Desulfurization wastewater treatment system and method for cross-system waste heat integrated utilization

Abstract

The present disclosure provides a desulfurization wastewater treatment system and method for cross-system waste heat integrated utilization. The system comprises a waste heat recovery unit, a multi-effect evaporation unit and a condensation unit. The waste heat recovery unit adopts an absorption heat pump, the evaporator of which is connected with the circulating water system of the power plant to recover the waste heat of the circulating water, and the absorber and condenser thereof are used to output the heat after being warmed up; the multi-effect evaporation unit comprises at least two evaporators connected in series, the heat source inlet of the first-effect evaporator is connected with the heat output end of the absorption heat pump, and the recovered waste heat is used to evaporate and concentrate the desulfurization wastewater; and the secondary steam generated by the last-effect evaporator is recovered as fresh water after being condensed. The present disclosure uses the absorption heat pump to upgrade the low-grade waste heat of the circulating water of the power plant to a high grade, and uses the upgraded waste heat as the heat source for the evaporation of the desulfurization wastewater, thereby realizing the cross-system waste heat integrated utilization, greatly reducing the energy consumption and operation cost of the desulfurization wastewater zero discharge treatment, and simultaneously realizing the efficient recovery of water resources.

Description

Technical Field

[0001] This disclosure belongs to the field of wastewater treatment and waste heat utilization technology, specifically relating to a desulfurization wastewater treatment system and method for cross-system waste heat integrated utilization. Background Technology

[0002] Desulfurization wastewater generated by wet desulfurization processes in coal-fired power plants is characterized by high salinity, high suspended solids, and heavy metal enrichment, making it one of the most difficult wastewaters to treat in power plants. With increasingly stringent environmental policies, zero discharge of desulfurization wastewater has become an inevitable requirement for the green transformation of the power industry.

[0003] Currently, the mainstream technologies for zero discharge of desulfurization wastewater include thermal-based processes (such as multi-effect evaporation (MED) and mechanical vapor recompression (MVR)) and membrane-coupled thermal processes. Among these, the thermal evaporation and concentration stage is extremely energy-intensive, typically consuming 100-150 kWh (as steam) per ton of water treated, accounting for 60%-70% of the total operating cost of a zero-discharge system. This high energy consumption has become a major bottleneck restricting the large-scale application of zero-discharge technology for desulfurization wastewater.

[0004] Coal-fired power plants possess a large amount of low-grade waste heat resources, such as turbine exhaust heat (approximately 30-50℃), circulating water waste heat (approximately 25-40℃), and air compressor waste heat. These waste heat resources are abundant and widespread, but due to their low grade, they are difficult to directly use to drive the evaporation and concentration process of desulfurization wastewater. While some existing technologies attempt to utilize flue gas waste heat for wastewater evaporation, this technology is highly susceptible to fluctuations due to unit load and requires atomization evaporation within the flue, posing a risk to dust removal efficiency and fly ash quality. Furthermore, low-grade heat sources such as circulating water waste heat and turbine exhaust heat have not yet been effectively utilized.

[0005] Therefore, developing a technical solution that can fully utilize the low-grade waste heat of power plants, achieve cross-system energy integration, and reduce the energy consumption of desulfurization wastewater treatment has significant engineering application value. Summary of the Invention

[0006] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a desulfurization wastewater treatment system and method that integrates and utilizes waste heat across systems.

[0007] A first aspect of this disclosure provides a desulfurization wastewater treatment system that integrates waste heat utilization across systems. The system comprises: a waste heat recovery unit, a multi-effect evaporation unit, and a condensation unit connected in sequence; wherein... The heat input terminal of the waste heat recovery unit is used to connect to the power plant's circulating water system to recover low-grade waste heat from the circulating water and output the heated heat. The multi-effect evaporation unit is connected to the heat output end of the waste heat recovery unit and the desulfurization wastewater system, respectively, to use the recovered waste heat to evaporate and concentrate the desulfurization wastewater, and at the same time use the secondary steam generated by evaporation as a heat source. The steam inlet of the condensing unit is connected to the steam outlet of the multi-effect evaporating unit, and is used to condense the secondary steam generated by the multi-effect evaporating unit into fresh water.

[0008] Optionally, the waste heat recovery unit includes an evaporator, an absorber, a condenser, a generator, and a solution heat exchanger; wherein, The heat source side of the evaporator is connected to the power plant's circulating water system to recover low-grade waste heat from the circulating water. The refrigerant vapor outlet of the generator is connected to the refrigerant inlet of the condenser, the refrigerant liquid of the condenser is connected to the refrigerant inlet of the evaporator, and the refrigerant vapor outlet of the evaporator is connected to the refrigerant inlet of the absorber. The hot water channel of the absorber and the hot water channel of the condenser are connected in parallel to form the heat output end of the waste heat recovery unit.

[0009] Optionally, the waste heat recovery unit employs an absorption heat pump.

[0010] Optionally, the lithium bromide absorption heat pump or the ammonia absorption heat pump is used. The lithium bromide absorption heat pump is suitable for operating conditions with an output temperature of 80-150℃ and has a high degree of matching with the heat source requirements of the multi-effect evaporator.

[0011] Optionally, a preheater is provided between the desulfurization wastewater system and the multi-effect evaporation unit; wherein, The preheater is connected to the heat output terminals of the absorber, the condenser, and the steam heat source output terminal of the multi-effect evaporation unit, respectively, and is used to raise the feed temperature of the desulfurization wastewater to near boiling before sending it into the multi-effect evaporation unit.

[0012] Optionally, the multi-effect evaporation unit includes at least two stages of evaporators connected in series, with the heat source inlet of the first-effect evaporator connected to the heat output terminal of the waste heat recovery unit and the preheater, respectively. The heat source inlet of the after-effect evaporator is connected to the secondary steam outlet of the first-effect evaporator, and its outlet is connected to the condensation unit. The steam outlet of each stage of the evaporator is connected to the preheater, and an exhaust valve is provided between the evaporator and the preheater.

[0013] Optionally, the multi-effect evaporation unit includes at least two evaporators connected in series, with the heat source inlet of the first-effect evaporator connected to the heat output terminal of the waste heat recovery unit, and the heat source inlet of the subsequent-effect evaporator connected to the secondary steam outlet of the first-effect evaporator.

[0014] Optionally, the multi-effect evaporation unit is a triple-effect evaporator, a quadruple-effect evaporator, or a quintuple-effect evaporator.

[0015] Optionally, the evaporators in a triple-effect, quadruple-effect, or five-effect evaporator can be falling film evaporators, rising film evaporators, or forced circulation evaporators. The more effects, the higher the thermal energy utilization rate, but the equipment investment also increases accordingly. An appropriate number of effects can be selected based on the power plant's waste heat resources and the scale of desulfurization wastewater treatment.

[0016] Optionally, the system further includes a vapor compression unit. The inlet of this vapor compression unit is connected to the subsequent evaporator, and its outlet is connected to both the condensing unit and the first-effect evaporator. This unit mechanically compresses the secondary steam from the subsequent evaporator to increase its temperature and pressure, and then returns a portion of the secondary steam to the first-effect evaporator as a supplementary heat source. This configuration allows for the supplementation of heat through mechanical vapor compression when the absorption heat pump output is insufficient or when the unit is operating at low load, ensuring stable system operation.

[0017] Optionally, a circulating water bypass pipeline is provided between the waste heat recovery unit and the power plant's circulating water system. A flow regulating valve is installed on the bypass pipeline to adjust the circulating water flow rate entering the absorption heat pump evaporator. By adjusting the circulating water flow rate, it is possible to adapt to changes in power plant unit load and fluctuations in desulfurization wastewater treatment volume, thereby achieving flexible adjustment of the heat output of the heat pump.

[0018] Optionally, a flow control valve is installed on the wastewater inlet pipe of the desulfurization wastewater system and the multi-effect evaporator to regulate the flow rate of the desulfurization wastewater.

[0019] Optionally, the system further includes a control unit; wherein, The control unit includes a controller, and a temperature sensor, a pressure sensor, and a flow sensor, which are electrically connected to the controller respectively. The temperature sensors are installed at the heat source inlet and outlet and the wastewater inlet and outlet of each evaporator to detect the temperature at the heat source and wastewater inlet and outlet sides. The pressure sensor is installed on the steam side of each evaporator and is used to detect the evaporation pressure of each evaporator. The flow sensors are installed in the circulating water bypass pipe and the wastewater inlet pipe, respectively, to detect the circulating water flow and the wastewater inlet flow. The controller is used to control each actuator based on the detection results of the temperature sensor, the pressure sensor, and the flow sensor.

[0020] Optionally, the system further includes: a control unit connected to the waste heat recovery unit, the multi-effect evaporation unit, and the condensation unit respectively; wherein, The control unit includes a controller and a temperature sensor, a pressure sensor, and a flow sensor electrically connected to the controller, respectively, for dynamically adjusting the operating parameters of the absorption heat pump and the operating conditions of the evaporator according to changes in power plant load and fluctuations in the quality of desulfurization wastewater.

[0021] Optionally, the control unit is equipped with a digital twin-based intelligent control model to predict in real time the matching status between the heat output of the heat pump and the heat load of the evaporation unit, and to automatically adjust the system operating parameters.

[0022] A second aspect of this disclosure proposes a method for treating desulfurization wastewater through cross-system waste heat integrated utilization, the method comprising: Low-grade waste heat in the power plant's circulating water is recovered using a waste heat recovery unit, and the low-grade waste heat is upgraded to high-grade heat. The high-grade heat is used as the heat source of the multi-effect evaporation unit to concentrate desulfurization wastewater through multi-effect evaporation and generate secondary steam. The secondary steam is condensed into fresh water using a condensation unit, which is then used for power plant makeup water or circulating water replenishment.

[0023] Optionally, the method further includes: dynamically adjusting the flow rate of circulating water entering the absorption heat pump evaporator according to the load changes of the power plant unit, so that the heat output by the absorption heat pump matches the heat load required by the multi-effect evaporation unit.

[0024] The desulfurization wastewater treatment system and method proposed in this disclosure, which integrates waste heat utilization across systems, has the following advantages over existing technologies: First, this disclosure utilizes an absorption heat pump to raise the low-grade waste heat (25-40℃) of power plant circulating water to a high-grade heat of 80-150℃, which serves as the heat source for the multi-effect evaporation unit, thus achieving integrated utilization of waste heat across systems. This solution fully utilizes the existing low-grade waste heat resources of the power plant, significantly reducing the dependence on external steam or electricity for zero-discharge treatment of desulfurization wastewater. While consuming a similar amount of high-grade steam as conventional steam-driven multi-effect evaporation, it additionally recovers the waste heat of circulating water that would otherwise be discharged into the environment, achieving resource utilization of waste heat. It also significantly reduces the heat load of the cooling system and the evaporation loss of makeup water, reducing the energy consumption per ton of water treated to 30-50 kWh, which is more than 40% more energy-efficient than traditional thermal processes.

[0025] Secondly, this disclosure adopts a process route that couples an absorption heat pump with a multi-effect evaporation unit. Compared with the scheme of directly utilizing the waste heat of flue gas, it avoids the impact of flue gas evaporation on dust removal efficiency and fly ash quality, and is not affected by the severe interference of unit load fluctuations, resulting in higher system operation stability.

[0026] Third, this disclosure further optimizes the thermal efficiency and adaptability of the system by setting up a preheater, a steam compression unit, and an intelligent control unit. The preheater utilizes waste heat to preheat the feed wastewater; the steam compression unit can supplement heat under low load conditions; and the intelligent control system based on digital twins achieves precise matching between heat pump output and evaporation load, ensuring efficient and stable operation of the system across the entire operating range.

[0027] Fourth, this disclosure reuses the freshwater generated by evaporation and condensation for power plant makeup water or circulating water replenishment, realizing the recycling of water resources and having significant environmental and economic benefits. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the desulfurization wastewater treatment system with cross-system waste heat integrated utilization according to Embodiment 1 of this disclosure; Figure 2 This is a flowchart of the desulfurization wastewater treatment method for cross-system waste heat integrated utilization according to Embodiment 3 of this disclosure. Detailed Implementation

[0029] Example 1 like Figure 1 As shown, this embodiment provides a desulfurization wastewater treatment system that integrates waste heat utilization across systems. The system includes: a waste heat recovery unit 100, a multi-effect evaporation unit 200, a condensation unit 300, a preheater 400, and a control unit 500.

[0030] The waste heat recovery unit 100 uses a lithium bromide absorption heat pump. The lithium bromide absorption heat pump is suitable for operating conditions with an output temperature of 80-150℃ and has a high degree of matching with the heat source requirements of the multi-effect evaporator. In other words, the waste heat recovery unit collects low-grade heat and raises the heat to the preset temperature to provide a driving heat source for the subsequent evaporation and concentration system.

[0031] Specifically, such as Figure 1 As shown, the waste heat recovery unit 100 includes an evaporator 110, an absorber 120, a condenser 130, a generator 140, and a solution heat exchanger 150.

[0032] Among them, such as Figure 1 As shown, the heat source side of the evaporator 110 is connected to the power plant's circulating water system 600 via a circulating water bypass pipe for recovering low-grade waste heat from the circulating water. A flow regulating valve 111 is installed on the bypass pipe to regulate the flow rate of the circulating water entering the absorption heat pump evaporator. By adjusting the circulating water flow rate, it is possible to adapt to changes in the power plant unit load and fluctuations in the amount of desulfurization wastewater treated, thus achieving flexible adjustment of the heat output of the heat pump. In this way, after the circulating water (approximately 35-40℃) enters the evaporator 110, the heat is absorbed by the working fluid, and the circulating water returns to the circulating water system after its temperature decreases.

[0033] Secondly, such as Figure 1 As shown, the connection relationships of the various structures in the waste heat utilization unit in the refrigerant cycle section are as follows: The refrigerant vapor outlet of generator 140 is connected to the refrigerant inlet of condenser 130. Heated by a driving heat source, the refrigerant (water) in the dilute lithium bromide solution evaporates into vapor and is sent to condenser 130. The refrigerant liquid outlet of condenser 130, after passing through a throttling device, is connected to the refrigerant inlet of evaporator 110. The refrigerant vapor condenses into liquid in the condenser, and the released heat is carried away by the hot water channel, raising the supply water temperature. The refrigerant vapor outlet of evaporator 110 is connected to the refrigerant inlet of absorber 120. The refrigerant liquid absorbs the low-grade waste heat from the power plant's circulating water in the evaporator, evaporates into vapor, and is sent to absorber 120. After absorbing the refrigerant vapor, the concentrated lithium bromide solution in absorber 120 is diluted, releasing heat to further heat the supply water, thus completing the refrigerant cycle. In other words, the refrigerant vapor generated by generator 140 enters condenser 130 for condensation and releases heat; the refrigerant liquid coming out of condenser 130 returns to evaporator 110 after throttling, absorbs heat from the power plant's circulating water again, evaporates into vapor, and is sent to absorber 120 to complete the refrigerant cycle.

[0034] Secondly, such as Figure 1 As shown, in the solution loop section, the connection relationships of each structure in the residual heat utilization unit are as follows: The dilute solution outlet of absorber 120 is connected to the cold-side inlet of solution heat exchanger 150. After the absorber absorbs refrigerant vapor, the lithium bromide solution concentration decreases, forming a dilute solution, which is then fed into the cold-side inlet of solution heat exchanger 150. The cold-side outlet of solution heat exchanger 150 is connected to the dilute solution inlet of generator 140, allowing the preheated dilute solution to be fed into generator 140. The concentrated solution outlet of generator 140 is connected to the hot-side inlet of solution heat exchanger 150. After the water in the dilute solution heated by the driving heat source evaporates, a high-temperature concentrated solution is formed and fed into the hot-side inlet of solution heat exchanger 150. The hot-side outlet of solution heat exchanger 150 is connected to the concentrated solution inlet of absorber 120, utilizing the high-temperature concentrated solution discharged from the generator to preheat the low-temperature dilute solution entering the generator, recovering heat and improving heat pump efficiency, thereby forming a complete solution circulation loop. In other words, the dilute solution in the absorber is sent to the generator for heating. After the water evaporates, it becomes a concentrated solution, which is cooled by the solution heat exchanger and then returns to the absorber. The refrigerant vapor from the generator enters the condenser for condensation, releasing heat. The refrigerant liquid from the condenser is throttled and returns to the evaporator to absorb heat from the circulating water again, completing the cycle.

[0035] In addition, the absorber 120 and condenser 130 output heat (approximately 90-120°C) after heating, which together constitutes the heat output end of the waste heat recovery unit. This heat is connected to the multi-effect evaporator 200 through a hot water circulation pipeline, outputting a portion of the heated heat. Simultaneously, this heat output end is also connected to the discharge pipeline of the desulfurization wastewater system, outputting another portion of the heated heat as a heating source for the desulfurization wastewater discharged from the system.

[0036] Furthermore, such as Figure 1 As shown, the hot water (temperature approximately 90-120°C) output from the absorber and condenser does not directly enter the multi-effect evaporation unit. Instead, it is first introduced into a closed flash tank. Specifically, the heat output ends of the absorber 120 and condenser 130 in the waste heat recovery unit 100 of this embodiment are connected to one end of the flash tank 900, while the other end of the flash tank 900 is connected to the first-effect evaporator 210 in the multi-effect evaporation unit 200. This is used to flash the hot water output from the waste heat recovery unit 100 into saturated steam at the corresponding pressure, which is then directly output to the multi-effect evaporation unit 200.

[0037] It should be noted that in this embodiment, the flash tank maintains a vacuum level corresponding to the heating steam pressure required by the first-effect evaporator in the multi-effect evaporation unit, allowing high-temperature hot water to flash-evaporate instantly, generating saturated steam at the corresponding pressure. This saturated steam, as a clean and constant-temperature heat source, enters the shell side of the first-effect evaporator, where condensation and heat release drive the evaporation of wastewater. The unevaporated hot water in the flash tank is circulated back to the absorption heat pump for further heating, or used to preheat desulfurization wastewater.

[0038] Furthermore, in some preferred embodiments, such as Figure 1 As shown, the system also includes a preheater 400, which is located between the feed pipe of the desulfurization wastewater system 800 and the multi-effect evaporation unit 200. One heat source input end of the preheater 400 is connected to the heat output end (i.e., condensate output end) of the absorber 120 and condenser 130, and the other heat source input end is connected to the steam heat source output end of the multi-effect evaporation unit. Simultaneously, the output end of the preheater is connected to the first-effect evaporator 210 in the multi-effect evaporator. In other words, the heat source of the preheater 400 is taken from a portion of the hot water output from the absorber 120 and condenser 130 of the absorption heat pump, or a portion of the secondary steam extracted from each stage of the multi-effect evaporator. Based on these heat sources, the desulfurization wastewater is preheated from ambient temperature to approximately 80°C before entering the first-effect evaporator 210, reducing the heat load on the first-effect evaporator and further improving the system's thermal efficiency.

[0039] It is easy to understand that a flow control valve 211 should also be installed on the wastewater inlet pipe between the preheater 400 and the desulfurization wastewater system 800 to control the flow rate of the desulfurization wastewater.

[0040] It should be noted that the multi-effect evaporation unit in this embodiment can preferably be an evaporator with at least two stages connected in series. The heat source inlet of the first-effect evaporator is connected to the heat output end of the waste heat recovery unit, and the heat source inlet of the second-effect evaporator is connected to the secondary steam outlet of the first-effect evaporator. This is used to evaporate and concentrate the desulfurization wastewater using the recovered waste heat. The second-effect evaporator uses the secondary steam generated by the first-effect evaporator as a heat source. In addition, the steam outlet of each stage of the evaporator is also connected to the preheater.

[0041] It should be further clarified that the first-effect evaporator here refers to the first-stage evaporator, and the subsequent evaporators refer to one or more evaporators connected in sequence after the first-effect evaporator.

[0042] It should be noted that the multi-effect evaporation unit in this embodiment can be a three-effect evaporator, a four-effect evaporator, or a five-effect evaporator; each effect evaporator can be a falling film evaporator, a rising film evaporator, or a forced circulation evaporator. The more effects, the higher the thermal energy utilization rate, but the equipment investment also increases accordingly. An appropriate number of effects can be selected based on the power plant's waste heat resources and the scale of desulfurization wastewater treatment.

[0043] In some preferred embodiments, such as Figure 1 As shown, the multi-effect evaporation unit in this example includes three evaporators connected in series: a first-effect evaporator 210, a second-effect evaporator 220, and a third-effect evaporator 230. Each evaporator is a falling film evaporator. The heat source inlet of the first-effect evaporator 210 is connected to the steam output end of the flash tank 900 and the preheater 400, respectively, to utilize recovered waste heat for evaporation and concentration of desulfurization wastewater. The secondary steam generated by the first-effect evaporator 210 serves as the heat source for the second-effect evaporator 220, and the secondary steam generated by the second-effect evaporator 220 serves as the heat source for the third-effect evaporator 230. Each evaporator has a concentrated brine discharge port at its bottom for discharging the concentrated high-salt wastewater, which is then sent to the subsequent crystallization unit for treatment. In other words, the desulfurization wastewater to be treated enters the first-effect evaporator to begin the evaporation and concentration process, producing steam (clear liquid) and wastewater concentrate. Then, the steam generated by the first-effect evaporator is used as a heat source to continue evaporating the wastewater, producing steam (clear liquid) and wastewater concentrate again. The steam generated by the second-effect evaporator is then used as a heat source to further evaporate the wastewater, producing steam (clear liquid) and the final wastewater concentrate. The wastewater concentrate from each of the above evaporators enters the next effect in sequence for further concentration, achieving step-by-step concentration and significantly reducing steam consumption.

[0044] It should also be noted that steam extraction valves should be installed on the steam connection pipelines between the first-effect evaporator 210, the second-effect evaporator 220, and the third-effect evaporator 230 and the preheater 400, so as to provide steam extraction heat source when the heat source provided by the waste heat recovery unit to the preheater is insufficient.

[0045] Furthermore, such as Figure 1As shown, the condensation unit 300 includes a surface condenser 310, a crystallizer 320, and a freshwater storage tank 330. The surface condenser 310 is connected to the steam outlet of the steam compression unit 700 and the wastewater concentrate outlet of the triple-effect evaporator 230, and is used to receive pressurized secondary steam and wastewater concentrate. It is also connected to an external cooling system to receive external cooling water. In this way, the secondary steam is condensed into distilled water through the convection exchange of cooling water. This distilled water is sent to the freshwater storage tank 330 for recycling and can be reused as makeup water for power plant circulating water or boiler feedwater. At the same time, the high-temperature wastewater concentrate is cooled by cooling water and sent to the crystallizer 320, where it is cooled / evaporated to crystallize and precipitate crystalline salts. Meanwhile, the desulfurization wastewater mother liquor is returned to the desulfurization wastewater system 800, while the circulating cooling water further flows to the power plant circulating water system 600.

[0046] In some preferred embodiments, such as Figure 1 As shown, the system also includes a vapor compression unit 700, which is located between the triple-effect evaporator 230 and the surface condenser 310, and includes a vapor compressor. When the absorption heat pump output is insufficient or the unit is operating at low load, the vapor compressor mechanically compresses the secondary steam in the triple-effect evaporator, increasing its temperature and pressure, and then partially returns it to the first-effect evaporator 210 as a supplementary heat source to maintain stable system operation. This arrangement allows for the supplementation of some heat through mechanical vapor compression when the absorption heat pump output is insufficient or the unit is operating at low load, ensuring stable system operation.

[0047] In other preferred embodiments, such as Figure 1 As shown, the system also includes a control unit 500, which comprises a controller, a temperature sensor, a pressure sensor, and a flow sensor. The controller is electrically connected to the temperature sensor, pressure sensor, flow sensor, and the actuators of each unit. The temperature sensor is located at the heat source inlet and outlet and wastewater inlet and outlet of each evaporator effect to detect the temperature at these locations. The pressure sensor is located on the steam side of each evaporator effect to detect the evaporation pressure. The flow sensor is located in the circulating water bypass pipe and wastewater inlet pipe to detect the inlet flow rate of the circulating water suction and wastewater inlet systems. These detection results are fed back to the controller, which controls the actions of each unit based on the feedback data. The actuators include flow regulating valves, steam compressors, absorption heat pump actuators, and unit valves. Thus, the controller controls the actuators based on the feedback data from the sensors, achieving closed-loop control of the system. For example, the controller is electrically connected to each sensor, valve, steam compressor, and absorption heat pump actuator to dynamically adjust the operating parameters of the absorption heat pump and the operating conditions of the evaporator according to changes in power plant load and fluctuations in desulfurization wastewater quality.

[0048] It should be noted that the controller in this example is equipped with a digital twin-based intelligent control model. This model integrates the thermodynamic model of the absorption heat pump, the heat and mass transfer model of the multi-effect evaporator, and machine learning algorithms based on historical operating data. By acquiring sensor data in real time, the digital twin model can predict the matching state between the heat output of the heat pump and the heat load of the evaporation unit, and automatically adjust the circulating water bypass flow rate, the amount of steam driven by the heat pump, and the speed of the steam compressor, so that the system always operates under optimal conditions, enabling accurate prediction and optimized control of the system's operating status.

[0049] The process flow of the system in this embodiment is as follows: After pretreatment, the desulfurization wastewater first enters the preheater 400, where it exchanges heat with a portion of the hot water output from the waste heat recovery unit 100 (absorption heat pump), preheating it to approximately 80°C. The preheated wastewater then enters the first-effect evaporator 210, where it is heated and evaporated by the hot water provided by the waste heat recovery unit 100, generating secondary steam. The secondary steam generated in the first effect serves as the heat source for the second-effect evaporator 220, and the secondary steam generated in the second effect serves as the heat source for the third-effect evaporator 230. Each evaporator continuously concentrates the wastewater. The secondary steam generated in the last effect is upgraded by the steam compressor 710 (if necessary), with a portion recycled back to the first effect, and the remainder condensed into fresh water in the surface condenser 310. The collected fresh water is then reused in the power plant's circulating water system.

[0050] On the waste heat recovery side, a portion of the circulating water (approximately 35-40°C) from the power plant's circulating water system enters the evaporator 110 of the waste heat recovery unit 100 via a bypass pipe. After releasing heat, the temperature drops to approximately 28-30°C before returning to the circulating water system. The waste heat recovery unit 100 is driven by a small amount of high-pressure steam (approximately 0.5-0.8 MPa) to raise the recovered circulating water waste heat to 90-120°C, which is then supplied to the multi-effect evaporator unit via a hot water circulation pipeline. Based on changes in the power plant unit load, the controller automatically adjusts the circulating water bypass flow rate to match the heat output of the heat pump with the evaporator unit's requirements.

[0051] Example 2 The difference between this embodiment and Embodiment 1 is that the absorption heat pump uses an ammonia absorption heat pump, which is suitable for operating conditions with higher output temperatures (up to 150°C or higher) and can be used to drive more efficient multi-effect evaporation systems or multi-effect crystallization systems. The multi-effect evaporation unit 200 in this embodiment uses a five-effect evaporator, further improving thermal energy utilization.

[0052] Example 3 This embodiment provides a desulfurization wastewater treatment method that integrates waste heat utilization across systems, such as... Figure 2 As shown, it includes the following steps: S100, Low-grade waste heat recovery steps: Utilize the evaporator of an absorption heat pump to recover low-grade waste heat from the power plant's circulating water.

[0053] Specifically, a portion of the circulating water (approximately 35-40°C) is drawn from the power plant's circulating water system and fed into the absorption heat pump evaporator to release heat. After the temperature decreases, the water returns to the circulating water system. The absorption heat pump is driven by a small amount of high-pressure steam to raise the recovered waste heat to a high-grade heat of 90-120°C, which is then output through the absorber and condenser.

[0054] S200 Wastewater Preheating Step: The desulfurization wastewater is fed into the preheater, and the wastewater is preheated to near the boiling point temperature by using part of the heat output from the absorption heat pump or part of the secondary steam extracted from the multi-effect evaporation unit.

[0055] S300 Multi-Effect Evaporation and Concentration Steps: The preheated desulfurization wastewater is sent to the first-effect evaporator of the multi-effect evaporation unit, where high-grade heat from an absorption heat pump is used as the heat source for evaporation and concentration. The secondary steam generated by the first-effect evaporator serves as the heat source for the second-effect evaporator, and the process is repeated step-by-step to achieve multi-effect evaporation. The secondary steam generated by the final-effect evaporator is upgraded in grade by a steam compression unit (as needed), with some of it being reused in the previous-effect evaporators and the remainder entering the condensation unit.

[0056] S400, Condensation Recovery Step: The secondary steam (or steam after steam compression) generated by the last-effect evaporator is passed into a surface condenser and condensed into fresh water. The collected fresh water is reused as makeup water for power plant circulating water or boiler feedwater.

[0057] S500 Intelligent Control Steps: Based on the changes in power plant unit load and the fluctuations in desulfurization wastewater quality, the system uses a digital twin model to predict in real time the matching status between the heat output of the heat pump and the heat load of the evaporation unit, and automatically adjusts the bypass flow of circulating water, the amount of steam driven by the absorption heat pump, and the operating parameters of the steam compressor, so that the system can operate efficiently and stably across the entire operating range.

[0058] The desulfurization wastewater treatment system and method proposed in this disclosure, which integrates waste heat from multiple systems, utilizes an absorption heat pump to upgrade the grade of low-grade waste heat from power plant circulating water and other sources, using it as a heat source for a multi-effect evaporation unit. This achieves cross-system energy integration and cascade utilization, significantly reducing energy consumption and operating costs for zero-discharge treatment of desulfurization wastewater. Furthermore, the system possesses flexible adjustment capabilities and intelligent control functions, enabling it to adapt to changes in power plant unit load and fluctuations in desulfurization wastewater quality, thus demonstrating broad application prospects.

[0059] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A desulfurization wastewater treatment system for cross-system waste heat integrated utilization, characterized in that, The system includes a waste heat recovery unit, a multi-effect evaporation unit, and a condensation unit connected in sequence; wherein... The heat input terminal of the waste heat recovery unit is used to connect to the power plant's circulating water system to recover low-grade waste heat from the circulating water and output the heated heat. The multi-effect evaporation unit is connected to the heat output end of the waste heat recovery unit and the desulfurization wastewater system, respectively, to use the recovered waste heat to evaporate and concentrate the desulfurization wastewater, and at the same time use the secondary steam generated by evaporation as a heat source. The steam inlet of the condensing unit is connected to the steam outlet of the multi-effect evaporating unit, and is used to condense the secondary steam generated by the multi-effect evaporating unit into fresh water.

2. The system according to claim 1, characterized in that, The waste heat recovery unit includes an evaporator, an absorber, a condenser, a generator, and a solution heat exchanger; wherein, The heat source side of the evaporator is connected to the power plant's circulating water system to recover low-grade waste heat from the circulating water. The refrigerant vapor outlet of the generator is connected to the refrigerant inlet of the condenser, the refrigerant liquid of the condenser is connected to the refrigerant inlet of the evaporator, and the refrigerant vapor outlet of the evaporator is connected to the refrigerant inlet of the absorber. The hot water channel of the absorber and the hot water channel of the condenser are connected in parallel to form the heat output end of the waste heat recovery unit.

3. The system according to claim 2, characterized in that, A preheater is provided between the desulfurization wastewater system and the multi-effect evaporation unit; wherein... The preheater is connected to the heat output terminals of the absorber, the condenser, and the steam heat source output terminal of the multi-effect evaporation unit, respectively, and is used to raise the feed temperature of the desulfurization wastewater to near boiling before sending it into the multi-effect evaporation unit.

4. The system of claim 3, wherein, The multi-effect evaporation unit includes at least two stages of evaporators connected in series, with the heat source inlet of the first-effect evaporator connected to the heat output terminal of the waste heat recovery unit and the preheater, respectively. The heat source inlet of the after-effect evaporator is connected to the secondary steam outlet of the first-effect evaporator, and its outlet is connected to the condensation unit. The steam outlet of each stage of the evaporator is connected to the preheater, and an exhaust valve is provided between the evaporator and the preheater.

5. The system of claim 4, wherein, A flash tank is also provided between the waste heat recovery unit and the multi-effect evaporation unit; The hot water inlet of the flash tank is connected to the heat output end of the absorber and condenser, and is used to flash the hot water output by the waste heat recovery unit into saturated steam at the corresponding pressure. The steam outlet of the flash tank is connected to the heat source inlet of the first-effect evaporator of the multi-effect evaporation unit.

6. The system of claim 4, wherein, The system also includes a vapor compression unit. The inlet of the vapor compression unit is connected to the after-effect evaporator, and its outlet is connected to the condensation unit and the first-effect evaporator, respectively. The vapor compression unit is used to mechanically compress the secondary steam of the after-effect evaporator to increase its temperature and pressure, and then send part of the secondary steam back to the first-effect evaporator as a supplementary heat source.

7. The system according to any of claims 1-6, characterized in that, A flow regulating valve is installed on the circulating water bypass pipeline between the waste heat recovery unit and the power plant's circulating water system to regulate the flow rate of the circulating water entering the absorption heat pump evaporator. The desulfurization wastewater system and the wastewater inlet pipe of the multi-effect evaporator are equipped with flow control valves to regulate the flow rate of the desulfurization wastewater.

8. The system of claim 7, wherein, The system also includes a control unit; wherein... The control unit includes a controller, and a temperature sensor, a pressure sensor, and a flow sensor, which are electrically connected to the controller respectively. The temperature sensors are installed at the heat source inlet and outlet and the wastewater inlet and outlet of each evaporator to detect the temperature at the heat source and wastewater inlet and outlet sides. The pressure sensor is installed on the steam side of each evaporator and is used to detect the evaporation pressure of each evaporator. The flow sensors are installed in the circulating water bypass pipe and the wastewater inlet pipe, respectively, to detect the circulating water flow and the wastewater inlet flow. The controller is used to control each actuator based on the detection results of the temperature sensor, the pressure sensor, and the flow sensor.

9. A desulfurization wastewater treatment method for cross-system waste heat integrated utilization, characterized in that, The method includes: Low-grade waste heat in the power plant's circulating water is recovered using a waste heat recovery unit, and the low-grade waste heat is upgraded to high-grade heat. The high-grade heat is used as the heat source of the multi-effect evaporation unit to concentrate desulfurization wastewater through multi-effect evaporation and generate secondary steam. The secondary steam is condensed into fresh water using a condensation unit, which is then used for power plant makeup water or circulating water replenishment.

10. The method of claim 9, wherein, The method further includes: dynamically adjusting the flow rate of circulating water entering the absorption heat pump evaporator according to the load changes of the power plant unit, so that the heat output of the absorption heat pump matches the heat load required by the multi-effect evaporation unit.

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