CN112807944A - Ammonia water flow adjusting system and method for tail gas denitration - Google Patents

Ammonia water flow adjusting system and method for tail gas denitration Download PDF

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Publication number
CN112807944A
CN112807944A CN202110140477.XA CN202110140477A CN112807944A CN 112807944 A CN112807944 A CN 112807944A CN 202110140477 A CN202110140477 A CN 202110140477A CN 112807944 A CN112807944 A CN 112807944A
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valve
ammonia water
flow rate
regulating valve
flow
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CN112807944B (en
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卓晓龙
冯一帆
陆宏
方自动
贾红建
钟小明
黄寅
郭晨星
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Zhejiang Products Huanneng Pujiang Thermal Power Co ltd
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Zhejiang Products Huanneng Pujiang Thermal Power Co ltd
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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
    • B01D53/30—Controlling by gas-analysis apparatus
    • 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
    • B01D53/346—Controlling the process
    • 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
    • B01D53/46—Removing components of defined structure
    • B01D53/54—Nitrogen compounds
    • B01D53/56—Nitrogen oxides
    • 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
    • B01D53/77—Liquid phase processes
    • B01D53/79—Injecting reactants
    • 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
    • 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
    • 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
    • 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
    • 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

Abstract

The invention discloses an ammonia water flow regulating system and method for tail gas denitration, which comprises an ammonia water main trunk line, a first ammonia water branch trunk line, a second ammonia water branch trunk line, a first flow regulating valve, a second flow regulating valve, a first nitrogen oxide sensor, a second nitrogen oxide sensor and a main control board.

Description

Ammonia water flow adjusting system and method for tail gas denitration
Technical Field
The invention relates to an ammonia water flow adjusting system and an ammonia water flow adjusting method for tail gas denitration, and belongs to the field of nitrogen oxide flue gas treatment.
Background
Residual nitrogen oxide content after SNCR + SCR coupling denitration treatment of flue gas that the thermoelectric boiler produced is the important index of fume emission, and along with the thermoelectric boiler transformation and then productivity increase, the flow of flue gas generally begins to increase, and corresponding aqueous ammonia flow also increases correspondingly. Less ammonia water causes unqualified nitrogen oxide content index in the treated flue gas, secondary treatment is needed, and the treatment cost is further increased. And excessive ammonia water can ensure that the content of nitrogen oxides reaches the standard, but the cost of the ammonia water is obviously increased. In particular, the production process of ammonia also has a considerable environmental impact, so that the use of excess ammonia for the treatment of nitrogen oxides is not justified for environmental protection. Therefore, how to ensure the matching between the ammonia water flow and the flue gas flow and reduce the ammonia water waste and the treatment cost on the basis of ensuring the standard of the nitrogen oxide index is very important.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an ammonia water flow regulating system and an ammonia water flow regulating method for tail gas denitration, which are used for matching and regulating ammonia water flow and flue gas flow so as to reduce flue gas treatment cost.
The technical scheme adopted by the invention is as follows:
an ammonia water flow regulating system for tail gas denitration is characterized by comprising an ammonia water main trunk line, a first ammonia water branch trunk line, a second ammonia water branch trunk line, a first flow regulating valve, a second flow regulating valve, a first nitrogen oxide sensor, a second nitrogen oxide sensor and a main control board, wherein the first ammonia water branch trunk line and the second ammonia water branch trunk line are connected to the ammonia water main trunk line in parallel, the first flow regulating valve is installed on the first ammonia water branch trunk line, the second flow regulating valve is installed on the second ammonia water branch trunk line, the first nitrogen oxide sensor is arranged at an air inlet, the second nitrogen oxide sensor is arranged at an air outlet, the ammonia water main trunk line is communicated between the air inlet and the air outlet, and the first flow regulating valve, the second flow regulating valve, the first nitrogen oxide sensor and the second nitrogen oxide sensor are electrically connected to the main control board;
the first flow regulating valve is a valve with equal percentage characteristic, the second flow regulating valve is a valve with linear characteristic, and the concentration of nitrogen oxide at the exhaust port is changed by regulating the first flow regulating valve and the second flow regulating valve.
The invention has the beneficial effects that:
the first nitrogen oxide sensor measures that the concentration of nitrogen oxide at an air inlet is a mg/L, the second nitrogen oxide sensor measures that the concentration of nitrogen oxide at an air outlet is b mg/L, the maximum flow of the first flow regulating valve is c kg/h, the maximum flow of the second flow regulating valve is d kg/h, and the single opening regulating quantity of the first flow regulating valve is n1The single opening degree regulating quantity of the second flow regulating valve is n2The first flow regulating valve is an equal percentage characteristic valve, and the second flow regulating valve is a linear characteristic valve.
The ammonia water in the first ammonia water branch road and the second ammonia water branch road converges in the ammonia water main road, and then the flue gas between the gas inlet and the gas outlet is treated. The first flow regulating valve serving as the equal percentage characteristic valve increases the opening degree every time, the corresponding ammonia water flow increment is gradually increased, basic ammonia water supply can be guaranteed, the opening degree is further increased under the condition that the flow rate in the first flow regulating valve is large, the ammonia water flow can be increased violently, and the concentration of low-concentration nitric oxide can be further effectively reduced, so that the concentration of the nitric oxide meets the emission standard. And the second flow control valve who is the straight line characteristic valve can make the aqueous ammonia flow equivalent change through the regulation of aperture to help reducing the difference between discharging nitrogen oxide concentration and emission standard, in order to avoid the excessive use of aqueous ammonia. The adjustment processes of the first flow regulating valve and the second flow regulating valve do not interfere with each other, so that the adjustment effects of the first flow regulating valve and the second flow regulating valve are stabilized. After the flue gas flow at the gas inlet after the boiler is transformed is stable, firstly, the first flow regulating valve is regulated to roughly regulate the flow of ammonia water, so that the concentration of nitrogen oxides at the gas outlet is obviously reduced, then, the second flow regulating valve is regulated to finely regulate the flow of ammonia water, so that the concentration of nitrogen oxides is ensured to be lower than the emission standard, meanwhile, the difference between the concentration of nitrogen oxides and the emission standard is reduced as far as possible, the cost of ammonia water is greatly reduced, and the balance is obtained between economic benefits and environmental benefits.
An adjusting method of an ammonia water flow adjusting system for tail gas denitration is characterized in that the single opening adjusting quantity of a first flow adjusting valve is n1The single opening degree regulating quantity of the second flow regulating valve is n2The opening degree of the first flow rate regulating valve is pn1P is a natural number not greater than x, xn1=1, opening degree of second flow rate regulating valve qn2Q is a natural number not greater than y, yn2=1。
The emission standard R mg/L is set, after a detection value a mg/L of a first nitric oxide sensor is stabilized, the opening degree of a first flow regulating valve is regulated to be 0, the opening degree of a second flow regulating valve is regulated to be 1, then the opening degree of the first flow regulating valve is gradually increased, when a detection value b mg/L of a second nitric oxide sensor is lower than R mg/L, the regulation of the first flow regulating valve is stopped, and the second flow regulating valve is started to be regulated, so that the difference value between b and R is reduced.
The second flow rate regulating valve of the present invention is regulated as follows:
step S1, adjusting the opening degree of the second flow rate adjustment valve to (y-1) n2If b is greater than R, the opening degree of the second flow rate regulating valve is regulated back to 1, and the regulation is finished, if b is less than R, the operation goes to step S2;
step S2: adjusting the opening degree of the second flow rate adjusting valve to 0, if b is less than R, ending the adjustment, and if b is more than R, entering the step S3;
step S3: and gradually increasing the opening of the second flow regulating valve until b is less than R, and finishing the regulation.
The flow rate and the opening degree of the first flow rate regulating valve are (x-1) n when the opening degree is 11The difference between the flow rates is smaller than d.
Invention n1＞n2。
Invention n1=0.25，n2=0.1。
In step S3, if the number of times of adjustment of the second flow rate adjustment valve is z and z is not less than 3, the time interval between the regulation of the second flow rate adjustment valve for the eta-1 th time and the regulation of the second flow rate adjustment valve for the eta-1 th time is tη-1Eta is a natural number of not less than 2 and not more than z, tη-1＜tη。
The main control board is electrically connected with an alarm and an electronic on-off valve, the electronic on-off valve is positioned at the air inlet, and if b is larger than R when the opening of the first flow regulating valve is 1, the main control board controls the alarm to give an alarm and controls the electronic on-off valve to be switched off.
When a of the invention is stable0-a1≤a≤a0+a1，a1=0.05a0。
Other features and advantages of the present invention will be disclosed in more detail in the following detailed description of the invention and the accompanying drawings.
Drawings
The invention is further described below with reference to the accompanying drawings:
FIG. 1 is a schematic view of a topological structure of an ammonia water flow rate adjusting system according to an embodiment of the present invention;
fig. 2 is a control flowchart of the ammonia water flow rate adjustment system according to the embodiment of the present invention.
Detailed Description
The technical solutions of the embodiments of the present invention are explained and illustrated below with reference to the drawings of the embodiments of the present invention, but the following embodiments are only preferred embodiments of the present invention, and not all embodiments. Based on the embodiments in the implementation, other embodiments obtained by those skilled in the art without any creative effort belong to the protection scope of the present invention.
In the following description, the appearances of the indicating orientation or positional relationship such as the terms "inner", "outer", "upper", "lower", "left", "right", etc. are only for convenience in describing the embodiments and for simplicity in description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and are not to be construed as limiting the present invention.
Example (b):
referring to fig. 1-2, the embodiment provides an ammonia water flow regulating system for denitration of tail gas, including an ammonia water main trunk 1, a first ammonia water branch trunk 2, a second ammonia water branch trunk 3, a first flow regulating valve 4, a second flow regulating valve 5, a first nitrogen oxide sensor 6, a second nitrogen oxide sensor 7 and a main control board 8.
Wherein the first ammonia water branch trunk 2 and the second ammonia water branch trunk 3 are connected in parallel to the ammonia water main trunk 1, the ammonia water main trunk 1 is communicated to the flue gas reaction chamber 13, the ammonia water in the first ammonia water branch trunk 2 and the second ammonia water branch trunk 3 converges in the ammonia water main trunk 1, then flows into the flue gas reaction chamber 13, and the flue gas rich in nitrogen oxides flows into the flue gas reaction chamber 13 from the gas inlet 11 of the flue gas reaction chamber 13. The nitrogen oxides in the flue gas react with the ammonia water in the flue gas reaction chamber 13 to reduce the content of the nitrogen oxides in the flue gas, and then the nitrogen oxides are discharged from the exhaust port 12. The flue gas moves faster in the ammonia flue gas reaction chamber 13, so in order to ensure the removal effect of nitrogen oxides, the flow rate of ammonia needs to be maintained at a higher level.
The first flow control valve 4 is installed on the first ammonia branch line 2, the first flow control valve 4 controls the ammonia water flow rate in the first ammonia branch line 2, the second flow control valve 5 is installed on the second ammonia branch line 3, and the second flow control valve 5 controls the ammonia water flow rate in the second ammonia branch line 3. The first nitrogen oxide sensor 6 is arranged at the air inlet 11, the first nitrogen oxide sensor 6 monitors the nitrogen oxide concentration at the air inlet 11, the second nitrogen oxide sensor 7 is arranged at the air outlet 12, and the second nitrogen oxide sensor 7 monitors the nitrogen oxide concentration at the air outlet 12.
The first flow regulating valve 4, the second flow regulating valve 5, the first nitrogen oxide sensor 6 and the second nitrogen oxide sensor 7 are electrically connected to a main control board 8, and the main control board 8 regulates and controls the first flow regulating valve 4 and the second flow regulating valve 5 according to monitoring data of the second nitrogen oxide sensor 7. In addition, the main control board 8 is also electrically connected with an alarm 9 and an electronic on-off valve 10, the electronic on-off valve 10 is located at the air inlet 11, and the electronic on-off valve 10 controls the on-off of the air inlet 11.
Specifically, the concentration of the nitrogen oxide at the air inlet 11 is measured to be a mg/L by the first nitrogen oxide sensor 6, the concentration of the nitrogen oxide at the air outlet 12 is measured to be b mg/L by the second nitrogen oxide sensor 7, the emission standard of the concentration of the nitrogen oxide is R mg/L, and the flow of the ammonia water is controlled by the first flow regulating valve 4 and the second flow regulating valve 5 so as to control b to be less than R. For example, in the case of a =1 and R =0.4, since the ammonia water and the nitrogen oxide are not completely reacted, when b =0.3, the flow rate of 20% ammonia water is about 35-40kg/h, which is equivalent to about 5-5.7kg/h for every 0.1 mg/L decrease of the nitrogen oxide concentration, but when b =0.2, the flow rate of 20% ammonia water is 50-70kg/h, which is equivalent to about 6.25-8.75kg/h for every 0.1 mg/L decrease of the nitrogen oxide concentration, and the utility ratio of the ammonia water is significantly reduced in consideration of the production cost of the ammonia water itself and the influence on the environment during the production process. Therefore, the present embodiment aims to reduce the difference between b and R as much as possible in the case of controlling b < R, thereby increasing the cost performance of ammonia water as much as possible.
Specifically, the first flow regulating valve 4 is a valve with equal percentage characteristics, the maximum flow of the first flow regulating valve 4 is c kg/h, and the single opening regulating quantity of the first flow regulating valve 4 is n1. The second flow regulating valve 5 is a linear valve, the maximum flow of the second flow regulating valve 5 is d kg/h, and the single opening regulating quantity of the second flow regulating valve 5 is n2. In order to ensure that the first and second flow rate adjustment valves 4, 5 can be fully utilized, the opening degrees of the first and second flow rate adjustment valves 4, 5 need to be up to 1. Simultaneously in order to ensure the flow of ammonia water in emergencyCan be adjusted to 0, the opening degrees of the first flow rate adjustment valve 4 and the second flow rate adjustment valve 5 need to be able to reach 0.
Based on this:
the opening degree of the first flow rate adjustment valve 4 is pn1P is a natural number not greater than x, i.e., the opening of the first flow rate adjustment valve 4 is 0, n1、2n1、3n1、4n1...（x-1）n1Or xn1，xn1And =1. The corresponding first flow rate regulating valve 4 has a flow rate of 0, λ1、λ2、λ3、λ4、...λx-1Or ckg/h. Corresponding lambda1-0＜λ2-λ1＜λ3-λ2...＜c-λx-1。
The opening degree of the second flow rate adjustment valve 5 is qn2Q is a natural number not greater than y, i.e., the opening of the second flow rate adjustment valve 5 is 0, n2、2n2、3n2、4n2...（y-1）n2Or yn2，yn2And =1. The corresponding second flow regulating valve 5 has a flow of 0, γ1、γ2、γ3、γ4、...γy-1Or dkg/h. Corresponding gamma1-0=γ2-γ1=γ3-γ2...=d-γy-1。
For example, when a =1.2 and R =0.3 and when b =1, the flow rate of ammonia water needs to be approximately ω1kg/h, ammonia flow approximately ω when b =0.82kg/h, when b =0.6, the ammonia flow rate needs to be approximately ω3kg/h, ammonia flow approximately ω when b =0.44kg/h，ω2-ω1＜ω3-ω2＜ω4-ω3. It can be seen that each time the value b is reduced, the increment of the ammonia water flow is increased and matched with the regulating characteristic of the first flow regulating valve 4. Therefore, the amount of change in the b value is constant every time the opening degree of the first flow rate adjustment valve 4 is increased, and by increasing the opening degree of the first flow rate adjustment valve 4, the basic ammonia water supply can be secured, which contributes to a rapid decrease in the b value to the vicinity of the R value. When b and R are closer, the first flow regulating valve 4 already hasThe flow of the ammonia water is larger at a certain opening degree, and d is less than c, so that the ratio of the flow of the second flow regulating valve 5 to the whole flow of the ammonia water is not large, but the flow of the ammonia water can be linearly changed slightly by regulating the second flow regulating valve 5, so that a specific flow value or flow value range of the ammonia water is found, and the difference between b and R is reduced as much as possible under the condition that b is less than R.
The specific flow regulating method of the ammonia water flow regulating system is as follows:
step S0, the opening degree of the first flow rate adjustment valve 4 is first adjusted to 0, the opening degree of the second flow rate adjustment valve 5 is first adjusted to 1, after a and b are stabilized, the opening degree of the first flow rate adjustment valve 4 is gradually increased until b is less than R, and the adjustment of the first flow rate adjustment valve 4 is stopped, at this time, the opening degree of the first flow rate adjustment valve 4 is p1n1The flow rate of the first flow rate regulating valve 4 is λp1The routine proceeds to step S1 to start adjusting the second flow rate adjustment valve 5; if the opening degree of the first flow regulating valve 4 is 1, and b is still larger than R, the first flow regulating valve 4 and the second flow regulating valve 5 cannot meet the boiler flue gas treatment requirement, the main control board 8 controls the alarm 9 to give an alarm, and controls the electronic on-off valve 10, the first flow regulating valve 4 and the second flow regulating valve 5 to be switched off, so that the first flow regulating valve 4 and the second flow regulating valve 5 can be replaced conveniently;
considering the actual use condition of the boiler, the value of a is used as a when a is stable in the step0The central value is floated up and down, the floating proportion is 5 percent, namely a0-a1≤a≤a0+a1，a1=0.05a0If a cannot satisfy the condition for a long time, it indicates that the boiler is abnormal in operation and needs to be overhauled. For convenience of explanation, in the present embodiment, a is regarded as a constant value a0。
Step S1, adjusting the opening of the second flow rate adjustment valve 5 to (y-1) n2If b > R, the opening of the second flow rate control valve 5 is adjusted back to 1, corresponding to a specific flow rate value of (lambda)p1+ d) kg/h, the adjustment is finished, if b is less than R, the process goes to step S2.
Step S2: the opening degree of the second flow regulating valve 5 is regulated to 0, if b is less than R, the corresponding specific flow value is lambdap1 kg/h，The regulation is finished, if b > R, the specific flow value is (lambda)p1+ d) kg/h and λ p1 kg/h, go to step S3.
Step S3: gradually increasing the opening degree of the second flow regulating valve 5 until b is less than R, wherein the opening degree of the second flow regulating valve 5 is q1n2At a flow rate of gammaq1The specific flow rate value is (lambda)p1+γq1) kg/h, and finishing the adjustment.
Based on the above-described operation procedure, in step S0, n1The value cannot be too small to ensure that b can quickly drop below R, reducing the number of adjustments to the first flow rate adjustment valve 4, in step S3, n2The value must not be too large to reduce the difference between b and R, so that n is reduced1＞n2。
Preferably, n is1=0.25，n2=0.1。
In step S3, if the number of times of adjustment of the second flow rate adjustment valve 5 is z and z is not less than 3, the time interval between the η -1 th adjustment and the η th adjustment of the second flow rate adjustment valve is tη-1Eta is a natural number of not less than 2 and not more than z, tη-1＜tη。
Taking the present embodiment as an example, in step S3, the second flow rate adjustment valve 5 is subjected to the opening degree increasing operation three times in total so that the opening degrees of the second flow rate adjustment valve 5 are changed from 0 to n in order2、2n2、3n2The flow rate of the corresponding second flow rate regulating valve 5 is changed from 0 to gamma in turn1、γ2、γ3Wherein the time interval between the first operation and the second operation is t1The time interval between the second operation and the third operation is t2. Since the second flow rate adjustment valve 5 is a linear valve, when the flow rate of the second flow rate adjustment valve 5 is adjusted from γ1Is lifted to gamma2Will produce more violent oscillation t1It needs to be larger to obtain a more stable b value when the flow rate of the second flow rate adjustment valve 5 is adjusted from γ2Is lifted to gamma3So that t is relatively gentle2Can be smaller, corresponding to t1＞t2。
Since the first flow rate adjusting valve 4 and the second flow rate adjusting valve 5 are respectively arranged on the first ammonia branch line 2 and the second ammonia branch line 3, the adjusting processes of the first flow rate adjusting valve 4 and the second flow rate adjusting valve 5 do not interfere with each other, and the adjusting effects of the first flow rate adjusting valve 4 and the second flow rate adjusting valve 5 are stabilized.
Further, the flow rate and the opening degree of the first flow rate adjusting valve 4 are (x-1) n when the opening degree is 11The difference between the flow rates of time is less than d, i.e. c-lambdax-1＜d。
In step S0, the opening degree of the first flow rate adjustment valve 4 is p1n1When b is less than R, the corresponding total flow of ammonia water is (lambda)p1+ d) kg/h, so when the opening of the first flow rate adjustment valve 4 is (p)1-1）n1When b is more than R, the total flow of ammonia water is (lambda)p1-1+d）kg/h。
In step S2, the total flow rate of ammonia water is λp1 kg/h。
λp1-1+d-λp1=d-（λp1-λp1-1）≥d-（c-λx-1) > 0, so that the ammonia water flow rate in step S2 is less than (lambda)p1-1+ d) kg/h, corresponding to b > R in step S2, thereby avoiding the condition that b < R in step S2, and avoiding the condition that b cannot be further close to R due to the range limitation of the second flow regulating valve 5.
While the invention has been described with reference to specific embodiments thereof, it will be understood by those skilled in the art that the invention is not limited thereto, and may be embodied in many different forms without departing from the spirit and scope of the invention as set forth in the following claims. Any modification which does not depart from the functional and structural principles of the present invention is intended to be included within the scope of the claims.

Claims (10)

1. An ammonia water flow regulating system for tail gas denitration is characterized by comprising an ammonia water main trunk line, a first ammonia water branch trunk line, a second ammonia water branch trunk line, a first flow regulating valve, a second flow regulating valve, a first nitrogen oxide sensor, a second nitrogen oxide sensor and a main control board, wherein the first ammonia water branch trunk line and the second ammonia water branch trunk line are connected to the ammonia water main trunk line in parallel, the first flow regulating valve is installed on the first ammonia water branch trunk line, the second flow regulating valve is installed on the second ammonia water branch trunk line, the first nitrogen oxide sensor is arranged at an air inlet, the second nitrogen oxide sensor is arranged at an air outlet, the ammonia water main trunk line is communicated between the air inlet and the air outlet, and the first flow regulating valve, the second flow regulating valve, the first nitrogen oxide sensor and the second nitrogen oxide sensor are electrically connected to the main control board;
the first flow regulating valve is a valve with equal percentage characteristic, the second flow regulating valve is a valve with linear characteristic, and the concentration of nitrogen oxide at the exhaust port is changed by regulating the first flow regulating valve and the second flow regulating valve.
2. The method for adjusting the ammonia water flow rate adjustment system for denitration of exhaust gas according to claim 1, wherein the single opening adjustment amount of the first flow rate adjustment valve is n1The single opening degree regulating quantity of the second flow regulating valve is n2The opening degree of the first flow rate regulating valve is pn1P is a natural number not greater than x, xn1=1, opening degree of second flow rate regulating valve qn2Q is a natural number not greater than y, yn2=1。
3. The adjusting method of an ammonia water flow rate adjusting system for denitration of exhaust gas according to claim 2, wherein an emission standard of R mg/L is set, after a detected value a mg/L of the first nox sensor is stabilized, the opening degree of the first flow rate adjusting valve is first adjusted to 0 and the opening degree of the second flow rate adjusting valve is 1, then the opening degree of the first flow rate adjusting valve is gradually increased, and when a detected value b mg/L of the second nox sensor is lower than R mg/L, the adjustment of the first flow rate adjusting valve is stopped and the adjustment of the second flow rate adjusting valve is started to reduce the difference between b and R.
4. The adjusting method of the ammonia water flow regulating system for denitration of tail gas as claimed in claim 3, wherein the adjusting method of the second flow regulating valve is as follows:
step S1, adjusting the opening degree of the second flow rate adjustment valve to (y-1) n2If b is greater than R, the opening degree of the second flow rate regulating valve is regulated back to 1, and the regulation is finished, if b is less than R, the operation goes to step S2;
step S2: adjusting the opening degree of the second flow rate adjusting valve to 0, if b is less than R, ending the adjustment, and if b is more than R, entering the step S3;
step S3: and gradually increasing the opening of the second flow regulating valve until b is less than R, and finishing the regulation.
5. The method of adjusting an ammonia water flow rate adjustment system for denitration of exhaust gas according to claim 4, wherein the flow rate and the opening degree of the first flow rate adjustment valve are (x-1) n when the opening degree is 11The difference between the flow rates is smaller than d.
6. The method for adjusting the ammonia water flow rate adjusting system for denitration of tail gas as claimed in claim 5, wherein n is n1＞n2。
7. The method for adjusting the ammonia water flow rate adjusting system for denitration of tail gas as claimed in claim 6, wherein n is n1=0.25，n2=0.1。
8. The method of adjusting an ammonia water flow rate regulation system for denitration of exhaust gas according to claim 4, wherein in step S3, if the number of times of adjustment of the second flow rate regulation valve is z and z is not less than 3, the time interval between the η -1 th adjustment and the η th adjustment of the second flow rate regulation valve is tη-1Eta is a natural number of not less than 2 and not more than z, tη-1＜tη。
9. The adjusting method of the ammonia water flow regulating system for denitration of tail gas as claimed in claim 3, wherein the main control board is electrically connected with an alarm and an electronic on-off valve, the electronic on-off valve is located at the gas inlet, if b > R when the opening degree of the first flow regulating valve is 1, the main control board controls the alarm to give an alarm, and simultaneously controls the electronic on-off valve to be turned off.
10. The method for adjusting the ammonia water flow rate regulation system for denitration of tail gas as claimed in claim 3, wherein a is stable0-a1≤a≤a0+a1，a1=0.05a0。
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