Boiler waste heat recovery device and recovery method thereof

Abstract

This invention relates to a boiler waste heat recovery device and method. The device includes a boiler, a heat exchanger, a heat pump, and a condensate treatment unit. The boiler is connected to the heat exchanger, which is configured to absorb flue gas from the boiler and generate condensate. The heat exchanger is connected to the condensate treatment unit, which is configured to treat the condensate and supply the treated condensate to the boiler. The water outlet of the heat exchanger is connected to the water inlet of the heat pump, and the water inlet of the heat exchanger is connected to the water outlet of the heat pump, forming a first circulation loop. The heat pump is configured to provide energy to the boiler based on the heat absorbed by the first circulation loop. This invention also provides a recovery method for this device, achieving a significant reduction in flue gas temperature, an improvement in heat pump operating efficiency, and the resource utilization of condensate.

Description

Technical Field

[0001] This invention relates to the field of boiler waste heat recovery technology, and in particular to a boiler waste heat recovery device and recovery method. Background Technology

[0002] Currently, the flue gas temperature of gas-fired boilers is generally between 90 and 110 degrees Celsius. The flue gas contains a large amount of water vapor, whose latent heat of vaporization accounts for 5% to 10% of the fuel's calorific value. Conventional metal economizers can only reduce the flue gas temperature to 70 to 90 degrees Celsius, and cannot recover the latent heat of condensation of water vapor, resulting in a large waste of waste heat. When the flue gas temperature drops below the dew point, the acidic gases in the flue gas will condense and severely corrode carbon steel or stainless steel heat exchangers. Therefore, traditional equipment does not dare to achieve deep cooling. Some technologies use compression heat pumps to recover waste heat from the flue gas, but ordinary heat exchange materials have poor thermal conductivity and are not corrosion resistant, resulting in low evaporation temperatures of the heat pumps and difficulty in improving their coefficient of performance.

[0003] In existing technologies, waste heat recovery systems of coupled heat pumps mostly adopt simple flue gas-water heat exchange, without forming an intermediate circulation loop with temperature matching. The heat transfer efficiency between the heat pump and the boiler is not high, and the flue gas condensate is usually acidic. Direct discharge pollutes the environment and wastes water resources. It is impossible to ensure the efficient operation of the heat pump and the resource utilization of condensate while achieving deep cooling of flue gas. Summary of the Invention

[0004] To address the shortcomings of existing production technologies, this applicant provides a boiler waste heat recovery device and method. The aim is to solve the problems of low evaporation temperature of boiler flue gas heat pumps leading to decreased coefficient of performance and direct discharge of flue gas condensate causing water waste. By setting up a heat exchanger to absorb heat from boiler flue gas and generate condensate, and connecting the water channel of the heat exchanger to the heat pump to form a circulation loop, the heat pump extracts heat from this loop and provides energy to the boiler. Simultaneously, the condensate generated by the heat exchanger is sent to a condensate treatment unit for processing and then returned to the boiler. This achieves a significant reduction in flue gas temperature, an improvement in heat pump operating efficiency, and the resource utilization of condensate.

[0005] The technical solution adopted in this invention is as follows: A boiler waste heat recovery device includes a boiler, a heat exchanger, a heat pump, and a condensate treatment unit; The boiler is connected to the heat exchanger, which is configured to absorb the flue gas from the boiler and generate condensate. The heat exchanger is connected to the condensate treatment unit, which is configured to treat the condensate and supply the treated condensate to the boiler. The water channel outlet of the heat exchanger is connected to the water channel inlet of the heat pump, and the water channel inlet of the heat exchanger is connected to the water channel outlet of the heat pump to form a first circulation loop. The heat pump is configured to provide energy to the boiler based on the heat absorbed by the first circulation loop.

[0006] Its further technical solution lies in: The heat exchanger is a graphene plate-fin flue gas heat exchanger, which includes a graphene core made of stacked plates and fins.

[0007] The boiler's water channel inlet is connected to the heat pump's water channel outlet, and the boiler's water channel outlet is connected to the heat pump's water channel inlet to form a second circulation loop. The heat pump is configured to provide energy to the boiler through the second circulation loop.

[0008] The heat pump includes a carbon dioxide heat pump zone, which uses carbon dioxide as a refrigerant and delivers the boosted heat to the boiler through the second circulation loop.

[0009] The carbon dioxide heat pump zone also includes an evaporator, an electronic expansion valve, and a regenerator. The water channel inlet of the evaporator is connected to the water channel outlet of the heat exchanger, and the water channel outlet of the evaporator is connected to the water channel inlet of the heat exchanger to form the first circulation loop. The evaporator is connected to the regenerator, and the regenerator is connected to the evaporator through the electronic expansion valve. The evaporator is configured to absorb heat from the first circulation loop, the electronic expansion valve is configured to depressurize the carbon dioxide, and the regenerator is configured to exchange heat between the carbon dioxide flowing out of the evaporator and the carbon dioxide flowing in from the electronic expansion valve.

[0010] The carbon dioxide heat pump zone includes a gas cooler, a compressor, and a regenerator. The regenerator is connected to the gas cooler through the compressor. The water channel outlet of the gas cooler is connected to the water channel inlet of the boiler, and the water channel outlet of the boiler is connected to the water channel inlet of the gas cooler to form the second circulation loop. The gas cooler is configured to release the heat of carbon dioxide to water in the second circulation loop, the compressor is configured to pressurize the carbon dioxide, and the regenerator is configured to preheat the carbon dioxide before it enters the compressor.

[0011] The condensate treatment unit includes a condensate collection tank, and the condensate outlet of the heat exchanger is connected to the inlet of the condensate collection tank.

[0012] The condensate treatment unit also includes a steam trap, the outlet of which is connected to the inlet of the steam trap, and the steam trap is configured to allow condensate to pass through while preventing flue gas leakage.

[0013] The condensate treatment unit also includes a neutralization tank, the outlet of which is connected to the inlet of the neutralization tank, and the neutralization tank is configured to neutralize the acidity of the condensate.

[0014] A method for recovering waste heat from a boiler includes the following operational steps: The high-temperature flue gas discharged from the boiler enters the flue gas passage of the heat exchanger. The flue gas exchanges heat with the circulating water in the water passage of the heat exchanger. The flue gas temperature drops below the dew point, and the water vapor in the flue gas condenses into condensate and flows out of the heat exchanger. The circulating water in the heat exchanger absorbs heat from the flue gas and its temperature rises. It flows out from the outlet of the heat exchanger's water channel and enters the inlet of the heat pump's water channel. The circulating water releases heat in the heat pump and its temperature drops. It then returns from the outlet of the heat pump's water channel to the inlet of the heat exchanger's water channel, forming the first circulation loop. The heat pump uses refrigerant circulation to raise the absorbed low-grade heat to a high-grade level, and then transfers the heat to the boiler through a second circulation loop for preheating boiler feedwater or heating return water. The condensate generated by the heat exchanger flows from the condensate outlet into the condensate treatment unit, where it is treated to become neutral clean water, and then sent back to the boiler for recycling.

[0015] The beneficial effects of this invention are as follows: (1) This invention uses a heat exchanger to absorb heat from boiler flue gas and generate condensate. The water channel of the heat exchanger is connected to a heat pump to form a first circulation loop. The heat pump extracts heat from this loop and provides energy to the boiler. At the same time, the condensate generated by the heat exchanger is sent to a condensate treatment unit for treatment and then returned to the boiler. Through the setting of the first circulation loop, the circulating water temperature at the outlet of the heat exchanger water channel is relatively high, which significantly increases the evaporation temperature of the heat pump, thereby improving the coefficient of performance of the heat pump, reducing the energy consumption of the heat pump, and realizing a significant reduction in flue gas temperature, an improvement in heat pump operating efficiency, and the resource utilization of condensate.

[0016] (2) This invention uses a graphene plate-fin flue gas heat exchanger as the heat exchanger, and its graphene core is formed by stacking plates and fins. Graphene material has the characteristics of high in-plane thermal conductivity, stable chemical properties, and the ability to be modified with hydrophobic coatings. Its excellent thermal conductivity reduces the volume required for the heat exchanger, while its acid resistance solves the problem of low-temperature flue gas corrosion, and the hydrophobic surface avoids water film thermal resistance, thereby achieving deep cooling of flue gas in a limited space, providing a higher temperature heat source for the heat pump, and further improving the overall system energy efficiency.

[0017] (3) The present invention connects the heat pump directly to the boiler through the second circulation loop. The heat pump directly returns the recovered flue gas waste heat to the boiler in the form of high-temperature hot water, replacing part of the gas heating and significantly reducing the boiler's fuel consumption. At the same time, since the second circulation loop is compatible with the original boiler system, waste heat recovery can be achieved without modifying the internal structure of the boiler, reducing the modification cost and implementation difficulty.

[0018] (4) The present invention uses a carbon dioxide heat pump zone, with carbon dioxide as the refrigerant. The carbon dioxide heat pump can produce hot water at 65 to 100 degrees Celsius, which is much higher than that of conventional working fluid heat pumps. At the same time, it has a large cooling capacity per unit volume and low flow resistance, and can operate stably even in low-temperature environments in winter. It solves the problems of insufficient heating temperature and low-temperature attenuation of traditional heat pumps, and improves the overall energy efficiency of the waste heat recovery system.

[0019] (5) This invention incorporates a regenerator in the carbon dioxide heat pump zone, which raises the temperature of the carbon dioxide entering the compressor, avoiding the risk of liquid carryover during compressor intake. Simultaneously, it increases the subcooling of the carbon dioxide entering the electronic expansion valve, resulting in more low-temperature liquid after throttling, thus improving the heat absorption capacity of the evaporator. Consequently, both the heating capacity and coefficient of performance of the heat pump are enhanced. The electronic expansion valve can adjust its opening in real time according to operating conditions, precisely controlling the optimal exhaust pressure, ensuring the heat pump always operates at its highest efficiency point.

[0020] (6) The present invention preheats the compressor intake gas through a regenerator, so that the carbon dioxide has a higher exhaust temperature when it enters the gas cooler, thereby heating the water in the second circulation loop to a higher temperature, meeting the needs of boiler feed water preheating and heating return water heating, and expanding the application scope of the waste heat recovery system.

[0021] (7) The present invention includes a condensate treatment unit comprising a condensate collection tank, a steam trap, a neutralization tank, and a filter. The condensate collection tank converts the water vapor originally emitted with the flue gas into liquid water and collects it, thus avoiding water waste. The steam trap enables automatic discharge of condensate and reliable sealing of the flue gas, preventing the leakage of acidic gases and harmful components in the flue gas, ensuring the safe operation of the condensate treatment unit, and avoiding pressure fluctuations and thermal efficiency reduction in the heat exchanger caused by flue gas leakage. The neutralization tank treats the strongly acidic condensate into neutral water, enabling it to be safely returned to the boiler or directly discharged, avoiding corrosion damage to boiler pipes and the environment caused by acidic water. The filter effectively removes solid impurities from the condensate, ensuring the cleanliness of the water returned to the boiler, preventing particulate matter from depositing and scaling inside the boiler, and extending the service life of the boiler and pipes.

[0022] (8) This invention integrates deep recovery of flue gas waste heat, improvement of heat quality and resource utilization of condensate into one closed-loop system, which comprehensively solves multiple technical problems such as waste of boiler flue gas waste heat, low temperature corrosion, low efficiency of heat pump and water consumption, and has significant energy saving, water saving, environmental protection and economic benefits. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the boiler waste heat recovery device provided in an embodiment of the present invention.

[0024] Figure 2 A schematic diagram of the flow channel structure of the graphene core provided in an embodiment of the present invention.

[0025] Figure 3 This is a schematic diagram of the structure of a carbon dioxide heat pump zone provided in an embodiment of the present invention.

[0026] Figure 4 This is a schematic diagram of the structure of the condensate treatment unit provided in an embodiment of the present invention.

[0027] The components include: 1. Boiler; 2. Heat exchanger; 3. Heat pump; 4. Condensate treatment unit. 31. Gas cooler; 32. Compressor; 33. Regenerator; 34. Electronic expansion valve; 35. Evaporator; 41. Condensate collection tank; 42. Steam trap; 43. Neutralization tank; 44. Filter. Detailed Implementation

[0028] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0029] like Figures 1-4 As shown in the figure, the boiler waste heat recovery device provided in this embodiment has the following specific structure and function: The system mainly includes a boiler 1, a heat exchanger 2, a heat pump 3, and a condensate treatment unit 4. The boiler 1 is connected to the heat exchanger 2, which is configured to absorb flue gas from the boiler 1 and generate condensate. The heat exchanger 2 is connected to the condensate treatment unit 4, which is configured to treat the condensate and supply the treated condensate to the boiler 1. The water outlet of the heat exchanger 2 is connected to the water inlet of the heat pump 3, and the water inlet of the heat exchanger 2 is connected to the water outlet of the heat pump 3, forming a first circulation loop. The heat pump 3 is configured to provide energy to the boiler 1 based on the heat absorbed by the first circulation loop.

[0030] Boiler 1 can be a gas-fired boiler or an oil-fired boiler, with its exhaust gas temperature typically above 90 degrees Celsius. Heat exchanger 2 can be a plate-fin heat exchanger with flue gas and water channels. The flue gas channel receives the high-temperature flue gas discharged from boiler 1, while the water channel circulates circulating water. The flue gas and water exchange heat through the walls of heat exchanger 2. Heat pump 3 can be a vapor compression heat pump, internally filled with refrigerant, and has an evaporator side and a condenser side. The evaporator side absorbs lower-grade heat, and the condenser side releases higher-grade heat. Condensate treatment unit 4 can be a combined device with collection, neutralization, and filtration functions, used to treat the acidic condensate generated during flue gas condensation into neutral clean water. The specific implementation of each component can be selected according to actual operating conditions, but all must meet the connection relationships and functional configurations outlined in this solution.

[0031] The high-temperature flue gas discharged from boiler 1 enters the flue gas passage of heat exchanger 2. During its flow, the flue gas transfers heat to the circulating water in the water passage, causing its own temperature to drop below the dew point. The water vapor in the flue gas condenses into condensate and flows out of heat exchanger 2. The circulating water in the water passage absorbs heat from the flue gas, its temperature rises, and it flows out from the water passage outlet of heat exchanger 2. It then enters the evaporator-side water passage inlet of heat pump 3 through a pipe. In the evaporator, the circulating water releases heat to the refrigerant of heat pump 3. After its own temperature drops, it flows out from the evaporator-side water passage outlet of heat pump 3 and returns to the water passage inlet of heat exchanger 2, forming the first circulation loop.

[0032] Heat pump 3 uses refrigerant circulation to raise the low-grade heat absorbed on the evaporator side to a high-temperature and high-pressure state, and releases the high-grade heat on the condenser side. This heat is then transferred to boiler 1 through the second circulation loop for preheating boiler 1's makeup water or heating return water.

[0033] The condensate generated on the flue gas side of heat exchanger 2 flows out from its condensate outlet and enters the condensate treatment unit 4. After treatment, it becomes neutral clean water and is then sent back to boiler 1 through the water inlet, realizing the recycling of condensate.

[0034] The beneficial effects of this embodiment are as follows: First, by reducing the flue gas temperature below the dew point through heat exchanger 2, the sensible heat and latent heat of vaporization of water vapor in the flue gas are effectively recovered, significantly reducing the heat loss of boiler 1. Second, because heat exchanger 2 cools the flue gas to a lower temperature, the circulating water temperature at its water channel outlet is higher, which significantly increases the evaporation temperature of heat pump 3, thereby improving the coefficient of performance of heat pump 3 and reducing its energy consumption. Third, the condensate generated during the flue gas condensation process is treated by condensate treatment unit 4 and then returned to boiler 1, saving water resources and avoiding the pollution caused by the direct discharge of acidic condensate. Finally, this device organically integrates heat exchanger 2, heat pump 3, and condensate treatment unit 4, forming a closed-loop system for deep recovery of flue gas waste heat, improvement of heat quality, and resource utilization of condensate. It comprehensively solves multiple technical problems such as waste of flue gas waste heat of boiler 1, low-temperature corrosion, low efficiency of heat pump 3, and water consumption, and has energy-saving, water-saving, environmental protection, and economic benefits.

[0035] like Figure 2 As shown, in some embodiments, the heat exchanger 2 includes a graphene plate-fin flue gas heat exchanger, which includes a graphene core formed by stacked plates and fins.

[0036] The graphene plate-fin flue gas heat exchanger is a plate-fin heat exchanger with graphene composite material as the main heat transfer element. Its core is composed of multiple layers of graphene plate fins stacked alternately, and flue gas channels and water channels are formed between adjacent plate fins. Graphene material has the characteristics of high in-plane thermal conductivity, stable chemical properties, and surface that can be modified with hydrophobic coatings.

[0037] The high-temperature flue gas discharged from boiler 1 enters the flue gas channel of the graphene core. The circulating water flows in the opposite direction in the adjacent water channel. The graphene plate fins quickly transfer the heat from the flue gas side to the water side. Since the thermal conductivity of graphene is far superior to that of conventional metals, the flue gas temperature can be quickly reduced to below the dew point. Water vapor condenses into water droplets on the fin surface and slides down the hydrophobic surface to the water collection tank, thereby achieving efficient sensible heat and latent heat recovery.

[0038] The beneficial effects of the embodiments of this application are that the excellent thermal conductivity of the graphene core reduces the required volume of the heat exchanger 2, while its acid resistance solves the problem of low-temperature flue gas corrosion, and the hydrophobic surface avoids water film thermal resistance, thereby achieving deep cooling of flue gas in a limited space, providing a higher temperature heat source for the heat pump 3, and further improving the overall system energy efficiency.

[0039] In some embodiments, the water channel inlet of boiler 1 is connected to the water channel outlet of heat pump 3, and the water channel outlet of boiler 1 is connected to the water channel inlet of heat pump 3 to form a second circulation loop, wherein heat pump 3 is configured to provide energy to boiler 1 through the second circulation loop.

[0040] The second circulation loop refers to a closed loop formed by connecting the water channel of boiler 1 and the water channel of heat pump 3 through a pipe. The inlet of the water channel of boiler 1 is connected to the outlet of the water channel of heat pump 3, and the outlet of the water channel of boiler 1 is connected to the inlet of the water channel of heat pump 3. Heat pump 3 can be a carbon dioxide transcritical heat pump 3, and its condenser side water channel is used to heat the circulating water flowing through boiler 1.

[0041] The return water or makeup water of boiler 1 flows out from the water channel outlet of boiler 1 and enters the water channel inlet of heat pump 3. In the condenser of heat pump 3, it is heated by high temperature and high pressure carbon dioxide refrigerant. After the temperature rises, it flows back from the water channel outlet of heat pump 3 to the water channel inlet of boiler 1, thus completing the heating process of the second circulation loop. Heat pump 3 continuously transfers the low-grade waste heat absorbed in the first circulation loop to the water in the second circulation loop through refrigerant circulation.

[0042] The beneficial effects of the implementation method of this application are that the heat pump 3 directly sends the recovered flue gas waste heat back to the boiler 1 in the form of high-temperature hot water, replacing part of the gas heating, which significantly reduces the fuel consumption of the boiler 1. At the same time, since the second circulation loop is compatible with the original boiler system, the waste heat can be reused without modifying the internal structure of the boiler 1.

[0043] like Figure 3 As shown, in some embodiments, the heat pump 3 includes a carbon dioxide heat pump zone, which uses carbon dioxide as a refrigerant and delivers the enhanced heat to the boiler 1 through a second circulation loop.

[0044] The circulating water in the first circulation loop carries the waste heat from the flue gas into the evaporator 35 of the carbon dioxide heat pump zone. The heat is absorbed by the low-temperature, low-pressure carbon dioxide, causing it to evaporate. The compressor 32 compresses the carbon dioxide to a supercritical state, causing its temperature and pressure to rise significantly. The high-temperature supercritical carbon dioxide releases high-grade heat in the gas cooler 31 to the water in the second circulation loop, thereby upgrading the low-grade waste heat into high-grade heat energy and delivering it to the boiler 1.

[0045] The beneficial effects of the embodiments of this application are that the carbon dioxide heat pump 3 can produce hot water at 65 to 100 degrees Celsius, which is much higher than that of conventional working fluid heat pump 3. At the same time, it has a large cooling capacity per unit volume and low flow resistance, and can operate stably even in low temperature environments in winter. It solves the problems of insufficient heating temperature and low temperature decay of traditional heat pump 3, and improves the overall energy efficiency of the waste heat recovery system.

[0046] In some embodiments, the carbon dioxide heat pump zone further includes an evaporator 35, an electronic expansion valve 34, and a regenerator 33. The water inlet of the evaporator 35 is connected to the water outlet of the heat exchanger 2, and the water outlet of the evaporator 35 is connected to the water inlet of the heat exchanger 2 to form a first circulation loop. The evaporator 35 is connected to the regenerator 33, and the regenerator 33 is connected to the evaporator 35 via the electronic expansion valve 34. The evaporator 35 is configured to absorb heat from the first circulation loop, the electronic expansion valve 34 is configured to depressurize the carbon dioxide, and the regenerator 33 is configured to exchange heat between the carbon dioxide flowing out of the evaporator 35 and the carbon dioxide flowing in from the electronic expansion valve 34.

[0047] Evaporator 35 can be a shell-and-tube or tubular heat exchanger 2, with its water-side channel connected to the first circulation loop and its refrigerant-side channel for carbon dioxide to flow through. Electronic expansion valve 34 can be a stepper motor-driven throttling device, with its inlet connected to the high-pressure side outlet of regenerator 33 and its outlet connected to the refrigerant inlet of evaporator 35. Regenerator 33 can be a shell-and-tube internal heat exchanger 2, with its high-pressure side channel connected between gas cooler 31 and electronic expansion valve 34, and its low-pressure side channel connected between evaporator 35 and compressor 32, thereby achieving heat exchange between high-pressure side carbon dioxide and low-pressure side carbon dioxide.

[0048] In the first circulation loop, the circulating water flows out of the graphene heat exchanger 2 and enters the water-side channel of the evaporator 35. In the evaporator 35, the circulating water releases heat to the low-temperature, low-pressure liquid carbon dioxide. The carbon dioxide absorbs heat and evaporates into gas. The circulating water, after its own temperature decreases, returns to the graphene heat exchanger 2 to absorb heat again. The low-temperature carbon dioxide gas flowing out of the evaporator 35 enters the low-pressure side of the regenerator 33, absorbs heat from the high-pressure side carbon dioxide, and after its temperature rises, enters the compressor 32. The high-pressure carbon dioxide flowing out of the gas cooler 31 first enters the high-pressure side of the regenerator 33, releases heat to the low-pressure side carbon dioxide, and then cools itself further. It then passes through the electronic expansion valve 34 for throttling and pressure reduction, becoming a low-temperature, low-pressure two-phase mixture, and finally enters the evaporator 35 to complete the cycle. The electronic expansion valve 34 controls the carbon dioxide flow rate and evaporation pressure by adjusting its opening, while the regenerator 33 ensures that the high-pressure side carbon dioxide is subcooled and the low-pressure side carbon dioxide is superheated.

[0049] The beneficial effects of this embodiment are that the regenerator 33 increases the temperature of the carbon dioxide entering the compressor 32, avoiding the risk of liquid carryover during compressor 32 intake. Simultaneously, it increases the subcooling of the carbon dioxide entering the electronic expansion valve 34, resulting in more cryogenic liquid after throttling, thus improving the heat absorption capacity of the evaporator 35. This, in turn, enhances both the heating capacity and coefficient of performance of the heat pump 3. The electronic expansion valve 34 can adjust its opening in real time according to operating conditions, precisely controlling the optimal discharge pressure, ensuring that the heat pump 3 always operates at its highest efficiency point.

[0050] In some embodiments, the carbon dioxide heat pump zone includes a gas cooler 31, a compressor 32, and a regenerator 33. The regenerator 33 is connected to the gas cooler 31 via the compressor 32. The water outlet of the gas cooler 31 is connected to the water inlet of the boiler 1, and the water outlet of the boiler 1 is connected to the water inlet of the gas cooler 31 to form a second circulation loop. The gas cooler 31 is configured to release the heat of the carbon dioxide to the water in the second circulation loop, the compressor 32 is configured to pressurize the carbon dioxide, and the regenerator 33 is configured to preheat the carbon dioxide before it enters the compressor 32.

[0051] The gas cooler 31 can be a shell-and-tube or tubular heat exchanger 2, with its refrigerant-side inlet connected to the exhaust port of the compressor 32, its refrigerant-side outlet connected to the high-pressure-side inlet of the regenerator 33, and its water-side passage connected to the second circulation loop. The compressor 32 can be a semi-hermetic reciprocating or scroll-type carbon dioxide compressor 32, with its suction port connected to the low-pressure-side outlet of the regenerator 33, and its exhaust port connected to the refrigerant inlet of the gas cooler 31. The regenerator 33 can be a shell-and-tube internal heat exchanger 2, with its high-pressure side connected between the gas cooler 31 and the electronic expansion valve 34, and its low-pressure side connected between the evaporator 35 and the compressor 32. In this embodiment, the regenerator 33 is configured to preheat the carbon dioxide before it enters the compressor 32. That is, the low-temperature, low-pressure gas flowing out of the evaporator 35 first flows through the low-pressure side of the regenerator 33, absorbs heat from the high-pressure side carbon dioxide, and its temperature rises before entering the suction port of the compressor 32.

[0052] In the second circulation loop, return water or makeup water from boiler 1 flows out of the water channel outlet of boiler 1 and enters the water-side inlet of gas cooler 31. In gas cooler 31, it undergoes counter-current heat exchange with high-temperature, high-pressure supercritical carbon dioxide, absorbing the heat released by the carbon dioxide and increasing in temperature. It then flows back from the water-side outlet of gas cooler 31 to the water channel inlet of boiler 1, completing the heating of the water in boiler 1. In the carbon dioxide heat pump zone, compressor 32 draws in medium-temperature, low-pressure carbon dioxide gas from the low-pressure side of regenerator 33. Through compression, it raises the pressure to eight to twelve MPa and the temperature to eighty to one hundred and twenty degrees Celsius, forming a supercritical state before being discharged into gas cooler 31. In gas cooler 31, the high-temperature supercritical carbon dioxide releases heat to the water in the second circulation loop, its own temperature decreases but it remains in a supercritical state, and then it enters the high-pressure side of regenerator 33 for further heat release. Carbon dioxide flowing from the high-pressure side of the regenerator 33 is throttled by the electronic expansion valve 34 and then enters the evaporator 35 to absorb heat. The cooled, low-pressure carbon dioxide gas then enters the low-pressure side of the regenerator 33 to absorb the residual heat from the high-pressure side carbon dioxide. After preheating, it returns to the suction port of the compressor 32, forming an internal circulation within the heat pump 3. The preheating effect of the regenerator 33 raises the suction temperature of the compressor 32, avoiding wet compression, and also increases the discharge temperature, which is beneficial for the gas cooler 31 to produce hot water at a higher temperature.

[0053] The beneficial effect of this application's implementation is that the preheating of the compressor 32's intake air by the regenerator 33 allows the carbon dioxide to have a higher exhaust temperature when it enters the gas cooler 31, thereby heating the water in the second circulation loop to 65 to 100 degrees Celsius, meeting the needs of boiler 1's water preheating and heating return water.

[0054] In some embodiments, the condensate treatment unit 4 includes a condensate collection tank 41, and the condensate outlet of the heat exchanger 2 is connected to the inlet of the condensate collection tank 41.

[0055] The condensate collection tank 41 can be a stainless steel tank, which is installed directly below the graphene plate-fin flue gas heat exchanger. The upper opening is sealed to the condensate outlet of the heat exchanger 2, and the bottom is provided with a drain outlet to collect the condensate that is released during the flue gas cooling process.

[0056] The high-temperature flue gas discharged from boiler 1 is cooled to below the dew point in graphene heat exchanger 2. Water vapor in the flue gas condenses into water droplets on the surface of graphene plates and fins. The water droplets slide down the hydrophobic coating to the condensate outlet at the bottom of heat exchanger 2 and then flow into the condensate collection tank 41. The bottom of the collection tank can be provided with an inclined surface so that the condensate automatically collects to the drain outlet.

[0057] The beneficial effect of the embodiments of this application is that the condensate collection tank 41 converts the water vapor that was originally emitted with the flue gas into liquid water and collects it, thus avoiding the waste of water resources.

[0058] In some embodiments, the condensate treatment unit 4 further includes a steam trap 42, the outlet of which is connected to the inlet of the steam trap 42, and the steam trap 42 is configured to allow condensate to pass through and prevent flue gas leakage.

[0059] The steam trap 42 can be a float type or a thermostatic type. Its inlet is connected to the outlet of the condensate collection tank 41, and its outlet is connected to the inlet of the neutralization tank 43. The steam trap 42 is equipped with a movable valve core and a sealing structure, which can automatically open and close according to changes in water level or temperature.

[0060] The condensate in the condensate collection tank 41 flows into the steam trap 42 by gravity. When the liquid level in the valve reaches the set height, the float rises or the thermostatic element is activated, the valve opens, and the condensate is discharged to the neutralization tank 43. When the condensate is drained or the flue gas pressure fluctuates, the valve closes quickly to prevent the flue gas in the heat exchanger 2 from leaking into the downstream pipeline with the water flow.

[0061] The beneficial effects of the embodiments of this application are that the steam trap 42 realizes the automatic discharge of condensate and reliable sealing of flue gas, prevents the leakage of acidic gases and harmful components in flue gas, ensures the safe operation of the condensate treatment unit 4, and avoids pressure fluctuations and thermal efficiency reduction of heat exchanger 2 caused by flue gas leakage, thereby improving the stability and reliability of the entire waste heat recovery system.

[0062] In some embodiments, the condensate treatment unit 4 further includes a neutralization tank 43, the outlet of which is connected to the inlet of the neutralization tank 43, and the neutralization tank 43 is configured to neutralize the acidity of the condensate.

[0063] The neutralization box 43 can be a sealed container filled with alkaline particles, such as limestone or calcium carbonate. The box has an inlet and an outlet. The inlet is connected to the outlet of the steam trap 42, and the outlet is connected to the inlet of the filter 44.

[0064] Acidic condensate enters through the inlet of neutralization tank 43, comes into contact with alkaline particles inside the tank, and undergoes an acid-base neutralization reaction. Acidic substances such as sulfuric acid and nitric acid in the condensate are converted into neutral salts and water, and the pH value of the condensate increases from three to five to six.5 to seven.5. After reaching the neutral standard, it flows out through the outlet of neutralization tank 43.

[0065] The beneficial effects of this application's implementation are that the neutralization tank 43 treats the strongly acidic condensate into neutral water, enabling it to be safely replenished to boiler 1 or directly discharged, avoiding corrosion damage to boiler 1 pipes and the environment caused by acidic water, while recovering valuable water resources and reducing the treatment cost and sewage discharge fee for boiler 1's makeup water.

[0066] In some embodiments, the condensate treatment unit 4 further includes a filter 44, the outlet of the neutralization tank 43 is connected to the inlet of the filter 44, the outlet of the filter 44 is connected to the water channel inlet of the boiler 1, and the filter 44 is configured to remove insoluble particles from the condensate.

[0067] The filter 44 can be a container with a multi-stage filter screen or quartz sand filter layer inside. Its inlet is connected to the outlet of the neutralization tank 43, and its outlet is connected to the water channel inlet of the boiler 1. It is used to intercept suspended particulate matter generated after the neutralization reaction.

[0068] The condensate flowing out of neutralization tank 43 contains insoluble microparticles such as calcium sulfate generated by the neutralization reaction. After entering filter 44, the condensate flows through multiple filter screens, where the particles are trapped on the surface of the filter screens or in the filter layers. The clean water flows out from the outlet of filter 44 and is sent to boiler 1 through the water inlet.

[0069] The beneficial effects of this application's implementation are that the filter 44 effectively removes solid impurities from the condensate, ensuring the cleanliness of the water used to replenish the boiler 1, preventing particulate matter from depositing and scaling inside the boiler 1, extending the service life of the boiler 1 and its pipes, while also improving the condensate reuse rate and reducing the pretreatment burden of the boiler 1's makeup water.

[0070] In actual work process: The high-temperature flue gas discharged from boiler 1 enters the flue gas passage of heat exchanger 2. The flue gas exchanges heat with the circulating water in the water passage of heat exchanger 2. The flue gas temperature drops below the dew point, and the water vapor in the flue gas condenses into condensate and flows out of heat exchanger 2. After the circulating water in the water channel of heat exchanger 2 absorbs heat from the flue gas, its temperature rises and it flows out from the water channel outlet of heat exchanger 2 and enters the water channel inlet of heat pump 3. After the circulating water releases heat in heat pump 3, its temperature drops and it returns from the water channel outlet of heat pump 3 to the water channel inlet of heat exchanger 2, forming the first circulation loop. Heat pump 3 increases the absorbed low-grade heat to high-grade heat through refrigerant circulation, and transfers the heat to boiler 1 through the second circulation loop for preheating boiler feedwater or heating return water. The condensate generated by heat exchanger 2 flows from the condensate outlet into the condensate treatment unit 4, where it is treated to become neutral clean water and then sent back to boiler 1 for recycling.

[0071] In the several embodiments provided by this invention, it should be understood that the disclosed systems and devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between devices or units, and may be electrical, mechanical, or other forms.

[0072] The units described as separate components may or may not be physically separate. The components of a unit may or may not be physical units; that is, they may be located in one place or distributed across multiple units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0073] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. Within the scope of protection of the present invention, any form of modification may be made.

Claims

1. A boiler waste heat recovery device, characterized in that: It includes a boiler (1), a heat exchanger (2), a heat pump (3), and a condensate treatment unit (4). The boiler (1) is connected to the heat exchanger (2), which is configured to absorb the flue gas from the boiler (1) and generate condensate. The heat exchanger (2) is connected to the condensate treatment unit (4), which is configured to treat the condensate and supply the treated condensate to the boiler (1). The water channel outlet of the heat exchanger (2) is connected to the water channel inlet of the heat pump (3), and the water channel inlet of the heat exchanger (2) is connected to the water channel outlet of the heat pump (3) to form a first circulation loop. The heat pump (3) is configured to provide energy to the boiler (1) based on the heat absorbed by the first circulation loop.

2. The boiler waste heat recovery device as described in claim 1, characterized in that: The heat exchanger (2) is a graphene plate-fin flue gas heat exchanger, which includes a graphene core made of stacked plates and fins.

3. The boiler waste heat recovery device as described in claim 1, characterized in that: The water channel inlet of the boiler (1) is connected to the water channel outlet of the heat pump (3), and the water channel outlet of the boiler (1) is connected to the water channel inlet of the heat pump (3) to form a second circulation loop. The heat pump (3) is configured to provide energy to the boiler (1) through the second circulation loop.

4. A boiler waste heat recovery device as described in claim 3, characterized in that: The heat pump (3) includes a carbon dioxide heat pump zone, which uses carbon dioxide as a refrigerant and delivers the boosted heat to the boiler (1) through the second circulation loop.

5. A boiler waste heat recovery device as described in claim 4, characterized in that: The carbon dioxide heat pump zone also includes an evaporator (35), an electronic expansion valve (34), and a regenerator (33). The water channel inlet of the evaporator (35) is connected to the water channel outlet of the heat exchanger (2), and the water channel outlet of the evaporator (35) is connected to the water channel inlet of the heat exchanger (2) to form the first circulation loop. The evaporator (35) is connected to the regenerator (33), and the regenerator (33) is connected to the evaporator (35) through the electronic expansion valve (34). The evaporator (35) is configured to absorb heat from the first circulation loop, the electronic expansion valve (34) is configured to depressurize carbon dioxide, and the regenerator (33) is configured to exchange heat between carbon dioxide flowing out of the evaporator (35) and carbon dioxide flowing in from the electronic expansion valve (34).

6. The boiler waste heat recovery device as described in claim 1, characterized in that: The carbon dioxide heat pump zone includes a gas cooler (31), a compressor (32), and a regenerator (33). The regenerator (33) is connected to the gas cooler (31) through the compressor (32). The water channel outlet of the gas cooler (31) is connected to the water channel inlet of the boiler (1), and the water channel outlet of the boiler (1) is connected to the water channel inlet of the gas cooler (31) to form the second circulation loop. The gas cooler (31) is configured to release the heat of carbon dioxide to water in the second circulation loop, the compressor (32) is configured to pressurize the carbon dioxide, and the regenerator (33) is configured to preheat the carbon dioxide before it enters the compressor (32).

7. A boiler waste heat recovery device as described in claim 1, characterized in that: The condensate treatment unit (4) includes a condensate collection tank (41), and the condensate outlet of the heat exchanger (2) is connected to the inlet of the condensate collection tank (41).

8. A boiler waste heat recovery device as described in claim 7, characterized in that: The condensate treatment unit (4) further includes a steam trap (42), the outlet of which is connected to the inlet of the steam trap (42), which is configured to allow condensate to pass through and prevent flue gas leakage.

9. A boiler waste heat recovery device as described in claim 8, characterized in that: The condensate treatment unit (4) further includes a neutralization tank (43), the outlet of which is connected to the inlet of the neutralization tank (43), which is configured to neutralize the acidity of the condensate.

10. A method for recovering waste heat from a boiler as described in claim 1, characterized in that: The following operational procedures are included: The high-temperature flue gas discharged from the boiler (1) enters the flue gas passage of the heat exchanger (2). The flue gas exchanges heat with the circulating water in the water passage of the heat exchanger (2). The flue gas temperature drops below the dew point, and the water vapor in the flue gas condenses into condensate and flows out of the heat exchanger (2). After the circulating water in the heat exchanger (2) absorbs heat from the flue gas, its temperature rises and flows out from the outlet of the heat exchanger (2) into the inlet of the heat pump (3). After the circulating water releases heat in the heat pump (3), its temperature drops and it returns from the outlet of the heat pump (3) to the inlet of the heat exchanger (2), forming the first circulation loop. The heat pump (3) increases the low-grade heat absorbed by the refrigerant to a high grade through the refrigerant circulation, and transfers the heat to the boiler (1) through the second circulation loop for preheating boiler feedwater or heating return water; The condensate generated by the heat exchanger (2) flows from the condensate outlet into the condensate treatment unit (4), where it is treated to become neutral clean water and then sent back to the boiler (1) for recycling.

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