CN114669193A - Reducing agent supply system for low-temperature SCR denitration of cement plant and control method - Google Patents
Reducing agent supply system for low-temperature SCR denitration of cement plant and control method Download PDFInfo
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- CN114669193A CN114669193A CN202210361689.5A CN202210361689A CN114669193A CN 114669193 A CN114669193 A CN 114669193A CN 202210361689 A CN202210361689 A CN 202210361689A CN 114669193 A CN114669193 A CN 114669193A
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- 239000003638 chemical reducing agent Substances 0.000 title claims abstract description 60
- 239000004568 cement Substances 0.000 title claims abstract description 37
- 238000000034 method Methods 0.000 title claims abstract description 25
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 166
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims abstract description 156
- 235000011114 ammonium hydroxide Nutrition 0.000 claims abstract description 156
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims abstract description 59
- 239000003546 flue gas Substances 0.000 claims abstract description 59
- 238000001816 cooling Methods 0.000 claims abstract description 33
- 239000007788 liquid Substances 0.000 claims description 99
- 229910021529 ammonia Inorganic materials 0.000 claims description 49
- 230000001105 regulatory effect Effects 0.000 claims description 44
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 34
- 239000002351 wastewater Substances 0.000 claims description 24
- 238000012856 packing Methods 0.000 claims description 14
- 239000007921 spray Substances 0.000 claims description 14
- 230000003068 static effect Effects 0.000 claims description 13
- 238000010438 heat treatment Methods 0.000 claims description 9
- 238000002156 mixing Methods 0.000 claims description 9
- 238000000926 separation method Methods 0.000 claims description 9
- 239000002699 waste material Substances 0.000 claims description 9
- 238000006243 chemical reaction Methods 0.000 claims description 7
- 238000004065 wastewater treatment Methods 0.000 claims description 7
- 238000010790 dilution Methods 0.000 claims description 5
- 239000012895 dilution Substances 0.000 claims description 5
- 239000000945 filler Substances 0.000 claims description 5
- 239000002918 waste heat Substances 0.000 claims description 4
- 238000005260 corrosion Methods 0.000 claims description 3
- 230000007797 corrosion Effects 0.000 claims description 3
- 230000000630 rising effect Effects 0.000 claims description 2
- 238000004868 gas analysis Methods 0.000 claims 2
- 239000003054 catalyst Substances 0.000 description 8
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 6
- 239000007789 gas Substances 0.000 description 5
- 238000012544 monitoring process Methods 0.000 description 5
- 238000005265 energy consumption Methods 0.000 description 4
- 238000007865 diluting Methods 0.000 description 3
- 238000001704 evaporation Methods 0.000 description 3
- 230000008020 evaporation Effects 0.000 description 3
- 238000002347 injection Methods 0.000 description 3
- 239000007924 injection Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 2
- 239000004202 carbamide Substances 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000009692 water atomization Methods 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005485 electric heating Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- 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
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/90—Injecting reactants
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- 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
- B01D53/74—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
- B01D53/8631—Processes characterised by a specific device
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- 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
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8696—Controlling the catalytic process
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2251/00—Reactants
- B01D2251/20—Reductants
- B01D2251/206—Ammonium compounds
- B01D2251/2062—Ammonia
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/02—Other waste gases
- B01D2258/0283—Flue gases
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Abstract
The invention belongs to the technical field of flue gas denitration, and particularly relates to a reducing agent supply system and a control method for low-temperature SCR denitration in a cement plant. The invention provides a reducing agent supply system for low-temperature SCR denitration of a cement plant and a control method, wherein ammonia water with the mass fraction of 15-25% is formed into high-purity ammonia gas in a low-temperature evaporation-self-cooling mode.
Description
Technical Field
The invention belongs to the technical field of flue gas denitration, and particularly relates to a reducing agent supply system for low-temperature SCR denitration in a cement plant and a control method.
Background
The prior art is as follows:
in recent years, environmental protection standards in China are becoming strict, and in the field of flue gas denitration, SCR denitration technology is high in denitration efficiency and reducing agent (NH)3) High utilization rate and wide application. The traditional medium-high temperature SCR denitration technology is suitable for the condition that the temperature of flue gas is more than 200 ℃, and the reducing agent is generally supplied by gasifying liquid ammonia and decomposing urea or directly spraying ammonia water with the mass fraction of 15-25% into the flue gas by using an atomizing spray gun. Among the three reducing agent supply modes: liquid ammonia is a dangerous product, and the danger coefficient is high in the using process; urea decomposition is relatively safe, but the cost is too high; the cost and the safety factor are comprehensively considered, and the ammonia water is suitable to be used as the reducing agent.
Most of SCR systems adopt a flue gas flue which directly sprays ammonia water into the SCR reactor by using an atomizing spray gun, see the patent of denitration systems
However, the present inventors have found that the above prior art has at least the following technical problems:
the service temperature of the low-temperature SCR denitration system is below 200 ℃, and the heat quality of the flue gas is low. If the ammonia water is directly sprayed into the flue by the atomizing spray gun under the temperature condition, the evaporation and gasification process of ammonia water droplets is slow, and NH is generated at the moment3The release of the components is incomplete, and the effective amount of a reducing agent participating in the denitration reaction is reduced; in addition, an atomizing spray gun is adopted to spray ammonia, ammonia water droplets are evaporated and absorb heat in flue gas to reduce the temperature of the flue gas, and when the temperature of the flue gas is reduced to be near the dew point of water, the temperature of the flue gas is reducedWater drops are condensed and gathered on the surface of the SCR catalyst and increase the water content of the flue gas; these factors all reduce the reaction efficiency of the SCR catalyst, resulting in a reduction in the denitration efficiency and the utilization of the reducing agent.
The difficulty and significance for solving the technical problems are as follows:
therefore, based on the problems, the reducing agent supply system and the control method for the low-temperature SCR denitration in the cement plant, which are used for forming high-purity ammonia gas by using ammonia water with the mass fraction of 15% -25% in a low-temperature evaporation-self-cooling mode, have important practical significance.
Disclosure of Invention
The application aims to solve the technical problems caused by the fact that ammonia water with the mass fraction of 15% -25% is adopted as a low-temperature SCR reducing agent in the prior art, and provides a reducing agent supply system and a control method for low-temperature SCR denitration of a cement plant, wherein the ammonia water with the mass fraction of 15% -25% is formed into high-purity ammonia gas in a low-temperature evaporation-self-cooling mode.
The technical scheme adopted by the embodiment of the application to solve the technical problems in the prior art is as follows:
a reducing agent supply system for low-temperature SCR denitration of a cement plant comprises an ammonia water storage and conveying module, an ammonia water low-temperature evaporation-self-cooling separation module, an ammonia gas dilution and heating module and a wastewater treatment module;
the ammonia water storage and delivery module comprises an ammonia water storage tank, the ammonia water storage tank is connected with the gas-liquid separator through an ammonia water pipeline, and an ammonia water delivery pump, an ammonia water flowmeter A and an ammonia water flow regulating valve A are sequentially arranged on the ammonia water pipeline;
the ammonia water low-temperature evaporation-self-cooling separation module comprises a gas-liquid separator, wherein a heater is arranged at the bottom of the gas-liquid separator and is connected with a steam pipeline, a steam flow regulating valve is arranged on the steam pipeline, a heat exchange packing layer is arranged in the middle of the gas-liquid separator, a self-cooling coil pipe connected with the ammonia water pipeline is arranged above the heat exchange packing layer, and a demister is arranged at the top of the gas-liquid separator;
the ammonia gas dilution and heating module comprises a static mixer, the static mixer is connected with the gas-liquid separator through an ammonia water mixing pipeline, the static mixer is connected with a flue gas mixing pipeline, an ammonia water flowmeter and an ammonia gas flow regulating valve are arranged on the ammonia water mixing pipeline, and a flue gas flowmeter and a flue gas flow regulating valve are arranged on the flue gas mixing pipeline;
the waste water treatment module contains the cold machine of combing, be equipped with the waste liquid shower nozzle in the cold machine of combing, the waste liquid shower nozzle passes through the waste water pipeline and is connected with vapour and liquid separator, be equipped with waste water delivery pump and waste water flow control valve on the waste water pipeline.
The embodiment of the application can also adopt the following technical scheme:
in the above reducing agent supply system for low-temperature SCR denitration in a cement plant, further, the ammonia water delivery pump is a variable frequency centrifugal pump or a corrosion-resistant pump, the ammonia water flowmeter a is an electromagnetic flowmeter, and the ammonia water flow regulating valve a is a pneumatic valve.
In foretell reductant feed system for cement plant low temperature SCR denitration, it is further, the top of ammonia holding vessel is equipped with the ammonia and unloads the car mouth and take the ammonia receiving opening of long tube, the long tube is gone deep into ammonia holding vessel bottom and is less than the ammonia liquid level, ammonia holding vessel upper portion is equipped with thermometer and pressure gauge, ammonia holding vessel side is equipped with the level gauge, ammonia holding vessel bottom is equipped with the drain.
In the above reducing agent supply system for low-temperature SCR denitration in a cement plant, further, the top of the gas-liquid separator is connected with the ammonia gas receiving port through an ammonia water return pipeline, and a safety valve is arranged on the ammonia water return pipeline.
In the above reducing agent supply system for low-temperature SCR denitration in a cement plant, further, a temperature sensor is arranged at the bottom of the gas-liquid separator, a pressure sensor is arranged at the top of the gas-liquid separator, and a liquid level meter is arranged on the side wall of the gas-liquid separator.
In the above reducing agent supply system for low-temperature SCR denitration in a cement plant, further, the heater adopts a plate heat exchanger, and the heat exchange filler layer adopts a high-efficiency filler structure.
In the above reducing agent supply system for low-temperature SCR denitration in a cement plant, further, the self-cooling coil is multi-layered, the self-cooling coil is spiral, and the self-cooling coil is provided with a liquid distribution nozzle.
In the above-mentioned reductant feed system for cement plant low temperature SCR denitration, it is further, the reductant feed system for cement plant low temperature SCR denitration still includes control module, control module includes SCR reactor entry flue gas analyzer, computer, aqueous ammonia flow control valve a, aqueous ammonia flowmeter a, ammonia flow control valve B, ammonia flowmeter B, flue gas flow control valve and flue gas flowmeter, the input and the SCR reactor entry flue gas analyzer of computer are connected, the output of computer is connected with aqueous ammonia flow control valve a, ammonia flow control valve B and flue gas flow control valve respectively, aqueous ammonia flow control valve a is connected with aqueous ammonia flowmeter a, ammonia flow control valve B is connected with ammonia flowmeter B, flue gas flow control valve is connected with flue gas flowmeter.
A reducing agent supply control method for low-temperature SCR denitration of a cement plant adopts any reducing agent supply system for low-temperature SCR denitration of the cement plant.
In the above reducing agent supply control method for low-temperature SCR denitration in a cement plant, further, the reducing agent supply control method for low-temperature SCR denitration in a cement plant includes the steps of:
step 1: ammonia water with the mass concentration of 15% -25% enters an ammonia water storage tank through an ammonia water unloading opening at the top of the ammonia water storage tank by utilizing an ammonia water tank truck self-carrying pump, the ammonia water in the ammonia water storage tank is subjected to flow regulation and control through an ammonia water delivery pump and an ammonia water flow regulating valve A, and the ammonia water with the flow meeting the requirement is delivered to the middle part of a gas-liquid separator;
and 2, step: the ammonia water delivered to the gas-liquid separator is sprayed into the gas-liquid separator through a multilayer self-cooling coil and a liquid distribution nozzle in the middle, the sprayed ammonia water drops perform heat exchange with ammonia gas evaporated from the bottom of the gas-liquid separator at a heat exchange packing layer, the ammonia gas enters the bottom of the gas-liquid separator after the temperature is raised, a heater is arranged at the bottom of the gas-liquid separator to heat the ammonia water, the heater takes steam from a waste heat boiler as a heat source and is controlled by a steam flow regulating valve, the evaporated ammonia gas rises along the inner cavity of the gas-liquid separator, the heat exchange is performed between the heat exchange packing layer and the newly sprayed ammonia water, the ammonia water is cooled, then the ammonia water passes through the multilayer self-cooling coil, a small amount of steam evaporated from the ammonia gas and low-temperature ammonia water in the self-cooling coil perform heat exchange to be condensed and then flows downwards, and other small water drops rising along with the ammonia gas flow are removed by a demister;
and step 3: the separated ammonia gas is used as a reducing agent to be mixed with part of flue gas at the outlet of the SCR reactor through a static mixer, diluted to be below 5 percent and sent to the inlet of the low-temperature SCR reactor to participate in denitration reaction;
and 4, step 4: the water in the gas-liquid separator is kept at a certain liquid level, and is conveyed to the grate cooler by the waste water conveying pump when the water is higher than the certain liquid level and is sprayed to clinker by the waste liquid spray nozzle for disposal, and the waste water flow regulating valve is used for regulating the flow of the waste water conveying pump.
One or more technical schemes provided in the embodiment of the application have at least the following beneficial effects:
1. the ammonia water storage and conveying module, the ammonia water low-temperature evaporation-self-cooling separation module, the wastewater treatment module and the control module are arranged; a heat source (hot steam or electric heating) indirectly exchanges heat with the ammonia water at the bottom of the gas-liquid separator, the ammonia water is heated, and mixed gas of ammonia gas and part of water vapor is formed due to the reduction of solubility; the mixed gas exchanges heat with low-temperature ammonia water through a plurality of layers of fillers (reinforced heat exchange) in the condensing tower, and the low-temperature ammonia water is heated to reduce the energy consumption of a heat source; the mixed gas and ammonia water are subjected to indirect heat exchange through an ammonia water conveying pipe coil, and the water vapor is condensed and flows to the bottom of the gas-liquid separator. The demister is arranged above the ammonia water conveying pipe coil, so that water drops carried in ammonia gas are reduced, and the purpose of thoroughly separating ammonia gas from water is finally achieved.
2. According to the invention, ammonia gas from a gas-liquid separator and partial flue gas at the outlet of an SCR reactor are mixed by a static mixer, the volume concentration of the ammonia gas is reduced to 5%, then the ammonia gas is conveyed to the SCR reactor for denitration reaction, water is discharged from the bottom of the gas-liquid separator, and is conveyed to the outlet of a grate cooler by a water pump to be sprayed into the grate cooler. Compared with the traditional method of using ammonia water atomization direct injection as a reducing agent, the method adopting the mixed gas as the reducing agent comprises the following steps: the ammonia and the water are separated thoroughly, the loss of the reducing agent is reduced, the reduction degree of the flue gas temperature is small, the water content of the flue gas is not increased, no water vapor is condensed on the surface of the catalyst, the utilization rate of the reducing agent of the low-temperature SCR system is high, and the denitration efficiency is high; the ammonia water and the ammonia water are all evaporated and sprayed into the SCR system to serve as a reducing agent, so that the energy consumption is reduced, the influence on the water content of the flue gas is reduced, the service environment of the catalyst is better, and the energy efficiency of the catalyst is favorably exerted.
3. Compared with the traditional method of using ammonia water for atomization and direct injection as a reducing agent, the method of the invention comprises the following steps: the ammonia and the water are separated thoroughly, the loss of the reducing agent is reduced, the reduction degree of the temperature of the flue gas is small, the water content of the flue gas is not increased, no water vapor is condensed on the surface of the catalyst, and the catalyst and the ammonia water are evaporated and sprayed into the SCR system to serve as the reducing agent, so that the energy consumption is reduced, and the influence on the water content of the flue gas is reduced. The reducing agent utilization rate of the low-temperature SCR system is high, and the denitration efficiency is high.
Drawings
Technical solutions of embodiments of the present application will be described in further detail below with reference to the accompanying drawings, but it should be understood that these drawings are designed for illustrative purposes only and thus do not limit the scope of the present application. Furthermore, unless otherwise indicated, the drawings are intended to be illustrative of the structural configurations described herein and are not necessarily drawn to scale.
Fig. 1 is a schematic diagram of a first embodiment of the present invention.
Fig. 2 is a schematic view of a self-cooling coil according to a first embodiment of the present invention.
Fig. 3 is a flowchart of a first embodiment of the invention.
In the figure:
1. an ammonia storage tank; 2. an ammonia water delivery pump; 3. an ammonia water flowmeter A; 4. an ammonia water flow regulating valve A; 5. a steam flow regulating valve; 6. a heater; 7. a liquid level meter; 8. a temperature sensor; 9. a heat exchange packing layer; 10. a self-cooling coil pipe; 11. a liquid distribution spray head; 12. a demister; 13. a safety valve; 14 a pressure sensor; 15. a gas-liquid separator; 16. an ammonia gas flow meter B; 17. an ammonia gas flow regulating valve B; 18. a flue gas flow regulating valve; 19. a flue gas flow meter; 20. a static mixer; 21. a wastewater delivery pump; 22. a waste water flow regulating valve; 23. a waste liquid spray head; 24. a grate cooler.
Detailed Description
In order to better understand the technical solution, the technical solution will be described in detail with reference to the drawings and the specific embodiments.
Example 1
The ammonia water cooling and heating system comprises an ammonia water storage and conveying module, an ammonia water low-temperature evaporation-self-cooling separation module, an ammonia gas diluting and heating module, a wastewater treatment module and a control module.
The ammonia water storage and delivery module comprises an ammonia water storage tank 1, an ammonia water delivery pump 2, an ammonia water flowmeter A3 and an ammonia water flow regulating valve A4.
The top of ammonia holding vessel 1 is equipped with the ammonia and unloads the ammonia mouth of car mouth and take the ammonia receiving opening of long tube, receives ammonia that ammonia relief valve 13 carried and come, and the long tube requires to go deep into ammonia holding vessel bottom and be less than the ammonia liquid level, and ammonia holding vessel upper portion is equipped with thermometer and pressure gauge, and jar side is equipped with the level gauge, jar body bottom is equipped with the drain. The ammonia water delivery pump 2 is generally a variable frequency centrifugal pump, and can also be a corrosion-resistant pump of other types. The ammonia water flowmeter A3 is an electromagnetic flowmeter for monitoring the flow of ammonia water. The ammonia water flow regulating valve A4 is a pneumatic valve for regulating the flow of ammonia water.
The ammonia water low-temperature evaporation-self-cooling separation module comprises a gas-liquid separator 15 and a steam flow regulating valve 5.
The gas-liquid separator 15 is a place for separating ammonia and water in ammonia water, and is internally provided with a heater 6, a liquid level meter 7, a temperature sensor 8, a heat exchange packing layer 9, a self-cooling coil 10, a demister 12, a safety valve 13 and a pressure sensor 14.
The ammonia gas diluting and heating module comprises an ammonia water flowmeter 16, an ammonia gas flow regulating valve 17, a flue gas flow regulating valve 18, a flue gas flowmeter 19 and a static mixer 20.
The waste water treatment module comprises a waste water delivery pump 21, a waste water flow regulating valve 22, a waste liquid spray head 23 and a grate cooler 24.
The control module comprises a control module which comprises an SCR reactor inlet flue gas analyzer, a computer, an ammonia water flow regulating valve A, an ammonia water flowmeter A, an ammonia gas flow regulating valve B, an ammonia gas flowmeter B, a flue gas flow regulating valve and a flue gas flowmeter. The control cable is connected with the computer and is mainly used for controlling the computer.
In order to realize more thorough ammonia and water separation, the heater 6 used by the system can adopt a plate heat exchanger, the heat exchange packing layer 9 can adopt a high-efficiency packing structure, and the outlet of the multilayer self-cooling coil 10 can be provided with a water distributor to replace a liquid distribution spray head 11 to increase the uniformity of ammonia water on the section of the gas-liquid separator 15 and increase heat exchange.
The technical scheme in the embodiment of the application at least has the following technical effects or advantages:
the reducing agent supply system can generate an ammonia mixer with the temperature equivalent to that of flue gas needing denitration and the volume concentration of less than 5%. Compared with the traditional method of using ammonia water atomization direct injection as a reducing agent, the method adopting the mixed gas as the reducing agent comprises the following steps: the reduction degree of the flue gas temperature is small, and no water vapor condenses on the surface of the catalyst; compared with the mode that ammonia water is completely evaporated and sprayed into the SCR system as a reducing agent, the method reduces energy consumption, reduces the influence on the water content of flue gas, and is high in utilization rate of the reducing agent and high in denitration efficiency of the low-temperature SCR system.
Example 2
The present embodiment comprises the following steps:
s1, feeding ammonia water with the mass concentration of 15% -25% into the ammonia water storage tank 1 through an ammonia water unloading opening at the top of the ammonia water storage tank by using a self-contained pump of an ammonia water tank truck; according to the denitration demand, the ammonia water in the ammonia water storage tank 1 is subjected to flow regulation and control through the ammonia water delivery pump 2 and the ammonia water flow regulating valve A4, and the ammonia water with the flow meeting the requirement is sent to the middle part of the gas-liquid separator 15.
S2, the ammonia water sent to the gas-liquid separator 15 is sprayed into the gas-liquid separator 15 from the cooling coil 10 and the liquid distribution nozzle 11 through the middle multiple layers. The sprayed ammonia liquid drops exchange heat with ammonia gas evaporated from the bottom of the gas-liquid separator 15 at the heat exchange filler layer 9, and the ammonia liquid drops enter the bottom of the gas-liquid separator 5 after the temperature is raised. The bottom of the gas-liquid separator 5 is provided with a heater 6 for heating the ammonia water, the heater 6 takes steam from a waste heat boiler as a heat source and is controlled by a steam flow regulating valve 5, and the ammonia gas is reduced in solubility due to the temperature rise, so that the ammonia gas is separated from the water. The ammonia that evaporates out rises along 15 inner chambers of vapour and liquid separator, carries out the heat transfer at heat transfer packing layer 9 and the ammonia water of newly spouting, and the cooling, then through multilayer self-cooling coil 10, the vapor that a small amount of evaporation came out in the ammonia carries out heat exchange with low temperature aqueous ammonia in the self-cooling coil 10 and takes place the downstream after the condensation, and other water droplets that rise along with the ammonia air current are detached by defroster 12, thoroughly realize the separation of ammonia and water.
S3, mixing the separated ammonia gas serving as a reducing agent with part of flue gas at the outlet of the SCR reactor through a static mixer 20, diluting the mixture to be below 5%, and sending the mixture to the inlet of the low-temperature SCR reactor to participate in denitration reaction. The waste heat of the flue gas is fully utilized to reduce the ammonia concentration to safe concentration, the temperature of the ammonia is increased, and the influence of the reduction of the temperature generated by the low-temperature ammonia on the denitration reaction is reduced.
S4, the water in the gas-liquid separator 15 should be kept at a certain liquid level, and when the liquid level is higher than the certain liquid level, the water is conveyed to the grate cooler 24 by the waste water conveying pump 21 and is sprayed to the clinker by the waste liquid spray head 23 for disposal. The waste water flow regulating valve 22 is used for regulating the flow of the waste water delivery pump and keeping the liquid level in the condensing tower stable.
S5, in the using process of the system, part of parameters need to be strictly controlled to achieve the aim of stably and thoroughly separating ammonia and water. Monitoring the temperature of a temperature sensor at the bottom of the gas-liquid separator 15, and controlling the temperature to be 70-90 ℃ by adjusting the amount of steam entering the heater 6; monitoring the liquid level height of the gas-liquid separator 15, and keeping the liquid level height in the gas-liquid separator 15 higher than the height of the heat exchanger 6 by adjusting a wastewater delivery pump and a wastewater adjusting valve; the pressure of the outlet pressure sensor 14 of the gas-liquid separator 15 is monitored, and when the pressure is higher than a predetermined value, the safety valve is opened to introduce ammonia gas into the ammonia water storage tank 1 for absorption.
S6, the control principle of the present system is as follows. The concentration of nitrogen oxides of a flue gas analyzer in front of the SCR reactor is monitored, the ammonia gas usage amount is obtained through computer calculation by combining the emission requirement of the nitrogen oxides, the ammonia gas flow valve A17 is adjusted to control the flow rate of ammonia gas, and the opening degree of the ammonia gas flow adjusting valve A17 is adjusted according to the ammonia gas flow meter A16, so that the actual flow rate of ammonia gas is in line with the calculated ammonia gas usage amount value. The volume fraction of the ammonia gas behind the static mixer 20 is ensured to be less than 5% by adjusting the flue gas flow through adjusting the flue gas flow adjusting valve 18 after the computer calculation, and the ammonia gas is monitored through the flue gas flowmeter 19. In order to ensure the stability of the system, the gas-liquid separator has no overpressure, and the ammonia water flow regulating valve A4 is regulated to regulate the flow of ammonia water entering the gas-liquid separator 15, and the ammonia water flow meter A3 is used for monitoring and regulating the ammonia water flow regulating valve A4 to make the flow of ammonia water accord with the calculated value of the ammonia gas consumption required by calculation. In order to ensure that the bottom of the gas-liquid separator is low-temperature evaporation, the opening of the steam flow regulating valve 5 is regulated by monitoring the value of a temperature sensor 8 at the bottom of the gas-liquid separator, and the temperature at the bottom of the gas-liquid separator is regulated to 70-90 ℃.
In summary, the invention provides a reducing agent supply system and a control method for low-temperature SCR denitration in a cement plant, wherein ammonia water with a mass fraction of 15% -25% is formed into high-purity ammonia gas through a low-temperature evaporation-self-cooling mode.
The present invention has been described in detail with reference to the above examples, but the description is only for the preferred examples of the present invention and should not be construed as limiting the scope of the present invention. Equivalent changes and improvements made according to the scope of the present invention, such as electrical heating is used as the heat source, a dilution fan is added at the outlet of the gas-liquid separator to dilute the ammonia gas, and the wastewater is sent to the water treatment system of the cement plant, should fall within the scope of the present invention.
Claims (10)
1. A reductant feed system for cement plant low temperature SCR denitration which characterized in that: the reducing agent supply system for the low-temperature SCR denitration of the cement plant comprises an ammonia water storage and conveying module, an ammonia water low-temperature evaporation-self-cooling separation module, an ammonia gas dilution and heating module and a wastewater treatment module;
the ammonia water storage and delivery module comprises an ammonia water storage tank, the ammonia water storage tank is connected with the gas-liquid separator through an ammonia water pipeline, and an ammonia water delivery pump, an ammonia water flowmeter A and an ammonia water flow regulating valve A are sequentially arranged on the ammonia water pipeline;
the ammonia water low-temperature evaporation-self-cooling separation module comprises a gas-liquid separator, wherein a heater is arranged at the bottom of the gas-liquid separator and is connected with a steam pipeline, a steam flow regulating valve is arranged on the steam pipeline, a heat exchange packing layer is arranged in the middle of the gas-liquid separator, a self-cooling coil pipe connected with the ammonia water pipeline is arranged above the heat exchange packing layer, and a demister is arranged at the top of the gas-liquid separator;
the ammonia gas dilution and heating module comprises a static mixer, the static mixer is connected with the gas-liquid separator through an ammonia water mixing pipeline, the static mixer is connected with a flue gas mixing pipeline, an ammonia water flowmeter and an ammonia gas flow regulating valve are arranged on the ammonia water mixing pipeline, and a flue gas flowmeter and a flue gas flow regulating valve are arranged on the flue gas mixing pipeline;
the waste water treatment module contains the cold machine of combing, be equipped with the waste liquid shower nozzle in the cold machine of combing, the waste liquid shower nozzle passes through the waste water pipeline and is connected with vapour and liquid separator, be equipped with waste water delivery pump and waste water flow control valve on the waste water pipeline.
2. The reducing agent supply system for low-temperature SCR denitration of a cement plant according to claim 1, wherein: the ammonia water delivery pump adopts a variable frequency centrifugal pump or a corrosion-resistant pump, the ammonia water flowmeter A is an electromagnetic flowmeter, and the ammonia water flow regulating valve A is a pneumatic valve.
3. The reducing agent supply system for low-temperature SCR denitration of a cement plant according to claim 1, wherein: the top of ammonia holding vessel is equipped with the ammonia gas receiving opening that the mouth was unloaded to the aqueous ammonia and took the long tube, the long tube is gone deep into the ammonia water holding vessel bottom and is less than the aqueous ammonia liquid level, ammonia holding vessel upper portion is equipped with thermometer and pressure gauge, ammonia holding vessel side is equipped with the level gauge, ammonia holding vessel bottom is equipped with the drain.
4. The reducing agent supply system for low-temperature SCR denitration of a cement plant according to claim 1, wherein: the top of the gas-liquid separator is connected with an ammonia receiving port through an ammonia water backflow pipeline, and a safety valve is arranged on the ammonia water backflow pipeline.
5. The reducing agent supply system for low-temperature SCR denitration of a cement plant according to claim 1, wherein: the bottom of the gas-liquid separator is provided with a temperature sensor, the top of the gas-liquid separator is provided with a pressure sensor, and the side wall of the gas-liquid separator is provided with a liquid level meter.
6. The reducing agent supply system for low-temperature SCR denitration of a cement plant according to claim 1, wherein: the heater adopts plate heat exchanger, the heat transfer packing layer adopts high-efficient filler structure.
7. The reducing agent supply system for low-temperature SCR denitration of a cement plant according to claim 1, wherein: the self-cooling coil is in a multilayer shape and is in a spiral shape, and the self-cooling coil is provided with a liquid distribution spray head.
8. The reducing agent supply system for low-temperature SCR denitration of a cement plant according to claim 1, wherein: a reductant feed system for cement plant low temperature SCR denitration still includes control module, control module includes SCR reactor entry flue gas analysis appearance, computer, aqueous ammonia flow control valve A, aqueous ammonia flowmeter A, ammonia flow control valve B, ammonia flowmeter B, flue gas flow control valve and flue gas flowmeter, the input and the SCR reactor entry flue gas analysis appearance of computer are connected, the output of computer is connected with aqueous ammonia flow control valve A, ammonia flow control valve B and flue gas flow control valve respectively, aqueous ammonia flow control valve A is connected with aqueous ammonia flowmeter A, ammonia flow control valve B is connected with ammonia flowmeter B, flue gas flow control valve is connected with flue gas flowmeter.
9. A reducing agent supply control method for low-temperature SCR denitration of a cement plant is characterized by comprising the following steps: the reducing agent supply control method for low-temperature SCR denitration of the cement plant adopts the reducing agent supply system for low-temperature SCR denitration of the cement plant as defined in any one of claims 1 to 8.
10. The reducing agent supply control method for low-temperature SCR denitration in a cement plant according to claim 9, characterized in that: the reducing agent supply control method for low-temperature SCR denitration of the cement plant comprises the following steps of:
step 1: ammonia water with the mass concentration of 15% -25% enters an ammonia water storage tank through an ammonia water unloading opening at the top of the ammonia water storage tank by utilizing an ammonia water tank truck self-carrying pump, the ammonia water in the ammonia water storage tank is subjected to flow regulation and control through an ammonia water delivery pump and an ammonia water flow regulating valve A, and the ammonia water with the flow meeting the requirement is delivered to the middle part of a gas-liquid separator;
step 2: the ammonia water delivered to the gas-liquid separator is sprayed into the gas-liquid separator through a multilayer self-cooling coil and a liquid distribution nozzle in the middle, the sprayed ammonia water drops perform heat exchange with ammonia gas evaporated from the bottom of the gas-liquid separator at a heat exchange packing layer, the ammonia gas enters the bottom of the gas-liquid separator after the temperature is raised, a heater is arranged at the bottom of the gas-liquid separator to heat the ammonia water, the heater takes steam from a waste heat boiler as a heat source and is controlled by a steam flow regulating valve, the evaporated ammonia gas rises along the inner cavity of the gas-liquid separator, the heat exchange is performed between the heat exchange packing layer and the newly sprayed ammonia water, the ammonia water is cooled, then the ammonia water passes through the multilayer self-cooling coil, a small amount of steam evaporated from the ammonia gas and low-temperature ammonia water in the self-cooling coil perform heat exchange to be condensed and then flows downwards, and other small water drops rising along with the ammonia gas flow are removed by a demister;
and 3, step 3: the separated ammonia gas is used as a reducing agent to be mixed with part of flue gas at the outlet of the SCR reactor through a static mixer, diluted to be below 5 percent and sent to the inlet of the low-temperature SCR reactor to participate in denitration reaction;
and 4, step 4: the water in the gas-liquid separator is kept at a certain liquid level, and is conveyed to the grate cooler by the waste water conveying pump when the water is higher than the certain liquid level and is sprayed to clinker by the waste liquid spray nozzle for disposal, and the waste water flow regulating valve is used for regulating the flow of the waste water conveying pump.
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