CN117815855A - Feedforward denitration control method, feedforward denitration control system and NOx concentration prediction model - Google Patents
Feedforward denitration control method, feedforward denitration control system and NOx concentration prediction model Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 58
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 208
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 80
- 238000006477 desulfuration reaction Methods 0.000 claims abstract description 42
- 230000023556 desulfurization Effects 0.000 claims abstract description 42
- 230000001105 regulatory effect Effects 0.000 claims abstract description 38
- 238000004364 calculation method Methods 0.000 claims description 60
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 51
- 239000001301 oxygen Substances 0.000 claims description 51
- 229910052760 oxygen Inorganic materials 0.000 claims description 51
- 239000000446 fuel Substances 0.000 claims description 49
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 32
- 239000003546 flue gas Substances 0.000 claims description 32
- 238000012937 correction Methods 0.000 claims description 19
- 239000000779 smoke Substances 0.000 claims description 6
- XKMRRTOUMJRJIA-UHFFFAOYSA-N ammonia nh3 Chemical compound N.N XKMRRTOUMJRJIA-UHFFFAOYSA-N 0.000 claims description 5
- 230000010354 integration Effects 0.000 claims description 3
- 238000002347 injection Methods 0.000 abstract description 19
- 239000007924 injection Substances 0.000 abstract description 19
- 238000013499 data model Methods 0.000 abstract description 9
- 230000008859 change Effects 0.000 abstract description 8
- 238000002485 combustion reaction Methods 0.000 abstract description 6
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- 238000004458 analytical method Methods 0.000 description 4
- 239000000428 dust Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000005507 spraying Methods 0.000 description 3
- 239000003054 catalyst Substances 0.000 description 2
- 238000011217 control strategy Methods 0.000 description 2
- 230000004069 differentiation Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000000738 capillary electrophoresis-mass spectrometry Methods 0.000 description 1
- 239000004202 carbamide Substances 0.000 description 1
- 238000010531 catalytic reduction reaction Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
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Abstract
The invention belongs to the technical field of desulfurization and denitrification, and particularly relates to a feedforward denitrification control method, a feedforward denitrification control system and a NOx concentration prediction model. According to the feedforward denitration control method, single-side control is respectively carried out on the side A and the side B of a denitration system; single-sided control refers to: firstly generating a unilateral ammonia gas flow control quantity according to a unilateral PID component, a model feedforward quantity and a dynamic feedforward quantity, inputting the unilateral ammonia gas flow control quantity and an actual ammonia gas flow into a PID, calculating deviation by the PID, and obtaining a unilateral ammonia gas regulating command. According to the method, multivariable feedforward is combined with unilateral control, the unilateral inlet ammonia injection amount is dynamically adjusted in real time, the ammonia injection amount is rapidly adjusted according to the change of the combustion working condition of the boiler and the change of the concentration of NOx at the SCR outlet, the stability of the concentration of NOx at the desulfurization outlet is ensured, the problem of limitation of single variable output by a data model in the prior art for control is solved, and the problem of unbalance on the two sides of A/B in the prior art is also solved.
Description
Technical Field
The invention belongs to the technical field of desulfurization and denitrification, and particularly relates to a feedforward denitrification control method, a feedforward denitrification control system and a NOx concentration prediction model.
Background
SCR (Selective catalytic reduction), which means the use of NH 3 Or reducing agent such as urea reacts with NOx selectively under the action of catalyst to generate N 2 And H 2 O. The amount of ammonia injected directly determines the amount of NOx reduced. The SCR process mainly comprises the following steps: the original flue gas is discharged from a boiler flue, enters a denitration tower for denitration at first on the left side and the right side, then enters a desulfurization tower and a dust removal chamber for desulfurization and dust removal after the flue gas on the two sides is converged, finally is discharged into the atmosphere from a chimney, and the flue gas after desulfurization and dust removal is called as 'clean flue gas', and is output after denitration, desulfurization and dust removal from the ammonia gas sprayed by contact in the process. The SCR technology has the characteristics of high denitration efficiency, large flue gas treatment capacity and mature technology, and becomes a main denitration mode of the coal-fired power plant. According to the requirements of the emission standard of atmospheric pollutants of a thermal power plant, the average value of NOx emission in hours must be controlled at 50mg/m 3 Within the inner part.
On one hand, the reaction mechanism of the SCR denitration system is complex, the concentration of the outlet NOx is influenced by various factors such as smoke temperature, smoke flow, oxygen content, catalyst activity and the like, and the control system of the SCR denitration system shows strong nonlinearity and large time lag after long-term operation of the SCR denitration system due to the hysteresis influence of CEMS instrument measurement. On the other hand, as the demand of the power grid for unit frequency modulation and peak shaving is improved, the combustion working condition of the boiler is frequently changed, the fluctuation of flue gas parameters is large, the control index of the SCR denitration system is directly influenced, and the denitration NOx concentration instantaneous value is often out of standard or the automatic control loop is in a manual adjustment state for a long time.
At present, the unit is generally used for controlling the ammonia injection amount by adopting closed-loop control or model and closed-loop control strategy. Conventional "closed loop control" controls the amount of ammonia injected at the inlet based solely on the outlet NOx concentration. The model and the closed-loop control strategy predict the concentration of NOx through a data model, and then calculate the ammonia injection amount of the inlet and the outlet for real-time regulation and control. Such as: the invention patent publication No. CN112221347A discloses an accurate ammonia spraying control method for an SCR denitration system, which predicts the concentration of NOx at an inlet in real time through data model analysis, so that the total amount of denitration ammonia spraying is adjusted in real time, and the ammonia spraying adjustment is fed forward to each subarea according to the concentration of NOx discharged from each subarea. The method has a certain effect on controlling the NOx emission concentration at the outlet of the denitration system, but along with the adjustment of coal quality and combustion working conditions, the adaptability of the data model has a certain limitation, the parameters of the data model need to be adjusted, and the problem of unbalance at the two sides of the A/B can not be solved only by controlling the total amount of ammonia injection.
Disclosure of Invention
Aiming at the problems that a data model in the prior art has limitations and unbalance of an A\B side cannot be solved only by controlling total ammonia injection amount, the invention provides a feedforward denitration control method, a feedforward denitration control system and a NOx concentration prediction model. The feedforward denitration control method adopts the technical idea of combining multivariable feedforward and single-side control, dynamically adjusts the ammonia injection quantity of the single-side inlet in real time, rapidly adjusts the ammonia injection quantity according to the change of the combustion working condition of the boiler and the change of NOx at the SCR outlet, ensures the stability of the concentration of NOx at the desulfurization outlet, solves the problem of limitation of control by means of single variable output by a data model in the prior art, and also solves the problem of unbalance at the two sides of the A/B in the prior art.
First, the present invention provides a feedforward denitration control method, more specifically, a multivariable feedforward denitration control method.
A feedforward denitration control method is used for respectively carrying out single-side control on an A side and a B side of a denitration system; the single-side control means: firstly, generating a unilateral ammonia gas flow control quantity according to a unilateral PID component, a model feedforward quantity and a dynamic feedforward quantity, inputting the unilateral ammonia gas flow control quantity and the unilateral actual ammonia gas flow into a PID, calculating deviation by the PID and obtaining a unilateral ammonia gas regulating instruction, and finally realizing real-time regulation and control of the unilateral ammonia gas input quantity by the unilateral ammonia gas regulating instruction.
The model feedforward quantity of the single side is mainly calculated by the predicted value of the NOx concentration of the SCR outlet and the real-time value of the NOx concentration of the SCR outlet of the single side.
The single-side dynamic feedforward amount is mainly obtained by superposition of the single-side theoretical ammonia amount, the single-side fuel dynamic feedforward amount, the single-side oxygen dynamic feedforward amount and the A/B side balance component.
Further, in order to better implement the present invention, the method for acquiring the PID component on one side refers to: and acquiring a real-time value of the NOx concentration at the desulfurization outlet and a set value of the NOx concentration at the desulfurization outlet, taking the deviation of the real-time value of the NOx concentration at the desulfurization outlet and the set value of the NOx concentration at the desulfurization outlet as the input quantity of the single-side PID, and obtaining the single-side PID component through proportional and integral calculation and amplitude limiting.
Further, in order to better implement the present invention, the method for obtaining the model feedforward quantity of the single side refers to: outputting a predicted value of the NOx concentration of the single-side SCR outlet through a single-side NOx concentration prediction model, and simultaneously obtaining a real-time value of the NOx concentration of the single-side SCR outlet; and (3) superposing a difference value differential value between the predicted value of the SCR outlet NOx concentration output by the NOx concentration prediction model and the real value of the SCR outlet NOx concentration, outputting through a slope function, and multiplying by a gain coefficient to obtain the model feedforward quantity of the single side.
Further, in order to better implement the present invention, the method for obtaining the predicted value of the SCR outlet NOx concentration refers to: respectively inputting a single-side SCR outlet NOx concentration set value and a flue gas oxygen real-time value into the NOx concentration prediction model, obtaining a prediction reference value after the SCR outlet NOx concentration set value passes through a hysteresis function block and then passes through a reference model function, and obtaining a prediction value coefficient after the flue gas oxygen real-time value passes through a coefficient function; meanwhile, the NOx concentration set value at the SCR outlet on one side is subjected to hysteresis function block and then is subjected to difference with the NOx concentration real-time value at the desulfurization outlet, and the difference value is subjected to integral calculation and amplitude limiting to obtain a correction quantity; then, the correction amount is added to the product of the predicted reference value and the predicted value coefficient to obtain the predicted value of the single-sided SCR outlet NOx concentration.
Further, in order to better implement the present invention, the method for acquiring the balance component on the a/B side refers to: firstly, calculating a difference value between an actual measured value of the NOx concentration of an SCR outlet on the A side and an actual measured value of the NOx concentration of an SCR outlet on the B side to obtain a deviation between the two sides of the A side and the B side, wherein the deviation is larger than a positive deviation dead zone, a positive fixed value is output, and the deviation is smaller than a negative deviation dead zone, and a negative fixed value is output; and then the output constant value is calculated through integration and subjected to amplitude limiting to obtain an A/B side balance component.
Further, in order to better implement the present invention, the method for obtaining the theoretical ammonia amount refers to: the method comprises the steps of multiplying the difference value between the NOx concentration real-time value of the SCR inlet and the NOx concentration set value of the SCR outlet on one side by the smoke amount, multiplying the smoke amount by the theoretical ammonia amount regulating coefficient after the ammonia nitrogen molar ratio function, and limiting amplitude to obtain the theoretical ammonia amount on the one side.
Further, in order to better implement the present invention, the method for acquiring the dynamic feed-forward amount of fuel refers to: the differential value of the total fuel quantity is multiplied by the fuel dynamic function, and the fuel dynamic feedforward coefficient is limited, so that the fuel dynamic feedforward quantity of a single side is obtained.
Further, in order to better implement the present invention, the method for obtaining the oxygen dynamic feed-forward amount refers to: the differential value of the oxygen content of the flue gas at one side is multiplied by the oxygen content feedforward coefficient through the oxygen content dynamic function and is limited to obtain the oxygen content dynamic feedforward content at the one side.
It should be noted that, an important idea in the feedforward denitration control method described in the present application is to perform one-side control on the denitration system, that is, to control the ammonia injection amount on the side a and the ammonia injection amount on the side B respectively. Therefore, the ammonia gas regulating command for implementing control and the PID component, the model feedforward quantity and the dynamic feedforward quantity which are required to be used for forming the ammonia gas regulating command are all processed by data acquisition and analysis according to a single side; the SCR outlet NOx concentration predicted value and the SCR outlet NOx concentration real-time value for calculating the model feedforward quantity, and the theoretical ammonia quantity and the oxygen quantity dynamic feedforward quantity for calculating the dynamic feedforward quantity are also subjected to data acquisition and analysis processing according to a single side. However, the "desulfurization outlet NOx concentration real-time value" and the "desulfurization outlet NOx concentration set value" used for calculating the PID component and the "fuel dynamic feed-forward amount" and the "a/B side balance component" used for calculating the dynamic feed-forward amount are subjected to data acquisition and analysis processing according to the entire denitration system.
The monitoring point corresponding to the real-time value of the concentration of the NOx at the desulfurization outlet and the set value of the concentration of the NOx at the desulfurization outlet is a flue outlet of the desulfurization zone, and the monitoring point is not divided into two sides. The flue gas is collected to a flue outlet of the desulfurization zone after denitration treatment on the two sides of the A/B, and the real-time value of the concentration of NOx at the desulfurization outlet is measured.
The "fuel dynamic feed forward" is calculated from the boiler fuel data. The boiler fuel is not divided into two sides, and the fuel dynamic feed-forward quantity of the A/B two sides is calculated according to the total fuel quantity.
The "a/B side balance component" itself means the difference between the a-side and B-side SCR outlet NOx concentrations, which when calculated on different sides are identical in absolute value but opposite in sign, and thus can be understood as single-sided data as other base data.
It should be noted that all data related to NOx in the present invention refer to the concentration of NOx unless otherwise specified.
The invention further provides a feedforward denitration control system which is used for realizing the feedforward denitration control method.
The feedforward denitration control system comprises a set of A/B side balance component calculation unit and two single-side control units; the two single-side control units are an A-side control unit and a B-side control unit. Each unilateral control unit comprises a set of PID component calculation unit, a model feedforward calculation unit, a dynamic feedforward calculation unit, an auxiliary calculation unit and a PID.
The A/B side balance component calculation unit is used for calculating an A/B side balance component;
the PID component calculation unit is used for calculating a PID component on one side;
the model feedforward amount calculating unit comprises a NOx concentration prediction model and is used for calculating model feedforward amount of a single side;
the dynamic feedforward amount calculating unit is used for calculating the dynamic feedforward amount of a single side according to the A/B side balance component, the theoretical ammonia amount of the same side, the dynamic feedforward amount of fuel and the dynamic feedforward amount of oxygen;
the auxiliary calculation unit is used for calculating the ammonia flow control quantity of a single side according to the PID component, the model feedforward quantity and the dynamic feedforward quantity of the same side;
the PID is used for calculating the deviation between the ammonia flow control quantity and the actual ammonia flow on the same side, generating a single-side ammonia regulating instruction, and then carrying out real-time regulation and control on the corresponding single-side ammonia input quantity according to the single-side ammonia regulating instruction.
Furthermore, the invention also provides a NOx concentration prediction model which is used for calculating the NOx concentration predicted value of the SCR outlet on one side.
The NOx concentration set value of the SCR outlet at one side and the real-time value of the oxygen content of the flue gas are input into a NOx concentration prediction model, the NOx concentration set value of the SCR outlet passes through a hysteresis function block and then passes through a reference model function to obtain a prediction reference value, and the real-time value of the oxygen content of the flue gas passes through a coefficient function to obtain a prediction value coefficient; meanwhile, the NOx concentration set value at the SCR outlet on one side is subjected to hysteresis function block and then is subjected to difference with the NOx concentration real-time value at the desulfurization outlet, and the difference value is subjected to integral calculation and amplitude limiting to obtain a correction quantity; then, the correction amount is added to the product of the predicted reference value and the predicted value coefficient to obtain the predicted value of the single-sided SCR outlet NOx concentration.
The beneficial effects of the invention are as follows:
(1) The feedforward denitration control method adopts a multivariable feedforward idea to realize real-time dynamic adjustment of the ammonia injection quantity of the inlet, can rapidly adjust the ammonia injection quantity according to the change of the combustion working condition of the boiler and the change of NOx at the SCR outlet, ensures the stability of the concentration of NOx at the desulfurization outlet, and solves the problem of limitation of control by means of a single variable output by a data model in the prior art;
(2) The feedforward denitration control method adopts a single-side control idea to control the ammonia injection quantity of the side A and the side B respectively, so that the problem of unbalance of the two sides A/B in the prior art is solved;
(3) The feedforward denitration control system can overcome the defects of large delay and large inertia of the traditional control system;
(4) The NOx concentration prediction model is used for obtaining the SCR outlet NOx concentration predicted value so as to support multivariable feedforward denitration control.
Drawings
Fig. 1 is a schematic diagram of a principle of generating a unilateral ammonia gas door regulating instruction in the feedforward denitration control method of the invention.
Fig. 2 is a schematic diagram of a main idea of a feedforward denitration control method in the invention.
Fig. 3 is a block diagram of a feedforward denitration control system in the present invention.
Fig. 4 is a schematic diagram of a data processing flow of a portion of an a-side PID component calculation unit, an a-side model feedforward calculation unit, and an a-side auxiliary calculation unit in the feedforward denitration control system.
Fig. 5 is a schematic diagram of a partial data processing flow of the dynamic feedforward calculation unit on the a side in the feedforward denitration control system.
FIG. 6 is a schematic diagram of a partial data processing flow of the A/B side balance component calculation unit in the feedforward denitration control system.
Detailed Description
Example 1:
when the traditional SCR denitration system operates, the denitration ammonia injection automatic regulating system has the phenomena of full tracking and overshoot, so that the problems of exceeding NOx, rising ammonia escape and the like are caused, and the reliability and the economical efficiency of a unit in a thermal power plant are influenced. In this embodiment, a 300MW unit is taken as an example, and long-term operation observation is performed on the unit, so that concentration fluctuation of NOx at a desulfurization outlet is large when denitration control is performed by adopting an existing denitration control method in the background art.
The embodiment discloses a feedforward denitration control method, and more specifically relates to a multivariable feedforward denitration control method.
A feedforward denitration control method is used for controlling the side A and the side B of a denitration system on one side respectively. As shown in fig. 1 and 2, the one-side control means: firstly, generating a unilateral ammonia gas flow control quantity according to a unilateral PID component, a model feedforward quantity and a dynamic feedforward quantity, inputting the unilateral ammonia gas flow control quantity and the unilateral actual ammonia gas flow into a PID, calculating deviation by the PID and obtaining a unilateral ammonia gas regulating instruction, and finally realizing real-time regulation and control of the unilateral ammonia gas input quantity by the unilateral ammonia gas regulating instruction.
The model feedforward quantity of the single side is mainly calculated by the predicted value of the NOx concentration of the SCR outlet and the real-time value of the NOx concentration of the SCR outlet of the single side. The single-side dynamic feedforward amount is mainly obtained by superposition of the single-side theoretical ammonia amount, the single-side fuel dynamic feedforward amount, the single-side oxygen dynamic feedforward amount and the A/B side balance component.
Based on PID closed loop control of total denitration ammonia injection amount, the feedforward denitration control method of the embodiment introduces model feedforward amount, theoretical ammonia amount, fuel dynamic feedforward amount, oxygen dynamic feedforward amount and A/B side balance component, adopts multivariable feedforward thought to realize real-time dynamic adjustment of inlet ammonia injection amount, can rapidly adjust ammonia injection amount according to the change of boiler combustion working condition and the change of SCR outlet NOx, and ensures stability of NOx concentration of a desulfurization outlet, thereby solving the problem of limitation of control by means of single variable output of a data model in the prior art.
For the whole denitration system, the ammonia gas regulating instruction is divided into an A-side ammonia gas regulating instruction and a B-side ammonia gas regulating instruction, and the two single-side ammonia gas regulating instructions are respectively used. And the A-side ammonia gas regulating instruction is used for regulating the ammonia gas input quantity of the A-side inlet of the denitration system. And the B-side ammonia gas regulating instruction is used for regulating the ammonia gas input quantity of the B-side inlet of the denitration system. Therefore, the control of the ammonia injection quantity at one side is realized, and the problem of unbalance at two sides of the A/B in the prior art is solved.
The feedforward denitration control method of the embodiment is put into operation in the unit DCS in a configuration mode, the ammonia injection amount is dynamically adjusted in the operation process, and the condition response to the severe fluctuation of the concentration of the flue gas NOx caused by the disturbance of the working condition of the boiler is rapid, so that the problems of large delay, large inertia and unbalanced A/B side of the traditional control system are effectively solved, and the stability of the concentration of the NOx at the desulfurization outlet is ensured.
The embodiment also provides a feedforward denitration control system for realizing the feedforward denitration control method.
As shown in FIG. 3, the feedforward denitration control system comprises a set of A/B side balance component calculation units and two single-side control units. The two single-side control units are an A-side control unit and a B-side control unit.
The A-side control unit comprises an A-side PID component calculation unit, an A-side model feedforward calculation unit, an A-side dynamic feedforward calculation unit, an A-side auxiliary calculation unit and an A-side PID.
The B-side control unit comprises a B-side PID component calculation unit, a B-side model feedforward calculation unit, a B-side dynamic feedforward calculation unit, a B-side auxiliary calculation unit and a B-side PID.
The A/B side balance component calculation unit is used for calculating an A/B side balance component.
And an A-side PID component calculation unit for calculating an A-side PID component. And a B-side PID component calculation unit for calculating a B-side PID component.
The a-side model feedforward amount calculation unit includes an a-side NOx concentration prediction model for calculating an a-side model feedforward amount. The B-side model feedforward amount calculation unit includes a B-side NOx concentration prediction model for calculating a B-side model feedforward amount.
And the A-side dynamic feedforward amount calculating unit is used for calculating the A-side dynamic feedforward amount according to the A/B-side balance component, the A-side theoretical ammonia amount, the A-side fuel dynamic feedforward amount and the A-side oxygen dynamic feedforward amount. And the B-side dynamic feedforward amount calculating unit is used for calculating the B-side dynamic feedforward amount according to the A/B-side balance component, the B-side theoretical ammonia amount, the B-side fuel dynamic feedforward amount and the B-side oxygen dynamic feedforward amount.
And the A-side auxiliary calculation unit is used for calculating the A-side ammonia flow control quantity according to the A-side PID component, the A-side model feedforward quantity and the A-side dynamic feedforward quantity. And the B-side auxiliary calculation unit is used for calculating the B-side ammonia flow control quantity according to the B-side PID component, the B-side model feedforward quantity and the B-side dynamic feedforward quantity.
And the A-side PID is used for calculating the deviation between the A-side ammonia flow control quantity and the A-side actual ammonia flow, generating an A-side ammonia gate regulating instruction, and regulating the ammonia input quantity of an A-side inlet of the denitration system according to the A-side ammonia gate regulating instruction. And the B-side PID is used for calculating the deviation between the B-side ammonia flow control quantity and the B-side actual ammonia flow, generating a B-side ammonia gate regulating instruction, and regulating the B-side inlet ammonia input quantity of the denitration system according to the B-side ammonia gate regulating instruction.
Example 2:
the present embodiment will be described in detail with reference to the drawings on the basis of embodiment 1. Fig. 4, 5, and 6 illustrate data processing flows of the a-side PID component calculation unit, the a-side model feedforward calculation unit, the a-side dynamic feedforward calculation unit, and the a-side auxiliary calculation unit in the a-side control unit, and the data processing flow in the B-side control unit corresponds to the data processing flow of the a-side control unit, so that the illustration is not repeated.
In this embodiment, as shown in fig. 4, the difference between the real value of the concentration of NOx at the desulfurization outlet and the set value of the concentration of NOx at the desulfurization outlet is taken as the input quantity of the single-side PID, and the single-side PID component is obtained through proportional and integral calculation and amplitude limitation.
In this embodiment, as shown in fig. 4, the single-side NOx concentration prediction model outputs a single-side SCR outlet NOx concentration predicted value, the difference between the single-side SCR outlet NOx concentration predicted value and the real-time SCR outlet NOx concentration value is superimposed by a differential value, and then the differential value is output through a slope function and multiplied by a gain coefficient, so as to obtain the single-side model feedforward quantity.
The method comprises the steps that a single-side SCR outlet NOx concentration set value and a flue gas oxygen real-time value are respectively used as input quantities of a NOx concentration prediction model, the SCR outlet NOx concentration set value is subjected to hysteresis function blocks and then subjected to reference model functions to obtain a prediction reference value, and the flue gas oxygen real-time value is subjected to coefficient functions to obtain a prediction value coefficient; meanwhile, the NOx concentration set value at the SCR outlet on one side is subjected to hysteresis function block and then is subjected to difference with the NOx concentration real-time value at the desulfurization outlet, and the difference value is subjected to integral calculation and amplitude limiting to obtain a correction quantity; then, the correction amount is added to the product of the predicted reference value and the predicted value coefficient to obtain the predicted value of the single-sided SCR outlet NOx concentration. That is, the single-sided SCR outlet NOx concentration predicted value=predicted reference value×predicted value coefficient+correction amount.
In this embodiment, as shown in fig. 5, the dynamic feedforward amount of the single side is mainly obtained by superposition of the theoretical ammonia amount of the single side, the dynamic feedforward amount of the fuel of the single side, the dynamic feedforward amount of the oxygen amount of the single side and the balance component of the a/B side.
The A/B side balance component represents the deviation of the NOx concentration at the outlet of the A/B side of the denitration system. The difference between the measured value of the NOx concentration at the outlet of the SCR on the A side and the measured value of the NOx concentration at the outlet of the SCR on the B side is used as the deviation of the concentration of the NOx at the outlet on the A/B side; the deviation is larger than the positive deviation dead zone to output a positive fixed value, and the deviation is smaller than the negative deviation dead zone to output a negative fixed value; whether positive or negative constant value is obtained, the output constant value is calculated through integration and limited by amplitude, and the A/B side balance component is obtained.
The difference between the single-side SCR inlet NOx concentration real-time value and the SCR outlet NOx concentration set value is multiplied by the flue gas amount, and after the ammonia nitrogen molar ratio function, the theoretical ammonia amount regulating coefficient is multiplied and limited, so that the single-side theoretical ammonia amount is obtained.
The differential value of the total fuel quantity is multiplied by the fuel dynamic function, and the fuel dynamic feedforward coefficient is limited, so that the fuel dynamic feedforward quantity of the single side is obtained.
The differential value of the single-side flue gas oxygen is multiplied by the oxygen dynamic function and limited by the oxygen feedforward coefficient to obtain the single-side oxygen dynamic feedforward quantity.
Other portions of this embodiment are the same as those of embodiment 1, and thus will not be described in detail.
Example 3:
this embodiment will be described in detail with reference to embodiment 1 and embodiment 2. Fig. 4, 5, and 6 illustrate data processing flows of the a-side PID component calculation unit, the a-side model feedforward calculation unit, the a-side dynamic feedforward calculation unit, and the a-side auxiliary calculation unit in the a-side control unit, and the data processing flow in the B-side control unit corresponds to the data processing flow of the a-side control unit, so that the illustration is not repeated.
A side ammonia flow control quantity=a side PID component+a side model feedforward quantity+a side dynamic feedforward quantity;
b-side ammonia flow control = B-side PID component + B-side model feedforward + B-side dynamic feedforward.
As shown in fig. 4, the a-side PID component is obtained by proportional and integral calculation of the deviation of the real value of the desulfurization outlet NOx concentration and the set value of the desulfurization outlet NOx concentration through the a-side PID and clipping. The B-side PID component is obtained by carrying out proportional and integral calculation and amplitude limiting on the deviation of the real-time value of the concentration of the NOx at the desulfurization outlet and the set value of the concentration of the NOx at the desulfurization outlet through the B-side PID.
As shown in FIG. 4, the A-side model feed forward, NOx concentration through the A-side SCR outletAfter the difference value between the predicted value and the real value of the concentration of NOx at the SCR outlet on the A side is overlapped by a difference value differential value, the difference value differential value is processed by a slope function f 13 (x) Output is multiplied by gain factor K 13 And obtaining the feedforward quantity of the A-side model. The feedforward quantity of the B side model is obtained by superposing the difference value differential quantity between the predicted value of the NOx concentration of the B side SCR outlet and the real value of the NOx concentration of the B side SCR outlet and then passing through the slope function f 23 (x) Output is multiplied by gain factor K 23 And obtaining the feedforward quantity of the B-side model.
Wherein, as shown in fig. 4, the a-side SCR outlet NOx concentration predicted value is obtained by:
the set value of the NOx concentration at the outlet of the SCR on the A side and the real-time value of the oxygen content of the flue gas on the A side are respectively used as the input quantity of an NOx concentration prediction model on the A side; the NOx concentration set value at the SCR outlet on the A side passes through a hysteresis function block and then passes through a reference model function f 11 (x) Obtaining a predicted reference value of the side A, and obtaining a real-time value of the oxygen content of the flue gas of the side A through a coefficient function f 12 (x) Obtaining an A-side predicted value coefficient; meanwhile, after passing through the hysteresis function block, the set value of the NOx concentration at the SCR outlet at the A side is subjected to difference with the real-time value of the NOx concentration at the desulfurization outlet, and the difference value is subjected to integral calculation and amplitude limiting to obtain an A side correction quantity; then, the product of the a-side prediction reference value and the a-side prediction value coefficient is added to the a-side correction amount to obtain an a-side SCR outlet NOx concentration predicted value. That is, the a-side SCR outlet NOx concentration predicted value=a-side predicted reference value×a-side predicted value coefficient+a-side correction amount.
Wherein, the predicted value of the NOx concentration of the SCR outlet on the side B is obtained by the following method:
the set value of the NOx concentration at the outlet of the SCR on the side B and the real-time value of the oxygen content of the flue gas on the side B are respectively used as the input quantity of a prediction model of the NOx concentration on the side B; the NOx concentration set value at the outlet of the SCR on the side B passes through a hysteresis function block and then passes through a reference model function f 21 (x) Obtaining a B-side prediction reference value, and obtaining a B-side flue gas oxygen real-time value through a coefficient function f 22 (x) Obtaining a B-side predicted value coefficient; meanwhile, after passing through the hysteresis function block, the set value of the NOx concentration at the outlet of the SCR at the B side is subjected to difference with the real-time value of the NOx concentration at the outlet of the desulfurization, and the difference value is subjected to integral calculation and amplitude limiting to obtain a correction quantity at the B side; then, the product of the B-side prediction reference value and the B-side prediction value coefficient is added with the B-side correction amount to obtain a B-side SCR outlet NOx concentration predicted value. That is, the B-side SCR outlet NOx concentration predicted value=b-side predicted reference value×b-side predicted value coefficient+b-side correction amount.
As shown in fig. 5, the a-side dynamic feedforward amount=a-side theoretical ammonia amount+a-side fuel dynamic feedforward amount+a-side oxygen amount dynamic feedforward amount+a/B-side balance component. B side dynamic feedforward amount=b side theoretical ammonia amount+b side fuel dynamic feedforward amount+b side oxygen dynamic feedforward amount+a/B side balance component. Note that, for the period of time, the a/B side balance component for calculating the a side dynamic feedforward amount and the a/B side balance component for calculating the B side dynamic feedforward amount are opposite in sign.
As shown in FIG. 5, the A-side theoretical ammonia amount is obtained by multiplying the difference between the A-side SCR inlet NOx concentration real-time value and the A-side SCR outlet NOx concentration set value by the A-side flue gas amount and passing through an ammonia nitrogen molar ratio function f 14 (x) Then multiplying the ammonia by the theoretical ammonia regulating factor K 14 And clipping the obtained product. The theoretical ammonia amount on the side B is obtained by multiplying the difference value between the real-time value of the NOx concentration at the inlet of the SCR on the side B and the set value of the NOx concentration at the outlet of the SCR on the side B by the flue gas amount on the side B and then by an ammonia nitrogen mole ratio function f 24 (x) Then multiplying the ammonia by the theoretical ammonia regulating factor K 24 And clipping the obtained product.
As shown in FIG. 5, the A-side oxygen dynamic feed-forward quantity is calculated by the A-side flue gas oxygen differential calculation and then passes through the oxygen dynamic function f 15 (x) Multiplying the oxygen feed-forward coefficient K 15 And clipping. The B side oxygen dynamic feedforward quantity is calculated by the B side flue gas oxygen differential calculation and then passes through the oxygen dynamic function f 25 (x) Multiplying the oxygen feed-forward coefficient K 25 And clipping.
As shown in FIG. 5, the A-side fuel dynamic feed forward quantity is calculated by total fuel quantity differentiation and then passes through a fuel dynamic function f 16 (x) After that, multiply with the fuel feed-forward coefficient K 16 And clipping. The B-side fuel dynamic feed-forward quantity is calculated through total fuel quantity differentiation and then passes through a fuel dynamic function f 26 (x) After that, multiply with the fuel feed-forward coefficient K 26 And clipping. The boiler fuel is not divided into two sides, and the fuel dynamic feed-forward quantity of the A/B two sides is calculated according to the total fuel quantity. That is, here, it is used to calculate the A-side fuel dynamic feed forward amountThe total fuel quantity of the B-side fuel dynamic feed-forward quantity is the same parameter, and the fuel dynamic function f 16 (x) Dynamic function f of fuel 26 (x) The two are the same, the feed-forward coefficient K of the fuel 16 Feed-forward coefficient K of fuel 26 Both identical.
As shown in fig. 6, the a/B side balance component is obtained by: calculating the difference value between the measured value of the NOx concentration of the SCR outlet on the A side and the measured value of the NOx concentration of the SCR outlet on the B side; when the difference > 2, the integral input value=1; when the difference value is < -2, the integral input value= -1; when the difference value of-2 is less than or equal to 2, the integral input value=0; and carrying out integral operation on the integral input value and amplitude limitation to obtain an A/B side balance component. The deviation of the NOx concentration of the outlet of the A/B side of the denitration system is represented by the difference value between the NOx concentration measured value of the outlet of the SCR on the A side and the NOx concentration measured value of the outlet of the SCR on the B side; the deviation is larger than the positive deviation dead zone to output a positive fixed value, and the deviation is smaller than the negative deviation dead zone to output a negative fixed value.
Based on the above, the control amount of the ammonia gas flow on the A side and the actual ammonia gas flow on the A side are input into the PID, the difference value between the control amount of the ammonia gas flow on the A side and the actual ammonia gas flow on the A side is calculated by the PID, an A-side ammonia gas regulating instruction is obtained, and finally, the real-time regulation and control of the input amount of the ammonia gas on the A side are realized by the A-side ammonia gas regulating instruction. And inputting the B-side ammonia gas flow control quantity and the B-side actual ammonia gas flow into a PID, calculating a difference value between the B-side ammonia gas flow control quantity and the B-side actual ammonia gas flow by the PID, obtaining a B-side ammonia gas regulating instruction, and finally realizing real-time regulation and control of the A-side ammonia gas input quantity by the B-side ammonia gas regulating instruction. Therefore, the ammonia flow rate of one-side input is respectively adjusted, so that the input ammonia flow rate tracks the ammonia flow rate control amount of the side.
Other portions of this embodiment are the same as those of embodiment 1 or embodiment 2, and thus will not be described in detail.
Example 4:
on the basis of the above embodiment, the present embodiment provides a NOx concentration prediction model for calculating a single-sided SCR outlet NOx concentration predicted value.
As shown in fig. 4, the single-side SCR outlet NOx concentration set value and the real-time value of the flue gas oxygen are input into a NOx concentration prediction model, the SCR outlet NOx concentration set value is subjected to a hysteresis function block and then is subjected to a reference model function to obtain a prediction reference value, and the real-time value of the flue gas oxygen is subjected to a coefficient function to obtain a prediction value coefficient; meanwhile, the NOx concentration set value at the SCR outlet on one side is subjected to hysteresis function block and then is subjected to difference with the NOx concentration real-time value at the desulfurization outlet, and the difference value is subjected to integral calculation and amplitude limiting to obtain a correction quantity; then, the correction amount is added to the product of the predicted reference value and the predicted value coefficient to obtain the predicted value of the single-sided SCR outlet NOx concentration.
Based on the above, the NOx concentration prediction model in the a-side control unit is used to calculate the a-side SCR outlet NOx concentration prediction value; and the NOx concentration prediction model in the B-side control unit is used for calculating a B-side SCR outlet NOx concentration predicted value.
The NOx concentration prediction model in this embodiment can perform self-adjustment in real time according to the accumulated amount of NOx concentration deviation at the desulfurization outlet. Therefore, based on the NOx concentration prediction model, when the feedforward denitration control system operates, the overall control effect is superior to that of the traditional denitration control method, and the method has the advantages of high tracking speed, small overshoot and strong anti-interference capability.
Other portions of this embodiment are the same as those of embodiment 1, embodiment 2 and embodiment 3, and thus will not be described in detail.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent variation, etc. of the above embodiment according to the technical matter of the present invention fall within the scope of the present invention.
Claims (10)
1. A feedforward denitration control method is characterized in that single-side control is respectively carried out on an A side and a B side of a denitration system; the single-side control means: firstly, generating a unilateral ammonia gas flow control quantity according to a unilateral PID component, a model feedforward quantity and a dynamic feedforward quantity, inputting the unilateral ammonia gas flow control quantity and the unilateral actual ammonia gas flow into a PID, calculating deviation by the PID and obtaining a unilateral ammonia gas regulating instruction, and finally realizing real-time regulation and control of the unilateral ammonia gas input quantity by the unilateral ammonia gas regulating instruction;
the model feedforward quantity of the single side is mainly calculated and obtained by the predicted value of the NOx concentration of the SCR outlet and the real-time value of the NOx concentration of the SCR outlet of the single side; the single-side dynamic feedforward amount is mainly obtained by superposition of the single-side theoretical ammonia amount, the single-side fuel dynamic feedforward amount, the single-side oxygen dynamic feedforward amount and the A/B side balance component.
2. The feedforward denitration control method according to claim 1, wherein the method for acquiring the PID component on one side is: and obtaining the difference value of the real-time value of the NOx concentration at the desulfurization outlet and the set value of the NOx concentration at the desulfurization outlet, taking the difference value of the real-time value of the NOx concentration at the desulfurization outlet and the set value of the NOx concentration at the desulfurization outlet as the input quantity of the single-side PID, and obtaining the single-side PID component through proportional and integral calculation and amplitude limiting.
3. The feedforward denitration control method according to claim 1, wherein the method for obtaining the model feedforward amount on one side is: outputting a predicted value of the NOx concentration of the single-side SCR outlet through a single-side NOx concentration prediction model, and simultaneously obtaining a real-time value of the NOx concentration of the single-side SCR outlet; and (3) superposing a difference value differential value between the predicted value of the SCR outlet NOx concentration output by the NOx concentration prediction model and the real value of the SCR outlet NOx concentration, outputting through a slope function, and multiplying by a gain coefficient to obtain the model feedforward quantity of the single side.
4. The feed-forward denitration control method according to claim 3, wherein the method for obtaining the SCR outlet NOx concentration predicted value is: respectively inputting a single-side SCR outlet NOx concentration set value and a flue gas oxygen real-time value into the NOx concentration prediction model, obtaining a prediction reference value after the SCR outlet NOx concentration set value passes through a hysteresis function block and then passes through a reference model function, and obtaining a prediction value coefficient after the flue gas oxygen real-time value passes through a coefficient function; meanwhile, the NOx concentration set value at the SCR outlet on one side is subjected to hysteresis function block and then is subjected to difference with the NOx concentration real-time value at the desulfurization outlet, and the difference value is subjected to integral calculation and amplitude limiting to obtain a correction quantity; then, the correction amount is added to the product of the predicted reference value and the predicted value coefficient to obtain the predicted value of the single-sided SCR outlet NOx concentration.
5. The feed-forward denitration control method according to claim 1, wherein the a/B-side balance component acquisition method is: firstly, calculating a difference value between an actual measured value of the NOx concentration of an SCR outlet on the A side and an actual measured value of the NOx concentration of an SCR outlet on the B side to obtain a deviation between the two sides of the A side and the B side, wherein the deviation is larger than a positive deviation dead zone, a positive fixed value is output, and the deviation is smaller than a negative deviation dead zone, and a negative fixed value is output; and then the output constant value is calculated through integration and subjected to amplitude limiting to obtain an A/B side balance component.
6. The feed-forward denitration control method according to claim 1, wherein the method for obtaining the theoretical ammonia amount is: the method comprises the steps of multiplying the difference value between the NOx concentration real-time value of the SCR inlet and the NOx concentration set value of the SCR outlet on one side by the smoke amount, multiplying the smoke amount by the theoretical ammonia amount regulating coefficient after the ammonia nitrogen molar ratio function, and limiting amplitude to obtain the theoretical ammonia amount on the one side.
7. The feed-forward denitration control method according to claim 1, wherein the method for acquiring the dynamic feed-forward amount of fuel is: the differential value of the total fuel quantity is multiplied by the fuel dynamic function, and the fuel dynamic feedforward coefficient is limited, so that the fuel dynamic feedforward quantity of a single side is obtained.
8. The feedforward denitration control method according to claim 1, wherein the method for acquiring the oxygen amount dynamic feedforward amount is: the differential value of the oxygen content of the flue gas at one side is multiplied by the oxygen content feedforward coefficient through the oxygen content dynamic function and is limited to obtain the oxygen content dynamic feedforward content at the one side.
9. A feedforward denitration control system for realizing the feedforward denitration control method according to claim 1, characterized in that the feedforward denitration control system comprises a set of a/B-side balance component calculation units and two single-side control units;
the two single-side control units are an A-side control unit and a B-side control unit, and each unit comprises a set of PID component calculation unit, a model feedforward calculation unit, a dynamic feedforward calculation unit, an auxiliary calculation unit and a PID;
the A/B side balance component calculation unit is used for calculating an A/B side balance component;
the PID component calculation unit is used for calculating a PID component on one side;
the model feedforward amount calculating unit comprises a NOx concentration prediction model and is used for calculating model feedforward amount of a single side;
the dynamic feedforward amount calculating unit is used for calculating the dynamic feedforward amount of a single side according to the A/B side balance component, the theoretical ammonia amount of the same side, the dynamic feedforward amount of fuel and the dynamic feedforward amount of oxygen;
the auxiliary calculation unit is used for calculating the ammonia flow control quantity of a single side according to the PID component, the model feedforward quantity and the dynamic feedforward quantity of the same side;
the PID is used for calculating the deviation between the ammonia flow control quantity and the actual ammonia flow on the same side, generating a single-side ammonia regulating instruction, and then carrying out real-time regulation and control on the corresponding single-side ammonia input quantity according to the single-side ammonia regulating instruction.
10. A NOx concentration prediction model is used for calculating a single-side SCR outlet NOx concentration predicted value;
the input of the NOx concentration prediction model is a single-side SCR outlet NOx concentration set value and a flue gas oxygen real-time value, the SCR outlet NOx concentration set value is subjected to a hysteresis function block and then is subjected to a reference model function to obtain a prediction reference value, and the flue gas oxygen real-time value is subjected to a coefficient function to obtain a prediction value coefficient; meanwhile, the NOx concentration set value at the SCR outlet on one side is subjected to hysteresis function block and then is subjected to difference with the NOx concentration real-time value at the desulfurization outlet, and the difference value is subjected to integral calculation and amplitude limiting to obtain a correction quantity; then, the correction amount is added to the product of the predicted reference value and the predicted value coefficient to obtain the predicted value of the single-sided SCR outlet NOx concentration.
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