Power plant multi-source waste heat collaborative recovery system and method based on slurry flash evaporation

Abstract

The invention discloses a power plant multi-source waste heat collaborative recovery system and method based on slurry flash evaporation, and relates to the technical field of thermal power plant energy conservation, the system comprises a flue gas waste heat recovery unit, the flue gas waste heat recovery unit comprises a flash evaporation tank, the slurry inlet and outlet of the flash evaporation tank is connected with a desulfurization tower, and the dead steam outlet of the flash evaporation tank is connected with a steam collecting cylinder; the deaerator exhaust waste heat recovery unit comprises a deaerator, a deaerator exhaust steam heat exchanger and a condensate water tank which are connected in sequence, and the condensate water tank is connected with the flash tank; the continuous drainage waste heat recovery unit comprises a continuous drainage flash tank and a continuous drainage multi-stage flash tank, and a dead steam outlet of the continuous drainage multi-stage flash tank is connected with the steam collecting cylinder; according to the method, waste heat from different sources is subjected to collaborative optimization recovery, the recovery efficiency of the waste heat is effectively improved, the equipment corrosion risk is reduced, and full recovery of continuous drainage is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy conservation in thermal power plants, and in particular relates to a system and method for collaboratively recovering multi-source waste heat from a power plant based on slurry flash evaporation. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] At present, power plants generate a lot of waste heat during operation, which comes from many aspects, such as low-temperature flue gas waste heat, deaerator exhaust waste heat, and continuous drainage waste heat. How to efficiently utilize this waste heat to improve energy efficiency and reduce environmental pollution has become an important issue facing the power industry.

[0004] Traditionally, waste heat utilization of deaerator exhaust is usually achieved by ejecting the deaerator exhaust or directly mixing it to heat cold water. However, there are significant technical bottlenecks in the above-mentioned waste heat utilization methods of deaerator exhaust. That is, due to the high oxygen content in the deaerator exhaust, the above-mentioned waste heat recovery methods do not release the oxygen in the deaerator exhaust, which can easily lead to corrosion of equipment, pipelines, etc., thereby shortening the service life of the waste heat recovery system.

[0005] In terms of waste heat recovery and utilization of continuous drainage, the existing technology generally adopts the method of flash evaporation in the continuous drainage tank to recover the waste heat. This treatment method can often only recover part of the heat in the continuous drainage, and there is still a large amount of waste heat that is not effectively utilized. In order to meet the emission requirements, it is also necessary to discharge it into a cooling pool for further cooling. At the same time, the recovery amount of continuous drainage is also limited, and the maximum utilization of water resources cannot be achieved. Summary of the invention

[0006] The purpose of the present invention is to provide a system and method for collaboratively recovering multi-source waste heat from a power plant based on slurry flash evaporation, which can effectively improve the recovery efficiency of waste heat, reduce the risk of equipment corrosion, and achieve full recovery and utilization of waste heat from different sources in the power plant through collaborative optimization and recovery.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions: In a first aspect, an embodiment of the present invention provides a system for coordinating the recovery of multi-source waste heat from a power plant based on slurry flash evaporation, comprising: The flue gas waste heat recovery unit comprises a flash tank, the slurry inlet and outlet of the flash tank are connected to the desulfurization tower, and the exhaust steam outlet of the flash tank is connected to the steam collecting cylinder; A deaerator exhaust waste heat recovery unit comprises a deaerator, a deaerator exhaust steam heat exchanger and a condensate tank connected in sequence, wherein the condensate tank is connected to the flash tank; The continuous blowdown waste heat recovery unit includes a continuous blowdown flash tank and a continuous blowdown multi-stage flash tank, and the exhaust steam outlet of the continuous blowdown multi-stage flash tank is connected to the steam collecting cylinder.

[0008] As a further technical solution, a multi-stage flash chamber is arranged in the continuous blowdown multi-stage flash tank, and the exhaust steam outlet of each stage of flash chamber is connected to the steam collecting cylinder.

[0009] As a further technical solution, a vacuum degree regulating valve is arranged at the exhaust steam outlet of each stage of flash chamber, and the pressure of the last stage of flash chamber is reduced to 5-8 kPa by a vacuum pump.

[0010] As a further technical solution, the steam outlet of the deaerator is connected to the deaerator exhaust steam heat exchanger, and in the deaerator exhaust steam heat exchanger, steam exchanges heat with condensate.

[0011] As a further technical solution, the steam outlet of the continuous blowdown flash tank is connected to the deaerator.

[0012] As a further technical solution, the steam collecting cylinder is connected to a lithium bromide heat pump, and the lithium bromide heat pump is connected to a vacuum pump.

[0013] As a further technical solution, an upper spray layer and a lower spray layer are arranged in the flash tank, the upper spray layer is connected to the condensate tank, and the lower spray layer is connected to the slurry outlet of the desulfurization tower.

[0014] In a second aspect, an embodiment of the present invention provides a method for collaborative recovery of multi-source waste heat in a power plant based on slurry flashing, including the following steps: The slurry in the flash tank enters the desulfurization tower to recover the waste heat of the flue gas, and the slurry after recovering the waste heat enters the flash tank for flashing. The flashed exhaust steam enters the steam collecting cylinder. The exhaust gas discharged from the deaerator exchanges heat through the deaerator exhaust steam heat exchanger, condenses into condensate and enters the condensate tank. The condensate in the condensate tank is pumped into the upper spray layer of the flash tank for spraying, and the oxygen in the condensate is discharged through the vacuum pump after being released. The continuous blowdown of the boiler enters the continuous blowdown flash tank for primary flashing. The continuous blowdown after flashing enters the multi-stage flash tank for multi-stage flashing. The steam generated by each stage of flashing enters the steam collecting cylinder, and the steam in the steam collecting cylinder enters the lithium bromide heat pump for heat release.

[0015] As a further technical solution, the temperature of the condensate generated by the deaerator exhaust steam heat exchanger is controlled at 40-50 °C.

[0016] As a further technical solution, the temperature of the continuous blowdown after primary flashing is 100-120 °C, and the temperature of the continuous blowdown after multi-stage flashing is 32-42 °C.

[0017] The beneficial effects of the above embodiments of the present invention are as follows: The multi-source waste heat collaborative recovery system for power plants based on slurry flash evaporation provided by the present invention deeply combines the slurry flash evaporation flue gas waste heat recovery technology with the deaerator exhaust waste heat and the continuous blowdown waste heat. One system realizes the comprehensive recovery of three kinds of waste heat in the power plant, significantly improves the energy utilization efficiency, and reduces energy waste; realizes the efficient collaborative recovery of multi-source waste heat, and fully utilizes the flue gas waste heat, the deaerator exhaust waste heat, and the continuous blowdown waste heat.

[0018] There is a problem in the traditional deaerator exhaust waste heat recovery method that oxygen in the deaerator exhaust cannot be precipitated, resulting in corrosion of equipment and pipelines. The present invention innovatively injects the high-oxygen condensate after heat exchange of the deaerator exhaust steam into the flash tank of the slurry flash evaporation system, and uses the negative pressure environment in the flash tank to release oxygen into the atmosphere, effectively reducing the oxygen content in the water, avoiding equipment corrosion, extending the service life of the equipment, and realizing the harmless recovery of water resources at the same time.

[0019] A large amount of waste heat in the existing continuous blowdown is still not utilized after flashing in the continuous blowdown tank, and the continuous blowdown discharge is large. The present invention uses the vacuum system of the slurry flash evaporation system to perform multi-stage flashing on the continuous blowdown, further improving the waste heat recovery efficiency. At the same time, the flashed steam is introduced into the absorption heat pump of the slurry flash evaporation system for waste heat recovery, increasing the superheat degree of the slurry flash evaporation steam, and recovering the clean water resources in the continuous blowdown by flashing.

[0020] The present invention continues to flash the continuous blowdown after cooling the continuous blowdown flash tank through the set continuous blowdown multi-stage flash tank. The flashed steam is mixed with the slurry flash evaporation steam from the flash tank after passing through the steam collector cylinder and then enters the lithium bromide heat pump together for heat release. This process realizes the deep recovery of continuous blowdown waste heat and water resources; in addition, a vacuum degree regulating valve is provided at the steam outlet of each stage of the flash chamber, which can adjust the pressure of different flash chambers in the continuous blowdown multi-stage flash tank according to the operating conditions, improving the flashing efficiency. Brief Description of the Drawings

[0021] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0022] Figure 1 It is the multi-source waste heat collaborative recovery system for power plants based on slurry flash evaporation of the present invention.

[0023] The schematic diagram is only for illustration; Among them, 1. desulfurization tower; 2. slurry circulation pump; 3. flash tank; 4. slurry reflux pump; 5. steam collector cylinder; 6. lithium bromide heat pump; 7. vacuum pump; 8. continuous blowdown flash tank; 9. continuous blowdown multi-stage flash tank; 10. continuous blowdown discharge pump; 11. vacuum degree regulating valve; 12. deaerator; 13. deaerator exhaust steam heat exchanger; 14. condensate tank; 15. condensate discharge pump. Detailed implementation mode

[0024] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0025] Embodiment 1 In a typical implementation mode of the present invention, as Figure 1 shown, a multi-source waste heat collaborative recovery system for a power plant based on slurry flashing is provided, including: A flue gas waste heat recovery unit, including a flash tank 3, the slurry inlet and outlet of the flash tank 3 are connected to the desulfurization tower 1, and the exhaust steam outlet of the flash tank 3 is connected to the steam collector cylinder 5; A deaerator exhaust waste heat recovery unit, including a deaerator 12, a deaerator exhaust steam heat exchanger 13 and a condensate tank 14 connected in sequence, and the condensate tank 14 is connected to the flash tank 3; A continuous blowdown waste heat recovery unit, including a continuous blowdown flash tank 8 and a continuous blowdown multi-stage flash tank 9, and the exhaust steam outlet of the continuous blowdown multi-stage flash tank 9 is connected to the steam collector cylinder 5.

[0026] Specifically, the slurry inlet of the flash tank 3 is connected to the slurry outlet at the bottom of the desulfurization tower 1, and a slurry circulation pump 2 is provided on the connected pipeline. Under the action of the slurry circulation pump 2, the slurry after recovering the flue gas waste heat enters the flash tank 3 for flashing. The slurry outlet of the flash tank 3 is connected to the slurry inlet at the top of the desulfurization tower 1, and a slurry reflux pump 4 is provided on the connected pipeline. Under the action of the slurry reflux pump 4, the flashed slurry enters the desulfurization tower 1 again to recover the waste heat of the flue gas.

[0027] In this embodiment, the steam outlet of the continuous blowdown flash tank 8 is connected to the deaerator. The steam generated after flashing is discharged from the top of the continuous blowdown flash tank 8 to the deaerator for utilization. The temperature of the continuous blowdown after flashing is reduced to 100-120 °C, and the cooled continuous blowdown enters the continuous blowdown multi-stage flash tank 9 to continue flashing.

[0028] In this embodiment, a multi-stage flash chamber is provided in the continuous drainage multi-stage flash tank 9. The exhaust steam outlets of each stage of flash chamber are connected to the steam collector cylinder 5, and a vacuum degree regulating valve 11 is provided at the exhaust steam outlet of each stage of flash chamber. The continuous drainage enters the first flash chamber on the top layer of the continuous drainage multi-stage flash tank 9 for flashing, and then sequentially enters the lower-stage flash chambers for flashing. The pressure in each stage of flash chamber is controlled by the opening degree of the vacuum degree regulating valve 11. Through the flashing in the multi-stage chambers in the continuous drainage multi-stage flash tank 9, the pressure of the last-stage flash chamber is reduced to 5-8 kPa by the vacuum pump 7.

[0029] In this embodiment, the steam outlet of the deaerator 12 is connected to the deaerator exhaust steam heat exchanger 13. In the deaerator exhaust steam heat exchanger, the steam exchanges heat with the condensed water. The steam is condensed into condensed water and enters the condensate tank 14. The condensate tank 14 is connected to the flash tank through the condensate discharge pump 15, and the condensed water enters the flash tank for flashing.

[0030] Further, an upper spray layer and a lower spray layer are provided in the flash tank 3. The upper spray layer is connected to the condensate tank 14, and the lower spray layer is connected to the slurry outlet of the desulfurization tower 1.

[0031] In this embodiment, the steam collector cylinder 5 is connected to the lithium bromide heat pump 6, and the lithium bromide heat pump 6 is connected to the vacuum pump 7. The non-condensable gas is periodically removed by the vacuum pump 7 to maintain a high-vacuum environment in the lithium bromide heat pump system, ensuring that the working medium (water) evaporates at a low temperature and maintaining the normal operation of the refrigeration cycle. Since the lithium bromide heat pump 6 is connected to the flash tank 3 and the continuous drainage multi-stage flash tank 9 through the steam collector cylinder, the vacuum pump 7 can maintain the negative pressure required for flashing in the flash tank 3 and the continuous drainage multi-stage flash tank 9.

[0032] The working process of the power plant multi-source waste heat collaborative recovery system based on slurry flashing provided in this embodiment is as follows: The power plant desulfurization tower 1 generally adopts a limestone wet desulfurization system, and the temperature of the desulfurization slurry is generally between 50-55 °C. The desulfurization slurry at the bottom of the desulfurization tower is pumped to the lower spray layer inside the flash tank 3 through the slurry circulation pump 2 for spraying. The pressure inside the flash tank is maintained between 5-8 kPa by the vacuum pump 7. The desulfurization slurry flashes under the negative pressure state of the flash tank. The exhaust steam generated by flashing the desulfurization slurry enters the evaporator inside the lithium bromide heat pump 6 through the exhaust port at the top of the flash tank 3 and is mixed with the continuous drainage flash exhaust steam from the continuous drainage multi-stage flash tank 9 through the steam collector cylinder 5 to release heat. The lithium bromide heat pump 6 absorbs the heat of the flash exhaust steam under the drive of the steam and transfers the heat to the heat network water or other cold source water.

[0033] The continuous blowdown water of the boiler undergoes primary flashing through the continuous blowdown flash tank 8. The steam generated after flashing is discharged from the top of the continuous blowdown flash tank 8 to the deaerator for utilization. After flashing, the temperature of the continuous blowdown water drops to 100 - 120 °C. The cooled continuous blowdown water enters the multi-stage flash tank 9 of the continuous blowdown water for further flashing. The multi-stage flash tank 9 of the continuous blowdown water can be designed with multiple flash chambers. The continuous blowdown water enters the first flash chamber on the top layer of the multi-stage flash tank 9 of the continuous blowdown water for flashing, and then sequentially enters the lower-level flash chambers for flashing. The pressure in each flash chamber is controlled by the opening degree of the vacuum regulating valve 11 to make the vacuum degree in the multiple flash chambers gradually increase from top to bottom and the temperature gradually decrease. The purpose of multi-stage flashing is mainly to enhance the flashing effect and obtain more exhausted steam. The pressure in the last flash chamber is reduced to 5 - 8 kPa by the vacuum pump 7, and the temperature of the continuous blowdown water drops to between 32 - 42 °C. The continuous blowdown water after the last stage of flashing is discharged through the continuous blowdown discharge pump 10. The exhausted steam flashed out from the multi-stage flash tank 9 of the continuous blowdown water is mixed with the slurry flashing exhausted steam from the flash tank 3 in the steam collecting cylinder 5 and then enters the lithium bromide heat pump 6 together for heat release. This process realizes the deep recovery of the waste heat and water resources of the continuous blowdown water.

[0034] The deaerator exhaust gas from the deaerator 12 is condensed after heat exchange with the cold source water in the deaerator exhaust gas heat exchanger 13, and the temperature after condensation is controlled between 40 - 50 °C. The condensate water after the condensation of the deaerator exhaust gas flows by gravity into the condensate tank 14 and is pumped to the upper spray layer of the flash tank 3 through the condensate discharge pump 15 for spraying. Due to the sudden drop in the internal pressure of the flash tank, the oxygen contained in the condensate water is instantly released, and the released oxygen is discharged to the atmosphere through the lithium bromide heat pump and then through the vacuum pump 7. The condensate water is flashed for further cooling and then sent to the desulfurization tower together with the desulfurization slurry for desulfurization. The heat of this part of the condensate water can be deeply recovered, and the recovered condensate water can be used as the makeup water for the desulfurization slurry to reduce the usage amount of the desulfurization slurry makeup water and realize the recovery and utilization of the condensate water.

[0035] Example 2 In a typical implementation manner of the present invention, a method for synergistically recovering multi-source waste heat in a power plant based on slurry flashing is provided, including the following steps: The slurry in the flash tank enters the desulfurization tower to recover the waste heat of the flue gas. After recovering the waste heat, the slurry enters the flash tank for flashing, and the flashed exhausted steam enters the steam collecting cylinder. The exhausted gas discharged from the deaerator is heat-exchanged through the deaerator exhaust gas heat exchanger, condensed into condensate water and enters the condensate tank. The condensate water in the condensate tank is pumped into the upper spray layer of the flash tank for spraying. After the oxygen in the condensate water is released, it is discharged through the vacuum pump. The continuous blowdown water of the boiler enters the continuous blowdown flash tank for primary flashing. After flashing, the continuous blowdown water enters the multi-stage flash tank for multi-stage flashing. The steam generated in each stage of flashing enters the steam collector cylinder, and the steam in the steam collector cylinder enters the lithium bromide heat pump for heat release.

[0036] Furthermore, the temperature of the condensate water generated by the deaerator exhaust steam heat exchanger is controlled at 40 - 50 °C.

[0037] Furthermore, the temperature of the continuous blowdown water after primary flashing is 100 - 120 °C, and the temperature of the continuous blowdown water after multi-stage flashing is 32 - 42 °C.

[0038] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A slurry flash evaporation-based power plant multi-source waste heat collaborative recovery system, characterized in that: include: The flue gas waste heat recovery unit comprises a flash tank, the slurry inlet and outlet of the flash tank are connected to the desulfurization tower, and the exhaust steam outlet of the flash tank is connected to the steam collecting cylinder; A deaerator exhaust waste heat recovery unit comprises a deaerator, a deaerator exhaust steam heat exchanger and a condensate tank connected in sequence, wherein the condensate tank is connected to the flash tank; The continuous drainage waste heat recovery unit comprises a continuous drainage flash tank and a continuous drainage multi-stage flash tank, wherein the exhaust steam outlet of the continuous drainage multi-stage flash tank is connected to the steam collecting cylinder.

2. The slurry flash evaporation-based power plant multi-source waste heat collaborative recovery system according to claim 1, characterized in that: A multi-stage flash chamber is arranged in the water-discharging multi-stage flash tank, and the exhaust steam outlet of each stage of the flash chamber is connected to the steam collecting cylinder.

3. The slurry flash evaporation-based power plant multi-source waste heat collaborative recovery system according to claim 2, characterized in that: A vacuum regulating valve is provided at the exhaust steam outlet of each flash chamber, and the pressure of the last flash chamber is reduced to 5-8 kPa by a vacuum pump.

4. The power plant multi-source waste heat collaborative recovery system based on slurry flash evaporation according to claim 1 is characterized in that: The steam outlet of the deaerator is connected to the exhaust steam heat exchanger of the deaerator, and in the exhaust steam heat exchanger of the deaerator, the steam exchanges heat with the condensed water.

5. The slurry flash evaporation-based power plant multi-source waste heat collaborative recovery system according to claim 1, characterized in that: The steam outlet of the series flash tank is connected to the deaerator.

6. The slurry flash evaporation-based power plant multi-source waste heat collaborative recovery system according to claim 1, characterized in that: The steam collecting cylinder is connected to a lithium bromide heat pump, and the lithium bromide heat pump is connected to a vacuum pump.

7. The slurry flash evaporation-based power plant multi-source waste heat collaborative recovery system according to claim 1, characterized in that: An upper spray layer and a lower spray layer are arranged in the flash tank, the upper spray layer is connected to the condensate tank, and the lower spray layer is connected to the slurry outlet of the desulfurization tower.

8. A method for collaboratively recovering waste heat from multiple sources in a power plant based on slurry flash evaporation, which is implemented by using a collaboratively recovering waste heat from multiple sources in a power plant as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: The slurry in the flash tank enters the desulfurization tower to recover the waste heat of the flue gas. After the waste heat is recovered, the slurry enters the flash tank for flash evaporation, and the exhaust steam generated by the flash evaporation enters the steam collecting cylinder. The exhaust gas discharged from the deaerator is heat exchanged through the exhaust steam heat exchanger of the deaerator, condensed into condensed water and enters the condensate tank. The condensed water in the condensate tank is pumped into the upper spray layer of the flash tank for spraying. The oxygen in the condensed water is released and discharged through the vacuum pump; The boiler drainage enters the continuous flash tank for initial flash evaporation. The drainage after flash evaporation enters the multi-stage flash tank for multi-stage flash evaporation. The steam generated by each stage of flash evaporation enters the steam collecting cylinder, and the steam in the steam collecting cylinder enters the lithium bromide heat pump for heat release.

9. The method for synergistically recovering waste heat from multiple sources in a power plant based on slurry flash evaporation according to claim 8, characterized in that: The temperature of the condensed water produced by the exhaust steam heat exchanger of the deaerator is controlled at 40-50°C.

10. The method for synergistically recovering waste heat from multiple sources in a power plant based on slurry flash evaporation according to claim 8, characterized in that: The temperature of the drain water after the initial flash evaporation is 100-120℃, and the temperature of the drain water after multi-stage flash evaporation is 32-42℃.

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