JPH0364170B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ammonia injection control device for a denitrification device, and particularly to a denitrification device suitable for reducing nitrogen oxides (hereinafter referred to as _NOx ) in a denitrification treatment gas. .

Recently, regulations on the total amount _{of NO} A stable reduction is required.

In a combustion system including a conventional flue gas denitrification device of this type (hereinafter simply referred to as a denitrification device), the first
As shown in the figure, combustion exhaust gas (hereinafter simply referred to as exhaust gas) generated in a combustion device 1 such as a boiler passes through an economizer 2, and after an appropriate amount of ammonia gas is injected by an ammonia flow control valve 8, a denitrification device 3 The _NOx contained in the air is decomposed there, and then it is discharged from the chimney 6 via the air heater 4 and EP5. On the other hand, combustion air is FDF
After being taken in from the (forced blower) 7, it passes through the air heater 4 and is then sent to the wind box (not shown) of the combustion device. The amount of ammonia gas injected above is determined by the ammonia flow rate transmitter 10, and the _NOx concentration (hereinafter referred to as
_{The NO _ _ _}
11, the amount of combustion air is measured by an air flow rate transmitter 12, respectively. Then, the ammonia gas injection control described above is performed based on these fixed values for each side.

Fig. 2 shows a system diagram of the above-mentioned control device. In this control system, first, the economizer outlet _NO
The _NO , this allows the total amount _{of NOx} in the exhaust gas to be determined. On the other hand, downstream of the primary multiplier 14A is the denitrification equipment outlet _NO
A feedback circuit is provided to maintain a constant value. Here, first, we will start with a total of ₁₁ NO
The detected signal is input to the proportional integrator 15,
It is compared with the denitrification device outlet _NOx concentration setting value inputted from the setting device 16. A signal proportional to this deviation is input to the secondary multiplier 14B, thereby correcting the NO _x total amount signal. The output from the secondary multiplier 14B is then sent to the proportional integrator 15 and compared with the signal from the ammonia flow rate transmitter 10, and the final opening command is output to the ammonia flow rate control valve 8 based on the deviation. It's summery.

However, in a control device with such a configuration, the ammonia injection amount is actually adjusted to increase or decrease after receiving the _NO
There is a large time delay as it requires calculation time, ammonia gas flow time, exhaust gas flow time, and reaction _time to reach the _NO This is a major problem especially when the load fluctuates.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ammonia injection control device for a denitrification device that can eliminate the drawbacks of the prior art described above and stably reduce _NOx in a denitrification treatment gas.

_In order to achieve the above object, the present invention provides a circuit that calculates _the total _NO A calculator that calculates the denitrification rate based on the _NO A function generator into which the relationship with the injection molar ratio is input, a multiplication circuit that multiplies the ammonia injection molar ratio calculated by the function generator by the total amount of _NO The apparatus is characterized by comprising a circuit for controlling the amount of ammonia gas injected into the apparatus.

With the above configuration, exhaust gas _NO
Even if the concentration changes, it is possible to make appropriate corrections to the total amount _{of NO} The outlet _NOx concentration can be stably maintained at a low value within the set value.

In the present invention, the signal input to the function generator may be only the required denitrification rate signal sent from the computing unit, but in addition to this, signals related to the load of the combustion device, such as a combustion air flow rate signal, a fuel amount signal, etc. It is also possible to input signals, load command signals, etc. (in this case, the function generator must be compatible with this), thereby improving the total amount _{of NOx} in response to changes in the load situation. It can be corrected to

Hereinafter, the present invention will be explained in more detail with reference to embodiments shown in the drawings.

FIG. 3 shows a system of a control device according to an embodiment of the present invention, which includes parts to which reference numerals and explanations similar to those shown in FIG.
It is composed of an adder 17, a divider 18, and a function generator 19, which are provided between the _NOx total 9 and the secondary multiplier 14B.

In the circuit of such a device, the economizer outlet NO _x detected in a total of 9
A part of the NO _X concentration signal is input to the adder 17,
Denitrification equipment outlet input from _NOX setting device 16
The difference is determined through comparison with the NO _X concentration set value. This difference signal is then sent to divider 18,
Here, it is divided by the economizer outlet _NOx concentration signal, and thus the denitrification rate η is determined. This signal of the NOx removal rate η is then input to the molar ratio calculator (function generator) 19, and the ammonia required to achieve the NOx removal rate η is determined by the function η = f (M) inputted here in advance. The injection molar ratio M is determined. This molar ratio M is then input to the secondary multiplier 14B, where it is multiplied by the total amount of _NOx in the exhaust gas determined in the same manner as in the case of FIG. After that, it is output as an opening command for the ammonia flow rate control valve 8.

This example focuses on the fact that there is a correlation between the denitrification rate η and the ammonia injection molar ratio M as shown in equation (1) below, and controls this relationship to keep the _NOx concentration at the denitrification equipment outlet constant. It was applied to

η=f(M)= _C1 − _C2 / _C1 ...(1) _C1 : Economizer outlet _NOX concentration (actual measurement value) _C2 : Denitrification equipment outlet _NOX concentration (set value; constant) This example According to the following formula, the amount of ammonia inflow is
(2) It is calculated as f(C ₁ −C ₂ /C ₁ )・C ₁・G (2) (where G is the amount of exhaust gas). Therefore, _the ammonia injection molar ratio required to keep _the denitrification equipment outlet _NO Control becomes possible. The control device of this embodiment is particularly suitable for denitrification processing in which the relationship between η and M does not deviate much even if the combustion load fluctuates.

Next, FIG. 4 shows a system of a control device according to another embodiment of the present invention, in which a flow rate signal of combustion air, which is a load signal (hereinafter referred to as LOAD) of a combustion device, is input to a molar ratio calculator. The control device has the same configuration as the control device shown in FIG. 3, except that a new circuit is provided to send data to the molar ratio calculator 19, and the function form input in advance to the molar ratio calculator is η=f(LOAD, M). . The amount of ammonia injected at this time can be determined by the following equation (3) f(C ₁ −C ₂ /C ₁ ·LOAD)·C ₁ ·G (3). As an example of this functional form is shown in Fig. 5, in particular, the ammonia injection molar ratio M
In the high range, the denitrification rate η differs depending on the LOAD (A, B, and C in the figure are respectively
(shows when LOAD is 100%, 75% and 50%),
If this embodiment is applied to such an area, it becomes possible to perform more fine-grained control. In other words, according to this embodiment, even if there is a large difference in the relationship between M and η due to load fluctuations in the combustion device,
The _NOx concentration at the outlet of the denitrification equipment can be maintained at a constant low value.

Although the above description has been made regarding typical embodiments of the present invention, the present invention is of course not limited to this, and it goes without saying that there are various other modifications and applications. . For example, in each of the above embodiments, the feedback of the _NO Of course, it is also possible to perform feedback on the _NOx concentration at the outlet of the denitrification equipment. This is particularly effective in cases where the relationship between η and M for each combustion device load may deviate due to a change in fuel type or the like.

As described above, according to the present invention, the required denitrification rate determined based on _the detected value of _NO This allows the multiplier circuit to correct the _total amount of exhaust gas _NO can be kept.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a conventional combustion device equipped with a denitration device, FIG. 2 is a system diagram of an ammonia injection control device applied to the denitration device of FIG. 1, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a system diagram of an ammonia injection control device for a denitration device according to another embodiment of the present invention, and FIG. 5 is a system diagram of an ammonia injection control device for a denitration device according to another embodiment of the present invention. This is a club of example function forms input to the function generator. 1... Combustion device, 2... Economizer, 3...
Denitrification device, 8...Ammonia flow rate control valve, 9...
Economizer outlet _NOX meter, 10...Ammonia flow rate transmitter, 11...Denitrification equipment outlet _NOX meter, 1
2...Air flow rate transmitter, 13...Exhaust gas amount calculator, 14A...Primary multiplier, 14B...Secondary multiplier, 15...Proportional integrator, 16...Setting device, 17
... Adder, 18 ... Divider, 19 ... Molar ratio calculator (function generator).

Claims (1)

[Claims] 1. A circuit that calculates the total amount of NO _X based on the detected NO _X concentration of the combustion exhaust gas that has passed through the economizer and the flow rate value, and the detected _NO A calculator that calculates the _NOx removal rate based on the NO A function generator into which the relationship is input, a multiplication circuit that multiplies the ammonia injection molar ratio calculated by the function generator by the total amount _{of NO} 1. An ammonia injection control device for a denitrification device, comprising a circuit for controlling injection amount. 2. An ammonia injection control device for a denitrification device according to claim 1, characterized in that the function generator described above is provided with an input circuit for load information regarding the combustion device.