CN111505940A - Has future NOXFlue gas denitration control method with discharge amount prediction function - Google Patents

Has future NOXFlue gas denitration control method with discharge amount prediction function Download PDF

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CN111505940A
CN111505940A CN202010332255.3A CN202010332255A CN111505940A CN 111505940 A CN111505940 A CN 111505940A CN 202010332255 A CN202010332255 A CN 202010332255A CN 111505940 A CN111505940 A CN 111505940A
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nox emission
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潘为刚
王目树
徐丽娜
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Shandong Jiaotong University
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Abstract

The invention discloses a flue gas denitration control method with a future NOx emission prediction function, which comprises the following steps: a) obtaining an opening instruction C of an ammonia spraying actuator; b) acquiring an actual value of the NOx emission; c) calculating a predicted value of the NOx emission amount; d) solving a correction value of the SP; e) the input control mode. According to the flue gas denitration control method, the model controller generates the opening instruction C of the ammonia spraying actuator through calculation and processing of the actual value PV of the NOx emission, the set value SP, the predicted value of the NOx emission, the main control output of the boiler and the total air volume, so that the opening instruction C can predict the change of the NOx emission, and therefore before the change of NOx is collected by the automatic flue gas monitoring system CEMS, the output instruction of the actuator is accurately corrected and controlled in advance, the problem that the existing PID control always generates obvious hysteresis overshoot and even has a divergence characteristic is solved, and stable and accurate NOx emission can still be continuously obtained on a production site with strong disturbance.

Description

Has future NOXFlue gas denitration control method with discharge amount prediction function
Technical Field
The invention relates to a flue gas denitration control method, in particular to a flue gas denitration control method with a future NOx emission prediction function.
Background
The emission control of nitrogen oxides (NOx) is listed as the key point of emission reduction at the present stage of China. Under the background, a denitration device is arranged in a matching way in a new thermal generator set, and an old set which is already built and put into production is also continuously arrangedAnd an SCR or SNCR denitration system is additionally arranged through equipment and process modification. The selective catalytic reduction SCR process is a mature industrial denitration technology and has the principle that NO and NOx are selectively reduced into N under the conditions that the flue gas temperature is 300 ℃ and 400 ℃ and the catalyst action2While almost no NH occurs3And O2Oxidation reaction of (3). Theoretically, by reasonably controlling the temperature and the ammonia injection amount in the reaction zone, NH can be ensured3The denitration efficiency is maintained above 90% while the escape amount is low.
In the SCR process, the most important control is the ammonia injection control. When NH is present3When the molar ratio of the mixed reaction zone and the NOx is 1, the denitration efficiency reaches the highest. If the ammonia injection amount is too low, the NOx content at the outlet of the SCR is relatively increased, the denitration efficiency is reduced, and the emission reduction requirement of an environmental protection department cannot be met; if the ammonia injection amount is too high, the ammonia escape amount will be increased, which is not only uneconomical, but also causes the blockage of the air preheater and the secondary pollution of the emission of toxic ammonia substances due to the crystallization generated by the reaction of the low-temperature area (air preheater) behind the SCR reaction area and the acidic substances in the flue gas.
The accurate and reasonable control of the ammonia injection flow is the premise of the efficient operation of the SCR process. However, due to NH3The reaction with NOx is a process with large delay and large inertia, and the filtering-continuous sampling-condensing-secondary filtering-chemical analysis process of the CEMS has obvious delay, in the system with large delay, after the ammonia injection flow regulating valve is changed, a long delay time is always needed to be passed through to influence NOXThe monitoring amount is changed, so that the traditional PID control always generates obvious hysteresis overshoot and even has divergence characteristics; moreover, the change of the NOx content in the boiler exhaust smoke is a very complicated process, is greatly influenced by parameters such as unit load, air quantity, coal type, SOFA (over-fire air) air door opening at the top of the low-nitrogen combustor and the like, and has different delay characteristics; in a peak regulation unit and even an AGC peak regulation unit, due to the time-varying property of coal feeding quantity and air quantity and the strong disturbance characteristic of change of NOx in flue gas, the internal disturbance and the external disturbance of a system are extremely large, and the problems of industrial control are difficult to solve by the traditional field control means such as manual control, PID automatic control and the like.
Disclosure of Invention
In order to overcome the defects of the technical problems, the invention provides a flue gas denitration control method with a future NOx emission prediction function.
The invention discloses a flue gas denitration control method with a future NOx emission prediction function, which is characterized by comprising the following steps of:
a) calculating an opening instruction of an ammonia spraying actuator, setting a set value of NOx emission as SP, inputting the set value by an operator according to requirements, and setting a model controller as Gc(ii) a The sum of the main control output and the total air volume of the boiler is used as the offset of the set value of the NOx emission, the sum is firstly added with SP, the obtained result is then subtracted from the corrected value D1 of the SP to obtain D2, D2 is the model controller GcInput signal of (2), via a model controller GcOutputting an opening instruction C of an ammonia spraying actuator after internal algorithm operation;
b) obtaining actual value of NOx emission, set GpFor industrial processes for controlling NOx emissions, GnIn order to cause the process of the disturbance of the NOx emission, STEP1 is a disturbance source; detecting and obtaining an actual value PV of NOx emission by using a sensor or a transmitter, wherein PV is an industrial process GpAnd the occurrence of a perturbation process GnThe amount of overlap of (a);
c) calculating the predicted value of NOx emission, and setting the mathematical model as GmSending the opening instruction of the ammonia spraying actuator into a mathematical model GmObtaining a predicted value of the NOx emission amount after operation;
d) the difference between the actual value PV of the NOx emission and the predicted value of the NOx emission is calculated and passed through a filter GfObtaining a correction value D1 and D1 of the set value SP of the NOx emission amount for correcting the SP; modified SP's are sent to model controller GcCalculating an opening instruction of an ammonia spraying actuator;
e) the input control mode, the coal burning system is continuously controlled by the control method from the step a) to the step d).
The invention relates to a flue gas denitration control method with a future NOx emission prediction function, which comprises the following closed-loop transfer functions:
Figure BDA0002465378680000031
wherein, ypv(s) is the system output state, rsp(s) is given for the system, n(s) is the system disturbance, GcFor model controller, GmAs a mathematical model, GpFor industrial processes for controlling NOx emissions, GfA filter controlled for the model; y ispv(s) is the actual value PV, r of the NOx emissionsp(s) Process G of disturbing the NOx emissions for the set value SP, n(s) of NOx emissionsn。
The invention relates to a flue gas denitration control method with a future NOx emission prediction function, and a mathematical model GmThe mathematical model G is obtained by data iteration and system identificationmThe parameters comprise transmission gain KI, delay time T and inertia time T; the method for obtaining the transmission gain KI comprises the following steps: when the flue gas denitration control system is in a steady state, a controlled object disturbance test method is adopted, the opening instruction C of the ammonia spraying actuator is changed by x%, the change of the actual value PV of the NOx emission is measured to be y%, and then the transmission gain KI is y/x;
the method for solving the delay time T and the inertia time T comprises the following steps: carrying out a disturbance test for not less than 48h, carrying out the disturbance test every 30-40 min, and setting the number of times of carrying out the disturbance test as n; in the ith disturbance test process, when the flue gas denitration control system is in a steady state, adding a step disturbance signal to an opening command C of an ammonia spraying actuator at the time t1i, monitoring the change time of an actual value PV of the NOx emission, recording the change time as t2i, and keeping the delay time ti which is t2i-t1 i; 1,2 …, n; the delay time t is 1/n (t1+ t2+ … + tn);
monitoring the change end time of the actual value PV of the NOx emission, recording as t3i, starting the inertia time from t2i and ending the time to t3 i; in the ith disturbance test process, the high peak value of the change of the opening command C of the ammonia injection actuator is differentiated from the underestimation value of the actual value PV of the NOx emission to obtain time T1i, and meanwhile, the high peak value of the actual value PV of the NOx emission is differentiated from the low valley value of the change of the opening command C of the ammonia injection actuator to obtain time T2i, i is 1,2 …, n; then the inertia time T is 1/n (T11+ T12+ … + T1n + T21+ T22+ … + T2n) 1/2.
The invention relates to a flue gas denitration control method with a future NOx emission prediction function, which is implemented by using a mathematical model G through a disturbance testmThe curve is regarded as a second-order inertia characteristic, the total inertia delay time range is 330-380 s, the delay time T range is 80-100 s, the inertia time T range is 250-350 s, and the transfer gain range is 0.6-0.8; and performing an iterative algorithm on the inertia time T and the delay time T within the obtained total time, sequentially substituting the inertia time T and the delay time T into a transfer function of the flue gas denitration control method, and comparing to obtain the representation that the best denitration effect is achieved when the NOx emission value is minimum, so as to obtain the optimal inertia time T and the optimal delay time T.
According to the flue gas denitration control method with the future NOx emission prediction function, the closed-loop Transfer function is a second-order inertia mathematical model and is characterized by connecting two Transfer Fcn functional blocks in series, and the Transfer function characterized by the Transfer Fcn functional blocks is as follows:
Figure BDA0002465378680000041
wherein u(s) and y(s) are respectively input and output of the system, nn and nd are respectively items of numerator and denominator coefficients, num(s) and den(s) comprise coefficients s of numerator and denominator with weight reduction, and the order of denominator is greater than or equal to that of numerator; for a single output system, the inputs and outputs of the functional block are scalar time domain signals.
The invention relates to a flue gas denitration control method with a future NOx emission prediction Function, wherein the main control output of a boiler is the NOx content in flue gas before denitration, the NOx content and the total air volume in the flue gas before denitration are respectively processed by a broken line Function S-Function and S-Function1 and then added, then the sum of the processed NOx content and the total air volume is added with the set value SP of the NOx emission as 50, and the obtained result is differed with the actual value PV of the NOx emission to obtain a model controller GcInput signal D2;
model controller GcIn turn by gainThe Gain control method comprises an algorithm block Gain3, a pole-zero algorithm block transfer Fcn6 and a pole-zero algorithm block transfer Fcn7 which are connected in series to realize the operation processing of an input signal D2 and output an opening instruction C of an ammonia spraying actuator, wherein the Gain of the Gain algorithm block Gain3 is-0.2, and the pole-zero algorithm block transfer Fcn6 and the transfer Fcn7 are (200s +1)/(180s + 1); the mathematical model is GmThe device sequentially comprises an amplitude limiting function block MinMax1, a Gain algorithm block Gain2, a pole-zero algorithm block transfer Fcn2, a pole-zero algorithm block transfer Fcn5 and a delay algorithm block transfer delay1, wherein the amplitude limiting value of the amplitude limiting function block MinMax1 is 10, the Gain of the Gain algorithm block Gain2 is-4, the pole-zero algorithm blocks transfer Fcn2 and transfer Fcn5 are both 1/(100s +1), and an ammonia spraying actuator opening instruction C is input to the amplitude limiting function block MinMax 1;
said industrial process GpThe denitration flue gas denitration system is composed of a multiplication function module Product1, a multiplication function module Product8, a Gain algorithm block Gain4, a Gain algorithm block Gain5, a Gain algorithm block Gain1, a zero pole algorithm block transfer Fcn1 and a Delay algorithm block transfer Delay2, wherein the pressure of flue gas before denitration and the concentration of NOx in the flue gas before denitration are multiplied by the multiplication function module Product8 and then processed by the Gain algorithm block Gain4, an ammonia injection pressure, an ammonia injection flow and an ammonia injection actuator opening instruction C are multiplied by the multiplication function module Product1 and then processed by the Gain algorithm block Gain5, output signals of a Gain algorithm block Gain4 and a Gain5 are subjected to difference operation and then input to the Gain algorithm block Gain1 for processing, an output signal of Gain1 is subjected to processing by the zero pole algorithm block transfer Fcn1 and then input to the Delay algorithm block transfer 1 and then input to the Delay algorithm block transfer Delay 638, and an output signal of a disturbance source 1 is added to the Delay algorithm block transfer Delay 638 and then input to the Delay algorithm block Delay algorithm block G638 and output in the Delay algorithm block Delay Delay 638pAnd the occurrence of a perturbation process GnThe amount of overlap of (a); the Gain of the Gain block Gain4 and the Gain block Gain5 are both 10, the zero-pole algorithm block transfer Fcn1 is 6/(20s +1), and the value of the disturbance source signal Constant1 is 23.
The invention has the beneficial effects that: the flue gas denitration control method takes a boiler main control output function and a total air volume function as the offset of a set value of NOx emission amount, namely SP, and adds the offset to the set value of the NOx emission amount; simultaneously, the actual value PV of the NOx emission amount and a mathematical model G are comparedmPrediction of outputThe values are subtracted and filtered to be used as a corrected value of a set value SP, the set value SP is added with an offset and then subtracted with the corrected value to obtain a signal which is used as an input signal of a model controller, so that the model controller generates an opening instruction C of an ammonia spraying actuator through calculation and processing of an actual NOx emission value PV, the set value SP, a predicted NOx emission value, boiler main control output and total air volume, the change of the NOx emission value can be predicted, accurate correction and control are carried out on an actuator output instruction in advance before the change of NOx is collected by a flue gas automatic monitoring system (CEMS), the problem that the existing PID control always generates obvious hysteresis overshoot and even has a divergence characteristic is solved, and stable and accurate NOx emission can be continuously obtained on a production site showing strong disturbance.
Drawings
FIG. 1 is a control schematic diagram of a flue gas denitration control method with a future NOx emission prediction function according to the present invention;
FIG. 2 is a SAMA engineering configuration diagram of the flue gas denitration control method with a future NOx emission prediction function according to the present invention;
fig. 3 is a Simlink diagram of the application of the flue gas denitration control method with the future NOx emission prediction function based on the MAT L AB platform.
Detailed Description
The invention is further described with reference to the following figures and examples.
Referring to fig. 1 and fig. 2, a control schematic diagram and a SAMA engineering configuration diagram of a flue gas denitration control method with a future NOx emission prediction function according to the present invention are respectively shown, in fig. 1, SP is a set value of NOx emission, GcFor model controller, GmAs a mathematical model, GpFor industrial processes for controlling NOx emissions, GnIn order to cause the process of the disturbance of the NOx emission, STEP1 is a disturbance source; PV is an industrial process GpAnd the occurrence of a perturbation process GnBO is the boiler master control output, FT is the total air volume, F (X) is a function, + is the addition, Delta is the deviation (difference) of solution, FI L TER is inertial filteringAnd C is an opening instruction of the ammonia spraying actuator. The flue gas denitration control method with the future NOx emission prediction function is realized by the following steps:
a) calculating an opening instruction of an ammonia spraying actuator, setting a set value of NOx emission as SP, inputting the set value by an operator according to requirements, and setting a model controller as Gc(ii) a The sum of the main control output and the total air volume of the boiler is used as the offset of the set value of the NOx emission, the sum is firstly added with SP, the obtained result is then subtracted from the corrected value D1 of the SP to obtain D2, D2 is the model controller GcInput signal of (2), via a model controller GcOutputting an opening instruction C of an ammonia spraying actuator after internal algorithm operation;
b) obtaining actual value of NOx emission, set GpFor industrial processes for controlling NOx emissions, GnIn order to cause the process of the disturbance of the NOx emission, STEP1 is a disturbance source; detecting and obtaining an actual value PV of NOx emission by using a sensor or a transmitter, wherein PV is an industrial process GpAnd the occurrence of a perturbation process GnThe amount of overlap of (a);
c) calculating the predicted value of NOx emission, and setting the mathematical model as GmSending the opening instruction of the ammonia spraying actuator into a mathematical model GmObtaining a predicted value of the NOx emission amount after operation;
d) the difference between the actual value PV of the NOx emission and the predicted value of the NOx emission is calculated and passed through a filter GfObtaining a correction value D1 and D1 of the set value SP of the NOx emission amount for correcting the SP; modified SP's are sent to model controller GcCalculating an opening instruction of an ammonia spraying actuator;
e) the input control mode, the coal burning system is continuously controlled by the control method from the step a) to the step d).
In fig. 1, the closed-loop transfer function of the flue gas denitration control method is as follows:
Figure BDA0002465378680000071
wherein, ypv(s) is the system output state, rsp(s) is given for the system,n(s) is system disturbance, GcFor model controller, GmAs a mathematical model, GpFor industrial processes for controlling NOx emissions, GfA filter controlled for the model; y ispv(s) is the actual value PV, r of the NOx emissionsp(s) Process G of disturbing the NOx emissions by the set value SP, n(s) for the NOx emissionsn。
When the filter GfWhen 1, assume a process element Gp、GmAnd GcAre stable, the controller gain Gc (0) and the model gain Gm (0) are reciprocal, the control deviation:
Figure BDA0002465378680000072
and the system can eliminate the static deviation after responding to the input deviation and the disturbance no matter any deviation or disturbance exists, and the tracking of PV on SP is realized. Therefore, the process mathematical model is similar to the field control law.
In fig. 2, the input of the NOx control process is expressed as the real-time monitored amount PV of NOx, and the output is expressed as the NOx removal actuator ammonia injection throttle command C. After the command opening C of the denitration actuator is established, the ammonia injection regulating valve is opened, and the ammonia-air mixed gas is sent into the SCR to react with NOx to change the NOx emission PV. This industrial process is a nitrogen oxide control process. And the NOx set value for automatic denitration control is generated by superposing an operator set value SP, a function of main control output of the boiler and a function of total air volume. The main control output of the boiler and the total air volume of the boiler are important factors influencing the NOx emission in the industrial process, so that a function of the main control output of the boiler and a function of the total air volume are selected.
Mathematical model GmThe mathematical model G is obtained by data iteration and system identificationmThe parameters comprise transmission gain KI, delay time T and inertia time T; the method for obtaining the transmission gain KI comprises the following steps: when the flue gas denitration control system is in a steady state, a controlled object disturbance test method is adopted, the opening instruction C of the ammonia spraying actuator is changed by x%, the change of the actual value PV of the NOx emission is measured to be y%, and then the transmission gain KI is y/x;
the method for solving the delay time T and the inertia time T comprises the following steps: carrying out a disturbance test for not less than 48h, carrying out the disturbance test every 30-40 min, and setting the number of times of carrying out the disturbance test as n; in the ith disturbance test process, when the flue gas denitration control system is in a steady state, adding a step disturbance signal to an opening command C of an ammonia spraying actuator at the time t1i, monitoring the change time of an actual value PV of the NOx emission, recording the change time as t2i, and keeping the delay time ti which is t2i-t1 i; 1,2 …, n; the delay time t is 1/n (t1+ t2+ … + tn);
monitoring the change end time of the actual value PV of the NOx emission, recording as t3i, starting the inertia time from t2i and ending the time to t3 i; in the ith disturbance test process, the high peak value of the change of the opening command C of the ammonia injection actuator is differentiated from the underestimation value of the actual value PV of the NOx emission to obtain time T1i, and meanwhile, the high peak value of the actual value PV of the NOx emission is differentiated from the low valley value of the change of the opening command C of the ammonia injection actuator to obtain time T2i, i is 1,2 …, n; then the inertia time T is 1/n (T11+ T12+ … + T1n + T21+ T22+ … + T2n) 1/2.
By disturbance test, the mathematical model G ismThe curve is regarded as a second-order inertia characteristic, the total inertia delay time range is 330-380 s, the delay time T range is 80-100 s, the inertia time T range is 250-350 s, and the transfer gain range is 0.6-0.8; and performing an iterative algorithm on the inertia time T and the delay time T within the obtained total time, sequentially substituting the inertia time T and the delay time T into a transfer function of the flue gas denitration control method, and comparing to obtain the representation that the best denitration effect is achieved when the NOx emission value is minimum, so as to obtain the optimal inertia time T and the optimal delay time T.
The closed loop Transfer function is a second-order inertial mathematical model and is characterized by two Transfer Fcn functional blocks which are connected in series, and the Transfer function characterized by the Transfer Fcn functional blocks is as follows:
Figure BDA0002465378680000081
wherein u(s) and y(s) are respectively input and output of the system, nn and nd are respectively items of numerator and denominator coefficients, num(s) and den(s) comprise coefficients s of numerator and denominator with weight reduction, and the order of denominator is greater than or equal to that of numerator; for a single output system, the inputs and outputs of the functional block are scalar time domain signals. Wherein the numerator coefficient vector of the transfer function at the inputs of the numerator coeffients and the Denominator coefficient vector of the transfer function at the inputs of the Denominator coeffients. In an embodiment, the second order inertial mathematical model is characterized by two Transfer Fcn function blocks in series, with T and T placed in the parameter table of the Transfer Fcn function block.
The input of the process mathematical model is an actuator opening degree C; the output is the theoretical discharge amount of the predicted NOx according to a mathematical model, and the theoretical discharge amount of the predicted NOx is subtracted from the actual NOx discharge amount PV to obtain the difference between the model and the actual NOx discharge amount, which represents the deviation D1 between the predicted NOx amount and the actual NOx discharge amount after the ammonia injection amount is changed by the action of an actuator of the denitration system.
The sum of the function of the main control output of the boiler and the function of the total air volume is used as the offset of the NOx set value, the offset is added with the output of the NOx operator set value, and the offset D1 obtained by the calculation is subtracted to obtain a new offset D2, and the specific SAMA schematic diagram is shown in figure 2. The meaning of the deviation D2 is that the change in the NOx set point, along with the model predicted deviation D1, is the basis for the next actuator command generation. The command operation unit for denitration automatic control is formed by connecting an inverse model controller MC and an inertia filter in series. And (3) a reverse model controller, namely, the reciprocal of a pure inertia link after a delay link is removed from a process mathematical model of the SISO denitration system.
The change rule of NOx is randomly changed along with time due to the changes of unit load and boiler operation conditions in the operation process, namely the control of NOx is a time-varying system, and a process mathematical model G of a controlled objectcDeviation occurs in the transmission rule of the on-site NOx control process, and then data before analysis is needed to be subjected to data coefficient iteration, the optimal parameters obtained in real time are brought into a process mathematical model GcIn (1).
As shown in fig. 3, a Simlink diagram applied based on the MAT L AB platform is shown, in fig. 3, ADD is an addition function block, Product is a multiplication function block, S-function is a segment function written in MAT L AB, Gain is a Gain algorithm block, Transfer fcn is a zero-pole algorithm block (lead-lag algorithm block), MinMax is a limiting function block, Transfer Delay is a Delay algorithm block, and subtrect is a deviation solving function block.
The main control output of the boiler is NOx content in the flue gas before denitration, the NOx content and the total air volume in the flue gas before denitration are respectively processed by a broken line Function S-Function and S-Function1 and then added, the sum is added with the set value SP of NOx emission to 50, and the obtained result is differed with the actual value PV of the NOx emission to obtain the model controller GcInput signal D2;
model controller GcThe device sequentially comprises a Gain algorithm block Gain3, a pole-zero algorithm block transfer Fcn6 and a pole-zero algorithm block transfer Fcn7 which are connected in series, so that the operation processing of an input signal D2 is realized, an opening instruction C of an ammonia spraying actuator is output, the Gain of the Gain algorithm block Gain3 is-0.2, and the pole-zero algorithm blocks transfer Fcn6 and transfer Fcn7 are (200s +1)/(180s + 1); the mathematical model shown is GmThe device sequentially comprises an amplitude limiting function block MinMax1, a Gain algorithm block Gain2, a pole-zero algorithm block transfer Fcn2, a pole-zero algorithm block transfer Fcn5 and a delay algorithm block transfer delay1, wherein the amplitude limiting value of the amplitude limiting function block MinMax1 is 10, the Gain of the Gain algorithm block Gain2 is-4, the pole-zero algorithm blocks transfer Fcn2 and transfer Fcn5 are both 1/(100s +1), and an ammonia spraying actuator opening instruction C is input to the amplitude limiting function block MinMax 1;
shown industrial Process GpThe denitration flue gas denitration system comprises a multiplication function module Product1, a multiplication function module Product8, a Gain algorithm block Gain4, a Gain algorithm block Gain5, a Gain algorithm block Gain1, a pole-zero algorithm block transfer Fcn1 and a Delay algorithm block Transport Delay2, wherein the pressure of flue gas before denitration and the concentration of NOx in the flue gas before denitration are multiplied by the multiplication function module Product8 and then processed by the Gain algorithm block Gain4, an ammonia injection pressure, an ammonia injection flow and an ammonia injection actuator opening instruction C are multiplied by the multiplication function module Product1 and then processed by the Gain algorithm block Gain5, and output signals of the Gain algorithm block Gain4 and the Gain5 are subjected to difference operation and then input to the Gain operation block Gain5Processing by a method block Gain1, processing an output signal of Gain1 by a zero-pole algorithm block transfer Fcn1, adding the processed output signal with a disturbance source signal Constant1, inputting the added output signal into a Delay algorithm block transfer Delay2, and outputting an industrial process G by a transfer Delay2pAnd the occurrence of a perturbation process GnThe amount of overlap of (a); the Gain of the Gain block Gain4 and the Gain block Gain5 are both 10, the zero-pole algorithm block transfer Fcn1 is 6/(20s +1), and the value of the disturbance source signal Constant1 is 23.
Compared with the prior art, the flue gas denitration optimization control system based on the mathematical model has the advantages that: according to the traditional automatic control method based on PI and PID, the output of an actuator and the obtained NOx emission always show hysteresis, and NOx is difficult to control in a strong disturbance production site.

Claims (6)

1. A flue gas denitration control method with a future NOx emission prediction function is characterized by comprising the following steps of:
a) calculating an opening instruction of an ammonia spraying actuator, setting a set value of NOx emission as SP, inputting the set value by an operator according to requirements, and setting a model controller as Gc(ii) a The sum of the main control output and the total air volume of the boiler is used as the offset of the set value of the NOx emission, the sum is firstly added with the SP, the obtained result is then subtracted from the corrected value D1 of the SP to obtain D2, and D2 is a model controller GcInput signal of (2), via a model controller GcOutputting an opening instruction C of an ammonia spraying actuator after internal algorithm operation;
b) obtaining actual value of NOx emission, set GpFor industrial processes for controlling NOx emissions, GnIn order to cause the process of the disturbance of the NOx emission, STEP1 is a disturbance source; using sensors or variablesThe actual value PV of the NOx emission is obtained by the detection of the transmitter, and PV is the industrial process GpAnd the occurrence of a perturbation process GnThe amount of overlap of (a);
c) calculating the predicted value of NOx emission, and setting the mathematical model as GmSending the opening instruction of the ammonia spraying actuator into a mathematical model GmObtaining a predicted value of the NOx emission amount after operation;
d) the difference between the actual value PV of the NOx emission and the predicted value of the NOx emission is calculated and passed through a filter GfObtaining a correction value D1 and D1 of the set value SP of the NOx emission amount for correcting the SP; modified SP's are sent to model controller GcCalculating an opening instruction of an ammonia spraying actuator;
e) the input control mode, the coal burning system is continuously controlled by the control method from the step a) to the step d).
2. The flue gas denitration control method with a future NOx emission prediction function according to claim 1, characterized in that the closed-loop transfer function of the flue gas denitration control method is:
Figure FDA0002465378670000011
wherein, ypv(s) is the system output state, rsp(s) is given for the system, n(s) is the system disturbance, GcFor model controller, GmAs a mathematical model, GpFor industrial processes for controlling NOx emissions, GfA filter controlled for the model; y ispv(s) is the actual value PV, r of the NOx emissionsp(s) Process G of disturbing the NOx emissions for the set value SP, n(s) of NOx emissionsn。
3. The flue gas denitration control method with a future NOx emission amount prediction function according to claim 1 or 2, characterized in that the mathematical model GmThe mathematical model G is obtained by data iteration and system identificationmIncluding the transfer gain KI, the delayTime T, inertia time T; the method for obtaining the transmission gain KI comprises the following steps: when the flue gas denitration control system is in a steady state, a controlled object disturbance test method is adopted, the opening instruction C of the ammonia spraying actuator is changed by x%, the change of the actual value PV of the NOx emission is measured to be y%, and then the transmission gain KI is y/x;
the method for solving the delay time T and the inertia time T comprises the following steps: carrying out a disturbance test for not less than 48h, carrying out the disturbance test every 30-40 min, and setting the number of times of carrying out the disturbance test as n; in the ith disturbance test process, when the flue gas denitration control system is in a steady state, adding a step disturbance signal to an opening command C of an ammonia spraying actuator at the time t1i, monitoring the change time of an actual value PV of the NOx emission, recording the change time as t2i, and keeping the delay time ti which is t2i-t1 i; 1,2 …, n; the delay time t is 1/n (t1+ t2+ … + tn);
monitoring the change end time of the actual value PV of the NOx emission, recording as t3i, starting the inertia time from t2i and ending the time to t3 i; in the ith disturbance test process, the high peak value of the change of the opening command C of the ammonia injection actuator is differentiated from the underestimation value of the actual value PV of the NOx emission to obtain time T1i, and meanwhile, the high peak value of the actual value PV of the NOx emission is differentiated from the low valley value of the change of the opening command C of the ammonia injection actuator to obtain time T2i, i is 1,2 …, n; then the inertia time T is 1/n (T11+ T12+ … + T1n + T21+ T22+ … + T2n) 1/2.
4. The flue gas denitration control method with a future NOx emission amount prediction function according to claim 3, characterized in that: by disturbance test, the mathematical model G ismThe curve is regarded as a second-order inertia characteristic, the total inertia delay time range is 330-380 s, the delay time T range is 80-100 s, the inertia time T range is 250-350 s, and the transfer gain range is 0.6-0.8; and performing an iterative algorithm on the inertia time T and the delay time T within the obtained total time, sequentially substituting the inertia time T and the delay time T into a transfer function of the flue gas denitration control method, and comparing to obtain the representation that the best denitration effect is achieved when the NOx emission value is minimum, so as to obtain the optimal inertia time T and the optimal delay time T.
5. The flue gas denitration control method with future NOx emission prediction function of claim 2, wherein the closed-loop Transfer function is a second-order inertial mathematical model, which is characterized by two Transfer Fcn function blocks in series, the Transfer function characterized by the Transfer Fcn function block being:
Figure FDA0002465378670000031
wherein u(s) and y(s) are respectively input and output of the system, nn and nd are respectively items of numerator and denominator coefficients, num(s) and den(s) comprise coefficients s of numerator and denominator with weight reduction, and the order of denominator is greater than or equal to that of numerator; for a single output system, the inputs and outputs of the functional block are scalar time domain signals.
6. The flue gas denitration control method with a future NOx emission amount prediction function according to claim 1, characterized in that: the main control output of the boiler is the NOx content in the flue gas before denitration, the NOx content and the total air volume in the flue gas before denitration are respectively processed by a broken line Function S-Function and an S-Function1 and then added, the sum is added with the set value SP (50) of the NOx emission, and the obtained result is differed with the actual value PV of the NOx emission to obtain the model controller GcInput signal D2;
model controller GcThe device sequentially comprises a Gain algorithm block Gain3, a pole-zero algorithm block transfer Fcn6 and a pole-zero algorithm block transfer Fcn7 which are connected in series, so that the operation processing of an input signal D2 is realized, an opening instruction C of an ammonia spraying actuator is output, the Gain of the Gain algorithm block Gain3 is-0.2, and the pole-zero algorithm blocks transfer Fcn6 and transfer Fcn7 are (200s +1)/(180s + 1); the mathematical model is GmThe amplitude limiting device sequentially comprises an amplitude limiting function block MinMax1, a Gain algorithm block Gain2, a pole-zero algorithm block transfer Fcn2, a pole-zero algorithm block transfer Fcn5 and a delay algorithm block transfer delay1, wherein the amplitude limiting value of the amplitude limiting function block MinMax1 is 10, the Gain of the Gain algorithm block Gain2 is-4, the pole-zero algorithm blocks transfer Fcn2 and transfer Fcn5 are both 1/(100s +1), and ammonia spraying is performedThe line driving device opening instruction C is input to the amplitude limiting function block MinMax 1;
said industrial process GpThe denitration flue gas denitration system is composed of a multiplication function module Product1, a multiplication function module Product8, a Gain algorithm block Gain4, a Gain algorithm block Gain5, a Gain algorithm block Gain1, a zero pole algorithm block transfer Fcn1 and a Delay algorithm block transfer Delay2, wherein the pressure of flue gas before denitration and the concentration of NOx in the flue gas before denitration are multiplied by the multiplication function module Product8 and then processed by the Gain algorithm block Gain4, an ammonia injection pressure, an ammonia injection flow and an ammonia injection actuator opening instruction C are multiplied by the multiplication function module Product1 and then processed by the Gain algorithm block Gain5, output signals of a Gain algorithm block Gain4 and a Gain5 are subjected to difference operation and then input to the Gain algorithm block Gain1 for processing, an output signal of Gain1 is subjected to processing by the zero pole algorithm block transfer Fcn1 and then input to the Delay algorithm block transfer 1 and then input to the Delay algorithm block transfer Delay 638, and an output signal of a disturbance source 1 is added to the Delay algorithm block transfer Delay 638 and then input to the Delay algorithm block Delay algorithm block G638 and output in the Delay algorithm block Delay Delay 638pAnd the occurrence of a perturbation process GnThe amount of overlap of (a); the Gain of the Gain block Gain4 and the Gain block Gain5 are both 10, the zero-pole algorithm block transfer Fcn1 is 6/(20s +1), and the value of the disturbance source signal Constant1 is 23.
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