JPS61153124A - Method for controlling injection of ammonia in noncatalytic denitrating process - Google Patents

Abstract

PURPOSE:To reduce the consumption of NH3 by obtaining the provisional amt. of NH3 to be injected from the amt. of combustion gas, the concn. of generated NOx, and the concn. of NOx after denitration, obtaining further the amt. to be injected by the concn. of the residual NH3, and controlling by a temp. selector. CONSTITUTION:The amt. of combustion gas is calculated by an arithmetic unit 13 of the amt. of combustion gas, and the amt. of NOx is calculated along with the signal from an NOx analyzer 10b. The signal 15 of the set NOx concn., the signal of the denitration rate by a denitration rate arithmetic unit 19, and the signal of an arithmetic unit 18 of the amt. of excess NOx are inputted to an arithmetic unit 21 of the amt. of injected NH3 to obtain a provisional amt. (I) of injected NH3. A provisional amt. (II) of injected NH3 is obtained at an arithmetic unit 28 of the amt. of injected NH3 from the signal of an arithmetic unit 22 of the amt. of residual NH3 and the signal of a storage device 25 of the amt. of injected NH3. The smaller value between the provisional amts. of injected NH3 (I) and (II) is selected by a low selector 29, inputted to a temp. selector 26, then inputted directly to a NH3 flow rate regulator 30 when the denitration temp. is appropriate, and NH3 is injected from a nozzle 6.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for controlling the amount of NH3 injected in a non-catalytic denitrification method when removing NOx from exhaust gas from a boiler or the like.

Conventional technology Conventionally, the non-catalytic denitrification method for exhaust gas from boilers, etc.
NHa is injected as described in Japanese Patent No. 0-35908, and the actual operation is as shown in FIG. In addition, NHa injection nozzle 40 is installed in the part unaffected by the flame behind 2 to 3 rows of water pipes.
6, an exhaust gas flow meter 409 and a NOx sensor 410 are attached to the flue 408 communicating with the outlet of the water pipe section 403, and the NH3 injection amount is measured by the exhaust gas flow meter 409 and the NOx sensor 410. The denitrification rate is determined from the concentrations of the two NOx sensors 405 and 410, and a large amount of NHa injection is determined from this and a preset denitrification rate ('n).

In other words, the conventional control factor for the large amount of NHa injection is the denitration rate, and even when the boiler is under low load, when the denitration rate is used as a control factor, NHs is always injected so that the set denitration rate is achieved. ◇Problems to be solved by the present invention In general, the NOx concentration in the combustion gas and the combustion gas temperature are dominated by the boiler load, as shown in Figures 5 and 6, and when the boiler is under low load. In this case, the NOx concentration and combustion gas temperature decrease.

However, when NH3 is injected with only the denitrification rate as a control factor, that is, even when the NOx concentration in the exhaust gas is low, NH8 is injected regardless of the boiler load. However, when the NOx concentration is low, NHa/No
Even if NH is injected so that the X ratio is the same, high No.
Compared to when xl is 1 degree, when the NOx concentration is low, the probability that NH3 molecules and NOx molecules will react is small, and therefore the denitrification rate is poor.

Therefore, when the NOx removal rate is the only control factor, a large amount of NHa is injected in order to obtain the set NOx removal rate, resulting in an increase in the amount of NH3 remaining in the exhaust gas.

In addition, in the conventional method, in order to maintain the combustion gas temperature within the denitrification reaction temperature range, the temperature is adjusted by adding excess air to the boiler 2-, using an afterburner, etc., but this results in a decrease in the efficiency of the boiler.

As mentioned above, conventional methods cannot cope with fluctuations in boiler load, NOx concentration, and gas temperature, resulting in poor denitrification efficiency, and the amount of NH3 remaining in exhaust gas due to increased consumption of NH3. The amount of NHa is within the permissible concentration (25 ppm
(below), and also lead to higher costs due to increased NH3 consumption.

Means for Solving the Problems The present invention is a non-catalytic denitrification method in which NOx in the exhaust gas of a boiler or the like is removed using NH3, and the amount of NOx in the combustion gas is determined by measuring the amount of combustion gas and the concentration of NOx generated. The provisional injection amount of NH3 is calculated from the NOx concentration after denitrification and the preset set discharge NOx concentration, and on the other hand, the amount of provisionally injected NH3 is calculated from the residual NH3 concentration in the exhaust gas and the preset discharge residual NH concentration. Find the NH, residual rate, compare this with the provisionally injected NH3 amount of the combustion gas, select the one with the smaller injected NH3 amount, and check whether the combustion gas temperature is the denitrification reaction temperature or not. This is a method for controlling the amount of NH3 injection in a non-catalytic denitrification method in which NHs is injected.

Functions and Effects The present invention is constructed as described above, and measures the generated NOx concentration, the NOx concentration in the exhaust gas after denitration, and the amount of combustion gas, and also measures the preset exhaust NOx concentration and the after-denitration concentration. The denitrification rate is determined from the NOx concentration of
Calculate the amount of Ha (this is set as the provisional injection amount ■).

On the other hand, calculate the residual NH3 concentration in the exhaust gas, compare it with the preset residual NH3 concentration, and calculate the amount of NH3 to be injected from the amount of combustion gas (this is temporarily e!2 piece 1 TIXL
, J-1 Provisional injection amounts (1) and (n) obtained as above
and select the one with the smaller amount of NHg.

That is, the provisional injection amount (1) is the provisional injection amount of NH3 calculated from the current denitrification rate, and the provisional injection amount (n) is the provisional injection amount calculated based on the residual NH3 concentration. (1
) is higher than the provisional amount (II), the residual NH3 concentration in the exhaust gas exceeds the preset residual NH3 concentration, so a lower value, that is, the provisional amount (If) is selected.

If the provisional amount (1) is lower than the provisional amount (It), there is no need to worry about the residual NH3 concentration in the exhaust gas, and in order to set the NOx concentration after denitrification to the set exhaust NOx concentration, The low value of the NH'a injection amount, i.e. the provisional amount (1
).

In addition, since the denitrification reaction is affected by the combustion gas temperature, the amount of injected NH3 selected as described above ~1200'O)
, adjust the valve opening of the NH3 flow rate adjustment valve to
3, and if it is outside the denitrification reaction temperature range, close the NH flow rate adjustment valve and remove residual NH, increase in amount, or remove NH3.
Prevents the increase in NOx due to oxidative decomposition of

As described above, the present invention temporarily determines the NH3 injection amount used in the non-catalytic denitration method of exhaust gas from boilers, etc. from the combustion gas amount 9 generated NOx concentration and the NOx concentration after denitration, and further calculates this amount from the NOx concentration remaining in the exhaust gas. Since the provisional injection amount is determined based on the NH3 concentration and is controlled by the temperature selector, the appropriate amount of NHg can be injected in response to fluctuations in the boiler load and the associated combustion gas temperature. This has the effect of preventing an excessive denitrification rate, controlling the amount of residual NHg in the exhaust gas within an acceptable range, and greatly reducing the amount of NH3 consumed.

Embodiment FIG. 1 shows an embodiment of the present invention. Next, the present invention will be specifically explained with reference to an illustrated example. The boiler 1 is connected to a furnace 2, a denitrification chamber 3 is connected to the furnace 2, and a water pipe group 4 is connected to the denitrification chamber 3. Also, the flue 5 and Karanashi following the water pipe group 4,
A nozzle 6 for NH injection, a thermometer (thermocouple thermometer) 7, and a NOx sensor 8a are installed in the denitration chamber 3, and an 02 sensor 9a1 NOx sensor is installed in the flue 5; It may be a boiler that does not.

The cotton gas passing through the boiler 1 is sequentially passed through the denitrification chamber 3, the water pipe group 4 and the flue 5 to be discharged.

The amount of combustion gas at this time is calculated as follows. That is, a fuel flow rate signal is output from the fuel flow meter (F'), inputted to the fuel flow rate transmitter 12, and further inputted to the combustion gas amount calculator 1.
3 is input. The combustion gas amount calculator 13 includes a flue 5
Detected by the 02 sensor 9a attached to the analyzer 9
The 02 concentration signal calculated in step b is input at the same time, and the combustion gas amount calculator 13 calculates the amount of combustion gas from the fuel flow rate signal and the 0□ concentration signal.

On the other hand, in the flue 5, the 02 sensor - 9a% NOx sensor 1
0a and residual NH3 sensor 11a detect the 0□ concentration, NOx concentration, and residual NHa concentration in the exhaust gas, respectively.
02 analyzer 9b% NOx analyzer 10b and rc mat SV respectively
Mouth, A 倀か慴Lklff? The concentration signal from the NOx analyzer 10b and the combustion gas amount signal from the fuel gas amount calculator 13 are output to the NOx amount calculator 14.
Calculate the amount of NOx in the exhaust gas by inputting the following information: Next, enter the preset NOx concentration signals 15 and 02.
The analyzer 9b and the 00□ concentration signal are converted into the NOx concentration converter 16.
, and convert the set NOx concentration to the set NOx concentration of 0□ concentration at that time. This is because it is necessary to convert the set NOx concentration to the NOx concentration at the specified 02 concentration (for example, 02-45b).

Furthermore, the setting NO converted by the NOx concentration converter 16
The x concentration signal and the combustion gas amount signal from the combustion gas amount calculator 13 are input to the set exhaust NOx amount calculator 1T, where they are converted into a set exhaust NOx amount signal, and the set exhaust NOx amount signal and the exhaust Inputting the actual discharged NOx amount signal calculated by the NOx amount calculator 14 to the excess NOx amount calculator 18,
The difference between the set exhaust NOx amount and the actual exhaust NOx amount is determined.

On the other hand, in the denitrification rate calculator 19, the exhaust NOx amount calculator 14
The denitrification rate is calculated by inputting the discharged NOx amount signal and the generated NOx amount signal obtained by the NOx amount calculator 20. The NOx amount calculator 20 is a NOx sensor 8a of the denitrification chamber 3.
The generated NOx amount is calculated from the generated NOx concentration signal obtained by the NOx analyzer 8b and the combustion gas amount signal calculated by the combustion gas amount calculator 13. Furthermore, the denitrification rate calculator 19
The denitrification rate signal obtained in step 1 and the signal of the difference between the set discharged NOx amount and the actual discharged NOx amount in the excess NOx amount calculator 18 are inputted to the injection NHs amount calculator 21 to calculate the injection NHa.
Calculate the amount (this is set as the provisional injection amount (I)).

In addition, the provisional amount (I) obtained by the injection NH and the amount calculation calculator
The exhaust NOx amount is calculated from the combustion gas amount, the generated NOx concentration, and the exhaust NOx concentration, and this is calculated based on the set exhaust NOx amount.

Next, residual NH! Detected by sensor 11a, residual NH
3 The residual NH3 concentration signal determined by the analyzer 11b and the combustion gas amount signal calculated by the combustion gas amount calculator 13 are
a, the remaining NHa amount is calculated by inputting it to the amount calculation calculator, and the set residual NHa concentration signal 23 that has been previously set and the combustion gas amount signal calculated by the combustion gas amount calculator 13 are used to calculate the set residual NHa amount. Input it into a ratio calculator to calculate the set residual NHs amount.

Furthermore, the combustion gas amount signal from the combustion gas amount calculator 13 is inputted to the injection NHs amount storage device 25, and the signal from the temperature selector 26 is also inputted, and the combustion gas passage time Δt to the denitrification NH3 sensor 11a is calculated. Residual NH! The amount of NH3 injected Δ hours before the time when residual NH was detected by the sensor 11a is stored. That is, after the denitrification reaction is completed and the residual NHa concentration is measured after NH3 is injected, it takes time depending on the combustion gas flow rate, and therefore the injected NH3
In order to compare the amount of residual NH3 and the amount of residual NH3, it is necessary to calibrate Δ by time. Incidentally, the amount of NH3 injected from the nozzle 6 of the denitrification chamber 3 is the injection amount determined by the temperature selector 26, which will be described later.

In addition, the residual N calculated by the residual NH3 amount calculating unit
The H3 amount signal and the injected NH3 amount signal Δ calculated by the injected NH3 amount memory 25 are input to the NH and residual rate calculator 27 to calculate the NH3 residual rate, and the set residual N
The setting residual NHg amount signal of the H3 amount calculator 24 and the NH3
The NH3 residual rate signal from the residual rate calculator 27 is input to the injected NH3 amount calculator to calculate the injected NH3 amount (this is set as the provisional injection amount ■). This provisional injection amount (If) is N
This is the amount of NHs injected assuming that the amount of residual NH3 that is discharged after a time of Δ after injecting % is the set amount of residual NH3, and that the residual rate of NHs remains the same.

Next, the provisional corporate amount (
II) Input the signal and the provisional injection amount (I) calculated by the injection NHa amount calculator to the low selector 29, and
Select the one with the smaller amount of H3. In other words, the provisional injection amount (■) calculated by the injection NH3 amount calculator - is the set residual NHa
The provisional injection amount (1) of the injection NH3 amount calculation calculator is the provisional injection amount of NHa calculated from the value of concentration 23. If the provisional amount (I) is higher than the provisional amount (II), the residual NHa concentration in the exhaust gas will exceed the preset residual NH3 concentration. select.

If the provisional amount (1) is lower than the provisional amount (If), there is no need to worry about the concentration of residual NH in the exhaust gas, and in order to set the NOx concentration after denitrification to the set exhaust NOx concentration and to reduce the amount of NHa consumption. s Low value of NHa injection amount, i.e. provisional amount (
Select I). Therefore, the low selector 29 selects the smaller amount of NHa to be injected.

Furthermore, the provisional injection amount (either provisional injection amount (I) or (If)) selected by the low selector 29 is transferred to the temperature selector 2.
Enter 6. The temperature signal from the thermometer 7 installed in the denitrification chamber 3 is input to the temperature selector 26, and if the temperature at this time is within the denitrification temperature range, the temperature selector 2
Injection NHa that finally determined the provisional injection amount entered in 6.
and the injected NHa amount signal is stored in the injected NHa amount memory 25.
and input to the NHs flow rate regulator 30, respectively.

In the NHs flow rate regulator 30, the NHi flowmeter 31 and the NH
3) Adjust the valve opening of the NH3 flow rate adjustment valve 33 so that the output signal of the flow rate transmitter 32 and the signal of the temperature selector 26 match, and inject NHa through the nozzle 6f).

Further, when the combustion gas temperature detected by the temperature selector 26 is outside the denitrification temperature range, the injection of NHs is stopped regardless of the exhaust NOx concentration or the residual NHs concentration. That is, when the combustion gas temperature is outside the denitrification reaction temperature range, NH
Even if 3 is injected, the denitrification reaction does not take place, and instead the residual NH
This may lead to an increase in the amount of a or decomposition of the injected NH3, and conversely lead to NO
x increases - F six-nare whistle ζ M easy f C down n Mf thousand-handed measure ＾f
When the NOx concentration is lower than the set NOx concentration, NHa can be controlled to be injected within the denitration reaction temperature range. Figure 2 shows the relationship between the combustion gas temperature and the denitrification rate, and Figure 3 shows the combustion The relationship between gas temperature and NH and injection amount is shown (the second factor is the solid line in Figure 3, which is the conventional method; the dotted line is the method of the present invention; the combustion gas temperature in the conventional method is approximately 950;
℃ shows the lowest denitrification rate. That is, at about 950°C, excessive denitrification reaction occurs.

In contrast, in the present invention, the combustion gas temperature is 800 to 1100.
It is possible to maintain a substantially constant denitrification rate within the denitrification reaction temperature.

In addition, as shown in FIG. 3, compared to the amount of NH3 injected in the conventional method, the amount of FlIJTJ3 in the present invention is indicated by diagonal lines.
Ritsu λ Banfuyu 1/j I Oka Sosu Otsu and 2.

As described above, the present invention compares the preset exhaust NOx concentration and the actual NOx concentration in the exhaust gas to determine whether the injected NHs
The amount of residual N in the exhaust gas is calculated provisionally and
The appropriate amount of NHs to be injected is calculated from the Ha concentration and the amount of NH temporarily determined from the preset residual NHa concentration, and the temperature is checked, so excessive denitration of the exhaust gas is suppressed, and the amount of NH in the exhaust gas is By suppressing the amount of residual NH3, NH3 in the exhaust gas is kept within the permissible concentration range, and at the same time, NH3 is
, the consumption amount can be reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of one embodiment of the present invention, Fig. 2 is a graph showing the denitrification rate with respect to combustion gas temperature, Fig. 3 is a graph of large amount of NHa injection with respect to combustion gas temperature, and Fig. 4 is a graph of the conventional method. In the explanatory diagram, the fifth factor is a graph showing the NOx generation concentration with respect to the boiler load, and FIG. 6 is a graph showing the combustion gas temperature with respect to the boiler load. 1: Boiler, 2: Furnace, 3: Denitrification room, 4: Water pipe section, 5
: Flue, 6: Injection nozzle, 7: Thermometer, 8a: Generated NO
x sensor, 8b: NOx analyzer, 9a: 0
2 sensors, 9b: 02 analyzer, 10a: NOx
Sensor, 10b: NOx analyzer, 11a: Residual NH3 sensor, 11b: Residual NH3 analyzer, 12: Fuel flow transmitter, 13: Combustion gas amount calculator, 14: Emission N
Ox amount calculator, 15: Setting NOx concentration signal, l @:
NOx concentration converter, 17: Setting ° discharge NOx amount calculator, 18: Excess NOx amount calculator, 19: Denitrification rate calculator, 2
0: N0xl calculator, 21: Injected NH3 amount calculator 2: Residual NH3 amount calculator 3: Set residual NHa concentration signal, 24: Set residual NHs amount calculator, 25: Injected NH3 amount calculator
s amount storage device, 26: Temperature selector, 27: NH3 residual rate calculator, 28: Injected NHa amount calculation calculator 9: Low selector, 30: NHs flow rate regulator, 31: NH
, I flowmeter, 32: NHs flow rate transmitter, 33:
NH, flow rate adjustment valve.

Claims (1)

[Claims] In the non-catalytic denitrification method, which removes NOx in exhaust gas from boilers, etc. using NH_3, the amount of combustion gas and the NOx concentration generated are measured to determine the amount of NOx in the combustion gas, and the NOx concentration after denitration is determined in advance. Calculate the provisional injection amount of NH_3 from the set exhaust NOx concentration, and calculate the remaining N in the exhaust gas.
The NH_3 residual rate in the exhaust gas is determined from the H_3 concentration and the preset discharge residual NH_3 concentration, the provisional injection NH_3 amount is calculated from this and the combustion gas amount, and the two provisional injection NH_3 amounts are compared. A method for controlling the amount of NH_3 injected in a non-catalytic denitrification method, characterized by selecting the smaller amount of NH_3 to be injected, and further checking whether the combustion gas temperature is at the denitrification reaction temperature before injecting NH_3.