Flue gas waste heat recovery system for desulfurization slurry flash evaporation and secondary absorption tower heat extraction

Abstract

The utility model discloses a flue gas waste heat recovery system for desulfurization slurry flash evaporation and secondary absorption tower heat extraction, and belongs to the technical field of coal-fired boiler waste heat heat supply. In order to solve the problem that the waste heat recovery amount is too low due to the fact that the vacuum degree of a desulfurization slurry flash evaporation and heat pump waste heat recovery system is difficult to increase, a method that a two-stage absorption heat exchange module is additionally arranged on the upper portion of a desulfurization tower to take heat and send the heat into a heat pump to be recovered is adopted, and the purpose of deeply recovering flue gas waste heat is achieved. Desulfurization slurry enters the flash tank to be subjected to flash evaporation and then returns to the slurry pond, and flash steam enters the shell-and-tube heat exchanger and conducts primary heating on heat supply network return water; a secondary absorption heat exchange module is additionally arranged at the upper part of the desulfurization tower, a gas-liquid separator is arranged at the lower part of the desulfurization tower, flue gas penetrates through the gas-liquid separator from bottom to top and is subjected to spraying heat exchange with low-temperature intermediate water, and the flue gas is sent out after being greatly cooled; the intermediate water is fed into a heat pump evaporator and returns to be circularly sprayed after releasing heat; the heat pump conducts secondary heating on heat supply network return water, waste heat of the smoke low-temperature section is deeply recycled, and the waste heat recycling amount is greatly increased.

Description

Technical Field

[0001] The utility model relates to a flue gas waste heat recovery system for desulfurized slurry flash evaporation and heat extraction from a secondary absorption tower, 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 boiler outlet flue 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 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 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 a good application prospect. However, it usually uses a flue gas waste heat spray tower to extract heat from the flue gas. 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 cause an increase in 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, instead of using a flue gas waste heat exchanger, the heat in the flue gas is taken out from the desulfurized slurry through a flash tank, and the flash steam is sent to the heat pump for waste heat recovery, and the return water of the heat network or other process water is heated, while the concentrated liquid returns 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 needed 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 to 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 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, and 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 even sometimes 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, in view of 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, to use desulfurized slurry flash evaporation to extract the waste heat of the high-temperature section of the flue gas to heat the return water of the heat network, and a secondary absorption heat exchange module is set in the desulfurization tower to recover the waste heat of the low-temperature section of the flue gas and send it to the heat pump to heat the return water of the heat network, so as to achieve deep waste heat recovery of the flue gas.

[0005] The specific description of the present utility model is: A flue gas waste heat recovery system for desulfurized slurry flash evaporation and heat extraction from a secondary absorption tower, which is composed of an integrated secondary desulfurization absorption tower system, a desulfurized slurry cascade flash evaporation heating subsystem, and a heat pump heating subsystem. It is characterized in that the integrated secondary desulfurization absorption tower system includes an integrated secondary desulfurization absorption tower 1, a raw flue gas inlet pipe 2, and a raw slurry pump 3. The integrated secondary desulfurization absorption tower 1 is divided into upper and lower zones. The lower part is a conventional desulfurization spray reaction zone, and the upper part is a secondary absorption heat exchange module 4. A gas-liquid separator 6 is arranged between the two zones, and N ventilation devices 5 are arranged on the gas-liquid separator 6, where N is greater than or equal to 1. The flue gas inlet of the integrated secondary desulfurization absorption tower 1 is communicated with the flue gas outlet pipe of the raw flue gas Y1 from the boiler outlet through the raw flue gas inlet pipe 2. The upper part of the flue gas inlet of the integrated secondary desulfurization absorption tower 1 is the conventional desulfurization spray reaction zone, where the flue gas flows from bottom to top, and the desulfurized slurry sprayed by the upper desulfurized slurry spraying device flows downward. The flue gas above the desulfurized slurry spraying device is converted into clean flue gas Y2, which enters from the lower inlet of the ventilation device 5 on the gas-liquid separator 6 upward, flows out from the upper ventilation opening of the ventilation device 5, and then passes through the intermediate water spraying area sprayed by the intermediate water spraying device, and then upward is the outlet of the ultra-clean flue gas Y3. The circulating liquid outlet of the desulfurized slurry pool at the bottom of the integrated secondary desulfurization absorption tower 1 is respectively communicated with the inlet of the raw slurry pump 3, the water inlet pipe of the desulfurization make-up water B, and the outlet of the final-stage concentrated slurry of the pre-flash tank 21. The outlet of the raw slurry pump 3 is connected to the inlet of the circulating slurry spraying device of the integrated secondary desulfurization absorption tower 1. The sewage outlet of the desulfurized slurry pool at the bottom of the integrated secondary desulfurization absorption tower 1 is communicated with the drain pipe of the desulfurized wastewater P. The desulfurized slurry cascade flash evaporation heating subsystem includes a pre-flash tank 21, a pre-heater 26, a vacuum pump 18, and connecting pipelines and components. The slurry inlet of the pre-flash tank 21 is connected to the waste heat slurry outlet of the desulfurized slurry pool at the bottom of the integrated secondary desulfurization absorption tower 1 through the waste heat slurry pump 10, and the concentrated slurry outlet of the pre-flash tank 21 is connected to the inlet of the raw slurry pump 3 or the desulfurized slurry pool. The flash steam outlet of the pre-flash tank 21 is connected to the steam inlet of the pre-heater 26 through the pre-connection pipe 25. The condensate outlet of the pre-heater 26 is connected to the inlet of the 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. The outlet of the pre-non-condensable gas S of the pre-heater 26 is connected to the air inlet of the vacuum pump 18. The exhaust outlet of the vacuum pump 18 is communicated with the raw flue gas inlet pipe 2 of the integrated secondary desulfurization absorption tower 1. The bottom intermediate water outlet of the gas-liquid separator 6 is connected to the heat source inlet of the evaporator 36c inside the heat pump 36 through the intermediate water pump 7. The heat source outlet of the evaporator 36c is connected to the inlet of the intermediate water spraying device of the secondary absorption heat exchange module 4 and the desulfurized slurry outlet of the pre-flash tank 21.The low-temperature water inlet of the preheater 26 is communicated with the water supply pipe of the return water H1 of the heat supply network, the low-temperature water outlet of the preheater 26 is connected to the low-temperature water inlet of the condenser assembly 36a of the heat pump 36, and the low-temperature water outlet of the condenser assembly 36a is communicated with the drain pipe of the return water H2 of the heat supply network.

[0006] The preheater 26 adopts a vertical tube heat exchange structure or a horizontal tube heat exchange structure. When the vertical tube heat exchange structure is adopted, 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 the horizontal tube heat exchange structure is adopted, a non-condensable gas discharge port is arranged at the upper part of one end on the condensate outlet side.

[0007] The vacuum pump 18 adopts a water-ring vacuum pump, a water jet air ejector or a Roots vacuum pump structure.

[0008] The heat pump 36 adopts an absorption heat pump or a compression heat pump type.

[0009] The outlet pipe of the pre-outlet condensate W1 is respectively communicated with the desulfurization make-up water B and the make-up water pipe inlet of 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) The flue gas waste heat recovery is divided into two processes: a high-temperature section and a low-temperature section. In the high-temperature section, the flue gas waste heat is recovered by the flash evaporation of the desulfurization slurry, and the flash steam heats the return water of the heat supply network through a tube heat exchanger for the first stage; while in the low-temperature section, the flue gas waste heat is recovered by adding a secondary absorption heat exchange module to heat the intermediate water and send it to the heat pump for waste heat recovery, which is used to heat the return water of the heat supply network for the second stage. In this way, the inherent problem that it is difficult to greatly improve the vacuum degree during the flash evaporation of the desulfurization slurry is avoided, and the waste heat recovery amount can be increased by more than 1 time at most.

[0012] (2) The direct heat exchange method is adopted to recover the waste heat of the desulfurization slurry to the greatest extent, the capacity of the heat pump is greatly reduced, and the energy efficiency ratio of the whole system is greatly improved.

[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, and the pressure of the flash tank can be effectively reduced, thereby effectively reducing the flue gas temperature.

[0014] (4) The requirement for vacuum extraction is reduced, and the complexity of the system and its operation and maintenance is reduced.

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

[0016] Figure 1 It is a system schematic diagram of the present utility model.

[0017] Figure 1 The numbers and names of each component in it are as follows.

[0018] Integrated secondary desulfurization absorption tower 1, raw flue gas inlet pipe 2, raw slurry pump 3, secondary absorption heat exchange module 4, ventilation device 5, gas-liquid separator 6, intermediate water pump 7, waste heat slurry pump 10, vacuum pump 18, preflash tank 21, preconnection pipe 25, preheater 26, precondensate pump 27, heat pump 36, condenser assembly 36a, evaporator 36c, desulfurization make-up water B, return water of heat supply network H1, return water discharged from heat supply network H2, desulfurization wastewater P, non-condensable gas in front S, condensate water discharged outside in front W1, raw flue gas Y1, clean flue gas Y2, ultra-clean flue gas Y3. Specific implementation mode

[0019] Figure 1 It is a system schematic diagram and an embodiment of the present utility model.

[0020] The specific embodiment of the present utility model is as follows.

[0021] Specific description of the embodiments of the present utility model: A flue gas waste heat recovery system for desulfurization slurry flash evaporation and heat extraction from a secondary absorption tower, which is composed of an integral secondary desulfurization absorption tower system, a desulfurization slurry cascade flash evaporation heating subsystem, and a heat pump heating subsystem. It is characterized in that the integral secondary desulfurization absorption tower system includes an integral secondary desulfurization absorption tower 1, a raw flue gas inlet pipe 2, and a raw slurry pump 3. The integral secondary desulfurization absorption tower 1 is divided into upper and lower zones. The lower part is a conventional desulfurization spray reaction zone, and the upper part is a secondary absorption heat exchange module 4. A gas-liquid separator 6 is arranged between the two zones, and N ventilation devices 5 are arranged on the gas-liquid separator 6, where N is greater than or equal to 1. The flue gas inlet of the integral secondary desulfurization absorption tower 1 is communicated with the flue gas outlet pipe of the raw flue gas Y1 from the boiler outlet through the raw flue gas inlet pipe 2. The upper part of the flue gas inlet of the integral secondary desulfurization absorption tower 1 is the conventional desulfurization spray reaction zone, where the flue gas flows from bottom to top, and the desulfurization slurry sprayed by the upper desulfurization slurry spraying device flows downward. The flue gas above the desulfurization slurry spraying device is converted into clean flue gas Y2, and the clean flue gas Y2 enters from the lower inlet of the ventilation device 5 on the gas-liquid separator 6 upward, flows out from the upper ventilation opening of the ventilation device 5, and then passes through the intermediate water spraying area sprayed by the intermediate water spraying device and is the outlet of the ultra-clean flue gas Y3 upward. The circulating liquid outlet of the desulfurization slurry pool at the bottom of the integral secondary desulfurization absorption tower 1 is respectively communicated with the inlet of the raw slurry pump 3, the inlet pipe of the desulfurization make-up water B, and the outlet of the final-stage concentrated slurry of the pre-flash tank 21. The outlet of the raw slurry pump 3 is connected to the inlet of the circulating slurry spraying device of the integral secondary desulfurization absorption tower 1. The sewage outlet of the desulfurization slurry pool at the bottom of the integral secondary desulfurization absorption tower 1 is communicated with the drain pipe of the desulfurization wastewater P. The desulfurization slurry cascade flash evaporation heating subsystem includes a pre-flash tank 21, a pre-heater 26, a vacuum pump 18, and connecting pipelines and components. 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 integral secondary desulfurization absorption tower 1 through the waste heat slurry pump 10, and the concentrated slurry outlet of the pre-flash tank 21 is connected to the inlet of the raw slurry pump 3 or the desulfurization slurry pool. The flash steam outlet of the pre-flash tank 21 is connected to the steam inlet of the pre-heater 26 through the pre-connection pipe 25. The condensate outlet of the pre-heater 26 is connected to the inlet of the 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. The outlet of the pre-non-condensable gas S of the pre-heater 26 is connected to the air inlet of the vacuum pump 18, and the exhaust outlet of the vacuum pump 18 is communicated with the raw flue gas inlet pipe 2 of the integral secondary desulfurization absorption tower 1. The bottom intermediate water outlet of the gas-liquid separator 6 is connected to the heat source inlet of the evaporator 36c inside the heat pump 36 through the intermediate water pump 7. The heat source outlet of the evaporator 36c is connected to the inlet of the intermediate water spraying device of the secondary absorption heat exchange module 4 and the desulfurization slurry outlet of the pre-flash tank 21.The low-temperature water inlet of the preheater 26 is communicated with the water supply pipe of the return water H1 of the heat supply network, the low-temperature water outlet of the preheater 26 is connected to the low-temperature water inlet of the condenser assembly 36a of the heat pump 36, and the low-temperature water outlet of the condenser assembly 36a is communicated with the drain pipe of the return water H2 of the heat supply network.;

[0022] The preheater 26 adopts a vertical tube heat exchange structure or a horizontal tube heat exchange structure. When the vertical tube heat exchange structure is adopted, 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 the horizontal tube heat exchange structure is adopted, a non-condensable gas discharge port is arranged at the upper part of one end on the condensate outlet side.

[0023] The vacuum pump 18 adopts a water ring vacuum pump, a water jet air ejector or a roots vacuum pump structure.

[0024] The heat pump 36 adopts an absorption heat pump or a compression heat pump type.

[0025] The outlet pipe of the pre-outlet condensate W1 is respectively communicated with the desulfurization make-up water B and the make-up water pipe inlet of the return water H1 of the heat supply network.

[0026] It should be noted that the present utility model is based on key technologies such as the combination of desulfurization slurry flash evaporation heat extraction and secondary absorption heat exchange module heat extraction, and proposes a complete set of new integrated systems for desulfurization slurry flash evaporation, direct heater and secondary absorption heat exchange module heat extraction and cascade heating by heat pump to recover the deep flue gas waste heat. 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 changing the type, stage, combination mode of the compressor, simple deformation of the flash steam and heat exchanger and simple adjustment of the relevant pipelines, or simple changes in the vacuum pumping method, condensate recovery and utilization method, etc., all fall within the protection scope of the present utility model.

Claims

1. A flue gas waste heat recovery system for flash evaporation of desulfurized slurry and heat extraction from a secondary absorption tower, comprising an integrated secondary desulfurized absorption tower system, a desulfurized slurry cascade flash evaporation heating subsystem and a heat pump heating subsystem, characterized in that: The integrated secondary desulfurization absorption tower system comprises an integrated secondary desulfurization absorption tower (1), a raw flue gas inlet pipe (2) and a raw slurry pump (3), wherein the integrated secondary desulfurization absorption tower (1) is divided into an upper and lower area, wherein the lower area is a conventional desulfurization spray reaction area, and the upper area is a secondary absorption heat exchange module (4), a gas-liquid separator (6) is arranged between the two areas, and N ventilation devices (5) are arranged on the gas-liquid separator (6), wherein N is greater than or equal to 1; the smoke inlet of the integrated secondary desulfurization absorption tower (1) is connected to the raw flue gas from the boiler outlet through the raw flue gas inlet pipe (2). The flue gas outlet pipe of (Y1) is connected, and the upper part of the flue gas inlet of the integral secondary desulfurization absorption tower (1) is a conventional desulfurization spray reaction zone, wherein the flue gas flows from bottom to top, and the desulfurization slurry sprayed by the upper desulfurization slurry spray device flows downward; the flue gas above the desulfurization slurry spray device is converted into clean flue gas (Y2), and the clean flue gas (Y2) enters upward from the lower inlet of the ventilation device (5) on the gas-liquid separator (6), flows out to the upper ventilation port of the ventilation device (5), and then passes through the intermediate water spray zone sprayed by the intermediate water spray device, and then flows upward to the outlet of the ultra-clean flue gas (Y3); The circulating liquid outlet of the desulfurization slurry pool at the bottom of the integral secondary desulfurization absorption tower (1) is respectively connected to the inlet of the raw slurry pump (3), the water inlet pipe of the desulfurization makeup water (B) and the concentrated slurry outlet of the front flash tank (21); the outlet of the raw slurry pump (3) is connected to the inlet of the circulating slurry spraying device of the integral secondary desulfurization absorption tower (1); the sewage outlet of the desulfurization slurry pool at the bottom of the integral secondary desulfurization absorption tower (1) is connected to the drainage pipe of the desulfurization wastewater (P); the desulfurization slurry cascade flash heating subsystem includes a front flash tank ( 21), a preheater (26), a vacuum pump (18) 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 integral secondary desulfurization absorption tower (1) through a waste heat slurry pump (10), and the concentrated slurry outlet of the pre-flash tank (21) is connected to the inlet of the raw slurry pump (3) or the desulfurization slurry pool; the flash steam outlet of the pre-flash tank (21) is connected to the steam inlet of the pre-heater (26) through a pre-connecting pipe (25), and the pre-heater 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 outlet of the pre-non-condensable gas (S) of the preheater (26) is connected to the air inlet of the vacuum pump (18), and the exhaust port of the vacuum pump (18) is connected to the original flue gas inlet pipe (2) of the integral secondary desulfurization absorption tower (1); the intermediate water outlet at the bottom of the gas-liquid separator (6) is connected to the evaporator (36) inside the heat pump (36) through the intermediate water pump (7). The heat source inlet of the evaporator (36c) is connected to the heat source inlet of the secondary absorption heat exchange module (4) and the desulfurized slurry outlet of the front flash tank (21); the low-temperature water inlet of the front heater (26) is connected to the water inlet pipe of the heat network return water (H1), the low-temperature water outlet of the front heater (26) is connected to the low-temperature water inlet of the condenser assembly (36a) of the heat pump (36), and the low-temperature water outlet of the condenser assembly (36a) is connected to the water return pipe of the heat network return water (H2).

2. A flue gas waste heat recovery system for flash evaporation of desulfurized slurry and heat extraction in a secondary absorption tower 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 flue gas waste heat recovery system for flash evaporation of desulfurized slurry and heat extraction from a secondary absorption tower 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.

4. A flue gas waste heat recovery system for flash evaporation of desulfurized slurry and heat extraction from a secondary absorption tower as claimed in claim 1, characterized in that The heat pump (36) is of absorption heat pump or compression heat pump type.

5. A flue gas waste heat recovery system for flash evaporation of desulfurized slurry and heat extraction from a secondary absorption tower as claimed in claim 1, characterized in that The outlet pipe of the front-end externally discharged condensate water (W1) is respectively connected to the inlet of the feed pipe of the desulfurization feed water (B) and the heat network return water (H1).

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