JPS64994Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention] The invention relates to an ammonia injection amount control device,
In particular, it relates to an ammonia injection amount control device to a coal-fired denitrification device.

[Background of the idea]

In recent years, in Japan, due to the tight supply of heavy oil, in order to correct our dependence on oil, we have been converting the fuel from conventional heavy oil-fired combustion to coal-fired combustion, and in particular, the large capacity of coal-fired boilers is increasing in commercial boilers. A thermal power plant is being built.

However, since coal fuel has poor fuel properties compared to petroleum fuel, NOx and unburned substances contained in exhaust gas are likely to be generated.In particular, measures to reduce NOx include flame splitting, exhaust gas recirculation, and two-stage combustion. And by using in-furnace denitrification, etc., to achieve slow combustion.
Efforts are also being made to reduce NOx.

In these coal-fired thermal power plants, there are few cases in which the boiler load is always operated at full load, but the load is increased or decreased to 80% load, 50% load, 25% load, or operation is stopped. A shift is being made to thermal power plants that handle intermediate loads by performing so-called daily start-stop (DSS) operations.

Additionally, in line with stricter regulations on NOx emission concentration, this coal-fired medium-load boiler is equipped with a dry catalytic reduction denitrification system that performs denitrification in the presence of a catalyst using _NH3 as a reducing agent, in addition to conventional combustion improvements. The number of plants being installed is increasing.

On the other hand, coal-fired boilers that perform DSS operation do not operate with only pulverized coal from start-up to full load; even though they are coal-fired boilers, light oil, heavy oil, Uses gas as fuel.

This is because at startup, exhaust gas and heated air for mill warming cannot be obtained from the boiler, and therefore the mill cannot be operated.

In addition, light oil, heavy oil, gas, etc. are used because the turndown ratio of the mill cannot be maintained at low loads, and the ignitability of pulverized coal itself is poor.

For example, when using light oil or heavy oil at startup, the boiler is fired using light oil as fuel from the time of startup until 15% load, and from 15% load to 40% load, the fuel is changed from light oil to heavy oil and fired. When the load exceeds % load, heavy oil and pulverized coal are co-fired, the amount of heavy oil fuel is gradually reduced, and pulverized coal fuel is increased to increase the pulverized coal co-firing ratio, resulting in a transition to actual coal-fired combustion.

In addition, when lowering the boiler load from 100% load in DSS operation, the exhaust gas temperature has also risen, which is different from when the boiler itself was started, so
Up to 30% load, the boiler burns pulverized coal and becomes a coal-fired boiler, and below 30% load, the fuel is switched to heavy oil or light oil.

However, in coal-fired medium-load boilers, in addition to the conventional combustion improvement, due to stricter regulations on NOx emission concentration, denitrification is performed in the presence of a catalyst that uses NH ₃ as a reducing agent, as shown in Figure 3. An increasing number of plants are installing dry catalytic reduction denitrification equipment.

Figure 3 shows a typical flue system for a coal-fired 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 transferred to the wind box 5.
The water is then supplied to the boiler 6.

On the other hand, the exhaust gas combusted in the boiler 6 is denitrified in the exhaust gas duct 4 by NH 3 from the NH ₃ injection pipe 7, and the denitrification is promoted in the catalyst ₉ in the denitrification device 8 disposed downstream. NOx is removed, passes through an air preheater 3 and an exhaust gas duct 4, is pressurized by an induced draft fan 10, and is released into the atmosphere.

On the other hand, ammonia gas from the ammonia gas pipe 11 and dilution air from the branch duct 12 are mixed in a dilution mixer 13, diluted to below the explosion limit, and injected from the NH ₃ injection pipe.

In addition, 14 is an oil burner, 15 is a pulverized coal burner,
16 is a coal hopper, 17 is a coal feeder, and 18 is a mill.

The outline of the conventional NH ₃ injection amount control device will be explained below using FIG. 4.

The air flow signal 20 from the air flow transmitter 19 of the boiler 6 shown in FIG. signal 24
is multiplied by the multiplier 25 to obtain the NOx amount signal 26.

A multiplier 29 multiplies this NOx amount signal 26 and a molar ratio signal 28 from a molar ratio setting and molar ratio correction circuit 27.
The ammonia gas request signal 30 is obtained by multiplying by .

This ammonia gas demand signal 30 and the ammonia gas flow rate signal 33 from the ammonia gas flow rate transmitter 31 and the square root calculator 32 are calculated by the ammonia gas flow rate controller 34, and a signal 35 is outputted so that there is no deviation, and electro-pneumatic conversion is performed. The ammonia gas flow rate was controlled by opening and closing an ammonia gas flow rate control valve 37 via a vessel 36.

In addition, in order to follow load changes during DSS operation, a steam flow rate signal 39 is sent from a steam flow rate transmitter 38.
Therefore, when the load increases, too much ammonia gas is injected through the over-under injection circuit 40, and when the load decreases, too little ammonia gas is injected in advance.

However, if the fuel itself is homogenized, such as heavy oil-only combustion or gas-only combustion, and the boiler burns immediately after fuel is input, the above-mentioned molar ratio setting and molar ratio correction circuit 2 is required.
7. This can be handled with the over-under injection circuit 40, but like coal firing, coal is fed into the coal hopper 16 and coal feeder 17, then crushed into pulverized coal in the mill 18 and combusted in the pulverized coal burner 15 to perform DSS operation. There are drawbacks that cannot be addressed by conventional technology and that do not satisfy recent environmental regulations.

[Purpose of invention]

The present invention attempts to eliminate such conventional drawbacks, and its purpose is to follow load changes and reduce NH ₃ even during DSS operation of coal-fired boilers started using heavy oil or gas fuel. The purpose of the present invention is to obtain an ammonia injection amount control device that can inject ammonia.

[Summary of the idea]

In order to achieve the above-mentioned purpose, the present invention divides the function generator into a function generator for dedicated combustion and a function generator for co-firing, and outputs the co-firing ratio as a signal from the function generator for co-firing after the function generator for co-firing. An exhaust gas amount setting circuit based on the mixed combustion ratio is provided, consisting of a multiplier that multiplies and an adder that adds the signals from both function generators.
The amount of exhaust gas during co-firing can be variably set.

[Example of idea]

Embodiments of the present invention will be described below with reference to the drawings. Fig. 1 is a system diagram of the NH ₃ injection amount control device according to the embodiment of the present invention, and Fig. 2 shows the exhaust gas amount on the vertical axis.
It is a characteristic curve diagram in which the horizontal axis shows the air flow rate.

In FIG. 1, numerals 19 to 40 indicate the same parts as in FIG.

41 is an exhaust gas amount setting circuit for the mixed combustion boiler of the present invention, and this exhaust gas setting circuit 41 includes a dedicated combustion function generator 42, a mixed combustion function generator 43, a multiplier 44, a fuel mixed combustion ratio transmitter 45, and a mixed combustion ratio signal 46. , an adder 47.

FIG. 2 shows the correlation between the air flow rate and the amount of exhaust gas. Curve A shows the characteristics when coal is fired exclusively, and curve B shows the characteristics when oil is fired exclusively, which are programmed into the function generator 42 for firing exclusively.

Curve C is obtained by subtracting curve B from curve A, and is programmed into the co-combustion function generator 43, and is the range of change in the amount of exhaust gas from oil-only combustion to coal-only combustion with a fuel co-combustion ratio of 0 to 100%.

Therefore, the co-firing ratio signal 46 from the fuel co-firing ratio transmitter 45 is passed through the multiplier 44 to the co-firing function generator 4.
The value multiplied by the co-combustion exhaust gas amount from 3 becomes the variation range of the exhaust gas amount due to the fuel co-combustion ratio.

That is, the air flow rate signal 20 from the air flow rate transmitter 19 is converted into the oil-only exhaust gas amount signal 48 by the dedicated combustion function generator 42, and the air amount signal 20 is converted into the mixed combustion exhaust gas amount signal 49 by the mixed combustion function generator 43. death,
The mixed combustion exhaust gas amount signal 49 and the mixed combustion ratio signal 46 are multiplied by a multiplier 44 . The product obtained by adding the multiplied signal 50 and the oil-only combustion exhaust gas amount signal 48 by an adder 47 becomes the exhaust gas amount signal 22 in the combustion state.

In this way, in the present invention, no matter how the fuel co-combustion ratio changes, the exhaust gas amount program can be automatically and variably set by the exhaust gas amount setting circuit 41.

Therefore, for example, when oil and coal are co-fired, DSS
Even if the coal-fired boiler is operated, the exhaust gas amount can always be variably set in accordance with the co-firing ratio using the exhaust gas amount setting circuit 41, so load followability is improved and the NOx emissions also meet the regulatory values. Become.

The NH ₃ injection amount is controlled based on this variably settable exhaust gas amount signal 22, but since the control is the same as the conventional one shown in FIG. 4, its explanation will be omitted.

[Effect of idea]

According to the present invention, even during DSS operation of a coal-fired boiler, it is possible to variably set the amount of exhaust gas in accordance with load changes, and moreover, it is possible to accurately inject ammonia in accordance with the load.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an ammonia injection amount control device according to an embodiment of the present invention, Fig. 2 is a characteristic curve diagram showing the correlation between exhaust gas amount and air flow rate, and Fig. 3 is a coal-fired system with a denitrification device installed. FIG. 4, which is a typical smoke and air duct system diagram of a boiler, is a system diagram of a conventional ammonia injection amount control device. 41...Exhaust gas amount setting circuit, 42...Function generator for dedicated combustion, 43...Function generator for mixed combustion, 44...Multiplier,
46... Mixed firing ratio signal, 47... Adder.

Claims (1)

[Scope of utility model registration request] Equipped with a function generator that converts the signal from the gas generation source into the amount of exhaust gas, and a calculator that calculates the NH ₃ demand signal by multiplying this amount of exhaust gas by the NOx amount at the denitrification inlet, and calculates the NH ₃ demand signal and the NH ₃ flow rate. In a device that controls the NH ₃ flow rate by a deviation signal from the signal, the function generator is divided into a function generator for exclusive combustion and a function generator for mixed combustion, and after the function generator for mixed combustion, a function generator for the mixed combustion ratio is set. An exhaust gas amount setting circuit based on the co-firing ratio is provided, consisting of a multiplier that multiplies the signal from the generator and an adder that adds the signals from both function generators, and is configured to variably set the amount of exhaust gas during co-firing. An ammonia injection amount control device characterized by: