JPS6342721A - Controlling device for injection amount of ammonia - Google Patents

Abstract

PURPOSE:To reduce the amount of NH3 to be leaked at a time for starting a boiler in case the temp. of exhaust gas is low by changing over a switching device to a start-up arithmetic unit calculating both the compensation signal of molar ratio and the correction signal of molar ratio based on the signal of NH3 concn. in an outlet and controlling the flow rate of NH3 to be necessitated. CONSTITUTION:At the time of starting a boiler, when the temp. of exhaust gas is low, the preset signal 43 of NH3 concn. in an outlet is converted to a precedence signal 46 of molar ratio, on the other hand, both a signal 41 of NH3 concn. at the outlet and the preset signal 43 are converted to a compensation signal 44 of molar ratio, and the precedence signal 46 of molar ratio is converted to a correction signal 48 of molar ratio. Both the correction signal 48 of molar ratio and a signal 19 of total NOX amount are multiplied in a multiplier 30 to obtain a signal 31 of flow rate of NH3 to be necessitated, the deviation between the signal 31 and a signal 33 of measured flow rate of NH3 is made to a control signal 35, and the flow rate of NH3 to be injected is controlled thereby. When the gas temp. of exhaust gas is increased and the deviation between a signal 25 of measured NOX concn. in the outlet and a signal 21 of NOX concn. in the outlet is made to zero, a switching device 38 is changed over to perform ordinary control for the flow rate of NH3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ammonia injection amount control device, and in particular, to a dry denitrification device that removes nitrogen oxides (NOx) from exhaust gas. This invention relates to an apparatus for controlling the amount of ammonia to be injected.

[Conventional technology]

In recent years, our FFL has been converting its fuel from heavy oil-only combustion to coal-fired and LNG (liquefied natural gas)-only combustion in order to correct its dependence on oil due to the tight supply of heavy oil, especially for commercial use. For boilers, coal-fired, LN
A large-capacity G-fired thermal power plant is being constructed.

However, since coal fuel has poor fuel properties compared to oil and gas fuels, NOx and unburned substances contained in the exhaust gas are likely to be generated.In particular, measures to reduce NOx include splitting the flame, recirculating the exhaust gas, Two-stage combustion, in-furnace denitrification, and the like are also being used to achieve slow combustion and reduce NOx.

And in this coal-fired thermal power and LNG-fired thermal power,
There are few boilers that are always operated at full load, and the load is raised and lowered to 75 cm, 50% load, 25 cm in the negative direction, and operation is stopped, so-called daily startup. Stop (Daily Start 5top below simply referred to as L) 88) operation, Weekend start/stop (Weekend start/stop)
ly' 5tart 5top hereafter simply referred to as WSS)
A transition is being made to thermal power plants that operate and handle intermediate loads.

On the other hand, in addition to this thermal power generation boiler, the so-called combined brand, which combines a gas turbine with good starting characteristics and an exhaust heat recovery boiler, is also used for intermediate load thermal power generation.
There are plans to build a system that will perform SS or WSS operation, operating only during the day when electricity demand is high, and shutting down at night.

However, with the tightening of NOx emission concentration regulations for intermediate-load boilers and gas turbines for coal and LNG combustion, in addition to the conventional combustion reform, NH is being used as a reducing agent in the presence of a catalyst. An increasing number of plants are installing dry catalytic reduction denitrification equipment.

In coal-fired boilers, the fuel has poor combustibility, so Noxlit increases, and in LNF-fired boilers.

In gas turbine plants, there are many oxygen caps and temperature controlled combustion is carried out, so similar to coal-fired boilers, the exhaust gas contains a large amount of NOx, so a denitrification device as shown in Figure 3 is installed. be done.

Figure 3 is a typical flue duct system diagram 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 from the wind box 5 to the boiler 6.

On the other hand, the exhaust gas combusted in the boiler 6 is denitrified by NH in the exhaust gas duct 4 and NH from the injection pipe 7, and the denitrification is promoted in the catalyst 9 in the denitrification device [8] disposed downstream. NOx is removed from the 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 such a denitrification device j18 differs depending on the type of catalyst 9, the temperature range in which acid also has high denitrification efficiency is a relatively high temperature range of 300 to 400°C, and the temperature range is quite narrow. In a boiler for load thermal power or a combined cycle which is constantly operated under DSS, there is a drawback that the θF scum temperature fluctuates under normal pressure due to load fluctuations, and the catalyst 90 is out of the range in which it can be used.

In this case, if the temperature of the used catalyst 9 is too high, the catalyst 9
The structure of the catalyst changes and the function of the catalyst 9 is impaired, and if the temperature of the gas used is too low, it reacts with sulfuric anhydride (So) present in the exhaust gas, which also deteriorates the function of the catalyst 90.

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

When the exhaust gas amount and NOx concentration caused by the reaction mechanism of NOx and NH in the catalyst 9-H fluctuate, such as during startup or load changes, NH, NH,
This is because the denitrification performance cannot follow load fluctuations even if the injection amount is changed.

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

In FIG. 4, the inlet NOx concentration signal 13 detected by the inlet No Exhaust gas flow rate number 17 is multiplier 18
The total N08 sweet signal 19 is calculated by multiplying by . On the other hand entrance N
The molar ratio calculator 22 is determined by the Ox concentration 1 signal 13 and the outlet NOx concentration setting signal 21 from the outlet NOx concentration setting device 20.
The preceding molar ratio (NOx amount and NH.

23, and add to it the measured outlet NOx concentration signal 25 detected by the outlet NOx concentration detector 24,
Outlet NOx whose deviation from the outlet NOx concentration setting signal 21 from the outlet NOx concentration setting device 20 is corrected by the controller 26
(M difference correction signal 27 and the preceding molar ratio signal 2 explained earlier)
3 is added by an adder 28 to calculate a corrected molar ratio signal 29.

Then, this modified molar ratio signal 29 and the total NOx amount signal 19
and the corrected molar ratio signal 29 are multiplied by the multiplier 30 to obtain the required NH,
A flow rate signal 31 is calculated.

The controller 34 compares the required NH, flow rate signal 31 and the actual measured NH, flow rate signal 33 detected by the NH, flow rate detector 32, and performs a proportional integral operation on the deviation, and a control signal 35 for the required valve opening.
The amount of ammonia injected was controlled by opening and closing the NH of the NH pipe 36 and the current control valve 37.

[Problem that the invention seeks to solve]

In this way, the conventional NH injection amount control device
During startup when the Ox concentration is high and the gas temperature is low,
When the denitrification system [8] shown in the figure is operated, there is a drawback that the leak NH concentration becomes abnormally high.

FIG. 5 is a characteristic curve diagram in which the vertical axis shows the denitrification rate and the horizontal axis shows the gas temperature. As shown in FIG. 5, the denitrification performance of the catalyst decreases when the gas temperature is low at startup.

FIG. 6 is a characteristic curve diagram in which the vertical axis shows NH, concentration, gas temperature, and NOx concentration, and the horizontal axis shows time.

In Figure 6, curve A is the gas temperature curve, curve B is the NOx concentration curve at the inlet of the denitrification equipment, and curve C is the exit N of the denitrification equipment.
The Ox concentration curve, the bending curve shows the NH injection amount curve, and the curve E shows the NH concentration curve at the outlet of the denitrification device.

As shown in Fig. 6, the gas temperature is low when the boiler is started, so even if NH is injected, the denitrification performance is low as shown in Fig. 5. When NH is injected using a conventional NH injection rate control device, the NOx concentration at the outlet of the denitrification device does not decrease to the set value as shown by F in the outlet NOx concentration curve C, so the injection rate curve The NH concentration at the outlet of the denitrification equipment becomes abnormally high, as shown by G in curve E, and the NR concentration at the outlet becomes abnormally high, as shown by H in curve E, which is unfavorable in terms of pollution control.

Therefore, it is not suitable as an NH and injection current control device when DSS operation or WSS operation is frequently performed as in recent years, and when the gas temperature is low, such as when starting up a boiler.

The present invention aims to eliminate such conventional drawbacks,
The purpose is to suppress the NH concentration at the outlet of the denitrification equipment even when the exhaust gas temperature is low immediately after starting the boiler, etc.
An object of the present invention is to provide an ammonia injection amount control device that can suppress NOx concentration during startup and shutdown.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides a switch between an adder and a multiplier, and also provides an output NH.

Outlet NH from the concentration detector,! I & signal and outlet NH, outlet NH from setting device, molar ratio correction from concentration setting signal 16
a controller that calculates the preceding molar ratio signal from the outlet NH and concentration setting signal, and a molar ratio adder that calculates the corrected molar ratio signal from the molar ratio correction deviation sign and the preceding molar ratio signal. A startup calculation device is installed, which consists of a
It is designed to control flow.

〔Example〕

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

FIG. 1 is a control system diagram of an ammonia injection amount control device according to an embodiment of the present invention, and FIG. 2 is a characteristic curve diagram in the control system diagram of FIG. 1.

In FIG. 1, numerals 1 to 37 indicate the same parts as in FIG.

38 is a switch provided between the adder 28 and the multiplier 300;
9 is a startup calculation device according to the present invention, 40 is an outlet N ratio concentration detector, 41 is an exit NH, Nokasu No., 42 is an exit NH,
Setting device, 43 is the outlet NH, concentration setting signal, 44 is the molar ratio correction No. 1g, 45 is the controller, 46 is the preceding molar ratio signal, 4
7 is a preceding molar ratio calculator, 48 is a modified molar ratio signal, 49 is a molar ratio adder, and 50 is a monitor relay.

In such a structure, the arithmetic unit 39 at startup has an output of N
H, concentration detector 40. Exit NH, concentration signal 41, exit N
H, setting device 42, outlet NH, concentration setting signal 43, molar ratio correction signal 44, controller 45, preceding molar ratio signal 46, preceding molar ratio calculator 47, corrected molar ratio signal 48, and molar ratio adder 49. At this startup, the arithmetic unit #t39
When the exhaust gas temperature is low, such as during DSS operation or WSS operation, the contacts b y c of the switch 38 are connected to control the NH injection amount, and the output NOx concentration setting signal 21 and the measured outlet NOx concentration signal 25 are When the deviation becomes zero, contact a of the switch 38 is activated.

C is filled with II%N, and contacts S and C are cut to control the injection amount of NH.

In FIG. 1, when starting a boiler or the like where the gas temperature is low, the exit Nu-1. The outlet NH and concentration setting signal 43 set by the setter 42 is converted into a preceding molar ratio signal 46 by a preceding molar ratio calculator 47. On the other hand, outlet NH3m degree spout 4
The exit NH8 concentration A6 41 detected by 0 and the previous exit NH, the concentration setting signal 43 are converted into a molar ratio correction signal 44 by the controller 45, and the previous preceding molar ratio is determined by the molar ratio g:;49. The signal 46 is corrected and transformed into a modified molar ratio signal 48. This modified molar ratio signal 48 and the total N0xt signal 19
is multiplied by the multiplier 30 to obtain the required NHa flow rate signal 31 at startup, and this required NH, flow rate signal 31 and the actual measured NH,
The deviation of the flow-Il number 33 is used as a control signal 35 to control the NH and injection flow.

As the gas temperature rises, the denitrification performance also increases and the NOx $2 at the outlet of the denitrification device also decreases. Here, the actual measured outlet NOx concentration signal 25 detected by the outlet NOx concentration detector 24
When the deviation of the outlet NOx concentration signal 21 established by the outlet NOx concentration setting device 20 is zero, the monitor relay 50 becomes the contact point of the switch 38 and switches from c to a + e, same as the control explained in FIG. 4. NH3 Kodaiamagase is controlled.

At startup when the exhaust gas temperature is low as described above, the required NH, flow rate deviation signal 31 is
is smaller than the conventional one, so the an
<N Hs injection curve I) As shown by -I, increase 7J
llIIli- decreases, gas temperature curve A1 population N
Even if the Ox concentration curve B1 output DNOx concentration curve C is the same as the conventional one, even if the number of scratches increases, the outlet Nn, *rg curve E becomes flat, there is less leakage NH, and less secondary hemorrhoids can be prevented. Take.

According to an embodiment of the invention, the outlet NH of the denitrification device.

Since the actual outlet NH is injected so that the actual outlet NH is within the set value, even when the boiler is started up when the gas temperature is low and the desired denitrification performance cannot be obtained, the outlet leak NHs is t decreases.

Furthermore, when the ammonia gas temperature rises and the specified denitrification performance is achieved, and the actual outlet NOx value becomes equal to the set NOx value, the conventional ammonia injection amount control device is switched to operation, so NOx fluctuations at the time of switching are reduced. You can drive smoothly without any problems.

In addition, the boiler with low gas temperature m i! [f& allows stable operation of the denitrification device ift, and it is also possible to suppress NOXf when starting a boiler or the like.

〔Effect of the invention〕

According to the invention, by performing DSS operation and Jfwss operation, even if the exhaust gas temperature after startup is low, the leakage N Il, - will be reduced, and the NOx immediately after startup and shutdown will be suppressed. be able to.

[Brief explanation of the drawing]

Fig. 1 is a control system diagram of the NH injection amount control device according to the embodiment of the present invention, Fig. 2 is a characteristic curve diagram of Fig. 1, and Fig. 3 is a typical boiler equipped with a denitrification device. Smoke duct system diagram,
Figure 4 is a control system diagram of a conventional NH injection control neck.
FIG. 5 is a temperature characteristic curve diagram of denitrification performance, and FIG. 6 is a characteristic curve diagram of FIG. 4. 12... Inlet NOx concentration detector, 13...
...Inlet NOx concentration signal, 14... Air flow f detector, 15... Air flow signal, 16...
・Function generator, 17... Exhaust gas flow No. ta, 18...
... Multiplier, 19 ... Total NOx amount signal, 2
0...Outlet NOx# degree setting device, 21...
・Exit NOx+! [Setting signal, 22...molar ratio calculator, 23...preceding molar ratio 1g, 24...
...Exit NOx concentration detector, 25...Actually measured outlet NOx concentration signal, 26...Adjustment needle, 27.
...Exit NOx deviation correction signal, 28...
Adder, 29...+h iE molar ratio number, 30
...... Multiplier, 31... Necessary NH1 flow rate key number, 32... N Hs flow rate detector, 33.
...Actual measured NH1 pitch signal, 37...N
H, Flow 1 key *I'i 7F, 38...Switcher,
39...Start-up calculation device, 40...Outlet NH, concentration detector, 41...Outlet NH, concentration signal, 42...Outlet NH, setting Vessel, 43...
... Outlet NH, $2 setting signal, 44 ... Molar ratio correction I = number, 45 ... Controller, 46 ...
...Advanced molar ratio signal, 47...Advanced molar ratio calculator, 48...Modified molar ratio signal, 49...
-Molar ratio adder.

Claims (1)

[Claims] A multiplier that calculates a total NO_x amount signal based on an exhaust gas flow rate signal converted by a function generator based on an air flow rate signal from an air flow rate detector and an inlet NO_x concentration signal from an inlet NO_x concentration detector, and an outlet NO_x concentration signal. A controller that calculates an outlet NO_x deviation correction signal from the outlet NO_x concentration setting signal from the setting device and the actually measured outlet NO_x signal from the outlet NO_x concentration detector, and the inlet NO_x concentration signal and the outlet NO_x concentration signal.
a molar ratio calculator that calculates a leading molar ratio signal from the x concentration setting signal; an adder that calculates a corrected molar ratio signal from the leading molar ratio signal and the exit NO_x deviation correction signal; A multiplier is provided to calculate the required NH_3 flow rate signal, and the difference between the required NH_3 flow rate signal and the measured NH_3 flow rate signal from the NH_3 flow rate detector is
In the H_3 flow control valve that opens and closes, a switch is provided between the adder and the multiplier, and the outlet NH_3
Outlet NH_3 concentration signal from the concentration detector and outlet NH_3
A controller that calculates a molar ratio correction signal from the outlet NH_3 concentration setting signal from the setting device, a leading molar ratio calculator that calculates a leading molar ratio signal from the outlet NH_3 concentration setting signal, a molar ratio correction signal and a leading molar ratio signal. A startup calculation device consisting of a molar ratio adder that calculates a corrected molar ratio signal from N is provided, and when the exhaust gas temperature is low, the startup calculation device is switched to the necessary
An ammonia injection amount control device, characterized in that the H_3 flow rate is controlled.