An air defense pre-filter ABS blockage flue gas waste heat recovery system

Abstract

The application discloses a flue gas waste heat recovery system for preventing air preheater ABS blockage, which comprises an air preheater, a cooler, a warm air heater, a low-temperature economizer water outlet, a low-temperature economizer water return, a first water pump and a second water pump. The cooler is arranged on the flue gas side of the air preheater and used for absorbing flue gas heat. The warm air heater is arranged on the air side of the air preheater and used for heating incoming air. The first water pump is connected between the low-temperature economizer water outlet and the cooler and used for leading condensate water into the water inlet of the cooler. The second water pump is connected between the low-temperature economizer water outlet and the warm air heater and used for leading condensate water into the water inlet of the warm air heater. The water outlet of the cooler is connected with the water inlet of the low-temperature economizer water return and / or the warm air heater. The water outlet of the warm air heater is connected with the low-temperature economizer water outlet or the low-temperature economizer water return. The application can simultaneously meet the flue gas waste heat recovery requirement and the requirement of preventing air preheater ABS blockage, and reduce the waste of heat exchange area.

Description

Technical Field

[0001] This invention relates to the field of thermal power generation technology, and in particular to a flue gas waste heat recovery system for air preheater ABS blockage. Background Technology

[0002] For most coal-fired boilers, the design inlet air temperature is generally around 25℃, and the flue gas temperature is around 125℃. Due to seasonal changes and fluctuations in unit load, the boiler inlet air temperature varies considerably, ranging from around -20℃ in winter to above 35℃ in summer. The boiler flue gas temperature also fluctuates between around 100℃ and 150℃.

[0003] Large fluctuations in boiler intake and exhaust temperatures have a negative impact on the unit's economy and safety stability. Excessive exhaust temperature leads to significant boiler exhaust heat loss, while excessively low exhaust temperature and air preheater inlet air temperature can cause corrosion and blockage of equipment such as the air preheater cold end and dust collector. Thermal power plants generally need to take certain measures to address these issues.

[0004] Flue gas heat loss is the largest component of boiler heat loss, and traditional technologies have developed many methods for recovering waste heat from boiler tail-end flue gas. From the perspective of improving unit economy and flue gas waste heat recovery, it is reasonable to use technologies such as low-temperature economizers to reduce the flue gas temperature to around 110℃ (the specific temperature should be determined according to the SO2 content in the flue gas to prevent low-temperature corrosion). In the high-temperature summer season, when the unit load is high, the boiler flue gas temperature is high, resulting in significant energy-saving effects. However, in the cold winter season, when the unit load rate is low, the boiler flue gas temperature will drop below 110℃, and there will be no flue gas waste heat to be recovered, requiring the waste heat recovery system to be shut down. Since the flue gas contains a certain concentration of SO2, although continued operation would still recover flue gas waste heat, the excessively low flue gas temperature and inlet water temperature would cause low-temperature corrosion of the flue gas cooler heat exchange tubes.

[0005] From a design perspective, higher flue gas temperatures are needed to heat condensate at higher temperatures, thereby displacing higher-quality steam from the low-pressure heater and achieving greater energy savings. Fluctuating flue gas temperatures, especially after water-based heat recovery, also cause changes in the outlet temperature of the water-based heat exchanger, posing challenges to the system design. Furthermore, the determination of the heat exchanger outlet temperature in actual flue gas waste heat recovery is primarily for safety reasons, mainly considering low-temperature corrosion of the flue gas. To prevent low-temperature corrosion of the waste heat recovery heat exchanger and its downstream equipment, when the boiler flue gas temperature is too low, not only can waste heat recovery not be performed to further reduce the flue gas temperature, but the flue gas temperature should also be increased to ensure the safety of downstream equipment.

[0006] Currently, due to the implementation of ultra-low emission retrofits in most coal-fired boilers, the commissioning of SCRs has resulted in a certain amount of ammonia escape. This escaped ammonia reacts with SO3 in the flue gas to produce ammonium bisulfate, which corrodes and clogs downstream equipment, causing ABS blockage. ABS blockage is particularly severe in rotary air preheaters. Most coal-fired power plants face increased resistance, increased fan power consumption, and even excessive fan output caused by air preheater blockage, ultimately preventing the unit from operating at full load and necessitating shutdown and air preheater cleaning.

[0007] The direct cause of ABS blockage in the air preheater is the deposition of ammonium bisulfate on the heat storage elements at low temperatures. The most effective method is to increase the cold-end temperature of the air preheater, typically measured as the combined cold-end temperature of the preheater, which is the sum of the flue gas temperature and the air preheater inlet temperature. During the cold winter months, both the boiler inlet and flue gas temperatures are low, resulting in a significant drop in the combined cold-end temperature of the preheater. For the same unit, without intervention, the combined flue gas temperature can decrease from 180 degrees Celsius at high summer loads to the 80s at low winter loads. The most common solution is to install a warm air heater before the air preheater, using auxiliary steam to raise the boiler inlet temperature, which also increases the flue gas temperature. Warm air heaters are standard equipment for coal-fired units in northern regions. However, this method uses auxiliary steam as the heat source for both boiler inlet and flue gas temperatures, consuming valuable heat and significantly impacting the unit's economic efficiency. Since ABS blockage in rotary air preheaters is a problem in most coal-fired power plants, and in some power plants it is so severe that it affects the safe operation of the units, technologies such as hot air recirculation, SO3 absorption, and thermal storage element modification have been developed. However, these technologies all have the problems of limited functionality and high modification costs.

[0008] With the development of waste heat utilization technology for boiler tail flue gas, a solution has also emerged that recovers waste heat from boiler tail flue gas to heat boiler intake air, namely a pre-heater. However, since more than 80% of the recovered heat circulates within the boiler, and only 20% of the heat can be absorbed by the boiler, the energy-saving effect of this technology is very limited. It should be classified as rotary air preheater anti-ABS blockage technology rather than waste heat recovery technology.

[0009] Due to the cyclical unevenness of electricity consumption and the large fluctuations in renewable energy power generation, most generating units have the problem of large load fluctuations. In particular, in recent years, a large number of coal-fired units have undergone flexibility transformation and become peak-shaving units, resulting in large cyclical fluctuations in actual operating loads. Therefore, there is a need for both flue gas waste heat recovery and prevention of air preheater ABS blockage.

[0010] However, existing technologies for boiler tail-end flue gas waste heat recovery and pre-air preheater ABS blockage prevention do not overlap in their application scenarios and tend to alternate. For example, high air temperature and high unit load correspond to high overall temperature at the preheater cold end, resulting in a low risk of ABS blockage and corrosion at the air preheater cold end. In this case, the pre-air preheater is shut down, the amount of flue gas waste heat that can be recovered is large, and the flue gas cooler needs to operate at full load. Conversely, low air temperature and low unit load correspond to low overall temperature at the preheater cold end, resulting in a high risk of ABS blockage and corrosion at the air preheater cold end. In this case, the pre-air preheater needs to operate at full load, the amount of flue gas waste heat that can be recovered is small, and the flue gas cooler needs to be shut down. The independently designed flue gas cooler for waste heat recovery and the flue gas absorber for pre-air preheater heat exchangers, when coexisting in the same unit, lead to wasted heat exchange area, increased investment, and higher flue gas resistance. Furthermore, it is difficult to simultaneously meet the requirements for both waste heat recovery and prevention of air preheater ABS blockage.

[0011] Therefore, how to simultaneously meet the requirements for flue gas waste heat recovery and prevent air preheater ABS blockage, while reducing the waste of heat exchange area, is a technical problem faced by those skilled in the art. Summary of the Invention

[0012] The purpose of this invention is to provide a flue gas waste heat recovery system that prevents air preheater ABS blockage, which can simultaneously meet the requirements for flue gas waste heat recovery and prevent air preheater ABS blockage, thereby reducing the waste of heat exchange area.

[0013] To solve the above-mentioned technical problems, the present invention provides a flue gas waste heat recovery system for preventing ABS blockage in air preheaters, including an air preheater, a cooler, a heater, a low-pressure heater outlet, a low-pressure heater return outlet, a first water pump, and a second water pump.

[0014] The cooler is located on the flue gas side of the air preheater and is used to absorb heat from the flue gas.

[0015] The heater is located on the air side of the air preheater and is used to heat the incoming air.

[0016] The first water pump is connected between the low-pressure water outlet and the cooler, and is used to introduce condensate into the water inlet of the cooler;

[0017] The second water pump is connected between the low-pressure water outlet and the heater, and is used to introduce condensate into the water inlet of the heater;

[0018] The outlet of the cooler is connected to the return water inlet of the low-pressure heater and / or the inlet of the heater.

[0019] The outlet of the heater is connected to either the low-pressure heater outlet or the low-pressure heater return outlet.

[0020] Preferably, it also includes a recirculation pump;

[0021] The recirculation pump is connected between the inlet and outlet of the cooler and is used to reintroduce some of the condensate after heat absorption from the outlet of the cooler back into the inlet of the cooler.

[0022] Preferably, the cooler is used to absorb heat from the flue gas to reduce the flue gas temperature to a level above a first preset temperature; wherein the first preset temperature is a temperature to prevent low-temperature corrosion of the flue gas.

[0023] Preferably, the heater is used to heat the intake air to raise the overall cold end temperature of the air preheater to a level above a second preset temperature; wherein, the overall cold end temperature of the air preheater is the sum of the air-side temperature and the flue gas-side temperature of the air preheater, and the second preset temperature is the temperature at which NH4HSO4 is prevented from depositing on the hot section heat storage element of the air preheater and causing low-temperature corrosion to the cold section heat storage element of the air preheater.

[0024] Preferably, the low-pressure water outlet is simultaneously connected to the outlets of multiple low-pressure heaters at different temperatures, and each low-pressure heater outlet is equipped with a flow regulating valve for adjusting its respective water flow rate.

[0025] Preferably, the low-pressure return water inlet is connected to the outlet of a single low-pressure heater.

[0026] Preferably, it further includes a first shut-off valve connected between the outlet of the cooler and the return water inlet of the low-pressure heater and whose on / off state is controllable, and a second shut-off valve connected between the outlet of the cooler and the inlet of the heater and whose on / off state is controllable.

[0027] Preferably, it further includes a third shut-off valve connected between the outlet of the heater and the return water port of the low-pressure heater, and a fourth shut-off valve connected between the outlet of the heater and the outlet ... outlet of the low-pressure heater, and a fourth shut-off valve connected between the outlet of the heater and the outlet of the low-pressure heater, and a fourth shut-off valve

[0028] Preferably, it further includes a fifth shut-off valve connected between the first water pump and the low-pressure outlet and whose on / off state is controllable, and a sixth shut-off valve connected between the second water pump and the low-pressure outlet and whose on / off state is controllable.

[0029] Preferably, both the first water pump and the second water pump are booster pumps.

[0030] The flue gas waste heat recovery system for preventing ABS blockage in the air preheater provided by this invention mainly includes an air preheater, a cooler, a heater, a low-pressure heater outlet, a low-pressure heater return outlet, a first water pump, and a second water pump. The air preheater primarily utilizes the waste heat from the flue gas in the boiler's tail flue to heat the air entering the boiler. The cooler, located on the flue gas side of the air preheater, mainly absorbs heat from the flue gas and cools it. The heater, located on the air side of the air preheater, mainly heats the incoming air. The low-pressure heater outlet is the condensate outlet of the boiler's low-pressure heater system, capable of drawing out condensate at a certain temperature as the water medium for the cooler and heater. The low-pressure heater return outlet is the condensate return outlet of the boiler's low-pressure heater system, mainly used for condensate recirculation. The first water pump connects the low-pressure heater outlet and the cooler, primarily used to draw condensate from the low-pressure heater outlet and send it to the cooler inlet. This allows the condensate to absorb heat from the flue gas on the air preheater's flue gas side within the cooler, achieving waste heat recovery. The second water pump connects the low-pressure heater outlet and the air heater, also primarily used to draw condensate from the low-pressure heater outlet and send it to the air heater inlet. This allows the condensate to heat the air intake air on the air preheater's air side within the air heater, increasing both the air-side and flue gas-side temperatures and preventing ABS blockage in the air preheater. Simultaneously, the cooler outlet connects to the low-pressure heater return outlet and / or the air heater inlet, allowing the condensate that has absorbed waste heat from the flue gas to flow directly back to the low-pressure heater system or continue into the air heater to heat the air intake air on the air preheater's air side. The outlet of the heater is connected to the outlet or return outlet of the low-pressure heater, so that the extracted condensate heats the incoming air on the air side of the air preheater and can flow directly back to the low-pressure heater system, or re-enter the cooler for heat absorption and release.

[0031] Thus, the flue gas waste heat recovery system for preventing ABS blockage in the air preheater provided by this invention utilizes the condensate from the boiler's low-pressure heater system extracted by the first and second water pumps as the heat exchange medium. This allows for heat recovery of the flue gas waste heat in the cooler, meeting the requirements for flue gas waste heat recovery. The recovered heat can be reabsorbed by the boiler or enter the air heater. Simultaneously, the recovered heat or the heat from the condensate can be used in the air heater to preheat the incoming air, appropriately increasing the air-side and flue gas-side temperatures of the air preheater, thus meeting the requirement to prevent ABS blockage in the air preheater. The coordinated operation of the cooler and the air heater reduces the waste of heat exchange area. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the initial state of the system under high wind temperature and high smoke temperature conditions.

[0034] Figure 2 for Figure 1 A schematic diagram of the system's operational status.

[0035] Figure 3 This is a schematic diagram of the initial state of the system under medium wind temperature and smoke temperature conditions.

[0036] Figure 4 for Figure 3 A schematic diagram of the system's operational status.

[0037] Figure 5 This is a schematic diagram of the initial state of the system under low wind temperature and low smoke temperature conditions.

[0038] Figure 6 for Figure 5 A schematic diagram of the system's operational status.

[0039] in, Figure 1 — Figure 6 middle:

[0040] Air preheater—1, cooler—2, air heater—3, low pressure heater outlet—4, low pressure heater return—5, first water pump—6, second water pump—7, recirculation pump—8, low pressure heater—9, flow regulating valve—10, first shut-off valve—11, second shut-off valve—12, third shut-off valve—13, fourth shut-off valve—14, fifth shut-off valve—15, sixth shut-off valve—16. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] In one specific embodiment of the present invention, the flue gas waste heat recovery system for air preheater 1 with ABS blockage mainly includes air preheater 1, cooler 2, heater 3, low pressure heater outlet 4, low pressure heater return outlet 5, first water pump 6 and second water pump 7.

[0043] Among them, the air preheater 1 is mainly used to heat the air entering the boiler by utilizing the waste heat of the flue gas in the boiler tail flue.

[0044] Cooler 2 is located on the flue gas side of air preheater 1 and is mainly used to absorb heat from the flue gas and cool it.

[0045] The heater 3 is located on the air side of the air preheater 1 and is mainly used to heat the incoming air.

[0046] Low-pressure heater outlet 4 is the condensate outlet of the boiler low-pressure heater system, which can draw out condensate at a certain temperature as the water medium for cooler 2 and air heater 3. Low-pressure heater return outlet 5 is the condensate return outlet of the boiler low-pressure heater system, mainly used for condensate return.

[0047] The first water pump 6 is connected between the low-pressure water outlet 4 and the cooler 2. It is mainly used to draw condensate from the low-pressure water outlet 4 and send it to the water inlet of the cooler 2, so that the condensate absorbs the flue gas heat on the flue gas side of the air preheater 1 in the cooler 2, thereby realizing the recovery of flue gas waste heat.

[0048] The second water pump 7 is connected between the low-pressure water outlet 4 and the air heater 3. It is mainly used to draw condensate from the low-pressure water outlet 4 and send it to the inlet of the air heater 3, so that the condensate heats the air intake air on the air side of the air preheater 1 in the air heater 3, thereby increasing the air side temperature and the flue gas side temperature, and thus preventing ABS blockage in the air preheater 1.

[0049] Meanwhile, the outlet of the cooler 2 is connected to the return water inlet 5 of the low-pressure heater and / or the inlet of the heater 3, so that the condensate that has absorbed the waste heat of the flue gas can flow directly back to the low-pressure heater system, or continue to enter the heater 3 to heat the air intake air on the air side of the air preheater 1.

[0050] The outlet of the heater 3 is connected to the outlet of the low-pressure heater 4 or the return outlet of the low-pressure heater 5, so that the extracted condensate heats the air intake air on the air side of the air preheater 1 and can flow directly back to the low-pressure heater system, or re-enter the cooler 2 for circulating heat absorption and release.

[0051] Thus, the flue gas waste heat recovery system for preventing ABS blockage in the air preheater 1 provided in this embodiment utilizes the condensate from the boiler low-pressure heater system extracted by the first water pump 6 and the second water pump 7 as the heat exchange medium. It can recover the waste heat of the flue gas in the cooler 2 to meet the waste heat recovery requirements. The recovered heat can be reabsorbed by the boiler or enter the air heater 3. At the same time, the recovered heat or the heat of the condensate can be used in the air heater 3 to preheat the incoming air, appropriately increasing the air side and flue gas side temperature of the air preheater 1, and meeting the requirement to prevent ABS blockage in the air preheater 1. The cooler 2 and the air heater 3 work together to reduce the waste of heat exchange area.

[0052] Generally, when the cooler 2 absorbs heat from the flue gas, it needs to reduce the flue gas temperature to above the first preset temperature. This first preset temperature is the temperature to prevent low-temperature corrosion of the flue gas, which is usually 110°C, that is, to ensure that the flue gas emission temperature is above 110°C.

[0053] Meanwhile, when the heater 3 heats the intake air, it needs to raise the overall temperature of the cold end of the air preheater 1 to a level above the second preset temperature. The overall temperature of the cold end is the sum of the air side temperature and the flue gas side temperature of the air preheater 1. The second preset temperature is the temperature at which NH4HSO4 is deposited on the hot section heat storage element of the air preheater 1 and causes low-temperature corrosion to the cold section heat storage element of the air preheater 1. It is usually above 170°C.

[0054] Based on the different external environment and boiler operating load, the system operating conditions can be basically divided into three operating modes: high air temperature and high flue gas temperature operating mode, medium air temperature and medium flue gas temperature operating mode, and low air temperature and low flue gas temperature operating mode.

[0055] like Figure 1 , Figure 2 As shown, Figure 1 This is a schematic diagram of the initial state of the system under high wind temperature and high smoke temperature conditions. Figure 2 for Figure 1 The diagram shows the system's operating status (arrows in the diagram indicate the direction of condensate flow, and branches without arrows indicate that no condensate flows through them).

[0056] In the first operating mode, when the combined cold-end temperature of the air preheater 1 is higher than the safe temperature and the flue gas temperature is higher than the design temperature, this condition typically occurs during the hot summer season when the unit load is also high. Under this condition, the safety of the air preheater 1 can be considered guaranteed, and only the recovery of waste heat from the flue gas needs to be considered. Under this condition, condensate is drawn from the low-pressure heater outlet 4 of the low-pressure heater system, pressurized by the first water pump 6, and enters the cooler 2. The condensate cools the flue gas temperature on the flue gas side of the air preheater 1 to the design temperature. After recovering the waste heat, the condensate returns to the low-pressure heater return outlet 5, thus reducing the extraction steam of the low-pressure heater system and saving energy. In this operating mode, the air heater 3 does not operate, and the second water pump 7 also does not operate. The energy saving comes from the reduced extraction steam in the low-pressure heater system, which increases power generation and reduces coal consumption for power generation.

[0057] Specifically, the inlet air temperature and exhaust gas temperature of air preheater 1 are set at 30℃ and 140℃ respectively. Under these conditions, the combined cold end temperature of air preheater 1 is 170℃. The operating conditions of air preheater 1 are safe, and the exhaust gas temperature is higher than 110℃, providing space for waste heat recovery from the flue gas. During operation, the first water pump 6 is started to draw condensate from the low-pressure heater outlet 4 and send it to cooler 2, reducing the exhaust gas temperature from 140℃ to 110℃ before discharge. The heated condensate returns to the low-pressure heater return outlet 5, displacing the low-pressure heater extraction steam and increasing the unit's power generation.

[0058] like Figure 3 , Figure 4 As shown, Figure 3 This is a schematic diagram of the initial state of the system under medium wind temperature and medium smoke temperature conditions. Figure 4 for Figure 3 The diagram shows the system's operating status (arrows in the diagram indicate the direction of condensate flow, and branches without arrows indicate that no condensate flows through them).

[0059] In the second operating mode, when the overall cold-end temperature of the air preheater 1 is lower than the safe temperature and the flue gas temperature is higher than the design temperature, this condition usually occurs when the air temperature is normal and the unit load is also average. At this time, the safety of the air preheater 1 cannot be guaranteed, but there is still room for flue gas waste heat recovery. Under this condition, condensate is drawn from the low-pressure heater outlet 4, pressurized by the first water pump 6, and enters the cooler 2. The condensate cools the flue gas temperature on the flue gas side of the air preheater 1 to the design temperature. The condensate after recovering the flue gas waste heat is divided into two paths according to a certain ratio: one path flows to the air heater 3 to heat the air intake air of the air preheater 1, and its flow rate ensures that the overall cold-end temperature of the air preheater 1 is higher than the safe value. The condensate after leaving the air heater 3 returns to the low-pressure heater outlet 4 - not in reverse backflow to the low-pressure heater outlet 4, but flows with the condensate to the inlet of the cooler 2 to achieve circulation; the other path flows directly back to the low-pressure heater return water port 5 to squeeze out the low-pressure heater system extraction steam for energy saving and consumption reduction. In this operating mode, cooler 2, heater 3, and first water pump 6 are all running, but second water pump 7 is not running. The energy saving comes from the reduced steam extraction in the low-pressure heating system, which increases power generation and reduces coal consumption for power generation, as well as the increased boiler evaporation caused by the heater 3 absorbing more heat.

[0060] Specifically, the inlet air temperature and exhaust gas temperature of air preheater 1 are set at 20℃ and 130℃ respectively. Under these conditions, the overall cold-end temperature of air preheater 1 is 150℃, which is lower than 170℃, making the operating conditions of air preheater 1 unsafe. Furthermore, the exhaust gas temperature is higher than 110℃, leaving room for waste heat recovery. During operation, the first water pump 6 is started to draw condensate from the low-pressure heater outlet 4 into the cooler 2, reducing the exhaust gas temperature from 139℃ (due to the operation of the air heater 3, the inlet air temperature of air preheater 1 is increased, resulting in a corresponding increase in exhaust gas temperature) to 110℃ before discharge. The heated condensate is divided into two paths: one path flows to the air heater 3 to heat the inlet air of air preheater 1, and the condensate flow rate of this branch is controlled to ensure that the overall exhaust gas temperature at the outlet of air preheater 1 is higher than 170℃; the other path flows directly back to the low-pressure heater return outlet 5 to displace the low-pressure heater extraction steam and increase the unit's power generation.

[0061] like Figure 5 , Figure 6 As shown, Figure 5 This is a schematic diagram of the initial state of the system under low air temperature and low smoke temperature conditions. Figure 6 for Figure 5 The diagram shows the system's operating status (arrows in the diagram indicate the direction of condensate flow, and branches without arrows indicate that no condensate flows through them).

[0062] In the third operating mode, when the combined cold-end temperature of the air preheater 1 is lower than the safe temperature and the flue gas temperature is also lower than the design temperature, this condition usually occurs during the winter season when the unit load is also low. At this time, the safety of the air preheater 1 cannot be guaranteed, and there is no waste heat from the flue gas to be recovered. Under this condition, the second water pump 7 is first turned on, and condensate is drawn from the low-pressure heater outlet 4 and pressurized by the second water pump 7 into the air heater 3 to heat the intake air of the air preheater 1, thereby increasing the flue gas temperature of the air preheater 1 and ensuring that the combined cold-end temperature of the air preheater 1 is higher than the safe value. The condensate flowing out of the air heater 3 flows directly back to the low-pressure heater return outlet 5. Then, the first water pump 6 is turned on, drawing some condensate from the low-pressure heater outlet 4 and sending it to the cooler 2. This reduces the flue gas temperature, which has increased due to the operation of the heater 3, to the design value. The condensate flowing out of the cooler 2 first enters the heater 3, using the absorbed waste heat from the flue gas to heat the intake air of the air preheater 1, and then flows back to the low-pressure heater return outlet 5. In this operating mode, the cooler 2, heater 3, first water pump 6, and second water pump 7 are all running. The energy consumption is due to the increased steam extraction rate of the low-pressure heater system caused by the condensate heating the intake air of the air preheater 1. The energy saving comes from the increased boiler evaporation caused by the heater 3 absorbing more heat from the boiler.

[0063] Specifically, assuming the inlet air temperature and exhaust gas temperature of air preheater 1 are -10℃ and 105℃ respectively, the overall cold-end temperature of air preheater 1 is 95℃, which is lower than 170℃, making the operating conditions of air preheater 1 unsafe. The exhaust gas temperature is also below 110℃, leaving no space for waste heat recovery, and cooler 2 and its downstream equipment are at risk of low-temperature corrosion. During operation, the second water pump 7 is first started to draw condensate from the low-pressure heater outlet 4 and send it to the air heater 3, raising the inlet air temperature of air preheater 1 to 36℃. Simultaneously, the exhaust gas temperature will rise to 135℃, bringing the overall cold-end temperature of air preheater 1 to 171℃, thus achieving safe operating conditions for air preheater 1. Meanwhile, with the operation of the heater 3, the exhaust gas temperature has exceeded 110℃, leaving room for waste heat recovery. The first water pump 6 is then started to draw condensate from the low-pressure heater outlet 4 and send it to the cooler 2, reducing the exhaust gas temperature from 135℃ to 110℃ before discharge. The cooler 2 and its downstream equipment and facilities have reached safe operating conditions. The heated condensate first enters the heater 3 to heat the intake air of the air preheater 1, and then flows back to the low-pressure heater return water outlet 5 to displace the low-pressure heater extraction steam and increase the unit's power generation.

[0064] Since the original flue gas temperature was below 110℃, the third operating mode is essentially equivalent to the condensate from the low-pressure heater system heating the air intake air of the air preheater 1 to supplement the boiler with heat, raising the flue gas temperature to 110℃. Simultaneously, some of the supplemented heat is absorbed by the boiler during its circulation cycle. Therefore, the temperature at the low-pressure heater return water inlet 5 is lower than the temperature at the low-pressure heater outlet 4. Based on the data in this example, when the flue gas temperature rises from 105℃ to 135℃, the boiler absorbs heat equivalent to an 8℃ flue gas temperature drop. The heat loss from the condensate can be estimated as equivalent to a 13℃ flue gas temperature drop. The efficiency of the heat absorbed by the boiler in performing work is higher than the efficiency of the low-pressure heater extraction steam. The reduction and increase in power generation coal consumption are similar, and the overall impact on the unit's power generation coal consumption is minimal. In other words, the operation of this system essentially maintains the unit's power generation coal consumption unchanged while transforming the unsafe operating conditions of the air preheater 1, cooler 2, and their downstream equipment into safe operating conditions.

[0065] In addition, to achieve low-temperature corrosion protection for cooler 2, a recirculation pump 8 is added in this embodiment. Specifically, the recirculation pump 8 is connected between the inlet and outlet of cooler 2, and is mainly used to reintroduce some of the condensate after heat absorption from the outlet of cooler 2 to the inlet of cooler 2, thereby ensuring that the inlet water temperature of cooler 2 is above the safe temperature.

[0066] To facilitate the rapid extraction of condensate by the first water pump 6 and the second water pump 7, in this embodiment, the low-pressure heater outlet 4 is simultaneously connected to the outlets of multiple low-pressure heaters 9 at different temperatures. Furthermore, a flow regulating valve 10 is installed at the outlet of each low-pressure heater 9. By adjusting the condensate outlet flow rate of different low-pressure heaters 9, the flow rate, temperature, and other parameters of the condensate extracted by the first water pump 6 and the second water pump 7 from the low-pressure heater outlet 4 can be controlled, thereby enabling more precise control of the temperature at various points in the system.

[0067] As for the low-pressure heater return port 5, in order to simplify the system structure, the low-pressure heater return port 5 can be connected only to the outlet of a single low-pressure heater 9.

[0068] To facilitate the control of the operation status of the cooler 2, the heater 3, the first water pump 6, and the second water pump 7, as well as the control of the condensate flow direction in the aforementioned three operating modes, this embodiment adds a first shut-off valve 11, a second shut-off valve 12, a third shut-off valve 13, a fourth shut-off valve 14, a fifth shut-off valve 15, and a sixth shut-off valve 16. The on / off states of the first shut-off valve 11, the second shut-off valve 12, the third shut-off valve 13, the fourth shut-off valve 14, the fifth shut-off valve 15, and the sixth shut-off valve 16 are all controllable, such as through electrical control.

[0069] The system comprises the following valves: a first shut-off valve 11 connects the outlet of the cooler 2 to the low-pressure heater return port 5; when the first shut-off valve 11 is open, condensate can flow back to the low-pressure heater return port 5. A second shut-off valve 12 connects the outlet of the cooler 2 to the inlet of the heater 3; when the second shut-off valve 12 is open, condensate can flow back to the heater 3. A third shut-off valve 13 connects the outlet of the heater 3 to the low-pressure heater return port 5; when the third shut-off valve 13 is open, condensate can flow back to the low-pressure heater return port 5. A fourth shut-off valve 14 connects the outlet of the heater 3 to the low-pressure heater outlet 4; when the fourth shut-off valve 14 is open, condensate can merge with condensate flowing from the low-pressure heater outlet 4 and enter the cooler 2. The fifth shut-off valve 15 is connected between the first water pump 6 and the low-pressure water outlet 4. When the fifth shut-off valve 15 is open, condensate can enter the cooler 2 through the first water pump 6. The sixth shut-off valve 16 is connected between the second water pump 7 and the low-pressure water outlet 4. When the sixth shut-off valve 16 is open, condensate can enter the heater 3 through the second water pump 7.

[0070] In a preferred embodiment of the first water pump 6 and the second water pump 7, in order to increase the flow rate of condensate, both the first water pump 6 and the second water pump 7 are booster pumps.

[0071] In summary, this embodiment, through joint operation, ensures the safe and stable operation of the air preheater 1 and its downstream equipment and facilities, improves the utilization rate of the heat exchanger, maximizes the recovery of recoverable flue gas waste heat, achieves safe and stable energy saving and consumption reduction, can significantly reduce the heat exchange area on the flue gas side, reduce the installation and layout pressure on the flue gas side, reduce the resistance on the flue gas side, and reduce the total project cost.

[0072] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A flue gas waste heat recovery system for preventing ABS blockage in an air preheater, comprising an air preheater (1), characterized in that, It also includes a cooler (2), a heater (3), a low-pressure water outlet (4), a low-pressure water return outlet (5), a first water pump (6), and a second water pump (7); The cooler (2) is located on the flue gas side of the air preheater (1) and is used to absorb heat from the flue gas. The heater (3) is located on the air side of the air preheater (1) and is used to heat the incoming air. The first water pump (6) is connected between the low-pressure outlet (4) and the cooler (2) to introduce condensate into the inlet of the cooler (2); The second water pump (7) is connected between the low-pressure outlet (4) and the heater (3) to introduce condensate into the inlet of the heater (3); The outlet of the cooler (2) is connected to the return water inlet (5) and / or the inlet of the heater (3); The outlet of the heater (3) is connected to the low-pressure water outlet (4) or the low-pressure water return outlet (5); The system is configured to achieve multi-mode operation under different working conditions by controlling the operation status of the cooler (2) and the heater (3) and the flow direction of condensate, based on the combined cold end temperature and flue gas temperature of the air preheater (1), including: When the overall temperature of the cold end is higher than the safe temperature and the flue gas temperature is higher than the design temperature, only the cooler (2) is operated to recover the waste heat of the flue gas. When the overall temperature of the cold end is lower than the safe temperature and the flue gas temperature is higher than the design temperature, the cooler (2) and the heater (3) are operated at the same time. Some of the condensate flows from the outlet of the cooler (2) into the heater (3) and then returns to the low-pressure water outlet (4). When the overall temperature of the cold end is lower than the safe temperature and the exhaust temperature is lower than the design temperature, the heater (3) is run first to increase the air temperature, and then the cooler (2) is run to recover the waste heat. The condensate flows from the outlet of the cooler (2) into the heater (3) and then returns to the low-pressure return water inlet (5).

2. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 1, characterized in that, It also includes a recirculation pump (8); The recirculation pump (8) is connected between the inlet and outlet of the cooler (2) and is used to reintroduce some of the condensate after heat absorption from the outlet of the cooler (2) to the inlet of the cooler (2).

3. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 1, characterized in that, The cooler (2) is used to absorb heat from the flue gas to reduce the flue gas temperature to a level above a first preset temperature; wherein the first preset temperature is the temperature at which low-temperature corrosion of the flue gas is prevented.

4. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 1, characterized in that, The heater (3) is used to heat the intake air to raise the overall temperature of the cold end of the air preheater (1) to a level above the second preset temperature; wherein, the overall temperature of the cold end of the air preheater (1) is the sum of the air-side temperature of the air preheater (1) and the flue gas-side temperature of the air preheater (1), and the second preset temperature is the temperature at which NH4HSO4 is prevented from depositing on the hot section heat storage element of the air preheater (1) and causing low-temperature corrosion to the cold section heat storage element of the air preheater (1).

5. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 1, characterized in that, The low-pressure water outlet (4) is simultaneously connected to the outlets of multiple low-pressure heaters (9) at different temperatures, and each low-pressure heater (9) is provided with a flow regulating valve (10) for adjusting its own water flow rate at its outlet.

6. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 5, characterized in that, The low-pressure return water inlet (5) is connected to the outlet of the single low-pressure heater (9).

7. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 1, characterized in that, It also includes a first shut-off valve (11) connected between the outlet of the cooler (2) and the low-pressure return water inlet (5) and whose on / off state is controllable, and a second shut-off valve (12) connected between the outlet of the cooler (2) and the inlet of the heater (3) and whose on / off state is controllable.

8. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 1, characterized in that, It also includes a third shut-off valve (13) connected between the outlet of the heater (3) and the low-pressure return water port (5) and whose on / off state is controllable, and a fourth shut-off valve (14) connected between the outlet of the heater (3) and the low-pressure outlet (4) and whose on / off state is controllable.

9. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 1, characterized in that, It also includes a fifth shut-off valve (15) connected between the first water pump (6) and the low-pressure outlet (4) and whose on / off state is controllable, and a sixth shut-off valve (16) connected between the second water pump (7) and the low-pressure outlet (4) and whose on / off state is controllable.

10. The flue gas waste heat recovery system for air raid preheater ABS blockage according to claim 1, characterized in that, Both the first water pump (6) and the second water pump (7) are booster pumps.

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