JPS6350567Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a pulverized coal combustion device, and in particular to a pulverized coal combustion device that recirculates exhaust gas into the furnace to reduce the _NOx emission level and control the temperature of the heat exchanger. It is something.

In addition to fuel components such as C and H, fossil fuels also contain N.
In particular, pulverized coal has a higher N content than gaseous fuel or liquid fuel. Therefore, _NOx generated when pulverized coal is combusted is larger than _NOx generated when gaseous fuel and liquid fuel are combusted, and therefore it is desired to reduce _NOx as much as possible.

A known method for reducing _NOx is to recirculate exhaust gas with a low oxygen concentration into the furnace, thereby lowering the temperature of the combustion flame and suppressing the reaction between oxygen and nitrogen. FIG. 1 is a schematic diagram of a conventional pulverized coal combustion apparatus using this method, in which 1 is a furnace, 2 is a burner provided in multiple stages vertically on the side wall of the furnace 1, and 3 is a bottom of the furnace 1. Hotsupaguchi established in 4
Reference numeral 5 indicates a superheater provided in the exhaust gas passage, 5 a reburner also provided in the exhaust gas passage, and 6 a gas recirculation fan for sucking a part of the exhaust gas and supplying it into the furnace 1. FIG. 2 shows a sectional view of the water-cooled wall structure, and the wall surface of the furnace 1 and the throats of the burners 2 at each stage are all of this water-cooled wall structure.

In such a combustion device, while the supplied water rises within the water-cooled wall of the furnace 1, it mainly receives radiant heat from the flame and becomes high-temperature steam, and is further heated in the superheater 4 to become superheated steam. . On the other hand, the flame cooled by the water-cooled wall is further cooled by the superheater 4, reheater 5, etc., and is discharged as exhaust gas. A portion of this exhaust gas is sucked into a hopper by a gas recirculation fan 6 in order to control the steam temperature of heat exchangers such as the superheater 4 and reheater 5, and to lower the _NOx emission level. It is introduced into the furnace 1 through the port 3.

By the way, when the amount of exhaust gas injected from the hopper port 3 increases, the flame 7 formed by the lowest stage burner 2 is agitated by the exhaust gas with a low oxygen concentration and a part of the self-generated gas, and the flame 7 is completely destroyed from the base. It becomes difficult to ignite. This is because the area near the bottom burner is cooled by the water-cooled throat with less radiant heat and the incoming exhaust gas, and the exhaust gas with a low oxygen concentration lowers the oxygen concentration in the atmosphere. The flame 7 of the lower burner was ignited and burned at a position farther from the burner, resulting in a so-called black skirt, which caused an increase in unburned content in the ash.

The present invention solves the above-mentioned drawbacks of the conventional technology,
The object of the present invention is to provide a pulverized coal combustion device that can reduce unburned content in ash. In order to achieve this objective, the present invention has developed a pulverized coal combustion apparatus that includes a furnace provided with multiple stages of burners in the vertical direction, and a means for recirculating exhaust gas from the furnace into the furnace from the lower part of the furnace. The burner throat at the lowest stage has a fireproof wall structure, and the throats for burners other than the lowest stage have a water-cooled wall structure.

An embodiment of the present invention will be described below with reference to FIG. FIG. 3 is a vertical sectional view of the main part of the pulverized coal combustion device according to the present invention, in which 1 is a furnace, 2
a is the lowest burner, 2b and 2c are burners provided sequentially above the lowest burner 2a, and 8 is the furnace 1.
The throat 9a of the lowest burner 2a has a fireproof wall structure such as heat-resistant bricks, and the throats 9b and 9c of the other burners 2b and 2c are the same as the conventional device. It has a water-cooled wall structure. In this way, ignition can be stabilized by making the throat 9a of the lowest stage burner 2a, which is easily affected by the exhaust gas supplied from the hopper port 3, with a fireproof wall structure that emits a lot of radiant heat, and the flame temperature is relatively high. By making the throats 9b and 9c of the other burners 2b and 2c have a water-cooled wall structure with less radiant heat, it is possible to reduce the generation of _NOx .

Furthermore, in this embodiment, a strong swirling force is applied to the combustion air sent from the wind box 8 to the lowermost burner 2a in order to further stabilize the ignition of the lowermost burner 2a. That is, using a swirling means such as an air register (not shown), the combustion air sent to the lowest stage burner 2a is given a swirl number of 0.6.
When a strong swirling force of ~1.0 is applied, the exhaust gas from the hopper port 3 is isolated from the bottom burner 2a due to this strong swirling airflow, so the bottom burner 2a is less affected by the recirculated exhaust gas, and is less likely to ignite. Stabilization can be achieved. If the ignition of the lowest stage burner 2a can be stabilized in this way, the lowest stage burner 2a has the longest residence time in the furnace compared to the other stage burners 2b and 2c, so it is sufficient to lower the air ratio to 0.8 or less. Combustion can be completed.

On the other hand, the upper stage burners 2 other than the lowest stage burner 2a
In cases b and 2c, ignition can be easily stabilized, so the swirling force of the combustion air is adjusted to a swirl number of 0.3 to 0.6.
The power is reduced by making it weaker in order to save power. However, these burners 2b and 2c have a shorter residence time in the furnace than the lowest stage burner 2a, so in order to compensate for this, the air ratio is slightly increased to 0.8 to 1.0, thereby reducing the unburned content in the ash. This is further reduced.

As described in detail above, according to the present invention, the throat of the lowest stage burner among multiple stage burners has a fireproof wall structure, and the throats of the other burners have a water-cooled wall structure, thereby reducing the influence of recirculated exhaust gas. It is possible to stabilize the ignition of the lowest burner, which is susceptible to ignition, and thereby reduce the amount of unburned matter in the ash.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional pulverized coal combustion device.
FIG. 2 is a sectional view of the water-cooled wall structure, and FIG. 3 is a longitudinal sectional view of the main part of the pulverized coal combustion apparatus of the present invention. 1... Furnace, 2a, 2b, 2c... Burner, 3... Hotsupa mouth, 9a, 9b, 9c... Throat.

Claims (1)

[Scope of utility model registration request] In a pulverized coal combustion equipment equipped with a furnace having multiple stages of burners in the vertical direction and a means for recirculating the exhaust gas from the furnace into the furnace from the lower part of the furnace, the throat for the lowest stage burner has a fireproof wall structure. A pulverized coal combustion device characterized in that burner throats other than the bottom stage have a water-cooled wall structure.