JPH01107832A - Control device for denitration agent injection - Google Patents

Abstract

PURPOSE:To properly control a precedent injection amount of denitration agent (NH3) without delay against changing operation rate of a combustion equipment, by combinably utilizing signals of operation program of the equipment, changing rate of air supply and fuel to it, and temp. of exhaust gas from it. CONSTITUTION:An inlet NOX signal 30 is calculated in an arithmetic unit 9 based on each signal 24, 21 detected by an inlet NOX concn. detector 4 and an air flow rate detector 3, and outputted to a multiplier 13. And, a set outlet NOX concn. signal 25 is changed into a mol ratio signal 28 through an arithmetic unit 10, and the deflection from the set outlet NOX concn. signal 25 is obtained from the signal 26 sent from an outlet concn. detector 6 to make it an outlet compensation mol ratio signal 27 and moreover a compensation mol ratio signal 29 is obtained at the multiplier 13. On the other hand, an precedent injection NH3 flow rate signal 34 is obtained from a load demand operation program signal 20 to output to an arithmetic unit 14, and at the same time a gas quantity compensation signal 33 is obtained from an air flow rate variation signal 21 (a fuel flow rate will also do) and a temp. signal 19. When the load is not changed, a switch 38 turns to change a signal 34 to a signal 33.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a denitrification agent injection control device, and more particularly to a device for properly injecting ammonia in a catalytic reduction denitrification device using ammonia.

[Conventional technology]

The ammonia catalytic reduction method, which is one of the flue gas denitrification methods, has many advantages in terms of the structure of the equipment that implements this method, the performance of the equipment, equipment and operating costs, and it is suitable for thermal power plants. It is also used in many boiler plants.

Traditionally, thermal power plants have an output of 10% as the base load for power generation.
However, as nuclear power generation increases, nuclear power generation, which is difficult to operate with load fluctuations, becomes the base load, and thermal power generation is forced to operate under intermediate load. We perform daily load fluctuation operation (DSS) in response to changing power demand during the day and night.
Weekly load variable operation (WSS) is increasingly being performed to vary the load between weekdays and weekends and holidays when demand is low. Boilers that perform such variable load operation are controlled to make large load changes in a very short period of time, so the inlet gas conditions of the denitrification equipment, that is, the gas temperature, change rapidly with these load changes. There is a need for a denitrification device that can immediately respond to the concentration of nitrogen oxides contained in the gas.

Figure 3 shows the relationship between the amount of ammonia (NH3) injected and the concentration of nitrogen oxides (NOx) at the outlet of the denitration equipment. It takes several minutes to an hour, and the ability to follow boilers that undergo sudden load changes is very poor. For this reason, control has conventionally been implemented to compensate for this low load followability.

In Figure 4, if the denitrification equipment is simply controlled in response to the boiler load, the nitrogen oxide concentration at the inlet of the denitrification equipment will temporarily exceed the regulation value, as shown by symbol A, due to its low load followability. A situation arose.

For this reason, conventionally, advance control has been carried out by injecting excess ammonia B1 when the load increases and injecting too little ammonia B2 when the load decreases with respect to the required amount of ammonia determined based on the following formula (1). This prevents an increase in the outlet nitrogen oxide concentration and the generation of surplus ammonia when the addition decreases, thereby compensating for the poor load followability of the denitrification equipment.

AQ = GQ

FIG. 2 specifically shows this control, and shows the advance control signal outputted from the advance control circuit 50 consisting of the load demand signal 20 based on the boiler load demand 2, the differentiator 16, and the function generators 17 and 18, that is, the first-order differential The signal is output to the adder 14 as an advance injection signal 36 and a quadratic differential advance control signal 35, and is output as an ammonia injection signal 32 to a control terminal such as an injection amount control valve (not shown). In addition to this control to pre-inject excessive or insufficient ammonia, the nitrogen oxide concentration (desired concentration) at the outlet of the denitrification equipment set in advance,
Feedback control is also used to adjust the ammonia injection amount based on the deviation from the actually measured outlet nitrogen oxide concentration.

[Problem that the invention seeks to solve]

As described above, in the prior art, measures have been devised and implemented to compensate for the poor load followability of the denitrification equipment, but these are not sufficient.

In other words, the fuel flow rate and the corresponding air flow rate of the boiler indirectly mean the amount of exhaust gas to be treated by the denitration equipment, but as shown in Figure 5, these fuel flow rates and air flow rates are dependent on the temperature control inside the boiler furnace. Therefore, it changes and has no direct relationship with load demand.

In this case, the air flow rate and fuel flow rate will have an overshoot O8 or an undershoe 1-US, but if the ammonia advance injection control is performed only based on the boiler load demand, as in the advance injection control method in conventional equipment, such overshoots and Area UA where it is impossible to deal with undershoot and control the outlet nitrogen oxide concentration
Generates I and UA2. For this reason, it is not possible to completely prevent the temporal increase in nitrogen oxide concentration.

[Means for solving problems]

The present invention has been constructed in view of the above-mentioned problems, and is a means for obtaining advance control elements in the injection control of denitrification agent such as ammonia to be injected upstream of the denitrification device, and is designed to improve the rate of change of the air flow rate and/or Alternatively, a means for measuring the fuel flow rate and a means for measuring the exhaust gas temperature at the outlet of the denitrification device are added, and the signals of the air flow rate, fuel flow rate, and exhaust gas temperature output from these means are replaced with the additional demand signal of the combustion device. Alternatively, it is a device configured to grasp the correct state of the exhaust gas by using it in conjunction with this, and to control the injection amount of the denitrification agent in accordance with the state of the exhaust gas.

[Effect]

If changes in exhaust gas conditions can be predicted by changes in the load of the combustion equipment, advance injection control is performed using the load demand signal, and if changes in exhaust gas conditions cannot be predicted by the load demand signal, the air flow rate and/or fuel injection for the combustion equipment is controlled. Switch to advance control using flow rate and exhaust gas temperature signals.

〔Example〕

Embodiments of the present invention will be specifically described below with reference to the drawings.

First, an outline of the configuration of the present invention will be explained.

The reaction rate of the denitrification reaction in the denitrification equipment, that is, the denitrification rate, is
In relation to the amount of gas to be denitrified, the reaction temperature, the amount of ammonia adsorbed on the catalyst, and the amount of denitrification catalyst filled in the denitrification equipment, it can be calculated using the following equations (2) and (3). Can be done.

I r (1-X)-' = KrXQX -... (
2) Kr=f(T) ... (3) Here, X is the denitrification rate, F is the amount of treated gas, T is the reaction temperature,
Q represents the amount of ammonia adsorbed on the catalyst, Ir represents the reaction rate constant, Kr represents the function of temperature T, and S represents the catalyst area.

As expressed in equations (1) to (3), the present invention is capable of controlling changes in exhaust gas amount and temperature that have the greatest effect on the performance of the denitrification equipment by using changes in fuel flow rate or air flow rate, and a temperature close to the catalyst layer temperature. This system detects the temperature of the exhaust gas at the outlet of the denitrification equipment and accurately ascertains the actual change in the boiler, thereby injecting ammonia appropriately.

In FIG. 1, the nitrogen oxide concentration at the inlet of the denitrification device is detected by a nitrogen oxide concentration detector 4 and output as a nitrogen oxide concentration signal 24. On the other hand, the air flow rate signal 21 detected by the air flow rate detector 3 is converted into an exhaust gas amount signal 23 by a function converter 8, and this exhaust gas amount signal 23 and the above-mentioned inlet nitrogen oxide concentration signal 24 are combined by a multiplier 9. The signal is multiplied at , and outputted to another multiplier 13 as the denitrification device inlet nitrogen oxide signal 30 .

An inlet nitrogen oxide concentration signal 24 and a set outlet nitrogen oxide concentration signal 25 set in the outlet nitrogen oxide setting device 5
is output to the arithmetic unit 10, and the molar ratio signal 28 is output from the arithmetic unit 10. Furthermore, the inlet nitrogen oxide concentration signal 2
4. Using the set outlet nitrogen oxide concentration signal 25 and the detected nitrogen oxide concentration signal 26 detected by the outlet nitrogen oxide detector 6, the arithmetic unit 11 calculates the set outlet nitrogen oxide concentration and the actually measured outlet nitrogen oxide concentration. The deviation from the nitrogen oxide concentration is determined, and this deviation is used as the exit correction molar ratio signal 27.

A corrected molar ratio signal 29 is obtained in the adder 12 using the molar ratio signal 28 and the exit corrected molar ratio signal 27, and a necessary amount of injected ammonia is calculated in the multiplier 13 using the inlet nitrogen oxide concentration signal 30 and this corrected molar ratio signal 29. Obtain signal 31.

On the other hand, when a load change occurs in the combustion device, the load change rate is obtained from the load demand signal 20 via the differentiator 16, and the pre-injected ammonia flow rate is determined in the function generator 37 based on this load change rate and the load demand signal 20. A signal 34 is obtained. This advance injection ammonia flow rate signal 34 and the required injection ammonia amount signal 31 are output to the adder 14,
This provides the injected ammonia flow rate signal 32.

In addition, the air flow rate change signal 22 obtained by differentiating the air flow rate signal 21 in the differentiator 7 and the temperature signal 19 obtained by the denitration equipment outlet temperature detector 1 are calculated in the function calculator 15 to determine the gas amount. A corrected advance injection signal 33 is obtained, but if there is no load change, the load change advance injection signal 34 is switched to this gas amount corrected advance injection signal 33 by a switch 38 and output to the adder 14.

In this way, the elements that control ammonia injection are changed in response to the changing conditions of the boiler, which is a combustion device, so ammonia injection can always be made to correspond to the operating conditions of the boiler, and the amount of injection can be controlled with high precision at all times. It can be performed.

In the device described above, one of the detectors for detecting the changing state of the combustion device is the air flow rate detector 3, and the load state of the combustion device is measured from the amount of air supplied to the combustion device. However, instead of or in addition to this air flow rate detector 3, a detector for detecting the fuel flow rate to the combustion device may be arranged, and the fuel flow rate may be used to determine the operating state of the combustion device. It is definitely possible.

〔effect〕

As the configuration of the present invention has been specifically shown above, the present invention is used as a means for obtaining advance control elements in the injection of a denitrification agent such as ammonia to be injected upstream of the denitrification device, and is used to control the rate of change of the air flow rate supplied to the combustion device and/or Alternatively, a means for measuring the fuel flow rate and a means for measuring the exhaust gas temperature at the outlet of the denitrification device are added, and the air flow rate, fuel flow rate,
By using the exhaust gas temperature signal instead of or in combination with the additional demand signal of the combustion equipment, it is possible to grasp the correct exhaust gas condition, so it is possible to always inject the correct amount of denitrification agent in accordance with the operating status of the combustion equipment. .

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a denitrification agent injection control device showing an embodiment of the present invention, Fig. 2 is a system diagram of a conventional denitrification agent injection control device, and Fig. 3 is a diagram showing ammonia injection amount and nitrogen oxide concentration at the denitrification device outlet. Figure 4 is a diagram showing the ammonia injection status with respect to combustion equipment load fluctuations in a conventional control device, and Figure 5 is a diagram showing the relationship between combustion equipment load changes and air and fuel quantity overflows. FIG. 3 is a diagram showing the states of shoots, undershoots, and the like. 1...Denitration equipment temperature detector 2...Load demand 3...Air flow rate detector 4...Inlet nitrogen oxide concentration detector 5...Outlet nitrogen oxide concentration setting device 6...Outlet Nitrogen oxide concentration detector 7... Differentiator 8... Function generator 19... Temperature signal 20... Load demand signal 21... Air flow rate signal 22... Air flow rate change signal 23.
...Exhaust gas flow rate signal 24...Inlet nitrogen oxide concentration signal 25...Setting outlet nitrogen oxide concentration signal 26...Outlet nitrogen oxide concentration signal 30...Inlet nitrogen oxide concentration signal 31... Required injection ammonia amount signal 32...Injection ammonia amount signal 38...Switcher Fig. 1 Fig. 2 Fig. 3 Fig. 4 Time Fig. 5

Claims (2)

[Claims] (1) In a device that controls the amount of denitrification agent injected in advance of changes in the load of the combustion equipment based on the load demand of the combustion equipment, the amount of air supplied to the combustion equipment, the established amount of nitrogen oxides at the outlet of the denitrification equipment, etc. A signal output from a means for measuring the rate of change of the air flow rate and/or a fuel flow rate supplied to the combustion device as an element, and a signal output from a means for measuring the exhaust gas temperature at the outlet of the denitrification device are added, and these means are added. Means capable of switching between at least one of an air flow rate signal, a fuel flow rate signal, and an exhaust gas temperature signal outputted from the load demand signal and the load demand signal is connected to a means for calculating the amount of denitrification agent to be injected, and the operation status of the combustion device is In response to this, the control element is a load demand signal of the combustion device, or in place of the load demand signal, at least one of an exhaust gas temperature signal, an air flow rate signal, and a fuel flow rate signal is used. Drug injection control device. (2) The denitrification agent injection control device according to claim (1), wherein the denitrification agent is ammonia.