Treatment method for solving ammonium bisulfate blockage at tail part of coal-fired boiler

Abstract

The invention provides a treatment method for solving blockage of ammonium bisulfate at the tail part of a coal-fired boiler, which comprises the following steps: in the operation process of the boiler, when the ammonium bisulfate causes blockage on a final-stage air pre-heater, opening a valve on an air bypass pipeline, so that the temperature of smoke flowing through the final-stage air pre-heater is increased, and a smoke cooler recovers smoke heat for heating water; valves on the first waterway pipeline and the second waterway pipeline are opened, a circulating pump is opened, hot water is pumped to the air heater, and the temperature of air entering the air heater is increased; and when the smoke temperature exceeds 147 DEG C, hardened ammonium bisulfate on the final-stage air pre-heater is cleaned, after cleaning is completed, a valve on an air bypass pipeline is closed, and when ammonium bisulfate deposition occurs on the heat exchange surface of the smoke cooler, crystal melting water with the temperature higher than 147 DEG C is introduced till ammonium bisulfate hardened on the smoke cooler is completely melted. The problem that ammonia escapes and reacts with SO3 in the flue gas and water to generate ammonium bisulfate, and the ammonium bisulfate is condensed on the tail heat exchange surface to cause blockage is solved.

Description

Technical Field

[0001] The invention relates to the technical field of coal-fired boiler flue gas denitration, and in particular to a treatment method for solving the blockage of ammonium bisulfate at the tail of a coal-fired boiler. Background Art

[0002] In order to meet the new environmental protection requirements, in recent years, coal-fired boilers are required to undergo ultra-low emission transformation, usually using SNCR and SCR, of which SCR is more commonly used. SCR is the selective catalytic reduction denitrification technology, which is to inject ammonia or other suitable reducing agents into the flue gas upstream of the catalyst to convert NOx in the flue gas into nitrogen and water at a temperature of 200-450℃. SO in the flue gas in the furnace of a coal-fired boiler 2 About 0.5% to 1.0% is oxidized to SO 3 After the SCR system is installed, the catalyst reduces NOx to N 2 At the same time, about 1.0% SO 2 Oxidation to SO 3 The unreacted escaped ammonia (NH 3 ), SO 3 It reacts with water vapor 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 form on the heat exchange surface. Especially in winter, when the ambient temperature is too low, the wall temperature of the final air preheater is low, and the air preheater is often blocked, resulting in a large pressure difference in the air preheater, increased power consumption of the fan, surge and stall, and even endangering the safe operation of the boiler.

[0003] Since ammonium bisulfate will form solid cakes below 147℃, it is difficult to clean with conventional soot blowers, and the use of high-pressure water guns also requires the boiler to be shut down, causing unplanned shutdowns. In addition, ammonium bisulfate is corrosive and causes corrosion of the heat exchange surface. The blockage problem of ammonium bisulfate has always been a difficult problem in boiler operation. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention aims to provide a method for solving the blockage of ammonium bisulfate at the tail of a coal-fired boiler, so as to solve the problem of ammonia escape from the SCR denitrification system of the coal-fired boiler and SO in the flue gas. 3 Ammonium bisulfate generated by reaction with water condenses on the tail heat exchange surface, causing blockage.

[0005] In order to achieve the above-mentioned object, the present invention proposes a method for solving the blockage of ammonium bisulfate at the tail of a coal-fired boiler, comprising a device for treating the blockage of ammonium bisulfate at the tail of a coal-fired boiler, wherein the device comprises a heater and an SCR denitrification device, an upper air preheater, a final air preheater, a flue gas cooler and a dust collector which are sequentially connected through a flue gas pipeline along the flue gas flow direction;

[0006] The heater is provided with an ambient air inlet, the air outlet of the heater is connected to the air inlet of the final air preheater through a first air duct, the air outlet of the final air preheater is connected to the air inlet of the upper air preheater through a second air duct, the air outlet of the upper air preheater is connected to the furnace of the coal-fired boiler through a third air duct, the first air duct is also branched into an air bypass duct connected to the air inlet of the upper air preheater, and a valve is provided on the air bypass duct; the water outlet of the heater is connected to the water inlet of the flue gas cooler through a first water duct, and the water outlet of the flue gas cooler is connected to the water inlet of the heater through a second water duct, thereby forming a heat exchange circulation water circuit, and a circulation pump is provided on the heat exchange circulation water circuit, 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, and valves are provided on the first water duct, the second water duct, the molten crystal water inlet pipeline and the molten crystal water outlet pipeline; the treatment method comprises the following steps:

[0007] S1. During the operation of the coal-fired boiler, when ammonium bisulfate is deposited on the heat exchange surface of the final air preheater and forms a block, the valve on the air bypass pipe is opened to increase the temperature of the flue gas flowing through the final air preheater; the flue gas cooler recovers the heat of the flue gas and uses it to heat water, the valves on the first water pipe and the second water pipe are opened, the circulation pump is turned on, and the hot water is pumped to the heater to increase the temperature of the air entering the heater;

[0008] S2. When the flue gas temperature exceeds 147°C, the ammonium bisulfate melts and the ammonium bisulfate caked on the final air preheater is cleaned. After cleaning, the valve on the air bypass pipe is closed, the final air preheater is put into use, and the flue gas cooler and heater continue to work to further reduce the flue gas temperature.

[0009] S3. When the wall temperature of the flue gas cooler is lower than 147°C, resulting in ammonium bisulfate deposition on its heat exchange surface, close the valves on the first water pipeline and the second water pipeline, open the valves on the melt water inlet pipeline and the melt water outlet pipeline, and introduce melt water with a temperature higher than 147°C until all the ammonium bisulfate caked on the flue gas cooler is melted.

[0010] In the above scheme: a flue gas duct connected to one side of the flue gas outlet of the final air preheater is branched into a flue gas bypass duct connected to the flue gas inlet of the dust collector, and a valve is provided on the flue gas bypass duct. In step S3, when molten crystal water with a temperature higher than 147°C is introduced, the valve on the flue gas bypass duct is opened to allow the flue gas to pass through the flue gas bypass duct to avoid the molten crystal water and reduce the high-temperature molten crystal water from heating the flue gas after the air preheater is cooled.

[0011] In the above scheme: the temperature of the crystal melting water is higher than 150° C., which has a better effect of melting the ammonium bisulfate.

[0012] In the above scheme: the flue gas coming out of the dust collector is sent to a desulfurization tower or a chimney to achieve exhaust of the flue gas.

[0013] The beneficial effects of the present invention are as follows: 1. By introducing air into the air bypass duct, heat exchange does not occur in the final air preheater or heat exchange is reduced, thereby increasing the flue gas temperature and melting the solidified ammonium bisulfate on the final air preheater; 2. The flue gas waste heat is recovered through the flue gas cooler and used to heat water, and the hot water is pumped to the heater through the circulating pump to increase the air temperature and compensate for the fluctuation of the boiler coal consumption caused by insufficient preheating of the air during crystal melting in the final air preheater, that is, to avoid the increase of coal consumption caused by the excessively high flue gas temperature at the outlet of the final air preheater and the insufficient temperature of the air entering the furnace due to the lack of one air preheater; when there is no solidification of ammonium bisulfate on the heat exchange surface of the final air preheater, it can also be used as a waste heat recovery device to further recover the flue gas waste heat and improve the boiler efficiency; 3. When ammonium bisulfate is deposited on the flue gas cooler, the ammonium bisulfate is melted by introducing crystal melting water, so that the flue gas cooler is cleaned and the heat exchange efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0015] Figure 1 It is a schematic diagram of the present invention. DETAILED DESCRIPTION

[0016] A method for solving the blockage of ammonium bisulfate at the tail of a coal-fired boiler, comprising a device for treating the blockage of ammonium bisulfate at the tail of a coal-fired boiler, such as Figure 1 As shown, the treatment device mainly consists of a heater 6 and an SCR denitrification device 1, an upper air preheater 2, a final air preheater 3, a flue gas cooler 5 and a dust collector 4 which are sequentially connected along the flue gas flow direction through a flue gas pipeline.

[0017] The flue gas from the dust collector 4 is sent to the desulfurization tower or chimney to be discharged.

[0018] The heater 6 is provided with an ambient air inlet, the air outlet of the heater 6 is connected to the air inlet of the final air preheater 3 through the 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 the second air duct, and the air outlet of the upper air preheater 2 is connected to the furnace of the coal-fired boiler through the 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, and a valve is provided on the air bypass duct b.

[0019] The water outlet of the heater 6 is connected to the water inlet of the flue gas cooler 5 through the first water pipe c, and the water outlet of the flue gas cooler 5 is connected to the water inlet of the heater 6 through the second water pipe d, thereby forming a heat exchange circulation water circuit, and a circulation pump is provided on the heat exchange circulation water circuit.

[0020] The water outlet of the flue gas cooler 5 is also connected to the melt water inlet pipeline e, and the water inlet of the flue gas cooler 5 is also connected to the melt water outlet pipeline f. Valves are provided on the first water pipeline c, the second water pipeline d, the melt water inlet pipeline c and the melt water outlet pipeline f.

[0021] The governance approach mainly consists of the following steps:

[0022] S1. During the operation of the coal-fired boiler, when ammonium bisulfate is deposited on the heat exchange surface of the final air preheater 3 and forms agglomerates to cause blockage, the valve on the air bypass pipe b is opened, and the flue gas and air do not exchange heat in the final heat exchanger 3 or the heat exchange is reduced (when the air bypass pipe b and the first air pipe a are both opened, since one side of the first air pipe a is connected to equipment and the equipment resistance is large, it is easier for air to enter from the air bypass pipe b), so that the temperature of the flue gas flowing through the final air preheater 3 rises; the flue gas cooler 5 recovers the heat of the flue gas for heating water, opens the valves on the first water pipe c and the second water pipe d, turns on the circulation pump, and pumps hot water to the heater 6 to increase the temperature of the air entering the heater 6.

[0023] S2. When the flue gas temperature exceeds 147°C, the ammonium bisulfate melts and the ammonium bisulfate caked on the final air preheater 3 is cleaned; after the cleaning is completed, the valve on the air bypass pipe b is closed, the final air preheater 3 is put into use, and the flue gas cooler 5 and the heater 6 continue to work to further reduce the flue gas temperature.

[0024] S3. After the flue gas cooler has been running for a period of time, the wall temperature of the flue gas cooler may be lower than the freezing point of ammonium bisulfate, 147°C, and ammonium bisulfate may also be deposited on its heat exchange surface. At this time, close the valves on the first water pipe c and the second water pipe d, open the valves on the melt water inlet pipe c and the melt water outlet pipe f, and introduce melt water with a temperature higher than 147°C until the ammonium bisulfate solidified on the flue gas cooler 5 is completely melted. The temperature of the melt water is preferably higher than 150°C, which has a better effect of melting the ammonium bisulfate.

[0025] A flue gas bypass pipe g is branched on 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 molten crystal water with a temperature higher than 150°C is introduced, 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 of it enters from the flue gas bypass pipe g), allowing the flue gas to pass through the flue gas bypass pipe g to avoid the molten crystal water and reduce the high-temperature molten crystal water from heating the flue gas after the air preheater is cooled.

Claims

1. A method for solving the blockage of ammonium bisulfate at the tail of a coal-fired boiler, characterized in that: The invention comprises a device for treating ammonium bisulfate blockage at the tail of a coal-fired boiler, the device comprising a heater (6) and an SCR denitrification device (1), an upper air preheater (2), a final air preheater (3), a flue gas cooler (5) and a dust collector (4) which are sequentially connected along the flue gas flow direction through a flue gas pipeline; The air heater (6) is provided with an inlet for ambient air, the air outlet of the air 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, the air outlet of the upper air preheater (2) is connected to the furnace of the coal-fired boiler through a third air duct, the first air duct (a) is further branched into an air bypass duct (b) connected to the air inlet of the upper air preheater (2), the air bypass duct (b) is provided with a valve; the water outlet of the air heater (6) is connected to the air inlet of the upper air preheater (2) through a first air duct (a), The water channel pipe (c) is connected to the water channel inlet of the flue gas cooler (5), and the water channel outlet of the flue gas cooler (5) is connected to the water channel inlet of the heater (6) through the second water channel pipe (d), thereby forming a heat exchange circulation water channel. The heat exchange circulation water channel is equipped with a circulation pump. The water channel outlet of the flue gas cooler (5) is also connected to a melt-crystal water inlet pipe (e), and the water channel inlet of the flue gas cooler (5) is also connected to a melt-crystal water outlet pipe (f). Valves are provided on the first water channel pipe (c), the second water channel pipe (d), the melt-crystal water inlet pipe (c) and the melt-crystal water outlet pipe (f). The treatment method comprises the following steps: S1. During the operation of a coal-fired boiler, when ammonium bisulfate is deposited on the heat exchange surface of the final air preheater (3) and forms a block, causing blockage, the valve on the air bypass pipe (b) is opened to increase the temperature of the flue gas flowing through the final air preheater (3); the flue gas cooler (5) recovers the heat of the flue gas for heating water, the valves on the first water pipe (c) and the second water pipe (d) are opened, the circulation pump is turned on, and the hot water is pumped to the heater (6) to increase the temperature of the air entering the heater (6); S2. When the flue gas temperature exceeds 147°C, the ammonium bisulfate melts and the ammonium bisulfate caked on the final air preheater (3) is cleaned. After the cleaning is completed, the valve on the air bypass pipe (b) is closed, the final air preheater (3) is put into use, and the flue gas cooler (5) and the air heater (6) continue to work to further reduce the flue gas temperature. S3. When the wall temperature of the flue gas cooler (5) is lower than 147°C, resulting in ammonium bisulfate deposition on its heat exchange surface, close the valves on the first water pipe (c) and the second water pipe (d), open the valves on the melt water inlet pipe (c) and the melt water outlet pipe (f), and introduce melt water with a temperature higher than 147°C until all the ammonium bisulfate deposited on the flue gas cooler (5) is melted.

2. The method for solving the blockage of ammonium bisulfate at the tail of a coal-fired boiler according to claim 1, characterized in that: A flue gas bypass pipe (g) is branched from the flue gas pipe connected to the flue gas outlet side 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). In step S3, when molten crystal water with a temperature higher than 147° C. is introduced, the valve on the flue gas bypass pipe (g) is opened to allow the flue gas to pass through the flue gas bypass pipe (g) to avoid the molten crystal water.

3. The method for solving the blockage of ammonium bisulfate at the tail of a coal-fired boiler according to claim 2, characterized in that: The temperature of the molten water is higher than 150°C.

4. The method for solving the blockage of ammonium bisulfate at the tail of a coal-fired boiler according to claim 1, characterized in that: The flue gas coming out of the dust collector (4) is directed to a desulfurization tower or a chimney.

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