Flue gas deep waste heat recovery system for two-stage large-temperature-difference flash evaporation of desulfurization slurry

Abstract

The utility model discloses a flue gas deep waste heat recovery system for two-stage large-temperature-difference flash evaporation of desulfurization slurry, and belongs to the technical field of waste heat supply of coal-fired boilers. The system aims at the scene that a large amount of low-temperature demineralized water, heat supply network supplementing water or other low-temperature process water needs to be heated, flue gas deep waste heat recovery is achieved through graded flash evaporation of desulfurization slurry and direct heating of the low-temperature heated water through flash steam, and the desulfurization slurry is firstly fed into a front flash evaporation tank to be subjected to primary negative pressure flash evaporation and then fed into a secondary flash evaporation tank to be subjected to secondary negative pressure flash evaporation; the flash steam preheats heat supply network return water; the first-stage concentrated slurry is sent to a final-stage flash tank for final-stage negative pressure flash evaporation, flash evaporation steam is used for heating demineralized water and the like at lower temperature, and final-stage slurry is returned to a desulfurized water system; flash steam condensation water is used as demister washing water, desulfurization replenishing water, heat supply network replenishing water and the like in the flash tank to realize comprehensive recycling; and the condensing heat exchanger adopts a vertical tube bundle, so that the vacuumizing device can maintain a large amount of non-condensable gas such as SO2 at a relatively high vacuum degree, and the exhaust gas temperature can be greatly reduced.

Description

Technical Field

[0001] The utility model relates to a flue gas deep waste heat recovery system with two-stage large temperature difference flash evaporation of desulfurization slurry, belonging to the technical field of waste heat heating of coal-fired boilers. Background Technique

[0002] A large amount of high-temperature flue gas is discharged during the heat production process of boilers. Recovering the waste heat of flue gas can not only reduce the heat loss of boilers, but also reduce fuel consumption and emissions of pollutants such as greenhouse gases, and improve the thermal efficiency of boilers. Existing flue gas waste heat recovery systems mainly include three categories: (1) The first category is to use a shell-and-tube heat exchanger to achieve flue gas waste heat recovery, that is, to use a low-temperature economizer, or an economizer, etc. An exchanger with a tubular structure or the like is installed on the boiler outlet flue to recover the flue gas waste heat and heat the boiler feed water or heating return water. This method has a simple system and relatively low total cost. The disadvantage is that the waste heat recovery rate is low. Affected by changes in the inlet temperature of the heated water, the flue gas discharge temperature, etc., the actual temperature difference is usually only about 20-30°C, which is about 1%-2% of the boiler heat output, and the latent heat of vaporization of the water vapor contained in the flue gas cannot be recovered. Therefore, deep heat recovery cannot be achieved. (2) The second category is to use an absorption heat pump for deep flue gas recovery technology. An absorption heat pump is used to recover the flue gas waste heat and heat the network return water, etc. The flue gas temperature can be greatly reduced to about 30°C, and the waste heat recovery amount is equivalent to 8%-15% of the boiler heat output. Therefore, deep heat recovery can be achieved. However, the absorption heat pump needs to consume high-level heat sources such as steam for driving, and a large amount of acidic condensate will be generated in the flue gas, and an anti-corrosion heat exchanger needs to be used, and the equipment investment is relatively high. (3) The third category is the total heat exchange recovery technology based on air-flue gas. By humidifying the air, the dew point temperature of the flue gas is increased, and the condensation heat of the flue gas is recovered in the tail flue. This method has a simple system structure, does not require an additional driving heat source, and has a low investment cost. In recent years, the "steam-carrying boiler flue gas waste heat recovery" series of patented technologies jointly developed by Tsinghua University and Beijing Qingda Tianguang Energy Technology Research Institute (patent numbers CN104110675B, CN107166420A, CN206929794U, etc.) have been widely promoted and applied at present and have good application prospects. However, its normal-pressure flue gas waste heat spray tower usually extracts heat from the flue gas at the last stage, and the size of the flue gas waste heat spray tower is very large, and a certain resistance will be increased on the flue gas side. If the outlet pressure margin of the original induced draft fan is insufficient, the fan needs to be replaced or a booster induced draft fan needs to be set up. The above situations will all increase the cost, and sometimes the site does not have the implementation conditions.

[0003] In recent years, in the second type of flue gas waste heat recovery method, a method of using desulfurized slurry flash evaporation + absorption heat pump has emerged, that is, abandoning the flue gas waste heat exchanger, instead extracting the heat in the flue gas from the desulfurized slurry through a flash tank, sending the flash steam into the heat pump for waste heat recovery, heating the return water of the heat network or other process water, and returning the concentrated liquid to the desulfurized circulating water. Its advantages are: there is no need to transform the flue gas system, reducing the on-site implementation difficulty; the quality of the condensate water is good, which is convenient for recycling. However, the disadvantages are also very obvious: the flue gas temperature can usually only be reduced to 42 - 45°C, recovering about half of the flue gas waste heat, which does not belong to deep heat recovery and can only be regarded as a half-finished project. There is still a large amount of flue gas waste heat escaping from the flue gas, and secondary transformation is still required in the future to achieve deep heat recovery. The cost calculated for the unit waste heat recovery amount is relatively high, and the investment payback period is long. The fundamental reasons why it cannot reduce the flue gas temperature to the 30°C level and achieve deep heat recovery are as follows: First, the desulfurized slurry flash evaporation complete set of equipment is a vacuum equipment, its system integration is relatively complex, the guarantee requirements are high, and the lower the flash steam temperature, the larger the specific volume, the larger the equipment volume, and the higher the cost; Second, a large amount of non-condensable gases such as SO2 will escape during the desulfurized slurry flash evaporation process. The flash steam is sent into the absorption heat pump, and it is difficult to evacuate during the condensation heat release process in the horizontal evaporator of the heat pump. The absolute pressure during actual operation can only be maintained at about 7 - 8 kPa. It is very difficult to further increase the vacuum degree with the existing equipment and conditions, and it is impossible to further increase the vacuum degree like a normal condenser. Therefore, the saturation temperature of the flash steam can only be reduced to the 38 - 40°C level, resulting in the flue gas temperature can only be reduced to the 40 - 45°C level; Third, this technical method still belongs to the heat pump method in essence, only the heat extraction device is different. It still requires a large amount of driving steam, with high operating costs, deteriorating the thermal power flexibility adjustment problem of the power plant, and sometimes even seriously affecting the technical and economic benefits of the power plant. Utility Model Content

[0004] The purpose and task of the present utility model are, aiming at the respective inherent technical limitations of the above-mentioned various flue gas waste heat recovery systems and their impacts on the economy of the power plant, if a thermal power plant or a heat source plant needs to supply a large amount of steam externally, thus requiring a large amount of desalted water makeup, or needs to supplement a large amount of heat network water, or there is other large amount of low-temperature process water in the plant that needs to be heated, then a brand-new integrated system for flue gas waste heat recovery with desulfurized slurry staged flash evaporation can be constructed to achieve deep flue gas waste heat recovery.

[0005] The specific description of the present utility model is: A flue gas deep waste heat recovery system with two-stage large temperature difference flash evaporation of desulfurization slurry, which consists of an original desulfurization tower system and a desulfurization slurry grading flash evaporation and heating process water subsystem. The original desulfurization tower system includes an original desulfurization tower 1, an original flue gas inlet pipe 2, and an original slurry pump 3. It is characterized in that the desulfurization slurry grading flash evaporation and heating process water subsystem includes a pre-flash tank 21, a pre-heater 26, a vacuum pump 18, a final flash tank 31, a final heater 36, and connecting pipelines and components. Among them, the slurry inlet of the pre-flash tank 21 is connected to the waste heat slurry outlet of the bottom desulfurization slurry tank of the original desulfurization tower 1 through a waste heat slurry pump 10, and the first-stage concentrated slurry outlet of the pre-flash tank 21 is connected to the slurry inlet of the final flash tank 31. The final-stage concentrated slurry outlet of the final flash tank 31 is connected to the inlet of the original slurry pump 3. Inside the upper part of the pre-flash tank 21, there is a pre-flash steam demister 22 and a pre-washing spray layer 23. Its flash steam outlet is connected to the steam inlet of the pre-heater 26 through a pre-connection pipe 25. The condensate outlet of the pre-heater 26 is connected to the inlet of a pre-condensate pump 27. The outlet of the pre-condensate pump 27 is communicated with the outlet pipe of the pre-external discharged condensate W1. Inside the upper part of the final flash tank 31, there is a final flash steam demister 32 and a final-washing spray layer 33. Its flash steam outlet is connected to the steam inlet of the final heater 36 through a final-connection pipe 35. The condensate outlet of the final heater 36 is connected to the inlet of a final-condensate pump 37. The outlet of the final-condensate pump 37 is respectively connected to the inlets of the pre-washing spray layer 23 and the final-washing spray layer 33, and is communicated with the outlet pipe of the final-external discharged condensate W2. The low-temperature water inlet of the final heater 36 is communicated with the incoming water pipe of the low-temperature process water C1. The low-temperature water outlet of the final heater 36 is respectively connected to the low-temperature water inlet of the pre-heater 26 and the outlet pipe of the low-temperature process water return C2 through valves. The low-temperature water inlet of the pre-heater 26 is also connected to the incoming water pipe of the heat network return water H1 through a valve. The low-temperature water outlet of the pre-heater 26 is respectively connected to the outlet pipe of the heat network return water discharge H2 and the outlet pipe of the low-temperature process water return C2 through valves. The outlet of the pre-non-condensable gas S of the pre-heater 26 is connected to the outlet of the final-non-condensable gas S2 of the final heater 36 through a non-condensable gas regulating valve 29, and is connected to the air inlet of the vacuum pump 18. The exhaust outlet of the vacuum pump 18 is communicated with the original flue gas inlet pipe 2 of the original desulfurization tower 1. The upstream of the original flue gas inlet pipe 2 is the inlet of the original flue gas Y1 from the boiler outlet, and the downstream is the flue gas inlet of the original desulfurization tower 1. The top of the original desulfurization tower 1 is the outlet of the clean flue gas Y2. The circulating liquid outlet of the bottom desulfurization slurry tank of the original desulfurization tower 1 is respectively communicated with the inlet of the original slurry pump 3, the inlet pipe of the desulfurization make-up water B, and the final-stage concentrated slurry outlet of the final flash tank 31. The outlet of the original slurry pump 3 is connected to the circulating slurry inlet of the original desulfurization tower 1. The sewage outlet of the bottom desulfurization slurry tank of the original desulfurization tower 1 is communicated with the drain pipe of the desulfurization wastewater P.

[0006] The preheater 26 and the final heater 36 respectively adopt a vertical tube heat exchange structure, with a condensate hot well provided at the bottom, and a non-condensable gas discharge port provided above the liquid level of the hot well.

[0007] The interiors of the preflash tank 21 and the final flash tank 31 are provided with a primary heat exchange zone or an N-stage heat exchange zone, where N is greater than or equal to 2. When an N-stage heat exchange zone is provided, the flash-concentrated slurry outlet of each stage of the heat exchange zone is connected to the slurry inlet of its next stage, and the low-temperature water inlet is connected to the low-temperature water outlet of its next stage.

[0008] The vacuum pump 18 adopts a water-ring vacuum pump, a water jet air ejector or a roots vacuum pump structure.

[0009] The outlet pipe of the final externally discharged condensate W2 is respectively communicated with the desulfurization make-up water B, the inlet of the make-up water pipe of the return water from the heat network H1 and / or the outlet pipe of the preexternally discharged condensate W1.

[0010] The beneficial effects of the present utility model are as follows.

[0011] (1) Heat is taken from the desulfurization slurry, and there is no need to add a flue gas waste heat exchanger and its flue gas resistance; the desulfurization slurry is subjected to staged flashing, and the water to be heated is also heated by staged countercurrent according to its temperature, so as to recover the flue gas waste heat to the greatest extent and reduce the flue gas temperature as much as possible, fundamentally avoiding the inherent disadvantages of the existing desulfurization slurry flashing + absorption heat pump technology method, and the maximum heat recovery amount can reach 2 to 3 times.

[0012] (2) The desulfurization slurry waste heat is recovered by the direct heat exchange method to the greatest extent. Among them, the flash steam with a lower pressure and temperature generated by the final flash tank is preferentially used to heat the process water at a lower temperature, such as demineralized water make-up water, heat network make-up water, low-temperature intermediate water for the first-stage preheating of the boiler inlet air, or other low-temperature process water, etc.; the flash steam with a higher temperature generated by the preflash tank can be used for the secondary heating of the above-mentioned low-temperature process water, or for heating process water at a higher temperature such as the return water from the heat network. The above system can achieve deep flue gas waste heat recovery without using an absorption heat pump and consuming a large amount of driving energy.

[0013] (3) The preheater 26 and the final heater 36 adopt a vertical tube bundle heat exchange structure. Although the non-condensable gas contains a large amount of SO2, etc., a large amount of non-condensable gas can still be pumped out by the vacuum pump 18 and the pressure of the flash tank can be effectively reduced, thereby effectively reducing the flue gas temperature.

[0014] (4) The demisters in each flash tank are washed with the condensate of the flash steam, which can maintain a higher demisting effect and replenish water for the desulfurization slurry to replace part or all of the original desulfurization make-up water B. The make-up water source of the latter is often wastewater with a very high chloride content. After replacing it with the condensate of the flash steam, it can help significantly reduce the discharge flow of the desulfurization wastewater P and greatly reduce the secondary pollution and operation and maintenance costs caused by it, and improve the operation effect of the desulfurization system.

[0015] (5) The condensate of the flash steam can also be used as the make-up water for the return water of the heat network, which helps to significantly reduce the water production volume and cost of softened water; at the same time, the comprehensive recycling and utilization of the condensate also correspondingly greatly reduces the consumption of water resources.

[0016] (6) This solution and system can be widely applied to the flue gas waste heat recovery and heating systems of thermal power plants and boiler houses, promoting the realization of the comprehensive technical and economic benefits of energy conservation and environmental protection integration. Brief Description of the Drawings

[0017] Figure 1 It is the system schematic diagram of the present utility model.

[0018] Figure 1 The numbers and names of each component in it are as follows.

[0019] Original desulfurization tower 1, original flue gas inlet pipe 2, original slurry pump 3, waste heat slurry pump 10, vacuum pump 18, pre-stage flash tank 21, flash steam pre-stage demister 22, pre-stage washing spray layer 23, pre-stage connecting pipe 25, pre-stage heater 26, pre-stage condensate pump 27, non-condensable gas regulating valve 29, final-stage flash tank 31, flash steam final-stage demister 32, final-stage washing spray layer 33, final-stage connecting pipe 35, final-stage heater 36, final-stage condensate pump 37, desulfurization make-up water B, low-temperature process water incoming water C1, low-temperature process water outgoing water C2, heat network return water incoming water H1, heat network return water outgoing water H2, desulfurization wastewater P, pre-stage non-condensable gas S, final-stage non-condensable gas S2, pre-stage discharged condensate W1, final-stage discharged condensate W2, original flue gas Y1, clean flue gas Y2. Detailed Embodiment

[0020] Figure 1 It is the system schematic diagram and embodiment of the present utility model.

[0021] The specific embodiment of the present utility model is as follows.

[0022] The specific description of the embodiment of the present utility model is: A flue gas deep waste heat recovery system with two-stage large temperature difference flashing of desulfurization slurry, which consists of an original desulfurization tower system and a desulfurization slurry staged flashing and heating process water subsystem. The original desulfurization tower system includes an original desulfurization tower 1, an original flue gas inlet pipe 2 and an original slurry pump 3. It is characterized in that the desulfurization slurry staged flashing and heating process water subsystem includes a pre-flash tank 21, a pre-heater 26, a vacuum pump 18, a final flash tank 31, a final heater 36 and connecting pipelines and components. Among them, the slurry inlet of the pre-flash tank 21 is connected to the waste heat slurry outlet of the bottom desulfurization slurry tank of the original desulfurization tower 1 through a waste heat slurry pump 10, and the primary concentrated slurry outlet of the pre-flash tank 21 is connected to the slurry inlet of the final flash tank 31. The final concentrated slurry outlet of the final flash tank 31 is connected to the inlet of the original slurry pump 3. Inside the upper part of the pre-flash tank 21, there are a pre-flash steam demister 22 and a pre-washing spray layer 23. Its flash steam outlet is connected to the steam inlet of the pre-heater 26 through a pre-connecting pipe 25. The condensate outlet of the pre-heater 26 is connected to the inlet of a pre-condensate pump 27. The outlet of the pre-condensate pump 27 is communicated with the outlet pipe of the pre-external discharged condensate W1. Inside the upper part of the final flash tank 31, there are a final flash steam demister 32 and a final washing spray layer 33. Its flash steam outlet is connected to the steam inlet of the final heater 36 through a final connecting pipe 35. The condensate outlet of the final heater 36 is connected to the inlet of a final condensate pump 37. The outlet of the final condensate pump 37 is respectively connected to the inlets of the pre-washing spray layer 23 and the final washing spray layer 33, and is communicated with the outlet pipe of the final external discharged condensate W2. The low-temperature water inlet of the final heater 36 is communicated with the incoming water pipe of the low-temperature process water C1. The low-temperature water outlet of the final heater 36 is respectively connected to the low-temperature water inlet of the pre-heater 26 and the outlet pipe of the low-temperature process water drain C2 through valves. The low-temperature water inlet of the pre-heater 26 is also connected to the incoming water pipe of the heat network return water H1 through a valve. The low-temperature water outlet of the pre-heater 26 is respectively connected to the outlet pipes of the heat network return water drain H2 and the low-temperature process water drain C2 through valves. The outlet of the pre-non-condensable gas S of the pre-heater 26 is connected to the outlet of the final non-condensable gas S2 of the final heater 36 through a non-condensable gas regulating valve 29, and is connected to the air inlet of the vacuum pump 18. The exhaust outlet of the vacuum pump 18 is communicated with the original flue gas inlet pipe 2 of the original desulfurization tower 1. The upstream of the original flue gas inlet pipe 2 is the inlet of the original flue gas Y1 from the boiler outlet, and the downstream is the flue gas inlet of the original desulfurization tower 1. The top of the original desulfurization tower 1 is the outlet of the clean flue gas Y2. The circulating liquid outlet of the bottom desulfurization slurry tank of the original desulfurization tower 1 is respectively communicated with the inlet of the original slurry pump 3, the inlet pipe of the desulfurization make-up water B and the final concentrated slurry outlet of the final flash tank 31. The outlet of the original slurry pump 3 is connected to the circulating slurry inlet of the original desulfurization tower 1. The sewage outlet of the bottom desulfurization slurry tank of the original desulfurization tower 1 is communicated with the drain pipe of the desulfurization wastewater P.

[0023] The preheater 26 and the final heater 36 respectively adopt a vertical tube-and-shell heat exchange structure, with a condensate hot well provided at the bottom and a non-condensable gas discharge port provided above the liquid level of the hot well.

[0024] The interior of the preflash tank 21 and the final flash tank 31 is set as a primary heat exchange zone or an N-stage heat exchange zone, where N is greater than or equal to 2. When the N-stage heat exchange zone is set, the flash-concentrated slurry outlet of each stage of the heat exchange zone is connected to the slurry inlet of its next stage, and the low-temperature water inlet is connected to the low-temperature water outlet of its next stage.

[0025] The vacuum pump 18 adopts a water-ring vacuum pump, a water jet air ejector or a roots vacuum pump structure.

[0026] The outlet pipe of the final externally discharged condensate W2 is respectively communicated with the desulfurization make-up water B, the inlet of the make-up water pipe of the return water H1 from the heat network and / or the outlet pipe of the pre-externally discharged condensate W1.

[0027] It should be noted that the present utility model is based on key technologies such as multi-stage flash evaporation of desulfurization slurry and using clean condensate as desulfurization make-up water to reduce the externally discharged flow of desulfurization wastewater, and proposes a complete set of new integrated systems and operation strategies for flash evaporation of desulfurization slurry for deep flue gas waste heat recovery. According to this overall solution, there can be different specific implementation measures and specific implementation devices with different structures. The above specific implementation manners are only one of them. Any other similar simple deformed implementation manners, such as simple deformations of flash steam and heat exchangers and simple adjustments of pipelines, or simple changes in the vacuum pumping method and the recycling method of condensate, etc., all fall within the protection scope of the present utility model.

Claims

1. A flue gas deep waste heat recovery system for two-stage large temperature difference flash evaporation of desulfurized slurry, comprising an original desulfurization tower system and a desulfurized slurry graded flash evaporation and heating process water subsystem, wherein the original desulfurization tower system comprises an original desulfurization tower (1), an original flue gas inlet pipe (2) and an original slurry pump (3), characterized in that: The desulfurization slurry graded flash evaporation and heating process water subsystem comprises a pre-flash tank (21), a pre-heater (26), a vacuum pump (18), a final flash tank (31), a final heater (36) and connecting pipelines and components, wherein the slurry inlet of the pre-flash tank (21) is connected to the waste heat slurry outlet of the desulfurization slurry pool at the bottom of the original desulfurization tower (1) via a waste heat slurry pump (10), and the first concentrated slurry outlet of the pre-flash tank (21) is connected to the slurry inlet of the final flash tank (31), and the final concentrated slurry outlet of the final flash tank (31) is connected to the inlet of the original slurry pump (3); the upper part of the pre-flash tank (21) is provided with A flash steam pre-demister (22) and a pre-washing spray layer (23), wherein the flash steam outlet is connected to the steam inlet of the pre-heater (26) via a pre-connecting pipe (25), the condensate outlet of the pre-heater (26) is connected to the inlet of a pre-condensation pump (27), and the outlet of the pre-condensation pump (27) is connected to the outlet pipe of the pre-exhaust condensate (W1); a flash steam final-stage demister (32) and a final-stage washing spray layer (33) are provided at the upper part of the interior of the final-stage flash tank (31), wherein the flash steam outlet is connected to the steam inlet of the final-stage heater (36) via a final-stage connecting pipe (35), and the condensate outlet of the final-stage heater (36) is connected to the final-stage condensate outlet. The inlet of the final stage condensation pump (37) is connected to the inlet of the pre-washing spray layer (23) and the final stage washing spray layer (33), respectively, and is connected to the outlet pipe of the final stage condensate (W2); the low-temperature water inlet of the final stage heater (36) is connected to the inlet pipe of the low-temperature process water (C1), and the low-temperature water outlet of the final stage heater (36) is connected to the low-temperature water inlet of the pre-heater (26) and the return pipe of the low-temperature process water (C2) through a valve, respectively. The low-temperature water inlet of the pre-heater (26) is also connected to the return pipe of the heating network return water (H1) through a valve, and the low-temperature water outlet of the pre-heater (26) is connected to the return pipe of the heating network return water (H1). The outlet of the preheater (26) is connected to the outlet of the final stage non-condensable gas (S2) of the final stage heater (36) through a non-condensable gas regulating valve (29), and is connected to the air inlet of the vacuum pump (18). The exhaust port of the vacuum pump (18) is connected to the original flue gas inlet pipe (2) of the original desulfurization tower (1). The upstream of the original flue gas inlet pipe (2) is the inlet of the original flue gas (Y1) from the boiler outlet, the downstream is the flue gas inlet of the original desulfurization tower (1), and the top of the original desulfurization tower (1) is the outlet of the clean flue gas (Y2).The circulating liquid outlet of the desulfurization slurry pool at the bottom of the original desulfurization tower (1) is respectively connected to the inlet of the original slurry pump (3), the water inlet pipe of the desulfurization makeup water (B) and the final concentrated slurry outlet of the final flash tank (31), the outlet of the original slurry pump (3) is connected to the circulating slurry inlet of the original desulfurization tower (1), and the sewage outlet of the desulfurization slurry pool at the bottom of the original desulfurization tower (1) is connected to the drainage pipe of the desulfurization wastewater (P). ; 2. A flue gas deep waste heat recovery system for two-stage large temperature difference flash evaporation of desulfurized slurry as claimed in claim 1, characterized in that The pre-heater (26) and the final-stage heater (36) respectively adopt a vertical tube-in-tube heat exchange structure, a condensate hot well is provided at the bottom, and a non-condensable gas discharge port is provided above the hot well liquid surface.

3. A flue gas deep waste heat recovery system for two-stage large temperature difference flash evaporation of desulfurized slurry as claimed in claim 1, characterized in that The interior of the pre-flash tank (21) and the final flash tank (31) is configured as a first-stage heat exchange zone or an N-stage heat exchange zone, wherein N is greater than or equal to 2. When N-stage heat exchange zones are configured, the flash concentrated slurry outlet of each stage heat exchange zone is connected to the slurry inlet of the next stage heat exchange zone, and the low-temperature water inlet is connected to the low-temperature water outlet of the next stage heat exchange zone.

4. A flue gas deep waste heat recovery system for two-stage large temperature difference flash evaporation of desulfurized slurry as claimed in claim 1, characterized in that The vacuum pump (18) adopts a water ring vacuum pump, a water jet steam extractor or a Roots vacuum pump structure.

5. A flue gas deep waste heat recovery system for two-stage large temperature difference flash evaporation of desulfurized slurry as claimed in claim 1, characterized in that The outlet pipe of the final-stage condensate (W2) is respectively connected to the inlet of the make-up pipe of the desulfurization make-up water (B), the return water of the heating network (H1) and / or the outlet pipe of the front-stage condensate (W1).

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