CN113419570A - Control method of flue gas denitration system of waste incineration power plant - Google Patents

Abstract

The invention discloses a control method of a flue gas denitration system of a waste incineration power plant, and relates to the field of domestic solid waste treatment. It comprises the following steps, step 1, NO_xCalculating the content; step 2, setting calculation of denitration efficiency; and step 3: to obtain NH₃/NO_xA molar ratio; and 4, step 4: determining a corrected molar ratio signal F; step 5, calculating the ammonia gas flow; and 6, controlling an ammonia gas flow regulating valve to realize automatic control of denitration and realize automatic control of denitration. The ammonia spraying amount of the invention is not along with the outlet NO_xThe change of the emission concentration is changed along with the change of the emission concentration, and NO is actually measured at an outlet_xThe value is only a correction of the ammonia injection amount, and therefore the system stability is improved to some extent.

Description

Control method of flue gas denitration system of waste incineration power plant

Technical Field

The invention relates to the field of domestic solid waste treatment, in particular to a control method of a flue gas denitration system of a waste incineration power plant.

Background

Pollutants in the incineration flue gas of the household garbage can be divided into particulate matters (dust) and acid gases (HCl, HF and SO)₂、NO_xEtc.), heavy metals (Hg, Pb, Cr, etc.) and organic highly toxic pollutants (dioxins, furans, etc.). In order to prevent secondary pollution to the environment in the waste incineration treatment process, strict measures must be taken, and a flue gas purification system is utilized to control the emission of waste incineration flue gas; removing NO in flue gas of conventional waste incineration power plant_xAnd adopting SNCR or SNCR + SCR combined denitration.

The denitration system aims to minimize ammonia escape amount, prolong the service life of the catalyst and minimize corrosion to an air preheater on the premise of ensuring denitration efficiency. Therefore, the reasonable control strategy is adopted to be the key for improving the availability ratio of the SNCR or SCR system, and the denitration system mainly controls the following three aspects: ensuring proper reaction temperature, ensuring proper NH3 injection amount and keeping certain activity of the catalyst; wherein controlling the appropriate NH3 input is again of central importance.

The most common ammonia injection rate control system relies on a simple feed forward loop (with feedback adjustment) based on stack NOx emissions and load dependent NO_xExperimental curves for the required ammonia injection. The ammonia adding amount is controlled by positive information given by the concentration of NOx at the upstream of the catalyst and the smoke amount, the control system positions the ammonia gas flow regulating valve according to the calculated ammonia demand signal to realize the automatic control of denitration, and the optimal ammonia spraying point is found by adjusting the ammonia gas flow under different loads. Meanwhile, the actual ammonia flow value is compared with the calculated ammonia flow value, and the ammonia spraying amount is corrected by using a feedback signal.

With this control scheme it is necessary to ensure inlet NO_xThe value fluctuates in a small range, otherwise violent oscillation of denitration efficiency is easily caused, the combustion temperature of the boiler is above 850 ℃, and NO is generated at the temperature_xMost sensitive region of (3), NO_xThe fluctuation of (c) is relatively large and thus the stability of this control scheme is not high. And if inlet NO_xWhen the concentration exceeds the designed value, the control system can give a signal for opening a large valve of the ammonia gas regulating valve, and the NH actually participates in the reaction₃Less than supplied NH₃Thus resulting in the reactor outletLarge ammonia slip

Therefore, it is necessary to develop a control method for a flue gas denitration system of a waste incineration power plant.

Disclosure of Invention

The invention aims to overcome the defects of the background technology and provides a control method of a flue gas denitration system of a waste incineration power plant.

In order to achieve the purpose, the technical scheme of the invention is as follows: the control method of the flue gas denitration system of the waste incineration power plant is characterized by comprising the following steps:

step 1, NO_xAnd (3) calculating the content:

total air quantity of boiler and NO at inlet of reactor_xThe product of the concentrations being NO_xThe flow signal, the formula is: e ═ FLOW × D

Wherein E is NO_xA flow signal; FLOW is flue gas FLOW in Nm³H; d is reactor inlet NO_xConcentration in mg/Nm³；

Step 2, setting calculation of denitration efficiency:

eta ═ NO (reactor inlet NO)_xConcentration-reactor outlet set NO_xValue) x 100%/reactor inlet NO_xConcentration; reactor outlet set of NO_xThe unit of the value is mg/Nm³；

Reactor outlet set of NO_xValue setting of NO through reactor outlet_xSetting by a setter;

and step 3: setting the denitration efficiency to be determined, setting NH₃/NO_xThe molar ratio can be obtained through a curve function f (x);

wherein r is ammonia escape concentration, and the unit is mu L/L;

C_NOis the concentration of NO in the inlet flue gas of the reactor, and the unit is mg/m³；

C_NO2For NO in the inlet flue gas of the reactor₂Concentration in mg/m³；

And 4, step 4: if the set NH is calculated₃/NO_xMolar ratio of NH set by the operator₃/NO_xWhen the molar ratio is large, actual output of NH is set by an operator₃/NO_xThe molar ratio. If NH is calculated₃/NO_xMolar ratio of NH set by the operator₃/NO_xWhen the molar ratio is small, the actual output is set to the calculated NH₃/NO_xA molar ratio; thereby determining a corrected molar ratio signal F;

and 5, calculating the ammonia gas flow:

calculated NO_xThe flow signal E is multiplied by the modified molar ratio signal F to obtain the desired NH₃A flow signal G;

G＝E×F

step 6, controlling an ammonia gas flow regulating valve:

by the desired NH₃And the flow signal G is used for positioning the ammonia gas flow regulating valve, so that the denitration is automatically controlled, and the denitration is automatically controlled.

Compared with the prior art, the invention has the following advantages:

1)NO_xemissions are a function of a number of variables, including boiler type, combustion temperature, fuel chemistry, design and operation of low nitrogen combustion control schemes, coal/air distribution, flue gas oxygen content, particle size of pulverized coal, etc., all of which are related to NO_xHas an effect on the formation of (a); and NO from flue_xSignal and analysis command delays tend to cause inaccurate ammonia injection, which results in poor control performance and, as a result, NO_xThe removal rate is reduced or the escape of ammonia is increased; the high ammonia dosage increases the generation of ammonium sulfate and ammonium bisulfate, and the deposition of the ammonium sulfate and the ammonium bisulfate on the catalyst reduces the service life of the catalyst and the efficiency reduction of an air preheater and other problems; the invention is based on the use of reactor outlet NO_xEmission concentration as control point, outlet NO_xOnce the emission concentration is determined, the denitration efficiency can be calculated, and NH can be known through the denitration efficiency₃/NO_xMolar ratio and passing through outlet NO_xSet emission concentration and measured NO_xConcentration comparison to correct NH₃/NO_xThe molar ratio is calculated to obtain an ammonia gas flow signal;

the ammonia spraying amount of the invention is not along with the outlet NO_xThe change of the emission concentration is changed along with the change of the emission concentration, and NO is actually measured at an outlet_xThe value is only a correction of the ammonia injection amount, and therefore the system stability is improved to some extent. And, once reactor inlet NO_xIf the value exceeds the design value, the calculation of NH is participated in₃/NO_xNH is automatically switched to design denitration efficiency according to molar ratio₃/NO_xThe mol ratio and the ammonia injection amount can not be further improved, and the ammonia escape rate can also be effectively controlled.

2) The present invention can take into account multiple objectives, both to reduce NO_XEmissions in turn improve the heat rate of the boiler, while still maintaining other parameters of the power plant, such as steam temperature, CO, etc., within desired ranges; by measuring critical outlet NO in closed-loop monitoring mode_XConcentration process parameters, and optimizing the performance of the denitration device by a DCS (distributed control System); the denitration control system can integrally improve the performances of a thermodynamic system and denitration; the system sets to a set point that dynamically adjusts for the optimum deviation or based on current plant operating conditions and the desired target.

Drawings

FIG. 1 is a schematic structural diagram of the present invention.

Detailed Description

The embodiments of the present invention will be described in detail with reference to the accompanying drawings, which are not intended to limit the present invention, but are merely exemplary. While the advantages of the invention will be apparent and readily appreciated by the description.

With reference to the accompanying drawings: the control method of the flue gas denitration system of the waste incineration power plant is characterized by comprising the following steps:

step 1, NO_xAnd (3) calculating the content:

total air quantity of boiler and NO at inlet of reactor_xThe product of the concentrations being NO_xThe flow signal, the formula is: e ═ FLOW × D

Wherein E is NO_xA flow signal; FLOW is flue gas FLOW in Nm³H; d is reactor inlet NO_xConcentration in mg/Nm³；

Step 2, setting calculation of denitration efficiency:

eta ═ NO (reactor inlet NO)_xConcentration-reactor outlet set NO_xValue) x 100%/reactor inlet NO_xConcentration; reactor outlet set of NO_xThe unit of the value is mg/Nm³；

Reactor outlet set of NO_xValue setting of NO through reactor outlet_xSetting by a setter;

and step 3: setting the denitration efficiency to be determined, setting NH₃/NO_xThe molar ratio can be obtained through a curve function f (x);

wherein r is ammonia escape concentration, and the unit is mu L/L;

C_NOis the concentration of NO in the inlet flue gas of the reactor, and the unit is mg/m³；

C_NO2For NO in the inlet flue gas of the reactor₂Concentration in mg/m³；

The above is data in the dry flue gas in the standard state and under the actual oxygen content;

and 4, step 4: if the set NH is calculated₃/NO_xMolar ratio of NH set by the operator₃/NO_xWhen the molar ratio is large, actual output of NH is set by an operator₃/NO_xThe molar ratio. If NH is calculated₃/NO_xMolar ratio of NH set by the operator₃/NO_xWhen the molar ratio is small, the actual output is set to the calculated NH₃/NO_xA molar ratio; thereby determining a corrected molar ratio signal F;

and 5, calculating the ammonia gas flow:

calculated NO_xFlow rate informationThe number E is multiplied by the modified molar ratio signal F to obtain the desired NH₃A flow signal G;

G＝E×F

step 6, controlling an ammonia gas flow regulating valve:

by the desired NH₃And the deviation of the flow signal G and the ammonia flow signal L corrected by the controller controls an ammonia flow regulating valve, so that the automatic control of denitration is realized.

In practical use, the invention is used for controlling NO at the outlet of the reactor_xEmission concentration, by the operator first specifying a reactor outlet NO_xValue, reactor outlet set to NO_xThe value is substituted into a formula to calculate to obtain the set denitration efficiency, then NH is set₃/NO_xThe molar ratio is determined by experimental curves, this signal being multiplied by the inlet NO_XThe flow signal is a basic ammonia flow signal, and the ammonia flow regulating valve is positioned according to the calculated ammonia flow signal, so that the automatic control of denitration is realized.

Other parts not described belong to the prior art.

Claims (1)

1. The control method of the flue gas denitration system of the waste incineration power plant is characterized by comprising the following steps:

step 1, NO_xAnd (3) calculating the content:

total air quantity of boiler and NO at inlet of reactor_xThe product of the concentrations being NO_xThe flow signal, the formula is: e ═ FLOW × D

Wherein E is NO_xA flow signal; FLOW is flue gas FLOW in Nm³H; d is reactor inlet NO_xConcentration in mg/Nm³；

Step 2, setting calculation of denitration efficiency:

eta ═ NO (reactor inlet NO)_xConcentration-reactor outlet set NO_xValue) x 100%/reactor inlet NO_xConcentration; reactor outlet set of NO_xThe unit of the value is mg/Nm³；

Reactor outlet set of NO_xThe value is set by the reactor outletNO_xSetting by a setter;

and step 3: setting the denitration efficiency to be determined, setting NH₃/NO_xThe molar ratio can be obtained through a curve function f (x);

wherein r is ammonia escape concentration, and the unit is mu L/L;

C_NOis the concentration of NO in the inlet flue gas of the reactor, and the unit is mg/m³；

C_NO2For NO in the inlet flue gas of the reactor₂Concentration in mg/m³；

And 4, step 4: if the set NH is calculated₃/NO_xMolar ratio of NH set by the operator₃/NO_xWhen the molar ratio is large, actual output of NH is set by an operator₃/NO_xThe molar ratio. If NH is calculated₃/NO_xMolar ratio of NH set by the operator₃/NO_xWhen the molar ratio is small, the actual output is set to the calculated NH₃/NO_xA molar ratio; thereby determining a corrected molar ratio signal F;

and 5, calculating the ammonia gas flow:

calculated NO_xThe flow signal E is multiplied by the modified molar ratio signal F to obtain the desired NH₃A flow signal G;

G＝E×F

step 6, controlling an ammonia gas flow regulating valve:

by the desired NH₃And the flow signal G is used for positioning the ammonia gas flow regulating valve, so that the denitration is automatically controlled, and the denitration is automatically controlled.

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