JPH0336580B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a mill for pulverizing coal into pulverized coal;
In particular, the present invention relates to a mill warming method for increasing the temperature of the mill metal using warmed air, exhaust gas, or other high-temperature gas.

In recent years, in Japan, due to the tight supply of heavy oil, in order to correct the dependence on oil, the fuel is being changed from the traditional heavy oil-burning to coal-burning. Capacity thermal power plants are being built.

However, coal fuel has poor combustibility compared to petroleum fuel, so nitrogen compounds (hereinafter simply referred to as NOx) and unburned substances contained in exhaust gas are likely to be generated.
In particular, the denitrification combustion method has been adopted in coal-fired power plants as a measure to reduce NOx.

For example, generated from combustion equipment such as boilers
NOx is fuel NOx that is generated when nitrogen components contained in fuel are oxidized during combustion.
When hydrocarbon fuel is burned, hydrocarbons react with nitrogen in the air, and prompt NOx is produced through several other reactions. Nitrogen molecules in the air combine with nitrogen at high temperatures. Thermal NOx is a type of NOx that is generated due to heat generation, and thermal NOx is particularly viewed as a problem.

It is said that the generation of thermal NOx increases as the combustion temperature increases, the O ₂ concentration in the combustion zone increases, and the residence time of combustion gas in the high temperature zone increases.

Therefore, in order to fundamentally suppress NOx, it is important to control the combustion temperature, O ₂ concentration, and residence time, especially when the combustion temperature exceeds 1600℃.
NOx tends to increase rapidly, and for this reason, a denitrification combustion method has been adopted in recent boilers to reduce NOx and unburned matter.

This denitrification combustion method suppresses the amount of NOx generated by performing incomplete combustion in the main burner, and performs low-oxygen combustion in the denitrification burner to convert the NOx generated in the main burner into harmless nitrogen by reducing intermediate products. This is a combustion method that reduces the amount of fuel to ₂ .

Figure 1 shows a schematic diagram of a boiler that employs this denitrification combustion method.

In FIG. 1, a boiler 1 has a front wall 2, a rear wall 3,
It is composed of side walls 4, 5 and a hopper 6.

A main burner 7 is provided on the front wall 2 and the rear wall 3.
The denitrification burner 8 and the after air port 9 are arranged in order from the bottom to the top of the boiler 1, and in order to reduce NOx in the boiler 1, the main burner 7 is supplied with an air amount that is approximately equal to the theoretical combustion air amount, or a theoretical amount of air. A slightly smaller amount of air than the combustion air amount is supplied from the wind box 10, and an air amount of 40 to 60% of the theoretical combustion air amount is supplied to the denitrification burner 8 from the wind box 11 and is combusted to produce combustion intermediates. Combustion in which NOx from the main burner 7 is reduced using CN, C ₂ and NH ₃ , which have high NOx reducing properties, and combustion air is further supplied from the after air port 9 in the wind box 12 to achieve complete combustion. It is a method.

Coal feeding to the main burner 7 and the denitrification burner 8 is carried out by connecting a coal feeder 13 and a ventilation pipe to the mill 15, respectively, and communicating with the main burner 7 and the denitrification burner 8 from the mill 15 through pulverized coal pipes 16, respectively. are doing.

The coal feeder 13 supplies a certain amount of coal to the mill 15 using a coal puncher 17, and the pulverized coal pulverized by the mill 15 is sent to the main burner through the pulverized coal pipe 16 by high-temperature gas such as air and exhaust gas from the ventilation pipe 14. 7 and a denitrification burner 8.

The above has provided an overview of the combustion and coal feeding of a coal-fired boiler that employs the denitrification combustion method.
Rapid startup of the boiler is required, and in order to meet this demand, warming the mill becomes an issue.

One of the reasons for this is that the mill itself has characteristics that make it unable to follow the boiler load, but the mill itself is cooled to room temperature in the early stages of operation, and for this reason, coal is not put into the mill and the mill is emptied. This is because coal cannot be pulverized unless the metal temperature is preheated to 65 to 80°C and warming is completed while the rotation is stopped.

And, since it takes about 10 to 15 minutes for the conventional Miroo stand to complete warming,
It takes too much time for multiple mills to complete warming and supply pulverized coal to the boiler.

Hereinafter, a conventional warming method for the mill 15 will be explained using the schematic sequence block diagrams of FIGS. 1 and 2.

When warming the mill 15, first the air preheater 1 is activated by the mill warming command 18 shown in FIG.
9 and start the primary air fan 20.

After the primary air fan 20 is started, the inlet control damper 21 of the mill 15 is opened to a warming degree, and the inlet valves 22 of the main burner 7 and the denitrification burner 8 are all opened.

The condition that the inlet temperature of mill 15 is equal to or higher than the specified value 23,
If the conditions 24 are satisfied (AND condition) 25 during the warming of the mill 15, the warming is completed 26 after a certain period of time has passed.

In this case, the primary air to the mill 15 is air warmed by the air preheater 19, or the air that has been preheated by passing the exhaust gas through the mill 15, or the exhaust gas is fed into the boiler 1 from the main burner 7 and the denitrification burner 8. is discharged.

On the other hand, the primary air flow rate of the warming air discharged to the main burner 7 and the denitrification burner 8 is approximately 15 to 17m/s
The primary air flow rate at this time is approximately 70% of the primary air volume equivalent to the rated mill load.
The flow rate corresponds to %.

As described above, a large amount of primary air is required during warming of the mill 15, so even if heavy oil is used in the boiler 1 for denitrification combustion to exclusively burn coal, the amount of primary air due to warming will not be enough for the boiler 1. It is inevitable that the air-fuel ratio will be unbalanced and NOx will rise when the boiler starts.

The present invention attempts to eliminate such conventional defects, and its purpose is to prevent the generation of NOx even when multiple mills are warmed at the same time, and also to enable quick start-up of the mills to reduce the load on the boiler. The aim is to develop a mill warming method that can measure the followability of the mill.

In order to achieve the above-mentioned object, the present invention provides flow control means for controlling the flow rate of high temperature gas to a large number of pulverized coal pipes, and when warming the mill, most of the flow control means are closed and some of the flow control means are closed. The means is opened to exhaust high-temperature gas during warming from a part of the control means.

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

FIG. 3 diagrammatically shows the warming system of a mill showing an embodiment of the present invention.
The side main burner 7 is shown. In the figure, reference numeral 27 denotes a mill outlet valve of the mill 15. The mill outlet valve 27 and the coal inlet valve 22 form a flow rate control means.For convenience of explanation, the pulverized coal pipe 16a, the coal The inlet valve 22a and the mill outlet valve 27a, which correspond to the main burners 7b, 7c, and 7d, will be described with reference symbols b, c, and d, respectively. 28 is a temperature control damper.

The one shown in Fig. 3 is used for warming with hot air, and the primary air fan 20 is started to heat one side of the primary air through the air preheater 19, and the other side is used to directly supply cold air to control the air temperature. The warm air is mixed at the inlet of the mill 15, and the warm air is introduced to the mill 15 to warm the mill 15.

This warm air is then transferred from the mill 15 to the pulverized coal pipe 16.
a, 16b, 16c, 16d from the main burner 7a,
Warming operation is performed by circulating the air to 7b, 7c, and 7d.

That is, in the conventional warming operation, warm air was supplied from the mill 15 to all the pulverized coal pipes 16a, 16b, 16c, 16d, but in the warming operation of the present invention, for example, the coal inlet valves 22b, 22c, 22d and mill outlet valve 27
b, 27c, 27d are closed and the main burners 7b, 7
The mill 15
The warm air for warming is made to flow from the mill 15 only to the pulverized coal pipe 16a.

That is, when there are four main burners 7a, 7b, 7c, and 7d for one mill 15 as shown in Fig. 3, warm air for warming is passed only to the main burner 7a, and the pulverized coal Warming is performed while ensuring the necessary flow velocity (15 to 17 m/s) to prevent residual coal settling in mill 16a or flashback to residual coal in mill 15.

In this way, by flowing the warm air for warming only into some of the pulverized coal pipes 16a, the amount of air required for warming is reduced, and therefore multiple mills can be warmed at the same time, and even with a small amount of warm air. As a result, sedimentation of residual coal and backfire can be prevented, and the air-fuel ratio of the denitrification combustion method will not be fundamentally disrupted.

FIG. 4 shows a schematic sequence block diagram of warming in the embodiment of FIG. 3. The difference from the sequence block diagram of FIG. 2 is that only the coal inlet valve 22a of the main burner 7a is opened and other coal The inlet valves 22b, 22c, and 22d are left closed.

If the mill outlet temperature falls below the specified value 29 after the completion of warming 26, the coal inlet valve 22
The other explanations are the same as those in FIG. 2, except that a is opened again by the warming start command 30.

The one in FIG. 5 shows another embodiment of the one in FIG. 3, in which the mill 15 is warmed by warm air from the air preheater 19, but the one in FIG. The system uses boiler exhaust gas in addition to warm air.

In addition, in the figure, 31 is an exhaust gas fan, 32 is an exhaust gas warming pipe, and 33 is a coal inlet valve 22b, 2.
2c, 22d and mill outlet valves 27b, 27c, 27
A sealing pipe that supplies sealing air or exhaust gas to the pulverized coal pipes 16b, 16c, and 16d between d.
Pulverized coal pipe 16 in which almost no high-temperature gas flows due to air and exhaust gas from this sealing pipe 33
Backfires from b, 16c, and 16d can be prevented, and warming can be performed with higher safety.

Since the present invention can warm the mill with a small amount of high-temperature gas, multiple mills can be warmed at the same time, the mill can be started quickly, and can follow the boiler load, and the air-fuel ratio for denitrification combustion can be disrupted. You can safely warm up without any problems.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a boiler that employs the denitrification combustion method, Figure 2 is a sequence block diagram showing an outline of the conventional mill warming method, and Figure 3 is a diagram showing the warming system of the mill of the present invention. , FIG. 4 is a sequence block diagram of FIG. 3, and FIG. 5 is a warming system diagram when warming the mill with exhaust gas. 7,8...burner, 15...mil, 16a,1
6b, 16c, 16d...pulverized coal pipe, 22a, 2
2b, 22c, 22d, 27a, 27b, 27
c, 27d...Flow rate control means.

Claims (1)

[Claims] 1. A mill in which high-temperature gas is guided to a mill to preheat the mill, and the preheated high-temperature gas is distributed from the mill to a number of pulverized coal pipes and exhausted from a pulverized coal burner into the furnace to warm the mill. Each pulverized coal pipe is provided with a flow rate control means for controlling the flow rate of high temperature gas, and when the mill is warming, most of the flow rate control means are closed and some of the flow rate control means are opened to control the flow rate of a part of the warmed high temperature gas. A method for warming a mill characterized by exhausting the air.