JPH09871A - Ammonia injection amount control device for a plurality of exhaust gas treatment systems - Google Patents

Abstract

PURPOSE: To prevent the outflow of excessive ammonia by sensing the outlet NOx concentration for respective systems and correcting the injected ammonia molar ratio based on the deviation between the sensed value and the outlet NOx concentration set value. CONSTITUTION: In a system in which exhaust gas exhausted out of a boiler 1 to denitration reactors 8 and 9 for respective systems through a gas flue of two systems and the denitration treatment is carried out, samplings 10 and 11 of exhaust gas on the downstream side of denitration reactors of respective systems are carried out respectively, and a mixed body of exhaust gas in both systems is fed to an outlet NOx concentration meter 13 and the average outlet NOx concentration is sensed. Based on the sensed values of inlet NOx concentration meters 2 and 3 for respective systems, the set value of an outlet NOx concentration setting device and the average outlet NOx concentration, the injected ammonia molar ratios for respective systems are computed. Based on the injected ammonia molar ratios and the exhaust gas flow rate, flow rate regulating valves 4 and 5 are controlled to control the injected ammonia amount for respective systems.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ammonia injection amount control device for a plurality of exhaust gas treatment systems, and more particularly to an ammonia injection amount control device for a denitration device using ammonia gas as a reducing agent. The present invention relates to an ammonia injection amount control device for an exhaust gas treatment system having an exhaust gas denitration reactor.

[0002]

2. Description of the Related Art FIG. 4 shows a flue system diagram when a boiler exhaust gas system has two systems A and B. The exhaust gas discharged from the boiler 1 flows into the A-type and B-type denitration reactors 8 and 9.
The exhaust gas treated by the denitration device is the air preheater 14, 15
The heat is recovered at 1, after which dust and desulfurization are carried out if necessary, and then discharged from the chimney 17. The injection amount control of ammonia for the denitration device is usually controlled so that the NOx concentration at the outlet of the denitration device becomes constant. Specifically, the NOx concentration detection signals of the NOx meters 2 and 3 provided at the inlet of the denitration device and the NOx concentration detection signals of the NOx meters 33 and 34 provided at the outlet of the denitration device are used to control the ammonia flow rate control valves 4 and 6.
Generally, as shown in FIG. 8, in a boiler that employs the opposed combustion method by providing fuel combustion burners 33 and 34 on the front side and the rear side of the can, respectively, in the furnace 1a, the combustion state of the burner differs between before and after the can. In other words, the combustion exhaust gases in different combustion states tend not to be sufficiently mixed and to be discharged from the furnace outlet as they are as shown in FIG.

Therefore, when the NOx concentration in the exhaust gas is removed by providing a NOx removal reactor for each system with the combustion exhaust gas flue as the two systems A and B at the furnace outlet, the inlet NOx concentration of each system A, B Since they are not the same, a denitration device control device is provided for each system to control them independently. It should be noted that the exhaust gas flow rate is provided with a damper, a denitration device, and an air preheater in each system, and the gas flow rate is not the same as A and B, but there is some deviation, but in general, 1/2 of the exhaust gas flow rate is used. It is processed assuming that it is flowing.

FIG. 5 shows an example of a control system for the actual ammonia injection amount. This control system corresponds to Fig. 4.
The system and the system B are independently configured. The concept of the ammonia injection amount control is that the difference between the inlet NOx concentration signal 19 and the outlet NOx concentration setting signal output from the analog memory 20 is divided by the inlet NOx concentration by the processing gas amount 25 obtained based on the load signal 18. The required ammonia injection molar ratio signal 26 obtained on the basis of
This is a method of correcting the required molar ratio by the deviation between the x concentration set value 20a and the measured outlet NOx concentration 21. The required ammonia amount 28 is obtained by multiplying the ammonia injection molar ratio signal 26a thus obtained and the processing gas amount 25, and the ammonia amount injected by the ammonia injection flow rate control valve 31 is the measured ammonia flow rate 24. It is controlled by the controller 30 so as to eliminate the deviation.

[0005]

Monitoring of NOx emission regulation from the boiler is usually performed by monitoring the chimney inlet N shown in FIG.
It is performed by the Ox densitometer 16. On the other hand, at the time of actual operation, the NOx set values for the A and B systems are adjusted, and the NOx concentration meter 33, 34 for denitration equipment controls the amount of ammonia injection to control the chimney inlet NO.
It is performed so that the x concentration is slightly lower than the regulation value.

However, the NOx setting value at the outlet of the denitration device is A,
Since the B system has two set values, it is difficult to match the NOx value of the chimney inlet to the target value. Therefore, the NOx concentration set value lower than the target value on the safe side in operation was set (this results in injection of excess ammonia). Further, since one NOx concentration meter is provided for each of the A and B systems (two in total) at the outlet of the denitration device, there has been a problem that the number of maintenance and inspections for these analyzers increases. Therefore, as shown in FIG. 6, the NOx concentration meter 13 at the outlet of the denitration device is used for both A and B systems, and the amount of ammonia injection is controlled by the average NOx concentration of both systems in which exhaust gas from both systems is sampled in equal amounts and mixed. However, when the measured values of the NOx concentration at the inlets of the A and B systems differ depending on the load of the boiler, etc., the NOx concentration values at the outlets of the A and B systems become unbalanced (Fig. 7).
However, there was a problem that the unreacted ammonia concentration increased on the side where an excessive amount of ammonia was injected, and the overall denitration efficiency of the A and B systems also decreased when viewed from the ammonia injection amount. .

[0007]

The invention claimed in the present application for solving the above problems is as follows. (1) Two or more exhaust gas flues for treating exhaust gas from an exhaust gas source are provided, and each system is provided with an ammonia injection device, a denitration reactor, and a NOx concentration meter at the reactor inlet DeNOx reactor outlet NOx
A concentration meter, a means for sampling exhaust gas on the downstream side of each system of the denitration reactor, and a mixture of exhaust gases of all the systems sampled by the means are supplied to the outlet NOx concentration meter to detect the average outlet NOx concentration. Means, means for calculating the injected ammonia molar ratio of each system based on the detected value of the inlet NOx concentration meter of each system, the set value of the outlet NOx concentration setting device, and the average outlet NOx concentration, and the injected ammonia molar ratio, The outlet NOx for each system is supplied to the outlet NOx concentration meter by the outlet exhaust gas for each system by means for controlling the amount of injected ammonia in each system based on the exhaust gas flow rate and the switching means provided in the exhaust gas sampling means. A means for detecting the concentration and a means for correcting the injected ammonia molar ratio based on the deviation between the detected value and the outlet NOx concentration set value. Ammonia injection quantity control device to a plurality of exhaust gas treatment system characterized in that a and.

(2) A plurality of exhaust gas flues for treating exhaust gas from the combustion device are provided, and each system has an ammonia injection device, a denitration reactor, a NOx concentration meter at the reactor inlet, and an outlet NO.
x concentration setting device and exhaust gas sampling means downstream of the reactor, the NOx concentration outlet NOx concentration meter provided for both systems and the outlet based on the mixed exhaust gas of all the systems sampled from the exhaust gas sampling pipe A means for detecting the average outlet NOx concentration by the NOx concentration meter, and a means for calculating the injection ammonia molar ratio to each system based on the output values of the inlet NOx concentration meter, the average outlet NOx concentration detecting means and the outlet NOx concentration setting device. , And means for controlling the amount of ammonia injected into each system on the basis of this injected ammonia molar ratio and the exhaust gas flow rate of each system at all times, and each system by a switching means connected to the exhaust gas sampling means every predetermined time. Based on the exhaust gas sampled for each Ammonia injection amount into a plurality of exhaust gas treatment systems, characterized by including means for detecting NOx concentration and means for correcting the injected ammonia molar ratio based on the detected value and the setting value of the outlet NOx concentration setting device. Control device.

(3) A plurality of combustion exhaust gas flues from the opposed combustion type boiler are provided, and an ammonia injection device, a denitration reactor, a NOx concentration meter at the inlet of the reactor, an NOx concentration outlet at the outlet, and the downstream of the reactor are provided in each system. Of the exhaust gas sampling pipe of the above system, one outlet NOx concentration meter provided for each system and the average outlet NOx concentration measured by the NOx concentration meter based on the exhaust gas collected from the chimney inlet flue where each system exhaust gas merges. Means for detecting concentration and the inlet NO
x concentration meter, outlet NOx concentration setting device and average outlet NOx
Means for calculating the injection ammonia molar ratio to each system based on the output value of the concentration detection means, means for controlling the ammonia injection amount to each system based on this injection ammonia molar ratio and the exhaust gas flow rate of each system, and a predetermined time Means for detecting the outlet NOx concentration for each system by the outlet NOx concentration meter based on the exhaust gas sampled for each system by the switching means connected to the exhaust gas sampling pipe downstream of the reactor for each system, and the detected value An ammonia injection amount control device for a plurality of exhaust gas treatment systems, characterized in that means for correcting the injected ammonia moles is provided based on the set value of the outlet NOx concentration setting device.

[0010]

The gas sampling pipe for the NOx concentration meter outlet of the denitration device is taken out from each of the A and B systems, and a switching valve is provided on the way to (1) sample from both the A and B systems.
A means for measuring the B system average outlet NOx concentration value, (2) a means for measuring the A system outlet NOx concentration, and (3) a means for measuring the B system outlet NOx concentration are provided. Then, the correction control is periodically performed to eliminate the deviation between the A / B system outlet NOx concentration actual value and the set outlet NOx concentration value so that the A / B system outlet NOx concentration does not vary.

During normal operation, control is performed to match the outlet NOx concentration of the A and B system average values to the set outlet NOx concentration, so the outlet NOx concentration set value is the chimney inlet NO.
Since it substantially matches the x concentration value (O ₂ % conversion value), the driving operation becomes simple.

[0012]

FIG. 1 shows a flue system diagram of an embodiment of the present invention. The difference from the conventional technology is the outlet N of the A and B system denitration equipment.
Sampling pipe for NOx meter 1 with Ox meter 13 also used
Of course, it is possible to measure the average outlet NOx concentration values of both A and B systems by providing the switching valve 12 at 0 and 11.
The outlet NOx concentration should be able to be measured by each of the system and B system alone.

FIG. 2 shows a control system diagram of an ammonia flow rate control valve which is an embodiment of the present invention. The difference from the prior art is that (1) the NOx concentration signal 21 at the outlet of the denitration device uses the average outlet NOx concentration value of the A and B systems. The control of the ammonia injection amount at the normal time is performed by using this average NOx concentration value. However, if the control is performed as it is, an imbalance occurs in the A and B systems at the outlet of the denitration device as described in the prior art. Therefore, (2) the outlet NOx concentration meter 13
Switched to use the measured NOx concentration at the outlet of system A alone 2
2. The point is that the ammonia injection molar ratio is corrected using the signal of the outlet NOx concentration measured value 23 of the B system alone. That is, the NOx concentration value 22 of the A system alone and the outlet N
Using the deviation of the Ox concentration set value 20a, the above A, B
The correction is further applied to the molar ratio correction value using the average outlet NOx concentration.

The main point of this embodiment is that the exit NO at every predetermined time.
The x concentration meter is switched and the respective values of the A and B systems are detected, and as shown in FIG. 3, the molar ratio correction is applied so that each outlet NOx concentration value matches the set outlet NOx concentration value. . This is indicated by the control circuit shown within the chain double-dashed line in FIG. From the average NOx concentration values of A and B, A,
The pitch at which the individual outlet NOx concentration values of the respective B systems are switched and the above-mentioned correction is applied can be made, for example, at the timing of automatic calibration of the NOx concentration meter 13. Therefore, the correction value is input as it is until the correction value is determined by the next independent measurement of the A and B systems. Since this method can have various patterns depending on the operating conditions of the plant such as the boiler, it may be changed each time.

Instead of the denitration outlet average NOx concentration signal 21 in FIG. 2, the chimney inlet NOx concentration meter 16 shown in FIG.
Signal may be used. Even in that case, the problem of unbalance of the NOx concentration of NOx outlets of the A and B systems described in the section of the prior art remains. It is necessary to correct it.

In addition, FIG. 2 shows an example in which the exhaust gas flow rate of each of the A and B systems is obtained from the boiler load signal, but the exhaust gas flow rate can be converted from the combustion air supply amount to the boiler. It is also possible to actually measure and obtain each of the A and B systems.

[0017]

The following effects can be expected by implementing the present invention. (1) When the NOx setting value at the outlet of the denitration device is normal, the NOx concentration setting value at the outlet is the same as the A and B systems.
This simplifies the operation of setting the outlet NOx concentration by the operator in order to match the x set value. (2) Since the number of NOx meters at the denitration outlet is reduced as compared with the conventional technology, the maintenance of the analytical meter becomes easier and the cost of the analytical meter becomes lower.

[Brief description of drawings]

FIG. 1 is a flue system diagram according to an embodiment of the present invention.

FIG. 2 is a control system diagram of an ammonia flow rate control valve according to an embodiment of the present invention.

FIG. 3 is a view showing A and B system ammonia injection amount correction pitches in an embodiment of the present invention.

FIG. 4 is a conventional flue system diagram.

FIG. 5 is a control system diagram of an ammonia flow rate control valve according to a conventional technique.

FIG. 6 is a flue system diagram when the NOx concentration meter at the outlet of the denitration device according to the related art is used for both A and B systems.

FIG. 7 is a denitration outlet NO for A and B in the prior art of FIG.
FIG. 6 is a conceptual diagram showing a state in which an imbalance occurs in x density.

FIG. 8 is a schematic diagram showing a flow state of boiler combustion exhaust gas to a flue.

[Explanation of symbols]

1 ... Boiler, 2 ... A system inlet NOx concentration meter, 3 ... B system inlet NOx concentration meter, 4 ... A system ammonia flow control valve, 5 ... A
System ammonia supply pipe, 6 ... B system ammonia flow rate control valve,
7 ... B system ammonia supply pipe, 8 ... A system denitration reactor, 9 ...
B-system denitration reactor, 10 ... A-system outlet NOx suction pipe, 11 ...
B system outlet NOx suction pipe, 12 ... switching valve, 13 ... outlet NO
x meter, 14 ... A system air heater, 15 ... B system air heater,
16 ... Chimney inlet NOx meter, 17 ... Chimney, 18 ... Load signal, 19 ... Inlet NOx signal, 20 ... Outlet NOx concentration setting device, 21 ... Average outlet NOx concentration signal, 22 ... A system outlet N
Ox concentration signal, 23 ... B system outlet NOx concentration signal, 24 ...
Ammonia flow rate, 25 ... Processing gas flow rate signal, 26 ... Required molar ratio, 27 ... Controller, 28 ... Required ammonia amount, 30
... Controller, 31 ... Ammonia flow rate control valve, 32 ... Ammonia preceding signal, 33 ... A system outlet NOx concentration meter, 34 ... B
System outlet NOx concentration meter.

Claims (3)

[Claims] 1. A system in which two or more exhaust gas flues for treating exhaust gas from an exhaust gas source are provided, and each system is provided with an ammonia injecting device, a denitration reactor and a NOx concentration meter at the inlet of the reactor NOx concentration meter at the outlet of the denitration reactor, means for sampling the exhaust gas on the downstream side of the denitration reactor of each system, and a mixture of the exhaust gases of all the systems sampled by the means are used as the outlet NOx.
Means for supplying the densitometer to detect the average outlet NOx concentration, and injection ammonia for each system based on the detection value of the inlet NOx concentration meter of each system, the set value of the outlet NOx concentration setter, and the average outlet NOx concentration A means for calculating the molar ratio, a means for controlling the injected ammonia amount of each system based on the injected ammonia molar ratio and the exhaust gas flow rate, and a switching means provided in the exhaust gas sampling means, the outlet exhaust gas for each system Means for supplying an NOx concentration meter to detect the outlet NOx concentration for each system, and means for correcting the injected ammonia molar ratio based on the deviation between the detected value and the outlet NOx concentration set value are provided. Ammonia injection amount control device for multiple exhaust gas treatment systems. 2. A plurality of exhaust gas flues for treating exhaust gas from a combustion device are provided, and an ammonia injection device, a denitration reactor, a NOx concentration meter at the inlet of the reactor, an NOx concentration setting device at the outlet, and a downstream of the reactor are provided in each system. In the exhaust gas sampling means provided, the NOx concentration meter outlet NOx concentration meter provided for both systems and the average outlet NOx concentration measured by the outlet NOx concentration meter based on the mixed exhaust gas of all systems sampled from the exhaust gas sampling pipe. Means for detecting, a means for calculating the molar ratio of ammonia injected into each system based on the output values of the inlet NOx concentration meter, the average outlet NOx concentration detecting means and the outlet NOx concentration setting device,
A means for controlling the amount of ammonia injected into each system based on the injected ammonia molar ratio and the exhaust gas flow rate of each system is provided, and at each predetermined time, sampling is performed for each system by the switching means connected to the exhaust gas sampling means. A means for detecting the outlet NOx concentration of each system by the outlet NOx concentration meter based on the exhaust gas, and a means for correcting the injected ammonia molar ratio by the detected value and the set value of the outlet NOx concentration setting device are provided. Ammonia injection amount control device for a plurality of exhaust gas treatment systems. 3. A plurality of combustion exhaust gas flues from an opposed combustion type boiler are provided, and an ammonia injection device, a denitration reactor, a NOx concentration meter at the inlet of the reactor, an NOx concentration outlet at the outlet, and a downstream of the reactor are provided in each system. In the case where an exhaust gas sampling pipe is provided, one outlet NOx concentration meter provided for each system and the average outlet NOx concentration measured by the NOx concentration meter based on the exhaust gas collected from the chimney inlet flue where each system exhaust gas merges Means for calculating the injection ammonia molar ratio to each system based on the output values of the inlet NOx concentration meter, the outlet NOx concentration setting device and the average outlet NOx concentration detecting means. Means for controlling the amount of ammonia injection into each system based on the exhaust gas flow rate of the system, and the exhaust gas sump downstream of the reactor of each system at predetermined time intervals A means for detecting the outlet NOx concentration of each system by the outlet NOx concentration meter based on the exhaust gas sampled for each system by the switching means connected to the ring pipe, and the detected value and the set value of the outlet NOx concentration setting device. A device for controlling the injection amount of ammonia into a plurality of exhaust gas treatment systems, characterized in that means for correcting the injected ammonia moles is provided.