CN106681381A - SCR denitration system ammonia spraying quantity optimal control system and method based on intelligent feedforward signals - Google Patents

SCR denitration system ammonia spraying quantity optimal control system and method based on intelligent feedforward signals Download PDF

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CN106681381A
CN106681381A CN201710002535.6A CN201710002535A CN106681381A CN 106681381 A CN106681381 A CN 106681381A CN 201710002535 A CN201710002535 A CN 201710002535A CN 106681381 A CN106681381 A CN 106681381A
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concentration
ammonia spraying
control
scr
furnace outlet
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杨婷婷
高阳
吕游
秦天牧
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North China Electric Power University
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D11/00—Control of flow ratio
    • G05D11/02—Controlling ratio of two or more flows of fluid or fluent material
    • G05D11/13—Controlling ratio of two or more flows of fluid or fluent material characterised by the use of electric means
    • G05D11/139—Controlling ratio of two or more flows of fluid or fluent material characterised by the use of electric means by measuring a value related to the quantity of the individual components and sensing at least one property of the mixture
    • 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
    • B01D53/90—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

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  • Environmental & Geological Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
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  • Oil, Petroleum & Natural Gas (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Automation & Control Theory (AREA)
  • General Physics & Mathematics (AREA)
  • Physics & Mathematics (AREA)
  • Treating Waste Gases (AREA)

Abstract

The invention relates to an SCR (Selective Catalytic Reduction) denitration system ammonia spraying quantity optimal control system and method based on intelligent feedforward signals. The SCR denitration system ammonia spraying quantity optimal control system based on intelligent feedforward signals is characterized in that as input parameters of a denitration system can be easily influenced by the combustion state of a boiler and for adapting to the requirement of large range of depth change of conditions for a thermal power generating unit, the SCR denitration system ammonia spraying quantity optimal control system based on intelligent feedforward signals takes the historical data of a power plant as the basis, utilizes the idea of data modeling, takes adjustable parameters at the boiler side as input and NOX concentration at the outlet of a hearth as output, utilizes a Least Squares Support Vector Machine algorithm to construct a prediction model which can be used for constructing an intelligent feedforward controller in a ammonia spraying quantity control strategy, and takes dynamic matrix control (DMC) as a main controller and PID as an auxiliary controller to construct a cascade feedback control structure; during the operating process, the intelligent feedforward controller outputs feedforward control signals in real time according to changes of the parameters at the boiler side, quickly gives a response to change of conditions of the unit, and forms an SCR system ammonia spraying quantity optimal control strategy together with feedback control, and can realize quick accurate control of the ammonia spraying quantity.

Description

A kind of SCR denitration system ammonia spraying amount Optimal Control System based on Intelligent Feed-forward signal And method
Technical field
The present invention relates to a kind of fired power generating unit SCR denitration system Optimal Control System and side based on Intelligent Feed-forward technology Method, belongs to thermal technics field.
Background technology
The flue gas that coal-fired power plant is produced is air NOxOne of important sources of pollution, in order to reduce NOxDischarge capacity, choosing Selecting property catalysis reduction (Selective Catalytic Reduction, SCR) flue gas denitrification system is advised greatly in thermal power plant Mould application.With the continuous improvement of environmental requirement, for the saving spray ammonia cost while discharge standard of national regulation is reached, The optimal control of SCR system gets the attention.
SCR denitration system is coupled closely with hearth combustion, and the smoke behavior of furnace outlet determines the cigarette of SCR system entrance Gas parameter, including flue-gas temperature, flue gas flow rate, flue gas NOxContent etc., the change of these parameters can affect SCR denitration to react Process and denitration efficiency.The smoke behavior of furnace outlet is affected by boiler operatiopn operating mode, including load and the adjustable input ginseng of boiler Number.Under the background of current power industry regenerative resource large-scale grid connection, fired power generating unit frequently participates in peak regulation, and peak regulation depth It is increasing.Therefore, boiler operatiopn operating mode frequently changes on a large scale so that furnace outlet flue gas parameter frequently changes.SCR systems System entrance and exit Gas Parameters signal detection exist it is delayed, along with SCR reactor reactions process exist it is big postpone, therefore, To such reaction mechanism complexity, with SCR denitration process the features such as non-linear, large delay, Multivariable Coupling, traditional PID Control cannot obtain satisfied control effect.Ammonia spraying amount can excessively cause the escaping of ammonia to increase so that air preheater fouling corrodes, Ammonia spraying amount crosses that I haven't seen you for ages and causes outlet NOxDischarge does not reach national emission request.
Therefore, when operating mode changes, rely solely on feedback control and realize outlet NOxThe accurate quick control of concentration is It is extremely difficult, the also system without effectively solving this problem or method in prior art.
The content of the invention
The present invention proposes a kind of SCR denitration system spray ammonia for adapting to unit working conditions change to overcome the deficiencies in the prior art Amount Optimal Control System and method, realize the quick and precisely control of ammonia spraying amount.
Technical scheme：To reach goal of the invention, the present invention is adopted the following technical scheme that：
A kind of SCR denitration system ammonia spraying amount Optimal Control System based on Intelligent Feed-forward signal of the present invention, including： NOXConcentration target value setting unit, Intelligent Feed-forward controller unit, DMC controller units, PID controller unit sprays ammonia valve Door, SCR reactors, wherein, the NOXConcentration target value setting unit passes through the input phase of subtractor and DMC controller units Even, as the input of PID controller unit after the output of DMC controller units is added with the output of Intelligent Feed-forward controller unit, The output of PID controller unit is connected with the input of spray ammonia valve door, and PID controller unit and spray ammonia valve door Jing unity negative feedbacks Inner looping control subsystem is constituted, the output for spraying ammonia valve door is connected with the input of SCR reactors, the wherein output of SCR reactors With NOXConcentration target value setting unit subtract each other after as DMC controller units input, constitute negative feedback control loop.
Further, the Intelligent Feed-forward controller unit includes furnace outlet NOXConcentration prediction module and the feedforward Amount conversion module, wherein, the furnace outlet NOXConcentration prediction module burner hearth according to boiler side |input paramete real-time estimate Outlet NOXConcentration, feedforward control amount conversion module is by above-mentioned furnace outlet NOXConcentration real-time estimate value is scaled valve and opens Degree variable quantity, as feedforward control amount.
Further, feedforward control amount conversion module is by the furnace outlet NOXConcentration real-time estimate value is scaled Valve opening variable quantity, used as feedforward control amount, its reduction formula is：
Δ y=k Δ n+b (2)
Wherein：Δ n is valve opening variable quantity；ΔcNOxIt is furnace outlet NOXConcentration change amount, is furnace outlet NOXIt is dense Degree real-time estimate value and current time NOXDifference between concentration actual value, unit is mg/m3；Q is flue gas flow, and unit is m3/h；η is denitration efficiency；MNOxIt is NH3And NOXMolal weight；Δ y is ammonia spraying amount variable quantity；Ammonia spraying amount and valve are opened It is linear function between degree, k and b is fitting coefficient in function, and calculated ammonia spraying amount variation delta y obtains valve through inverse Door aperture variation delta n.
Further, the |input paramete includes：Boiler load, total blast volume, coal pulverizer coal-supplying amount, total fuel quantity, oxygen amount, Secondary wind, burnout degree etc., change according to boiler side |input paramete and adjust in advance SCR system ammonia spraying amount.
Further, the furnace outlet NOXModel in concentration prediction module is built using data modeling, and step is such as Under：
1) the boiler side |input paramete is chosen, as the input variable of model, with the furnace outlet NOXConcentration conduct Model output variable；
2) the stable history data of certain hour length is chosen from unit historical data, and carries out data and located in advance Reason；
3) modeling is trained to data using least square method supporting vector machine LS-SVM algorithms, and carries out model accuracy Checking.
A kind of optimal control method of the SCR denitration system ammonia spraying amount Optimal Control System based on Intelligent Feed-forward signal, its In with the outlet NO of the SCR reactorsXConcentration is controlled volume, and the spray ammonia valve opening is used as controlled quentity controlled variable.
Further, wherein the DMC controller units adopt DMC forecast Control Algorithms, rung with the step of controlled device Model basis is should be, the SCR reactors implement Spline smoothing to ammonia spraying amount, obtain outlet NOXThe step response curve of concentration.
Further, the optimization time domain in the DMC forecast Control Algorithms and control time domain are gathered with reference to emulation side using examination Method.
Further, the PID controller is used to adjust the spray ammonia valve opening, is adjusted using PI and is adjusted, and adjusts and adopts Use attenuation curve method.
Further, NO is exportedXConcentration set point is set to 40-50mg/m3。
Beneficial effect：Compared with prior art, the SCR denitration system based on Intelligent Feed-forward signal proposed by the present invention sprays ammonia Amount optimal control method, constructs measurable furnace outlet NOXThe mathematical model of concentration, reflects in real time the combustion conditions of burner hearth, Feed-forward control signals are provided in time, ammonia spraying amount is adjusted, detecting system delay and SCR system large delay characteristic can be overcome to be brought Control problem, reduce control overshoot, save ammonia spraying amount on the premise of also reduce the escaping of ammonia, realize the accurate control of ammonia spraying amount System.
Description of the drawings
Comprising in the description and accompanying drawing and the description of the part that constitutes description together illustrates the present invention's Exemplary embodiment, feature and aspect, and for explaining the principle of the present invention.
Fig. 1 is the SCR denitration system ammonia spraying amount optimal control method schematic diagram based on Intelligent Feed-forward signal of the present invention.
Fig. 2 is the structure chart of Intelligent Feed-forward controller unit of the present invention.
Fig. 3 is furnace outlet NO of the present inventionXConcentration prediction model training sample prediction curve figure.
Fig. 4 is furnace outlet NO of the present inventionXConcentration prediction model forecast sample prediction curve figure.
Fig. 5 is using the inventive method and the outlet NO obtained using traditional cas PID control deviceXConcentration control effect pair Than figure.
Fig. 6 is using the inventive method and the ammonia spraying amount control effect comparison diagram obtained using traditional cas PID control device.
Fig. 7 is using the inventive method and the escaping of ammonia control effect comparison diagram obtained using traditional cas PID control device.
Specific embodiment
In order that present disclosure is easier to be clearly understood, below according to specific embodiment and accompanying drawing is combined, it is right The present invention is described in further detail, it should be understood that these embodiments are merely to illustrate the present invention rather than limit the present invention's Scope, after the present invention has been read, modification of the those skilled in the art to the various equivalent form of values of the present invention falls within this Shen Please claims limited range.
As shown in accompanying drawing 1-7, the present invention is to adapt to the requirement of operating condition wide variation, and the present invention adopts data modeling Thought, using power plant's historical data, using boiler side adjustable parameter as input, with furnace outlet NOXConcentration as output, Mould is built using least square method supporting vector machine (Least Squares Support Vector Machine, LS-SVM) algorithm Type, the model can be used to build the Intelligent Feed-forward controller in ammonia spraying amount control strategy.In actual moving process, the feedforward Device exports in real time feed-forward control signals, the change of quick response unit operating mode according to the Parameters variation of boiler side.The feedforward with Dynamic matrix control (Dynamic Matrix Control, DMC) method constitutes SCR system control strategy, realizes ammonia spraying amount Quick and precisely control.
The characteristics of present invention frequently changes on a large scale for thermal power unit operation operating mode, proposes that a kind of unit operating mode that adapts to becomes The SCR denitration system ammonia spraying amount Optimal Control System of change and method, realize the quick and precisely control of ammonia spraying amount.Control method principle As shown in figure 1, the SCR denitration system ammonia spraying amount Optimal Control System based on Intelligent Feed-forward signal, including NOXConcentration target value sets Unit is put, Intelligent Feed-forward controller unit, DMC controller units, PID controller unit sprays ammonia valve door, SCR reactors.
The NOXConcentration target value setting unit is connected by subtractor with the input of DMC controller units, DMC controls The output of device unit is exported after being added as the input of PID controller unit, PID controller list with Intelligent Feed-forward controller unit The output of unit is connected with the input of spray ammonia valve door, and PID controller unit constitutes inner looping with spray ammonia valve door Jing unity negative feedbacks Control subsystem, the output for spraying ammonia valve door is connected with the input of SCR reactors, wherein NOXConcentration target value setting unit and SCR The output of reactor subtract each other after as DMC controller units input, constitute negative feedback control loop, i.e., external loop control system System.
Intelligent Feed-forward controller unit includes furnace outlet NOXConcentration prediction module and feedforward control amount conversion module.Its In, furnace outlet NOXConcentration prediction module is according to boiler side |input paramete real-time estimate furnace outlet NOXConcentration, overcomes detection system System is delayed, and the |input paramete is included but is not limited to：Boiler load, total blast volume, coal pulverizer coal-supplying amount, total fuel quantity, oxygen amount, two Secondary wind, burnout degree etc., change according to boiler side |input paramete and adjust in advance SCR system ammonia spraying amount.Feedforward control amount conversion module By above-mentioned furnace outlet NOXConcentration real-time estimate value is scaled valve opening variable quantity, used as feedforward control amount.
Feedforward control amount conversion module is by furnace outlet NOXConcentration real-time estimate value is scaled valve opening change Amount, used as feedforward control amount, its reduction formula is：
Δ y=k Δ n+b (2)
Wherein：Δ n is valve opening variable quantity；ΔcNOxIt is furnace outlet NOXConcentration change amount, is furnace outlet NOXIt is dense Degree real-time estimate value and current time NOXDifference between concentration actual value, unit is mg/m3；Q is flue gas flow, and unit is m3/h；η is denitration efficiency；MNOxIt is NH3And NOXMolal weight；Δ y is ammonia spraying amount variable quantity；Ammonia spraying amount and valve are opened It is linear function between degree, k and b is fitting coefficient in function, and calculated ammonia spraying amount variation delta y obtains valve through inverse Door aperture variation delta n.
Furnace outlet NOXModel in concentration prediction module is built using data modeling, and establishment step is as follows：
1) choose affects larger boiler |input paramete to boiler combustion status, used as the input variable of model.With burner hearth Outlet NOXConcentration is used as model output variable；
2) the stable history run number of the certain hour length of selected input/output variable is chosen from unit historical data According to line number of going forward side by side Data preprocess；
3) modeling is trained to data using least square method supporting vector machine (LS-SVM) algorithm, and it is accurate to carry out model Property checking；
Thus the furnace outlet NO for setting upXConcentration prediction model collectively forms intelligence with feedforward control amount conversion module Feedforward controller unit, when boiler side |input paramete changes, can in time predict furnace outlet NOXConcentration change, in advance Output ammonia spraying amount control signal, overcomes detection delayed.
With SCR reactor outlet NOXConcentration is controlled volume, and, used as controlled quentity controlled variable, design is based on before intelligence for spray ammonia valve opening The ammonia spraying amount optimal control method of feedback signal, realizes the optimal control of ammonia spraying amount.
Preferably, the DMC controller units are using DMC forecast Control Algorithms, the step response with controlled device is Model basis, the SCR reactors implement Spline smoothing to ammonia spraying amount, obtain outlet NOXThe step response curve of concentration.
Preferably, the optimization time domain and control time domain in the DMC forecast Control Algorithms is gathered with reference to emulation side using examination Method.
Preferably, the PID controller is used to adjust spray ammonia valve opening, is adjusted using PI and adjusted, adjusted and adopted Method be attenuation curve method.
Preferably, the outlet NOXConcentration set point is set to 40-50mg/m3。
Below by taking the data of certain factory 350MW units and emulation as an example, present invention is described in detail.Based on should use Scape, above-mentioned correlation step and parameter are：
Furnace outlet NOXThe establishment step of the model in concentration prediction unit is as follows：
1) several groups of combustion characteristics, (4) descriptions one of coal pulverizer coal-supplying amount are represented with unit load, total blast volume, total fuel quantity Impact of the secondary air quantity to boiler combustion, secondary air register aperture (8) represents secondary air distribution mode to combustion effects, and after-flame air door is opened Degree (2) represents 2 layers of after-flame wind effect, and First air and secondary wind affect respectively the early stage and after burning situation of coal dust, after-flame Wind makes lower furnace portion form reproducibility atmosphere, reduces outlet NOXContent, the shadow into stove oxygen amount is described with flue gas oxygen content Ring, 18 input variables are chosen altogether, set up boiler export NOXConcentration prediction model.
2) choose certain unit load under 180MW-330MW 85 groups of data used as training sample, 25 groups of data are used as test Sample, carries out data prediction, by formula (3) by data normalization to [- 1,1], carries out instead by formula (4) after being exported Normalization.
X'=(2x-xmax-xmin)/(xmax-xmin) (3)
X=[x'(xmax-xmin)+xmax+xmin]/2 (4)
3) modeling is trained to data using LS-SVM algorithms, and model is verified.Furnace outlet NOxConcentration is pre- The training effect for surveying model and prediction effect verify curve as shown in Figure 3 and Figure 4, it can be seen that model prediction accuracy It is higher, furnace outlet NO can be metxThe requirement of real-time estimate.
SCR reactor phantoms take its mechanism model, and ammonia flow is taken as to the transmission function of control valve aperture：
Optimization time domain M=2, control time domain P=10 in DMC control methods, the control of PID submaster controllers adoption rate, ginseng Number is adjusted as P=0.1, NOXConcentration target value is set to 50mg/m3, it is controlled emulation.Respectively to conventional cascade PID and Ben Fa Intelligent Feed-forward DMC-PID of bright proposition is controlled effect emulation.At the T=3000 seconds, operating condition changes, and simulated effect is such as Shown in Fig. 5, Fig. 6 and Fig. 7.
From analogous diagram as can be seen that the overshoot in step response of cas PID control mode is larger, although outlet NOXConcentration Less than 50, non-discharge beyond standards, but ammonia spraying amount is drastically raised, and causes the waste of reducing agent, while also bringing the escaping of ammonia numerical value to swash Increase, this can have a strong impact on the normal operation of air downstream preheater.And the DMC control methods of Intelligent Feed-forward signal are based in step Export steady in response process, in outlet NOXOn the premise of control effect non-overshoot, ammonia spraying amount and the escaping of ammonia are all controlled reasonable Scope, control effect is good.When operating mode changes, in PID control scheme, postponed and SCR denitration within 120 seconds due to detection System itself postpones for 54 seconds, causes to export NOXAfter concentration change in 174 seconds, valve does not have action, then slow through detection in 120 seconds Prolong, at 3300 seconds, valve experienced NOXConcentration change, starts to adjust ammonia spraying amount, exports NOXFluctuation of concentration is larger, eventually passes through Certain hour, SCR outlet NOXConcentration is stable in 50mg/m3.In feedforward DMC control programs, after adding feed-forward control signals, valve Door immediately begins to adjust ammonia spraying amount, so after detection in 120 seconds postpones, its outlet NOXConcentration change is less, although ammonia spraying amount Fluctuation is slightly larger than PID control scheme, but its escaping of ammonia rate and outlet NOXConcentration is respectively less than PID control scheme and DMC controlling parties Case, reduces secondary pollution, in control SCR outlet NOXWhile concentration, precise control ammonia spraying amount reduces the escaping of ammonia rate.
The above, the only specific embodiment of the present invention, but protection scope of the present invention is not limited thereto, any Those familiar with the art the invention discloses technical scope in, change or replacement can be readily occurred in, all should contain Cover within protection scope of the present invention.

Claims (10)

1. a kind of SCR denitration system ammonia spraying amount Optimal Control System based on Intelligent Feed-forward signal, it is characterised in that：Including：NOX Concentration target value setting unit, Intelligent Feed-forward controller unit, DMC controller units, PID controller unit sprays ammonia valve door, SCR reactors, wherein, the NOXConcentration target value setting unit is connected by subtractor with the input of DMC controller units, The output of DMC controller units is controlled after being added with the output of Intelligent Feed-forward controller unit as the input of PID controller unit, PID The output of device unit processed is connected with the input of spray ammonia valve door, and PID controller unit is constituted with spray ammonia valve door Jing unity negative feedbacks Inner looping control subsystem, the output for spraying ammonia valve door is connected with the input of SCR reactors, wherein the output of SCR reactors and NOX Concentration target value setting unit is input into after subtracting each other as DMC controller units, constitutes negative feedback control loop.
2. system according to claim 1, it is characterised in that：The Intelligent Feed-forward controller unit includes furnace outlet NOX Concentration prediction module and feedforward control amount conversion module, wherein, the furnace outlet NOXConcentration prediction module is defeated according to boiler side Enter furnace outlet NO described in parameter real-time estimateXConcentration, feedforward control amount conversion module is by above-mentioned furnace outlet NOXConcentration Real-time estimate value is scaled the feedforward control amount.
3. system according to claim 2, it is characterised in that：Feedforward control amount conversion module is by the furnace outlet NOXConcentration real-time estimate value is scaled valve opening variable quantity, and used as feedforward control amount, its reduction formula is：
Δ n = ( Δc N O x · Q · M NH 3 · η M N O x · 10 - 6 - b ) / k - - - ( 1 )
Δ y=k Δ n+b (2)
Wherein：Δ n is valve opening variable quantity；ΔcNOxIt is furnace outlet NOXConcentration change amount, is furnace outlet NOXConcentration reality When predictive value and current time NOXDifference between concentration actual value, unit is mg/m3；Q is flue gas flow, and unit is m3/h；η For denitration efficiency；MNOxIt is NH3And NOXMolal weight；Δ y is ammonia spraying amount variable quantity；Ammonia spraying amount and valve opening it Between be linear function, k and b is fitting coefficient in function, and calculated ammonia spraying amount variation delta y obtains valve and open through inverse Degree variation delta n.
4. the system according to Claims 2 or 3, it is characterised in that：The furnace outlet NOXConcentration prediction module input ginseng Number includes：Boiler load, total blast volume, coal pulverizer coal-supplying amount, total fuel quantity, oxygen amount, secondary wind, burnout degree etc., according to described defeated Enter parameter change and adjust SCR system ammonia spraying amount in advance.
5. system according to claim 4, it is characterised in that：The furnace outlet NOXModel in concentration prediction module is adopted Built with data modeling, step is as follows：
1) the boiler side |input paramete is chosen, as the input variable of model, with the furnace outlet NOXConcentration is used as model Output variable；
2) the stable history data of certain hour length, line number of going forward side by side Data preprocess are chosen from unit historical data；
3) modeling is trained to data using least square method supporting vector machine LSSVM algorithms, and carries out model accuracy checking.
6. a kind of optimal control method of the networked control systems according to any one of claim 1-5, wherein anti-with the SCR Answer the outlet NO of deviceXConcentration is controlled volume, and the spray ammonia valve opening is used as controlled quentity controlled variable.
7. method according to claim 6, it is characterised in that：Wherein described DMC controller units adopt DMC PREDICTIVE CONTROLs Method, with the step response of controlled device as model basis, the SCR reactors are implemented Spline smoothing, are gone out to ammonia spraying amount Mouth NOXThe step response curve of concentration.
8. method according to claim 7, it is characterised in that：Optimization time domain and control in the DMC forecast Control Algorithms Time domain processed is gathered using examination and combines emulation mode.
9. the method according to claim 7 or 8, it is characterised in that：The PID controller is used to adjust the spray ammonia valve door Aperture, is adjusted using PI and is adjusted, and is adjusted using attenuation curve method.
10. the method according to any one of claim 6-9, it is characterised in that：The outlet NOXConcentration set point is set to 40-50mg/m3。
CN201710002535.6A 2017-01-03 2017-01-03 SCR denitration system ammonia spraying quantity optimal control system and method based on intelligent feedforward signals Pending CN106681381A (en)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090252665A1 (en) * 2008-04-07 2009-10-08 William Downs Enhancement of conventional scr and sncr processes with ammonia destruction catalyst
CN104607042A (en) * 2014-12-26 2015-05-13 东南大学 Selective catalytic reduction (SCR) denitration system and method based on constraint predictive control
CN104826493A (en) * 2015-04-23 2015-08-12 华北电力大学（保定） Control method for selective catalytic reduction flue gas denitrification system
CN105700504A (en) * 2016-02-24 2016-06-22 东南大学 SCR system automatic control method based on ammonia spraying sensitive valve locking
CN105739302A (en) * 2016-02-29 2016-07-06 西安西热锅炉环保工程有限公司 Control method for SCR denitration system based on sensitive factor analysis
CN105786035A (en) * 2016-03-29 2016-07-20 东南大学 Thermal power set SCR denitration optimization control system based on heuristic prediction control technology

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090252665A1 (en) * 2008-04-07 2009-10-08 William Downs Enhancement of conventional scr and sncr processes with ammonia destruction catalyst
CN104607042A (en) * 2014-12-26 2015-05-13 东南大学 Selective catalytic reduction (SCR) denitration system and method based on constraint predictive control
CN104826493A (en) * 2015-04-23 2015-08-12 华北电力大学（保定） Control method for selective catalytic reduction flue gas denitrification system
CN105700504A (en) * 2016-02-24 2016-06-22 东南大学 SCR system automatic control method based on ammonia spraying sensitive valve locking
CN105739302A (en) * 2016-02-29 2016-07-06 西安西热锅炉环保工程有限公司 Control method for SCR denitration system based on sensitive factor analysis
CN105786035A (en) * 2016-03-29 2016-07-20 东南大学 Thermal power set SCR denitration optimization control system based on heuristic prediction control technology

Cited By (63)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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