Desulfurization slurry flash evaporation flue gas waste heat recovery system based on injection type heat pump

Abstract

The utility model discloses a desulfurization slurry flash evaporation flue gas waste heat recovery system based on an injection type heat pump, and belongs to the technical field of coal-fired boiler waste heat heat supply. Desulfurization slurry flash evaporation and an injection type heat pump technology are combined, flue gas deep waste heat recovery is achieved, heat supply network return water and other process water are heated, desulfurization slurry is fed into a flash evaporation tank to be subjected to negative pressure flash evaporation, flash steam is fed into a negative pressure ejector and is driven by heat supply steam to be pressurized into medium-pressure steam, and then the heat supply network return water is subjected to large-temperature-difference heating; returning the concentrated slurry to a desulfurized water system; the pressure of injection medium-pressure exhaust steam is higher, and non-condensable gas with high SO2 content on the liquid level of exhaust steam condensed water can be pumped out by a conventional vacuum pump and sent to a desulfurizing tower for treatment; by adopting the ejector, the temperature of slurry in the flash tank can be greatly reduced, so that the temperature of flue gas is greatly reduced; and a graded flash evaporation and graded injection mode can be adopted, so that the outlet water temperature of the heat supply network return water is greatly improved. And compared with a conventional absorption heat pump, the energy efficiency ratio is higher, and the waste heat recovery amount is larger.

Description

Technical Field

[0001] The utility model relates to a desulfurized slurry flash evaporation flue gas waste heat recovery system based on an ejector heat pump, 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 realize the waste heat recovery of the flue gas, 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 waste heat of the flue gas and heat the boiler feed water or heating return water. This method has a simple system and a relatively low total cost. The disadvantage is that the waste heat recovery rate is low, and it is affected by the changes in the inlet temperature of the heated water, the flue gas temperature, etc. Usually, the actual temperature difference is 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 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 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-heat-carrying boiler flue gas waste heat recovery" series of patented technologies jointly developed by Tsinghua University and Beijing Qingda Tiangong Energy Technology Research Institute (patent numbers CN104110675B, CN107166420A, CN206929794U, etc.) have been widely promoted and applied at present and have good application prospects. However, usually, the atmospheric pressure flue gas waste heat spray tower extracts heat from the flue gas by intermediate water, 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 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, instead of using a flue gas waste heat exchanger, the heat in the flue gas is extracted 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 recovery 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 to the absorption heat pump, and it is difficult to evacuate during the condensation and 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, 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, 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, to adopt the ejector heat pump technology to construct a brand-new integrated flue gas waste heat recovery system.

[0005] The specific description of the present utility model is: A desulfurized slurry flash evaporation flue gas waste heat recovery system based on an ejector heat pump, which consists of an original desulfurization tower subsystem and a desulfurized slurry flash evaporation and heating process water subsystem. The original desulfurization tower subsystem 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 flash evaporation and heating process water subsystem includes an ejector flash evaporation tank 11, an ejector 15, an ejector heater 16, a vacuum pump 18, and connecting pipelines and components. Among them, the slurry inlet of the ejector flash evaporation tank 11 is connected to the waste heat slurry outlet of the bottom desulfurization slurry pool of the original desulfurization tower 1 through a waste heat slurry pump 10, and the concentrated slurry outlet of the ejector flash evaporation tank 11 is connected to the inlet of the original slurry pump 3; an internal upper part of the ejector flash evaporation tank 11 is provided with a flash steam ejector demister 12 and an ejector washing spray layer 13, and its flash steam outlet is connected to the low-pressure steam inlet pipe 15b of the ejector 15. The high-pressure steam inlet pipe 15a of the ejector 15 is communicated with the steam supply pipe of the heating steam Q through an ejector regulating valve 14. The medium-pressure exhaust pipe 15c of the ejector 15 is connected to the steam inlet of the ejector heater 16. The condensate outlet of the ejector heater 16 is connected to the inlet of an ejector condensate pump 17, and the outlet of the ejector condensate pump 17 is respectively communicated with the inlet of the ejector washing spray layer 13 and the outlet pipe of the ejector external discharged condensate W; the low-temperature water inlet of the ejector heater 16 is communicated with the incoming water pipe of the return water from the heat network H1, and the low-temperature water outlet of the ejector heater 16 is respectively communicated with the low-temperature water inlet of the ejector heater 16 and the return water pipe of the return water from the heat network H2; the outlet of the non-condensable gas S of the ejector heater 16 is connected to the air inlet of the vacuum pump 18, and 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, 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 pool of the original desulfurization tower 1 is respectively communicated with the inlet of the original slurry pump 3, the incoming water pipe of the desulfurization makeup water B, and the final concentrated slurry outlet of the final 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 desulfurization slurry pool of the original desulfurization tower 1 is communicated with the drain pipe of the desulfurization wastewater P.

[0006] The ejector heater 16 adopts a vertical tube heat exchange structure, and 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.

[0007] The inside of the ejector flash evaporation tank 11 is set as a primary heat exchange area or an N-stage flash evaporation area, where N is greater than or equal to 2. When setting the N-stage flash evaporation area, the flash evaporation concentrated slurry outlet of each stage of heat exchange area is connected to the slurry inlet of its next stage of heat exchange area, and the low-temperature water inlet is connected to the low-temperature water outlet of its next stage of heat exchange area; correspondingly, N ejectors 15 are also set, and N ejector heaters 16 are also set.

[0008] The ejector 15 adopts the structure of an efficient wide-range negative-pressure ejector with nearly equal-proportion adjustment of the internal flow cross-sectional area.

[0009] The heating steam Q is steam greater than atmospheric pressure or negative-pressure steam; the outlet pipes for ejecting and discharging the condensate W 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 beneficial effects of the present utility model are as follows.

[0011] (1) Heat is taken from the desulfurization slurry without adding a flue gas waste heat exchanger and its flue gas resistance; the flash evaporation + ejector heat pump technology is adopted. The flash steam is heated and pressurized by the ejector heat pump composed of ejectors and is used to heat the return water of the heat supply network, so as to realize the deep heat recovery of the flue gas. The flue gas temperature can be reduced to the 30°C level, avoiding the inherent disadvantages of the existing desulfurization slurry flash evaporation + absorption heat pump technology method. The maximum heat recovery amount can reach 1.5 to 3 times.

[0012] (2) The ejector heat pump system is composed of equipment components such as the ejector flash tank 11, the ejector 15, and the ejector heater 16, recovering a part of the desulfurization slurry waste heat. The ejector 15 adopts the structure of an efficient wide-range negative-pressure ejector with nearly equal-proportion adjustment of the internal flow cross-sectional area, so that the ejector heat pump can flexibly adapt to the changes in technical conditions such as the inlet and outlet temperatures, pressures, and flows on the flash evaporation side of the desulfurization slurry and the heat supply network return water heating side, and always maintain a very high system energy efficiency ratio, thereby greatly reducing the steam consumption of the driving steam. Its steam consumption is only a fraction of that of the conventional desulfurization slurry flash evaporation + absorption heat pump method. Therefore, the comprehensive energy efficiency ratio of the entire waste heat recovery system can reach 2 to 3 times, far higher than the conventional method.

[0013] (3) If the range of temperature rise required for the return water of the heat supply network is large, the multi-stage flash evaporation + multi-stage ejector + multi-stage countercurrent heating method can be selected.

[0014] (4) The steam side pressure of the ejector heater 16 is inherently high, so the technical requirements for the vacuum pump 18 for extracting non-condensable gases are reduced; at the same time, the ejector heater 16 adopts a vertical tube heat exchange structure, which is also beneficial to improving the extraction of non-condensable gases by the vacuum pump 18 and maintaining a higher vacuum degree.

[0015] (5) The condensate of the flash steam is used to wash the demister in the flash tank, which can maintain a higher demisting effect and make up water for the desulfurization slurry to replace a 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 being replaced by the condensate of the flash steam, it can help significantly reduce the external 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.

[0016] (6)The condensate water 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 water also correspondingly greatly reduces the consumption of water resources.

[0017] (7)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 comprehensive technical and economic benefits of energy conservation and environmental protection integration. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the system of the present utility model.

[0019] Figure 1 The numbers and names of the various components in it are as follows.

[0020] Original desulfurization tower 1, original flue gas inlet pipe 2, original slurry pump 3, waste heat slurry pump 10, ejector flash tank 11, flash steam ejector demister 12, ejector washing spray layer 13, ejector regulating valve 14, ejector 15, high-pressure steam inlet pipe 15a, low-pressure steam inlet pipe 15b, medium-pressure exhaust pipe 15c, ejector heater 16, ejector condensate pump 17, vacuum pump 18, desulfurization makeup water B, heat network return water incoming water H1, heat network return water outgoing water H2, desulfurization wastewater P, heating steam Q, non-condensable gas S, ejector external discharged condensate water W, original flue gas Y1, clean flue gas Y2. Detailed Embodiment

[0021] Figure 1 It is a schematic diagram of the system and an embodiment of the present utility model.

[0022] The specific embodiments of the present utility model are as follows.

[0023] Specific description of the embodiments of the present utility model: A desulfurized slurry flash evaporation flue gas waste heat recovery system based on an ejector heat pump, which consists of an original desulfurization tower subsystem and a desulfurized slurry flash evaporation and heating process water subsystem. The original desulfurization tower subsystem 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 flash evaporation and heating process water subsystem includes an ejector flash evaporation tank 11, an ejector 15, an ejector heater 16, a vacuum pump 18, and connecting pipelines and components. Among them, the slurry inlet of the ejector flash evaporation tank 11 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 concentrated slurry outlet of the ejector flash evaporation tank 11 is connected to the inlet of the original slurry pump 3; an internal upper part of the ejector flash evaporation tank 11 is provided with a flash steam ejector demister 12 and an ejector washing spray layer 13, and its flash steam outlet is connected to the low-pressure steam inlet pipe 15b of the ejector 15. The high-pressure steam inlet pipe 15a of the ejector 15 is communicated with the steam supply pipe of the heating steam Q through an ejector regulating valve 14. The medium-pressure exhaust pipe 15c of the ejector 15 is connected to the steam inlet of the ejector heater 16. The condensate outlet of the ejector heater 16 is connected to the inlet of an ejector condensate pump 17. The outlet of the ejector condensate pump 17 is respectively communicated with the inlet of the ejector washing spray layer 13 and the outlet pipe of the ejector external discharged condensate W; the low-temperature water inlet of the ejector heater 16 is communicated with the water supply pipe of the return water from the heat network H1, and the low-temperature water outlet of the ejector heater 16 is respectively communicated with the low-temperature water inlet of the ejector heater 16 and the return water pipe of the return water from the heat network H2; the outlet of the non-condensable gas S of the ejector heater 16 is connected to the air inlet of the vacuum pump 18, and 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, 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 water inlet pipe of the desulfurization makeup water B, and the final concentrated slurry outlet of the final 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 desulfurization slurry tank of the original desulfurization tower 1 is communicated with the drain pipe of the desulfurization wastewater P.

[0024] The ejector heater 16 adopts a vertical tube heat exchange structure, and 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.

[0025] The inside of the ejector flash evaporation tank 11 is set as a first-stage heat exchange area or an N-stage flash evaporation area, where N is greater than or equal to 2. When setting the N-stage flash evaporation area, the flash evaporation concentrated slurry outlet of each stage of heat exchange area is connected to the slurry inlet of its next stage of heat exchange area, and the low-temperature water inlet is connected to the low-temperature water outlet of its next stage of heat exchange area; correspondingly, N ejectors 15 are also set, and N ejector heaters 16 are also set.

[0026] The ejector 15 adopts a high-efficiency wide-range negative-pressure ejector structure with nearly equal-proportion adjustment of the internal flow cross-sectional area.

[0027] The heating steam Q is steam greater than atmospheric pressure or negative-pressure steam; the outlet pipes for ejecting and discharging the condensed water W are respectively communicated with the inlet of the water supply pipe for desulfurization makeup water B and the return water H1 of the heat network.

[0028] It should be noted that the present utility model is based on key technologies such as desulfurization slurry flash evaporation + ejector heat pump for pressurizing and heat exchanging flash steam, using clean condensed water as desulfurization makeup water to reduce the external discharge flow of desulfurization wastewater, etc., and proposes a complete set of new integrated systems and operation strategies for deep flue gas waste heat recovery by desulfurization slurry flash evaporation. 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, the recovery and utilization method of condensed water, 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 based on an ejector heat pump, comprising an original desulfurization tower subsystem and a desulfurized slurry flash evaporation and heating process water subsystem, wherein the original desulfurization tower subsystem 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 flashing and heating process water subsystem comprises an ejector flash tank (11), an ejector (15), an ejector heater (16), a vacuum pump (18), and connecting pipelines and components, wherein the slurry inlet of the ejector flash tank (11) 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 concentrated slurry outlet of the ejector flash tank (11) is connected to the inlet of the original slurry pump (3); the flash steam ejector demister (12), ejector heater (16), vacuum pump (18), and connecting pipelines and components; The ejector (15) is provided with an ejector washing spray layer (13), wherein the flash steam outlet is connected to the low-pressure steam inlet pipe (15b) of the ejector (15), the high-pressure steam inlet pipe (15a) of the ejector (15) is connected to the steam supply pipe of the heating steam (Q) via the ejector regulating valve (14), the medium-pressure steam exhaust pipe (15c) of the ejector (15) is connected to the steam inlet of the ejector heater (16), the condensate outlet of the ejector heater (16) is connected to the inlet of the ejector condensate pump (17), and the outlet of the ejector condensate pump (17) is connected to the inlet of the ejector washing spray layer (13) and the outlet of the ejector condensate pump (17) respectively. The outlet pipe of the ejector heater (16) is connected to the outlet pipe of the condensed water (W) discharged from the ejector; the low-temperature water inlet of the ejector heater (16) is connected to the water inlet pipe of the return water (H1) of the heating network, and the low-temperature water outlet of the ejector heater (16) is respectively connected to the low-temperature water inlet of the ejector heater (16) and the return water outlet pipe of the heating network return water (H2); the outlet of the non-condensable gas (S) of the ejector heater (16) 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 original desulfurization tower (1); the upstream of the original flue gas inlet pipe (2), i.e. It is the inlet of the original flue gas (Y1), 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 desulfurization slurry flash flue gas waste heat recovery system based on an ejector heat pump as claimed in claim 1, characterized in that The ejector heater (16) adopts 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 desulfurization slurry flash flue gas waste heat recovery system based on an ejector heat pump as claimed in claim 1, characterized in that The interior of the ejector flash tank (11) is configured as a first-stage heat exchange zone or an N-stage flash zone, wherein N is greater than or equal to 2. When N-stage flash 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; corresponding ejectors (15) are also configured in N numbers, and ejector heaters (16) are also configured in N numbers.

4. A desulfurization slurry flash flue gas waste heat recovery system based on an ejector heat pump as claimed in claim 1, characterized in that The ejector (15) adopts a high-efficiency wide-range negative pressure ejector structure in which the internal flow cross-sectional area is adjusted in nearly equal proportion.

5. A desulfurization slurry flash flue gas waste heat recovery system based on an ejector heat pump as claimed in claim 1, characterized in that The heating steam (Q) is steam with a pressure greater than normal pressure or negative pressure steam; the outlet pipe of the ejected condensate (W) is connected to the inlet of the feed pipe of the desulfurization feed water (B) and the heat network return water (H1).

Images