Desulfurization slurry two-stage flash evaporation coupling absorption heat pump flue gas waste heat recovery system

Abstract

The utility model discloses a flue gas waste heat recovery system for a desulfurization slurry two-stage flash evaporation coupling absorption heat pump, and belongs to the technical field of coal-fired boiler waste heat heat supply. Flue gas deep waste heat recovery is carried out in a cascade flash evaporation and cascade heating mode, desulfurization slurry sequentially enters two stages of serial flash evaporation tanks to be subjected to pressure grading flash evaporation, and flash steam of a front flash evaporation tank enters a front heater to primarily preheat return water of a heat supply network; flash steam of the second-stage flash tank is fed into an absorption heat pump for second-stage waste heat recovery, the heat pump conducts second-stage heating on heat supply network return water subjected to primary preheating and supplies the heat supply network return water out, a large amount of non-condensable gas escaped from the flash steam in the condensation heat release process of a transverse evaporator of the absorption heat pump is discharged in a graded mode, firstly, the non-condensable gas is pumped out through a micro-differential-pressure vacuumizing device, and the non-condensable gas is pumped out through a micro-differential-pressure vacuumizing device; after being mixed with non-condensable gas of the front heater, the gas is discharged by the secondary vacuum pump, and the micro-differential-pressure vacuumizing device comprises one or more Roots compressors or negative-pressure ejectors. Compared with a conventional single-stage mode, the waste heat recovery amount of the system is doubled or above.

Description

Technical Field

[0001] The utility model relates to a desulfurized slurry double-stage flash evaporation coupled with an absorption heat pump flue gas waste heat recovery system, belonging to the technical field of waste heat heating of coal-fired boilers. Background Technique

[0002] During the heat production process of boilers, a large amount of high-temperature flue gas is discharged. Recovering the waste heat of the flue gas can not only reduce the heat loss of the boiler, but also reduce the fuel consumption and pollutant emissions such as greenhouse gases, and improve the thermal efficiency of the boiler. The 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 recover the waste heat of the flue gas, that is, to install a heat exchanger with a tubular structure or the like on the outlet flue of the boiler to recover the waste heat of the flue gas and heat the boiler feed water or heating return water. This method has a simple system, but it cannot achieve deep heat recovery. (2) The second category is to use the absorption heat pump flue gas deep recovery technology. The absorption heat pump is used to recover the waste heat of the flue gas and heat the network return water, etc. The flue gas temperature can be greatly reduced to about 30°C, and the recovered waste heat is equivalent to 8% - 15% of the boiler heat output. Therefore, deep heat recovery can be achieved. However, the absorption heat pump needs to be driven by high-level heat sources such as steam, 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. At present, it has been widely promoted and applied and has good application prospects. However, its normal-pressure flue gas waste heat spray tower usually extracts heat from the flue gas by MVR, 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 increase the cost, and sometimes the on-site conditions do not allow for implementation.

[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, 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. In the future, secondary transformation is still needed 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 reason why it cannot reduce the flue gas temperature to the 30°C level and achieve deep heat recovery is 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 improve the vacuum degree with the existing equipment and conditions, and it is impossible to further improve 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, has high operating costs, worsens the thermal power flexibility adjustment problem of the power plant, and even sometimes seriously affects 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 various flue gas waste heat recovery systems and their impacts on the economy of the power plant, adopting the methods of stepped flash evaporation of desulfurized slurry, stepped recycling and utilization of flash steam, and stepped pressurization and discharge of non-condensable gases, greatly compressing the capacity and cost of the absorption heat pump, and realizing deep waste heat recovery of flue gas.

[0005] The specific description of the present utility model is: A desulfurized slurry two-stage flash evaporation coupled with an absorption heat pump flue gas waste heat recovery system, which consists of an original desulfurization tower system and a desulfurized slurry cascade flash evaporation heating and vacuum control 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 desulfurized slurry cascade flash evaporation heating and vacuum control subsystem includes a pre-stage flash evaporation tank 21, a pre-stage heater 26, a final-stage flash evaporation tank 31, an absorption heat pump 36, a vacuum pump 18, a micro-pressure difference vacuum pumping device 38, and connecting pipelines and components. Among them, the slurry inlet of the pre-stage flash evaporation tank 21 is connected to the waste heat slurry outlet of the bottom desulfurized slurry pool of the original desulfurization tower 1 through a waste heat slurry pump 10, and the first-stage concentrated slurry outlet of the pre-stage flash evaporation tank 21 is connected to the slurry inlet of the final-stage flash evaporation tank 31. The final-stage concentrated slurry outlet of the final-stage flash evaporation tank 31 is connected to the inlet of the original slurry pump 3 or the desulfurized slurry pool; the flash steam outlet of the pre-stage flash evaporation tank 21 is connected to the steam inlet of the pre-stage heater 26 through a pre-stage connecting pipe 25. The condensate outlet of the pre-stage heater 26 is connected to the inlet of a pre-stage condensate pump 27, and the outlet of the pre-stage condensate pump 27 communicates with the outlet pipe of the pre-stage discharged condensate W1; the flash steam outlet of the final-stage flash evaporation tank 31 is connected to the heat source inlet of an evaporator 36c inside the absorption heat pump 36 through a final-stage connecting pipe 35. The heat source outlet of the evaporator 36c is connected to the inlet of a final-stage condensate pump 37, and the outlet of the final-stage condensate pump 37 communicates with the outlet pipe of the final-stage discharged condensate W2; inside the absorption heat pump 36, there is also a generator 36b and an absorber condenser assembly 36a that communicate with the driving steam; the low-temperature water inlet of the pre-stage heater 26 communicates with the incoming water pipe of the heat network return water H1, and the low-temperature water outlet of the pre-stage heater 26 is connected to the low-temperature water inlet of the absorber condenser assembly 36a of the absorption heat pump 36. The low-temperature water outlet of the absorber condenser assembly 36a communicates with the return water pipe of the heat network return water H2; the outlet of the non-condensable gas S2 at the final stage of the evaporator 36c is connected to the inlet of the micro-pressure difference vacuum pumping device 38, and the outlet of the micro-pressure difference vacuum pumping device 38 is respectively connected to the outlet of the non-condensable gas S of the pre-stage heater 26 and the air inlet of the vacuum pump 18. The exhaust port of the vacuum pump 18 communicates 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 desulfurized slurry pool of the original desulfurization tower 1 communicates 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-stage flash evaporation tank 31 respectively. 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 bottom desulfurized slurry pool of the original desulfurization tower 1 communicates with the drain pipe of the desulfurized wastewater P.

[0006] The preheater 26 adopts a vertical tube - type heat - exchange structure or a horizontal tube - type heat - exchange structure. When adopting the vertical tube - type heat - exchange structure, a condensate hot well is arranged at the bottom, and a non - condensable gas discharge port is arranged above the liquid level of the hot well; when adopting the horizontal tube - type heat - exchange structure, a non - condensable gas discharge port is arranged at the upper part of one end on the condensate outlet side.

[0007] The micro - differential pressure vacuum pumping device 38 adopts one or more Roots compressors or negative - pressure ejectors. When adopting a Roots compressor, the outlet of the micro - differential pressure vacuum pumping device 38 is respectively connected to the outlet of the pre - non - condensable gas S of the preheater 26 and the inlet of the vacuum pump 18 through a boost bypass valve 38b; when adopting a negative - pressure ejector, the outlet of the micro - differential pressure vacuum pumping device 38 is communicated with the steam inlet of the preheater 26 through a pressure - reduction bypass valve 38a.

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

[0009] The outlet pipes of the pre - discharged condensate W1 and the last - stage discharged condensate W2 are respectively communicated with the inlet of the make - up water pipes of the desulfurization make - up water B and the return water H1 of the heat supply network.

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

[0011] (1) Cascade flash evaporation and cascade heat extraction are carried out from the desulfurization slurry without adding a flue - gas waste - heat exchanger and its flue - gas resistance; the desulfurization slurry undergoes single - stage or multi - stage flash evaporation, and the water to be heated also undergoes single - stage or multi - stage counter - current heating, so as to recover the flue - gas waste heat to the greatest extent, reduce the flue - gas temperature as much as possible, thus greatly compressing the capacity and cost of the absorption heat pump, and the waste - heat recovery amount can reach up to 2 - 3 times at most. For the conventional desulfurization slurry flash evaporation + absorption heat pump scheme, the ratio of waste - heat recovery amount to driving steam is only about 0.7, while this patent can increase it to about 1.4 - 5.0, greatly reducing the demand for driving steam and improving the flexibility of the adjustment of the whole - plant cogeneration system.

[0012] (2) The waste heat of the desulfurization slurry is recovered by the direct heat - exchange method to the greatest extent. The flash steam with lower pressure and temperature generated by the pre - flash tank first conducts primary heating on the return water of the heat supply network; the flash steam with even lower temperature generated by the last - stage flash tank is recovered by the absorption heat pump and can be used for secondary heating of the return water of the heat supply network, thus realizing deep flue - gas waste - heat recovery.

[0013] (3) The preheater 26 adopts a vertical tube - bundle heat - exchange structure. Although a large amount of SO2 and the like are contained in the non - condensable gas, a large amount of non - condensable gas can still be pumped out by the vacuum pump 18, effectively reducing the pressure of the flash tank, and further effectively reducing the flue - gas temperature.

[0014] (4) The micro differential pressure vacuum pumping device 38 can be used to effectively discharge the non-condensable gas on the condensate side of the flash steam in the evaporator of the absorption heat pump, creating a higher vacuum degree for the final flash tank, thereby significantly reducing the outlet temperature of the desulfurization slurry and the outlet temperature of the flue gas, and achieving deep heat recovery.

[0015] (5) The condensate of the flash steam can also be used as makeup 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 recovery and utilization of the condensate also correspondingly significantly 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 a schematic diagram of the system 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, pre-stage connecting pipe 25, pre-stage heater 26, pre-stage condensate pump 27, final flash tank 31, final connecting pipe 35, absorption heat pump 36, absorber condenser assembly 36a, generator 36b, evaporator 36c, final condensate pump 37, micro differential pressure vacuum pumping device 38, pressure reduction bypass valve 38a, pressure increase bypass valve 38b, desulfurization makeup water B, heat network return water incoming water H1, heat network return water discharging water H2, desulfurization wastewater P, pre-stage non-condensable gas S, final non-condensable gas S2, pre-stage externally discharged condensate water W1, final externally discharged condensate water W2, original flue gas Y1, clean flue gas Y2. Detailed Embodiment

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

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

[0022] Specific description of the embodiment of the present utility model: A desulfurized slurry two-stage flash evaporation coupled with an absorption heat pump flue gas waste heat recovery system, which consists of an original desulfurization tower system and a desulfurized slurry cascade flash evaporation heating and vacuum control 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 desulfurized slurry cascade flash evaporation heating and vacuum control subsystem includes a pre-stage flash evaporation tank 21, a pre-stage heater 26, a final-stage flash evaporation tank 31, an absorption heat pump 36, a vacuum pump 18, a micro-pressure difference vacuum pumping device 38, and connecting pipelines and components. Among them, the slurry inlet of the pre-stage flash evaporation tank 21 is connected to the waste heat slurry outlet of the bottom desulfurized slurry pool of the original desulfurization tower 1 through a waste heat slurry pump 10, and the first-stage concentrated slurry outlet of the pre-stage flash evaporation tank 21 is connected to the slurry inlet of the final-stage flash evaporation tank 31. The final-stage concentrated slurry outlet of the final-stage flash evaporation tank 31 is connected to the inlet of the original slurry pump 3 or the desulfurized slurry pool; the flash steam outlet of the pre-stage flash evaporation tank 21 is connected to the steam inlet of the pre-stage heater 26 through a pre-stage connecting pipe 25. The condensate outlet of the pre-stage heater 26 is connected to the inlet of a pre-stage condensate pump 27, and the outlet of the pre-stage condensate pump 27 is communicated with the outlet pipe of the pre-stage external discharged condensate W1; the flash steam outlet of the final-stage flash evaporation tank 31 is connected to the heat source inlet of an evaporator 36c inside the absorption heat pump 36 through a final-stage connecting pipe 35. The heat source outlet of the evaporator 36c is connected to the inlet of a final-stage condensate pump 37, and the outlet of the final-stage condensate pump 37 is communicated with the outlet pipe of the final-stage external discharged condensate W2; inside the absorption heat pump 36, there is also a generator 36b and an absorber condenser assembly 36a communicated with the driving steam; the low-temperature water inlet of the pre-stage heater 26 is communicated with the incoming water pipe of the heat network return water H1, and the low-temperature water outlet of the pre-stage heater 26 is connected to the low-temperature water inlet of the absorber condenser assembly 36a of the absorption heat pump 36. The low-temperature water outlet of the absorber condenser assembly 36a is communicated with the return water pipe of the heat network return water H2; the outlet of the non-condensable gas S2 at the final stage of the evaporator 36c is connected to the inlet of the micro-pressure difference vacuum pumping device 38. The outlet of the micro-pressure difference vacuum pumping device 38 is respectively connected to the outlet of the pre-stage non-condensable gas S of the pre-stage heater 26 and the air inlet of the vacuum pump 18. The exhaust port 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 desulfurized slurry pool 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-stage flash evaporation 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 bottom desulfurized slurry pool of the original desulfurization tower 1 is communicated with the drain pipe of the desulfurized wastewater P.

[0023] The preheater 26 adopts a vertical tube - type heat exchange structure or a horizontal tube - type heat exchange structure. When adopting the vertical tube - type heat exchange structure, a condensate hot well is arranged at the bottom, and a non - condensable gas discharge port is arranged above the liquid level of the hot well; when adopting the horizontal tube - type heat exchange structure, a non - condensable gas discharge port is arranged at the upper part of one end on the condensate outlet side.

[0024] The micro - differential pressure vacuum pumping device 38 adopts one or more roots compressors or negative - pressure ejectors. When adopting the roots compressor, the outlet of the micro - differential pressure vacuum pumping device 38 is respectively connected to the outlet of the pre - non - condensable gas S of the preheater 26 and the inlet of the vacuum pump 18 through a boost bypass valve 38b; when adopting the negative - pressure ejector, the outlet of the micro - differential pressure vacuum pumping device 38 is communicated with the steam inlet of the preheater 26 through a pressure - reducing bypass valve 38a.

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

[0026] The outlet pipes of the pre - discharged condensate W1 and the last - stage discharged condensate W2 are respectively communicated with the inlet of the make - up water pipes of the desulfurization make - up water B and the return water of the heat supply network H1.

[0027] It should be noted that the present utility model is based on key technologies such as the cascade flash evaporation of desulfurization slurry, the cascade heating of flash steam, and the cascade pressurization and discharge of non - condensable gases, and proposes a complete set of new integrated systems for the cascade flash evaporation of desulfurization slurry, the cascade heating of direct heaters and absorption heat pumps for deep flue - gas waste - heat recovery of flue gas. According to this overall solution, there can be different specific implementation measures and specific implementation devices with different structures. The above - mentioned specific implementation manners are just one of them. Any other similar simple - deformation implementation manners, such as changing the type, stage number, and combination method of the compressor, simple deformation of the relevant flash steam and heat exchanger, and simple adjustment of the relevant pipelines, or simple changes in the vacuum pumping method and the condensate recovery and utilization method, etc., all fall within the protection scope of the present utility model.

Claims

1. A desulfurization slurry two-stage flash evaporation coupled absorption heat pump flue gas waste heat recovery system, comprising an original desulfurization tower system and a desulfurization slurry step flash evaporation heating and vacuum control 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 cascade flash heating and vacuum control subsystem comprises a pre-flash tank (21), a pre-heater (26), a final flash tank (31), an absorption heat pump (36), a vacuum pump (18), a micro-pressure differential vacuum pump (38) 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) or the desulfurization slurry pool; the flash slurry of the pre-flash tank (21) The steam outlet is connected to the steam inlet of the preheater (26) through the pre-connecting pipe (25), the condensate outlet of the preheater (26) is connected to the inlet of the pre-condensate pump (27), and the outlet of the pre-condensate pump (27) is connected to the outlet pipe of the pre-exhaust condensate (W1); the flash steam outlet of the final flash tank (31) is connected to the heat source inlet of the evaporator (36c) inside the absorption heat pump (36) through the final connecting pipe (35), the heat source outlet of the evaporator (36c) is connected to the inlet of the final condensate pump (37), and the outlet of the final condensate pump (37) is connected to the outlet pipe of the final condensate (W2); the absorption heat pump (36) is also provided with a generator connected to the driving steam. The low-temperature water inlet of the preheater (26) is connected to the water inlet pipe of the heat network return water (H1), the low-temperature water outlet of the preheater (26) is connected to the low-temperature water inlet of the absorber condenser assembly (36a) of the absorption heat pump (36), and the low-temperature water outlet of the absorber condenser assembly (36a) is connected to the water return pipe of the heat network return water (H2); the outlet of the final non-condensable gas (S2) of the evaporator (36c) is connected to the inlet of the micro-pressure differential vacuum pump (38), and the outlet of the micro-pressure differential vacuum pump (38) is connected to the outlet of the pre-non-condensable gas (S) of the preheater (26) and the air inlet of the vacuum pump (18), respectively. 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 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 desulfurization slurry two-stage flash evaporation coupled absorption heat pump flue gas waste heat recovery system as claimed in claim 1, characterized in that The preheater (26) adopts a vertical shell-and-tube heat exchange structure or a horizontal shell-and-tube heat exchange structure, wherein when the vertical shell-and-tube heat exchange structure is adopted, a condensate hot well is arranged at the bottom, and a non-condensable gas discharge outlet is arranged above the hot well liquid surface; when the horizontal shell-and-tube heat exchange structure is adopted, a non-condensable gas discharge outlet is arranged at the upper part of one end on the condensate outlet side.

3. A desulfurization slurry two-stage flash evaporation coupled absorption heat pump flue gas waste heat recovery system as claimed in claim 1, characterized in that The micro-pressure differential vacuum pumping device (38) adopts one or more Roots compressors or negative pressure ejectors. When a Roots compressor is adopted, the outlet of the micro-pressure differential vacuum pumping device (38) is respectively connected to the outlet of the pre-heater (26) non-condensable gas and the air inlet of the vacuum pump (18) through a boost bypass valve (38b); when a negative pressure ejector is adopted, the outlet of the micro-pressure differential vacuum pumping device (38) is connected to the steam inlet of the pre-heater (26) through a drop bypass valve (38a).

4. A desulfurization slurry two-stage flash evaporation coupled absorption heat pump flue gas waste heat recovery system 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 desulfurization slurry two-stage flash evaporation coupled absorption heat pump flue gas waste heat recovery system as claimed in claim 1, characterized in that The outlet pipes of the front-stage externally discharged condensed water (W1) and the final-stage externally discharged condensed water (W2) are respectively connected to the inlet pipes of the desulfurization feed water (B) and the heat network return water (H1).

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