JPH1057769A - Method for controlling injection of denitrating ammonia into coal-fired boiler and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inject a required amt. of ammonia even at a load decreasing as well as at a load increasing and to prevent the outlet NOx of a denitrater from exceeding a stipulated value. SOLUTION: When the load of a coal-fired boiler is increased, the waste gas flow rate 8 is obtained practically in follow-up to the change in the combustion rate command signal 7, the required ammonia injection 10 is obtained based on the waste gas flow rate 8, the inlet NOx of a denitrater and the molar ratio and outputted. Meanwhile, when the load of the coal-fired boiler is decreased, the waste gas flow rate 8 is obtained in follow-up to the change in the combustion rate command signal 2 so that the preset time lag is secured, and the required ammonia injection 10 is obtained based on the flow rate 8, the inlet NOx of the denitrater and the molar ratio and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling an injection amount of denitrified ammonia in a coal-fired boiler.

[0002]

2. Description of the Related Art Generally, nitrogen oxides (NOx) are contained in exhaust gas discharged from a coal-fired boiler, and such NOx must be removed by a denitration device.

FIG. 3 shows an example of a conventional coal-fired boiler, where 1 is a coal-fired boiler and 2 is a coal-fired boiler.
3 is a denitration device provided in the middle of the duct 2 and filled with a catalyst, 4 is an induction ventilator, 5 is an inlet NOx contained in exhaust gas flowing into the denitration device 3 (unit). Is [ppm])
Reference numeral 6 denotes an outlet NOx meter for detecting outlet NOx (unit: [ppm]) contained in exhaust gas that has passed through the denitration device 3. By reducing NOx contained in the exhaust gas from the boiler 1, the outlet NOx detected by the outlet NOx meter 6 is suppressed to a specified value or less. ,
The calculation is performed in a control device as shown in FIG.

[0004] The control device includes a combustion amount command signal (FF).
D) Exhaust gas flow rate 8 based on 7 (unit is [Nm ³ / h])
And a function generator 9 for calculating and outputting a proportional constant κ and an inlet NOx total 5 for an exhaust gas flow rate 8 output from the function generator 9.
Is multiplied by the molar ratio at the inlet NOx of the denitration apparatus 3 detected by the above method, and the required ammonia injection amount 10 (unit is [kg /
h]), and calculates and outputs the actual ammonia injected into the duct 2 based on the required ammonia injection amount 10 calculated by the arithmetic unit 11. The adjustment of the injection amount is performed. The molar ratio is a numerical value represented by the number of moles of ammonia necessary for 1 mole of NOx to be removed when the outlet NOx is suppressed to a specified value or less.

[0005] A function as shown in FIG. 5 is input to the function generator 9. The function is to increase or decrease the exhaust gas flow rate 8 substantially in proportion to the increase or decrease of the combustion amount command signal 7. The arithmetic unit 11 has three multipliers 11a, 11b and 11c.

As a result, when the load of the coal-fired boiler 1 is increased, as shown in FIG. 6, the amount of ammonia injected is increased with the passage of time in a manner substantially proportional to the combustion amount command signal. At the time of load reduction, as shown in FIG. 6, the ammonia injection amount is reduced with time in a manner substantially proportional to the combustion amount command signal.

[0007]

In the case of the coal-fired boiler 1 as described above, pulverized coal as fuel is supplied from a mill (not shown). As shown in FIG. 6, the actual combustion amount with respect to the combustion amount command signal tends to be slightly smaller when the load increases, and slightly larger when the load decreases.

Therefore, as described above, when the amount of injected ammonia is determined based on the combustion amount command signal, when the load increases, a little more amount of ammonia than the amount of injected ammonia corresponding to the actual amount of combustion is injected into the duct 2. There is no problem, but when the load drops, only a little less ammonia than the amount of ammonia injected corresponding to the actual combustion amount is injected into the duct 2 and the denitration device 3
Exit NOx may exceed the specified value.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to inject a required amount of ammonia not only at the time of load increase but also at the time of load decrease, and that the NOx at the outlet of the denitration apparatus exceeds a specified value. An object of the present invention is to provide a method and an apparatus for controlling the amount of denitrified ammonia injection into a coal-fired boiler that can be prevented.

[0010]

According to the present invention, when the load of a coal-fired boiler rises, the flow rate of the exhaust gas is obtained by substantially following the change in the combustion amount command signal.
While obtaining and outputting the required ammonia injection amount based on Ox and the molar ratio, when the load of the coal-fired boiler falls, the exhaust gas flow rate is obtained by following a change in the combustion amount command signal so that a predetermined time delay occurs, The present invention relates to a method for controlling a denitration ammonia injection amount of a coal-fired boiler, wherein a required ammonia injection amount is obtained and output based on the exhaust gas flow rate, the NOx at the inlet of the denitration device, and the molar ratio.

Further, the present invention provides a primary output signal for outputting a combustion amount command primary delay signal by following a change in the combustion amount command signal so that a predetermined time delay occurs when the combustion amount command signal changes. A delay unit, a combustion signal command output from the primary delay unit, a high signal selector for selecting a higher value of the primary delay signal and the combustion signal command signal and outputting the selected signal as a combustion command selection signal; A function generator that calculates and outputs an exhaust gas flow rate based on a combustion amount command selection signal output from the selector, and a proportional constant to the exhaust gas flow rate output from the function generator and an inlet of the denitration device detected by an inlet NOx meter The present invention relates to a denitration ammonia injection amount control device for a coal-fired boiler, comprising: an arithmetic unit for multiplying NOx by a molar ratio to obtain and output a required ammonia injection amount.

According to the above means, the following effects can be obtained.

In the method for controlling the amount of denitrified ammonia injected into a coal-fired boiler according to the present invention, when the load on the coal-fired boiler rises, the flow rate of the exhaust gas is obtained substantially following the change in the combustion command signal. The required ammonia injection amount is calculated and output based on the inlet NOx and the molar ratio of the fuel, and the actual ammonia injection amount is adjusted based on the required ammonia injection amount. The exhaust gas flow rate is obtained by following the change in the amount command signal such that a preset time delay occurs, and the required ammonia injection amount is obtained and output based on the exhaust gas flow rate, the NOx and the molar ratio at the inlet of the denitration device, and output. Adjustment of the actual ammonia injection amount is performed based on the required ammonia injection amount.

As a result, when the load of the coal-fired boiler rises, the amount of injected ammonia is increased with the passage of time in a manner substantially proportional to the combustion amount command signal. At least approximately the same amount of ammonia as the corresponding amount of ammonia can be injected into the duct, so that the outlet NOx of the denitration device does not exceed a specified value.

In the apparatus for controlling the amount of denitrated ammonia injected into a coal-fired boiler according to the present invention, when the load on the coal-fired boiler rises, the combustion amount command signal also increases, and the combustion amount command signal is input to the first-order lag device. The primary delay unit follows the change in the combustion amount command signal such that a preset time delay occurs, and outputs a combustion amount command primary delay signal to a high signal selector. The higher one of the combustion amount command primary delay signal and the combustion amount command signal output from, that is, the combustion amount command signal is selected, and the combustion amount command signal is output to the function generator as a combustion amount command selection signal as it is. The function generator determines the exhaust gas flow rate based on the combustion amount command selection signal output from the high signal selector in the function generator and outputs the calculated exhaust gas flow rate to an arithmetic unit. The flow rate of the exhaust gas output from the function generator is multiplied by the proportionality constant, the NOx at the inlet of the denitration apparatus detected by the inlet NOx meter, and the molar ratio, and the required ammonia injection amount is obtained and output, and is calculated by the calculator. Based on the required amount of injected ammonia, the actual amount of injected ammonia to be injected into the duct is adjusted. On the other hand, when the load of the coal-fired boiler drops, the combustion amount command signal also decreases, and the combustion amount command signal becomes primary. Input to the delay unit, the primary delay unit follows the change in the combustion amount command signal such that a preset time delay occurs, and the combustion amount command primary delay signal is output to the high signal selector, and the high signal selection is performed. The higher of the combustion amount command primary delay signal and the combustion amount command signal output from the primary delayer, that is, the combustion amount command primary delay signal, is selected. The next delay signal is output to the function generator as a combustion amount command selection signal, and the function generator determines the exhaust gas flow rate on the basis of the combustion amount command selection signal output from the high signal selector. Is output to the calculator, the proportionality constant is multiplied by the exhaust gas flow rate output from the function generator by the NOx inlet NOx and the molar ratio detected by the inlet NOx meter, and the required ammonia injection amount is determined. The actual amount of ammonia injected into the duct is adjusted based on the required amount of ammonia that is output and calculated by the arithmetic unit.

As a result, when the load of the coal-fired boiler rises, the ammonia injection amount is increased with the passage of time in a manner substantially proportional to the combustion amount command signal. The amount of injected ammonia is reduced with the passage of time in a manner substantially proportional to the signal, and even when the load is reduced, at least approximately the same amount of ammonia as the amount of injected ammonia corresponding to the actual combustion amount is injected into the duct. It is possible to prevent the NOx at the outlet of the denitration apparatus from exceeding a specified value.

[0017]

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

FIGS. 1 and 2 show an example of an embodiment of the present invention. In the drawings, the portions denoted by the same reference numerals as those in FIGS. 3 to 6 represent the same components. 3 to 6
However, the present embodiment is characterized in that when the combustion amount command signal 7 changes as shown in FIGS. On the other hand, a primary delay unit 12 that outputs a combustion amount command primary delay signal 7 ′ while following a preset time delay, and a combustion amount command primary delay signal 7 ′ output from the primary delay unit 12 and a combustion amount High signal selector 13 which selects the higher value of command signal 7 and outputs it as combustion amount command selection signal 7 "
The function generator 9 obtains the exhaust gas flow rate 8 based on the combustion amount command selection signal 7 "output from the high signal selector 13 and outputs it to the arithmetic unit 11.
At the exhaust gas flow rate 8 output from the function generator 9
Is multiplied by the molar ratio and the NOx at the inlet of the denitration device 3 detected by the inlet NOx meter 5 to obtain and output the required ammonia injection amount 10. The required ammonia injection amount 10 calculated by the calculator 11 Based on the above, the actual amount of ammonia injected into the duct 2 is adjusted.

Next, the operation of the illustrated example will be described.

When the load of the coal-fired boiler 1 rises, the combustion amount command signal 7 also increases, and the combustion amount command signal 7 is input to the primary delay unit 12, and the primary delay unit 12 changes the combustion amount command signal 7. On the other hand, a combustion amount command primary delay signal 7 ′ is output to the high signal selector 13 so as to follow a preset time delay, and the combustion amount command output from the primary delay unit 12 in the high signal selector 13. The higher value of the primary delay signal 7 'and the combustion amount command signal 7, that is, the combustion amount command signal 7, is selected, and the combustion amount command signal 7 is output to the function generator 9 as it is as the combustion amount command selection signal 7 ". Then, the function generator 9 calculates the exhaust gas flow rate 8 based on the combustion amount command selection signal 7 "output from the high signal selector 13 and outputs it to the calculator 11. In Then, the exhaust gas flow rate 8 output from the function generator 9 is multiplied by the proportionality constant κ, the NOx at the inlet of the denitration device 3 detected by the inlet NOx meter 5 and the molar ratio, and the required ammonia injection amount 10 is obtained and output. And the required ammonia injection amount 1 calculated by the arithmetic unit 11
Based on 0, adjustment of the actual amount of ammonia injected into the duct 2 is performed.

On the other hand, when the load of the coal-fired boiler 1 drops,
The combustion amount command signal 7 also decreases, and the combustion amount command signal 7 is input to the primary delay unit 12, and the primary delay unit 12 follows the change in the combustion amount command signal 7 such that a preset time delay occurs. , The combustion amount command primary delay signal 7 ′ is output to the high signal selector 13, and the combustion amount command primary delay signal 7 ′ and the combustion amount command signal 7 output from the primary delay device 12 in the high signal selector 13. The higher value, ie, the combustion amount command primary delay signal 7 'is selected, and the combustion amount command primary delay signal 7' is output to the function generator 9 as the combustion amount command selection signal 7 ", and the function generator 9 is selected. The exhaust gas flow rate 8 is obtained by the function generator 9 based on the combustion amount command selection signal 7 ″ output from the high signal selector 13 and output to the arithmetic unit 11, where the function generator 9 outputs Output The gas flow rate 8 is multiplied by the proportional constant κ and the inlet NOx detected by the inlet NOx meter 5 and the molar ratio, and the required ammonia injection amount 10 is obtained and output, and calculated by the calculator 11. Based on the required ammonia injection amount 10, the actual ammonia injection amount injected into the duct 2 is adjusted.

As a result, when the load of the coal-fired boiler 1 increases, as shown in FIG. 2, the ammonia injection amount is increased with time in a manner substantially proportional to the combustion amount command signal 7, while the coal-fired boiler 1 At the time of load reduction, as shown in FIG. 2, the ammonia injection amount is reduced with time in a manner substantially proportional to the combustion amount command primary delay signal 7 '. A substantially same amount of ammonia as the corresponding amount of ammonia can be injected into the duct 2, so that the outlet NOx of the denitration device 3 does not exceed a specified value.

If the time delay preset in the primary delay unit 12 with respect to the change in the combustion amount command signal 7 is made slightly longer, the amount of ammonia injected into the duct 2 is reduced by the amount of ammonia injected corresponding to the actual combustion amount. Needless to say, it can be slightly larger than the amount.

In this way, not only when the load rises but also when the load drops, the required amount of ammonia can be injected, and the NOx at the outlet of the denitration device 3 can be prevented from exceeding a specified value.

It should be noted that the method and apparatus for controlling the amount of denitrated ammonia injected into a coal-fired boiler of the present invention are not limited to the illustrated examples described above, and various changes can be made without departing from the scope of the present invention. Of course.

[0026]

As described above, according to the method and apparatus for controlling the amount of denitrated ammonia injected into a coal-fired boiler according to the present invention, it is possible to inject a required amount of ammonia not only at the time of increasing the load but also at the time of decreasing the load. Therefore, an excellent effect of preventing the outlet NOx of the denitration device from exceeding a specified value can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a combustion amount command signal, an ammonia injection amount, and a combustion amount when the load is increased and when the load is decreased in an example of an embodiment of the present invention.

FIG. 3 is an overall schematic configuration diagram of a conventional example.

FIG. 4 is a block diagram of a conventional example.

FIG. 5 is a diagram showing functions set in the function generator shown in FIG. 4;

FIG. 6 is a diagram showing a relationship between a combustion amount command signal, an ammonia injection amount, and a combustion amount when the load is increased and when the load is decreased in the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coal-fired boiler 3 Denitration device 5 Inlet NOx meter 7 Combustion amount command signal 7 'Combustion amount command primary delay signal 7 "Combustion amount command selection signal 8 Exhaust gas flow 9 Function generator 10 Required ammonia injection amount 11 Computing unit 12 Primary delay unit 13 High signal selector

Claims (2)

[Claims] When the load of a coal-fired boiler rises, an exhaust gas flow rate is obtained by substantially following a change in a combustion amount command signal, and a required ammonia injection amount is obtained based on the exhaust gas flow rate, the NOx at the inlet of the denitration apparatus, and the molar ratio. On the other hand, when the load of the coal-fired boiler drops, the exhaust gas flow rate is obtained by following the change in the combustion amount command signal so that a preset time delay occurs, and the exhaust gas flow rate, the NOx and the molar ratio at the inlet of the denitration device are determined. A method for controlling a denitration ammonia injection amount of a coal-fired boiler, wherein a required ammonia injection amount is obtained and output based on the following. 2. A primary delay unit that outputs a combustion amount command primary delay signal by following a change in the combustion amount command signal such that a predetermined time delay occurs when the combustion amount command signal changes, A high signal selector that selects the higher value of the combustion amount command primary delay signal and the combustion amount command signal output from the primary delay unit and outputs the selected value as a combustion amount command selection signal; A function generator for obtaining and outputting an exhaust gas flow rate based on a combustion amount command selection signal to be output, a proportional constant to the exhaust gas flow rate output from the function generator, and an inlet NOx and a molar ratio of a NOx detector detected by an inlet NOx meter. And a calculator for calculating and outputting a required ammonia injection amount. The denitrification ammonia injection amount control device for a coal-fired boiler.