Coal-fired boiler tail ammonium bisulfate blockage treatment system
By setting up a flue gas cooler and air heater at the tail of the coal-fired boiler, a circulating water circuit is formed, and ammonium bisulfate is cleaned by using high-temperature melting water and air bypass to clean up ammonium bisulfate, the problem of ammonium bisulfate at the tail of the coal-fired boiler is solved, and the boiler operation stability and efficiency are improved.
Patent Information
- Application Number
- CN202422838514.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-21
- Publication Date
- 2025-07-22
- Estimated Expiration
- 2034-11-21
AI Technical Summary
In the SCR denitrification system of coal-fired boilers, ammonia escape reacts with SO3 in the flue gas to produce ammonium bisulfate, resulting in blockage of the tail heat exchange surface, which is difficult to clean under low temperature conditions, affecting the safe operation of the boiler.
Flue gas cooler and air heater are installed at the tail of the coal-fired boiler to form a heat exchange circulation water path, melt ammonium bisulfate through high-temperature melting crystal water, and regulate air flow in the air bypass to avoid low-temperature heat exchange, and combine with the flue gas bypass to prevent the smoke temperature from rising, so as to achieve cleaning of ammonium bisulfate.
Effectively melt and clean ammonium bisulfate, avoid blockage, improve heat exchange efficiency, stabilize boiler operation, reduce unplanned downtime, and protect equipment safety.
Smart Images
Figure CN223137912U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of flue gas denitrification of coal-fired boilers, and particularly relates to a treatment system for plugging of ammonium bisulfate at the tail of a coal-fired boiler. Background Technique
[0002] In order to meet the new environmental protection requirements, in recent years, coal-fired boilers have been required to undergo ultra-low emission transformation, usually by two methods of SNCR and SCR, and SCR is mostly adopted. SCR, namely selective catalytic reduction denitrification technology, is to inject ammonia or other suitable reducing agents into the flue gas upstream of the catalyst, and convert NOx in the flue gas into nitrogen and water at a temperature of 200-450°C. About 0.5% - 1.0% of SO2 in the flue gas in the furnace of the coal-fired boiler is oxidized into SO3. After installing the SCR system, while the catalyst reduces NOx to N2, about 1.0% of SO2 is oxidized into SO3. The unreacted escaping ammonia (NH3), SO3 and water vapor in the flue gas at the outlet of the SCR reactor react to form ammonium bisulfate or ammonium sulfate. When the wall temperature of the heat exchange surface is lower than 147°C, the ammonium bisulfate in the flue gas will solidify and agglomerate on the heat exchange surface. Especially in winter, when the environmental temperature is too low, due to the low wall temperature of the last-stage air preheater, the air preheater is often blocked, resulting in a large pressure difference of the air preheater, causing problems such as increased power consumption of the fan and surge stall, and even endangering the safe operation of the boiler.
[0003] Since ammonium bisulfate forms a solid agglomerate below 147°C, conventional soot blowers are difficult to clean, and using a high-pressure water gun also requires the boiler to be shut down, resulting in unplanned shutdown. In addition, ammonium bisulfate is also corrosive, causing corrosion of the heat exchange surface. The plugging problem of ammonium bisulfate has always been a difficult problem in boiler operation. Content of the Utility Model
[0004] Aiming at the problems existing in the above-mentioned prior art, the utility model aims to provide a treatment system for plugging of ammonium bisulfate at the tail of a coal-fired boiler to solve the problem that the coal-fired boiler is blocked due to ammonia escape from the SCR denitrification system, and the reaction of ammonia with SO3 and water in the flue gas to form ammonium bisulfate, which condenses on the tail heat exchange surface.
[0005] To achieve the above purpose, the utility model provides a treatment system for plugging of ammonium bisulfate at the tail of a coal-fired boiler, including an SCR denitrification device, an upper-stage air preheater, a last-stage air preheater and a dust collector arranged in sequence along the flue gas flow direction. The flue gas outlet of the SCR denitrification device and the flue gas inlet of the upper-stage air preheater, and the flue gas outlet of the upper-stage air preheater and the flue gas inlet of the last-stage air preheater are both connected through flue gas pipelines. The system also includes a flue gas cooler and a warm air heater;
[0006] The flue gas inlet of the flue gas cooler is connected to the flue gas outlet of the last-stage air preheater through a flue gas pipeline, and the flue gas outlet of the flue gas cooler is connected to the flue gas inlet of the dust collector through a flue gas pipeline;
[0007] The air heater is provided with an inlet for ambient air. The air outlet of the air heater is connected to the air inlet of the last-stage air preheater through a first air pipeline. The air outlet of the last-stage air preheater is connected to the air inlet of the upper-stage air preheater through a second air pipeline. The air outlet of the upper-stage air preheater is connected to the furnace of the coal-fired boiler through a third air pipeline. The first air pipeline also branches into an air bypass pipeline that is connected to the air inlet of the upper-stage air preheater, and a valve is provided on the air bypass pipeline.
[0008] The water outlet of the air heater is connected to the water inlet of the flue gas cooler through a first water pipeline. The water outlet of the flue gas cooler is connected to the water inlet of the air heater through a second water pipeline, thereby forming a heat exchange circulating water path. A circulation pump is equipped on the heat exchange circulating water path.
[0009] In the above solution: The water outlet of the flue gas cooler is also connected to a molten crystal water inlet pipeline, and the water inlet of the flue gas cooler is also connected to a molten crystal water outlet pipeline. Valves are provided on the first water pipeline, the second water pipeline, the molten crystal water inlet pipeline, and the molten crystal water outlet pipeline. When ammonium bisulfate deposition occurs on the flue gas cooler, the valves on the first water pipeline and the second water pipeline are closed, and the valves on the molten crystal water inlet pipeline and the molten crystal water outlet pipeline are opened to introduce molten crystal water (>150 °C) to melt ammonium bisulfate, so as to clean the flue gas cooler and improve the heat exchange efficiency.
[0010] In the above solution: A flue gas bypass pipeline branches from the flue gas pipeline connected to the flue gas outlet side of the last-stage air preheater and is connected to the flue gas inlet of the dust collector. A valve is provided on the flue gas bypass pipeline. When the flue gas cooler melts the crystal, the flue gas can pass through the flue gas bypass pipeline to prevent the flue gas temperature from rising due to heat exchange between the flue gas and hot water.
[0011] In the above solution: The flue gas from the dust collector goes to the desulfurization tower or the chimney to realize the external discharge of the flue gas.
[0012] The beneficial effects of the present utility model are as follows: 1. By adding an air bypass pipeline, heat exchange does not occur or heat exchange is reduced in the last-stage air preheater, the flue gas temperature is increased, thereby melting the ammonium bisulfate solidified and caked on the last-stage air preheater; 2. By adding a flue gas cooler behind the last-stage air preheater to heat water, and through a circulation pump, the hot water is pumped to the air heater added on the air side to increase the air temperature, making up for the fluctuation of the coal combustion amount of the boiler caused by insufficient preheating of the air when the last-stage air preheater melts the crystal, that is, avoiding the increase in the coal combustion amount caused by the fact that the air entering the furnace has insufficient temperature due to one less stage of air preheater while the flue gas temperature at the outlet of the last-stage air preheater is too high; when there is no ammonium bisulfate solidification on the heat exchange surface of the last-stage air preheater, it can also be used as a waste heat recovery device to further recover the waste heat of the flue gas and improve the boiler efficiency. Description of the Drawings
[0013] The above and / or additional aspects and advantages of the present utility model will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, where:
[0014] Figure 1 is the schematic diagram of the present utility model. Detailed implementation mode
[0015] As Figure 1 shown, a system for treating ammonium bisulfate blockage at the tail of a coal-fired boiler mainly consists of a warm air heater 6 and an SCR denitration device 1, an upper air preheater 2, a final air preheater 3, a flue gas cooler 5, and a dust collector 4 arranged in sequence along the flue gas flow direction of the coal-fired boiler.
[0016] Between the flue gas outlet of the SCR denitration device 1 and the flue gas inlet of the upper air preheater 2, and between the flue gas outlet of the upper air preheater 2 and the flue gas inlet of the final air preheater 3, they are all connected by flue gas pipelines. The flue gas inlet of the flue gas cooler 5 is connected to the flue gas outlet of the final air preheater 3 through a flue gas pipeline, and the flue gas outlet of the flue gas cooler 5 is connected to the flue gas inlet of the dust collector 4 through a flue gas pipeline. The flue gas coming out of the dust collector 4 goes to the desulfurization tower or chimney to realize the external discharge of the flue gas.
[0017] The warm air heater 6 is provided with an inlet for ambient air. The air outlet of the warm air heater 6 is connected to the air inlet of the final air preheater 3 through a first air pipeline a. The air outlet of the final air preheater 3 is connected to the air inlet of the upper air preheater 2 through a second air pipeline. The air outlet of the upper air preheater 2 is connected to the furnace of the coal-fired boiler through a third air pipeline. The first air pipeline a also branches into an air bypass pipeline b connected to the air inlet of the upper air preheater 2, and a valve is provided on the air bypass pipeline b.
[0018] The water outlet of the warm air heater 6 is connected to the water inlet of the flue gas cooler 5 through a first water pipeline c. The water outlet of the flue gas cooler 5 is connected to the water inlet of the warm air heater 6 through a second water pipeline d, thereby forming a heat exchange circulating water path. A circulation pump is equipped on the heat exchange circulating water path.
[0019] The water outlet of the flue gas cooler 5 is also connected to a molten crystal water inlet pipeline e, and the water inlet of the flue gas cooler 5 is also connected to a molten crystal water outlet pipeline f. Valves are provided on the first water pipeline c, the second water pipeline d, the molten crystal water inlet pipeline c, and the molten crystal water outlet pipeline f. When ammonium bisulfate deposits on the flue gas cooler 5, the valves on the first water pipeline c and the second water pipeline d are closed, and the valves on the molten crystal water inlet pipeline c and the molten crystal water outlet pipeline f are opened, and molten crystal water at >150°C is introduced to melt ammonium bisulfate, so as to clean the flue gas cooler 5 and improve the heat exchange efficiency.
[0020] A flue gas bypass pipe g branches from the flue gas pipe connected to the flue gas outlet side of the final air preheater 3 and is connected to the flue gas inlet of the dust collector 4. A valve is provided on the flue gas bypass pipe g. When the flue gas cooler 5 is defrosting, the flue gas can pass through the flue gas bypass pipe g to prevent the flue gas temperature from rising due to heat exchange between the flue gas and hot water.
[0021] The working principle of the present utility model is as follows:
[0022] During the operation of the boiler, since the air temperature at the inlet of the final air preheater 3 is relatively low, the wall temperature on this heat exchange surface is relatively low, and ammonium bisulfate deposits and agglomerates on the heat exchange surface. At this time, the valve on the air bypass pipe b is opened, and the flue gas and air do not exchange heat or exchange less heat in the final heat exchanger 3 (when both the air bypass pipe b and the first air pipe a are opened, since there is equipment connected to one side of the first air pipe a and the equipment resistance is large, the air is more likely to enter from the air bypass pipe b), so that the temperature of the flue gas flowing through the final air preheater 3 rises. When the flue gas temperature exceeds 147 °C, the ammonium bisulfate melts, and thus the ammonium bisulfate agglomerated on the final air preheater 3 is cleaned. To avoid the flue gas temperature at the outlet of the final air preheater 3 being too high and the air entering the furnace having insufficient temperature due to one less air preheater, resulting in an increase in coal consumption, a flue gas cooler 5 is added after the final air preheater 3 to recover the heat of the flue gas for heating water, and through a circulation pump, the hot water is pumped to the air heater 6 provided on the air side to increase the air temperature. After the final air preheater 3 is cleaned, the valve on the air bypass pipe b is closed, and the final air preheater 3 is put into use. The flue gas cooler 5 and the air heater 6 can still be used to reduce the flue gas temperature to a lower temperature and recover the waste heat of the flue gas.
[0023] After the flue gas cooler has been operating for a period of time, since the wall temperature may be lower than the freezing point of ammonium bisulfate, which is 147 °C, ammonium bisulfate may also deposit on its heat exchange surface. At this time, the valves on the first water pipe c and the second water pipe d are closed, and the valves on the defrosting water inlet pipe c and the defrosting water outlet pipe f are opened to introduce defrosting water (>150 °C). To reduce the heating of the flue gas cooled by the air preheater by the high-temperature defrosting water, the valve on the flue gas bypass pipe g is opened (also because the resistance on one side of the equipment is large, the flue gas is more likely to enter from the flue gas bypass pipe g, and almost all enters from the flue gas bypass pipe g) until all the ammonium bisulfate agglomerated on the flue gas cooler 5 melts.
Claims
1. A system for treating ammonium bisulfate blockage at the tail of a coal-fired boiler, comprising an SCR denitration device (1), an upper air preheater (2), a final air preheater (3) and a dust collector (4) arranged in sequence along the flow direction of flue gas, wherein the SCR denitration device (1) can receive flue gas generated by combustion in the coal-fired boiler, and the flue gas outlet of the SCR denitration device (1) and the flue gas inlet of the upper air preheater (2), and the flue gas outlet of the upper air preheater (2) and the flue gas inlet of the final air preheater (3) are connected via flue gas ducts, characterized in that: The air heater (6) further comprises a flue gas cooler (5) and a flue gas heater (6), wherein the flue gas inlet of the flue gas cooler (5) is connected to the flue gas outlet of the final air preheater (3) through a flue gas duct, and the flue gas outlet of the flue gas cooler (5) is connected to the flue gas inlet of the dust collector (4) through a flue gas duct; the air heater (6) is provided with an inlet for ambient air, the air outlet of the heater (6) is connected to the air inlet of the final air preheater (3) through a first air duct (a), the air outlet of the final air preheater (3) is connected to the air inlet of the upper air preheater (2) through a second air duct, and the upper air preheater (4) is connected to the flue gas outlet of the final air preheater (3) through a second air duct. The air outlet of the heater (2) is connected to the furnace of the coal-fired boiler through a third air duct; the first air duct (a) also branches into an air bypass duct (b) connected to the air inlet of the upper air preheater (2); a valve is provided on the air bypass duct (b); the water outlet of the heater (6) is connected to the water inlet of the flue gas cooler (5) through a first water duct (c); the water outlet of the flue gas cooler (5) is connected to the water inlet of the heater (6) through a second water duct (d), thereby forming a heat exchange circulation water circuit; a circulation pump is provided on the heat exchange circulation water circuit.
2. The ammonium bisulfate blockage treatment system for the tail of a coal-fired boiler according to claim 1, characterized in that: The water outlet of the flue gas cooler (5) is also connected to a melt-crystal water inlet pipeline (e), and the water inlet of the flue gas cooler (5) is also connected to a melt-crystal water outlet pipeline (f). Valves are provided on the first water pipeline (c), the second water pipeline (d), the melt-crystal water inlet pipeline (e) and the melt-crystal water outlet pipeline (f).
3. The ammonium bisulfate blockage treatment system for the tail of a coal-fired boiler according to claim 2, wherein: A flue gas bypass pipe (g) is branched from the flue gas pipe connected to one side of the flue gas outlet of the final air preheater (3) and connected to the flue gas inlet of the dust collector (4). A valve is provided on the flue gas bypass pipe (g).
4. The ammonium bisulfate blockage treatment system for the tail of a coal-fired boiler according to claim 1, wherein: The flue gas coming out of the dust collector (4) is directed to a desulfurization tower or a chimney.