Three-proofing solution for air pre-heater after thermal decomposition of ammonium bisulfate

Abstract

The invention discloses a three-proofing solution for an air pre-heater after thermal decomposition of ammonium bisulfate, which adopts high-temperature high-speed airflow to purge the air pre-heater to reduce the generation of ammonium bisulfate. The problems that the air pre-heater is corroded and blocked due to ammonium bisulfate, and air leakage occurs are effectively controlled.

Description

Technical Field

[0001] The invention relates to a method for solving the problem of air preheater corrosion, blockage and air leakage. Background Art

[0002] The air preheater of the main equipment of the boiler is referred to as the air preheater. The three-proof solution of the air preheater after thermal decomposition of ammonium bisulfate belongs to the technical field of boiler air preheater specification.

[0003] The most important thing for the boiler during combustion is to have the right coal powder fineness and temperature and sufficient oxygen to meet the combustion. The main function of the air preheater is to provide sufficient air volume and heat to the pulverizing system to meet the drying output of the pulverizing system and the hot air powder delivery. The second function is to provide sufficient oxygen and initial combustion air temperature to the furnace. High air temperature is conducive to the ignition and burnout of coal powder. The third function is that the working environment of the air preheater is harsh. Here, the cold air and hot flue gas absorb and release heat through the rotating heat transfer element corrugated plate, transferring the flue gas heat to the cold air, reducing the boiler exhaust temperature, increasing the furnace calorific value, meeting the combustion requirements, and improving the overall efficiency of the boiler.

[0004] However, a large amount of nitrogen oxides NOx is produced during boiler combustion, which needs to be neutralized with ammonia NH3 into nitrogen N2 and water vapor H2O. In the process of denitrification, it is inevitable that some ammonia will escape and flow into the air preheater with the flue gas. Sulfides SO2 and SO3 are inevitably generated during the coal combustion of the boiler. When the sulfides are mixed with ammonia and water vapor and decompose and react, ammonium bisulfate NH4HSO4 is generated and deposited on the dense corrugated plate of the air preheater. Ammonium bisulfate is highly corrosive and is also an unstable substance that changes with temperature. It has solid, liquid and gaseous states. When it changes to liquid due to temperature changes, it sticks to the corrugated plate like snot, which not only corrodes the corrugated plate, but also absorbs fly ash particles in the flue gas and sticks to the corrugated plate, and also causes the corrugated plate of the air preheater to accumulate dust and clog. The service life of the corrugated plate is bound by the maintenance cycle of the boiler. In addition, the ammonium bisulfate corrosion on the corrugated plate caused the pressure difference between the inlet and outlet of the smoke and air duct to increase, and the air leakage of the air preheater increased significantly. As time went on, the air leakage of the air preheater doubled, and in severe cases, the air leakage rate reached more than 30%, limiting the fan output and directly affecting the safe combustion of the boiler. This problem is very common, but it has never been completely solved.

[0005] The flue gas temperature of the air preheater flue gas side drops from about 390℃ to about 120℃. On the primary and secondary air side of the air preheater, the cold air absorbs heat from about 20℃ to about 340℃. On the flue gas side, when the flue gas temperature is greater than 450℃, ammonia NH3 and sulfuric acid H2SO4 in the flue gas no longer react. Using the reaction characteristics of ammonium bisulfate NH4HSO4 to reduce the amount of water vapor in the flue gas is one of the means to control the reaction of ammonia NH3 and sulfuric acid H2SO4 in the flue gas. The ash accumulation on the flue gas side corrugated plate is purged with a 500℃ high-temperature and high-speed airflow. The high-temperature airflow can not only reduce the generation of ammonium bisulfate in some areas and delay the change of ammonium bisulfate from gas to liquid, but also play a role in reducing the corrosion and clogging of the air preheater by ammonium bisulfate. On the primary and secondary air side, affected by the inlet cold air temperature, the temperature of the large area corrugated plate is lower than 147℃, which prompts the ammonium bisulfate to change from liquid to crystalline solid. On the flue gas side, the snot-like viscous ammonium bisulfate adheres to the fly ash particles in the flue gas, and rotates to the primary and secondary air sides. The liquid fly ash will turn into more crystalline solids, and solidify tightly in the gaps between the corrugated plates. Its hardness is like cement pouring. The blockage not only hinders the smooth flow of the primary and secondary air, but also increases the resistance, and the wind pressure needs to be increased to overcome the resistance to compensate. Increasing the primary and secondary air pressure will increase the positive wind pressure to flow to the dynamic and static gaps and to the negative pressure side of the flue gas, and the air preheater leakage rate will increase exponentially. This causal relationship between corrosion, blockage, and air leakage of the air preheater cannot be eliminated by any existing soot blowing method.

[0006] Because steam soot blowing is the most common form, taking steam soot blowing as an example, steam soot blowing relies on high temperature and high pressure heat energy to clear the dust and scale on the corrugated plate. There is a set of steam soot blower nozzles above and below the air preheater. The steam consumption of a single steam soot blower is 6-8 tons / hour, that is, the daily steam consumption is about 72 tons. The higher the purge steam temperature, the better. It is limited by the corresponding pressure of the soot blowing steam, and the steam pressure is limited by the bearing capacity of the corrugated plate. If the pressure is too high, the corrugated plate will be directly damaged. So far, there has been no report that the air preheater steam soot blower can remove the corrosion and blockage of the corrugated plate by ammonium bisulfate.

[0007] The air preheater steam soot blower relies on jet soot blowing, and the medium blowing area is limited, which cannot fully cover the area that needs to be cleaned. The diffused water vapor increases the moisture content in the flue gas, which increases the flue gas dew point temperature, thereby increasing the ash blocking and corrosion phenomenon at the cold end of the air preheater corrugated plate. The air preheater steam soot blowing has high operating costs and consumes a large amount of working medium. Usually, it is purged three times a day, and the daily steam consumption is about 72t / h. Calculated as 300 days a year, the loss of high-quality steam and water is about 20,000 tons, and the power generation is reduced by about hundreds of thousands of kilowatt-hours. Because the cost is too high, steam soot blowing is not continuous, which provides retention conditions for ammonium bisulfate deposition and corrosion on the corrugated plate, because the generation of ammonium bisulfate is continuous and accumulated.

[0008] In thermal power generation technology, air preheater plays a major role in thermal power generation. It not only increases air temperature and reduces exhaust gas temperature, but also helps to improve boiler combustion. As the boiler combustion efficiency is improved, water-cooled wall corrosion and ash accumulation are reduced, the boiler thermal efficiency is improved, thereby improving the efficiency and safety of the entire power generation system.

[0009] However, as the continuous operation time of coal-fired boiler air preheater increases, the corrosion and blockage of the air preheater corrugated plate will affect the safe and efficient operation of the boiler. The reasons are as follows: The sulfur content in the coal is greater than the design value, which will cause the dew point temperature of the tail flue gas to decrease, thus causing condensation at the cold end of the air preheater. After condensation, the fly ash particles in the flue gas will stick to it, and the soot blowing will be intermittent instead of continuous, resulting in the corrugated plate to accumulate ash and corrode and clog.

[0010] B. During the operation of the SCR denitrification system, due to equipment or operation reasons, or due to frequent load fluctuations of the unit due to grid dispatching, NOx generation changes with load changes, and there is a certain lag in the ammonia injection adjustment, resulting in incomplete reaction of ammonia and a certain amount of ammonia escape. The sulfur oxides in the flue gas, the ammonia escape and the water vapor generate ammonium bisulfate at a certain temperature.

[0011] C. Since the air preheater is upstream of the dust collector in the flue, the flue gas contains a large amount of ash, and the gap between the corrugated plates of the air preheater is very narrow. In addition, ammonium bisulfate easily turns into a snot-like liquid with temperature, which is not only highly corrosive but also highly viscous. When the flue gas dust flows through the corrugated plates, it is adhered to and accumulated by the viscous ammonium bisulfate. Once the ash is not removed and blockage occurs, it will lead to a vicious cycle until complete corrosion and blockage.

[0012] D. The blockage is not only primary, but also secondary air circulation is blocked, the air leakage increases, and the exhaust gas temperature is reduced by the leaked cold air, which aggravates the deposition of ammonium bisulfate and the corrosion and blockage of the air preheater body and corrugated plate.

[0013] E. Steam soot blowers cannot completely remove sticky or hard ammonium bisulfate on the corrugated plate. Steam soot blowing itself increases the water vapor in the flue gas, which promotes the combination of sulfide and ammonia escape in the flue gas to form ammonium bisulfate. Summary of the invention

[0014] The object of the present invention is to provide a three-protection solution for an air preheater after thermal decomposition of ammonium bisulfate, which is effective in protecting the air preheater from corrosion, blockage and air leakage.

[0015] The technical solution of the present invention is: A three-defense solution for an air preheater after thermal decomposition of ammonium bisulfate is characterized in that a high-temperature and high-speed airflow is used to purge the air preheater to reduce the generation of ammonium bisulfate.

[0016] The temperature of the high-temperature and high-speed airflow is 400-500°C.

[0017] The specific method is: (1) The first group of nozzles is set near the flue gas side of the air duct isolation plate, and a high-temperature and high-speed airflow is used to blow downward from the flue gas inlet at the hot end of the air preheater, and the temperature of the corrugated plate in the blown area is increased to above 450°C; (2) A second set of nozzles is arranged on the primary air side close to the flue gas side, so that the high-temperature and high-speed airflow not only sweeps the corrugated plate, but also blocks the primary air leakage to the flue gas; Furthermore, a third set of nozzles is arranged on the secondary air duct side and at the secondary air inlet near the primary air side, and a high-temperature and high-speed airflow is used to blow the cold-end corrugated plate to rapidly increase the temperature of the corrugated plate again. When the temperature rises above 120°C, decomposition begins. Ammonia and other substances are generated at around 270°C. The decomposition rate increases with increasing temperature, thereby reducing corrosion and clogging of the corrugated plate by liquid ammonium bisulfate.

[0018] The nozzle openings of the nozzles are in a flat rectangular or circular shape and are arranged in a line on the mother pipe, forming high-temperature and high-speed airflow nozzles that are densely connected on the left and right.

[0019] Ammonia monitoring devices are installed in the primary air duct and the secondary air outlet duct.

[0020] The three-protection solution for the air preheater after thermal decomposition of ammonium bisulfate in the present invention aims to solve the problem that the conditions for the generation of ammonium bisulfate and the form and shape of ammonium bisulfate in the air preheater can be changed by high-temperature and high-speed airflow purge, thereby eliminating the corrosion, blockage and increased air leakage caused by ammonium bisulfate in the operation of the air preheater. The corrosion, blockage and air leakage of the heat transfer elements of the air preheater caused by ammonium bisulfate are controlled from the conditions for the generation of ammonium bisulfate, and the three-protection purposes of air preheater anti-corrosion, anti-blockage and anti-air leakage desired by the industry are truly achieved.

[0021] At present, the function of soot blowers such as steam soot blowing, sonic soot blowing, high-pressure water washing, compressed air soot blowing, and gas shock wave soot blowing is to blow soot, but they do not solve the problem of ammonium bisulfate. The root cause of air preheater corrosion and blockage is that ammonium bisulfate is sticky like snot in liquid state, sticking to the corrugated plate, and the gap between the corrugated plates is small, so the dust in the flue gas is naturally stuck together, causing the air preheater corrosion and blockage to be unable to solve the difficult old problem. The blockage will inevitably cause the inlet and outlet differential pressure to increase, and the large differential pressure will inevitably lead to large air leakage, which has always been a hidden danger affecting the safe, economical and environmentally friendly operation of the boiler.

[0022] The present invention aims to replace steam soot blowing by high temperature and high speed air blowing, and has the following characteristics: The operating cost is almost negligible, so the corrugated plate can be blown continuously to keep it dry, clean and unobstructed.

[0023] The sootblower does not need to be started or stopped for operation, and can blow soot continuously, so the equipment maintenance is also almost zero.

[0024] What is worth noting is that steam soot blowing can prevent unnecessary water vapor from entering the flue gas, cut off the combination of sulfide and ammonia escape in the flue gas, and reduce the formation of ammonium bisulfate.

[0025] d. 500℃ high-temperature and high-speed airflow is blown along the flue gas flow direction. The high temperature forces the decomposition reaction of ammonium bisulfate in some areas on the flue gas side to stop, delaying the formation of ammonium bisulfate, reducing the area where ammonium bisulfate turns into liquid, and reducing the residence time of liquid ammonium bisulfate that is most harmful to the corrugated plate.

[0026] e. 500℃ high-temperature and high-speed airflow blows along the primary air flow direction. Since the nozzle is arranged on the primary air side of the isolation plate between the flue gas side and the primary air side, the high-speed airflow cuts off the leakage formed by the high primary air pressure flowing to the negative pressure flue gas side. At this time, most of the liquid ammonium bisulfate on the corrugated plate will absorb a large amount of fly ash and dust particles in the flue gas due to its viscosity, and will be quickly transformed into crystalline solid ammonium bisulfate by the primary air cooling wind, which is a phenomenon that cannot be removed by ordinary soot blowers. The high-temperature and high-speed airflow blowing immediately prevents this situation from continuing in the corrugated plate.

[0027] f. 500℃ high-temperature and high-speed airflow blows along the secondary air flow direction, and then blows again at high temperature and high speed after high-temperature blowing in the primary air area, awakening the thermal decomposition reaction of liquid ammonium bisulfate. Since ammonium bisulfate is an unstable object, it begins to decompose when the temperature rises above 120℃, and ammonia begins to be produced when it rises above 270℃. The decomposition rate reaches the maximum at 370℃. The decomposition products include ammonia, nitrogen, sulfur dioxide and water vapor. This is the key to the high-temperature and high-speed airflow blowing on the corrugated plate of the air preheater to solve the corrosion, blockage and air leakage of the air preheater. It is a special effect function that no other air preheater soot blower can do at present. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0029] Figure 1 It is a schematic diagram of the flow direction of air preheater flue gas, primary and secondary air, and high-temperature and high-speed airflow.

[0030] Figure 2 It is a schematic diagram of the air preheater structure of an embodiment of the present invention.

[0031] Reference numerals: 1. Air preheater center axis, 2. Air preheater hot end, 3. Air preheater cold end, 4. Air preheater shell, 5. The first group of high-temperature and high-speed airflow nozzles, 6. The second group of high-temperature and high-speed airflow nozzles, 7. Cold end secondary air side soot blower, 8. Hot end flue gas inlet flow direction, 9. Cold end flue gas outlet flow direction, 10. Cold end primary air inlet flow direction, 11. Hot end primary air outlet flow direction, 12. Cold end secondary air inlet flow direction, 13. Hot end secondary air inlet flow direction, 14. Air preheater high temperature section, 15. Air preheater medium temperature section, 16. Air preheater low temperature section. 17. Flue gas and air baffle at hot end, 18. Flue gas and air baffle at cold end, 19. Primary and secondary air baffle at hot end, 20. Primary and secondary air baffle at cold end, 21. Manual main isolating valve for hot air flow, 22. Main regulating valve for hot air flow, 23. Flue gas soot blower regulating valve, 24. Primary air soot blower regulating valve, 25. Secondary air soot blower regulating valve, 26. Secondary air outlet ammonia detection device. DETAILED DESCRIPTION

[0032] Schematic diagram of the flow direction of air preheater flue gas, primary and secondary air, and high-temperature and high-speed airflow Figure 1 As shown in the figure, on the right side of the air preheater is the flue gas channel, where the flue gas flows from top to bottom 8, and the heat in the flue gas is transferred to the corrugated plate of the heat storage element, and the flue gas temperature decreases from top to bottom. The corrugated plate of the heat transfer element rotates to the left side of the air preheater, and the left side is the primary and secondary air channels. When the cold air passes through the corrugated plate, it absorbs the temperature on the corrugated plate. The primary air completes the powder making and powder feeding, and the secondary air completes the wind temperature and oxygen content required for boiler combustion, that is, the air volume.

[0033] The main cause of corrosion and blockage of air preheater is ammonium bisulfate produced in flue gas. Flue gas contains SO2, SO3 and NH3, plus water vapor in flue gas. When the flue gas temperature is lower than 450℃, the reaction begins. When the temperature reaches 370℃, the decomposition rate reaches the maximum. At a temperature of 270-370℃, the molecular decomposition reaction generates ammonium bisulfate gas. When the temperature drops below 270℃, the ammonium bisulfate changes to a viscous liquid and sticks to the corrugated plate. At this time, it is highly corrosive and will adhere to fly ash particles to form blockage. When the temperature drops below 147℃, the ammonium bisulfate appears to be crystalline solid.

[0034] Ammonium bisulfate is an unstable object that changes with temperature. The chemical mechanism of ammonium bisulfate is used to control the hidden danger of ammonium bisulfate corrosion and blockage in air preheaters. When the temperature is greater than 450°C, the generation of ammonium bisulfate can be prevented. Controlling the water vapor in the flue gas can control the generation of ammonium bisulfate. By increasing the temperature again, the generated ammonium bisulfate can be thermally decomposed to generate ammonia, nitrogen, sulfur dioxide and water vapor, thereby controlling the corrosiveness of ammonium bisulfate.

[0035] The real cause of corrosion and blockage in air preheaters is liquid ammonium bisulfate, that is, the temperature is between 147-230℃. Using the chemical mechanism of ammonium bisulfate to control the hidden danger of corrosion and blockage of air preheaters caused by ammonium bisulfate is customized according to the chemical characteristics of ammonium bisulfate. High-temperature and high-speed airflow is used to continuously purge the corrugated plate to prevent corrosion and blockage of air preheaters.

[0036] by Figure 1 , Figure 2 As shown in the figure, after the boiler is overhauled, the corrugated plates of the heat transfer elements of the air preheater are neat and clean. The central axis 1 of the air preheater divides the air preheater into the flue gas side and the air duct side. The upper part of the air preheater is commonly known as the hot end 2 of the air preheater, and the lower part of the air preheater is commonly known as the cold end 3 of the air preheater. Ammonium bisulfate is generated at the hot end of the flue gas side, where the temperature is suitable for mixing SO2, SO3 and NH3 in the flue gas with water H2O to generate ammonium bisulfate. There is no ammonium bisulfate generation on the air duct side. Ammonium bisulfate is an unstable object. It has gaseous, liquid and solid states with temperature changes. Among them, the most harmful is the liquid state. The liquid state is snot-like and sticky. It will not only stick to the corrugated plate and corrode the corrugated plate, but more seriously, the adhered fly ash will become solid with temperature changes. The corrugated plates are like hard plates cast with cement, causing the corrugated plates to rot. Over time, they will not be able to operate normally. After the corrugated plate is blocked, the differential pressure between the inlet and outlet of the air duct increases, especially the primary fan output requires a higher wind pressure to overcome the large resistance of the differential pressure. The flue gas channel adjacent to the primary air is a negative pressure area, which increases the leakage of the primary air. The air preheater leakage is mainly due to the primary air leakage, because the primary air pressure is the highest.

[0037] The first set of high-temperature and high-speed airflow nozzles (soot blowers) 5 are installed on the flue gas side of the baffle (hot end flue gas and air baffle) 17. The high-temperature and high-speed airflow enters from the hot end and exits from the cold end along the flue gas flow. The high-temperature section 14 of the air preheater, where the temperature of the purged corrugated plate is greater than 450°C, temporarily stops the generation of ammonium bisulfate, and the corrugated plate originally in the medium-temperature section 15 of the air preheater below 230°C will turn into liquid and move downward, thus reducing the generation of ammonium bisulfate in the high-temperature section and the condensation and adhesion in the corrugated plate area. The corrugated plate is purged with high-temperature and high-speed airflow on the flue gas side to dry the moisture on the corrugated plate. More importantly, it greatly reduces the water vapor in the flue gas and avoids the generation of water vapor during steam soot blowing, which increases the generation of ammonium bisulfate.

[0038] When the air preheater rotates to the duct side, the air inlet temperature at the primary air cooling end is low, and the corrugated plate temperature is lower than 147°C, the liquid ammonium bisulfate crystallizes and solidifies and sticks to the corrugated plate. This phenomenon is of great concern and poses the greatest threat to the air preheater equipment. If it cannot be removed in time, the viscous ammonium bisulfate adsorbs fly ash and dust and accumulates continuously. As the temperature decreases, it crystallizes into a solid state. The corrugated plates are as hard as cement. With the corrosiveness of ammonium bisulfate, any soot blower is powerless to remove it. At the same time, blockage causes the differential pressure to increase, and the fan needs a higher wind pressure to overcome the resistance, and the air leakage of the air preheater increases exponentially.

[0039] At the primary air duct side baffle (cold end flue gas and air baffle) 18, the primary air inlet is close to the flue gas side, which is the low temperature section 16 of the air preheater. The second group of high temperature and high speed airflow nozzles (soot blowers) 6 use high temperature and high speed airflow to cut off the leakage of the cold end primary air to the flue gas side of the negative pressure area, greatly reducing the air preheater leakage rate. Controlling the leakage of the primary air means controlling the leakage of the air preheater. The soot blower airflow sweeps the corrugated plate to clean the dust and adhesion on the corrugated plate.

[0040] On the secondary air duct side baffle (hot end primary and secondary air baffle) 19, the secondary air inlet is close to the primary air side, which is the cold end section 16 of the air preheater. The ambient temperature is the lowest, and ammonium bisulfate turns to a crystalline solid state when it is transferred here. The cold end secondary air soot blower (the third group of high-temperature and high-speed airflow nozzles) 7 further strengthens the purge after the high-temperature purge of the primary air side. The biggest effect is to quickly raise the temperature of the corrugated plate to above 270°C, because the higher the ambient temperature, the higher it is. Raise the temperature of the upper corrugated plate of the air preheater to 370°C in advance. There is sufficient oxygen in the secondary air, which can thermally decompose ammonium bisulfate into ammonia, nitrogen, sulfur dioxide and water vapor. This makes it impossible for ammonium bisulfate to take root in the corrugated plate. The thermal decomposition reaction of ammonium bisulfate is first heated and then released, which is very helpful to increase the temperature of the primary and secondary air.

[0041] The chemical mechanism of ammonium bisulfate is used to control the hidden dangers of ammonium bisulfate corrosion and blockage of the air preheater. A high-temperature and high-speed airflow soot blower is used for continuous and uninterrupted blowing to keep the corrugated plate dry and clean at all times. After the boiler is ignited, ammonium bisulfate and fly ash particles cannot stick to the corrugated plate, and the temperature change is used to change the control of the survival form of ammonium bisulfate. Control the conversion of ammonium bisulfate to thermal decomposition, eliminate the corrosion and blockage of the corrugated plate by ammonium bisulfate, and resolve the increase in air leakage rate caused by high differential pressure, so that the air preheater equipment components are guaranteed and the service life is extended. In order to facilitate monitoring during operation, an ammonia detection device is installed on each of the primary and secondary air ducts at the hot air outlet of the air preheater to effectively control the thermal decomposition of ammonium bisulfate, where the ammonia decomposed by ammonium bisulfate can be detected. When there is no ammonia display on the primary air side, open the primary air soot blower regulating valve 24, and when there is no ammonia display on the secondary air side, open the secondary air soot blower regulating valve. In the initial stage of commissioning, open the hot air flow main regulating valve 22 to meet the numerical display of the two ammonia detection meters, and then close them one by one for debugging.

[0042] Ammonium bisulfate is generated in the flue gas side of the air preheater. The flue gas at the flue inlet carries a large amount of fly ash dust, including SO2, SO3, ammonia escape NH3 and water vapor H2O. These substances will generate ammonium bisulfate NH4HSO4 under the action of appropriate temperature, causing blockage and corrosion of the air preheater channel and increasing the air leakage of the air preheater. However, if there is no moisture in the flue, sulfur oxide and ammonia will not generate ammonium bisulfate. Therefore, high-temperature and high-speed airflow continuously and uninterruptedly blows and cleans the corrugated plate to reduce the generation of ammonium bisulfate. Because high-temperature and high-speed airflow is used for soot blowing instead of steam soot blowing, water vapor generated by steam soot blowing is eliminated. Controlling the moisture in the flue gas is to control the generation of ammonium bisulfate.

[0043] The flue gas side of the air preheater is the main area for the generation of ammonium bisulfate. The first group of high-temperature and high-speed airflow nozzles are installed on the flue gas side close to the air duct isolation plate. The high-temperature and high-speed airflow purge uses a 500°C high-temperature airflow to purge downward from the flue gas inlet at the hot end of the air preheater, and the temperature of the corrugated plate in the purged area is raised to above 450°C. When the temperature in the flue is above 450°C, the sulfur oxides and ammonia and water vapor in the flue gas will stop reacting to form ammonium bisulfate. High-temperature barriers are used to delay the generation of ammonium bisulfate in some areas in order to further control the amount of ammonium bisulfate generated.

[0044] The primary air pressure in the air preheater is high, and the adjacent one is a negative pressure flue gas channel. The primary air leaks to the adjacent negative pressure flue gas side, and a small amount leaks to the secondary air side. When the primary air channel is partially blocked and the pressure difference between the primary air inlet and outlet increases, the primary air leakage increases with the pressure difference. The high leakage rate of the air preheater mainly refers to the large leakage of the primary air. A second set of nozzles is installed on the primary air side close to the flue gas side. The high-temperature and high-speed airflow not only sweeps away the dust accumulated on the corrugated plate, but also plays a linear blocking role for the primary air leakage to the flue gas. Because the high-speed airflow prevents the primary air from passing horizontally, controlling the leakage of the primary air means controlling the leakage of the air preheater.

[0045] The air duct side of the air preheater does not have the ability to generate ammonium bisulfate, but the corrugated plate rotates about once a minute and carries ammonium bisulfate, which is in a viscous liquid or solid state. In a cold wind environment, the ammonium bisulfate is further solidified and crystallized on the corrugated plate, which is the main source of corrosion and blockage in the air preheater. The third group of high-temperature and high-speed nozzles is close to the primary air side, and the cold end corrugated plate is purged with a 500℃ high-temperature and high-speed airflow, which quickly raises the temperature of the corrugated plate again. Unstable ammonium bisulfate is highly dependent on temperature, and the decomposition products are different at different temperatures. High temperature awakens the thermal decomposition reaction of liquid ammonium bisulfate. When the temperature rises above 120℃, it begins to decompose, and when it rises above 270℃, ammonia begins to be produced. The decomposition rate reaches the maximum at 370℃. The decomposition products include ammonia, nitrogen, sulfur dioxide and water vapor. This is the key to the high-temperature and high-speed airflow to purge the corrugated plate of the air preheater to solve the corrosion, blockage and air leakage of the air preheater. It is a special effect function that no air preheater soot blower can currently achieve.

[0046] The air preheater rotates about one circle per minute. If ammonium bisulfate cannot stay in the air preheater, it will float with the wind and smoke. There is no corrosion without blockage and ash accumulation. The power of high-temperature and high-speed airflow mainly comes from the shape of the airflow nozzle. The ratio of the flow area of ​​the mother pipe to the flow area of ​​the nozzle is the source of high speed. This principle is used to speed up the airflow nozzle at the hot flue gas inlet, the primary air inlet, and the secondary air duct inlet of the air preheater. The nozzle mouth on the mother pipe is flat and rectangular (circular or other suitable shapes can also be used), arranged in a line, forming a high-temperature and high-speed airflow nozzle connected to the left and right. Each corrugated plate is continuously purged uninterruptedly, and liquid ammonium bisulfate is just generated. It is purged about twice a minute, just like a rag, so ammonium bisulfate cannot solidify and stick to the corrugated plate, and there is no ash blockage on the corrugated plate of the air preheater heat transfer element, and the corrosion of ammonium bisulfate on the corrugated plate can be effectively controlled.

[0047] Ammonia monitoring devices are installed in the primary air duct and the secondary air outlet duct to monitor whether the air volume of the high-temperature and high-speed airflow soot blower is normal and whether the airflow temperature meets the requirements of thermal decomposition of ammonium bisulfate. When the high-temperature and high-speed airflow blows the corrugated plate at 500°C and the temperature rises to 270°C, the ammonium bisulfate is thermally decomposed into ammonia and sulfuric acid. Sulfuric acid is still highly corrosive and will quickly combine with ammonia and water to form ammonium bisulfate when it rotates to the flue gas side. When the hot air flow area continues to heat up to 400°C, sulfuric acid is decomposed into sulfur trioxide and water. Subsequently, sulfur trioxide reacts with ammonia, oxygen, etc. to generate ammonia and other substances. Two ammonia monitoring devices are installed in the secondary air outlet duct, and ammonia can be detected, indicating that the high-temperature and high-speed airflow soot blower plays a protective role in the blowing of the corrugated plate, solving the problem of the inability to remove ammonium bisulfate.

[0048] The cost of putting into use the three-proof solution of the air preheater after thermal decomposition of ammonium bisulfate is almost zero. It can continuously and uninterruptedly purge the corrugated plate, and the surface of the corrugated plate is always kept dry and clean. The ammonium bisulfate is not solidified and crystallized on the corrugated plate before it is purged and decomposed by the hot air flow, eliminating the problem of ammonium bisulfate sticking to the corrugated plate and accumulating dust and corroding and clogging from the root. Because there is no need to start and stop operations, the maintenance and operation labor is low, and the equipment reliability is extremely high.

[0049] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A three-proof solution for air preheater after thermal decomposition of ammonium bisulfate, characterized by: Use high-temperature and high-speed airflow to purge the air preheater to reduce the generation of ammonium bisulfate.

2. The three-defense solution for air preheater after thermal decomposition of ammonium bisulfate according to claim 1 is characterized by: The temperature of the high-temperature and high-speed airflow is 400-500°C.

3. The three-defense solution for air preheater after thermal decomposition of ammonium bisulfate according to claim 1 or 2 is characterized in that: The specific method is: (1) The first group of nozzles is set near the flue gas side of the air duct isolation plate, and a high-temperature and high-speed airflow is used to blow downward from the flue gas inlet at the hot end of the air preheater, and the temperature of the corrugated plate in the blown area is increased to above 450°C; (2) A second set of nozzles is arranged on the primary air side close to the flue gas side, so that the high-temperature and high-speed airflow can not only sweep the corrugated plate, but also block the primary air leakage to the flue gas.

4. The three-defense solution for air preheater after thermal decomposition of ammonium bisulfate according to claim 3 is characterized by: A third set of nozzles is set on the secondary air duct side and near the primary air side of the secondary air inlet to blow the cold-end corrugated plate with high-temperature and high-speed airflow to quickly increase the temperature of the corrugated plate again. When the temperature rises above 120°C, it begins to decompose. Ammonia and other substances are produced at 270°C. The decomposition rate increases with the increase of temperature, reducing the corrosion and clogging of the corrugated plate by liquid ammonium bisulfate.

5. The three-defense solution for air preheater after thermal decomposition of ammonium bisulfate according to claim 3 is characterized by: The nozzle openings of the nozzles are arranged in a line on the mother pipe, forming high-temperature and high-speed airflow nozzles that are closely connected on the left and right.

6. The three-defense solution for air preheater after thermal decomposition of ammonium bisulfate according to claim 1 or 2 is characterized by: Ammonia monitoring devices are installed in the primary air duct and the secondary air outlet duct.

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