exchanger B3. Heat exchanger A2 contains a phase change medium. The inlet of heat exchanger A2 is connected to the outlet of the waste heat recovery unit 1. Heat exchanger A2 and heat exchanger B3 are connected. The phase change medium in heat exchanger A2 is used to condense the flue gas into phase change medium vapor, which then flows back to heat exchanger B3. Heat exchanger B3 is used to condense the phase change medium vapor... The vapor condenses to form a liquid phase change medium and flows back to heat exchanger A2. A compressor 4 is installed between the outlet of heat exchanger A2 and the inlet of heat exchanger B3. The compressor 4 is used to regulate the pressure of the phase change medium vapor. Through the heat exchange of the phase change medium in heat exchanger A2 and heat exchanger B3, the inner wall temperature of heat exchanger A2 is made higher than the dew point temperature, thus reducing the corrosion of heat exchanger A2. An electrochemical anti-corrosion module is installed on heat exchanger A2. The electrochemical anti-corrosion module regulates the potential information of heat exchange element A21 in heat exchanger A2 to reduce the corrosion of heat exchanger A2.

[0034] In one specific embodiment, the heat exchanger A2 includes a shell A and a heat exchange element A21. The heat exchange element A21 is disposed inside the shell A and contains a phase change medium. The compressor is used to regulate the pressure of the vapor of the phase change medium inside the heat exchange element A21. A gas-liquid separator 5 is disposed above the shell A and is connected to the outlet of the heat exchange element A21. The outlet of the gas-liquid separator 5 is connected to the compressor 4. The gas-liquid separator 5 includes a plurality of corrugated plates 51 stacked sequentially along the vertical direction of the heat exchange element A21. In this embodiment, there are five corrugated plates 51. In this invention, heat exchange element A21 is a heat exchange tube, and heat exchange elements B31 are arranged longitudinally. The gas-liquid separator 5 is used for gas-liquid separation of the phase change medium vapor and liquid phase change medium within heat exchange element A21. After gas-liquid separation by the gas-liquid separator 5, the compressor 4 (MVR) compresses the vapor and delivers it to heat exchange element A21 within heat exchanger A2, increasing the temperature of the phase change medium and improving the heat exchange efficiency between the phase change medium and the heat exchanger. The outlet of heat exchanger A2 is connected to a desulfurization tower 17, through which flue gas is discharged. In this embodiment, the heat exchange elements A21 can be arranged longitudinally.

[0035] In one specific embodiment, a liquid storage tank 7 is provided below the heat exchanger A2, and the liquid storage tank 7 is connected to the inlet of the heat exchange element A21. An overflow port 6 is provided on the side wall of the gas-liquid separator 5, and the liquid storage tank 7 is connected to the overflow port 6 via a downcomer 8. A power transmission mechanism 81 is provided on the downcomer 8. In this embodiment, the power transmission mechanism 81 is a pump. The overflow port 6 on the side wall of the gas-liquid separator 5 allows liquid to flow into the liquid storage tank 7 through the downcomer 8 when the liquid level is too high. When the liquid level is too high, forced circulation is achieved by the pump, or natural circulation occurs through the overflow port 6, allowing the liquid to flow into the liquid storage tank 7. This prevents the liquid level in the gas-liquid separator 5 from being too high, thus affecting the gas-liquid separation effect of the gas-liquid separator 5.

[0036] In one specific embodiment, the electrochemical corrosion prevention module includes an acid collection tank 9 and an active metal. The acid collection tank 9 is used to collect sulfuric acid and is located at the bottom of the heat exchange element A21, with the lower end of the heat exchange element A21 in contact with the sulfuric acid. The active metal is disposed inside the acid collection tank 9. The active metal and the heat exchange element A21 are connected by a wire. The active metal regulates the potential information of the heat exchange element A21 to reduce the corrosion of the heat exchanger A2. An acid guide pipe 91 is provided on the acid collection tank 9, and one end of the acid guide pipe 91 extends through the outer wall of the outer casing A and is connected to the acid collection tank 10. This invention employs an electrochemical method, including a sacrificial material method. An electrochemical corrosion protection circuit is formed by connecting an active metal and heat exchange element A21 via a wire. When the active metal is corroded, electrons are generated and transferred to the protected heat exchange element A21, placing its potential in a low corrosion rate region. This prevents electron loss from the heat exchange element A21, thus preventing corrosion and improving the corrosion protection effect. In this invention, the sacrificial material is not limited to this arrangement; it can also be placed on the external heating surface of the heat exchange element A21, or an external current can be applied.

[0037] In this invention, the acid collection tank 9 is equipped with an acid guide pipe 91. One end of the acid guide pipe 91 extends through the outer wall of the outer shell A and connects to the acid collection tank 10. The condensed sulfuric acid is collected into the acid collection tank 10 through the acid guide pipe 91. The bottom of the acid collection tank 9 is inclined to increase the fluidity of the sulfuric acid liquid formed after acid condensation in the heat exchange element, thereby improving the sulfuric acid collection capacity. In this invention, the heat exchange element A21, the acid collection tank 9, and the acid guide pipe 91 are made of corrosion-resistant materials, such as enamel or fluoroplastics. In this embodiment, the heat exchange element A21, the acid collection tank 9, and the acid guide pipe 91 are all made of enamel.

[0038] In one specific embodiment, the gas-liquid separator 5 is equipped with a level detector 11, a temperature detector A12, and a pressure detector 13. The level detector 11, the temperature detector A12, and the power transmission mechanism 81 are all signal-connected. The level detector 11 is used to detect the liquid level of the gas-liquid separator 5 and to adjust the liquid level and temperature of the gas-liquid separator 5. The pressure detector 13 is signal-connected to the compressor 4 and is used to detect the pressure inside the heat exchanger A2 and to adjust the pressure of the phase change medium vapor inside the heat exchanger A2. The level detector 11 detects the liquid level of the gas-saving liquid separator 5. When the liquid level is too high, on the one hand, it flows into the downcomer 8 through the overflow port 6 and then back into the storage tank 7. That is, the overflow port 6 naturally circulates down into the storage tank 7. The downcomer 8 is equipped with a solenoid valve V1, which is connected to the level detector 11. The level detector 11 can control the opening of the solenoid valve V1 to adjust the flow rate of the phase change medium liquid that flows naturally down through the overflow port 6. On the other hand, when the level detector 11 detects that the liquid level of the gas-saving liquid separator 5 is too high, the level detector 11 signals to control the power transmission mechanism 81, that is, to start the pump and open the solenoid valve V1. The pump forces the phase change medium liquid into the storage tank 7. Temperature sensor A12 is used to detect the temperature of gas-liquid separator 5. Solenoid valve V1 is connected to temperature sensor A12 via signal connection. Temperature sensor A12 controls the opening of solenoid valve V1, allowing the phase change medium liquid in overflow port 6 to circulate naturally or be forced to circulate by a pump, thereby regulating the temperature of gas-liquid separator 5. Pressure sensor 13 is connected to compressor 4 via signal connection. Pressure sensor 13 is used to detect the pressure inside heat exchanger A2 and regulate the pressure of phase change medium vapor inside heat exchanger A2, thereby controlling the vacuum level in heat exchanger A2.

[0039] In one specific embodiment, a diversion pipe 14 is provided between the inlet of the waste heat recovery unit 1 and the inlet of the heat exchanger A2. A temperature detector B141 is provided in front of the connection between the heat exchanger A2 and the diversion pipe 14 along the flow direction of the heat exchanger A2. The temperature detector B141 is used to detect the temperature of the flue gas at the inlet of the heat exchanger A2 and adjust the flue gas flow rate in the diversion pipe 14 to control the temperature of the flue gas at the inlet of the heat exchanger A2. A solenoid valve V2 is provided on the diversion pipe 14. The solenoid valve V2 is signal-connected to the temperature detector B141. By detecting the temperature of the flue gas at the inlet of the heat exchanger A2 through the temperature detector B141, the opening degree of the solenoid valve V2 is controlled, thereby adjusting the flue gas flow rate in the diversion pipe 14 to control the temperature of the flue gas at the inlet of the heat exchanger A2.

[0040] In one specific embodiment, temperature detector A12 is also connected to the diversion pipe 14. Temperature detector A12 is used to detect the temperature inside the gas-liquid separator 5 and adjust the flue gas flow rate in the diversion pipe 14 to regulate the temperature of the gas-liquid separator 5. Temperature detector A12 is also signal-connected to solenoid valve V2. Temperature detector A12 detects the temperature inside the gas-liquid separator 5 and can control the opening of solenoid valve V2, thereby adjusting the flue gas flow rate in the diversion pipe 14 to control the temperature of the flue gas at the inlet of heat exchanger A2, and thus controlling the gas-liquid separation temperature of the gas-liquid separator 5.

[0041] In one specific embodiment, the heat exchanger B3 includes a shell B and heat exchange elements B31. The inlet of the heat exchange element B31 is connected to an external water supply inlet, which is connected to an external water supply device 15. The outlet of the heat exchange element B31 is connected to a waste heat recovery unit 1. After the external water supply condenses the phase change medium vapor, it is heated by the waste heat recovery unit 1 and then flows back to other heat exchange devices 18. The outlet of the shell B is connected to the liquid storage tank 7 through a return pipe, and the inlet of the shell B is connected to the outlet of the gas-liquid separator 5. In this invention, the heat exchange element B31 is a heat exchange tube. The arrangement of the heat exchange elements B31 can be longitudinal, transverse, annular, staggered, or equally spaced, etc. In this embodiment, the heat exchange elements B31 are arranged in an annular arrangement. The inlet of the heat exchange element B31 is connected to the external water supply inlet, and the water in the external water supply inlet is external water, such as demineralized water from a boiler or heating water, etc. The purpose is to condense the phase change medium vapor in the heat exchanger B3, so no specific limitation is made. After the externally supplied water condenses the phase change medium steam, the outlet of heat exchange element B31 is connected to waste heat recovery unit 1. The flue gas in waste heat recovery unit 1 can further heat the externally supplied water in heat exchanger B3, raising its temperature from 70-90℃ to 100-120℃, and the flue gas temperature drops from 130-150℃ to 100-120℃. After being heated by waste heat recovery unit 1, the flue gas flows back to other heat exchange equipment 18, achieving deep waste heat utilization of the flue gas and improving boiler efficiency. The inlet of waste heat recovery unit 1 is also connected to air preheater 16. Air preheater 16 preheats the air entering the boiler to a certain temperature through internal heat sinks, which is used to improve the boiler's heat exchange performance, reduce energy consumption, and achieve deep waste heat utilization of the flue gas, thereby improving boiler efficiency.

[0042] In one specific embodiment, the phase change medium is water.

[0043] Working principle: When the flue gas from the boiler tail enters the air preheater 16, the air preheater 16 preheats the air entering the boiler to a certain temperature through its internal heat exchange fins, thereby improving the boiler's heat exchange performance. Then, the flue gas continues to flow into the waste heat recovery unit 1, further heating the external water supply in heat exchanger B3 from 70-90℃ to 100-120℃, while the flue gas temperature decreases from 130-150℃ to 100-120℃. Finally, the flue gas continues to flow into heat exchange tube A, where the liquid phase change medium in heat exchange element A21 exchanges heat with the flue gas. The heat causes the liquid phase change medium to heat up from 50-70℃ to 70-80℃, forming phase change medium vapor, which flows back into heat exchanger B3. The external water supply in heat exchange element B31 in heat exchanger B3 exchanges heat with the phase change medium vapor, causing the phase change medium vapor to cool down from 70-120℃ to a liquid state of 50-70℃. The liquid phase change medium then flows back into heat exchange element A21. Through the circulating heat exchange process of the phase change medium in heat exchangers B3 and A2, the temperature of the heat exchanger wall is higher than the dew point temperature, thus avoiding low-temperature dew point corrosion.

[0044] After the liquid phase change medium in heat exchange element A21 exchanges heat with the flue gas, the flue gas condenses, and the sulfuric acid vapor in the flue gas condenses to form a sulfuric acid solution. The sulfuric acid solution flows along the wall of heat exchange element A21 into acid collection tank 9. The bottom and lower end of heat exchange element A21 are in contact with sulfuric acid. An active metal is placed in acid collection tank 9. The active metal and heat exchange element A21 are connected by a wire. The potential information of heat exchange element A21 is controlled by the active metal to reduce the corrosion of heat exchanger A2. The sulfuric acid solution in acid collection tank 9 is collected into acid collection tank 10 through acid guide pipe 91 to realize acid recovery in the tail flue and reduce the corrosion of heat exchanger A2.

[0045] When the liquid phase change medium in heat exchange element A21 exchanges heat with the flue gas, phase change medium vapor is formed. The outlet of heat exchange element A21 is connected to gas-liquid separator 5, and the outlet of gas-liquid separator 5 is connected to compressor 4. Gas-liquid separator 5 is used for gas-liquid separation of phase change medium vapor and liquid phase change medium in heat exchange element A21. After the compressor 4 compresses the vapor, it is sent to heat exchange element A21 in heat exchanger A2. Pressure detector 13 is used to detect the pressure in heat exchanger A2 and adjust the pressure of phase change medium vapor in heat exchanger A2 to control the vacuum degree in heat exchanger A2. At the same time, temperature detector A12 is used to detect the temperature of gas-liquid separator 5. Solenoid valve V1 is connected to temperature detector A12. Temperature detector A12 controls the opening of solenoid valve V1 so that the phase change medium liquid in overflow port 6 can circulate naturally or be forced to circulate by a pump, thereby adjusting the temperature of gas-liquid separator 5 and the temperature of phase change medium. At the same time, it also improves the heat exchange efficiency between phase change medium and heat exchanger.

[0046] Furthermore, along the flow direction of heat exchanger A2, a temperature detector B141 is installed in front of the connection end between heat exchanger A2 and the diversion pipe 14. The temperature detector B141 is used to detect the temperature of the flue gas at the inlet of heat exchanger A2 and adjust the flue gas flow rate in the diversion pipe 14 to control the temperature of the flue gas at the inlet of heat exchanger A2. The gas-liquid separator 5 is equipped with a liquid level detector 11, which detects the liquid level of the gas-liquid separator 5. When the liquid level is too high, it flows into the downcomer 8 through the overflow port 6 and then back into the storage tank 7, that is, the overflow port 6 naturally... The liquid flows down into the intermediate storage tank 7. A solenoid valve V1 is installed on the downcomer pipe 8. The solenoid valve V1 is connected to the liquid level detector 11. The liquid level detector 11 can control the opening of the solenoid valve V1 to adjust the flow rate of the phase change medium liquid that flows down naturally through the overflow port 6. On the other hand, when the liquid level detector 11 detects that the liquid level of the gas-liquid separator 5 is too high, the liquid level detector 11 signals to control the power transmission mechanism 81, that is, to start the pump and open the solenoid valve V1. The phase change medium liquid is forced to flow into the intermediate storage tank 7 through the pump.

[0047] Finally, after the external water supply condenses the phase change medium steam, the outlet of heat exchange element B31 is connected to waste heat recovery unit 1. The flue gas in waste heat recovery unit 1 can further heat the external water supply in heat exchanger B3, raising its temperature from 70-90℃ to 100-120℃, and lowering the flue gas temperature from 130-150℃ to 100-120℃. After being heated by waste heat recovery unit 1, the flue gas is returned to other heat exchange equipment 18, thus achieving deep waste heat utilization of the flue gas and improving boiler efficiency.

[0048] It should be noted that the connection relationships of components not specifically mentioned in this invention are all assumed to be based on existing technology. Since they do not involve the inventive point and are commonly used in existing technology, the structural connection relationships are not described in detail.

[0049] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0050] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A low-temperature waste heat utilization system that combines electrochemical regulation and phase change temperature control for synergistic corrosion prevention, characterized in that, Includes a waste heat recovery unit (1) and a heat exchange module installed along the flue gas flow direction at the tail end of the flue. The heat exchange module includes heat exchanger A (2) and heat exchanger B (3). Heat exchanger A (2) contains a phase change medium. The inlet of heat exchanger A (2) is connected to the outlet of the waste heat recovery unit (1). Heat exchanger A (2) and heat exchanger B (3) are connected. The phase change medium in heat exchanger A (2) is used to condense the flue gas to form phase change medium steam, which flows back to heat exchanger B (3). Heat exchanger B (3) is used to condense the phase change medium steam to form liquid phase change medium, which flows back to heat exchanger A (2). A compressor (4) is provided between the outlet of heat exchanger A (2) and the inlet of heat exchanger B (3). The compressor (4) is used to adjust the pressure of the phase change medium steam. Through the heat exchange of the phase change medium in heat exchanger A (2) and heat exchanger B (3), the inner wall temperature of heat exchanger A (2) is higher than the dew point temperature, which reduces the corrosion of heat exchanger A (2). The heat exchanger A (2) is equipped with an electrochemical anti-corrosion module. The heat exchanger A (2) is equipped with a heat exchange element A (21). The potential information of the heat exchange element A (21) is adjusted by the electrochemical anti-corrosion module to reduce the corrosion of the heat exchanger A (2).

2. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 1, characterized in that, The heat exchange element A (21) contains a phase change medium. The compressor (4) is used to adjust the pressure of the phase change medium vapor in the heat exchange element A (21). A gas-liquid separator (5) is provided above the heat exchanger A (2). The gas-liquid separator (5) is connected to the outlet of the heat exchange element A (21). The outlet of the gas-liquid separator (5) is connected to the compressor (4). The gas-liquid separator (5) includes multiple corrugated plates (51) stacked sequentially along the vertical direction of the heat exchange element A (21).

3. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 2, characterized in that, The heat exchanger A (2) is provided with a liquid storage tank (7) below it. The liquid storage tank (7) is connected to the inlet of the heat exchange element A (21). The side wall of the gas-liquid separator (5) is provided with an overflow port (6). The liquid storage tank (7) is connected to the overflow port (6) through a downcomer (8). The downcomer (8) is provided with a power transmission mechanism (81).

4. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 1, characterized in that, The electrochemical corrosion prevention module includes an acid collection tank (9) for collecting sulfuric acid. The acid collection tank (9) is located at the bottom of the heat exchange element A (21) and the lower end of the heat exchange element A (21) is in contact with the sulfuric acid. An active metal is provided in the acid collection tank (9). The active metal and the heat exchange element A (21) are connected by a wire. The potential information of the heat exchange element A (21) is controlled by the active metal to reduce the corrosion of the heat exchanger A (2).

5. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 4, characterized in that, The acid collection tank (9) is provided with an acid guide pipe (91), and one end of the acid guide pipe (91) passes through the outer wall of the heat exchanger A (2) and is connected to the acid collection tank (10).

6. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 3, characterized in that, The gas-liquid separator (5) is equipped with a liquid level detector (11), a temperature detector A (12) and a pressure detector (13). The liquid level detector (11), the temperature detector A (12) and the power transmission mechanism (81) are all connected by signal. The liquid level detector (11) is used to detect the liquid level of the gas-liquid separator (5) and to adjust the liquid level and temperature of the gas-liquid separator (5). The pressure detector (13) is connected by signal to the compressor (4) and is used to detect the pressure inside the heat exchanger A (2) and to adjust the pressure of the phase change medium vapor inside the heat exchanger A (2).

7. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 6, characterized in that, A diversion pipe (14) is provided between the inlet of the waste heat recovery unit (1) and the inlet of the heat exchanger A (2). A temperature detector B (141) is provided in front of the connection end of the heat exchanger A (2) and the diversion pipe (14) along the flow direction of the heat exchanger A (2). The temperature detector B (141) is used to detect the temperature of the flue gas at the inlet of the heat exchanger A (2) and adjust the flue gas flow rate in the diversion pipe (14) to control the temperature of the flue gas at the inlet of the heat exchanger A (2).

8. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 7, characterized in that, Temperature detector A (12) is also connected to the diverter pipe (14). Temperature detector A (12) is used to detect the temperature inside the gas-liquid separator (5) and adjust the flue gas flow rate inside the diverter pipe (14) to adjust the temperature of the gas-liquid separator (5).

9. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 3, characterized in that, Heat exchanger B (3) is equipped with heat exchange element B (31). The inlet of heat exchange element B (31) is connected to the external water supply inlet. The outlet of heat exchange element B (31) is connected to waste heat recovery device (1). After the external water supply condenses the phase change medium vapor, it is heated by waste heat recovery device (1) and then flows back to other heat exchange equipment (18). Heat exchanger B (3) is connected to the liquid storage tank (7) through the return pipe. The inlet of heat exchanger B (3) is connected to the outlet of gas-liquid separator (5).

10. The low-temperature waste heat utilization system with electrochemical regulation and phase change temperature control for synergistic corrosion prevention according to claim 1, characterized in that, The phase change medium is water.

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