Gradient deep recovery system for flue gas waste heat of desulfurization slurry

Abstract

The utility model discloses a stepped deep recovery system for flue gas waste heat of desulfurization slurry, relates to the field of heat energy recovery, and aims to solve the problems that an existing system is insufficient in waste heat recovery, needs additional energy cooling equipment and is high in improvement cost. The system comprises a desulfurizing tower, a flash tower, a primary absorption heat pump, a secondary heat pump and a vacuumizing device, part of slurry in the desulfurizing tower enters the flash tower for flash evaporation, flash evaporation dead steam exchanges heat through the first-stage absorption heat pump to heat return water of a heat supply network, generated dead steam tail gas and heat of the vacuumizing device are further recycled to the return water of the heat supply network through the second-stage absorption heat pump, and the vacuumizing device maintains the vacuum degree of the flash tower. The system does not need to transform an original flue gas system on a large scale, recycles waste heat in a stepped mode, improves the energy utilization rate, recycles condensate water, reduces cost and energy consumption, and is suitable for waste heat recovery scenes after coal-fired flue gas desulfurization.

Description

Technical Field

[0001] This utility model relates to the field of heat energy recovery, specifically to a cascade deep recovery system for waste heat from desulfurization slurry flue gas. Background Technology

[0002] Flue gas from coal combustion contains a large amount of sulfur dioxide, which cannot be directly emitted to protect the environment and must be desulfurized before being released. The most common industrial desulfurization method is based on a desulfurization tower, which thoroughly mixes the flue gas with desulfurization slurry to extract sulfur from the flue gas and prevent it from being released into the atmosphere.

[0003] Even after desulfurization, flue gas still retains a large amount of latent heat. Finding ways to recover the waste heat from the flue gas and apply it to the heating network can save energy, reduce environmental pollution, and ensure the safe and stable operation of the original process. This has become the current development trend of the industry.

[0004] The conventional heat recovery method involves the following steps: After desulfurization, the flue gas enters a spray tower and comes into contact with circulating water from a steam-type absorption heat pump. The circulating water absorbs heat from the flue gas and is then pumped back to the steam-type absorption heat pump to participate in its working cycle. Heat network water is pumped into the steam-type absorption heat pump by a heat network booster pump. The heat pump, driven by steam, transfers heat from the circulating water to the heat network water. The heated heat network water can be directly supplied to users or further heated by a heat network heater before being sent to users. In this scheme, the flue gas flowing upwards in the spray tower comes into full contact with the circulating water. The circulating water absorbs heat, while the flue gas releases heat. The water vapor in the flue gas cools and condenses into water. The condensed water dissolves a large amount of sulfur dioxide, resulting in acidic condensate water that mixes with the residual hot water from the spray, making the overall circulating water acidic. Even with the addition of a wastewater treatment system to neutralize the water, it is necessary to use highly corrosion-resistant materials for the subsequent piping network, increasing equipment investment costs.

[0005] Furthermore, if the above system is a modification of an existing emission system, a new spray tower needs to be built, and the flow direction of the flue gas discharged from the desulfurization tower needs to be changed to introduce it into the spray tower. The spray tower has high requirements for site space, and the addition of the spray tower will also increase the pressure loss in the flue during the flue gas emission process. This may cause the original fan power of the system to be unable to adapt to the modified operating conditions, thus requiring further replacement of the fan system and increasing the modification cost.

[0006] Chinese patent CN223004998U discloses a two-stage flash evaporation coupled absorption heat pump flue gas waste heat recovery system for desulfurization slurry. This system extracts heat from the flue gas through two-stage flash evaporation towers. The heat extracted in the first-stage flash evaporation tower directly exchanges heat with the return water from the heating network, heating the return water. The second-stage flash evaporation tower further extracts heat from the desulfurization slurry. The steam from the second-stage flash evaporation is sent to a heat pump for waste heat recovery, which then reheats the return water or other process water. The concentrated desulfurization slurry, from which water has been extracted, is returned to the desulfurization tower to continue participating in desulfurization. Its advantages are: no modification to the flue gas system is required, reducing on-site implementation difficulty; the condensate has good water quality, facilitating recycling. However, it still has the following disadvantages:

[0007] First, using a steam-driven heat pump requires an additional high-quality heat source. Second, while the design considers heat extraction from the desulfurization slurry, in practical applications, the vacuum pump itself generates heat to maintain the vacuum level of the flash evaporation system, requiring additional cooling. Furthermore, some components of the heat pump system itself generate heat to maintain operation, also necessitating additional cooling. In other words, both of these aspects still require additional energy to maintain system operation.

[0008] Third, the exhaust steam from the outlet of the absorption heat pump still contains a certain amount of water vapor, which has not been recovered. Utility Model Content

[0009] The technical problem to be solved by this utility model is to provide a cascade deep recovery system for waste heat from desulfurization slurry flue gas.

[0010] The specific technical solution of this utility model to solve the above-mentioned technical problems is as follows:

[0011] A cascaded deep recovery system for waste heat from desulfurization slurry flue gas includes a desulfurization tower, a flash tower, a primary absorption heat pump, a secondary heat pump, and a vacuum pumping device.

[0012] The bottom of the desulfurization tower is connected to a spray device inside the tower via a slurry pump and a slurry main pipe. The slurry main pipe is also connected to the flash tower via a slurry branch pipe. The bottom of the flash tower is connected to the spray device via a slurry return pump and a slurry return pipe. The flash tower is used to extract flash exhaust steam from the desulfurization slurry. The top of the flash tower is connected to the tube side of the evaporator in the first-stage absorption heat pump via an exhaust steam pipe. The tube side of the absorber and condenser of the first-stage absorption heat pump is connected to the return water of the heating network. The first-stage absorption heat pump is used to transfer the heat from the flash exhaust steam to the return water of the heating network. The bottom of the evaporator tube-side outlet of the first-stage absorption heat pump is the first condensate drain port, and the top of the evaporator tube-side outlet is the exhaust gas outlet. The first condensate drain port is connected to the condensate recovery device, and the exhaust gas outlet is connected to the vacuum device. That is, exhaust gas and condensate are discharged from the tube-side outlet of the evaporator in the first-stage absorption heat pump. The condensate is connected to the condensate recovery device, and the exhaust gas is connected to the vacuum device. The vacuum device is used to extract non-condensable gases from the discharged exhaust gas and to provide the required vacuum level for the flash tower.

[0013] The condenser tube side of the secondary heat pump is connected to the return water of the heating network. The secondary heat pump is used to transfer the heat of the exhaust gas to the return water of the heating network, or to transfer the heat generated by the vacuum device and the heat of the exhaust gas to the return water of the heating network.

[0014] The present invention has the following advantages over the prior art:

[0015] In existing technologies, the heat generated by the vacuum pump and its components requires additional energy to cool. This invention utilizes a two-stage heat pump to recover this previously discarded heat, not only reducing the energy consumption required for cooling but also using the recovered heat to heat the heating network water, thereby reducing the heat load on the hot water boiler and significantly improving the energy efficiency of the entire system.

[0016] This system not only efficiently recovers the heat from the flash steam in the desulfurization slurry using a flash tower and a primary absorption heat pump to heat the return water of the heating network, but also innovatively incorporates a secondary heat pump. This secondary heat pump recovers the residual heat in the exhaust gas from the evaporator outlet of the primary absorption heat pump, and further recovers the heat generated by the vacuum pump that would otherwise require additional cooling, transferring it to the return water of the heating network. Through the cascade heating of the primary and secondary absorption heat pumps, deep and multi-level recovery of waste heat from the flue gas is achieved, maximizing energy utilization and minimizing heat loss.

[0017] The system ingeniously integrates a flash tower, a primary absorption heat pump, a secondary heat pump, and a vacuum pump, utilizing the desulfurization slurry itself as a medium for waste heat extraction. This eliminates the need for large-scale modifications to the existing flue gas system, such as the addition of spray towers, thus reducing the difficulty and cost of on-site implementation. Simultaneously, the condensate recovery device allows the generated condensate to be used as makeup water for the heating network or the desulfurization slurry, achieving water resource recycling.

[0018] By using a vacuum pump to extract non-condensable gases from the exhaust gas, the required vacuum level of the flash tower is effectively maintained, ensuring the stable and efficient operation of the flash process. This also prevents non-condensable gases from crowding out the heat exchange area inside the evaporator, thus ensuring the heat exchange efficiency of the heat pump evaporator.

[0019] Furthermore, the primary absorption heat pump is a hot water driven heat pump, and the driving heat source is the heat network outlet water obtained by heating with a hot water boiler. Part of the heat network outlet water is connected to the tube side of the generator of the primary absorption heat pump.

[0020] The beneficial effect of adopting the above-mentioned further solution is that, compared with existing steam-driven heat pumps, this utility model selects a hot water-driven first-stage absorption heat pump, whose driving heat source is directly the effluent from the heating network after being heated by a hot water boiler. This design cleverly utilizes the existing effluent from the heating network within the system as the driving energy, eliminating the need to introduce additional external high-grade driving heat sources such as steam, thereby significantly reducing dependence on external energy. Simultaneously, because only a small portion of the effluent from the heating network is needed to drive the first-stage absorption heat pump, although the temperature of this portion of the effluent decreases after driving the first-stage absorption heat pump, the impact on the overall effluent temperature of the heating network is negligible. This simplifies the system's heat source supply structure and reduces the equipment investment and operating costs incurred from obtaining external high-grade heat sources.

[0021] Furthermore, the secondary heat pump is an electrically driven heat pump.

[0022] Employing an electrically driven heat pump as a secondary heat pump offers advantages such as compact structure, convenient installation, and flexible control, enabling rapid response to system heat recovery needs. By consuming minimal electrical energy, it efficiently recovers heat generated by the vacuum pump and / or residual heat from exhaust gas, upgrading low-grade heat energy into usable high-grade heat energy and transferring it to the heat network return water. This further enhances the system's waste heat recovery efficiency and energy conversion flexibility, making it particularly suitable for applications with limited space or high control precision requirements.

[0023] Furthermore, when the secondary heat pump only recovers heat from the exhaust gas, the exhaust gas is directly introduced into the secondary heat pump to recover heat from it. The exhaust gas outlet is connected to the tube-side inlet of the evaporator of the secondary heat pump, the bottom of the tube-side outlet of the evaporator is connected to the condensate recovery device, and the top of the tube-side outlet of the evaporator is connected to the vacuum device; the vacuum device is cooled by additional cooling water.

[0024] In this operating mode, the system at least achieves the recovery of heat from the exhaust gas.

[0025] The exhaust gas first enters the tube side of the secondary heat pump evaporator, where it exchanges heat with the working fluid and releases the heat it carries. During this process, the water vapor in the exhaust gas condenses into liquid water, which is then discharged from the bottom of the tube side outlet to the condensate recovery device for collection and reuse. The discharged medium also contains some gas, mainly non-condensable gases, which are then connected from the top of the evaporator tube side outlet to the vacuum pump to be discharged from the system, maintaining the vacuum environment required by the system.

[0026] In this structure, the vacuum pump generates heat during operation, requiring additional cooling water for cooling to ensure its proper functioning. Because the exhaust gas pressure is very low while the cooling water pressure is relatively high, both cannot be simultaneously fed into the secondary heat pump for heat recovery. Therefore, while this structure can achieve heat recovery from the exhaust gas, it inevitably sacrifices the heat generated during the operation of the vacuum pump.

[0027] Furthermore, it also includes a pre-condenser, which is used to condense water vapor in the exhaust gas into liquid water. The exhaust gas outlet is connected to the shell-side inlet of the pre-condenser, and the shell-side outlet of the pre-condenser discharges the final-stage exhaust gas and condensate. That is, the top of the shell-side outlet of the pre-condenser is the final-stage exhaust gas outlet, and the bottom of the shell-side outlet of the pre-condenser is the second condensate outlet, which is connected to a condensate recovery device. The final-stage exhaust gas outlet is connected to the vacuum device. The tube-side outlet of the pre-condenser is connected to... The tube side of the evaporator of the secondary heat pump is connected to the inlet of the evaporator tube side, the outlet of the evaporator tube side of the secondary heat pump is connected to the inlet of the waste water pump, and the outlet of the waste water pump is connected to the inlet of the tube side of the pre-condenser; the tube side of the pre-condenser and the tube side of the evaporator of the secondary heat pump are filled with closed-loop waste water; that is, the pre-condenser uses closed-loop waste water to provide cooling capacity, the closed-loop waste water is connected to the tube side of the pre-condenser, and the closed-loop waste water after heat exchange in the pre-condenser enters the shell side of the evaporator of the secondary heat pump, releases heat, and then returns to the pre-condenser via the waste water pump.

[0028] Cooling is achieved using closed-loop waste water. The closed-loop waste water, after heat exchange in the pre-condenser, is fed into the shell side of the evaporator of the secondary heat pump for further heat exchange, and then returns to the pre-condenser via a waste water pump. This design cleverly combines the cooling requirements of the pre-condenser with the heat recovery function of the secondary heat pump, forming a highly efficient heat recovery and cooling cycle system. Specifically, the closed-loop waste water first absorbs heat from the exhaust gas in the tube side of the pre-condenser, raising its temperature. Then, this heated closed-loop waste water enters the tube side of the evaporator of the secondary heat pump, serving as a low-temperature heat source for the secondary heat pump. It transfers the heat it carries to the heat pump working fluid in the shell side of the evaporator, lowering its own temperature. Finally, the cooled closed-loop waste water, driven by the waste water pump, returns to the pre-condenser to continue its cooling and heat collection tasks. Through this process, the system not only efficiently recovers the low-grade heat (heat from exhaust gas) that would otherwise be carried away by the cooling water, using it to heat the return water of the heating network and improve energy utilization efficiency, but also eliminates the need to set up a separate cooling water source and heat dissipation equipment for the pre-condenser, simplifying the system structure and reducing equipment investment and operating costs.

[0029] Furthermore, the outlet of the waste water pump is also connected to the inlet of the cooling channel of the vacuum device, and the outlet of the cooling channel of the vacuum device is connected to the inlet of the evaporator tube side of the secondary heat pump.

[0030] That is, the vacuum pumping device also uses closed-loop waste water for cooling. The closed-loop waste water after heat exchange from the pre-condenser and the closed-loop waste water after heat exchange from the vacuum pumping device are combined and fed into the evaporator tube side of the secondary heat pump to participate in heat exchange. Then, the waste water is pumped back to the pre-condenser and the vacuum pumping device.

[0031] The beneficial effect of the above scheme is that by combining and collecting the heat generated by the pre-condenser and the vacuum pump, and using the same closed-loop waste water stream to introduce the heat from both into the evaporator tubes of the secondary heat pump, the low-grade heat that would otherwise require additional cooling is centrally recovered and utilized. Specifically, the closed-loop waste water from the pre-condenser increases in temperature after absorbing heat from the exhaust gas, while the closed-loop waste water from the vacuum pump also increases in temperature after absorbing heat generated during its operation. The confluence of these two heated closed-loop waste water streams allows the waste water entering the secondary heat pump evaporator to carry a larger amount of recoverable heat, thereby improving the heating efficiency and heat output of the secondary heat pump. This design not only avoids the equipment redundancy and energy waste caused by setting up separate cooling systems for the pre-condenser and the vacuum pump, but also maximizes the exploitable waste heat potential of the system through centralized heat recovery, further reducing the demand for external energy and improving the overall energy utilization efficiency of the entire system. Meanwhile, after the closed-loop waste water is collected and releases heat in the secondary heat pump, it is pressurized and returned to the pre-condenser and vacuum pump by the waste water pump, forming a compact and efficient circulation loop. This simplifies the piping layout, reduces power consumption, and ensures that the pre-condenser and vacuum pump can obtain a stable cooling water source, thus guaranteeing the normal operation of their respective equipment and the stable operation of the entire system.

[0032] Furthermore, the tube-side outlet of the condenser of the first-stage absorption heat pump and the tube-side outlet of the condenser of the second-stage heat pump are both connected to the inlet of the hot water boiler. That is, the return water from the heating network heated by the first-stage absorption heat pump and the return water from the heating network heated by the second-stage heat pump are combined and then connected to the hot water boiler.

[0033] This design allows the return water from the heating network to be heated sequentially or separately by a primary absorption heat pump and a secondary heat pump, fully absorbing the heat recovered from different heat sources by both pumps and integrating the previously dispersed waste heat for utilization. Before entering the hot water boiler, the temperature of the return water has been significantly increased, effectively reducing fuel consumption or energy input in the hot water boiler during the process of heating it to the target supply water temperature. This centralized heating method avoids the uneven distribution or heat loss problems that may occur when the heating network water is in the two heat pump systems, ensuring that the waste heat recovered in stages can maximize its effect on heating the heating network water, further optimizing the energy flow of the entire system, improving the overall efficiency and economy of waste heat recovery, and making the system more efficient and integrated in energy utilization.

[0034] Furthermore, the slurry main pipe and the slurry return pipe merge before entering the desulfurization tower.

[0035] This design allows the desulfurization slurry returning from the flash evaporator to be fully mixed with the fresh slurry pumped from the bottom of the desulfurization tower before entering the spraying device inside the tower. This mixing allows for adjustment of the spray slurry's temperature and concentration, making it more suitable for the desulfurization reaction and ensuring stable desulfurization efficiency. Simultaneously, the combined slurries can enter the desulfurization tower through a single pipeline, simplifying the piping layout inside and before the tower, reducing the risk of blockages and maintenance workload that might result from multiple pipelines, and also helping to maintain stable slurry pressure and flow at the spraying device inlet, ensuring uniform spraying and improving the overall operational performance of the desulfurization tower.

[0036] Furthermore, the condensate is used as makeup water for the heating network or as makeup water for the desulfurization slurry.

[0037] This design enables efficient recycling of water resources and avoids waste caused by direct discharge of condensate. When condensate is used as makeup water for the heating network, its temperature is relatively higher than that of ambient water, which can reduce the energy consumption of the heating network water during the heating process. When used as makeup water for desulfurization slurry, it can directly replenish the water lost in the desulfurization tower due to evaporation and discharge, maintain the stability of the desulfurization slurry level and concentration, and reduce the demand for fresh industrial water. Thus, it saves water and reduces water treatment costs, meeting the requirements of energy conservation and environmental protection. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the system structure of Example 1;

[0039] Figure 2 This is a schematic diagram of the system structure in Example 2;

[0040] Figure 3 This is a schematic diagram of the system structure in Example 3.

[0041] The following is a list of component names represented by the reference numerals in the attached diagram:

[0042] 1. Desulfurization tower; 2. Flash evaporator; 3. Hot water boiler; 4. Primary absorption heat pump; 5. Slurry pump; 6. Slurry return pump; 7. Pre-condenser; 8. Vacuum pump; 9. Secondary heat pump; 10. Condensate tank; 11. Condensate pump; 12. Waste hot water pump; 13. Heat network booster pump; 401. Heat network three-way regulating valve; 402. First heat network water regulating valve; 403. Third heat network water regulating valve; 901. Second heat network water regulating valve. Detailed Implementation

[0043] The principles and features of this utility model are described below with reference to the accompanying drawings. The examples given are only for explaining this utility model and are not intended to limit the scope of this utility model.

[0044] Example 1:

[0045] In this embodiment, the exhaust gas directly enters the secondary heat pump 9, and is independently cooled by the vacuum pump 8, as detailed below. Figure 1 As shown, a cascaded deep recovery system for waste heat from desulfurization slurry flue gas includes a desulfurization tower 1, a flash tower 2, a primary absorption heat pump 4, a secondary heat pump 9, and a vacuum pumping device 8.

[0046] The bottom of the desulfurization tower 1 is connected to the spray device inside the desulfurization tower 1 via a slurry pump 5 and a slurry main pipe. The slurry main pipe is also connected to the flash tower 2 via a slurry branch pipe. The bottom of the flash tower 2 is connected to the spray device via a slurry return pump 6 and a slurry return pipe. The slurry main pipe and the slurry return pipe merge before entering the desulfurization tower 1. The flash tower 2 is used to flash extract flash exhaust steam from the desulfurization slurry. The top of the flash tower 2 is connected to the tube side of the evaporator in the first-stage absorption heat pump 4 via an exhaust steam pipe. The tube side of the absorber and condenser of the first-stage absorption heat pump 4 is connected to the heat network return water. The amount of heat network return water entering the tube side of the absorber and condenser of the first-stage absorption heat pump 4 is pressurized by the heat network. Pump 13 and the first heating network water regulating valve 402 control the primary absorption heat pump 4, which is used to transfer the heat in the flash exhaust steam to the heating network return water. The flash exhaust steam releases heat in the tube side of the evaporator in the primary absorption heat pump 4. Most of the water vapor condenses into liquid condensate, and a small portion of water vapor and non-condensable gases constitute exhaust gas. That is, the tube side outlet of the evaporator in the primary absorption heat pump 4 will discharge liquid condensate and gaseous exhaust gas. The bottom of the tube side outlet of the evaporator of the primary absorption heat pump 4 is the first condensate discharge port, which is connected to the condensate recovery device; the top of the tube side outlet of the evaporator of the primary absorption heat pump 4 is the exhaust gas discharge port, which is connected to the vacuum device 8.

[0047] The primary absorption heat pump 4 is a hot water driven heat pump. The driving heat source is the heat network outlet water obtained by heating the hot water boiler 3. The heat network outlet water output from the outlet of the hot water boiler 3 is connected to the tube side of the generator of the primary absorption heat pump 4 via the heat network three-way regulating valve 401. The heat network three-way regulating valve 401 is used to control the amount of heat network outlet water entering the tube side of the generator of the primary absorption heat pump 4.

[0048] The secondary heat pump 9 is an electrically driven heat pump. The condenser tube side of the secondary heat pump 9 is connected to the return water of the heating network, and the secondary heat pump 9 is used to transfer the heat of the exhaust gas to the return water of the heating network.

[0049] The exhaust gas outlet is connected to the tube-side inlet of the evaporator of the secondary heat pump 9, and the bottom of the tube-side outlet of the evaporator of the secondary heat pump 9 is connected to the condensate recovery device. In this embodiment, the condensate recovery device is a condensate tank 10, and a condensate pump 11 is connected to the bottom of the condensate tank 10. The top of the tube-side outlet of the evaporator of the secondary heat pump 9 is connected to the vacuum device 8; the tube-side of the condenser of the secondary heat pump 9 is connected to the heat network return water, and the amount of heat network return water entering the tube-side of the condenser of the secondary heat pump 9 is controlled by the heat network booster pump 13 and the second heat network water regulating valve 901.

[0050] The vacuum pumping device 8 is used to extract non-condensable gases from the exhaust gas and provide the required vacuum level for the flash tower 2; the vacuum pumping device 8 is cooled by additional cooling water.

[0051] The heat network return water heated by the primary absorption heat pump 4 and the heat network return water heated by the secondary heat pump 9 are collected in the heat network return water main pipe and then connected to the inlet of the hot water boiler 3. The hot water boiler 3 further heats the heat network return water to the target temperature.

[0052] The return water main of the heating network is also connected to the outlet water main of the heating network via the third heating network water regulating valve 403, which is used to regulate the hot water supplied to users by the system.

[0053] The working process of this solution is as follows:

[0054] Driven by slurry pump 5, the desulfurization slurry at approximately 49°C at the bottom of desulfurization tower 1 is partially transported to the spray device for spray desulfurization via the slurry main pipe, while the other part enters flash tower 2 through the slurry branch pipe. Inside flash tower 2, due to the reduced system pressure, some of the water in the slurry flashes into flash exhaust steam. The slurry, now at approximately 43°C, is pressurized by slurry return pump 6 and then flows through the slurry return pipe, merging with the fresh slurry in the slurry main pipe before entering desulfurization tower 1. Together, they enter the spray device, cooling the flue gas inside desulfurization tower 1 to approximately 40°C-45°C. The flash exhaust steam generated in flash tower 2, at 35°C to 45°C, enters the evaporator tube side of the first-stage absorption heat pump 4, where it exchanges heat with the working fluid in the evaporator shell side. After releasing heat, it condenses to form condensate at 34°C-44°C and exhaust steam containing a small amount of non-condensable gases. Condensate is collected by a condensate recovery unit, while exhaust gas is directly fed into the tube side of the evaporator of the secondary heat pump 9. Within the tube side of the evaporator in the secondary heat pump 9, the exhaust gas exchanges heat again with the working fluid in the shell side, further releasing heat and lowering the temperature to 20°C. It is then discharged from the tube side outlet of the evaporator in the secondary heat pump 9. During the heat release process, water vapor condenses into liquid water and flows to the condensate recovery unit. The remaining gas (mainly non-condensable gases) enters the vacuum pump 8. During operation, the vacuum pump 8 is cooled by additional cooling water to maintain its normal operating temperature. The cooling water absorbs heat and is either directly discharged or cooled by external heat dissipation equipment and then recycled. The vacuum pump 8 extracts non-condensable gases from the system, thus ensuring the required vacuum environment within the flash tower 2. Simultaneously, the heat network return water at approximately 45°C enters the condenser tube side of both the primary absorption heat pump 4 and the secondary heat pump 9 to absorb heat. In the first-stage absorption heat pump 4, a portion of the heat network effluent heated by the hot water boiler 3 is introduced into the generator tubes as a driving heat source to drive the heat pump working fluid circulation. This transfers the heat absorbed from the flash steam to the heat network return water, raising its temperature to approximately 60°C. In the second-stage heat pump 9, electrical energy is consumed to drive the working fluid circulation, transferring the heat recovered from the exhaust steam to another heat network return water, also raising its temperature to approximately 60°C. The two streams of heated heat network return water converge and enter the hot water boiler 3, where they are further heated to the set heat network supply water temperature before being delivered to the heat network users. The condensate collected by the condensate recovery device can be used as makeup water for the heat network pipeline to replenish water losses in the heat network, or as makeup water for the desulfurization slurry to maintain the slurry level and concentration in the desulfurization tower 1, depending on system requirements.

[0055] Example 2

[0056] In this embodiment, a pre-condenser 7 is installed before the secondary heat pump 9. The closed-loop waste water in the pre-condenser 7 is connected to the secondary heat pump 9, while the vacuum device 8 is cooled independently.

[0057] Specifically, such as Figure 2As shown, unlike Embodiment 1, this embodiment further includes a pre-condenser 7, which is used to condense water vapor in the exhaust gas into liquid water. The exhaust gas outlet is connected to the shell-side inlet of the pre-condenser 7, and the shell-side outlet of the pre-condenser 7 discharges the final-stage exhaust gas and condensate. The top of the shell-side outlet of the pre-condenser 7 is the final-stage exhaust gas outlet, and the bottom of the shell-side outlet of the pre-condenser 7 is the second condensate outlet, which is connected to a condensate recovery device. The final-stage exhaust gas outlet is connected to the vacuum device 8. The tube-side outlet of the pre-condenser 7 is connected to the secondary heat pump. The evaporator tube-side inlet of the secondary heat pump 9 is connected to the inlet of the waste water pump 12, and the outlet of the waste water pump 12 is connected to the tube-side inlet of the pre-condenser 7. The tube-side of the pre-condenser 7 and the tube-side of the evaporator of the secondary heat pump 9 are filled with closed-loop waste water. That is, the pre-condenser 7 uses closed-loop waste water to provide cooling capacity. The closed-loop waste water is connected to the tube-side of the pre-condenser 7. The closed-loop waste water, after heat exchange in the pre-condenser 7, enters the evaporator tube-side of the secondary heat pump 9, releases heat, and then returns to the pre-condenser 7 via the waste water pump 12. In this example, the closed-loop waste water flow rate is approximately 370 m³ / h. ３ / h, the temperature before entering the pre-condenser 7 is 15℃, and the temperature rises to 25℃ after exiting the pre-condenser 7. The condenser tube side of the secondary heat pump 9 is connected to the heat network return water, transferring the heat recovered by the pre-condenser 7 to the heat network return water, thereby realizing the recovery of heat in the exhaust gas.

[0058] The vacuum pumping unit 8 is cooled by independent cooling water, with an inlet water temperature of 15℃, an outlet water temperature of 18℃, and a flow rate of 62 m³ / s. 3 / h.

[0059] The working principle of this scheme is as follows: The desulfurization slurry at the bottom of desulfurization tower 1, driven by slurry pump 5, partially enters flash tower 2 for flash evaporation. The flash evaporation exhaust steam enters the tube side of the evaporator of the first-stage absorption heat pump 4 for heat exchange. The resulting condensate enters the condensate recovery device, while the exhaust steam containing non-condensable gases first enters the shell side of the pre-condenser 7. In the pre-condenser 7, the exhaust steam in the shell side exchanges heat with the closed-loop waste water in the tube side. Most of the water vapor in the exhaust steam condenses into liquid water due to heat release, and together with the existing condensate, flows into the condensate recovery device. The remaining final-stage exhaust gas (mainly non-condensable gases) is discharged from the shell side outlet of the pre-condenser 7 and enters the vacuum device 8. The closed-loop waste water in the tube side of the pre-condenser 7 absorbs a large amount of latent heat and sensible heat released by the exhaust gas, resulting in a significant temperature increase. It is then transported to the evaporator tube side of the secondary heat pump 9, transferring the heat it carries to the working fluid of the secondary heat pump 9. After its own temperature decreases, it returns to the tube side of the pre-condenser 7 under the drive of the waste water pump 12, forming a closed-loop cycle and continuously providing cooling capacity to the pre-condenser 7. When the vacuum device 8 extracts the final stage exhaust gas to maintain the vacuum level of the flash tower 2, the heat generated during its operation is carried away by an independent cooling water system. The cooling water absorbs heat and is either directly discharged or treated by external cooling equipment for reuse. The heating path of the heat network return water is similar to that in Embodiment 1, absorbing heat through the primary absorption heat pump 4 and the secondary heat pump 9 respectively, then converging before entering the hot water boiler 3 to be heated to the target supply water temperature. The condensate collected by the condensate recovery device can also be used as heat network makeup water or desulfurization slurry makeup water. This solution, by setting up a pre-condenser 7, can efficiently recover a large amount of latent heat of water vapor in the exhaust gas, significantly improving the heat source quality and heat input of the secondary heat pump 9. Simultaneously, it condenses and separates most of the water vapor, effectively reducing the humidity of the gas entering the vacuum pumping device 8, minimizing the risk of liquid slugging, and ensuring the stable operation of the vacuum pumping device 8. However, since the vacuum pumping device 8 still uses independent cooling, the heat generated during its operation cannot be recovered and utilized, resulting in some energy waste. The overall comprehensiveness and integration of waste heat recovery need further improvement.

[0060] Example 3

[0061] In this embodiment, a pre-condenser 7 is installed before the secondary heat pump 9. Both the pre-condenser 7 and the vacuum pump 8 are connected to the secondary heat pump 9 for heat recovery.

[0062] Specifically, such as Figure 3As shown, unlike Embodiment 2, in this example, the vacuuming device 8 also uses closed-loop waste water for cooling. The outlet of the waste water pump 12 is also connected to the inlet of the cooling channel of the vacuuming device 8, and the outlet of the cooling channel of the vacuuming device 8 is connected to the inlet of the evaporator tube side of the secondary heat pump 9. The closed-loop waste water after heat exchange from the pre-condenser 7 and the closed-loop waste water after heat exchange from the vacuuming device 8 are combined and fed into the evaporator tube side of the secondary heat pump 9 to participate in heat exchange, and then returned to the pre-condenser 7 and the vacuuming device 8 via the waste water pump 12.

[0063] The working principle of this solution is as follows:

[0064] The desulfurization slurry at the bottom of desulfurization tower 1, driven by slurry pump 5, partially enters flash tower 2 for flash evaporation. The flash evaporation exhaust gas enters the tube side of the evaporator of the first-stage absorption heat pump 4 for heat exchange, and the resulting condensate enters the condensate recovery device. The exhaust gas containing non-condensable gases first enters the shell side of the pre-condenser 7. In the pre-condenser 7, the exhaust gas in the shell side exchanges heat with the closed-loop waste water in the tube side. Most of the water vapor in the exhaust gas condenses into liquid water and flows into the condensate recovery device. The remaining final-stage exhaust gas (mainly non-condensable gases) is discharged from the shell side outlet of the pre-condenser 7 and enters the vacuum pump 8. The closed-loop waste water in the tube side of the pre-condenser 7 absorbs the heat released by the exhaust gas, causing its temperature to rise. When the vacuum pump 8 extracts the final-stage exhaust gas to maintain the vacuum level of flash tower 2, the heat generated during its operation, as well as the small amount of heat that may remain in the final-stage exhaust gas, is absorbed by the closed-loop waste water that cools it, causing the temperature of the closed-loop waste water to rise. Subsequently, the heated closed-loop waste water flowing directly from the pre-condenser 7 and the closed-loop waste water flowing out after heat exchange from the vacuum device 8 merge and enter the evaporator tube side of the secondary heat pump 9. Within the evaporator tube side of the secondary heat pump 9, the combined high-temperature closed-loop waste water transfers its total heat (including the heat from the exhaust gas recovered by the pre-condenser 7, the working heat recovered by the vacuum device 8, and the residual heat from the final stage exhaust gas) to the heat pump working fluid in the evaporator shell side, thus lowering its own temperature. Driven by the waste water pump 12, the cooled closed-loop waste water is divided into two parts: one part returns to the tube side of the pre-condenser 7 to continue absorbing heat from the exhaust gas, and the other part returns to the vacuum device 8 to continue absorbing its working heat and the residual heat from the final stage exhaust gas, forming a complete and efficient heat recovery closed-loop cycle. The treatment of the heat network return water is similar to the aforementioned embodiment, entering the condenser tube sides of the primary absorption heat pump 4 and the secondary heat pump 9 respectively to absorb heat, and then entering the hot water boiler 3 to be heated to the target supply water temperature. The condensate from the condensate recovery unit can also be used as makeup water for the heating network or desulfurization slurry. This solution efficiently recovers a large amount of latent and sensible heat from the exhaust gas through the pre-condenser 7, and innovatively incorporates the originally independently cooled vacuum pumping device 8 into the closed-loop waste water system. This allows the working heat and residual heat from the final stage exhaust gas to be fully recovered and utilized, flowing into the same heat source and entering the secondary heat pump 9. This achieves "step-by-step" recovery of low-grade heat from different sources within the system, maximizing the overall energy recovery efficiency and avoiding the hassle of setting up a separate cooling system for the vacuum pumping device 8. It is the solution with the best overall performance.

[0065] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A system for the recovery of flue gas waste heat in stages and at depth from a desulphurization slurry, comprising a desulphurization tower (1), characterized in that, The system further comprises a flash tower (2), a primary absorption heat pump (4), a secondary heat pump (9) and a vacuumizing device (8); The bottom of the desulfurization tower (1) is connected to the spray device in the desulfurization tower (1) through a slurry pump (5) and a slurry main pipe, the slurry main pipe is also connected to the flash tower (2) through a slurry branch pipe, the bottom of the flash tower (2) is connected to the spray device through a slurry return pump (6) and a slurry return pipe; the flash tower (2) is used for extracting flash steam from the desulfurization slurry, the top of the flash tower (2) is connected to the tube side of the evaporator in the primary absorption heat pump (4) through a flash steam pipe, the tube sides of the absorber and the condenser of the primary absorption heat pump (4) are connected to the heat network return water; The bottom of the outlet of the tube side of the evaporator of the primary absorption heat pump (4) is a first condensate water discharge port, which is connected to a condensate water recovery device; The top of the outlet of the tube side of the evaporator of the primary absorption heat pump (4) is a flash steam tail gas discharge port, which is connected to the vacuumizing device (8); The tube side of the condenser of the secondary heat pump (9) is connected to the heat network return water, the secondary heat pump (9) is used for transferring the heat of the flash steam tail gas to the heat network return water, or transferring the heat generated by the vacuumizing device (8) and the heat of the flash steam tail gas to the heat network return water.

2. The system for flue gas waste heat recovery in stepwise depth of desulphurized slurry according to claim 1, characterized in that, The primary absorption heat pump (4) is a hot water driven heat pump.

3. The system for flue gas waste heat recovery in stepwise depth of desulphurized slurry according to claim 1, characterized in that, The secondary heat pump (9) is an electric driven heat pump.

4. The system for recovery of flue gas residual heat from desulphurization slurry according to any one of claims 1 to 3, characterized in that, When the secondary heat pump (9) only recovers the heat in the flash steam tail gas, the flash steam tail gas discharge port is connected to the tube side inlet of the evaporator of the secondary heat pump (9), the bottom of the tube side outlet of the evaporator of the secondary heat pump (9) is connected to the condensate water recovery device, and the top of the tube side outlet of the evaporator of the secondary heat pump (9) is connected to the vacuumizing device (8); the vacuumizing device (8) is cooled by cooling water.

5. The system for recovery of flue gas residual heat from desulphurization slurry according to any one of claims 1 to 3, characterized in that, The system further comprises a pre-condenser (7), the flash steam tail gas discharge port is connected to the shell side inlet of the pre-condenser (7), the top of the shell side outlet of the pre-condenser (7) is a final stage tail gas discharge port, the bottom of the shell side outlet of the pre-condenser (7) is a second condensate water discharge port, the second condensate water discharge port is connected to a condensate water recovery device, and the final stage tail gas discharge port is connected to the vacuumizing device (8); The tube side outlet of the pre-condenser (7) is connected to the tube side inlet of the evaporator of the secondary heat pump (9), the tube side outlet of the evaporator of the secondary heat pump (9) is connected to the inlet of a waste heat water pump (12), and the outlet of the waste heat water pump (12) is connected to the tube side inlet of the pre-condenser (7); The tube side of the pre-condenser (7) and the tube side of the evaporator of the secondary heat pump (9) are filled with closed loop waste heat water.

6. The system for recovery of flue gas residual heat in stages with deep desulfurization slurry according to claim 5, characterized in that, The outlet of the waste heat water pump (12) is also connected to the cooling channel inlet of the vacuumizing device (8), and the cooling channel outlet of the vacuumizing device (8) is connected to the tube side inlet of the evaporator of the secondary heat pump (9).

7. The system for recovery of flue gas residual heat from desulphurization slurry according to any one of claims 1 to 3, characterized in that, The tube side outlet of the condenser of the primary absorption heat pump (4) and the tube side outlet of the condenser of the secondary heat pump (9) are both connected to the water inlet of a hot water boiler (3).

8. The system for recovery of flue gas residual heat in stages with deep desulfurization slurry according to claim 5, characterized in that, The slurry main pipe and the slurry return pipe merge before entering the desulfurization tower (1).

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