JP2004355329A - Process value controlling method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device capable of controlling a process value of a control object for preventing it from hunting even when an equilibrium condition of the process value is greatly disturbed because of a rapid load change, a change of a carbon type, disturbance, or the like. <P>SOLUTION: When the process value of the control object is an injection amount of ammonia (NH<SB>3</SB>) into a processed gas to be put into a NOx removal reactor, control sensitivity of a NOx concentration change is lowered in this NOx removal reactor ammonia injection flow rate controlling method if a change ratio of an actually measured NOx concentration in the processed gas is lowered below a predetermined value to fall within a predetermined hunting area while a load change of the NOx removal reactor is finished or a predetermined time passes after the start of operation or after the stop of the operation. If the actually measured NOx concentration change goes out of the hunting area and is stabilized, reduction in the NOx concentration change control sensitivity is released and can be returned to ordinary NOx concentration change control sensitivity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for controlling a process value using feedback control.
[0002]
[Prior art]
As an example of controlling the process value, ammonia in the gas to be treated in a flue gas denitration apparatus in which a nitrogen oxide (NOx) component in the gas to be treated (exhaust gas) is injected with ammonia (NH ₃ ) and then removed by a denitration catalyst. A description will be given of a conventional process value control method using an ammonia injection flow rate control device for adjusting an (NH ₃ ) injection flow rate.
[0003]
In the flue gas denitration apparatus, NOx in the gas to be treated reacts with NH ₃ injected into the gas to be treated, and becomes nitrogen and water. Therefore, the amount of NH ₃ to be injected basically becomes the amount of NOx to be treated. You will inject the right amount. However, it must be taken into account that the injected NH ₃ is not only used for the reaction with NOx but also adsorbs as much as possible on the catalyst surface.
[0004]
On the other hand, if the amount of NH ₃ injected into the gas to be treated is insufficient with respect to the amount of NOx to be treated, NOx cannot be completely treated, and the NOx concentration at the outlet of the denitration reactor may exceed a specified value. FIG. 3 is a system diagram of a denitration reaction control installed in a conventional flue gas denitration apparatus.
[0005]
NH ₃ injection rate calculator 9 for calculating a NH ₃ injection rate commensurate with the amount of NOx to be treated in the gas inlet NOx concentration of the denitration reactor, the outlet NOx concentration setting, suitable from the outlet NOx concentration and the amount of exhaust gas, etc. This is for calculating the NH ₃ injection amount. That is, the total NOx amount signal 30 is calculated by multiplying the inlet NOx concentration signal 13 detected by the inlet NOx analyzer 12 of the denitration reactor and the gas flow signal 29 of the gas amount 28 to be processed by the multiplier 31. I do.
[0006]
On the other hand, at the inlet NOx concentration signal 13 and the denitration reactor outlet NOx concentration setter 15 must NH ₃ molar ratio calculation unit 18 having a subtractor 19 which performs subtraction between the set NOx concentration signal 16 which is set by the NH ₃ moles of A required molar ratio (NH ₃ mole / NOx mole) signal 20 which is a ratio to the NOx mole number is calculated, and a deviation between the actually measured outlet NOx concentration signal 23 detected by the outlet NOx analyzer 22 and the set NOx concentration signal 16 is calculated. Is calculated by the subtractor 24, the NOx control deviation 67 at the outlet of the denitration reactor is calculated by the proportional-integral calculator 25, and then added by the adder 26 to correct the required molar ratio signal 20. The necessary corrected molar ratio correction signal 27 obtained is multiplied by the total NOx amount signal 30 and the multiplier 32 to calculate the required NH ₃ flow rate signal 33.
[0007]
The required NH ₃ flow rate signal 33 and the actually measured NH ₃ flow rate signal 39 detected by the NH ₃ flow meter 38 are subtracted by a subtractor 40 to calculate an NH ₃ flow rate deviation signal 41, which is calculated by a proportional-integral calculator 42. The signal is converted into an opening signal 43 and converted into an NH ₃ flow control valve control signal 45 by a vacuum converter 44, and the NH ₃ flow control valve 10 provided in the middle of the NH ₃ pipe 5 is opened and closed.
[0008]
A denitration outlet NOx deviation correction bias output signal 64 for increasing / decreasing the NH ₃ flow rate from the denitration reactor exit NOx control deviation 67 (the denitration reactor exit control deviation 67 differs from the function generator 54 for setting a bias in accordance with the deviation). And a residual NH ₃ adsorption amount correction bias signal 65 (outlet NOx concentration signal 23) for increasing or decreasing the NH ₃ flow rate in consideration of the residual NH ₃ adsorption amount in the denitration reactor. The difference between the NOx concentration signal 13 and the inlet NOx concentration signal 13 is calculated by a subtractor 57, and the difference is multiplied by a multiplier 58 by a multiplier 58 to calculate the amount of residual NOx in the denitration reactor. NH ₃ flow rate is calculated by the subtractor 56 on the basis of the measured NH ₃ flow rate signal 39, the residual adsorbed NH ₃ amount from the deviation of the detected value of the flow rate _of NH ₃ consumed and the leakage NH ₃ flow rate detector 59 which is A positive bias signal 65 is obtained by the adder 61, and a correction gain 63 from the denitration reactor outlet control deviation 67 (a function for setting the control deviation 67 to a gain corresponding to the deviation) is added to the obtained addition value. obtained by treating with generator 52 and the first-order lag function generator 53.) to obtain a corrected required NH ₃ injection correction output signal 66 by multiplying, which the necessary NH ₃ flow rate signal 33 in the adder 51 In addition, the required NH ₃ flow rate signal 68 after the correction is calculated.
[0009]
In addition, there are known examples of the control circuit described below.
{Circle around (1)} JP-A-62-231305, "Temperature control device": The invention is characterized in that the gain of the integral operation is reduced when hunting exceeding a specified temperature occurs in the temperature of the controlled object. Temperature control device.
[0010]
{Circle around (2)} JP-A-2-31201, "Feedback control device": The present invention is a feedback control device including a control circuit for lowering a gain when a continuous vibration change occurs.
[0011]
(3) Japanese Patent Application Laid-Open No. 3-179501, "Control Device for Hydraulic Servo System": The invention relates to determining that hunting has occurred when the frequency coincides with a preset hunting occurrence frequency. A control device comprising a gain adjusting means for suppressing the noise.
[0012]
[Patent Document 1]
JP-A-62-231305
[Patent Document 2]
JP-A-2-31201
[Patent Document 3]
JP-A-3-179501
[Problems to be solved by the invention]
In the above-described conventional NH ₃ flow rate control device for the denitration reactor, the sensitivity of increasing or decreasing the control amount (NH ₃ amount) as much as possible in order to shorten the time until the NOx concentration at the outlet of the denitration reactor approaches the control set value. If the boiler's operating conditions are significantly different, such as rapid load changes, coal type changes, unpredictable disturbances, etc. (when the boiler's equilibrium state is greatly disrupted), a hunting phenomenon will occur. There was an event to do.
[0016]
Furthermore, even when the hunting phenomenon occurs, the timing for lowering the sensitivity of the control amount is not considered, and there is an event that promotes the hunting.
[0017]
For this reason, when the boiler's equilibrium state is significantly disrupted due to a rapid load change, a change in coal type, a disturbance, or the like in which the operation state of the boiler is significantly different, a phenomenon occurs in which the control target process value hunts.
[0018]
The problem of the present invention is that the process value of the controlled object does not hunt even when the process value is rapidly disturbed due to a rapid change in load, a change in coal type, disturbance, etc. To provide a control method and apparatus.
[0019]
[Means for Solving the Problems]
In order to solve the above problems, the present invention mainly employs the following configuration.
(1) A process value control method for a controlled device in which a process value caused by a load change of a process target and a process value caused by the process target changes, wherein a change rate of the process value of the control target device becomes smaller than a predetermined value. When it is determined that the change in the measured process value falls within the predetermined hunting region and that the load change of the control target device has ended, or that a predetermined time has elapsed after the start of operation or the stop of operation, A process value control method for adjusting a process value of a device to be controlled by lowering a control amount sensitivity.
[0020]
(2) Inlet nitrogen oxide concentration, outlet nitrogen oxide concentration set value, outlet nitrogen oxide concentration and treatment of a denitration reactor for removing nitrogen oxides in the gas to be treated by injecting ammonia into the gas to be treated In a method for controlling the ammonia injection flow rate in a denitration reactor in which the flow rate of ammonia injected into the gas to be treated is adjusted by a parameter including the gas amount, the rate of change of the measured nitrogen oxide concentration becomes smaller than a predetermined value, and the change of the measured nitrogen oxide concentration changes. Is within a predetermined hunting region, and when the load change of the denitration reactor is completed, or when a predetermined time has elapsed after the start of operation or the stop of operation, the control sensitivity of the nitrogen oxide concentration change is reduced. Ammonia injection flow control method.
Here, when the change in the measured NOx concentration comes out of the hunting region and stabilizes, the reduction in the control sensitivity of the NOx concentration change can be canceled to return to the normal control sensitivity for the NOx concentration change.
[0021]
(3) A process value control device of a controlled device in which a process value caused by a load change of a processing target and a process value caused by the processing target changes, and a process value adjusting unit for adjusting a process value of the control target device; A process value change direction determiner for determining whether the rate of change of the process value is smaller than a predetermined value; a hunting determiner for determining whether a change in the measured process value is within a predetermined hunting region; A load change end time limit judging device for judging whether or not a predetermined time has elapsed after the start of the load change or after the start of the operation or the stop of the operation, and the three judgment devices are all judged as “yes”. A process value control device provided with a switch for lowering the control amount sensitivity of the process value when the process value is low.
[0022]
(4) Inlet nitrogen oxide concentration, outlet nitrogen oxide concentration set value, outlet nitrogen oxide concentration and treatment of a denitration reactor for removing nitrogen oxides in the gas to be treated by injecting ammonia into the gas to be treated In a denitration reactor ammonia injection flow rate control device that adjusts an ammonia injection flow rate into a gas to be treated by a parameter including a gas amount, an inlet nitrogen oxide concentration, an outlet nitrogen oxide concentration set value, an outlet nitrogen oxide concentration of a denitration reactor A required ammonia injection flow rate calculator for calculating the ammonia injection flow rate into the gas to be processed based on parameters including the concentration and the processing gas amount, a required ammonia injection flow rate calculated by the required ammonia injection flow rate calculator and an actually measured ammonia injection flow rate With an ammonia injection flow rate controller for injecting into the denitration reactor while adjusting the ammonia injection flow rate based on the deviation of In the ammonia flow control device, an actual measured nitrogen oxide concentration change direction determiner that determines whether the rate of change of the actual measured nitrogen oxide concentration is smaller than a predetermined value, and a change in the actually measured nitrogen oxide concentration in a predetermined hunting region. A hunting determiner that determines whether or not a load change of the denitration reactor has been completed, or a load change end time limit determiner that determines whether a predetermined time has elapsed after start-up or operation stop. A denitration reactor ammonia injection flow control device, comprising: a switch for lowering the control sensitivity of the nitrogen oxide concentration change when all of the three determination devices make a “yes” determination.
The switching device may be configured to have a function of returning to a set value based on the control sensitivity of the NOx concentration change when all three determination devices make a “No” determination.
[0023]
[Action]
The present invention will be described with reference to FIG. 1. A change direction of a process value to be controlled is always determined by a process change direction determination signal 87, and a certain time has elapsed after an event such as a load change, start, or stop has ended. If the hunting determination signal 88 is satisfied, the hunting determination signal 86 and the hunting occurrence of the process value to be controlled are established when the hunting determination signal 88 is satisfied. The sensitivity of the control amount is switched by the change rate limiting switch 82, so that hunting can be promptly improved.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
The denitration control device according to the embodiment of the present invention will be described below with reference to the drawings.
FIG. 2 is a schematic diagram of a denitration reactor. The denitration reactor 1 introduces a gas G to be treated, for example, exhaust gas from a boiler, which is a source of the gas G to be treated, from an inlet duct 2, performs a denitrification process by injecting NH ₃ , and discharges the gas to an outlet duct 3. It is discharged outside by a chimney not shown. At this time, the NH ₃ injection tube 4 provided in the inlet duct 2, NH ₃ commensurate with the amount of NOx in the gas to be treated G is injected through the ammonia flow meter 38 and the ammonia flow control valve 10, the gas to be treated NOx in G is decomposed into harmless water vapor and nitrogen gas by the action of a denitration catalyst (not shown) filled in the denitration reactor 1 and removed. Normally, the operation of the denitration reactor 1 is controlled so that the outlet NOx concentration of the denitration reactor 1 becomes equal to or lower than a predetermined value even when the load of the source of the gas G to be treated, for example, a boiler or the like, changes. Here, the inlet NOx concentration in the gas to be treated G is measured by the inlet NOx analyzer 12, and the outlet NOx concentration is measured by the outlet NOx analyzer 22.
[0025]
Hereinafter, an overall structure of a control device according to an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a diagram showing an embodiment of an ammonia control device for a denitration reactor provided in the denitration reactor 1.
[0026]
The ammonia control device shown in FIG. 1 is different from the conventional ammonia control device shown in FIG. 3 in that even if the load injection command value fluctuates the equilibrium state of the ammonia injection flow into the gas G to be treated, the ammonia injection flow is reduced. This is a circuit in which control is performed to prevent hunting. That is, in addition to the injection amount calculator 9 for calculating the NH ₃ injection amount in the gas to be processed and the necessary NH ₃ flow rate calculator 50 in advance, a control amount sensitivity switching signal 85 is provided.
[0027]
The specific operation method is as follows.
The change direction of the NH ₃ injection flow rate into the target gas to be controlled is always determined by the process change direction determination signal 87, and a certain period of time has elapsed after an event such as a load change / start / stop has ended. Is determined by the determination signal 86 after the end of the load change.
[0028]
The process change (NH ₃ injection flow rate change) direction determination signal 87 is obtained by differentiating the NOx concentration signal 23 at the outlet of the denitration reactor by the differentiating circuit 78, and when the rate of change reaches the lower limit value (the rate of change becomes smaller and the process value becomes smaller). Is stable).
[0029]
Further, both signals of the lower determination unit 76 and the upper determination unit 77 of the NOx concentration signal 23 at the outlet of the denitration reactor are input to the AND circuit 79, and when the signals are output from the AND circuit 79, the NH ₃ injection flow rate changes greatly. As a result, hunting occurs, and the output signal of the AND circuit 79 becomes a hunting determination signal 88. That is, the determination signal 88 is output based on whether or not the conditions of both the lower determination unit 76 and the upper determination unit 77 are satisfied. When there is an input from both the process change direction determination signal 87 and the hunting determination signal 88 to the AND circuit 81, the output of the AND circuit 81 is input to the AND circuit 75.
[0030]
The AND circuit 75 can receive a post-load-change end time determination signal 86 for determining whether a predetermined time has elapsed after the load change of the boiler or the like has ended, or after the start of operation or the stop of operation.
[0031]
The post-load change end time determination signal 86 is differentiated by a differentiating circuit 69 of a load request command value (a command value generated by a load change, start or stop of a boiler or the like), and the differentiated value is obtained by an upper judgment unit 70 and a lower judgment unit. When any one of the conditions 71 is satisfied, there is an output from the OR circuit 72, and the output is obtained by passing through the NOT circuit 73 and the on-delay circuit 74.
[0032]
When the output from the AND circuit 81 that operates based on the input from both the post-load change end time determination signal 86, the previous process change direction determination signal 87, and the hunting determination signal 88 is input to the AND circuit 75. Since the three conditions are satisfied, the change rate-limited switch 82 operates. The operation of the change rate limiting switch 82 is performed by switching between the constant values of the two constant generators 83 and 84. The output of the change rate limiting switch 82 is input to the first-order lag function generator 53 of the NOx concentration control deviation 67 at the outlet of the denitration reactor, and the required NH ₃ injection flow rate correction output of the required NH ₃ injection flow rate calculator 50 is output. It is included in the signal 66.
[0033]
In this manner, the sensitivity of the control amount of the NH ₃ injection flow rate is reduced only in the range where the hunting determination signal 88 is established, and the sensitivity of the control amount is reduced in a direction in which the hunting phenomenon of the NH ₃ injection flow rate to be controlled is converged. Since the hunting can be quickly improved by switching the switch 82 with the change rate limit, as a result, the sensitivity adjustment of the control amount of the NOx concentration at the outlet of the denitration reactor can be appropriately performed, and the appropriate control amount can be constantly adjusted. Sensitivity can be ensured.
[0034]
Further, when the output of the OR circuit 72 of the differential value of the load request command value disappears and the hunting phenomenon converges, the AND circuit 75 does not operate after a predetermined time by passing through the on-delay circuit 74. The operation of 82 is also eliminated, and the sensitivity of the control amount can be returned to the initial set value.
[0035]
In this manner, the convergence of the hunting phenomenon after the control operation is determined from the behavior of the NH ₃ injection flow rate to be controlled, and the sensitivity of the control amount can be returned to the initial set value at an appropriate timing.
[0036]
The three prior arts described in the above-mentioned prior art are all characterized by lowering the control gain when a hunting phenomenon occurs. It is important to consider the range, and if neglected it often promotes divergence or hunting.
[0037]
On the other hand, in the above-described embodiment of the present invention, when the hunting phenomenon occurs, the sensitivity of the manipulated variable is reduced, and the process value to be controlled is always stabilized. The feature is that the sensitivity is returned to the control amount sensitivity before the occurrence of hunting, and the hatching can be easily converged without considering the timing and range of decreasing the gain, and stable control can be automatically performed.
[0038]
【The invention's effect】
In the present invention, a difference occurs between the sensitivity of the control amount and the sensitivity of the process value to be controlled, and even when a hunting phenomenon occurs, the sensitivity of the operation amount is reduced without requiring an artificial action, and the control object is always controlled. If the hunting phenomenon converges by stabilizing the process value, control is returned to the control amount sensitivity before hunting occurs again, so that the control can be expected to have the effect of shortening the time until it gradually approaches the control set value. It is a method.
[Brief description of the drawings]
FIG. 1 is a control circuit diagram showing an embodiment of a denitration control device according to the present invention.
FIG. 2 is a schematic diagram showing a nitrogen oxide measurement position and an ammonia injection position of a denitration reactor.
FIG. 3 is a control circuit diagram of a denitration control device according to the related art.
[Explanation of symbols]
1 denitration reactor 2 inlet duct 3 the outlet duct 4 NH ₃ injection tube 5 NH ₃ pipe 8 prior denitrating controller 9 NH ₃ injection rate calculator 10 NH ₃ flow rate control valve 12 inlet NOx analyzer 13 inlet NOx concentration signal 15 outlet NOx Concentration setting unit 16 Set NOx concentration signal 18 Required NH ₃ molar ratio calculation unit 19, 24, 40, 56, 57, 60 Subtractor 20 Required molar ratio signal 22 Outlet NOx analyzer 23 Outlet NOx concentration signal 25, 42 Proportional integral calculation Units 26, 51, 61 Adder 27 Required molar ratio correction signal 28 Gas to be processed 29 Gas flow signal to be processed 30 Total NOx amount signal 31, 32, 58, 62 Multiplier 33 Required NH ₃ flow signal 38 NH ₃ flow meter 39 measured NH ₃ flow signal 41 NH ₃ flow deviation signal 43 valve opening signal 44 vacuum converter 45 NH ₃ flow control valve control signal 50 required NH ₃ flow rate calculators 52 and 54 Function generator 53 First order lag function generator 55 Change rate controller 59 Leak NH ₃ flow rate detector 63 Out NOx deviation correction gain output signal 64 DeNOx outlet NOx deviation correction bias output signal 65 Remaining NH ₃ Adsorption amount correction bias signal 66 Correction required NH ₃ injection correction output signal 67 Denitration outlet NOx control deviation 68 Corrected required NH ₃ flow rate signal 69, 78 Differentiation circuit 70, 77 Upper decision unit 71, 76, 80 Lower decision unit 72 OR circuit 73 Negation circuit 74 On-delay circuits 75, 79, 81 AND circuit 82 Switches 83, 84 with rate-of-change limiting constant generator 85 Control amount sensitivity switching signal 86 Load change end time limit judgment signal 87 Process change direction judgment signal 88 Hunting judgment signal G Gas to be processed

Claims (6)

There is a change in the load of the object, a process value control method of the controlled device in which the process value due to the object changes,
The rate of change of the process value of the control target device becomes smaller than a predetermined value, the change of the measured process value falls within a predetermined hunting area, and the load change of the control target device is completed, or after starting up or stopping operation. A process value control method characterized in that when it is determined that a predetermined time has elapsed, the process value of the controlled device is adjusted by lowering the control amount sensitivity of the process value. Nitrogen oxide in the gas to be treated is removed by injecting ammonia into the gas to be treated. In the denitration reactor ammonia injection flow rate control method of adjusting the ammonia injection flow rate into the gas to be treated by including parameters,
The rate of change of the measured nitrogen oxide concentration becomes smaller than a predetermined value, the change of the measured nitrogen oxide concentration falls within a predetermined hunting region, and the load change of the denitration reactor is completed, or after starting up or after shutting down. A method for controlling the ammonia injection flow rate in a denitration reactor, wherein the control sensitivity of the nitrogen oxide concentration change is reduced after a predetermined time has elapsed. When the change in the measured nitrogen oxide concentration stabilizes after coming out of the hunting region, the reduction in the control sensitivity of the nitrogen oxide concentration change is released to return to the normal control sensitivity for the nitrogen oxide concentration change. The method for controlling the ammonia injection flow rate in a denitration reactor according to claim 2. There is a change in the load of the object to be processed, a process value control device of a controlled device in which a process value due to the object to be processed changes,
A process value adjusting means for adjusting a process value of the device to be controlled;
A process value change direction determiner for determining whether the change rate of the process value has become smaller than a predetermined value,
A hunting determiner for determining whether a change in the measured process value is within a predetermined hunting region,
The load change of the control target device ends, or after the load change end time limiter to determine whether a predetermined time has elapsed after start-up or operation stop,
A process value control device, further comprising: a switch for lowering the control amount sensitivity of the process value when all of the three determiners make a “Yes” determination. Nitrogen oxide in the gas to be treated is removed by injecting ammonia into the gas to be treated. In the denitration reactor ammonia injection flow rate control device that adjusts the ammonia injection flow rate into the gas to be treated by including the parameters,
A required ammonia injection flow rate calculator for calculating the ammonia injection flow rate into the gas to be processed by parameters including the nitrogen oxide concentration at the inlet of the denitration reactor, the nitrogen oxide concentration set value at the outlet, the nitrogen oxide concentration at the outlet, and the processing gas amount. ,
An ammonia injection flow controller for injecting into the denitration reactor while adjusting the ammonia injection flow based on the difference between the required ammonia injection flow calculated by the required ammonia injection flow calculator and the actually measured ammonia injection flow,
In the ammonia flow control device of the denitration device equipped with
A measured nitrogen oxide concentration change direction determiner for determining whether a change rate of the measured nitrogen oxide concentration has become smaller than a predetermined value,
A hunting determiner for determining whether a change in the measured nitrogen oxide concentration has entered a predetermined hunting region,
After the load change of the denitration reactor is completed, or after the load change end time limiter to determine whether a predetermined time has elapsed after the start of the start or the operation stop,
A switching device for lowering the control sensitivity of the change in the nitrogen oxide concentration when all of the three determination devices make a determination of "yes". 6. The denitration apparatus according to claim 5, wherein the switching unit has a function of returning the control sensitivity of the nitrogen oxide concentration change to the original set value when the hunting determination unit makes a "No" determination. Reactor ammonia injection flow control device.

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