JPH1015354A - Denitrification control of denitrification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To denitrify exhaust gas by making a denitrification rate accurately constant, if there is a sharp load variation. SOLUTION: An addition molar ratio m2 is sought by adding a molar ratio correction value mc which corrects a rate of denitrification so that the rate is constant, if there is a load variation, to a molar ratio ml complying with a fuel demand 2. Further, an ammonia flow rate is controlled so that a calculated quantity of ammonia 6 obtained by multiplying the addition molar ratio m2 by a total quantity of NOX 5 and an actual quantity of ammonia 8 show a deviation of O. On the other hand, a residual quantity of ammonia 27 obtained by subtracting the rate of denitrification 23 obtained based on the actual quantity of ammonia 8 from a value 1 is multiplied by a differential rate of variation 29 in NOX at the entrance which is obtained by differentiating a rate of variation 11 in NOX at the entrance to seek a correction value 31. In addition, an estimated rate of variation 33 in NOX at the exit obtained by adding the correction value 31 to a rate of variation 12 in NOX at the exit and the rate of variation 11 in NOX at the entrance are used to seek an actual rate of denitrification 14. Further, the molar ratio correction value mc is sought based on a deviation between the actual rate of denitrification 14 and a set rate of denitrification 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitration control method for a denitration apparatus, and is particularly effective when applied to a denitration apparatus installed in a thermal power plant.

[0002]

BACKGROUND OF THE INVENTION thermal power plant, in order to prevent the occurrence of pollution, have established denitration apparatus for removing combustion gas (exhaust gas) of nitrogen oxides in (hereinafter referred to as "NO _X"). In such a denitration apparatus, ammonia is added to a combustion gas, mixed well, and then put into a catalyst layer (for example, ceramics). By doing so, the NO _x in the combustion gas
And ammonia react rapidly by the action of a catalyst, turning into harmless nitrogen and water vapor. In the denitration reaction, 1 mol of N
H ₃ with one mole of the NO _X react, is decomposed into N ₂ and H ₂ O.

Here, a conventional control circuit of a denitration apparatus will be described with reference to FIG. In the function generator 1 shown in the figure, a molar ratio static characteristic that defines the relationship between the fuel demand 2 and the molar ratio is set. When a fuel demand 2 which is a fuel command signal is input, the function generator 1 outputs a molar ratio m1 obtained from the molar ratio static characteristic.

An adder 3 adds a molar ratio m1 and a molar ratio correction value mc (a method for calculating this value will be described later) for correcting the denitration rate to be constant even when the load changes. The ratio m2 is output. The multiplier 4 multiplies the NO _X amount 5 to the addition molar ratio m2, and outputs an operation flow rate of ammonia 6.

A subtractor 7 receives a calculated ammonia flow rate 6 and an actual ammonia flow rate 8 indicating the actual flow rate of ammonia supplied to the denitration apparatus for denitration, and calculates the difference between the two flow rates 6 and 8. It outputs a certain deviation flow rate Δ. The proportional integrator 9 performs a proportional integral operation on the deviation flow rate Δ to output an opening signal K for controlling the opening of a flow rate control valve (not shown) for adjusting the ammonia flow rate. By adjusting the opening of the flow control valve with the opening signal K, the actual ammonia flow 8
Is equal to the calculated ammonia flow rate 6, that is,
Feedback control is performed such that the deviation flow rate Δ becomes zero.

Next, a description will be given of a circuit portion for obtaining the above-mentioned molar ratio correction value mc. Subtractor 10, the outlet shown from the inlet NO _X variation 11 showing changes in the amount of NO _X at the inlet of the denitrification system, a change in the amount of NO _X at the outlet of denitrator NO
_{The X} change amount 12 is subtracted. The divider 13 divides the subtraction value of the subtractor 10 by the inlet NO _X change amount 11 to output an actual denitration rate 14 which is an actual denitration rate in the denitration apparatus.

The subtracter 15 subtracts the actual denitration ratio 14 from the set denitration ratio 16 and outputs a deviation denitration ratio 17. The proportional integrator 18 performs a proportional integral operation on the deviation denitration rate 17 and outputs a molar ratio correction value mc.

The molar ratio correction value m obtained as described above
By controlling the ammonia flow rate based on the added molar ratio m2 obtained by adding c to the molar ratio m1 in the adder 3,
Even if a load change occurs, control can be performed to keep the denitration rate constant. In other words, when the load is constant, even if the control is performed based on the molar ratio m1 obtained from the fuel demand 2 and the molar ratio static characteristic (function of the fuel demand) of the function generator 1, the denitration rate is kept constant. However, if a load change occurs, the denitration rate cannot be made constant unless control is performed based on the added molar ratio m2 obtained by adding the molar ratio correction value mc to the molar ratio m1.

By the way, the inlet NO _X change amount 11 and the outlet N
Phase of the O _X variation 12, denitration reaction delay and sampling delay caused is different. However, the conventional control circuit does not take the phase difference into account, so the denitration rate is not exactly constant but fluctuates.
When the phase difference became large due to aging, an alarm was sometimes issued.

[0010]

In THE INVENTION Problem to be Solved by the control of the denitration unit in a conventional thermal power plant, in case of performing the feedback control such as NOx removal efficiency or outlet NO _X amount of change, the sample delay of the outlet NO _X amount of change The correct molar ratio correction value mc is not added to the molar ratio mc1,
Denitration ratio or outlet NO _X amount of change is not controlled to be constant, the addition molar ratio m2 is fluctuates, the alarm due to aging had led to events occurring.

Here, a schematic relational expression between the outlet NO _X change amount, the inlet NO _X change amount, and the denitration rate is shown below. Outlet NO _X change amount = Inlet NO _X change amount × (1.0−DeNOx rate). (1.0-denitration rate) means the amount of ammonia not actually used for denitration.

Therefore, when the denitration rate is 0.8, the inlet NO
_{If the X} change amount changes by 10 ppm, the outlet NO _X change amount will change by 2 ppm after the sample delay. Further, since there is actually a delay in the denitration reaction or the like, if the change amount of the outlet NO _{X is} directly used as a feedback signal, there is a possibility that control disturbance will occur.

The present invention has been made in view of the above-mentioned prior art, and has been developed in consideration of an entrance NO.
By compensating for the phase lag of the outlet NO _X amount of change with respect to _{the X} variation, there is provided a denitration control method of denitration device capable of load conditions to a constant accurately denitration rate changes.

[0014]

Configuration of the present invention to solve the above problems SUMMARY OF THE INVENTION are, in the denitration apparatus for removing NO _X by mixing ammonia into the exhaust gas containing NO _X, to the denitrification rate constant To control the flow rate of ammonia,
From a function that defines the relationship between the fuel demand and the molar ratio to obtain the molar ratio corresponding to the current fuel demand, in fact from the NO _X amount of change at the outlet of the NO _X amount of change and the denitrification device at the inlet of the denitrification system seeking denitration rate, determine the molar ratio correction value deviation based on the setting denitration rate and the actual NOx removal rate, the ratio between the molar ratio correction value and a by multiplying the NO _X amount to an addition molar ratio by adding operations A denitration apparatus that obtains an ammonia flow rate and adjusts the opening of a flow rate control valve that adjusts the ammonia flow rate so that the deviation between the actual ammonia flow rate, which is the ammonia flow rate supplied for denitration, and the calculated ammonia flow rate is zero. In the denitration control method, the denitration rate with respect to the current amount of ammonia in the apparatus is determined from a function that defines the relationship between the in-apparatus ammonia amount and the denitration rate in which the actual ammonia flow rate is first-order delayed. Residual ammonia amount is subtracted value, obtained by differentiating the inlet NO _X variation differential inlet NO _X
Multiplying the change amount compensation value is obtained, determine the expected outlet NO _X amount of change by adding the correction value to the outlet NO _X amount of change, when calculating the actual NOx removal rate to determine the molar ratio correction value as NO _X amount of change at the outlet of denitrator, and obtains the actual NOx removal rate by calculation using the estimated outlet NO _X amount of change.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.
This will be described in detail based on FIG. Note that the same reference numerals are given to portions that perform the same functions as in the related art, and overlapping descriptions will be omitted.

A first-order delay circuit 21 performs a first-order lag process on an actual ammonia flow rate 8 indicating the flow rate of ammonia injected into the denitration apparatus, and outputs an in-apparatus ammonia quantity 20 indicating the amount of ammonia present in the denitration apparatus. I do. That is, the amount of ammonia (20) used in the denitration reaction inside the denitration device is approximated by a value that is a first-order delay from the actual ammonia flow rate 8 actually supplied to the denitration device.

In the function generator 22, a function that defines the relationship between the in-device ammonia amount 20 and the denitration rate is set. When the in-device ammonia amount 20 is input, the function generator 22 outputs a denitration rate 23 obtained from the function. Note that the denitration rate is determined by the amount of ammonia held in the catalyst (the amount of ammonia in the device).

The signal generator 24 outputs a unit signal 25 having a value of "1". The subtracter 26 subtracts the denitration rate 23 from the unit signal 25 and outputs a residual ammonia amount 27 having a value of (1−denitration rate). This residual ammonia amount 28 indicates the amount of ammonia that was not actually used for denitration.

The differentiator 28 differentiates the inlet NO _X variation 11 and outputs a differentiated inlet NO _X variation 29.

The multiplier 30 determines the residual ammonia amount 27
Minute entrance NO_XMultiplies the amount of change 29 and outputs a correction value 31
You. This correction value 31 indicates that the residual ammonia amount 27 is large.
When (that is, whether it is actually used for denitration in the denitration equipment
When the amount of ammonia is large), and the differential inlet NO_X
When the change amount 29 is large (the load NO _X
(When the change amount 11 suddenly changes).

The adder 32 has an exit NO_XCompensation for change amount 12
Add the positive value 31 to get the expected exit NO _XOutput variation 33
I do. This expected exit NO_XThe change amount 33 is actually used for denitration.
When the amount of unused ammonia is large or the load changes suddenly
Exit NO_XThe amount of change 12 actually increases
It becomes larger at the timing before. In other words, denitration is actually
When the amount of unused ammonia increases,
When the load changes suddenly, exit NO_XThe amount of change 12 is
The timing changes after the occurrence of such an event
But expected exit NO_XThe change amount 33 is obtained by performing a prediction operation.
Timing delay for the occurrence of the event
Instead, it changes with good tracking.

Conventionally, the outlet NO _X change amount 12 and the inlet N
O _X variation 11 had determined the actual NOx removal efficiency 14 thus deviation denitrification efficiency 17 and the molar ratio correction value mc used, in the present embodiment, using the estimated outlet NO _X amount of change 33 and the inlet NO _X amount of change 11 Thus, the actual denitration ratio 14 and thus the deviation denitration ratio 17 and the molar ratio correction value mc are determined. That is,
The calculation is performed using the predicted exit NO _X change amount 33 instead of the exit NO _X change amount 12.

That is, the subtractor 10 subtracts the expected outlet NO _X change 33 from the inlet NO _X change 11 indicating the change in the NO _X amount at the inlet of the denitration apparatus. The divider 13 divides the subtraction value of the subtractor 10 by the inlet NO _X change amount 11 to output an actual denitration rate 14 which is an actual denitration rate in the denitration apparatus.

The subtractor 15 subtracts the actual denitration ratio 14 from the set denitration ratio 16 and outputs a deviation denitration ratio 17. The proportional integrator 18 performs a proportional integral operation on the deviation denitration rate 17 and outputs a molar ratio correction value mc.

The molar ratio correction value m obtained as described above
By controlling the ammonia flow rate based on the added molar ratio m2 obtained by adding c to the molar ratio m1 in the adder 3,
Even if a load change occurs, control can be performed to keep the denitration rate constant. Moreover, the expected exit NO _X change amount 33 is
To compensate for the sampling delay with respect to the denitration reaction delays and inlet NO _X amount of change 11, because that is the substantially the same phase as the inlet NO _X amount of change 11, the molar ratio correction value mc turn, adds the molar ratio m2 is detection delay of The value has no effect.

As a result, when the inlet NO _X change amount 11 rises sharply, the correction value 31 increases even if the outlet NO _X change amount 12 does not change, and the molar ratio correction value mc becomes equal to the inlet NO _{X amount.} It changes sharply in accordance with the sudden increase of the change amount 11.
Therefore, a good follow-up property can be obtained with respect to the change of the inlet NO _X change amount 11, and the denitration control can always be satisfactorily performed, for example, prevention of excessive injection of ammonia.

The present invention is not limited to the denitration apparatus provided in the thermal power plant, but also includes N2 in exhaust gas from another plant or apparatus.
O _X a it can be applied to a denitration apparatus for removing.

[0028]

As described above in detail with the embodiments, according to the present invention, it is possible to output a proper molar ratio correction value in all operating states of a thermal power plant, No more wasted movement. As a result, unnecessary over-injection of ammonia can be prevented, and the total amount of injected ammonia can be reduced. Further, since there is no excessive ammonia inflow, the life of the ceramic used as a denitration catalyst can be extended.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram illustrating an embodiment of the present invention.

FIG. 2 is a control circuit diagram showing a conventional technique.

[Explanation of symbols]

1 function generator 2 fuel demand third adder 4 multipliers 5 NO _X amount 6 arithmetic ammonia flow 7 subtracter 8 actual ammonia flow 9 proportional integrator 10 subtractor 11 inlet NO _X variation 12 outlet NO _X variation 13 divider 14 Actual denitration rate 15 Subtractor 16 Set denitration rate 17 Deviation denitration rate 18 Proportional integrator 20 Amount of ammonia in the apparatus 21 Primary delay circuit 22 Function generator 23 Denitration rate 24 Signal generator 25 Unit signal 26 Subtractor 27 Residual ammonia quantity 28 Differentiator 29 Differential inlet NO _X change amount 30 Multiplier 31 Correction value 32 Adder 33 Expected outlet NO _X change amount m1 Mole ratio m2 Addition mole ratio mc Mole ratio correction value Δ Deviation flow rate K Opening signal

Claims (1)

[Claims] 1. NO_XMixing ammonia with exhaust gas containing
NO by doing _XIn the denitration equipment that removes
To control the flow rate of ammonia to keep the nitrate constant
From the function that defines the relationship between fuel demand and molar ratio,
Find the molar ratio corresponding to the current fuel demand_XChange amount and at the exit of the denitration equipment
NO_XCalculate the actual denitration rate from the change amount,
The molar ratio correction value is determined based on the deviation from the denitration rate, and the molar ratio is obtained by adding the molar ratio and the molar ratio correction value.
NO_XThe calculated ammonia flow rate is obtained by multiplying the total amount, and the actual ammonia flow rate is the ammonia flow rate supplied for denitration.
Make the deviation between the ammonia flow and the calculated ammonia flow zero
Adjust the opening of the flow control valve to adjust the ammonia flow
In the denitration control method of the denitration device, the ammonia in the device whose actual ammonia flow rate is delayed first order
From the function that defines the relationship between the amount and the denitration rate,
Calculate the denitration rate for the amount of ammonia, and subtract the denitration rate from the value 1.
And the entrance NO_XDifferentiation entrance NO obtained by differentiating the amount of change_XStrange
Multiplied by the amount of conversion to obtain a correction value, and the exit NO_XAdd the correction value to the amount of change and estimate the exit NO_Xchange
Calculate the actual deNOx rate to obtain the molar ratio correction value
At the outlet of the denitration equipment_XAs the amount of change,
Sou Exit NO_XCalculate the actual denitration rate by using the change amount
A denitration control method for a denitration apparatus.