A system and method for recycling flue gas waste heat in an ammonia desulfurization process

Abstract

The application discloses a flue gas waste heat recycling system and method for ammonia desulfurization process, and aims to solve technical problems of large temperature difference of gas and liquid required by different functional areas in an ammonia desulfurization tower, generation of a large number of ammonium sulfite fine particles difficult to capture caused by ammonia volatilization, and difficulty in recycling a large amount of flue gas waste heat in a desulfurization device.Based on an ammonia wet desulfurization device, gas and liquid waste heat in a washing and absorption section of the desulfurization tower is recycled to heat air inlet of a fan, so as to reduce the temperature of the gas and liquid in the washing and absorption section and control ammonia volatilization and fine particle generation; flue gas waste heat after an air preheater is recycled to heat air outlet of the fan, and the temperature of air inlet of the desulfurization tower is controlled according to heat demand of a concentration and crystallization section; two-stage waste heat of air inlet of the air preheater is used to increase the volume of boiler exhaust gas, high-temperature waste heat of high-temperature expanded gas is recycled by setting an expansion coal economizer to heat boiler feed water, the operation energy consumption of a deaerator is reduced, and high-temperature waste heat recycling is realized.

Description

Technical Field

[0001] This application relates to the field of new energy, specifically to a flue gas waste heat recovery system and method for ammonia desulfurization process. Background Technology

[0002] The ammonia-based desulfurization process uses liquid ammonia, ammonia water, or ammonium bicarbonate solution as the absorbent to neutralize SO2 in the flue gas. The intermediate product, ammonium sulfite, is oxidized by aeration to produce ammonium sulfate. The process involves heat exchange, evaporation, concentration, and crystallization of the absorbed and oxidized ammonium sulfate solution with high-temperature flue gas to prepare solid ammonium sulfate crystals. The ammonia-based desulfurization absorption reaction is a gas-liquid two-phase neutralization reaction, which has advantages such as fast reaction speed, low liquid-to-gas ratio and low operating resistance, and high absorbent utilization rate. Furthermore, the desulfurization byproduct, ammonium sulfate, is an excellent nitrogen fertilizer, enabling the resource utilization of pollutants.

[0003] Ammonia-based desulfurization takes place inside a desulfurization tower. To simultaneously ensure the efficiency of ammonia-based desulfurization, the oxidation of ammonium sulfite, and the concentration and crystallization of ammonium sulfate, the tower is equipped with a washing and absorption section and a concentration and crystallization section, while an oxidation tank is located outside the tower. In the washing and absorption section, liquid ammonia, ammonia water, or ammonium bicarbonate solution neutralizes and reacts with SO2 in the flue gas to generate ammonium sulfite solution, which then enters the oxidation tank outside the tower for oxidation to generate ammonium sulfate solution. The oxidized ammonium sulfate solution is then sent to the concentration and crystallization section to exchange heat with the high-temperature flue gas, evaporating and concentrating to generate ammonium sulfate crystals. Due to the instability of liquid ammonia water, a large amount of ammonia volatilizes during ammonia-based desulfurization. The volatilized gaseous ammonia readily reacts with SO2 in the flue gas to generate submicron and ammonium sulfite fine particles that are difficult to capture. To control the emission of particulate matter from ammonia-based desulfurization, a water washing section is also installed above the washing and absorption section for capturing and demisting fine ammonium sulfite particles in the desulfurization tail gas.

[0004] Waste heat from industrial flue gas emissions is the main cause of high heat loss and low energy utilization efficiency, and it is also a difficult point to recover and utilize low-grade waste heat from industrial emissions. Summary of the Invention

[0005] Based on the characteristics of the ammonia-based desulfurization process, in the concentration and crystallization stage, a higher inlet flue gas temperature is beneficial for the efficient concentration and crystallization of ammonium sulfate solution; in the washing and absorption stage, a lower washing liquid temperature is unfavorable for the volatilization of ammonia in the solution, which is beneficial for controlling the production of fine ammonium sulfite particles; in the water washing stage, lower flue gas and water washing temperatures are more conducive to the capture of submicron-sized ammonium sulfite particles. Therefore, different process stages of the ammonia-based desulfurization process have different requirements for the gas-liquid temperature of the purification process, further increasing the difficulty of recovering and utilizing waste heat from flue gas emissions in the ammonia-based desulfurization process.

[0006] This application provides a flue gas waste heat recovery system and method for ammonia-based desulfurization processes. Addressing the technical challenges of large temperature differences between gas and liquid components in different functional zones of the ammonia-based desulfurization tower, the generation of large amounts of difficult-to-capture ammonium sulfite fine particles due to ammonia volatilization, and the difficulty in recovering and utilizing large amounts of flue gas waste heat within the desulfurization unit, this application, based on an ammonia-based wet desulfurization unit, recovers waste heat from the gas and liquid components of the desulfurization tower's washing and absorption section for heating the fan inlet air, thereby reducing the gas and liquid temperature of the washing and absorption section and controlling ammonia volatilization and fine particulate matter generation. It also recovers waste heat from the flue gas after the air preheater for heating the fan outlet air, and controls the desulfurization tower inlet air temperature according to the heat requirements of the concentration and crystallization section. Furthermore, it increases the boiler exhaust volume through two stages of waste heat from the air preheater inlet air, and recovers high-temperature waste heat from the high-temperature expansion gas using an expansion economizer for heating boiler feedwater, reducing the deaerator's operating energy consumption and achieving high-temperature waste heat recovery and utilization.

[0007] A flue gas waste heat recovery system for ammonia desulfurization process includes: a primary warm air heat exchanger, a fan, a secondary warm air heat exchanger, an air preheater, a low-temperature heat exchanger, an expansion economizer, an absorption heat pump, a desulfurization tower, and a water treatment workshop.

[0008] The desulfurization tower consists of a concentration and crystallization section, a washing and absorption section, a water washing section, and a flue gas discharge outlet, arranged from bottom to top. The concentration and crystallization section consists of a crystallization circulation pool, a flue gas inlet, and a concentration heat exchange section, arranged from bottom to top. The washing and absorption section is equipped with an absorption section heat exchanger, and the water washing section is equipped with a first water washing section heat exchanger and a second water washing section heat exchanger, arranged from bottom to top.

[0009] The air preheater is provided with an air passage for air circulation and a flue gas passage for flue gas circulation. The air outlet of the air preheater's air passage is connected to the air inlet of the boiler furnace through an air duct, and the flue gas inlet of the air preheater's flue gas passage is connected to the boiler flue gas outlet through a flue.

[0010] The inlet of the fan is connected to the atmospheric environment through the air intake duct, and the outlet of the fan is connected to the air inlet of the air preheater through the air outlet duct. The air intake duct of the fan is equipped with a primary warm air heat exchanger, and the air outlet duct of the fan is equipped with a secondary warm air heat exchanger.

[0011] The expansion economizer and the air preheater are installed in parallel. The flue gas inlet of the expansion economizer is connected to the boiler flue gas outlet through a flue. The flue gas outlets of both the expansion economizer and the air preheater are connected to the flue gas inlet of the low-temperature heat exchanger through a flue. The flue gas outlet of the low-temperature heat exchanger is connected to the flue gas inlet of the desulfurization tower through a flue.

[0012] The primary heating air heat exchanger, secondary heating air heat exchanger, absorption section heat exchanger, first water washing section heat exchanger, second water washing section heat exchanger, low temperature heat exchanger, and expansion economizer are all metal tube box type structures. The metal tubes are used for the flow of heat exchange liquid, and the gaps between the metal tubes are used for the flow of gas.

[0013] The absorption heat pump is equipped with a demineralized water flow pipeline and a heat transfer oil flow pipeline.

[0014] The medium flowing inside the metal tubes of the primary heating air heat exchanger, the absorption section heat exchanger, the secondary heating air heat exchanger, and the low-temperature heat exchanger is demineralized water. The inlet of the primary heating air heat exchanger is connected to the outlet of the absorption section heat exchanger via a pipeline, and the outlet of the primary heating air heat exchanger is connected to the inlet of the absorption section heat exchanger via a pipeline. The inlet of the secondary heating air heat exchanger is connected to the outlet of the low-temperature heat exchanger via a pipeline, and the outlet of the secondary heating air heat exchanger is connected to the inlet of the low-temperature heat exchanger via a pipeline.

[0015] The medium flowing in the second water washing section heat exchanger is boiler feedwater / raw water, and the medium flowing in the metal tubes of the first water washing section heat exchanger is demineralized water. The inlet of the second water washing section heat exchanger is connected to the raw water supply pipeline, and the outlet of the second water washing section heat exchanger is connected to the inlet of the water treatment workshop through a pipeline. The demineralized water outlet of the water treatment workshop is connected to the demineralized water inlet of the first water washing section heat exchanger through a pipeline. The demineralized water outlet of the first water washing section heat exchanger is connected to the demineralized water inlet of the absorption heat pump through a pipeline. The demineralized water outlet of the absorption heat pump is connected to the demineralized water inlet of the boiler deaerator through a pipeline.

[0016] The medium flowing inside the metal tube of the expansion economizer is heat transfer oil. The heat transfer oil inlet of the expansion economizer is connected to the heat transfer oil outlet of the absorption heat pump through a pipeline, and the heat transfer oil outlet of the expansion economizer is connected to the heat transfer oil inlet of the absorption heat pump through a pipeline.

[0017] Optionally, the first and second water washing section heat exchangers are installed above the washing and absorption section to condense and capture submicron and ammonium sulfite particles in the flue gas after desulfurization, and to recover the heat of the clean flue gas after desulfurization for boiler feedwater heating. The second water washing section heat exchanger is used to heat the boiler feedwater to ensure that the inlet water temperature of the water treatment workshop is at the optimal operating condition for membrane separation or resin adsorption in the raw water desalination process. The second water washing section heat exchanger is used to heat the outlet water of the water treatment workshop.

[0018] As a preferred option, by adjusting the heat exchange time and heat exchange area of ​​the circulating medium in the water washing section heat exchanger, the raw water outlet temperature of the second water washing section heat exchanger is controlled to be 23-27℃, and the demineralized water outlet temperature of the first water washing section heat exchanger is controlled to be 37-42℃.

[0019] Optionally, the absorption section heat exchanger is installed above the concentration and crystallization section. The connecting pipeline between the absorption section heat exchanger and the first-stage warm air heat exchanger is equipped with a demineralized water drive pump and valve, which is used to drive low-temperature demineralized water into the absorption section heat exchanger to exchange heat and cool down the washing slurry and flue gas, reduce ammonia volatilization and the generation of submicron ammonium sulfite particles, and use the high-temperature demineralized water after heat exchange for heating the fan intake air, so as to realize the recovery of gas-liquid waste heat in the washing absorption section.

[0020] As a preferred option, by adjusting the demineralized water flow rate and heat exchange area, the outlet air temperature rise of the primary warm air heat exchanger is controlled to be 10-25℃, and the outlet flue gas temperature of the washing and absorption section is 46-50℃.

[0021] Optionally, the secondary warm air heat exchanger is installed in the air outlet duct connecting the fan outlet and the air inlet of the air preheater. A demineralized water drive pump and valve are provided on the connecting pipeline between the secondary warm air heat exchanger and the low-temperature heat exchanger. The pump is used to drive the low-temperature demineralized water into the low-temperature heat exchanger to exchange heat with the flue gas at the air preheater outlet and send the high-temperature demineralized water after heat exchange to the secondary warm air heat exchanger for heating the air preheater inlet air. The pump also controls the temperature of the flue gas entering the concentration and crystallization section of the desulfurization tower to ensure efficient evaporation and crystallization of the ammonium sulfate solution.

[0022] In order to balance the waste heat recovery of the flue gas at the air preheater outlet and the evaporation and crystallization efficiency of the ammonium sulfate solution in the concentration and crystallization section, the preferred method is to control the outlet air temperature of the secondary warm air heat exchanger to 50-80℃ and the outlet flue gas temperature of the low-temperature heat exchanger to 100-120℃ by adjusting the demineralized water flow rate and heat exchange area.

[0023] Optionally, the expansion economizer is installed in parallel with the air preheater. The expansion economizer is used to facilitate the flow of flue gas whose exhaust volume expands due to the increase in boiler exhaust temperature caused by preheating of the hot air heat exchanger, ensuring that the flue gas velocity in the flue gas passage of the air preheater is within the design velocity range.

[0024] Optionally, a heat transfer oil drive pump and valve are provided on the connecting pipeline between the expansion economizer and the heat transfer oil pipeline of the absorption heat pump. The heat transfer oil is used to drive the heat transfer oil into the expansion economizer to exchange heat with the high-temperature expansion flue gas flowing through the expansion economizer and raise its temperature. The heat-exchanged high-temperature heat transfer oil is then sent to the heat transfer oil inlet pipeline of the absorption heat pump as the driving heat source for the absorption heat pump heating.

[0025] As a preferred option, the outlet temperature of the heat transfer oil in the expander economizer is controlled to be 80-90℃ by adjusting and controlling the flow rate of the heat transfer oil.

[0026] Optionally, the inlet of the demineralized water flow pipeline of the absorption heat pump is connected to the outlet of the heat exchanger in the first water washing section through a pipeline. The absorption heat pump uses the high-temperature heat transfer oil entering its heat transfer oil flow pipeline as the driving heat source to heat the demineralized water entering its demineralized water channel in two stages, and then sends the heated high-temperature demineralized water to the boiler deaerator for deoxygenation and removal of non-condensable gases, so as to ensure the quality of the boiler drum feed water.

[0027] As a preferred option, the outlet demineralized water temperature of the absorption heat pump should be controlled at 87-95℃.

[0028] This application also provides a method for recovering waste heat from flue gas in an ammonia-based desulfurization process, preferably using the recovery system described in this application, including:

[0029] (1) Ambient air is sent to the boiler furnace by the fan through the air channel in the air preheater and mixed with fuel for combustion. The demineralized water driven pump installed on the connecting pipeline between the primary warm air heat exchanger and the absorption section heat exchanger drives the demineralized water into the absorption section heat exchanger to exchange heat with the flue gas and washing liquid of the ammonia washing absorption section, thereby reducing the gas-liquid reaction temperature of the washing absorption section, reducing the volatilization rate of ammonia in the washing liquid, controlling the generation of submicron and ammonium sulfite particles, and controlling the outlet flue gas emission temperature of the washing absorption section at 46-50℃. The demineralized water that has completed heat exchange and temperature rise is sent to the primary warm air heat exchanger installed in the fan inlet air duct to preheat the fan inlet air, raising the fan inlet air temperature by 10-25℃.

[0030] (2) The demineralized water drive pump installed on the connecting pipeline between the secondary warm air heat exchanger and the low temperature heat exchanger drives the demineralized water into the low temperature heat exchanger to exchange heat with the high temperature flue gas flowing through the low temperature heat exchanger, and sends the high temperature demineralized water that has completed the heat exchange to the secondary warm air heat exchanger installed in the fan outlet duct for preheating the fan outlet air. In order to ensure that the heat contained in the desulfurization tower inlet air temperature meets the requirements for concentration and crystallization of ammonium sulfate solution in the desulfurization tower, the outlet air temperature of the secondary warm air heat exchanger is controlled to be 50-80℃ and the outlet flue gas temperature of the low temperature heat exchanger is 100-120℃ by adjusting the demineralized water flow rate and heat exchange area.

[0031] (3) After two stages of preheating, the air enters the boiler furnace through the air circulation channel of the air preheater, which causes the temperature of the flue gas discharged from the boiler and the flue gas flowing through the air preheater to rise and expand in volume, thereby increasing the flue gas velocity. In order to prevent the high-speed flue gas containing dust from scouring and wearing the air preheater and to ensure the stable operation of the air preheater, an expansion economizer connected in parallel with the air preheater is installed outside the air preheater to introduce the flue gas that has expanded due to the temperature rise into the expansion economizer. In the expansion economizer, heat transfer oil is used as the heat exchange medium to exchange heat with the high-temperature flue gas and realize the recovery of high-temperature waste heat. In order to ensure the stable operation of the air preheater and the expansion economizer, the outlet temperature of the heat transfer oil of the expansion economizer is controlled at 80-90℃.

[0032] (4) Boiler feedwater is sent to the second water washing section heat exchanger below the flue gas outlet in the desulfurization tower via the pipeline. It exchanges heat with the desulfurized flue gas and is heated to 23-27°C before being sent to the water treatment workshop. Within this temperature range, the ion exchange resin or reverse osmosis membrane in the raw water softening and desalination process is in the best operating condition, which can effectively improve the service life and stability of the raw water softening and desalination system in the water treatment workshop. The demineralized water that has completed softening and desalination is sent to the first water washing section heat exchanger to continue to exchange heat with the desulfurized flue gas and be heated to 37-42°C. While realizing the recovery and utilization of waste heat from the ammonia desulfurization tail gas, it also efficiently captures the submicron-sized ammonium sulfate fine particles entering the water washing section.

[0033] (5) The demineralized water that has completed two-stage heating in the water washing section is sent to the demineralized water flow pipeline of the absorption heat pump through the pipeline. The absorption heat pump uses the high-temperature heat transfer oil entering the heat transfer oil pipeline as the driving heat source to heat the demineralized water to 87-95℃. After that, it is sent to the deaerator through the pipeline to remove oxygen and non-condensable components, thereby reducing the energy consumption of the deaerator. The heat transfer oil well pipeline that has completed the driving heating is sent to the collision economizer to continue to exchange heat with the high-temperature flue gas and increase the temperature.

[0034] Compared with the prior art, this application has at least one of the following beneficial effects:

[0035] (1) This application provides a technical solution to improve the operating energy efficiency of the ammonia desulfurization process: by setting up an absorption section heat exchanger in the washing absorption section, the gas-liquid reaction temperature of the washing absorption section is controlled, thereby reducing the amount of ammonium sulfite fine particles generated during the ammonia desulfurization washing process due to ammonia volatilization; by setting up a two-stage water washing section heat exchanger in the water washing section above the ammonia desulfurization tower, the collection efficiency of slurry droplets and fine particles in the water washing section of the ammonia desulfurization is improved and some water resources are recovered; by setting up a low-temperature heat exchanger in the flue gas inlet of the desulfurization tower, the flue gas inlet temperature of the concentration and crystallization section of the ammonia desulfurization tower is controlled, thereby effectively ensuring the concentration and crystallization rate of the ammonium sulfate solution.

[0036] (2) This application provides a technical solution for recovering low-grade waste heat from boiler flue gas emissions and preparing high-grade waste heat to reduce boiler operating energy consumption: by setting up two-stage warm air heat exchangers on the inlet and outlet air ducts of the blower, the low-grade waste heat of the washing absorption section and water washing section in the ammonia desulfurization tower is recovered for boiler air supply heating, thereby increasing the boiler inlet air temperature and exhaust volume, and the high-temperature flue gas waste heat in the expansion economizer due to temperature rise is recovered as the driving heat source of the absorption heat pump to heat the boiler feed water and reduce the deaerator operating energy consumption, thereby realizing the recovery of low-grade heat source to displace high-grade heat source and recycling, thereby reducing boiler operating energy consumption.

[0037] (3) This application provides a technical solution to improve the operational stability of the boiler feedwater preparation system: the boiler feedwater is sent to the desulfurization tower water washing section for heat exchange and temperature rise, and the temperature of the raw water outlet is controlled within the optimal temperature range required by the ion exchange resin and reverse osmosis membrane in the raw water softening and desalination process, thereby improving the operating efficiency and lifespan of the ion exchange resin and reverse osmosis membrane. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the recycling system in this application;

[0039] Figure 2 Process flow diagram of the method for recycling this application.

[0040] The diagram is labeled as follows: 1- Primary heating air heat exchanger; 2- Fan; 3- Secondary heating air heat exchanger.

[0041] 4-Air preheater; 5-Low-temperature heat exchanger; 6-Expansion economizer

[0042] 7-Absorption heat pump 8-Desulfurization tower 9-Watering workshop

[0043] 81-Absorption section heat exchanger; 82-First water washing section heat exchanger; 83-Second water washing section heat exchanger; 84-Concentration and crystallization section Detailed Implementation

[0044] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0046] like Figure 1 As shown, a flue gas waste heat recovery system for ammonia desulfurization process includes: a primary warm air heat exchanger 1, a fan 2, a secondary warm air heat exchanger 3, an air preheater 4, a low-temperature heat exchanger 5, an expansion economizer 6, an absorption heat pump 7, a desulfurization tower 8, and a water treatment workshop 9.

[0047] The desulfurization tower 8 contains, from bottom to top, a concentration and crystallization section 84, a washing and absorption section, a water washing section, and a flue gas discharge port. The concentration and crystallization section contains, from bottom to top, a crystallization circulation pool, a flue gas inlet (the arrow in the figure is only for the purpose of indicating the flue gas inlet), and a concentration heat exchange section. The washing and absorption section is equipped with an absorption section heat exchanger 81. The water washing section contains, from bottom to top, a first water washing section heat exchanger 82 and a second water washing section heat exchanger 83.

[0048] The air preheater 4 is equipped with an air passage for air circulation and a flue gas passage for flue gas circulation. The air outlet of the air passage of the air preheater 4 is connected to the air inlet of the boiler furnace through an air duct, and the flue gas inlet of the air preheater 4 is connected to the flue gas outlet of the boiler through a flue.

[0049] The inlet of fan 2 is connected to the atmospheric environment through the air intake duct, and the outlet of fan 2 is connected to the air inlet of the air preheater 4 through the air outlet duct. A primary warm air heat exchanger 1 is installed in the air intake duct of fan 2, and a secondary warm air heat exchanger 3 is installed in the air outlet duct of fan 2.

[0050] The expansion economizer 6 and the air preheater 4 are installed in parallel. The flue gas inlet of the expansion economizer 6 is connected to the boiler flue gas outlet through a flue. The flue gas outlets of both the expansion economizer 6 and the air preheater 4 are connected to the flue gas inlet of the low-temperature heat exchanger 5 through a flue. The flue gas outlet of the low-temperature heat exchanger 5 is connected to the flue gas inlet of the desulfurization tower 8 through a flue.

[0051] In one optional embodiment, the primary air heat exchanger 1, the secondary air heat exchanger 3, the absorption section heat exchanger 81, and the low-temperature heat exchanger 5 all adopt a metal tube box structure. The heat exchange liquid flows inside the metal tubes, and the gaps between the metal tubes are used for gas flow. Regarding the selection of the heat exchange liquid, the medium flowing inside the metal tubes of the primary air heat exchanger, the absorption section heat exchanger, the secondary air heat exchanger, and the low-temperature heat exchanger is demineralized water. The demineralized water inlet of the primary air heat exchanger 1 is connected to the demineralized water outlet of the absorption section heat exchanger 81 via a pipeline, and the demineralized water outlet of the primary air heat exchanger 1 is connected to the demineralized water inlet of the absorption section heat exchanger 81 via a pipeline. The demineralized water inlet of the secondary air heat exchanger 3 is connected to the demineralized water outlet of the low-temperature heat exchanger 5 via a pipeline, and the demineralized water outlet of the secondary air heat exchanger 3 is connected to the demineralized water inlet of the low-temperature heat exchanger 5 via a pipeline.

[0052] The absorption heat pump 7 is equipped with a demineralized water flow pipeline and a heat transfer oil flow pipeline. The demineralized water flow pipeline has a demineralized water inlet and a demineralized water outlet, and the heat transfer oil flow pipeline has a heat transfer oil inlet and a heat transfer oil outlet. Demineralized water flows in the demineralized water flow pipeline, and heat transfer oil flows in the heat transfer oil flow pipeline. The expansion economizer has a metal tube box structure. The heat exchange liquid flows inside the metal tubes, and the gaps between the metal tubes are used for gas flow. As the heat exchange liquid selection for the economizer, the medium flowing inside the metal tubes of the expansion economizer is heat transfer oil. The heat transfer oil inlet of the expansion economizer 6 is connected to the heat transfer oil outlet of the absorption heat pump 7 through a pipeline, and the heat transfer oil outlet of the expansion economizer 6 is connected to the heat transfer oil inlet of the absorption heat pump 7 through a pipeline.

[0053] The first water washing section heat exchangers 8 and 83 also adopt a metal tube box structure. The heat exchange liquid flows inside the metal tubes, and the gaps between the metal tubes are used for gas flow. The medium flowing inside the second water washing section heat exchanger 83 is boiler feedwater. The medium flowing inside the metal tubes of the first water washing section heat exchanger 82 is demineralized water. The boiler feedwater inlet of the second water washing section heat exchanger 83 is connected to the feedwater pipeline, and the outlet of the second water washing section heat exchanger 83 is connected to the inlet of the water treatment workshop 9 through a pipeline. The demineralized water outlet of the water treatment workshop 9 is connected to the demineralized water inlet of the first water washing section heat exchanger 82 through a pipeline. The demineralized water outlet of the first water washing section heat exchanger 82 is connected to the demineralized water inlet of the absorption heat pump 7 through a pipeline. The demineralized water outlet of the absorption heat pump 7 is connected to the demineralized water inlet of the boiler deaerator through a pipeline.

[0054] The first water washing section heat exchanger 82 and the second water washing section heat exchanger 83 are installed above the washing and absorption section. They are used to condense and capture submicron and ammonium sulfite particles in the flue gas after desulfurization, and to recover the heat of the clean flue gas after desulfurization for boiler feedwater heating. The second water washing section heat exchanger 83 is used to heat the boiler feedwater, ensuring that the inlet water temperature of the water treatment workshop 9 is at the optimal operating condition for membrane separation or resin adsorption during the raw water desalination process. The second water washing section heat exchanger 83 is also used to heat the effluent water from the water treatment workshop. Preferably, by adjusting the heat exchange time and heat exchange area of ​​the circulating medium in the water washing section heat exchangers, the raw water outlet temperature of the second water washing section heat exchanger 83 is controlled to be 23-27℃, and the demineralized water outlet temperature of the first water washing section heat exchanger 82 is controlled to be 37-42℃.

[0055] The absorption section heat exchanger 81 is installed above the concentration and crystallization section 84. A demineralized water drive pump and valves (not shown in the figure) are installed on the connecting pipeline between the absorption section heat exchanger 81 and the first-stage warm air heat exchanger 1. These pumps drive low-temperature demineralized water into the absorption section heat exchanger 81 to exchange heat and cool the washing slurry and flue gas, reducing ammonia volatilization and the formation of submicron-sized ammonium sulfite particles. The high-temperature demineralized water after heat exchange is then used to heat the intake air of the fan 2, achieving the recovery of waste heat from the washing and absorption section. Preferably, by adjusting the demineralized water flow rate and heat exchange area, the outlet air temperature rise of the first-stage warm air heat exchanger is controlled to be 10-25℃, and the outlet flue gas temperature of the washing and absorption section is controlled to be 46-50℃.

[0056] The secondary warm air heat exchanger 3 is installed in the air outlet duct connecting the outlet of fan 2 and the air inlet of air preheater 4. A demineralized water drive pump and valves (not shown in the figure) are installed on the connecting pipeline between the secondary warm air heat exchanger 3 and the low-temperature heat exchanger 5. These pumps drive the low-temperature demineralized water into the low-temperature heat exchanger 5 to exchange heat with the flue gas at the outlet of air preheater 4, and then send the heat-exchanged high-temperature demineralized water to the secondary warm air heat exchanger 3 for heating the air preheater intake. To balance the waste heat recovery from the air preheater outlet flue gas and the evaporation and crystallization efficiency of the ammonium sulfate solution in the concentration and crystallization section, preferably, the outlet air temperature of the secondary warm air heat exchanger is controlled at 50-80℃ and the outlet flue gas temperature of the low-temperature heat exchanger is controlled at 100-120℃ by adjusting the demineralized water flow rate and heat exchange area.

[0057] The expansion economizer 6 is installed in parallel with the air preheater 4. The expansion economizer 6 is used to ensure the flue gas flow is within the design velocity range when the boiler exhaust temperature rises due to the preheating of the hot air heat exchanger.

[0058] A heat transfer oil drive pump and valves (not shown in the figure) are installed on the connecting pipeline between the expansion economizer 6 and the absorption heat pump 7. These pumps drive the heat transfer oil into the expansion economizer 6 to exchange heat with the high-temperature flue gas flowing through it. The high-temperature heat transfer oil after heat exchange is then sent to the heat transfer oil inlet pipeline of the absorption heat pump 7, serving as the driving heat source for the absorption heat pump 7. Preferably, the heat transfer oil outlet temperature of the expansion economizer is controlled to be 80-90℃ by adjusting the heat transfer oil flow rate.

[0059] The inlet of the demineralized water flow pipeline of the absorption heat pump 7 is connected to the outlet of the heat exchanger 82 in the first water washing section via a pipeline. The absorption heat pump 7 uses the high-temperature heat transfer oil entering its heat transfer oil flow pipeline as the driving heat source to perform two-stage heating of the demineralized water entering its demineralized water channel. The high-temperature demineralized water after heating is then sent to the boiler deaerator for deoxygenation and removal of non-condensable gases, ensuring the quality of the boiler drum feed water. Preferably, the outlet demineralized water temperature of the absorption heat pump is controlled at 87-95℃.

[0060] Methods for recovering waste heat from flue gas in ammonia desulfurization processes using the above system include:

[0061] (1) Ambient air is sent to the boiler furnace by the fan through the air channel in the air preheater and mixed with fuel for combustion. The demineralized water driven pump installed on the connecting pipeline between the primary warm air heat exchanger and the absorption section heat exchanger drives the demineralized water into the absorption section heat exchanger to exchange heat with the flue gas and washing liquid of the ammonia washing absorption section, thereby reducing the gas-liquid reaction temperature of the washing absorption section, reducing the volatilization rate of ammonia in the washing liquid, controlling the generation of submicron and ammonium sulfite particles, and controlling the outlet flue gas emission temperature of the washing absorption section at 46-50℃. The demineralized water that has completed heat exchange and temperature rise is sent to the primary warm air heat exchanger installed in the fan inlet air duct to preheat the fan inlet air, raising the fan inlet air temperature by 10-25℃.

[0062] (2) The demineralized water drive pump installed on the connecting pipeline between the secondary warm air heat exchanger and the low temperature heat exchanger drives the demineralized water into the low temperature heat exchanger to exchange heat with the high temperature flue gas flowing through the low temperature heat exchanger, and sends the high temperature demineralized water that has completed the heat exchange to the secondary warm air heat exchanger installed in the fan outlet duct for preheating the fan outlet air. In order to ensure that the heat contained in the desulfurization tower inlet air temperature meets the requirements for concentration and crystallization of ammonium sulfate solution in the desulfurization tower, the outlet air temperature of the secondary warm air heat exchanger is controlled to be 50-80℃ and the outlet flue gas temperature of the low temperature heat exchanger is 100-120℃ by adjusting the demineralized water flow rate and heat exchange area.

[0063] (3) After two stages of preheating, the air enters the boiler furnace through the air circulation channel of the air preheater, which causes the temperature of the flue gas discharged from the boiler and the flue gas flowing through the air preheater to rise and expand in volume, thereby increasing the flue gas velocity. In order to prevent the high-speed flue gas containing dust from scouring and wearing the air preheater and to ensure the stable operation of the air preheater, an expansion economizer connected in parallel with the air preheater is installed outside the air preheater to introduce the flue gas that has expanded due to the temperature rise into the expansion economizer. In the expansion economizer, heat transfer oil is used as the heat exchange medium to exchange heat with the high-temperature flue gas and realize the recovery of high-temperature waste heat. In order to ensure the stable operation of the air preheater and the expansion economizer, the outlet temperature of the heat transfer oil of the expansion economizer is controlled at 80-90℃.

[0064] (4) Boiler feedwater is sent to the second water washing section heat exchanger below the flue gas outlet in the desulfurization tower via the pipeline. It exchanges heat with the desulfurized flue gas and is heated to 23-27°C before being sent to the water treatment workshop. Within this temperature range, the ion exchange resin or reverse osmosis membrane in the raw water softening and desalination process is in the best operating condition, which can effectively improve the service life and stability of the raw water softening and desalination system in the water treatment workshop. The demineralized water that has completed softening and desalination is sent to the first water washing section heat exchanger to continue to exchange heat with the desulfurized flue gas and be heated to 37-42°C. While realizing the recovery and utilization of waste heat from the ammonia desulfurization tail gas, it also efficiently captures the submicron-sized ammonium sulfate fine particles entering the water washing section.

[0065] (5) The demineralized water that has completed two-stage heating in the water washing section is sent to the demineralized water flow pipeline of the absorption heat pump through the pipeline. The absorption heat pump uses the high-temperature heat transfer oil entering the heat transfer oil pipeline as the driving heat source to heat the demineralized water to 87-95℃. After that, it is sent to the deaerator through the pipeline to remove oxygen and non-condensable components, thereby reducing the energy consumption of the deaerator. The heat transfer oil well pipeline that has completed the driving heating is sent to the collision economizer to continue to exchange heat with the high-temperature flue gas and increase the temperature.

[0066] The above steps (1) to (5) are not necessarily performed in order. After the system is running stably, the above steps can be performed simultaneously or some channels can be selectively opened.

[0067] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A flue gas waste heat recovery system for ammonia desulfurization process, characterized in that, include: Primary heating air heat exchanger, fan, secondary heating air heat exchanger, air preheater, low temperature heat exchanger, expansion economizer, absorption heat pump, desulfurization tower and water treatment workshop; The desulfurization tower consists of a concentration and crystallization section, a washing and absorption section, a water washing section, and a flue gas discharge outlet, arranged from bottom to top. The concentration and crystallization section consists of a crystallization circulation pool, a flue gas inlet, and a concentration heat exchange section, arranged from bottom to top. The washing and absorption section is equipped with an absorption section heat exchanger, and the water washing section is equipped with a first water washing section heat exchanger and a second water washing section heat exchanger, arranged from bottom to top. The air preheater is provided with an air passage for air circulation and a flue gas passage for flue gas circulation. The air outlet of the air preheater's air passage is connected to the air inlet of the boiler furnace through an air duct, and the flue gas inlet of the air preheater's flue gas passage is connected to the boiler flue gas outlet through a flue. The inlet of the fan is connected to the atmospheric environment through the air intake duct, and the outlet of the fan is connected to the air inlet of the air preheater through the air outlet duct. The air intake duct of the fan is equipped with a primary warm air heat exchanger, and the air outlet duct of the fan is equipped with a secondary warm air heat exchanger. The expansion economizer and the air preheater are installed in parallel. The flue gas inlet of the expansion economizer is connected to the boiler flue gas outlet through a flue. The flue gas outlets of both the expansion economizer and the air preheater are connected to the flue gas inlet of the low-temperature heat exchanger through a flue. The flue gas outlet of the low-temperature heat exchanger is connected to the flue gas inlet of the desulfurization tower through a flue. The primary heating air heat exchanger, secondary heating air heat exchanger, absorption section heat exchanger, first water washing section heat exchanger, second water washing section heat exchanger, low temperature heat exchanger, and expansion economizer are all metal tube box type structures. The metal tubes are used for the flow of heat exchange liquid, and the gaps between the metal tubes are used for the flow of gas. The absorption heat pump is equipped with a demineralized water flow pipeline and a heat transfer oil flow pipeline. The medium flowing inside the metal tubes of the primary heating air heat exchanger, the absorption section heat exchanger, the secondary heating air heat exchanger, and the low-temperature heat exchanger is demineralized water. The inlet of the primary heating air heat exchanger is connected to the outlet of the absorption section heat exchanger via a pipeline, and the outlet of the primary heating air heat exchanger is connected to the inlet of the absorption section heat exchanger via a pipeline. The inlet of the secondary heating air heat exchanger is connected to the outlet of the low-temperature heat exchanger via a pipeline, and the outlet of the secondary heating air heat exchanger is connected to the inlet of the low-temperature heat exchanger via a pipeline. The medium flowing in the second water washing section heat exchanger is boiler feedwater / raw water, and the medium flowing in the metal tubes of the first water washing section heat exchanger is demineralized water. The inlet of the second water washing section heat exchanger is connected to the raw water supply pipeline, and the outlet of the second water washing section heat exchanger is connected to the inlet of the water treatment workshop through a pipeline. The demineralized water outlet of the water treatment workshop is connected to the demineralized water inlet of the first water washing section heat exchanger through a pipeline. The demineralized water outlet of the first water washing section heat exchanger is connected to the demineralized water inlet of the absorption heat pump through a pipeline. The demineralized water outlet of the absorption heat pump is connected to the demineralized water inlet of the boiler deaerator through a pipeline. The medium flowing inside the metal tube of the expansion economizer is heat transfer oil. The heat transfer oil inlet of the expansion economizer is connected to the heat transfer oil outlet of the absorption heat pump through a pipeline, and the heat transfer oil outlet of the expansion economizer is connected to the heat transfer oil inlet of the absorption heat pump through a pipeline.

2. The flue gas waste heat recovery system for ammonia desulfurization process according to claim 1, characterized in that, The first and second water washing section heat exchangers are installed above the washing and absorption section. They are used to condense and capture submicron and ammonium sulfite particles in the flue gas after desulfurization, and to recover the heat of the clean flue gas after desulfurization for boiler feed water heating. The second water washing section heat exchanger is used to heat the boiler feed water to ensure that the inlet water temperature of the water treatment workshop is at the optimal operating condition for membrane separation or resin adsorption in the raw water desalination process. The second water washing section heat exchanger is used to heat the outlet water of the water treatment workshop. By adjusting the heat exchange time and heat exchange area of ​​the circulating medium in the water washing section heat exchanger, the raw water outlet temperature of the second water washing section heat exchanger is controlled to be 23-27℃, and the demineralized water outlet temperature of the first water washing section heat exchanger is controlled to be 37-42℃.

3. The flue gas waste heat recovery system for ammonia desulfurization process according to claim 2, characterized in that, The heat exchanger in the absorption section is installed above the concentration and crystallization section. The connecting pipeline between the heat exchanger in the absorption section and the first-stage warm air heat exchanger is equipped with a demineralized water drive pump and valves, which are used to drive low-temperature demineralized water into the heat exchanger in the absorption section to exchange heat and cool down the washing slurry and flue gas, reduce ammonia volatilization and the generation of submicron ammonium sulfite particles, and use the high-temperature demineralized water after heat exchange to heat the air intake of the fan, so as to realize the recovery of gas-liquid waste heat in the washing absorption section. By adjusting the demineralized water flow rate and heat exchange area, the outlet air temperature rise of the primary heating air heat exchanger is controlled to be 10-25℃, and the outlet flue gas temperature of the washing and absorption section is 46-50℃.

4. The flue gas waste heat recovery system for ammonia desulfurization process according to claim 3, characterized in that, The secondary warm air heat exchanger is installed in the air outlet duct connecting the fan outlet and the air inlet of the air preheater. The connecting pipeline between the secondary warm air heat exchanger and the low-temperature heat exchanger is equipped with a demineralized water drive pump and valves, which are used to drive the low-temperature demineralized water into the low-temperature heat exchanger to exchange heat with the flue gas at the air preheater outlet and send the high-temperature demineralized water after heat exchange to the secondary warm air heat exchanger for heating the air preheater inlet air, and control the temperature of the flue gas entering the concentration and crystallization section of the desulfurization tower to ensure efficient evaporation and crystallization of ammonium sulfate solution. By adjusting the demineralized water flow rate and heat exchange area, the outlet air temperature of the secondary warm air heat exchanger is controlled at 50-80℃, and the outlet flue gas temperature of the low-temperature heat exchanger is controlled at 100-120℃.

5. The flue gas waste heat recovery system for ammonia desulfurization process according to claim 4, characterized in that, The expansion economizer is installed in parallel with the air preheater. The expansion economizer is used to ensure the flue gas flow is within the design velocity range as the boiler exhaust temperature rises due to the preheating of the hot air heat exchanger.

6. The flue gas waste heat recovery system for ammonia desulfurization process according to claim 5, characterized in that, The connecting pipeline between the expansion economizer and the heat transfer oil pipeline of the absorption heat pump is equipped with a heat transfer oil drive pump and valve, which is used to drive the heat transfer oil into the expansion economizer to exchange heat with the high-temperature expansion flue gas flowing through the expansion economizer and raise its temperature. The heat-exchanged high-temperature heat transfer oil is then sent to the heat transfer oil inlet pipeline of the absorption heat pump as the driving heat source for the absorption heat pump heating. By adjusting the flow rate of the heat transfer oil, the outlet temperature of the heat transfer oil in the expander economizer can be controlled to be 80-90℃.

7. The flue gas waste heat recovery system for ammonia desulfurization process according to claim 6, characterized in that, The inlet of the demineralized water flow pipeline of the absorption heat pump is connected to the outlet of the demineralized water of the first water washing section heat exchanger through the pipeline. The absorption heat pump uses the high-temperature heat transfer oil entering its heat transfer oil flow pipeline as the driving heat source to heat the demineralized water entering its demineralized water channel in two stages, and then sends the heated high-temperature demineralized water to the boiler deaerator to remove oxygen and non-condensable gases, so as to ensure the quality of the boiler drum feed water. The outlet demineralized water temperature of the absorption heat pump is controlled at 87-95℃.

8. A method for recovering waste heat from flue gas in an ammonia desulfurization process, characterized in that, The process utilizes the flue gas waste heat recovery system of the ammonia desulfurization process as described in claim 7, comprising: (1) Ambient air is sent to the boiler furnace by the fan through the air channel in the air preheater and mixed with fuel for combustion. The demineralized water driven pump installed on the connecting pipeline between the primary warm air heat exchanger and the absorption section heat exchanger drives the demineralized water into the absorption section heat exchanger to exchange heat with the flue gas and washing liquid of the ammonia washing absorption section, thereby reducing the gas-liquid reaction temperature of the washing absorption section, reducing the volatilization rate of ammonia in the washing liquid and controlling the generation of submicron and ammonium sulfite particles, and controlling the outlet flue gas emission temperature of the washing absorption section at 46-50℃. The demineralized water that has completed heat exchange and temperature rise is sent to the primary warm air heat exchanger installed in the fan inlet air duct to preheat the fan inlet air, thereby raising the fan inlet air temperature by 10-25℃. (2) The demineralized water drive pump installed on the connecting pipeline between the secondary warm air heat exchanger and the low temperature heat exchanger drives the demineralized water into the low temperature heat exchanger to exchange heat with the high temperature flue gas flowing through the low temperature heat exchanger, and sends the high temperature demineralized water that has completed the heat exchange to the secondary warm air heat exchanger installed in the fan outlet duct for preheating the fan outlet air. In order to ensure that the heat contained in the desulfurization tower inlet air temperature meets the requirements for concentration and crystallization of ammonium sulfate solution in the desulfurization tower, the outlet air temperature of the secondary warm air heat exchanger is controlled to be 50-80℃ and the outlet flue gas temperature of the low temperature heat exchanger is 100-120℃ by adjusting the demineralized water flow rate and heat exchange area. (3) After two stages of preheating, the air enters the boiler furnace through the air circulation channel of the air preheater, which causes the temperature of the flue gas discharged from the boiler and the flue gas flowing through the air preheater to rise and expand in volume, thereby increasing the flue gas velocity. In order to reduce the scouring and wear of the high-speed flue gas containing dust on the air preheater and to ensure the stable operation of the air preheater, an expansion economizer connected in parallel with the air preheater is installed outside the air preheater to introduce the flue gas that has expanded due to the temperature rise into the expansion economizer. In the expansion economizer, heat transfer oil is used as the heat exchange medium to exchange heat with the high-temperature flue gas and realize the recovery of high-temperature waste heat. In order to ensure the stable operation of the air preheater and the expansion economizer, the outlet temperature of the heat transfer oil of the expansion economizer is controlled at 80-90℃. (4) Boiler feedwater is sent to the second water washing section heat exchanger below the flue gas outlet in the desulfurization tower via the pipeline. It exchanges heat with the desulfurized flue gas and is heated to 23-27℃ before being sent to the water treatment workshop. Within this temperature range, the ion exchange resin or reverse osmosis membrane in the raw water softening and desalination process is in the best operating condition, which can effectively improve the service life and stability of the raw water softening and desalination system in the water treatment workshop. The demineralized water that has completed softening and desalination is sent to the first water washing section heat exchanger to continue to exchange heat with the desulfurized flue gas and be heated to 37-42℃. While realizing the recovery and utilization of waste heat from the ammonia desulfurization tail gas, it also efficiently captures the submicron-sized ammonium sulfate fine particles entering the water washing section. (5) The demineralized water that has completed two-stage heating in the water washing section is sent to the demineralized water flow pipeline of the absorption heat pump through the pipeline. The absorption heat pump uses the high-temperature heat transfer oil entering the heat transfer oil pipeline as the driving heat source to heat the demineralized water to 87-95℃. After that, it is sent to the deaerator through the pipeline to remove oxygen and non-condensable components, thereby reducing the energy consumption of the deaerator. The heat transfer oil well pipeline that has completed the driving heating is sent to the collision economizer to continue to exchange heat with the high-temperature flue gas and increase the temperature.

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