CN112604400A - Flue gas purification method and flue gas purification system - Google Patents
Flue gas purification method and flue gas purification system Download PDFInfo
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- CN112604400A CN112604400A CN202011373122.7A CN202011373122A CN112604400A CN 112604400 A CN112604400 A CN 112604400A CN 202011373122 A CN202011373122 A CN 202011373122A CN 112604400 A CN112604400 A CN 112604400A
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
- B01D46/02—Particle separators, e.g. dust precipitators, having hollow filters made of flexible material
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- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/343—Heat recovery
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/346—Controlling the process
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/76—Gas phase processes, e.g. by using aerosols
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8621—Removing nitrogen compounds
- B01D53/8625—Nitrogen oxides
- B01D53/8628—Processes characterised by a specific catalyst
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Abstract
The invention discloses a flue gas purification method and a flue gas purification system, which aim to solve the technical problem of reducing the influence of flue gas on the catalytic activity of an SCR (selective catalytic reduction) catalyst. The method is used for removing dust, sulfur oxides and nitrogen oxides contained in the flue gas of a target to be purified, and comprises the following steps: injecting ammonia into the object flue gas so as to obtain first process flue gas, wherein the injection amount of the ammonia can ensure the required reaction in the following processes; fully mixing ammonia in the first process flue gas with the target flue gas to obtain a second process flue gas containing sulfate particles generated by the reaction of the oxysulfide and the ammonia; carrying out gas-solid separation treatment on the second process flue gas so as to obtain a third process flue gas from which the sulfate particles and dust are removed; and enabling the third process flue gas to pass through an SCR (selective catalytic reduction) catalyst so as to obtain the target flue gas with the nitrogen oxides removed. By means of gas-solid separation treatment before ammonia addition and SCR catalytic denitration, the subsequent denitration efficiency can be improved, and the effects of dust removal and desulfurization can be achieved.
Description
Technical Field
The present invention relates to a flue gas purification method and a flue gas purification system for removing dust, sulfur oxides and nitrogen oxides contained in a target flue gas to be purified.
Background
The alkali furnace is the main equipment for treating black liquor in the paper making industry at present. The black liquor is concentrated and then used as fuel, and fed into an alkali furnace to be combusted, the combusted liquid is discharged from the furnace bottom and is reduced into alkali after causticization, and the steam becomes secondary energy to be reused. Although the alkaline furnace is the necessary industrial equipment in pulping enterprises in the paper making industry, the existence of nitrogen-containing element alkali in the raw material black liquor causes NO in the flue gas of the alkaline furnacexThe concentration of (A) is out of the limits and the fluctuation is large.
Currently, the most widely and effectively applied flue gas denitration technology is NH3Selective catalytic reduction of NOxTechnology (i.e., SCR technology). The SCR catalyst commonly used is titanium-based vanadium catalyst (V)2O5-WO3/TiO2) The SCR catalyst operating window temperature is typically 320-420 ℃.
Because the working window temperature of the SCR catalyst is higher, the SCR denitration device is usually arranged in front of the bag-type dust remover, and thus, a large amount of substances such as alkali dust, sulfur dioxide and the like in the flue gas of the alkali furnace easily cause the SCR catalyst to be poisoned and lose activity, and further the denitration efficiency cannot meet the emission requirement.
In order to avoid the poisoning of the SCR catalyst, an SCR denitration device can be arranged behind the electrostatic dust collector. However, the temperature of the alkali furnace flue gas after passing through the electrostatic precipitator is generally reduced to 160-170 ℃, which is far lower than the temperature of the working window of the conventional SCR catalyst; even if a common low-temperature SCR denitration catalyst (the working window temperature is 220-280 ℃) is adopted, the flue gas still needs to be heated and heated in front of the SCR denitration device, so that the energy consumption is caused.
Disclosure of Invention
The invention aims to provide a flue gas purification method and a flue gas purification system, and aims to solve the technical problem of reducing the influence of flue gas on the catalytic activity of an SCR (selective catalytic reduction) catalyst.
According to an aspect of the present invention, there is provided a flue gas cleaning method for removing dust, sulfur oxides, and nitrogen oxides contained in a target flue gas to be cleaned, including: injecting ammonia into the object flue gas so as to obtain first process flue gas, wherein the injection amount of the ammonia can ensure the required reaction in the following processes; fully mixing ammonia in the first process flue gas with the target flue gas to obtain a second process flue gas containing sulfate particles generated by the reaction of the oxysulfide and the ammonia; carrying out gas-solid separation treatment on the second process flue gas so as to obtain a third process flue gas from which the sulfate particles and dust are removed; and enabling the third process flue gas to pass through an SCR (selective catalytic reduction) catalyst so as to obtain the target flue gas with the nitrogen oxides removed.
Preferably, the target flue gas is pre-dedusted and has a temperature of 90-280 ℃. The subject flue gas may be temperature reduced to 90-280 ℃ by the pre-dedusting and/or other processes prior to pre-dedusting. The pre-dedusting can also adopt a bag-type dust remover and/or an electric dust remover. The object smoke can also be obtained by pre-dedusting smoke from an alkali furnace or other industrial kilns.
Preferably, the SCR catalyst adopts a low-temperature SCR denitration catalyst, and the working window temperature of the low-temperature SCR denitration catalyst is 90-220 ℃; meanwhile, the object smoke is a smoke having a temperature of 90-220 ℃, and there is no heating of the smoke from the outside in the process of gradually changing from the object smoke to the target smoke.
Further, the preferred application temperature of the low-temperature SCR denitration catalyst is 100-200 ℃, and the more preferred application temperature is 120-180 ℃; accordingly, the temperature of the subject flue gas is preferably 100-.
According to an aspect of the present invention, there is provided a flue gas cleaning system for removing dust, sulfur oxides and nitrogen oxides contained in a target flue gas to be cleaned, comprising the following devices connected in series by a pipeline in order: the ammonia injection device is used for injecting ammonia into the object flue gas so as to obtain first process flue gas, and the injection amount of the ammonia can ensure the reaction required in the following steps; an ammonia-smoke mixing device for thoroughly mixing ammonia in the first process smoke with the target smoke to obtain second process smoke containing sulfate particles generated by the reaction of the sulfur oxides and ammonia; the gas-solid separation device is used for carrying out gas-solid separation treatment on the second process flue gas so as to obtain a third process flue gas from which the sulfate particles and the dust are removed; and the SCR catalytic denitration device is used for enabling the third process flue gas to pass through an SCR catalyst so as to obtain the target flue gas from which the nitrogen oxides are removed.
Optionally, the ammonia injection device includes an ammonia injection grid, the ammonia injection grid is installed on a cross section of a pipeline in the flue gas conveying pipeline of the object, and ammonia injection ports are distributed on a side surface of the ammonia injection grid along the flue gas flow of the object.
Optionally, the ammonia-smoke mixing device includes an ammonia-smoke mixer, and a diversion structure is arranged in the ammonia-smoke mixer to form a zigzag ammonia-smoke mixed airflow channel.
Optionally, the gas-solid separation device comprises a denitration pretreatment tower, and a filtering filler is filled in a region between a lower air inlet and an upper air outlet in the denitration pretreatment tower.
Optionally, the SCR catalytic denitration device includes a denitration tower, and an SCR catalyst is filled in a region between a lower air inlet and an upper exhaust port in the denitration tower.
Preferably, the SCR catalyst adopts a low-temperature SCR denitration catalyst, the working window temperature of the low-temperature SCR denitration catalyst is 90-220 ℃, and an external heating device for heating the smoke in the smoke purification system does not exist.
Further, the SCR catalyst is preferably used at a temperature of 100-200 deg.C, and more preferably at a temperature of 120-180 deg.C.
According to the flue gas purification method and the flue gas purification system, by means of ammonia addition required by SCR denitration and gas-solid separation treatment before SCR catalytic denitration, substances such as dust and sulfur dioxide which can affect catalytic activity of an SCR catalyst are removed, subsequent denitration efficiency can be improved, and dust removal and desulfurization effects can be achieved.
When the target flue gas is pre-dedusted and has a temperature of 90-280 ℃, the pre-dedusted precursor flue gas is subjected to pre-dedusting by the currently commonly used mature dedusting means (such as bag dedusting, electrostatic dedusting and the like) to greatly reduce the dust content, so that the gas-solid separation treatment pressure is greatly reduced, and the ammonia consumption is reduced.
When the SCR catalyst adopts the low-temperature SCR denitration catalyst with the working window temperature of 90-220 ℃, the flue gas does not need to be heated from the outside in the process of gradually changing from the object flue gas to the target flue gas, and the redundant energy consumption is avoided.
The invention is further described with reference to the following figures and detailed description. Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to assist in understanding the relevant embodiments, and are incorporated in and constitute a part of this specification, with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to that as illustrated and described herein. In the drawings:
FIG. 1 is a schematic diagram of the composition of an embodiment of the flue gas purification system of the present invention.
FIG. 2 is a schematic structural diagram of an ammonia injection device in an embodiment of a flue gas purification system of the present invention.
FIG. 3 is a schematic structural diagram of an ammonia-smoke mixing device in an embodiment of the flue gas purification system of the invention.
Detailed Description
The invention will be described more fully hereinafter with reference to the accompanying drawings. Those skilled in the art will be able to implement the invention based on these teachings. Before the present invention is described in detail with reference to the accompanying drawings, it is to be noted that:
in the present specification, the technical solutions and the technical features provided in the respective portions including the following description may be combined with each other without conflict.
Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention.
The terms "comprises" and "comprising," and any variations thereof, in this specification and in the claims and any related parts, are intended to cover non-exclusive inclusions.
FIG. 1 is a schematic diagram of the composition of an embodiment of the flue gas purification system of the present invention. As shown in fig. 1, a flue gas purification system for removing dust, sulfur oxides and nitrogen oxides contained in a target flue gas 1 to be purified includes an ammonia injection device 2, an ammonia-flue gas mixing device 4, a gas-solid separation device 5 and an SCR catalytic denitration device 6 which are connected in series in sequence by a pipeline.
The ammonia injection device 2 is used for injecting ammonia into the object flue gas 1 so as to obtain first process flue gas, and the injection amount of the ammonia can ensure the required reaction in the following processes; the ammonia-smoke mixing device 4 is used for fully mixing ammonia in the first process smoke with the target smoke 1 so as to obtain second process smoke containing sulfate particles generated by the reaction of the sulfur oxides and the ammonia; the gas-solid separation device 5 is used for carrying out gas-solid separation treatment on the second process flue gas so as to obtain a third process flue gas from which the sulfate particles and the dust are removed; the SCR catalytic denitration device 6 is used for enabling the third process flue gas to pass through an SCR catalyst so as to obtain the target flue gas without the nitrogen oxides. The target flue gas may be discharged through a stack 7.
Preferably, the object flue gas 1 is a flue gas which is subjected to pre-dedusting and has a temperature of 90-280 ℃. The subject flue gas may be temperature reduced to 90-280 ℃ by the pre-dedusting and/or other processes prior to pre-dedusting. The pre-dedusting can also adopt a bag-type dust remover and/or an electric dust remover. The object flue gas 1 can also be obtained by pre-dedusting flue gas from an alkali furnace or other industrial kilns.
Preferably, the SCR catalyst adopts a low-temperature SCR denitration catalyst, and the working window temperature (namely the active temperature window) of the low-temperature SCR denitration catalyst is 90-220 ℃; meanwhile, the object flue gas 1 is a flue gas having a temperature of 90 to 220 ℃, and there is no heating of the flue gas from the outside in the process of gradually changing from the object flue gas to the target flue gas.
Further, the preferred application temperature of the low-temperature SCR denitration catalyst is 100-200 ℃, and the more preferred application temperature is 120-180 ℃; accordingly, the temperature of the subject flue gas is preferably 100-.
According to the flue gas purification system, by means of ammonia addition required by SCR denitration and gas-solid separation treatment before SCR catalytic denitration, substances such as dust and sulfur dioxide which can affect catalytic activity of an SCR catalyst are removed, subsequent denitration efficiency can be improved, and dust removal and desulfurization effects can be achieved.
When the target flue gas 1 is a flue gas which is subjected to pre-dedusting and has a temperature of 90-280 ℃, the pre-dedusting of the precursor flue gas of the target flue gas 1 can be performed by a mature dedusting means (such as bag dedusting, electrostatic dedusting and the like) commonly used at present, so that the dust content is greatly reduced, the gas-solid separation treatment pressure is greatly reduced, and the consumption of ammonia can be reduced.
When the SCR catalyst adopts the low-temperature SCR denitration catalyst with the working window temperature of 90-220 ℃, the heating of the flue gas from the outside in the process of gradually changing from the object flue gas 1 to the target flue gas is not needed, and the redundant energy consumption is avoided.
FIG. 2 is a schematic structural diagram of an ammonia injection device in an embodiment of a flue gas purification system of the present invention. FIG. 3 is a schematic structural diagram of an ammonia-smoke mixing device in an embodiment of the flue gas purification system of the invention. The structures of the ammonia injection device 2, the ammonia-smoke mixing device 4, the gas-solid separation device 5 and the SCR catalytic denitration device 6 in the embodiment of the flue gas purification system of the present invention will be further described with reference to fig. 2 to 3.
As shown in fig. 2, the ammonia injection device 2 may specifically include an ammonia injection grid 202, wherein the ammonia injection grid 202 is installed on a cross section of a flue gas conveying pipe 201 of a subject, and ammonia injection ports 203 are distributed on a side surface of the ammonia injection grid 202 along a flue gas flow of the subject. According to fig. 2, since the ammonia injection grid 202 is installed on a duct cross section in the object flue gas transport duct 201, the corresponding duct cross section of the object flue gas transport duct 201 is subdivided into a plurality of different regions by the ammonia injection grid 202, so that the object flue gas 1 flows through the subdivided regions; meanwhile, the ammonia spraying openings 203 are distributed on one side surface of the ammonia spraying grid 202 along the flue gas flow of the object, so that the air flow subdivided by the ammonia spraying grid 202 is mixed with the ammonia gas sprayed from the ammonia spraying openings 203, and the effect of improving the mixing uniformity of the ammonia smoke is achieved.
In addition, it is obvious that the ammonia injection grid 202 is also connected to the ammonia source 3 through an ammonia supply pipe 204 or other possible means. The ammonia source 3 may use liquid ammonia and supply ammonia to the ammonia injection grid 202 by vaporizing the liquid ammonia (or diluting it with air).
As shown in fig. 3, the ammonia-smoke mixing device may specifically include an ammonia-smoke mixer 401, and a diversion structure 402 is disposed in the ammonia-smoke mixer 401 to form a tortuous ammonia-smoke mixture gas flow passage 403. More specifically, the flow directing structure 402 employs a flow directing plate.
The gas-solid separation device 5 may specifically include a denitration pretreatment tower, in which a region between a lower air inlet and an upper air outlet is filled with a filter filler. Wherein, the lower part air inlet of denitration preliminary treatment tower is used for receiving the second process flue gas, and the upper portion gas vent of denitration preliminary treatment tower is used for discharging the third process flue gas.
The SCR catalytic denitration device comprises a denitration tower, wherein an SCR catalyst is filled in a region between a lower air inlet and an upper exhaust outlet in the denitration tower. Wherein, the lower part air inlet of denitration tower is used for receiving the third process flue gas, and the upper portion gas vent of denitration tower is used for discharging the target flue gas.
The SCR catalyst is preferably a low-temperature SCR catalyst which has been successfully commercially popularized by the applicant of the present invention. The technical information related to the low-temperature SCR catalyst and the low-temperature SCR denitration technology can refer to the patent documents that the applicant of the present invention has filed and published and the following contents:
1) overview of low-temperature SCR flue gas denitration technology
The low-temperature SCR flue gas denitration technology is researched and developed on the basis of the traditional SCR denitration technology. Currently, the most widely and effectively applied flue gas denitration technology is NH3Selective catalytic reduction of NOxTechnology (SCR). The catalyst serving as the core of the SCR denitration method becomes the key for reaching the emission reduction index of nitrogen oxides, and the commercial catalyst system commonly used at present is a titanium-based vanadium catalyst (V)2O5-WO3/TiO2) The active temperature window is high (320-420 ℃), an SCR device needs to be arranged in front of an air preheater and behind an economizer, the temperature of flue gas can reach the temperature area, and high-concentration dust and SO exist in the temperature area2Easily causing catalyst poisoning and reducing service life. The main bottleneck limiting the popularization of the SCR technology is that the requirement on the reaction temperature is relatively high, so that the energy consumption in the denitration process is high, and the corresponding engineering investment cost is high.
In order to overcome the defects, the inventor successfully develops a low-temperature flue gas denitration technology through long-term basic research and engineering application research and development, perfects the process technology through long-term repeated small-scale and medium-scale tests, obtains a large amount of industrial data, and actively promotes industrial application and popularization in various industries at present.
2) Principle of the technology
The low-temperature SCR denitration technology is obtained by optimizing on the basis of the traditional SCR denitration technology, has the same technical principle as the traditional SCR denitration technology, and mainly uses NH under the action of a catalyst3As reducing agent, selectively with NO in the flue gasxReacting and generating nontoxic and pollution-free N2And H2And O. The reductant may also be a hydrocarbon (e.g., methane, propane, etc.), ammonia, urea, etc. By NH3For the reducing agent example, the reaction formula is as follows:
4NH3+4NO+O2→4N2+6H2O (1-1)
4NH3+2NO2+O2→3N2+6H2O (1-2)
8NH3+6NO2→7N2+12H2O (1-3)
the low-temperature SCR denitration technology is characterized by low-temperature catalysis, which is different from the traditional vanadium catalyst with the ignition temperature as high as 400 ℃, the low-temperature SCR catalyst used by the novel catalysis method can have good activity at 90 ℃, the better applicable temperature window is 100-200 ℃, and the better applicable temperature is 120-180 ℃.
The service life of the low-temperature SCR catalyst is generally 3-5 years, the catalyst needs to be replaced after being deactivated, and the deactivated catalyst can be returned to a factory for regeneration and secondary activation and can be recycled.
3) Technical characteristics
The technical difficulty of low-temperature catalysis is successfully overcome by changing high-temperature catalytic oxidation into low-temperature catalytic oxidation and effectively combining the adsorption function of the activated carbon with the catalytic function of the catalyst when the working window temperature of the low-temperature SCR denitration catalyst is 90-220 ℃. The working window temperature of the low-temperature SCR denitration catalyst is 90-220 ℃, the catalytic effect cannot be achieved when the temperature is too low, and the adsorption effect is influenced when the temperature is too high.
4) Low temperature SCR catalyst parameters
The low-temperature denitration catalyst takes a carbon-based material as a carrier and vanadium, tungsten and cerium as active components, firstly uses a nitric acid solution to carry out surface treatment on active carbon, and then uses an impregnation method to load the vanadium, tungsten and cerium active components on the carbon-based material. The load capacity of vanadium is 1-8 wt% of the weight of the carbon base, the load capacity of tungsten is 1-5 wt% of the weight of the carbon base, and the load capacity of cerium is 1-10 wt% of the weight of the carbon base.
Experimental example 1
In this experimental example, the flue gas device behind the alkali recovery furnace dust pelletizing system of processing: the concentration of nitrogen oxides is 250mg/Nm3Concentration of sulfur dioxide<20mg/Nm3Dust concentration<10mg/Nm3The water vapor content is 23%, and the gas content is about 5000Nm3The temperature is about 130-160 ℃.
The flue gas to be treated coming out of the alkali recovery furnace dust removal system enters the ammonia spraying grid 2 through the first inlet, and is mixed with the ammonia entering through the first ammonia inlet in the ammonia spraying grid 2, and the volume ratio of the ammonia to the nitrogen oxides is controlled to be 1.05: 1, the flue gas enters an ammonia-smoke mixer 4 from a flue gas inlet II, the flue gas is further mixed through a guide plate, a small amount of sulfur dioxide in the flue gas reacts with ammonia gas to generate sulfate in the mixing process, the completely mixed flue gas enters a pretreatment tower 5 through a flue gas inlet III, the flue gas passes through a filtering layer of the pretreatment tower, sulfate particles and alkali dust generated in the flue gas are further treated, the sulfate particles and the alkali dust are discharged through a flue gas outlet III on the right side of the pretreatment tower 5, the flue gas enters a denitration tower 6 through a flue gas inlet IV on the left side of the denitration tower 6, and the air speed of an empty tower of the denitration tower 6 is controlled at 3500-1After passing through the catalyst bed, nitrogen oxides in the flue gas are catalytically reduced into nitrogen and water, and the clean flue gas is discharged through a chimney 7.
The flue gas is discharged into the atmosphere after passing through the denitration reaction tower, and the denitration efficiency is improved>80% outlet NOx concentration<50mg/Nm3Concentration of sulfur dioxide<5mg/Nm3Dust concentration<5mg/Nm3And the standard of ultralow emission of the power plant boiler is achieved.
Experimental example 2
In this experimental example, the flue gas device behind the alkali recovery furnace dust pelletizing system of processing: the concentration of nitrogen oxides is 280mg/Nm3Concentration of sulfur dioxide<10mg/Nm3Dust concentration<10mg/Nm3Water vapor content 25%, gas content aboutIs 3000Nm3The temperature is about 140-.
The flue gas to be treated coming out of the alkali recovery furnace dust removal system enters the ammonia spraying grid 2 through the first inlet, and is mixed with the ammonia entering through the first ammonia inlet in the ammonia spraying grid 2, and the volume ratio of the ammonia to the nitrogen oxides is controlled to be 1.05: 1, the flue gas enters an ammonia-smoke mixer 4 from a flue gas inlet II, the flue gas is further mixed through a guide plate, a small amount of sulfur dioxide in the flue gas reacts with ammonia gas to generate sulfate in the mixing process, the completely mixed flue gas enters a pretreatment tower 5 through a flue gas inlet III, the flue gas passes through a filter layer of the pretreatment tower, sulfate particles and alkali dust generated in the flue gas are further treated, the sulfate particles and the alkali dust are discharged through a flue gas outlet III on the right side of the pretreatment tower 5, then the flue gas enters a denitration tower 6 through a flue gas inlet IV on the left side of the denitration tower 6, the air speed of an empty tower of the denitration tower 6 is controlled at 1500-1After passing through the catalyst bed, nitrogen oxides in the flue gas are catalytically reduced into nitrogen and water, and the clean flue gas is discharged through a chimney 7.
The flue gas is discharged into the atmosphere after passing through the denitration reaction tower, and the denitration efficiency is improved>85% outlet NOx concentration<50mg/Nm3Concentration of sulfur dioxide<5mg/Nm3Dust concentration<5mg/Nm3And the standard of ultralow emission of the power plant boiler is achieved.
The contents of the present invention have been explained above. Those skilled in the art will be able to implement the invention based on these teachings. All other embodiments, which can be derived by a person skilled in the art from the description above without inventive step, shall fall within the scope of protection of the present invention.
Claims (10)
1. A flue gas cleaning method for removing dust, sulfur oxides and nitrogen oxides contained in a target flue gas to be cleaned, characterized by comprising:
injecting ammonia into the object flue gas so as to obtain first process flue gas, wherein the injection amount of the ammonia can ensure the required reaction in the following processes;
fully mixing ammonia in the first process flue gas with the target flue gas to obtain a second process flue gas containing sulfate particles generated by the reaction of the oxysulfide and the ammonia;
carrying out gas-solid separation treatment on the second process flue gas so as to obtain a third process flue gas from which the sulfate particles and dust are removed; and
and enabling the third process flue gas to pass through an SCR (selective catalytic reduction) catalyst so as to obtain the target flue gas with the nitrogen oxides removed.
2. The flue gas purification method according to claim 1, wherein: the object flue gas is pre-dedusted and has a temperature of 90-280 ℃.
3. The flue gas purification method according to claim 2, wherein: the temperature of the object smoke is reduced to 90-280 ℃ by the pre-dedusting and/or other processes before the pre-dedusting.
4. The flue gas purification method according to claim 2, wherein: the pre-dedusting adopts a bag-type dust collector and/or an electrostatic precipitator.
5. The flue gas purification method according to any one of claims 2 to 4, wherein: the target flue gas is obtained by pre-dedusting flue gas from an alkali furnace or other industrial kilns.
6. The flue gas purification method according to any one of claims 2 to 4, wherein: the SCR catalyst adopts a low-temperature SCR denitration catalyst, and the working window temperature of the low-temperature SCR denitration catalyst is 90-220 ℃; the object flue gas is a flue gas with a temperature of 90-220 ℃, and there is no heating of the flue gas from the outside in the process of gradually changing from the object flue gas to the target flue gas.
7. The flue gas purification method according to claim 6, wherein: the preferred application temperature of the low-temperature SCR denitration catalyst is 100-200 ℃, and the more preferred application temperature is 120-180 ℃; accordingly, the temperature of the subject flue gas is preferably 100-.
8. A flue gas purification system for removing dust, sulfur oxides and nitrogen oxides contained in the flue gas of an object to be purified is characterized by comprising the following devices which are connected in series in sequence by pipelines:
the ammonia injection device is used for injecting ammonia into the object flue gas so as to obtain first process flue gas, and the injection amount of the ammonia can ensure the required reaction in the following processes;
an ammonia-smoke mixing device for thoroughly mixing ammonia in the first process smoke with the target smoke to obtain second process smoke containing sulfate particles generated by the reaction of the sulfur oxides and ammonia;
the gas-solid separation device is used for carrying out gas-solid separation treatment on the second process flue gas so as to obtain a third process flue gas from which the sulfate particles and the dust are removed;
and the SCR catalytic denitration device is used for enabling the third process flue gas to pass through an SCR catalyst so as to obtain the target flue gas from which the nitrogen oxides are removed.
9. The flue gas purification system of claim 8, wherein:
the ammonia spraying device comprises an ammonia spraying grid, the ammonia spraying grid is arranged on the cross section of one pipeline in the object flue gas conveying pipeline, and ammonia spraying openings are distributed on one side surface of the ammonia spraying grid along the object flue gas flow;
and/or the ammonia and smoke mixing device comprises an ammonia and smoke mixer, wherein a flow guide structure is arranged in the ammonia and smoke mixer to form a zigzag ammonia and smoke mixed gas flow channel;
and/or the gas-solid separation device comprises a denitration pretreatment tower, wherein a filtering filler is filled in a region between a lower gas inlet and an upper gas outlet in the denitration pretreatment tower;
and/or the SCR catalytic denitration device comprises a denitration tower, wherein an SCR catalyst is filled in a region between a lower air inlet and an upper exhaust outlet in the denitration tower.
10. The flue gas purification system according to claim 8 or 9, wherein: the SCR catalyst adopts a low-temperature SCR denitration catalyst, the working window temperature of the low-temperature SCR denitration catalyst is 90-220 ℃, the preferred use temperature is 100-200 ℃, and the more preferred use temperature is 120-180 ℃; and, there is no external heating device in the flue gas cleaning system to heat the flue gas therein.
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