JPH02219903A - Method for reducing nitrogen oxides in coal-fired boilers - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for reducing nitrogen oxides in a coal-fired boiler.

[Prior art] Especially when pulverized coal is burned in a pulverized coal burner in the furnace of a coal-fired boiler, if the ratio between the amount of pulverized coal and the amount of air is maintained for good combustion, the flame temperature may rise too much. There is a problem that the amount of nitrogen oxides generated increases due to the nitrogen compounds contained in the coal, and in order to suppress the generation of nitrogen oxides, it is necessary to carry out combustion at a lower flame temperature. It is.

An example of a method for reducing nitrogen oxides in a conventional coal-fired boiler is explained with reference to FIG. 2. A plurality of pulverized coal burners 3 (for example, 4 burners) installed in the width direction are installed on the front and rear walls of the furnace 2 of the boiler body 1. A forced draft fan 5 is installed in a plurality of stages (3 stages in FIG. 2, 6 stages in total) in the direction of the wind box 4 so that combustion air can be introduced into each of the pulverized coal burners 3. A combustion air passage 7 that can supply combustion air that has been blown and preheated by an air preheater 8 is connected to the combustion air passage 7, and an overcoat that is bored in the wall of the furnace 2 above the pulverized coal burner 3 is connected to the combustion air passage 7. A pipe IO equipped with a forced fan 9 is connected to the air port (OAP) 8 so that combustion air can be injected.
11 is a damper provided in the pipe 10, 12 is an exhaust gas passage,
13 is a denitrification device, 14 is a dust collector, 15 is an ammonia supply device, and 15' is a nitrogen oxide detector.

The air blown from the forced draft fan 5 is preheated by heat exchange with exhaust gas in the air preheater B, and then sent as combustion air through the combustion air passage 7 into the wind box 4, where the pulverized coal from the pulverized coal burner 3 is sent. At this time, when the flame temperature increases, the production of NOx is promoted, so
By ゜, a part of the combustion air is taken out from the combustion air passage 7 and injected into the furnace 2 above the pulverized coal burner 3 from the over air port 8, and at this time, the mixture of gases in the furnace 2 is maintained. Therefore, combustion air is sent in by a forced fan 9 while adjusting the injection amount by a damper 11, thereby lowering the combustion temperature in the furnace 2.

The combusted exhaust gas with the generation of nitrogen oxides suppressed passes through the exhaust gas passage 12 from the boiler body 1, passes through the denitrification device 13, the air preheater 6, and the dust collector 4, and is finally released into the atmosphere. The amount of nitrogen oxides at the outlet of the denitrification device 13 is detected by a detector 15', and the amount of ammonia supplied to the front of the denitrification device 13 is adjusted by the ammonia supply device 15 based on the detected value.

FIG. 3 shows another example of a conventional method for reducing nitrogen oxides in a coal-fired boiler, in which a bias air port (BAP) 16 is bored in the wall of the furnace 2 between a plurality of pulverized coal burners 3. A piping 17 equipped with a damper 11 and a forced fan 9 is connected between the bias air port 1B and the combustion air passage 7 so that combustion air can be injected into the combustion air passage 16. By separating a part of the combustion air led to the charcoal burner 3 and injecting it into a part other than the burner 3, the combustion temperature in the furnace 2 is lowered.

[Problems to be Solved by the Invention] However, according to the above-described conventional method for reducing nitrogen oxides in a coal-fired boiler, the over air port 8 or the bias air port 16 for injecting combustion air is
It is necessary to drill into the wall of the furnace 2, as well as the piping 10.1.
7. Since it is necessary to provide the push-in fan 9, damper 11, etc., there is a problem in that the equipment cost and construction cost increase.

In view of the above circumstances, the present invention aims to provide a method for reducing nitrogen oxides in a coal-fired boiler, which can reduce equipment costs and construction costs.

[Means for Solving the Problems] The present invention provides primary air supply through a primary air passage to an idle preliminary pulverized coal mill that is connected to a part of a pulverized coal burner of a coal-fired boiler via a pulverized coal supply passage. The present invention is characterized in that only primary air is introduced into some of the pulverized coal burners through the pulverized coal supply passage of the preliminary pulverized coal mill.

[Function] Therefore, it is possible to utilize the idle preliminary pulverized coal mill, reducing equipment and construction costs. Also, since the primary air is injected into the furnace, the draft is high and the penetration power is high, making it effective. Nitrogen oxides can be reduced.

[Implementation example] Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows one embodiment of the present invention, and Figures 2 and 3 in the figure show an embodiment of the present invention.
Parts with the same reference numerals as those in the figures represent the same parts.

Normally, in the case of a coal-fired boiler that has a total of six stages of pulverized coal burners 3, three stages at the front and rear as shown in Figure 1, the pulverized coal burners 3
Six pulverized coal mills are installed for each stage to supply pulverized coal to the pulverized coal mills. Of these, 5 are operated at all times to maintain the rated load, and the other one is used as a standby pulverized coal mill (18 cm). It has been suspended as a. The preliminary pulverized coal mill 18, like other pulverized coal mills for continuous operation (not shown), has a coal introduction passage 19 and a passageway 19 at the top for feeding the pulverized coal to the pulverized coal burner 3 together with primary air. A possible pulverized coal supply passage 20 is connected to the lower part, and primary air blown by the forced draft fan 5 and the primary air fan 21 and preheated by the air preheater 6 is introduced into the preliminary pulverized coal mill 18. A primary air passage 22 is connected thereto.

Normally, among the pulverized coal burners 3, the uppermost pulverized coal burner 23 on the front and rear sides is inactive, and the existing preliminary pulverized coal mill 18, which is inactive, is connected to this inactive pulverized coal burner 23. . Note that 24 is a damper for adjusting the temperature of the primary air.

When operating a coal-fired boiler, combustion air blown by a forced draft fan 5 and preheated by an air preheater 6 is passed through a combustion air passage 7 to a pulverized coal burner 8 via a wind box 4.
Coal is introduced into the furnace 2 and burned in the furnace 2. At this time, the existing preliminary pulverized coal mill 18, which is currently inactive and connected to the uppermost pulverized coal burner 23, receives coal from the coal introduction passage 19. The supply is suspended, and on the other hand, primary air pressurized by the forced draft fan 5 and the primary air fan 21 is supplied through the air preheater B and the primary air passage 22, so that the preliminary pulverized coal mill 18 The primary air supplied to the furnace 2 passes through the pulverized coal supply passage 20 without pulverized coal and is introduced into the furnace 2 from the uppermost pulverized coal burner 23.

Normally, the draft of the primary air is higher than that of the combustion air, so it has a penetrating force, so it is effectively injected into the furnace 2 through the uppermost pulverized coal burner 23, and nitrogen oxidation occurs due to the reduction of the combustion temperature in the furnace 2. It is possible to exhibit the effect of reducing the amount of substances satisfactorily.

Incidentally, the same procedure can be performed even when the position of the pulverized coal burner to be stopped is other than the uppermost stage. As described above, since the existing preliminary pulverized coal mill 18 which is currently out of service is utilized to reduce nitrogen oxides, both equipment costs and construction costs can be significantly reduced.

In addition, in the event that another pulverized coal mill that is in continuous operation breaks down and the preliminary pulverized coal mill 18 has to be used as a normal pulverized coal mill that is in continuous operation, - temporarily, the ammonia supply device 15 Nitrogen oxides can be reduced by increasing the amount of ammonia supplied to the denitrification device 13.

[Effects of the Invention] According to the method for reducing nitrogen oxides in a coal-fired boiler of the present invention, an existing preliminary pulverized coal mill can be utilized, which significantly reduces equipment costs and construction costs. Since primary air with a large force is used, excellent effects such as a good nitrogen oxide reduction effect can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an example of an apparatus for implementing the method of the present invention, Fig. 2 is a system diagram showing an apparatus for implementing an example of the conventional method, and Fig. 3 is a system diagram for implementing another example of the conventional method. FIG. In the figure, 3 is a pulverized coal burner, 18 is a preliminary pulverized coal mill, and 20
2 represents a pulverized coal supply passage, and 22 represents a primary air passage. Figure 2 Figure 3

Claims (1)

[Claims] 1) Primary air is supplied through a primary air passage to an idle preliminary pulverized coal mill that is connected to a part of a pulverized coal burner of a coal-fired boiler via a pulverized coal supply passage, and the pulverized powder of the preliminary pulverized coal mill is A method for reducing nitrogen oxides in a coal-fired boiler, comprising introducing only primary air into some of the pulverized coal burners through a coal supply passage.