A waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation

Abstract

This utility model relates to the field of waste heat recovery technology for desulfurization slurry, and more particularly to a waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation. The system includes a flue gas desulfurization tower, a flash tank, a steam-water heat exchanger, a boiler air heater, and a condensate tank. The bottom first slurry outlet of the flue gas desulfurization tower is connected to the upper slurry circulation inlet, and the bottom second slurry outlet is connected to the flash tank. The flash tank converts the water in the desulfurization slurry into steam through flash evaporation. The steam outlet of the flash tank sends the steam to the steam-water heat exchanger through a steam pipeline. The liquid outlet of the flash tank is connected to the liquid inlet of the flue gas desulfurization tower. The steam-water heat exchanger is connected to the boiler air heater, and the condensate outlet of the steam-water heat exchanger is connected to the condensate tank. This utility model achieves waste heat utilization of the desulfurization slurry through flash evaporation, reducing the final flue gas temperature of the boiler and improving the primary energy conversion efficiency of the boiler.

Description

Technical Field

[0001] This utility model relates to the field of waste heat recovery technology for desulfurization slurry, and in particular to a waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation. Background Technology

[0002] Flue gas heat loss accounts for a very high proportion of heat loss in large power plant boilers and medium-sized industrial boilers, making it a key factor affecting boiler thermal efficiency. With increasingly stringent environmental standards, the industry widely adopts limestone / gypsum wet desulfurization processes to treat boiler flue gas. During this process, a large amount of energy that was originally lost as flue gas heat is transferred to the desulfurization slurry. Therefore, recovering and utilizing the waste heat contained in the desulfurization slurry is essentially equivalent to effectively recovering waste heat from boiler flue gas, which has significant energy-saving implications.

[0003] Currently, most existing technologies for recovering waste heat from desulfurization slurry employ direct heat exchange processes such as spraying and absorption. However, these direct heat exchange methods have significant technical limitations: Firstly, during direct heat exchange, the desulfurization slurry comes into direct contact with the heat exchange medium (such as air or water), which easily leads to scaling and corrosion on the surface of the heat exchange equipment. This not only affects the stability of heat exchange efficiency but also shortens the equipment's service life and increases maintenance costs. Secondly, direct heat exchange offers relatively limited utilization of waste heat, making it difficult to flexibly match heat supply according to the actual needs of the boiler system. Furthermore, for low-grade desulfurization slurry waste heat, efficient recovery and cascade utilization are often not achieved, resulting in energy waste and failing to fully realize the energy-saving potential of desulfurization slurry waste heat. In addition, using such direct heat exchange processes increases the resistance to flue gas flow, which adversely affects the operation of the boiler's original flue gas desulfurization system, potentially leading to increased induced draft fan load, higher energy consumption, and even affecting the normal output of the boiler. Utility Model Content

[0004] To address at least one of the aforementioned technical problems, this invention proposes a waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation. By utilizing the waste heat of the desulfurization slurry through flash evaporation, the final exhaust temperature of the boiler is reduced, thereby improving the conversion efficiency of the boiler's primary energy.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation includes a flue gas desulfurization tower, a flash tank, a steam-water heat exchanger, a boiler air heater, and a condensate tank.

[0007] The bottom first slurry outlet of the flue gas desulfurization tower is connected to the upper slurry circulation inlet of the flue gas desulfurization tower via a first slurry pipeline. The bottom second slurry outlet of the flue gas desulfurization tower is connected to the flash tank with vacuum via a second slurry pipeline. The flash tank is used to convert water in the desulfurization slurry into steam by flash evaporation. The steam outlet of the flash tank is sent to the steam-water heat exchanger via a steam pipeline. The liquid outlet of the flash tank is connected to the liquid inlet of the flue gas desulfurization tower via a third slurry pipeline. The steam-water heat exchanger is connected to the boiler heater via a circulating water pipeline. The steam-water heat exchanger is used to realize heat exchange between steam and circulating water in the boiler heater. The condensate outlet of the steam-water heat exchanger is connected to the condensate tank.

[0008] Preferably, the upper part of the flash tank is provided with a demister, which is used to perform gas-liquid separation treatment on the steam to improve the dryness of the steam.

[0009] Preferably, the outlet of the steam-water heat exchanger is connected to a vacuum pumping unit via a vacuum pumping pipeline. The vacuum pumping unit includes a water ring vacuum pump, a buffer dehumidification tank, and a Roots vacuum pump arranged sequentially on the vacuum pumping pipeline. The outlet of the Roots vacuum pump is connected to the outside.

[0010] Preferably, the absolute pressure inside the flash tank is 10 kPa.

[0011] Preferably, the outlet of the flash tank is higher than the liquid level of the desulfurization slurry in the flue gas desulfurization tower.

[0012] Preferably, the flash tank is made of stainless steel, and the first, second, and third slurry pipelines are all made of carbon steel, with a rubber layer on the inner wall.

[0013] Preferably, the waste heat recovery system further includes an alkali tank, the outlet of which is connected to the inlet of the condensate tank via an alkali pipeline, and an alkali delivery pump is provided on the alkali pipeline.

[0014] Preferably, the first slurry pipeline and the second slurry pipeline are respectively equipped with a first slurry circulation pump and a second slurry circulation pump.

[0015] Preferably, the circulating water pipeline includes a circulating water inlet pipeline connecting the outlet of the boiler air heater and the inlet of the steam-water heat exchanger, and a circulating water return pipeline connecting the outlet of the steam-water heat exchanger and the inlet of the boiler air heater, wherein a circulating water pump is provided on the circulating water inlet pipeline.

[0016] Preferably, the temperature of the desulfurization slurry in the flue gas desulfurization tower is 50-55°C, the temperature of the steam in the flash tank is 46°C, and the temperature of the circulating water return of the boiler heater is not higher than 35°C.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention converts the water in the desulfurization slurry into steam through a flash evaporator, and then transfers the heat of the steam to the circulating water of the boiler heater through a steam-water heat exchanger. This replaces the traditional method of heating the circulating water with a steam heat source, which not only achieves the purpose of recovering and utilizing the waste heat of the desulfurization slurry, but also reduces the heat loss of the boiler, improves the energy utilization rate, and reduces coal consumption, thereby achieving the goal of energy saving.

[0019] By setting up a buffer dehumidifier between the water ring vacuum pump and the Roots vacuum pump, the main function is to buffer gas flow fluctuations, eliminate flow fluctuations when the water ring vacuum pump is pumping, make the gas flow entering the Roots vacuum pump more stable, and avoid damage to the Roots vacuum pump due to sudden load changes. At the same time, it further adsorbs or condenses the water vapor carried in the gas, reducing the moisture entering the Roots vacuum pump and protecting its working efficiency and lifespan. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation.

[0021] In the diagram: 1. Flue gas desulfurization tower; 2. First slurry pipeline; 3. First slurry circulation pump; 4. Second slurry circulation pump; 5. Second slurry pipeline; 6. Third slurry pipeline; 7. Flash tank; 8. Steam pipeline; 9. Steam-water heat exchanger; 10. Condensate tank; 11. Water ring vacuum pump; 12. Buffer dehumidification tank; 13. Roots vacuum pump; 14. Boiler air heater; 15. Circulating water pump; 16. Alkali transfer pump; 17. Alkali tank. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions in this utility model, the technical solutions in the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments in this utility model, and not all of the embodiments in this utility model.

[0023] Please refer to Figure 1 A waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation, characterized in that it includes a flue gas desulfurization tower 1, a flash tank 7, a steam-water heat exchanger 9, a boiler air heater 14, and a condensate tank 10.

[0024] The bottom first slurry outlet of the flue gas desulfurization tower 1 is connected to the upper slurry circulation inlet of the flue gas desulfurization tower 1 through the first slurry pipeline 2. The bottom second slurry outlet of the flue gas desulfurization tower 1 is connected to the vacuum flash tank 7 through the second slurry pipeline 5. The flash tank 7 is used to convert the water in the desulfurization slurry into steam through flash evaporation. The steam outlet of the flash tank 7 sends the steam into the steam-water heat exchanger 9 through the steam pipeline 8. The liquid outlet of the flash tank 7 is connected to the liquid inlet of the flue gas desulfurization tower 1 through the third slurry pipeline 6. The steam-water heat exchanger 9 is connected to the boiler air heater 14 through the circulating water pipeline. The steam-water heat exchanger 9 is used to realize the heat exchange between the steam and the circulating water in the boiler air heater 14. The condensate outlet of the steam-water heat exchanger 9 is connected to the condensate tank 10.

[0025] In this embodiment, the water in the desulfurization slurry is converted into steam by flash evaporation in the flash tank 7, and the heat of the steam is transferred to the circulating water of the boiler heater 14 through the steam-water heat exchanger 9. This replaces the traditional method of heating the circulating water with steam heat source, which not only realizes the purpose of recovering and utilizing the waste heat of desulfurization slurry, but also reduces the heat loss of the boiler, improves the energy utilization rate, and reduces coal consumption, thereby achieving the purpose of energy saving.

[0026] Meanwhile, the desulfurization slurry after flash evaporation in the flash tank 7 is transported back to the flue gas desulfurization tower 1 through the third slurry pipeline 6, realizing the recycling of the desulfurization slurry.

[0027] It should be noted that the Flash Tank 7 is a device that uses the "flash effect" to achieve gas-liquid separation or waste heat extraction. The core principle is to reduce the ambient pressure so that the high-temperature liquid can be rapidly vaporized under low pressure, thereby separating the steam and recovering the heat.

[0028] Generally, flash tanks are vertical or horizontal closed containers that can withstand a certain degree of vacuum and temperature. They can be made of stainless steel and typically include a feeding area, a flashing area, a gas-liquid separation area, and a discharging area.

[0029] Specifically, the feeding area is typically located at the top of the flash tank 7. The desulfurization slurry enters this area through the feed pipe. In this embodiment, the temperature of the desulfurization slurry is approximately 50–55°C. Some flash tanks 7 are equipped with spraying devices here, such as slurry distribution tube bundles and slurry nozzles. The desulfurization slurry enters the slurry distribution tube bundle, is pressurized by the slurry pump, and then sprayed through the slurry nozzles to break it into small droplets, increasing the contact area between the slurry and the tank interior space, facilitating subsequent flash evaporation.

[0030] The flash zone is generally located in the middle of the tank and is where flash evaporation mainly occurs. When the desulfurization slurry is sprayed down from the top into this zone, the pressure is low due to the vacuum environment inside the tank. In this embodiment, the absolute pressure inside the flash tank 7 is approximately 10 kPa. We know that the boiling point of a liquid decreases as the pressure decreases; at this pressure, the boiling point of water is approximately 46°C. At this pressure, the slurry temperature is higher than the boiling point at this pressure, and some of the water will rapidly vaporize ("flash evaporation"), forming steam.

[0031] To monitor the liquid level and pressure inside the tank and ensure stable operation, level gauges, pressure sensors, etc. can be installed on the flash tank 7.

[0032] In this embodiment, the flash tank 7 can be made of stainless steel, which has good corrosion resistance and can resist the corrosion of desulfurization slurry, extending the service life of the equipment. The first slurry pipeline 2, the second slurry pipeline 5, and the third slurry pipeline 6 are all made of carbon steel, and the inner wall is provided with a rubber layer, which can not only ensure the strength of each pipeline, but also enhance the corrosion resistance of the pipeline, reduce pipeline wear and corrosion, reduce maintenance costs, and ensure the safe and stable transportation of desulfurization slurry in the pipeline.

[0033] In this embodiment, the first slurry pipeline 2 and the second slurry pipeline 5 are respectively equipped with a first slurry circulation pump 3 and a second slurry circulation pump 4. Their function is to provide power for the circulation of desulfurization slurry in the slurry pipeline, ensuring that the desulfurization slurry can circulate between the desulfurization tower and the flash tank 7 according to the design requirements, so that the desulfurization process and the flash waste heat recovery process can proceed stably and ensure the normal operation of the system.

[0034] In this embodiment, the circulating water pipeline includes a circulating water inlet pipeline connecting the outlet of the boiler heater 14 and the inlet of the steam-water heat exchanger 9, and a circulating water return pipeline connecting the outlet of the steam-water heat exchanger 9 and the inlet of the boiler heater 14. A circulating water pump 15 is provided on the circulating water inlet pipeline.

[0035] The function of the aforementioned circulating water pump 15 is to provide power for the flow of circulating water between the steam-water heat exchanger 9 and the boiler air heater 14. This ensures that the circulating water can continuously absorb heat from the steam in the steam-water heat exchanger 9 and transfer the heat to the boiler air heater 14, achieving continuous waste heat recovery and heat utilization, and maintaining the system's heat exchange efficiency. In this embodiment, the return water temperature of the circulating water in the boiler air heater 14 does not exceed 35°C.

[0036] In this embodiment, the flue gas desulfurization tower 1 is provided with a flue gas inlet and a flue gas outlet. The structure and desulfurization principle of the flue gas desulfurization tower 1 not mentioned in this embodiment belong to the prior art and will not be described in detail here.

[0037] In order to improve the dryness of the steam, a demister is provided on the upper part of the flash tank 7 in this embodiment. The demister is used to perform gas-liquid separation treatment on the steam.

[0038] Specifically, a demister utilizes inertial collision, centrifugal separation, or interception effects to cause liquid droplets entrained in the gas (such as small droplets of desulfurization slurry carried in flash steam) to collide with the blades, wire mesh, and other structures of the demister. After the droplets accumulate, they fall due to gravity, thereby achieving gas-liquid separation.

[0039] Common structures of demisters mainly include baffle demisters (blade type), wire mesh demisters, and cyclone demisters. Among them, baffle demisters are widely used in industrial equipment due to their high separation efficiency and low resistance.

[0040] The function of the demister is to remove liquid from the steam, so as to prevent liquid droplets from scouring and corroding the pipes and steam-water heat exchanger 9. At the same time, it also prevents liquid droplets from entering the steam-water heat exchanger 9. Steam with high humidity has a smaller heat exchange area, which affects the heat exchange efficiency.

[0041] To facilitate the autonomous reflux of the desulfurization slurry in the flash tank 7 back into the flue gas desulfurization tower 1, in this embodiment, the outlet of the flash tank 7 is higher than the liquid level of the desulfurization slurry in the flue gas desulfurization tower 1. Specifically, by utilizing the liquid level difference, no additional power equipment is needed to drive the slurry reflux, reducing system energy consumption. At the same time, it ensures the stability of the slurry circulation and maintains the normal operation of the desulfurization system.

[0042] It is understandable that the desulfurization slurry after flash treatment in flash tank 7 can also be transported to the slurry pool through pipelines. This application does not limit this, and the specific operation can be selected according to the needs.

[0043] Please refer to Figure 1 In this embodiment, the outlet of the steam-water heat exchanger 9 is connected to the vacuum pumping unit through a vacuum pumping pipeline. The vacuum pumping unit includes a water ring vacuum pump 11, a buffer dehumidification tank 12 and a Roots vacuum pump 13 arranged sequentially on the vacuum pumping pipeline. The outlet of the Roots vacuum pump 13 is connected to the outside.

[0044] Specifically, the vacuum pumping unit consists of a water ring vacuum pump 11, a buffer dehumidification tank 12, and a Roots vacuum pump 13 connected in series in the vacuum pumping pipeline. The gas is ultimately discharged to the outside through the outlet of the Roots vacuum pump 13. The water ring vacuum pump 11 uses water as its working medium and can start at relatively high pressure (close to atmospheric pressure), making it suitable as a backing pump. It first pumps the pressure inside the flash tank 7 to the applicable range of the Roots vacuum pump 13, and then works in conjunction with the Roots vacuum pump 13 to achieve a deep vacuum.

[0045] The Roots vacuum pump 13 is a positive displacement vacuum pump, mainly used to provide a large pumping volume in the medium to high vacuum range (at lower pressure). It can further reduce the system pressure from a lower level to a deep vacuum. However, its inlet cannot withstand excessively high pressure and is sensitive to water vapor. The exhaust port of the Roots vacuum pump 13 is directly connected to the outside, safely discharging the pumped gas (containing a small amount of water vapor and non-condensable gases).

[0046] Therefore, in this embodiment, a buffer dehumidifier 12 is set between the water ring vacuum pump 11 and the Roots vacuum pump 13. Its main function is to buffer gas flow fluctuations, eliminate flow fluctuations when the water ring vacuum pump 11 pumps gas, make the gas flow entering the Roots vacuum pump 13 more stable, and avoid damage to the Roots vacuum pump 13 due to sudden load changes. At the same time, it further adsorbs or condenses the water vapor carried in the gas, reduces the moisture entering the Roots vacuum pump 13, and protects its working efficiency and lifespan.

[0047] In this embodiment, the “series collaboration” of the Roots vacuum pump 13 and the water ring vacuum pump 11 can take advantage of the starting advantage of the water ring vacuum pump 11 and the high vacuum capability of the Roots vacuum pump 13 to ensure that the flash tank 7 maintains a stable low-pressure environment (such as 10 kPa) and ensures the flash evaporation efficiency of the desulfurization slurry (rapid vaporization of water to release waste heat).

[0048] In this embodiment, the waste heat recovery system also includes an alkali tank 17. The outlet of the alkali tank 17 is connected to the inlet of the condensate tank 10 via an alkali pipeline. An alkali transfer pump 16 is installed on the alkali pipeline. It is understood that the condensate tank 10 is connected to the alkali tank 17. By adding an alkaline solution (e.g., sodium hydroxide or sodium carbonate solution) to the condensate tank 10, the pH value in the condensate tank 10 is adjusted so that the liquid in the condensate tank 10 can be used as desulfurization makeup water.

[0049] This application identifies a more reasonable approach to waste heat utilization for the low-temperature heat source obtained from the flash evaporation of desulfurization slurry. Compared to traditional waste heat recovery methods, it eliminates the need to add a heat pump to upgrade low-grade waste heat, simplifying the boiler flue gas desulfurization slurry waste heat recovery system, reducing investment in retrofit projects, and improving system reliability and primary energy conversion efficiency.

[0050] This system is applicable to various coal-fired boilers using limestone / gypsum wet flue gas desulfurization technology and equipped with air heaters, covering large power plant boilers and various industrial boilers. In practical applications, it can reduce the flue gas temperature at the outlet of the original desulfurization tower by 10℃-15℃, and the recovered low-temperature waste heat can be directly used as the heating source for the boiler air heater 14. The above description is a specific implementation of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation, characterized in that, It includes a flue gas desulfurization tower (1), a flash tank (7), a steam-water heat exchanger (9), a boiler air heater (14), and a condensate tank (10); The bottom first slurry outlet of the flue gas desulfurization tower (1) is connected to the upper slurry circulation inlet of the flue gas desulfurization tower (1) through a first slurry pipeline (2). The bottom second slurry outlet of the flue gas desulfurization tower (1) is connected to the flash tank (7) with vacuum through a second slurry pipeline (5). The flash tank (7) is used to convert the water in the desulfurization slurry into steam by flash evaporation. The gas outlet of the flash tank (7) is connected to the steam pipe (8) to release the steam. The steam is fed into the steam-water heat exchanger (9). The outlet of the flash tank (7) is connected to the inlet of the flue gas desulfurization tower (1) through the third slurry pipeline (6). The steam-water heat exchanger (9) is connected to the boiler heater (14) through the circulating water pipeline. The steam-water heat exchanger (9) is used to realize the heat exchange between the steam and the circulating water in the boiler heater (14). The condensate outlet of the steam-water heat exchanger (9) is connected to the condensate tank (10).

2. The waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation according to claim 1, characterized in that, The flash tank (7) is equipped with a demister at the top, which is used to perform gas-liquid separation treatment on the steam to improve the dryness of the steam.

3. The waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation according to claim 1, characterized in that, The outlet of the steam-water heat exchanger (9) is connected to the vacuum pumping unit through a vacuum pumping pipeline. The vacuum pumping unit includes a water ring vacuum pump (11), a buffer dehumidification tank (12), and a Roots vacuum pump (13) arranged sequentially on the vacuum pumping pipeline. The outlet of the Roots vacuum pump (13) is connected to the outside.

4. The waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation according to claim 1, characterized in that, The absolute pressure inside the flash tank (7) is 10 kPa.

5. The waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation according to claim 1, characterized in that, The outlet of the flash tank (7) is higher than the liquid level of the desulfurization slurry in the flue gas desulfurization tower (1).

6. The waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation according to claim 1, characterized in that, The flash tank (7) is made of stainless steel, and the first slurry pipeline (2), the second slurry pipeline (5) and the third slurry pipeline (6) are all made of carbon steel and have a rubber layer on the inner wall.

7. The waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation according to claim 1, characterized in that, The waste heat recovery system also includes an alkali tank (17), the outlet of which is connected to the inlet of the condensate tank (10) via an alkali pipeline, and an alkali transfer pump (16) is provided on the alkali pipeline.

8. The boiler flue gas desulfurization slurry waste heat recovery system based on flash evaporation according to any one of claims 1-7, characterized in that, The first slurry pipeline (2) and the second slurry pipeline (5) are respectively equipped with a first slurry circulation pump (3) and a second slurry circulation pump (4).

9. The waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation according to any one of claims 1-7, characterized in that, The circulating water pipeline includes a circulating water inlet pipeline connecting the outlet of the boiler heater (14) and the inlet of the steam-water heat exchanger (9) and a circulating water return pipeline connecting the outlet of the steam-water heat exchanger (9) and the inlet of the boiler heater (14). A circulating water pump (15) is provided on the circulating water inlet pipeline.

10. The waste heat recovery system for boiler flue gas desulfurization slurry based on flash evaporation according to any one of claims 1-7, characterized in that, The temperature of the desulfurization slurry in the flue gas desulfurization tower (1) is 50-55℃, the temperature of the steam in the flash tank (7) is 46℃, and the temperature of the circulating water return of the boiler heater (14) is not higher than 35℃.

Images