CN108452677B - SCR flue gas denitration method and device using ammonia water as denitration reducing agent - Google Patents
SCR flue gas denitration method and device using ammonia water as denitration reducing agent Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
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- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
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Abstract
The invention discloses a method and a device for denitration of SCR flue gas by taking ammonia water as a denitration reducing agent, wherein the method utilizes boiler flue gas to heat part of boiler cold primary air and/or cold secondary air into hot air and takes the hot air as a heat source for ammonia water gasification, and ammonia gas and water vapor obtained after ammonia water gasification are mixed with the hot air to form an ammonia-air mixture which is returned to be mixed with the boiler flue gas for flue gas denitration; the device comprises an ammonia water gasification injection unit, an SCR denitration reactor inlet flue, an SCR denitration reactor and an air preheater, wherein the SCR denitration reactor inlet flue is positioned between the boiler economizer and the SCR denitration reactor, and the air preheater is arranged at the outlet of the SCR denitration reactor. The invention can solve the SCR flue gas denitration problem of the rotary air preheater boiler flue gas by taking ammonia water as a reducing agent, and simultaneously solve the problems of complex SCR flue gas denitration process and AIG blockage, thereby achieving the purposes of reducing investment, running cost and energy consumption.
Description
Technical Field
The invention relates to the technical field of flue gas denitration, in particular to an SCR flue gas denitration method and device using ammonia water as a denitration reducing agent.
Background
The flue gas denitration reducing agent mainly comprises liquid ammonia, ammonia water and urea, wherein the liquid ammonia belongs to high-risk chemicals, has harsh transportation and storage requirements and is more and more limited by policies and regulations, and the flue gas denitration reducing agent is extremely inconvenient; although the urea can be conveniently transported, stored and used, a great deal of heat and energy are consumed for decomposing the urea into gas ammonia; ammonia water has both liquid ammonia and urea characteristics, and especially has cost performance advantage for coal-fired boilers or thermal power plants with ammonia water byproducts around.
The ammonia water contains NH as main component 3 ·H 2 O, containing a small amount of NH 4+ And OH (OH) - Ammonia water is easy to decompose into NH by light and heat 3 And water. Ammonia water is used as a flue gas denitration reducing agent, a common process is to set an independent ammonia water stripping device, gasify and purify ammonia water into ammonia gas, and then inject pure ammonia gas into flue gas for denitration, and the ammonia water gasification investment cost and the operation cost of the process are high.
The Chinese patent with publication number of CN202844886U discloses a waste heat furnace SCR flue gas denitration device for directly injecting ammonia water into an outlet flue of a combustion engine, and the technology of the patent is mainly suitable for flue gas denitration of the waste heat furnace of the combustion engine and is not suitable for a coal-fired boiler.
The publication No. CN203437023U discloses a denitration reducing agent ammonia water gasification device, a gasification heat source adopts gas with the temperature of more than 200 ℃ of a boiler, and the technology can only be used for denitration of boiler flue gas of a tubular air preheater without flue gas leakage in engineering implementation, namely, the boiler heat primary/secondary air can be used as a heat source for ammonia water gasification. In the case of the boiler of the rotary air preheater, because the flue gas leaks, the hot primary air/secondary air contains dust, if the hot primary air/secondary air serves as a heat source for ammonia water gasification, the ammonia water gasifier and an Ammonia Injection Grid (AIG) are blocked to influence denitration, so that the technology is not suitable for a large-scale coal-fired boiler, and is especially not suitable for the boiler flue gas denitration of the rotary air preheater.
The Chinese patent publication No. CN106422772A discloses a method for gasifying ammonia water directly sprayed in an SCR flue gas denitration inlet flue, and the sprayed ammonia water is difficult to ensure uniform mixing with flue gas after gasifying in the technology, so that the denitration efficiency is affected.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide the SCR flue gas denitration method and the device using ammonia water as a denitration reducing agent, which can solve the SCR flue gas denitration problem of the rotary air preheater boiler flue gas using ammonia water as the reducing agent, solve the problems of complex SCR flue gas denitration process and AIG blockage, and achieve the purposes of reducing investment, running cost and energy consumption.
In one aspect, the invention discloses an SCR flue gas denitration method using ammonia water as a denitration reducing agent, which utilizes boiler flue gas to heat part of boiler cold primary air and/or cold secondary air into hot air and uses the hot air as a heat source for ammonia water gasification, and ammonia gas and water vapor obtained after ammonia water gasification are mixed with the hot air to form an ammonia-air mixture which is returned to be mixed with the boiler flue gas for flue gas denitration.
According to one embodiment of the SCR flue gas denitration method using ammonia water as a denitration reducing agent, the part of the primary cold air and/or the secondary cold air of the boiler come from an air preheater and account for 0.5-5% of the total air quantity, and the pressure of the part of the primary cold air and/or the secondary cold air of the boiler is 2-15 kP and the temperature is 0-50 ℃.
According to one embodiment of the SCR flue gas denitration method using ammonia water as a denitration reducing agent, the temperature of the boiler flue gas is 280-450 ℃, and the temperature of the hot air is 150-350 ℃.
The invention further discloses an SCR flue gas denitration device taking ammonia water as a denitration reducing agent, which comprises an ammonia water gasification injection unit, an SCR denitration reactor inlet flue, an SCR denitration reactor and an air preheater, wherein the SCR denitration reactor inlet flue is positioned between a boiler economizer and the SCR denitration reactor, and the air preheater is arranged at an outlet of the SCR denitration reactor;
the ammonia water gasification injection unit comprises an air pipe, an air-flue gas pipe heat exchanger, a hot air pipeline, an ammonia water gasifier and an ammonia gas-air mixture pipeline, wherein the air-flue gas pipe heat exchanger is arranged in an inlet flue of the SCR denitration reactor, a gas inlet of the air-flue gas pipe heat exchanger is connected with the air preheater through the air pipe, a gas outlet of the air-flue gas pipe heat exchanger is connected with a gas inlet of the ammonia water gasifier, a gas outlet of the ammonia water gasifier is connected with the ammonia gas-air mixture pipeline, and a gas outlet of the ammonia gas-air mixture pipeline is positioned in the inlet flue of the SCR denitration reactor.
According to one embodiment of the SCR flue gas denitration device using ammonia water as a denitration reducing agent, the ammonia water gasification injection unit further comprises an ammonia gas injection grid arranged at a gas outlet of the ammonia gas-air mixture pipeline.
According to one embodiment of the SCR flue gas denitration device using ammonia water as a denitration reducing agent, the ammonia injection grid is arranged between a boiler economizer and an air-flue gas tubular heat exchanger.
According to one embodiment of the SCR flue gas denitration device taking ammonia water as a denitration reducing agent, an adjusting control valve is arranged on the air pipe, and a temperature monitor is arranged on the ammonia-air mixture pipeline.
According to one embodiment of the SCR flue gas denitration device taking ammonia water as a denitration reducing agent, an ammonia water atomizing spray gun is arranged in the ammonia water gasifier, and the ammonia water atomizing spray gun is connected with ammonia water.
According to one embodiment of the SCR flue gas denitration device taking ammonia water as a denitration reducing agent, the air pipe is connected with part of primary cold air and/or secondary cold air of a boiler in the air preheater, wherein the part of primary cold air and/or secondary cold air of the boiler accounts for 0.5-5% of the total air quantity, the pressure is 2-15 kP, and the temperature is 0-50 ℃.
Compared with the prior art, the SCR flue gas denitration method and device using ammonia water as the denitration reducing agent solve the problems of complex SCR denitration process, high energy consumption and high investment and operation cost of using conventional ammonia water as the denitration reducing agent, and solve the problem of blocking of the SCR flue gas denitration AIG using the conventional ammonia water as the reducing agent; the method is beneficial to improving the uniformity of the ammonia-air mixture and the flue gas, improving the SCR denitration efficiency, reducing the ammonia water gasification energy consumption and plant power consumption of the SCR denitration reducing agent and saving the running cost; in addition, the improvement has little or negligible impact on the boiler, and does not affect the operation of the existing process and device.
Drawings
Fig. 1 shows a schematic structural diagram of an SCR flue gas denitration device using ammonia water as a denitration reducing agent according to an exemplary embodiment of the present invention.
Reference numerals illustrate:
1-flue gas, 2-ammonia water, 3-economizer, 4-SCR denitration reactor inlet flue, 5-SCR denitration reactor, 6-ammonia water gasification injection unit, 61-tuber pipe, 611-regulation control valve, 62-air-flue gas tubular heat exchanger, 63-hot air pipeline, 64-ammonia water gasifier, 641-ammonia water atomizing spray gun, 65-ammonia gas-air mixture pipeline, 651-temperature detector, 66-ammonia gas injection grid, 7-air preheater.
Detailed Description
All of the features disclosed in this specification, or all of the steps in a method or process disclosed, may be combined in any combination, except for mutually exclusive features and/or steps.
Any feature disclosed in this specification may be replaced by alternative features serving the same or equivalent purpose, unless expressly stated otherwise. That is, each feature is one example only of a generic series of equivalent or similar features, unless expressly stated otherwise.
The following describes in detail the SCR flue gas denitration method using ammonia water as denitration reducing agent.
In consideration of the defects in the existing denitration method, part of the cold primary air and/or cold secondary air of the boiler is/are heated into hot air by creatively utilizing the boiler flue gas, the obtained hot air is used as a heat source for ammonia water gasification, and an ammonia-air mixture formed by mixing ammonia gas and water vapor obtained after the ammonia water gasification with the hot air is returned to be mixed with the boiler flue gas for flue gas denitration.
Preferably, part of the primary air and/or the secondary air of the boiler comes from the air preheater and accounts for 0.5-5% of the total air quantity, and the pressure of the part of the primary air and/or the secondary air of the boiler is 2-15 kP, and the temperature is 0-50 ℃.
Wherein the temperature of the boiler flue gas is 280-450 ℃, the temperature of hot air obtained by heating part of the cold primary air and/or the cold secondary air of the boiler is 150-350 ℃, and the temperature isWarm air is sufficient to effect vaporization of the denitration reductant ammonia. Then under the action of a denitration catalyst, ammonia gas and NOx in the boiler flue gas are subjected to chemical reaction to generate harmless N 2 And water to achieve the aim of denitration.
The method effectively solves the SCR flue gas denitration problem of the rotary air preheater boiler flue gas by taking ammonia water as a reducing agent, and simultaneously utilizes dustless boiler cold primary air and/or secondary air, thereby solving the problems of complex SCR flue gas denitration process and AIG blockage and achieving the purposes of reducing investment, running cost and energy consumption.
The invention also provides an SCR flue gas denitration device using ammonia water as a denitration reducing agent. Fig. 1 shows a schematic structural diagram of an SCR flue gas denitration device using ammonia water as a denitration reducing agent according to an exemplary embodiment of the present invention.
As shown in fig. 1, according to an exemplary embodiment of the present invention, the SCR flue gas denitration device using ammonia water as a denitration reducing agent includes an ammonia water gasification injection unit 6, an SCR denitration reactor inlet flue 4, an SCR denitration reactor 5, and an air preheater 7, wherein the SCR denitration reactor inlet flue 4 is located between the boiler economizer 3 and the SCR denitration reactor 5, and the air preheater 7 is disposed at an outlet of the SCR denitration reactor 5. The boiler economizer 3, the SCR denitration reactor 5 and the air preheater 7 can all adopt structures and arrangement commonly used in the field, and 1-4 layers of catalysts are preferably arranged inside the SCR denitration reactor 5.
The ammonia water gasification injection unit 6 comprises an air pipe 61, an air-flue gas pipe heat exchanger 62, a hot air pipeline 63, an ammonia water gasifier 64 and an ammonia-air mixture pipeline 65, wherein the air-flue gas pipe heat exchanger 62 is arranged in the inlet flue 4 of the SCR denitration reactor, the gas inlet of the air-flue gas pipe heat exchanger 62 is connected with the air preheater 7 through the air pipe 61, the gas outlet is connected with the gas inlet of the ammonia water gasifier 64, the gas outlet of the ammonia water gasifier 64 is connected with the ammonia-air mixture pipeline 65, and the gas outlet of the ammonia-air mixture pipeline 65 is positioned in the inlet flue 4 of the SCR denitration reactor.
Specifically, the inlet end of the air pipe 61 is connected with the air preheater 7, and is connected with a part of the cold primary air and/or cold secondary air of the boiler in the air preheater 7, wherein the part of the cold primary air and/or cold secondary air of the boiler accounts for 0.5-5% of the total air quantity, the pressure is 2-15 kP, and the temperature is 0-50 ℃. The outlet end of the air pipe 61 is connected with an air-flue gas pipe heat exchanger 62 arranged in the inlet flue 4 of the SCR denitration reactor, so that part of the cold primary air and/or cold secondary air of the boiler is sent into the air-flue gas pipe heat exchanger 62 to exchange heat with the boiler flue gas 1.
The air-flue gas tubular heat exchanger 62 is arranged in the inlet flue 4 of the SCR denitration reactor, the air-flue gas tubular heat exchanger 62 can specifically adopt a heat exchange tube structure, and high-temperature boiler flue gas flowing from the surface of the air-flue gas tubular heat exchanger 62 exchanges heat with part of boiler cold primary air and/or cold secondary air flowing in the air-flue gas tubular heat exchanger 62, so that heating of part of boiler cold primary air and/or cold secondary air is realized. Specifically, the boiler flue gas 2 with the temperature of 280-450 ℃ exchanges heat with part of the cold primary air and/or the cold secondary air of the boiler, obtaining hot air with the temperature of 150-350 ℃. Preferably, the air duct 61 is provided with a regulating control valve 611, and specifically, the temperature of the hot air and the subsequent ammonia-air mixture can be regulated by adjusting the opening of the regulating control valve 611.
Wherein the arrangement of the air-flue gas tubular heat exchanger 62 has little or even negligible impact on the boiler, such as a 300MW grade SCR flue gas denitration device, and the arrangement of the air-flue gas tubular heat exchanger 62 has no more than 3 ℃ of flue gas temperature drop in the area and has almost negligible impact on the boiler.
The air-flue gas tubular heat exchanger 62 is connected with the ammonia water gasifier 64 through a hot air pipeline 63, and the hot air with the temperature of 150-350 ℃ is sent into the ammonia water gasifier 64 through the hot air pipeline 63 to heat and gasify the denitration catalyst ammonia water.
The ammonia vaporizer 61 is preferably provided therein with an ammonia atomizing spray gun 641, the ammonia atomizing spray gun 641 receiving ammonia, the ammonia atomizing spray gun 641 atomizing the ammonia 2 into fine droplets, which are then heated by hot air introduced through a hot air pipe 63, decomposed into ammonia gas and form an ammonia-air mixture with air.
The ammonia water gasifier 61 has a gas outlet connected to the ammonia-air mixture conduit 65 and the gas outlet of the ammonia-air mixture conduit 65 is located in the SCR denitration reactor inlet flue 4, whereby the ammonia-air mixture is fed into the SCR denitration reactor inlet flue 4 through the ammonia-air mixture conduit 65 for subsequent denitration treatment.
Preferably, the ammonia gasification injection unit 6 further comprises an ammonia injection grid 66 arranged at the gas outlet of the ammonia-air mixture conduit 65. More preferably, the ammonia injection grid 66 is arranged between the boiler economizer 3 and the air-flue gas tubular heat exchanger 62, and the air-flue gas tubular heat exchanger also has a rectifying function, so that the uniformity of mixing the ammonia-air mixture with the flue gas can be improved, and the SCR denitration efficiency can be improved. The ammonia injection grid 66 is capable of more uniformly dispersing the ammonia-air mixture in the SCR denitration reactor inlet flue 4, facilitating uniform mixing of the ammonia-air mixture with the boiler flue gas.
Preferably, a temperature monitor 651 is provided on the ammonia-air mixture pipe 65 for detecting the temperature of the ammonia-air mixture. Specifically, the opening degree of the adjustment control valve 611 provided on the air duct 61 may be adjusted according to the feedback of the detection signal of the temperature detector 651 provided on the ammonia-air mixture pipe 65, so that the ammonia-air mixture temperature is maintained at 150 ℃.
The flue gas 1 from the boiler passes through the economizer 3 and then forms an ammonia-flue gas mixture with the flue gas 1 after passing through the ammonia-air mixture injected by the ammonia water gasification injection unit 6, then the ammonia and the flue gas are uniformly mixed through carding and rectifying of the air-flue gas tubular heat exchanger 62, then enter the SCR denitration reactor 5 through the SCR denitration reactor inlet flue 4, and the ammonia and NOx in the flue gas are subjected to chemical reaction to generate harmless N 2 And water to achieve the aim of denitration.
The invention will be further illustrated with reference to specific examples and comparative examples.
Examples:
the embodiment adopts the method and the device.
Specifically, the smoke volume of the 300MW coal-fired boiler is 1063617Nm 3 And/h, wherein the concentration of NOx is 250mg/Nm 3 (6% O, dry) the denitration efficiency was designed to be 80%.
The outlet flue gas temperature of the economizer is 384 ℃, and the air pressure is 10kPa and the air quantity is 4700Nm when the air pipe is used for introducing air pressure from the air preheater to the air-flue gas pipe type heat exchanger 3 After heat exchange of an air-flue gas tubular heat exchanger, the cold primary air of/h (accounting for 2.2% of the total cold primary air of the boiler) is heated into hot air at 350 ℃ and is sent into an ammonia water gasifier through a hot air pipeline, 425kg/h of 20% ammonia water is sprayed into the ammonia water gasifier through an ammonia water atomization spray gun to form an ammonia-air mixture at 155 ℃, and the ammonia-air mixture is sent into an inlet flue of an SCR denitration reactor through an ammonia-air mixture pipeline to be mixed with flue gas to realize denitration, wherein the flue gas temperature is reduced to 2.5 ℃.
The boiler fire coal is only increased by 40kg/h on the basis of 110t/h, the influence on the boiler is negligible, and the denitration operation performance parameters are specifically as follows: denitration efficiency is 83.6 percent, SO 2 /SO 3 Conversion was 0.4% and ammonia slip was 1.2mg/Nm 3 。
Comparative example 1:
the design flue gas parameters and performance requirements are the same as those of the embodiment, and the denitration operation performance parameters of adopting an electric heating (electric heating of 600 kW) or steam stripping (introducing saturated steam of 800kg/h at 350 ℃) technology as a heat source for preparing ammonia are as follows: the denitration efficiency is 82.4 percent, SO 2 /SO 3 Conversion was 0.6% and ammonia slip was 2.2mg/Nm 3 。
Comparative example 2:
the design flue gas parameters and performance requirements are the same as those of the embodiment, and the denitration operation performance parameters of directly spraying ammonia water (namely the patent technology of publication No. CN 106422772A) by adopting a flue are as follows: the denitration efficiency is 80.6 percent, SO 2 /SO 3 Conversion was 1.0% and ammonia slip was 3.0mg/Nm 3 。
Therefore, the SCR flue gas denitration method and device using ammonia water as the denitration reducing agent can well solve the SCR flue gas denitration problem of the rotary air preheater boiler flue gas using ammonia water as the reducing agent, and can better promote SCR denitration performance and save energy compared with the method in the prior art.
The invention is not limited to the specific embodiments described above. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification, as well as to any novel one, or any novel combination, of the steps of the method or process disclosed.
Claims (7)
1. The SCR flue gas denitration method using ammonia water as a denitration reducing agent is characterized in that part of boiler cold primary air and/or cold secondary air is heated into hot air by utilizing boiler flue gas in an air-flue gas tubular heat exchanger arranged in an inlet flue gas channel of an SCR denitration reactor, the hot air is used as a heat source for ammonia water gasification, the inlet flue gas channel of the SCR denitration reactor is positioned between a boiler economizer and the SCR denitration reactor, ammonia gas and water vapor obtained after ammonia water gasification are mixed with the hot air to form an ammonia-air mixture, the ammonia-air mixture is returned to an ammonia injection grid arranged between the boiler economizer and the air-flue gas tubular heat exchanger, and then the ammonia injection grid and the air-flue gas tubular heat exchanger are mixed with boiler flue gas to perform flue gas denitration, and the ammonia injection grid and the air-flue gas tubular heat exchanger are positioned in a vertical section of the inlet flue gas channel of the SCR denitration reactor.
2. The method for denitration of SCR flue gas by using ammonia water as denitration reducing agent according to claim 1, wherein the part of the primary air and/or the secondary air of the boiler is from an air preheater and accounts for 0.5-5% of the total air quantity, and the pressure of the part of the primary air and/or the secondary air of the boiler is 2-15 kP and the temperature is 0-50 ℃.
3. The SCR flue gas denitration method using ammonia water as denitration reducing agent according to claim 1, wherein the temperature of the boiler flue gas is 280-450 ℃, and the temperature of the hot air is 150-350 ℃.
4. The SCR flue gas denitration device taking ammonia water as a denitration reducing agent is characterized by comprising an ammonia water gasification injection unit, an SCR denitration reactor inlet flue, an SCR denitration reactor and an air preheater, wherein the SCR denitration reactor inlet flue is positioned between a boiler economizer and the SCR denitration reactor, and the air preheater is arranged at an outlet of the SCR denitration reactor;
the ammonia water gasification injection unit comprises an air pipe, an air-flue gas pipe heat exchanger, a hot air pipeline, an ammonia water gasifier and an ammonia gas-air mixture pipeline, wherein the air-flue gas pipe heat exchanger is arranged in an inlet flue of the SCR denitration reactor, a gas inlet of the air-flue gas pipe heat exchanger is connected with the air preheater through the air pipe, a gas outlet of the air-flue gas pipe heat exchanger is connected with a gas inlet of the ammonia water gasifier, a gas outlet of the ammonia water gasifier is connected with the ammonia gas-air mixture pipeline, and a gas outlet of the ammonia gas-air mixture pipeline is positioned in the inlet flue of the SCR denitration reactor;
the ammonia water gasification injection unit further comprises an ammonia gas injection grid arranged at a gas outlet of the ammonia gas-air mixture pipeline; the ammonia injection grid is arranged between the boiler economizer and the air-flue gas tubular heat exchanger, and the ammonia injection grid and the air-flue gas tubular heat exchanger are positioned in the vertical section of the inlet flue of the SCR denitration reactor.
5. The SCR flue gas denitration device using ammonia water as a denitration reducing agent according to claim 4, wherein an adjusting control valve is arranged on the air pipe, and a temperature monitor is arranged on the ammonia-air mixture pipeline.
6. The SCR flue gas denitration device using ammonia water as a denitration reducing agent according to claim 4, wherein an ammonia water atomizing spray gun is arranged in the ammonia water gasifier, and the ammonia water atomizing spray gun is connected with ammonia water.
7. The SCR flue gas denitration device using ammonia water as a denitration reducing agent according to claim 4, wherein the air pipe is connected with part of the primary air and/or the cold secondary air of the boiler in the air preheater, wherein the part of the primary air and/or the cold secondary air of the boiler accounts for 0.5-5% of the total air quantity, the pressure is 2-15 kP, and the temperature is 0-50 ℃.
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