JPS59173604A - Fine coal combustion device - Google Patents

Abstract

PURPOSE:To restrict a concentration of NOx to a lower value even if a gaseous phase reduction is insufficient in a boiler by a method wherein a bypass pipe is arranged in respect to a piping for use in discharging combustion gas from a boiler and a denitrization device is arranged in respect to this bypass pipe. CONSTITUTION:A bypass pipe 13 is connected to the discharged gas pipe 12 of a boiler 1 and a denitrization device 14 is arranged in respect to this bypass pipe 13. As the concentration of NOx sensed by an NOx sensor 21 exceeds the predetermined value, a control box 16 opens the damper 20 in the bypass pipe 13 and closes the damper 22 in the discharged gas pipe 12, thereby discharged gas G is introduced into the bypass pipe 13 to remove NOx at the denitrification device 14, and thereafter it may be discharged through a chimney 15. With this arrangement, even if a gaseous phase reduction is insufficient or impossible, it is possible to restrict a concentration of NOx in the discharged gas to a lower value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulverized coal combustion device, and particularly relates to a pulverized coal
The present invention relates to a pulverized coal combustion device that constantly suppresses the amount of emissions of (Ox) to a small amount.

Due to reasons such as rising prices of petroleum-based fuels, there is a remarkable tendency to switch to coal as the fuel for large boilers for power plants. In this case, the coal is pulverized into fine particles by a pulverizer (hereinafter, the pulverized coal is referred to as 1 pulverized coal), and transported by air flow to a burner to be burned. Since pulverized coal has an increased surface area per volume, its combustibility is greatly improved, and controllability is also improved accordingly, so all large boilers for coal-fired power plants use this pulverized coal combustion method. On the other hand, even in this pulverized coal combustion boiler, there is a strict requirement to reduce NOx in the exhaust gas. There are many ways to achieve low NOx, but one of them is to significantly reduce the air-fuel ratio of some of the burners installed in the boiler (for example, to about 0.4). 02 NH2, ON, G! with reducing properties generated by combustion! A method of reducing NOx in a gas phase using an intermediate product such as O is attracting attention and being put into practical use.

However, this method may cause failure of the pulverizer that supplies the pulverized coal to the reduction burner that generates the intermediate product, or
Alternatively, if the burner itself breaks down, the amount of NOx increases rapidly, polluting the atmosphere.

-This invention was constructed in view of the above-mentioned problems,
It is an object of the present invention to provide a pulverized coal combustion device in which the amount of NOx emissions does not increase even when flame formation in a reduction burner becomes impossible due to a failure of a pulverizer or the like.

In short, this invention provides a bypass line for the line that discharges combustion gas from the boiler, and arranges a denitrification device for this bypass line, so that when it is impossible to form a reducing flame, etc.
This is a pulverized coal combustion device configured to introduce exhaust gas into a denitrification device when the NOx concentration in the exhaust gas increases.

An embodiment of the present invention will be described below.

In FIG. 1, 1 is a pulverized coal combustion boiler, and 2 and 3 are main burners provided for this boiler, which mainly bear the thermal load of this boiler 1. 4 is a reduction burner arranged downstream of these main burners. Among the above burners, the lowermost main burner 2 is connected to a crushing device 8 through a pipe line, and another main burner 3 located downstream of this main burner 2
are each connected to the crushing device 9 via a pipe line. Similarly, the reducing burner 4 is connected to the crushing device 10 through a pipe line.

6 is a coal hopper that supplies coal to each crushing device; 7
1 is a metering feeder, and 11 is a supply pipe for feeding coal to each pulverizer.

A bypass pipe line 13 is connected to a part of the exhaust gas pipe line 12 of the boiler 1, and a denitrification device 14 is arranged to this bypass pipe line 13. 15 is a chimney.

The operating state of the above device will be explained.

Although the device can be operated manually, an example will be described below in which a control box 16 for storing and issuing command signals is used.

Normally, the pulverized coal air-transported from the crushers 8 and 9 is burned at an air-fuel ratio of about 1 in the main burners 2 and 3, thereby bearing the heat load of the boiler 1.

On the other hand, pulverized coal is supplied to the reduction burner 4 from the pulverizer @10, and combustion is performed at a low air-fuel ratio of, for example, about 0.2 to 0.6. In this case, in order not to increase the partial pressure of 02 and to maintain the gas flow rate for air flow transport, in addition to supplying air A to the crusher 10, part of the exhaust gas G from the boiler 1 is supplied through the exhaust gas introduction pipe 17. supply. The control box 16 adjusts the opening degrees of the damper 18 of the air pipe line and the damper 19 of the exhaust gas supply line 17 to maintain the air-fuel ratio in the reduction burner 4 at an appropriate level of 1 Bi.
Let's do it.

By the above control, the flame F of main burners 2 and 3
The NOx in 2 is reduced in the gas phase by the reducing intermediate product in the flame F3 of the reducing burner 4 and becomes N2.

On the other hand, the unburned content mainly generated by the reduction flame F is combusted by the air A supplied from the air boat 5. In this case, since NOx is sufficiently removed by gas phase reduction, the damper 20 of the bypass line 13 is kept closed, and the exhaust gas G is discharged into the atmosphere from the chimney 15 via the exhaust gas line 12. During this time, the control box 16 constantly detects the NOx concentration in the exhaust gas using the NOx detector 21 provided in the boiler 1.

If the NOx concentration detected by the NOx detector 21 exceeds the set value, the control box 16 opens the damper 20 of the bypass pipe 13.
By closing the damper 22 of the exhaust gas pipe 12, the exhaust gas G is introduced into the bypass pipe 13, NOx is removed in the denitration device 14, and then exhausted from the chimney 15. In the above case, the control box 16 and the crushing device 1
It may be configured such that a failure signal T of 0 is input.

In this case, if the damper control in +iii is performed based on the signal from the NOx detector 21 or the failure signal, whichever is manually generated earlier, the control can be performed more quickly.

By inputting the signal T, the dampers 18 and 19 of the air pipe and exhaust gas supply pipe 17 to the crushing device 1f10 are fully closed,
Make repairs possible.

Next, if the heat load of the boiler 1 can be reduced to some extent by the boiler load confirmation input to the control box 16, the damper 19 connected to the crusher 9 (open and the main burner 3 may be lowered to function as a reduction burner to achieve low NOx.In this case, it is more effective if the boiler exhaust gas G is passed through the denitrification device 14, and the main burner There is no need to extremely lower the air-fuel ratio of 3.

By carrying out this invention, even if the gas phase reduction in the boiler becomes insufficient or impossible due to a failure of the crushing device, etc., the N in the exhaust gas can be reduced by using the denitrification device in combination.
Ox concentration can be kept low at all times.

[Brief explanation of the drawing]

It is a systematic diagram. 1... Boiler for pulverized coal combustion 2.3... Main burner 4... Reduction burner 8.9... Main burner crushing device 10...・・・
-Reducing burner crushing device 12...Exhaust gas pipe line 13...Bypass pipe work 4...Denitrification device 16...Control box 17... ...Exhaust gas supply pipe 18, 19.19.20.22 ...Damper 2
1...NOx detector G...Exhaust gas

Claims (1)

[Claims] 1. In a device that reduces nitrogen oxides in the gas phase by burning pulverized coal produced by pulverization in a pulverizer in a main burner and a reduction burner, a bypass pipe is connected to the exhaust gas pipe of the combustion device. The pulverized coal combustion bag W is characterized in that a denitrification device is arranged in the bypass pipe and the flow path of the exhaust gas is switched in accordance with the concentration of nitrogen oxides in the exhaust gas. 2. Dampers are provided for the exhaust gas pipe, the bypass pipe, the pipe that supplies air to the pulverizer that supplies pulverized coal to the reduction burner, and the pipe that supplies exhaust gas to the pulverizer. 2. The pulverized coal combustion apparatus according to claim 1, wherein the pulverized coal combustion apparatus is controlled by a control box which inputs signals from a NOx detector and issues command signals. 3. Connect a pipe line that supplies exhaust gas to the pulverizer that supplies pulverized coal to the main burner, and connect the damper of this pipe line and the damper of the air supply pipe to each control box with a control signal circuit. The pulverized coal combustion apparatus according to claim 2, wherein the main burner is used as a reduction burner when the nitrogen oxide concentration increases.