JPH0337965B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an ammonia catalytic reduction denitrification device,
In particular, the present invention relates to a denitrification device that is suitable for responding to load fluctuations.

Various methods are known for removing nitrogen oxides (hereinafter referred to as _NO It is often used in commercial boilers.

As shown in Fig. 1, a conventional device of this type includes a denitrification reactor 1 filled with a dry denitrification catalyst, and an upstream side for guiding _NOx- containing gas to be treated, such as combustion exhaust gas, to the denitrification reactor 1. A duct 2, a downstream duct 3 for discharging gas after denitrification processing, an inlet 15 for injecting ammonia provided in the upstream duct 2 on the inlet side of the denitrification reactor 1, and various types of inlets for reaction control. It mainly consists of a control system. In such a configuration _{, NO
The} value of X ₄ (referred to as _{X 4} ) is measured by the NO On the other hand, the amount of gas to be treated X ₅ is measured by the flow meter 5 and then multiplied by the above-mentioned X ₈ by the multiplier 9 to give the required amount of NO _X to be treated per unit time X ₉ (mol/min). Since this X ₉ is also the required injection amount of ammonia (because the denitrification reaction is an equimolar reaction), it can be added to the controller 11 that controls the ammonia flow control valve 12 after passing through the adder 10 . On the other hand, the value _{X 6} of NO _X (hereinafter simply referred to as outlet _NO is compared with NO _X target value C ₀ , and the resulting difference signal X ₃₀ is
The signal is sent to the PID controller 31. The output X ₃₁ is input to the adder 7, and the denitrification rate set value X ₀ is corrected to give the above-mentioned required denitrification rate X ₇ . Because it has such an effect, even in the case of the above-mentioned device, the inlet can be maintained not only in static conditions but also in the event of load fluctuations.
When NO _X fluctuations are gentle or when the amount of exhaust gas does not change, satisfactory controllability can be achieved even for fairly large fluctuations in the inlet NO _X.

However, when a rapid and large load change (gas amount change) as shown in FIG. 2a occurs, there is a drawback that sufficient controllability cannot be obtained. Therefore, an ammonia advance injection circuit as shown at 20 in FIG. 1 has been devised. In the circuit 20, 21
and 22 are change rate detectors, respectively, and 21
At 22, the rate of change X ₂₁ of the signal X ₉ is determined, and at 22 the rate of change X ₂₂ of the boiler load or air demand signal 24 (which may lead to the actual gas flow signal X ₅ ). The obtained rate-of-change signals are then added together in an adder 23, and the added signal _X23 is sent to an adder ₁₀ and added to the previously mentioned signal It is possible to speed up the process accordingly. Due to this improvement, the load response is improved from the solid line to the broken line in FIG. 2b.

The reasons for the above improvement will be discussed below. First, the outlet _NOx amount G ₀ is given by the following equation (1), or its fluctuation amount ΔG ₀ is given by the equations (2) and (3). _Here , if the denitrification rate η is 80%, if the inlet _NO 2% (ΔG ₀ /Q.Ci=0.02) G ₀ =Q・C ₀ =(1−η)Q・Ci……(1) ΔG ₀ =(1−η)・Q・ΔCi+ (1−η)・Ci・ΔQ−Q・Ci・Δη …(2) ΔG ₀ /Q・Ci=(1−η)・ΔCi/Ci+ (1−η)・ΔQ/Q−Δη …(3) However, G _{0 : Amount} ^of _NO ^_ It is about the denitrification rate.

However, even if ΔCi=0, the gas amount ΔQ is 10
% change, the term (1-η)ΔQ/Q is +2%, but in addition, the denitrification rate η decreases due to the decrease in reaction time (residence time) as the gas amount increases.
That influence is taken into account. This reduction Δη is reduced by 8% (Δη
= -0.08), it is known that the outlet _NOx will increase by 10% overall, and from this it can be seen that the gas amount change has a greater influence than the inlet _NOx change.

As _is clear from _{equation (4) below, the signal X 21 in FIG. 1 is a differential} signal of = η ₀・Q・dCi/dt+η ₀・Ci・dQ/dt……(4) Correction of ammonia injection amount for NO _x fluctuations in the first and second terms of equations (2) and (3), respectively However, since a correction signal is not provided for the third term (change in η) in each equation, the differential value of signal 24 corresponding to the exhaust gas amount is used for this purpose.
The amount of ammonia injection is corrected using _X22 .

In this way, the improved device described above achieves control based on the theoretical input amount of ammonia during steady and transient conditions, and the control performance has also been further improved. Performance control may be desired.

An object of the present invention is to provide an ammonia catalytic reduction and denitrification apparatus that further develops the above-mentioned control technology and is capable of controlling the ammonia injection amount even more effectively when the load fluctuates.

In order to achieve the above object, the present invention provides an ammonia contactor equipped with a denitrification reactor that performs catalytic reduction of _NOx in a gas to be treated in the presence of ammonia injected from an ammonia injection means provided on the inlet side. The reduction denitrification apparatus is characterized in that a second ammonia injection means is provided in an intermediate portion of the denitrification reactor, which is sent based on a preceding injection signal.

With the above configuration, the activity distribution of the denitrification catalyst in the denitrification reactor can be changed between the part activated by ammonia (hereinafter referred to as primary ammonia) injected from the inlet side of the denitrification reactor and the intermediate part. Since it can be bimodal, including a part activated by ammonia (hereinafter referred to as secondary ammonia) injected from The disadvantage of a transient increase in outlet NO _x due to a decrease in reaction time can be overcome by injection of secondary ammonia.

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

The apparatus shown in FIG. 3 divides the denitrification reactor into an upstream denitrification reactor 1A and a downstream denitrification reactor 1B, provides an ammonia inlet 16 in the middle of the two, and supplies ammonia to the ammonia inlet 16. The device is similar in construction to the device of FIG. 1, except for the provision of a pre-injection control circuit 40 for supplying the same numerals.

In the apparatus configured as described above, the ammonia pre-injection signal X ₂₃ is derived from the same circuit 20 as shown in FIG. (nozzle)
15 control signals _X9 .

At the same time, the remainder of the signal X ₂₃ is sent to the coefficient unit 4.
2, and then sent to the PID controller 43 of the secondary ammonia injection device (nozzle) 16. 4
4 is an ammonia flow control valve that operates based on a signal sent from the control device 43, and 45 is an ammonia flow meter, which constitute an ammonia flow control system. Preliminary injection of ammonia is carried out in this manner, and the effects thereof will be explained with reference to FIG. Figure 4 is a diagram explaining the activation state of the dry denitrification catalyst, where the horizontal axis shows the relative distance of the denitrification reactor along the gas flow from left to right, and the vertical axis shows the activity of the catalyst. It is shown.

In Fig. 4, curve A indicates the desired denitrification rate (for example, η≒80
%) is the activity distribution of the catalyst necessary to achieve this, and b is the similar activity distribution at full load.
This shows that if the contact time decreases due to an increase in the gas flow rate, it is necessary to compensate for this by increasing the activation area, and therefore, when the load is reduced from 50% to
When increasing to 100%, add ammonia and increase the area of the activated catalyst from A to B.
It is understood that the total amount of ammonia required to reduce _NOx must be injected.

However, when this required ammonia is injected only from the primary ammonia injector, it takes a certain amount of time for the activity curve to change from A to B, and this delay causes a transient flow at the outlet when the load increases. Causes an increase in _NOx .

However, according to the present invention, if ammonia is injected transiently (only when the load increases) from the secondary ammonia injection nozzle, it is possible to separately form a catalyst activation region as shown by curve C, thereby increasing the denitrification reaction. It is possible to improve the transient response of the reactor and, along with this, to improve the transient denitrification performance.

Although typical embodiments of the present invention have been described above, the present invention is of course not limited thereto, and various other modifications and applications are possible within the scope of the present invention. For example, the injection of secondary ammonia, in addition to being carried out under the control of the pre-injection control circuit 40, can also be carried out by applying a portion of the signal X ₁₀ used in the apparatus of FIG.
A similar effect can be obtained.

As described above, according to the present invention, the secondary ammonia injection means is provided in the middle part of the denitrification reactor, and the catalyst activity distribution is changed from the conventional monomodal to bimodal. Even if the time decreases, it is possible to increase the catalyst activation area sufficiently to compensate for this, and as a result, the transient response of the denitrification reactor is improved, and along with this, the transient denitrification performance is improved. Ru.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a conventional ammonia catalytic reduction and denitrification equipment, Fig. 2a is a diagram showing an example of load fluctuation when applying the equipment in Fig. 1, and Fig. 2b is a diagram showing the load as shown in Fig. 2a. FIG. 1 is a diagram showing an example of the control performance of the device in response to fluctuations, FIG. 3 is a system diagram of the ammonia catalytic reduction and denitrification device according to the embodiment of the present invention, and FIG. 4 is a diagram explaining the effects of the embodiment of the present invention. FIG. 2 is a graph showing changes in catalyst activity. 1...Denitration reactor, 1A...Upstream denitrification reactor, 1B...Downstream denitrification reactor, 2...Upstream duct, 3...Downstream duct, 4... _NOx meter, 5
...Flowmeter, 6... _NOX meter, 7...Adder, 8,
9... Multiplier, 10... Adder, 11... Controller, 12... Ammonia flow rate control valve, 15, 16
...Ammonia injection port, 20...Ammonia advance injection circuit, 21, 22...Change rate detector, 23...
... Adder, 24 ... Boiler load or air demand signal, 30 ... Subtractor, 31 ... PID controller,
40...Ammonia advance injection control circuit, 42...
Coefficient unit, 43...PID controller, 44...Ammonia flow rate control valve, 45...Ammonia flow meter.

Claims (1)

[Claims] 1. In an ammonia catalytic reduction denitrification apparatus equipped with a denitrification reactor that performs catalytic reduction of _NO An ammonia catalytic reduction denitrification device characterized in that a second ammonia injection means is provided in the intermediate portion, and the second ammonia injection means is sent based on a preceding injection signal.