JPS6245326A - Method of denitrating exhaust gas of boiler - Google Patents

Abstract

PURPOSE:To remove the adhered substance on a preheater, by passing a part of exhaust gas through a first regeneration type air preheater through a denitration apparatus to heat secondary air and passing the remainder of the exhaust gas through a second regeneration type air preheater and bypassing secondary air to send the same to a boiler. CONSTITUTION:The exhaust gas 2 issued from a coal firing boiler 1 is divided into two systems and a part of the exhaust gas is mixed with NH3 from an ammonia injection nozzle 3 to perform denitration in a denitration apparatus 4 and guided to an electric precipitator 7 through a first regeneration type air preheater 20 while the remainder of the exhaust gas is directly guided to the electric precipitator 7 through a second regeneration type air preheater 21. When the adhered substance of the first preheater 20 is removed, a damper B is opened to allow secondary air 6b to bypass the first preheater 20 and said air 6b is heated only by a steam type air preheater 12 to be supplied to the boiler 1 while primary water 6a is heated by the second preheater 21. Whereupon, the temp. of the first preheater 20 rises and acidic ammonium sulfate is decomposed and the adhered substance is removed without stopping the operation of the boiler.

Description

[Detailed description of the invention] Industrial applications Mitsuaki Ki is a 1st year student who is concerned with denitrification methods for boiler exhaust gas.

BACKGROUND OF THE INVENTION FIG. 4 shows the flow of a conventional exhaust gas denitrification method. Conventionally, ammonia gas is injected into the exhaust gas 2 from the coal-fired boiler 1 through the injection nozzle 3, and when it touches the catalyst of the denitrification device 4 installed in front of the IA biological air preheater 5, the next reaction occurs. was generated to reduce nitrogen oxides.

In this case, a portion of the injected surplus ammonia is decomposed into plants and water by the following reaction.

However, the injected ammonia that is not decomposed by the catalytic action undergoes a fire reaction after passing through the denitrification device and becomes acidic ammonium sulfate.

NH3+SO3+H20-NHq H3O+The generated acidic ammonium sulfate becomes liquid at 220-230°C. Denitration equipment 4
The exhaust gas 2 that has exited the exhaust gas 2 enters the regenerative air preheater 5 and exchanges heat with the air 6 to lower its temperature. After this, exhaust gas 2
1m electric collector 7, induction fan 8, denitrification device 9, chimney 10
be led to. The air 6 supplied to the boiler 1 is guided through the forced fan 11 to the steam air preheater 12 and the regenerative air preheater 5, and then the secondary air 6b is directly supplied to the boiler 1.
The primary air 6a is supplied by a primary air fan 13 and a small coal machine 1.
4 and then supplied to the boilerco. 15 is a coal bunker that supplies coal to the pulverizer 14.

Problems to be Solved by the Invention By the way, when the temperature of the exhaust gas 2 barreled in the regenerative air preheater 5 decreases, liquid acidic ammonium sulfate condenses and adheres to the element of the regenerative air preheater 5. becomes. and,
The liquid acidic ammonium sulfate that adheres to the surface of the element is caused by dust in the exhaust gas and 71'? Grows by taking in the 1st class (150°C
(At certain temperatures, acidic ammonium sulfate becomes solid) and its resistance increases.

During normal boiler operation, this is removed by soot blowing, but after about half a year, the pressure in the regenerative air preheater 5 increases, making it impossible to continue operation! I ffi [
become. Therefore, in the past, the element was washed with water after stopping the irradiation.

The present invention aims to solve such problems by providing a control system for boiler waste.

Means for Solving the Problems In order to overcome the above-mentioned problems, the boiler gas denitrification method of the present invention involves injecting annine into a part of the IJ! gas discharged from the boiler. l device and remove it.
After RL, the first regeneration J (is placed in an air preheater to preheat the secondary air supplied to the boiler, while the remainder of the exhaust gas is sent to a second iQ raw air heater). When decomposing the ammonium sulfate compound contained in the first regenerative air preheater described in 11 for preheating the primary air supplied to the boiler, avoid bypassing the secondary air described in 11i.
Supplied directly to the boiler and raised the temperature of the first regenerative air preheater! /? I tried to let them do it.

Function When performing IIQ monitoring of boiler exhaust gas using this method,
Even if the resistance of the first regenerative air preheater increases due to adhesion of acidic ammonium sulfate, the element can be thermally cleaned without stopping the boiler.

In other words, 15. When performing the above thermal cleaning using the conventional method, continuous operation of the boiler was required because the air side was completely bypassed, and it was impossible to obtain the primary air heat necessary for drying the coal. However, according to Japan's Akira method, even when performing thermal cleaning, 1
Since the second regenerative air preheater for secondary air is in normal operation, it is possible to operate the second regenerative air preheater without stopping the boiler. It becomes possible to remove and cover the deposits that become No. 1.

Practical Examples Examples of the method of the present invention will be described below with reference to the drawings. Incidentally, those having the same configuration as those described in the conventional example No. 111 are designated by the same reference numerals and the explanation thereof will be omitted.

In FIG. 1, 20 is a first regenerative air preheater, 21
is a second regenerative air preheater, in which a part 2a of the boiler exhaust gas 2 and the secondary air 6b are sent to the first regenerative air preheater 20, and the remaining boiler exhaust gas 2b is sent to the second regenerative air preheater S21. The primary air 6a is configured to pass through each heat exchanger. 22 is a cooling device located behind the first regenerative air preheater 20 and installed in the exhaust gas 2a line, and 23 is a bypass line installed in the middle of the secondary air 6b line, as will be described later. When thermally cleaning the first regenerative air preheater 2o, the secondary air 6b is bypassed and guided directly to the boiler 1.

(A) and (B) are dampers disposed at appropriate locations along the air lines 5a, 5b, and 23.

First, during normal operation, open the damper (^) and close the damper (8).
After the primary air 6a is heated by the steam air preheater 12, it is passed through the second regenerative air preheater 21 from the primary air fan 13 to the pulverizer 14, and is sent together with the pulverized coal to the boiler 1. supply to. The secondary air 6b is supplied to the boiler 1 through a steam air preheater 12 and a first regenerative air preheater 20.

On the other hand, the exhaust gas 2 that exits the boiler 1 is divided into two systems, and a part of the exhaust gas 2a is mixed with ammonia gas injected from the injection nozzle 3 and denitrified in the denitrification device 4, and then transferred to the first regenerative air preheater. 20 to the electrostatic precipitator 7. In this case, the order of the cooling devices 22 is i! do not have. The remaining exhaust gas 2b is directly sent to the electrostatic precipitator 7 through the second regenerative air preheater 21.

Since ammonium sulfate compounds (J) are generated from the residual ammonia from the denitrification device 4, the first regenerative air is fed to the heater 20, but the system does not have a denitrification device. Second regeneration (does not occur in the air preheater 21. There-C1I
The increase in resistance caused by the first step of the A/1 compound is the first reason (if it is necessary to remove deposits caused by Jffl generation in the air preheater 20, use the tamper (8) on the air side). After closing and listening to the tamper (B), the secondary air 6b is transferred to the first recycler (
Bypassing the air preheater 20, the steam air preheater 12
It is heated to j11 at t1'j and supplied to boiler 1. The primary constricted air 6a, which is air for drying pulverized coal necessary for continuous operation of the boiler 1, is heated by a second regenerative air preheater 21,
The pulverized coal is supplied to the boiler 1 via a pulverized coal feeder 14.

In the first regeneration stage, the air that had been previously cooled flows into the air preheater 20, and only the waste at a temperature of 370 to 400°C passes through the preheater 20. The temperature of Niremen 1 is 1-1. As a result, acid ammonium sulfate, l1iff acid iron ammonium t\, etc. are decomposed (thermal cleaning) and carried away by the flow of exhaust gas 2a, leaving only dust and soot on the element surface. .This remaining grass, dust, etc. can be removed by soot blowing.

Since the exhaust gas 2a exiting the first regenerative air preheater 20 has a high temperature, if it is directly fed into the electrostatic precipitator 7, troubles will occur due to the heat. After cooling with the cooling device 22,
It is led to the electrostatic precipitator 7.

, Fig. 2 and Fig. 3 show actual W examples. As shown in Figure 2,
85% of exhaust gas 2 coming out of boiler 1 (44000ON
m/h) 2 a to the first regenerative air preheater 20,
When 15% (8000ON rrt/h) is led to the second regenerative air preheater 21 (outlet temperature 400°C, outlet NOX 300ppl), the NOX concentration of the exhaust gas 2 released from the chimney 10 is 83.25pl) Became TI,
It was significantly lower than the regulation value of 200+)l)TI. On the other hand, as shown in FIG.
/h) 2b is led to the second regenerative air preheater 21 (outlet temperature 400°C, output [1N OX 300p
DII), N O of the exhaust gas 2 released from the f end 10
The X concentration was 172.5p111, which was within the regulation value.

In this example, the regenerative air preheater 2 is used for explanation purposes.
0.21 was divided into two units, but if a Rotemühle type twin flow type regenerative air preheater is adopted, it is possible to create the same flow with one unit.〇Yota coal-fired boiler 1
Although this method has been described as an example, the present method can also be applied to boilers using other fuels such as oil and 10,000 sq.

According to the light method, J,
Therefore, even if the resistance of the first regenerative air preheater increases, the element can be thermally cleaned without stopping the boiler.

[Brief explanation of drawings]

Figures 1 and 3 are a flow diagram of the present Komei method, and Figure 4 (a flow diagram of the conventional method).

Claims (1)

[Claims] 1. Injecting ammonia into a part of the exhaust gas discharged from the boiler and guiding it to a denitrification device, and after denitration, leading it to a first regenerative air preheater to preheat the secondary air supplied to the boiler, On the other hand, the remainder of the exhaust gas is guided to a second regenerative air preheater to preheat the primary air supplied to the boiler, and ammonium sulfate compounds adhering to the inside of the first regenerative air preheater are decomposed. In this case, the secondary air is bypassed and directly supplied to the boiler to raise the temperature of the first regenerative air preheater.