JPS61254229A - Apparatus for controlling injection amount of ammonia - Google Patents

Abstract

PURPOSE:To eliminate the response delay at the time of rising in load, by providing comparators for comparing a necessary NH3 flow amount signal with an actually measured NH3 flow amount signal and injecting a constant amount of NH3 when the former is smaller than the latter or the deviation of both signals is small. CONSTITUTION:The signals from an inlet NOX concn. detector 12 and an air flow amount detector 14 are sent to an operator 18 through a function converter 16 to calculate a total NOX amount signal 19 while a necessary mol ratio setting signal 23 is calculated and this signal 23, the correction signal 27 obtained from an outlet NOX concn. detector 24 through an adder 26 and the total NOX amount signal 19 are operated by an operator 28 to calculate a necessary NH3 flow amount signal 29 which is, in turn, compared with an actually measured NH3 flow amount signal 31 by a comparator 32 and a deviation signal 33 is sent to a proportional integrator 34. A low signal selector 40 is provided to the downstream side of said integrator 34 and when a valve opening degree signal 35 comes to zero or the actually measured NH3 flow amount signal 31 is smaller than the necessary NH3 flow amount signal 29, an NH3 flow amount control valve 39 is opened to inject a constant flow amount of NH3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ammonia injection amount control device, and particularly to an ammonia injection amount control device for removing nitrogen oxides (NOX) from exhaust gas.

[Background of the invention]

In recent years, in Japan, due to the tight supply of heavy oil, in order to correct the dependence on oil, fuels have been changed from conventional heavy oil-only combustion to coal-only combustion and LNG (liquefied natural gas)-only combustion, especially for commercial boilers. Large-capacity coal-fired and LNG-fired thermal power plants are being constructed in the area.

However, coal fuel has poor fuel properties compared to petroleum fuel and gas fuel, so NOx and unburned substances contained in exhaust gas are likely to be generated. Also, methods such as two-stage combustion and in-furnace denitrification have been adopted to perform slow combustion to eliminate NOx.

And in this coal-fired thermal power and LNG-fired thermal power,
A boiler with 9 loads that is always operated at full load has a low tr (
, increase or decrease the load to 75% valve load, 50% load, 25% load, and operate the machine.
t 5top (hereinafter referred to as single KDSS) operation to moderate the intermediate valve chamber.On the other hand, in addition to this thermal power boiler, gas turbines with good starting characteristics and gas turbines with good starting characteristics are being used for intermediate load thermal power generation. A so-called combined plant that combines an exhaust heat recovery boiler is also used, and D
A system is about to be built that will operate the SS train during the day, when electricity demand is high, and shut down at night.

However, with the tightening of regulations regarding NOx emission concentration in these coal-fired and LNG-fired intermediate-load boilers and gas turbines, in addition to conventional combustion improvements, denitrification in the presence of a catalyst using MHI as a reducing agent has been introduced. An increasing number of plants are installing dry catalytic reduction denitrification equipment.

This is because in coal-fired boilers, the combustibility of the fuel is poor, so NOXi increases, and in LNG-fired boilers and gas turbine plants, there is a large amount of NOXi in the exhaust gas because of the high oxygen content and high temperature combustion in LNG-fired boilers and gas turbine plants. NO
Since it contains X, a denitrification device as shown in FIG. 3 is installed.

Figure 3 shows a typical flue duct system of a boiler equipped with a denitrification device.

The combustion air in the air duct 1 is pressurized by the forced draft fan 2, heated by the exhaust gas from the exhaust gas duct 4 in the air preheater 3, and then supplied to the boiler 6 from the wind box 5.

On the other hand, the exhaust gas combusted in the boiler 6 is denitrated by the NH3 in the exhaust gas duct 4 and the NH) injection pipe 7, and the denitration is promoted in the catalyst 9 in the denitrification device 8 disposed downstream, and NOx in the exhaust gas is removed. removed air preheater 3,
Dust collector10. The pressure is increased by the induced draft fan 11 and released into the atmosphere.

However, although the reaction temperature range of the denitrification device 8 differs depending on the scale of the catalyst 9, the temperature range with the highest denitrification efficiency is a relatively high temperature of 300 to 400°C, and the temperature range is quite narrow, so it is not suitable for intermediate loads. For those that are constantly operated by DSS, such as thermal power boilers and combined cycle,
There is a drawback that the exhaust gas temperature constantly fluctuates due to load fluctuations, which causes the catalyst 9 to be out of the usable range.

In this case, if the temperature of the gas used in the catalyst 9 is too high, the catalyst 9
If the temperature of the gas used is too low, it will react with sulfuric anhydride (Sol) present in the exhaust gas, and the function of the catalyst 90 will also deteriorate.

On the other hand, in thermal power generation boilers and combined cycle systems that are constantly operated under DSS, the amount of exhaust gas and the concentration of NOx fluctuate, which has the disadvantage that the followability of denitrification performance deteriorates.

That is, when the exhaust gas 1 and NOX 8 degrees caused by the reaction mechanism of NOX and NHt on the catalyst 9 fluctuate, such as during startup or self-defense changes, NH1
This is because denitrification performance cannot follow load fluctuations even if an injection chamber is used.

In order to avoid these problems, a typical example of a conventional NHJ injection amount control device is shown in FIG.

In FIG. 4, an inlet NOx signal 13 detected by an inlet NOx concentration detector 12 and an air flow rate signal 15 detected by an air flow rate detector 14 are converted by a function converter 16, and this converted signal 17 is calculated. The total NOx i is calculated by the unit 18.
ff signal 19 is calculated. On the other hand, the required molar ratio (NOx tension and NH
31ft ratio) Calculate signal 23 and add exit NOX to this.
Dormitory measurement port number detected by concentration detector 24! An adder 26 performs correction with the signal 25, and a calculation unit 28 uses the correction signal 27 and the above-mentioned total NOX amount signal 19 to calculate a necessary NH3 landscape signal 29.

A comparator 32 compares this required NHs flow rate signal 29 with an actual NH3 flow rate signal 31 detected by an actual NHy flow p outflow detector to calculate a deviation signal 33, which is then converted into a valve opening degree signal by a proportional integrator 34. 35 and converted into a control signal 37 by a snow/sky converter 36, which opens and closes the NH3 flow rate control valve 39 of the NH3 pipe 38.

In this way, in the conventional NH > injection amount control device, the DS
If the NOx view at the inlet of the denitrification equipment becomes lower than the planned exit NOx view due to S operation, fuel conversion, etc., that is, the required NHs
When the flow rate signal 29 becomes smaller than the actual measured NH and flow rate signal 31, NH>Flow rate control valve 39 is fully closed, and NH
) into the denitrification equipment.

Therefore, if the conventional NH3 injection mass control device shown in Fig. 4 is adopted in the denitrification equipment of a plant designed to reduce NOx,
In those that perform DSS operation, there is a drawback that there is a delay in the response of denitration when the load increases.

Figure W5 is a characteristic curve diagram in which the vertical axis shows the boiler load and N0Xf, and the horizontal axis shows time.

In Fig. 5, curve A is the boiler load, curve B is the inlet NOx Jl of the denitrification equipment, dashed line C is the planned exit NOx amount of the denitrification equipment, the curved line is the NH3 injection amount, and the dashed line E is the NH3
The injection injection point zero point 'flJF is the actual measured outlet NOx of the denitrification equipment.
Indicate quantity.

As shown in Figure 5, the boiler load is at point G on curve A.

If you go down like H and I, the amount of NOx at the inlet of the denitration equipment will be track #B.
As shown by the t [KAG, H, I, it descends to points G, H, I as shown by the NHs injection oil line, and then to point H.

1, the amount of NH3 injected becomes zero as shown by the curved line.

Then, when the boiler load increases from point I on curve A to point J, the NOX i at the inlet of the denitration equipment increases from Al on curve B to point J, and the NH3 injection amount also increases from point I on curve B to point J. do.

However, as shown by the curved line in Figure 5, the Al
Until then, the amount of NH) injected is zero, and even if the NHs injection is increased from point I to point J as the boiler load increases, most of the NH in the initial stage of injection is adsorbed by the catalyst and does not participate in the denitrification reaction. Therefore, the actual measured outlet N0xf of the denitration equipment is point K on curve F in FIG.

As with L and M, a response delay appears, which is not desirable.

[Purpose of the invention]

The present invention aims to eliminate such conventional drawbacks,
The purpose of this is to eliminate response delays when the load increases and to reduce NOx emissions during restart and when the load is low.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention provides a button low signal selector between the comparator and the ammonia flow rate control valve, and as a result of comparing both signals, the measured ammonia flow rate signal is higher than the ammonia flow rate signal. In at least one of the cases where the deviation between the signals is small and the deviation between both signals is small, ammonia of a constant amount t is injected.

〔Example〕

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

FIG. 1 is a system 1t diagram of the injection amount control device for NI according to an embodiment of the present invention, and the acid diagram 2 is a characteristic curve diagram for the wholesale system shown in FIG. 1.

In FIG. 1, numerals 14 to 39 indicate the same elements as in FIG. 4.

40 is a low signal selector interposed between the comparator 32 and the NHj flow t7 control valve 39, and this low signal selector 40 is also a limiter for the NH injection amount.

Further, the symbols A to J in Figure 2 refer to those in Figure 5. Point 0. P indicates the injection amount of Nl.

In such a structure, the NH3 injection amount control device shown in FIG. 4 and the NHs injection injection side control device of the present invention shown in FIG.
is set, and the valve opening signal 35 becomes zero or the required N
When the measured NH1 flow rate signal 31 is smaller than the H, @J signal 29, the NHt flow rate control valve 39 is opened to inject NH3 at a constant flow rate.

In other words, in the NHs injection amount control according to the present invention, the inlet NOXt shown by the curve B in FIG.
The difference between the two is small, or the inlet NOx t lowers the outlet NOx amount from point H to Al, and the valve opening signal 35 from the proportional integrator 34 causes the NH engineering flow control valve 39 to open when the engine is fully closed. In the case of a constant flow rate signal 35, the low signal selector 40 keeps the opening degree of the NH3 flow rate control valve 39 constant from point 0 to point P on the curve in FIG. 2
NH3 (the diagonal part in the figure) is continuously injected.

In this way, even when the load is low, there is surplus NH between points 0 and 2 on the curve in Figure 2! Since fi is supplied to the denitrification equipment and adsorbed by the catalyst, the boiler load is as shown in Figure 2!
! li! Even if the temperature rises sharply from AI at A to point J, this surplus NH3 injected at low load will help the denitrification reaction,
As shown by curve F in FIG. 2, the response delay of the denitrification device is eliminated.

In addition, in the conventional NH) injection amount control device, the required N
If the difference between the H3 injection amount signal 29 and the measured NH3 injection signal 31 is small, the Pa of the NH3 flow control valve 39 becomes unstable, but in the NH3 injection amount control device of the present invention, both signals 29 , 30 is small, a constant flow t (hatched area in figure F2) always flows, so NH) v! of the flow control valve 39. 41! ? becomes stable.

〔Effect of the invention〕

The present invention provides a low signal selector between the comparator and the ammonia flow control valve, and compares both signals. In at least one case, since ammonia is injected at a constant f°, the responsiveness of the denitrification device is excellent, and the amount of NOx can be reduced even when the load increases, when restarting, etc.

[Brief explanation of the drawing]

Fig. 1 is a control system diagram of an NH3 injection amount control device according to an embodiment of the present invention, Fig. 2 is a characteristic curve diagram of Fig. 1, and Fig. 3 is a typical smoke of a boiler equipped with a denitrification device. Wind duct system diagram,
Figure 4 is a control system diagram of a conventional NH1 injection amount control device.
FIG. 5 is a characteristic curve diagram of FIG. 4. 29... Necessary N) 14 flow rate signal, 31...
... Actual measurement N) It flow rate signal, 32 ... Comparator,
39...N I (3 flow rate control valve, 4o...
...Low signal selector.・；r、）仄r Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A comparator is provided to compare the required ammonia flow rate signal and the measured ammonia flow rate signal, and the ammonia flow rate control valve is opened and closed based on the deviation signal from the comparator to control the ammonia flow rate, wherein the ammonia flow rate is controlled by the comparator and the ammonia flow rate signal. A low signal selector is installed between the control valves, and as a result of comparing both signals,
An ammonia injection amount control device characterized in that a fixed amount of ammonia is injected in at least one of the cases where the measured ammonia flow rate signal is smaller than the required ammonia flow rate signal and the deviation between both signals is small. .