CN109489065B - Combustion optimization control method based on nitrogen oxide emission index constraint condition - Google Patents
Combustion optimization control method based on nitrogen oxide emission index constraint condition Download PDFInfo
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- CN109489065B CN109489065B CN201811200114.5A CN201811200114A CN109489065B CN 109489065 B CN109489065 B CN 109489065B CN 201811200114 A CN201811200114 A CN 201811200114A CN 109489065 B CN109489065 B CN 109489065B
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N3/00—Regulating air supply or draught
- F23N3/005—Regulating air supply or draught using electrical or electromechanical means
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N5/00—Systems for controlling combustion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2223/00—Signal processing; Details thereof
- F23N2223/06—Sampling
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2223/00—Signal processing; Details thereof
- F23N2223/10—Correlation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2235/00—Valves, nozzles or pumps
- F23N2235/02—Air or combustion gas valves or dampers
- F23N2235/06—Air or combustion gas valves or dampers at the air intake
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2900/00—Special features of, or arrangements for controlling combustion
- F23N2900/05003—Measuring NOx content in flue gas
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- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
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Abstract
The invention belongs to the field of industrial gas boilers, and particularly relates to a combustion control method. The invention relates to a combustion optimization control method based on a nitrogen oxide emission index constraint condition, which comprises the following steps: 1. setting a standard value Ah for the concentration emission of the gaseous pollutants by connecting an environmental protection competent department or looking up local environmental protection requirements; 2. and acquiring a nitrogen oxide concentration value Ai, setting the nitrogen oxide sampling frequency as M according to field setting by considering the type of the gas industrial boiler and the sampling period TNOx of the flue gas analyzer, and carrying out mean value processing. The invention has the beneficial effects that: the gas industrial boiler is subjected to restrictive control and soft control through the flue gas information flow provided by the flue gas online analysis system, so that the emission of the gas industrial boiler is ensured to reach the national standard, and the combustion efficiency of the boiler is enabled to reach the highest.
Description
Technical Field
The invention belongs to the field of industrial gas boilers, and particularly relates to a combustion control method.
Background
The coal gas-reforming project is started in 2000, and the nitrogen oxides are not controlled in the existing control equipment for more than ten years at present; in addition, the nitrogen oxides and the combustion load are reverse indexes in the actual operation process of the gas industrial boiler, and the generation rate of the nitrogen oxides is higher when the combustion firepower is higher; when the combustion firepower is smaller, the generation of nitrogen oxides is reduced in a nonlinear manner according to the combustion temperature, so that the emission of the nitrogen oxides is easy to exceed the standard by the existing boiler combustion control method.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a combustion control method for controlling oxynitride.
The invention relates to a combustion optimization control method based on a nitrogen oxide emission index constraint condition, which comprises the following steps:
1. setting a standard value Ah for the concentration emission of the gaseous pollutants by connecting an environmental protection competent department or looking up local environmental protection requirements;
2. acquiring a nitrogen oxide concentration value Ai, setting the nitrogen oxide sampling frequency as M according to field setting by considering the type of a gas industrial boiler and the sampling period TNOx of a flue gas analyzer, and carrying out mean value processing;
ai is the ith sampled value of the concentration of nitrogen oxide,representing the mean value of M times of sampling, and TNOx representing the sampling period of nitrogen oxide;
2. acquiring a flue gas oxygen concentration value Oi, considering the type of a gas industrial boiler and the sampling period TO2 of a flue gas analyzer, setting the sampling frequency TO be N according TO the oxygen amount set on site, calculating an excess air coefficient alpha, and carrying out mean value processing;
ai represents the ith air excess factor,
3. and (3) a combustion regulation control algorithm:
the incremental combustion control is adopted, and the specific algorithm is as follows:
combustion load output u (k) ═ u (k-1) + Δ u (k),
Δu(k)=Kp*e(k)+Ki*e(k-1)+Kd*e(k-2),
e (k) is the target load Ptarget minus the actual load Ptarget,
kp, Ki and Kd are coefficients of conventional PID after calculation and variation;
4. combustion optimization regulation control under nitrogen oxide constraint condition
① creating a table look-up system for extracting load P, burner air door opening degree Y and nitrogen oxides under the condition of no nitrogen oxides restricting the combustion operation of the boilerAnd excess air ratioEstablishing a table look-up system according to the corresponding operation data sample;
combustion optimization control under the constraint condition of nitrogen oxides:
setting a safety width threshold value A0 of nitrogen oxide emission, the load is P, and the target value of the load is PTarget(ii) a The precision of the flue gas analyzer is Am
After the boiler is normally operated, the load is adjusted as follows:
u(k)=u(k-1)+Δu(k),
The allowable load deviation value is set to K0 in consideration of the accuracy of the existence of the device itself for detecting the load and the operation profile of the device
When Δ p > - [ K0, the combustion control outputs
u(k)=u(k-1)+Δu(k)
When Δ p < K0, combustion control output
u (k) di u (k-1) +
Wherein Yh1 is the upper limit value of the air door opening, Yl1 is the lower limit value of the air door opening, and Delta A is the set nitrogen oxide emission change step length;
to prevent the output of the damper opening from changing too quickly to cause a rapid change in nitrogen oxides, the design control steps must therefore be as small as possible. A combustion system of a small and medium-sized gas industrial boiler is generally completed by adopting one combustor. The normal adjusting range of the air door actuating mechanism of the burner is 25% -100%, the adjusting range is 75%, the travel time of the air door actuating mechanism of the burner tested from 25% -100% is calculated to be 30S, and therefore the travel accuracy of the burner is 75% ÷ 30%/S, and is 2.5%/S. In addition, according to the performance parameters of the flue gas on-line analyzer, preferably, Δ a is the measurement accuracy value Am of nitrogen oxides.
When the content is less than 2.5%, the content is 2.5%
Therefore, when Δ p < K0, the combustion control outputs:
the invention has the beneficial effects that: the gas industrial boiler is subjected to restrictive control and soft control through the flue gas information flow provided by the flue gas online analysis system, so that the emission of the gas industrial boiler is ensured to reach the national standard, and the combustion efficiency of the boiler is enabled to reach the highest.
Detailed Description
The present invention will be described in further detail below, but it should not be construed that the scope of the above-described subject matter of the present invention is limited to the above-described embodiments.
A combustion optimization control method based on a nitrogen oxide emission index constraint condition comprises the following steps:
the proportion of nitrogen contained in the natural gas components in the gas industrial boiler is low, and therefore the proportion of fuel type production in the production of nitrogen oxides is low. Because the combustion temperature in the gas industrial boiler is very high, the thermal generated nitrogen oxide is mainly considered. During the starting process of the boiler, the flame temperature is very low, basically below 1000 ℃, and generally, nitrogen oxides are generated less below 1300 ℃, so the invention only considers the constraint control of the nitrogen oxides in the regulating process of the boiler load from small load to full load after stable combustion;
1. acquiring a nitrogen oxide concentration value Ai, setting the nitrogen oxide sampling frequency as M according to field setting by considering the type of a gas industrial boiler and the sampling period TN0x of a flue gas analyzer, and carrying out mean value processing;
ai is the ith sampled value of the concentration of nitrogen oxide,represents the mean of M samples, TN0x represents the sampling period of NOx;
2. acquiring a flue gas oxygen concentration value Oi, considering the type of a gas industrial boiler and the sampling period TO2 of a flue gas analyzer, setting the sampling frequency TO be N according TO the oxygen amount set on site, calculating an excess air coefficient alpha, and carrying out mean value processing;
ai represents the ith air excess factor,
3. and (3) a combustion regulation control algorithm:
the incremental combustion control is adopted, and the specific algorithm is as follows:
combustion control output u (k) ═ u (k-1) + Δ u (k),
Δu(k+1)=Kp*e(k)+Ki*e(k-1)+Kd*e(k-2),
e (k) is the target value Ptarget of the load minus the actual value of the load Ptarget
Kp, Ki, Kd: respectively are the coefficients of the conventional PID after operation variation;
4. combustion optimization regulation control under nitrogen oxide constraint condition
① extracting load P, burner air door opening degree Y and nitrogen oxides under the condition of no nitrogen oxide constraint boiler combustion operationAnd excess air ratioAnd (4) correspondingly operating the data samples to establish a table look-up system.
Combustion optimization control under the constraint condition of nitrogen oxides:
according to the generation mechanism of nitrogen oxides, combustion is controlled in a grading manner, optimization management is carried out, and in order to avoid the overshoot of the emission of the nitrogen oxides, a proper deviation value A0 is set according to the precision of a flue gas analyzer; the load is P, and the target load value is PTarget
After the boiler is normally operated, the load is adjusted as follows:
y(k)=u(k)=u(k-1)+Δu(k)
The optimal operation state of the boiler is A0 → 0 and delta P → 0, and the system not only meets the requirement of environmental protection, but also achieves the purpose of saving energy. However, in the actual operation process, due to the constraint of the nitrogen oxide content, the conventional PID regulation cannot meet the requirement of the optimal load according to the current incremental control algorithm. In order to infinitely approach the optimal matching point of combustion, when the boiler operates stably, the system is disconnected from PID adjustment, and combustion optimization control is carried out by adopting an artificial approach control algorithm and a table look-up system.
Considering the accuracy of the presence of the device itself detecting the load and the device operating profile, the final value of the load deviation is therefore determined as K0
When | Δ p | ≦ K0, the combustion control outputs
y(k)=u(k)=u(k-1)+Δu(k)
When Δ p > K0, the combustion control output will gradually decrease according to the PID operation tendency, and the concentration of nitrogen oxides will gradually decrease according to the nitrogen oxide generation mechanism, so the combustion control output
y(k)=u(k)=u(k-1)+Δu(k)
When Δ p < K0, the load does not reach the target value, and in order to allow the combustion control output and nox to smoothly transition to the optimum values, the system employs a softness control algorithm, the combustion control output:
y(k)=u(k)+
according to the curve relation between the temperature and the nitrogen oxides and a table look-up system, the range from the nitrogen oxides (Ah-Ao) to the Ah and the wind opening YL1~YH1The interval establishes an approximate proportional relation, then
In order to prevent the rapid change of the nitrogen oxide caused by the too fast change of the opening degree of the air door of the burner, the design control step is required to be as small as possible. A combustion system of a small and medium-sized gas industrial boiler is generally completed by adopting one combustor. The normal adjusting range of the air door actuating mechanism of the burner is 25-100% of opening degree, the adjusting range is 75%, the travel time of the air door actuating mechanism of the burner tested from 25-100% is calculated to be 30S, and therefore the travel precision of the air door actuating mechanism is 75% ÷ 30 ═ 2.5%/S. In addition, according to the performance parameters of the online flue gas analyzer, the precision value of the nitrogen oxide is set to Am.
When the content is less than 2.5%, the content is 2.5%
Therefore, when Δ p < K0, the combustion control outputs:
Claims (2)
1. a combustion optimization control method based on a nitrogen oxide emission index constraint condition comprises the following steps:
a) setting a standard value Ah for the concentration emission of the gaseous pollutants by connecting an environmental protection competent department or looking up local environmental protection requirements;
b) acquiring a nitrogen oxide concentration value Ai, setting the nitrogen oxide sampling frequency as M according to field setting by considering the type of a gas industrial boiler and the sampling period TNOx of a flue gas analyzer, and carrying out mean value processing;
ai is the ith sampled value of the concentration of nitrogen oxide,representing the mean value of M times of sampling, and TNOx representing the sampling period of nitrogen oxide;
acquiring a flue gas oxygen concentration value Oi, considering the type of a gas industrial boiler and the sampling period TO2 of a flue gas analyzer, setting the sampling frequency TO be N according TO the oxygen amount set on site, calculating an excess air coefficient alpha, and carrying out mean value processing;
ai represents the ith air excess factor,
c) and (3) a combustion regulation control algorithm:
the incremental combustion control is adopted, and the specific algorithm is as follows:
combustion control output u (k) ═ u (k-1) + Δ u (k),
Δu(k)=Kp*e(k)+Ki*e(k-1)+Kd*e(k-2),
e (k) subtracting the actual load Ptarget from the target load Ptarget,
kp, Ki and Kd are coefficients of conventional PID after calculation and variation;
d) combustion optimization regulation control under nitrogen oxide constraint condition
① creating a table look-up system for extracting load P, burner air door opening degree Y and nitrogen oxides under the condition of no nitrogen oxides restricting the combustion operation of the boilerAnd excess air ratioEstablishing a table look-up system according to the corresponding operation data sample;
combustion optimization control under the constraint condition of nitrogen oxides:
setting a safety width threshold value A0 of nitrogen oxide emission, the load is P, and the target value of the load is PTarget;
After the boiler is normally operated, the load is adjusted as follows:
u(k)=u(k-1)+Δu(k),
Setting the allowable load deviation value to K0
When Δ p > -K0, the combustion output
u(k)=u(k-1)+Δu(k)
When Δ p < K0, combustion output
u(k)=u(k-1)+
Where Yh1 is the upper limit value of the throttle opening, Yl1 is the lower limit value of the throttle opening, and Δ a is the set nitrogen oxide emission change step.
2. The combustion optimization control method based on the nitrogen oxide emission index constraint condition as recited in claim 1, characterized in that Δ a is a measured precision value Am of nitrogen oxide.
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