JPH0811171B2 - Ammonia injection amount control device - Google Patents

Description

The present invention relates to an ammonia injection amount control device, and in particular,
The present invention relates to an ammonia injection amount control device that injects ammonia (NH ₃ ) into a dry denitration device that removes nitrogen oxides (NO _x ) in exhaust gas.

[Conventional technology]

In recent years, in Japan, fuel is being converted from conventional heavy oil burning to coal burning and LNG (liquefied natural gas) burning in order to correct the dependence on petroleum due to the tight supply of heavy oil, especially for commercial boilers. Has built a large-capacity thermal power plant that exclusively burns coal and LNG.

However, since coal fuel has a poorer fuel property than petroleum fuel and gas fuel, NO _X and unburned matter contained in the exhaust gas are likely to be generated, and especially flames are divided to reduce NO _X.
Exhaust gas recirculation, two-stage combustion and in-furnace denitration are also used to slow combustion to reduce NO _X.

In this coal-only burning power and LNG burning power, the boiler load is not always operated at full load, and the load is increased to 75% load, 50% load, 25% load and lowered to operate. Or stop the operation, so-called daily start stop (hereinafter simply referred to as DSS) operation,
Weekly Start Stop (WSS)
It is in operation and is shifting to a thermal power plant that bears intermediate loads.

On the other hand, for this intermediate load thermal power, in addition to this thermal power generation boiler, a so-called combined plant, which is a combination of a gas turbine and an exhaust heat recovery boiler with a good starting specification, is also used,
It is about to be constructed by operating DSS and WSS only during the daytime when there is a large demand for electricity and stopping the operation at night.

However, in the coal-fired and LNG-fired intermediate load boilers and gas turbines as well, along with the tightening of regulations on NO _X emission concentrations, in addition to the conventional combustion improvement, denitration was performed in the presence of a catalyst using NH ₃ as a reducing agent. The number of plants that install dry catalytic reduction NOx removal equipment is increasing.

Since the combustibility of the fuel is poor in the coal-fired boiler, the amount of NO _X increases, and in the LNF-fired boiler and gas turbine plant, the amount of oxygen is large and high-temperature combustion is performed. A large amount of NO _X
Therefore, a denitration device as shown in FIG. 3 is installed.

FIG. 3 is a typical flue wind system diagram of a boiler in which a denitration device is installed.

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

On the other hand, the exhaust gas burned in the boiler 6 is exhaust gas duct 4
Is denitrified by NH ₃ from the NH ₃ injection pipe 7, and the denitration is promoted by the catalyst 9 in the denitration device 8 arranged downstream, NO _X in the exhaust gas is removed, and the air preheater 3 and the dust collector Ten,
The pressure is increased by the induction fan 11 and released to the atmosphere.

However, although the reaction temperature range of the denitration device 8 is somewhat different depending on the type of the catalyst 9, the temperature range with the highest denitration efficiency is a relatively high temperature of 300 to 400 ° C., and the temperature range is extremely narrow. In the case of a boiler for intermediate load thermal power generation or a combined cycle that is always operated by DSS, there is a drawback that the exhaust gas temperature constantly fluctuates due to load fluctuations, and the catalyst 9 deviates from the usable range.

In this case, if the temperature of the gas used in the catalyst 9 is too high, the structure of the catalyst 9 changes and the function as the catalyst 9 is impaired.
If the temperature of the used gas is too low, the function of the catalyst 9 is deteriorated by reacting with sulfuric anhydride (SO ₃ ) existing in the exhaust gas.

On the other hand, in the thermal power generation boiler and the combined cycle that are always operated by DSS or WSS, the amount of exhaust gas and
NO _X concentration is varied, the follow-up of'll go-between denitration performance in this is there is a drawback to deteriorate.

This is because when the exhaust gas amount and NO _X concentration due to the reaction mechanism of NO _X and NH ₃ on the catalyst 9 fluctuate, such as at start-up and when the load changes, the NH ₃ injection amount should be adjusted according to the load change. This is because the denitration performance cannot follow the load fluctuation even if it is changed.

In order to avoid these problems, a typical example of a conventional NH ₃ injection amount control device is shown in FIG.

In FIG. 4, the inlet NO _X concentration signal 13 detected by the inlet NO _X concentration detector 12 and the air flow rate signal 15 detected by the air flow rate detector 14 are converted by the function converter 16, and the converted exhaust gas flow rate The signal 17 is multiplied by the multiplier 18 to calculate the total NO _X amount signal 19. On the other hand, inlet NO _X concentration signal 13 and outlet NO _X concentration setter
From the 20 to the outlet NO _X concentration setting signal 21, the molar ratio calculator 22
Calculate the leading molar ratio (ratio of NO _X amount and NH ₃ amount) signal 23 with
And the measured outlet NO _X concentration signal 25 which is detected by the outlet NO _X concentration detector 24 to the outlet NO _X concentration outlet NO _X concentration setting outlet NO to the deviation corrected in adjusting meter 26 and the signal 21 from the setter 20 _{The X} deviation correction signal 27 and the preceding molar ratio signal 23 described above are added to the adder 28.
Then, the corrected molar ratio signal 29 is calculated.

Then, the corrected molar ratio signal 29, the total NO _X amount signal 19 and the corrected molar ratio signal 29 are multiplied by the multiplier 30 to obtain the required NH ₃ flow rate signal 31.
Is calculated.

This necessary NH ₃ flow rate signal 31 and the actually measured NH ₃ flow rate signal 33 detected by the NH ₃ flow rate detector 32 are compared by the controller 34, the deviation is proportionally integrated, and the control signal 35 of the required valve opening is converted. The opening amount of the NH ₃ flow control valve 37 of the NH ₃ pipe 36 was opened and closed to control the injection amount of ammonia.

[Problems to be solved by the invention]

High NO _X concentration in such the conventional NH ₃ injection rate control unit, when operating the denitration equipment 8 in FIG. 3 at the time of startup gas temperature is low, there is a disadvantage that the leakage NH ₃ concentration becomes abnormally high.

FIG. 5 is a characteristic curve diagram showing the denitration rate on the vertical axis and the gas temperature on the horizontal axis. As shown in FIG. 5, the denitration performance of the catalyst decreases at the time of starting when the gas temperature is low.

Figure 6 shows the NH ₃ concentration, gas temperature, and NO _X concentration on the vertical axis.
It is a characteristic curve figure which showed time on the horizontal axis.

In FIG. 6, a curve A is a gas temperature curve, a curve B is an inlet NO _X concentration curve of the denitration apparatus, and a curve C is an outlet NO _{X of the} denitration apparatus.
The concentration curve, curve D, shows the NH ₃ injection amount curve, and curve E shows the NH ₃ concentration curve at the outlet of the denitration device.

As shown in Fig. 6, since the gas temperature is low at boiler startup, even if NH ₃ is injected, the denitration performance becomes low as shown in Fig. 5, and under such conditions, as shown in Fig. 4. Traditional
When injected with NH ₃ in NH ₃ injection rate control device, injection amount of NH ₃ is NH ₃ injection rate curves for the outlet NO _X concentration is not decreased until the set value as indicated by F of the outlet NO _X concentration curve C of the denitration device extremely increased as shown by D of G, the outlet NH ₃ concentrations of the denitration apparatus abnormality is high as shown outlet NH ₃ concentration is H curve E, the pollution control undesirable.

Therefore, as in recent years, DSS operation and WSS operation are frequently performed, and it is not suitable as an NH ₃ injection flow rate control device at the time of starting a boiler where the gas temperature is low.

The present invention is intended to eliminate such conventional drawbacks, and its purpose is to suppress the NH ₃ concentration at the outlet of the denitration device even when the exhaust gas temperature immediately after starting such as a boiler is low, and to suppress NO at the time of starting and stopping. _An ammonia injection amount control device capable of suppressing the _X concentration is provided.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides a first calculation means for calculating a necessary NH ₃ injection amount determined according to the NO _X amount to be treated in a reactor having a denitration catalyst, and an outlet NH ₃ concentration. and second calculating means for calculating a required NH ₃ injection rate to be determined in accordance with, that when the exhaust gas temperature is low, that includes a switching means for controlling the necessary NH ₃ injection rate on the basis of the second calculation means It is a feature.

In addition, the required NH calculated by the first calculating means
_{3 The} injection amount is specifically calculated from, for example, the NH ₃ molar ratio signal obtained from the inlet NO _X concentration detection signal, the outlet NO _X concentration setting signal and the outlet NO _X concentration detection signal, and the inlet NO _X concentration detection signal. This is the required NH ₃ injection amount.

Also, the required NH calculated by the second calculating means
_{The 3} injection amount is specifically a necessary NH ₃ injection amount calculated from, for example, the outlet NH ₃ concentration setting signal and the outlet NH ₃ concentration detection signal.

〔Example〕

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

In FIG. 1, reference numerals 1 to 37 denote the same as those in FIG.

38 is a switching device provided between the adder 28 and the multiplier 30, 39 is a startup arithmetic unit according to the present invention, 40 is an outlet NH ₃ concentration detector, 4
1 is an outlet NH ₃ concentration signal, 42 is an outlet NH ₃ concentration setter, 43 is an outlet NH ₃ concentration setting signal, 44 is a molar ratio correction signal, 45 is a controller, 46 is a preceding molar ratio signal, 47 is a preceding molar ratio An arithmetic unit, 48 is a modified molar ratio signal, 49 is a molar ratio adder, and 50 is a monitor relay.

In such a configuration, the startup arithmetic unit 39 is
₃ Concentration detector 40, outlet NH ₃ concentration signal 41, outlet NH ₃ setter 4
2, outlet NH ₃ concentration setting signal 43, molar ratio correction signal 44, controller
45, the preceding molar ratio signal 46, the preceding molar ratio calculator 47, the modified molar ratio signal 48, and the molar ratio adder 49.The start-up calculating device 39 is the exhaust gas temperature as in the DSS operation and the WSS operation. When the output is low, the contacts b and c of the switch 38 are connected to control the NH ₃ injection amount, and when the deviation between the outlet NO _X concentration setting signal 21 and the measured outlet NO _X concentration signal 25 becomes zero, the contact of the switch 38 The a and c are connected, the contacts b and c are disconnected, and the injection amount of NH ₃ is controlled.

In Fig. 1, the outlet NH ₃ concentration setting signal set by the outlet NH ₃ setting device 42 at the time of starting a boiler with a low gas temperature.
43 is converted into a preceding molar ratio signal 46 by a preceding molar ratio calculator 47. On the other hand, the outlet NH ₃ concentration signal 41 detected by the outlet NH ₃ concentration detector 40 and the previous outlet NH ₃ concentration setting signal 43 are converted into a mole ratio correction signal 44 by a controller 45, and a mole ratio adder 49
The preceding molar ratio signal 46 is corrected by
Convert to. The corrected mole ratio signal 48 and the total NO _X amount signal 19 are multiplied by the multiplier 30 to obtain the required NH ₃ flow rate signal 31 at the time of startup, and the deviation between the required NH ₃ flow rate signal 31 and the actually measured NH ₃ flow rate signal 33 is calculated. As the control signal 35, the NH ₃ injection flow rate is controlled.

Outlet concentration of NO _X accompanied not denitration performance increased denitration apparatus to an increase in the gas temperature coming lowered. Here, if the deviation between the measured outlet NO _X concentration signal 25 detected by the outlet NO _X concentration detector 24 and the outlet NO _X concentration signal 21 established by the outlet NO _X concentration setting device 20 is zero, switching is performed by the monitor relay 50. The contact point of the device 38 is switched from b, c to a, c, and the NH ₃ injection amount is controlled in the same manner as the control described in FIG.

During startup such as exhaust gas temperature is low, the need NH ₃ flow rate signal 31 Te startup operation device 39 Niyotsu of Figure 1 is smaller than the conventional, NH ₃ injection rate as shown in Figure 2 amount increasing as indicated by the curve D-I is reduced, the gas temperature curve a, the inlet NO _X concentration curve B, the outlet NO _X concentration curve C is also increasing rapidly as with conventional, the outlet NH ₃ concentration curve E It becomes flat, the amount of leaked NH ₃ is small, and secondary pollution can be prevented.

According to the embodiment of the present invention, the outlet NH ₃ amount of the denitration device is set, and the NH ₃ amount is injected so that the actual outlet NH ₃ amount falls within the set value, so that the gas temperature is low and the predetermined denitration performance is achieved. Even when the boiler is not activated, the amount of NH _{3 at} the outlet leak decreases.

Furthermore, when the exhaust gas temperature rises and a predetermined denitration performance is obtained, and the actual outlet NO _X value becomes equal to the set NO _X value, the conventional ammonia injection amount control device is switched and the operation is performed. _X You can drive smoothly without fluctuation.

Further, the denitration device can be stably operated immediately after starting the boiler with a low gas temperature, and the NO _X amount at the time of starting the boiler can be suppressed.

〔The invention's effect〕

According to the present invention, even if the exhaust gas temperature immediately after starting / stopping by performing DSS operation or WSS operation is low, the amount of leak NH ₃ is small, and the NO _X concentration immediately after starting / stopping can be suppressed.

[Brief description of drawings]

FIG. 1 is a control system diagram of an NH ₃ 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 boiler equipped with a denitration device. Smoke passage system diagram, Fig. 4 is the control system diagram of the conventional NH ₃ injection amount control device, Fig. 5
FIG. 6 is a temperature characteristic curve diagram of denitration performance, and FIG. 6 is a characteristic curve diagram of FIG. 12 …… Inlet NO _X concentration detector, 13 …… Inlet NO _X concentration signal, 14
…… Air flow rate detector, 15 …… Air flow rate signal, 16 …… Function generator, 17 …… Exhaust gas flow rate signal, 18 …… Multiplier, 19 ……
Total NO _X amount signal, 20 …… Exit NO _X concentration setting device, 21 …… Exit NO
_X concentration setting signal, 22 …… Molar ratio calculator, 23 …… Preceding molar ratio signal, 24 …… Out NO _X concentration detector, 25 …… Measured outlet NO _X
Concentration signal, 26 …… Controller, 27 …… Exit NO _X deviation correction signal, 28 …… Adder, 29 …… Corrected mole ratio signal, 30 …… Multiplier, 31 …… Necessary NH ₃ flow rate signal, 32… … NH ₃ flow detector, 33
…… Measured NH ₃ flow rate signal, 37 …… NH ₃ flow rate control valve, 38 …… Switcher, 39 …… Start-up operation device, 40 …… Outlet NH ₃ concentration detector, 41 …… Outlet NH ₃ concentration signal, 42 …… Exit NH ₃ setting device, 43
...... Outlet NH ₃ concentration setting signal, 44 …… Molar ratio correction signal, 45
...... Controller, 46 …… Leading mole ratio signal, 47 …… Leading mole ratio calculator, 48 …… Modified mole ratio signal, 49 …… Mol ratio adder.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01D 53/74 B01D 53/34 ZAB

Claims (1)

[Claims] 1. NO _X to be treated in a reactor having a denitration catalyst.
First calculating means for calculating a required NH ₃ injection rate to be determined depending on the amount, the second calculating means for calculating a required NH ₃ injection rate to be determined depending on the outlet NH ₃ concentrations, when the exhaust gas temperature is low And a switching means for controlling the required NH ₃ injection amount based on the second calculation means, and an ammonia injection amount control device.