JPH036403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulverized coal combustion boiler, and particularly to a pulverized coal combustion boiler that enables improved combustion efficiency and low _NOx combustion.

[Conventional technology]

Conventionally, in a pulverized coal combustion boiler, a mixed flow of primary air for transport and pulverized coal from a pulverizer is transported by a mixture transport pipe and injected into the furnace from a pulverized coal burner, while a secondary for one-stage combustion, Tertiary air is mixed from around the mixed flow into the inside, and is supplied from the first stage combustion air port of the pulverized coal burner so that the air ratio is less than 1, and the pulverized coal is burned in a reducing atmosphere. Complete combustion is achieved by the second-stage combustion air supplied from the second-stage combustion air port near the middle part.

[Problem that the invention seeks to solve]

However, according to the above-mentioned conventional pulverized coal combustion boiler, ordinary air is used for the production and transportation of pulverized coal, and as secondary and tertiary air for first-stage combustion and air for second-stage combustion, resulting in the following problems. It was hot.

(1) In the direct combustion method, spontaneous combustion of coal or coal dust explosion may occur during pulverization in the coal pulverizer.

(2) In storage combustion systems, spontaneous combustion and explosions may occur when pulverized coal is stored.

(3) The amount of primary air must be reduced in order to perform combustion in a reducing atmosphere, but in order to prevent the combustion flame from receding, the amount of primary air cannot be significantly reduced, so it is necessary to adjust the amount of oxygen to an appropriate oxygen atmosphere. I can't easily do what I want to do.

(4) When using coal with a wide variety of properties, high combustion efficiency may not be obtained;
This is accompanied by an increase in unburned content in the ash.

The present invention solves these conventional problems by simultaneously utilizing nitrogen-enriched air and oxygen-enriched air to make the system atmosphere inert and safe during pulverized coal production, storage, transportation, and combustion. It is an object of the present invention to provide an excellent pulverized coal combustion boiler that can simultaneously achieve improvement in combustion efficiency through adjustment control to an appropriate oxygen atmosphere in reducing atmosphere combustion.

[Means for solving problems]

In order to achieve the above object, the present invention provides an oxygen-enriched membrane unit that separates air into oxygen-enriched air and nitrogen-enriched air, and a pulverizer that connects the nitrogen-enriched air supplied from the oxygen-enriched membrane unit. a pulverized coal transport pipe for transporting a mixed flow of pulverized coal and pulverized coal; a pulverized coal burner attached to a furnace to burn the pulverized coal transported by the pulverized coal transport pipe; A first-stage combustion air pipe that supplies oxygen-enriched air to the first-stage combustion air port of the burner, and a second-stage combustion air pipe that supplies oxygen-enriched air supplied from the oxygen-enriched membrane unit to another first-stage combustion air port of the pulverized coal burner. The present invention is characterized in that it includes a separate single-stage combustion air pipe and a second-stage combustion air pipe that supply the air to the combustion air port.

[Effect]

The present invention has the following effects due to the above configuration. That is, air is supplied to the polymer membrane in the oxygen enrichment membrane unit and is separated into oxygen enriched air that has passed through the membrane and nitrogen enriched air that has not passed through the membrane. Oxygen-enriched air is used as secondary and tertiary air for first-stage combustion in pulverized coal burners and second-stage combustion air in furnaces, and nitrogen-enriched air is used as primary air in direct combustion systems for pulverized coal production and pulverized coal transportation. It is used for blowing out to the pulverized coal burner and for secondary and tertiary air for first-stage combustion.Furthermore, in the case of a storage combustion method, it is used for blowing out to the pulverized coal burner as well as for pulverized coal machine, pulverized coal silo, and pulverized coal transportation. Used for secondary and tertiary air for first-stage combustion.

In the furnace, pulverized coal is burned in stages,
Following the rapid ignition and temperature rising process of pulverized coal, the furnace is controlled so that it becomes a reducing atmosphere in the first stage combustion zone and an oxidizing atmosphere in the second stage combustion zone of the furnace. In the above-mentioned combustion process under oxygen-enriched air, the ignition of the pulverized coal is promoted and stabilized, and a rapid reaction takes place, resulting in a high temperature, which enables sufficient reductive combustion at high temperatures.In addition, In two-stage combustion, a combustion reaction of unburned gas and unburned particles progresses. In this way, the combustion reaction of the pulverized coal is significantly promoted and completed, so that less unburned matter remains in the ash, resulting in high combustion efficiency and suppressing _NOx emissions. Furthermore, by controlling the amount of oxygen-enriched air supplied according to the type of coal, the amount of oxygen in the surrounding air in the combustion zone can be adjusted and suppressed, making it possible to adjust the amount of oxygen in the surrounding air in the combustion zone. It becomes possible to perform combustion control and _NOx control.

Nitrogen-enriched air is used in pulverizers, pulverized coal silos, and pulverized coal transport pipes and pulverized coal burners, and in order to inert the atmosphere inside these devices, it prevents the occurrence of spontaneous combustion during pulverized coal operation. This makes it possible to use fine coal with a high level of safety.In addition, by introducing sufficient nitrogen-enriched air into pulverized coal machines and pulverized coal transport pipes, equipment It is possible to secure a sufficient internal flow velocity and prevent the accumulation of pulverized coal.Furthermore, in pulverized coal burners, even if the pulverized coal flow rate is reduced, the occurrence of flame regression etc. is reduced, so the turndown ratio is can be significantly increased.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of one embodiment of the present invention, and shows the case of a direct combustion method.
In FIG. 1, 10 is a boiler furnace, 12 is a pulverized coal burner, 14 is a pulverized coal machine, 24 is an air preheater, and 46 is an oxygen enrichment membrane unit. coal 58
is supplied to the pulverizer 14 by a coal feeder 56 and pulverized. On the other hand, the air 40 is supplied by a forced air blower 42.
The oxygen is supplied to the oxygen-enriching membrane unit 46 by the blower 4, and a sufficient pressure difference acts on both sides of the polymer membrane in the oxygen-enriching membrane unit 46, so that the oxygen permeates through the oxygen-enriching membrane unit 46.
8 maintains a reduced pressure state, and in particular uses a polymer membrane made of polydimethylsiloxane or the like with a high oxygen permeability coefficient to separate oxygen and nitrogen into oxygen-enriched air 50 and nitrogen-enriched air 52. is obtained. Nitrogen-enriched air 52 is heated by an air preheater 24, boosted in pressure by a primary blower 54, and supplied to the pulverizer 14, where it is used to pulverize coal and is used to pulverize coal and nitrogen-enrich it. The mixed flow with air 52 is transported by a pulverized coal transport pipe 16, connected to a pulverized coal burner 12, and the pulverized coal is injected into the furnace 10. Oxygen-enriched air 50 is heated by an air preheater 24 and supplied through an air pipe 22 from a secondary air port 18 and a tertiary air port 20, which are air ports for single-stage combustion provided in the pulverized coal burner 12, Provides the amount of oxygen necessary for pulverized coal combustion.

Further, the nitrogen-enriched air 52a branched from the primary blower 54 is supplied from a secondary air port 56 and a tertiary air port 58, which are air ports for single-stage combustion provided separately in the pulverized coal burner 12, and is supplied with the oxygen-enriched air 52a. The amount of oxygen necessary for pulverized coal combustion is provided together with the pulverized air 50, and by adjusting the flow rates of both, the combustion atmosphere in the first stage combustion zone forms a reducing atmosphere.

Next, an air port 30 for two-stage combustion is provided in the furnace 10, to which an air pipe 26 from the oxygen-enriched air outlet side of the air heater 24 is connected, and with a blower 28, a two-stage combustion zone is formed. The necessary oxygen-enriched air is supplied for this purpose. Exhaust gas 32 from the furnace 10 and a steam generating section (not shown) passes through an air preheater 24 and is separated from flyash and the like by a dust collector 34, and then is discharged from the system through a chimney 38 by an induced draft fan 36.

In the pulverized coal burner 12, oxygen enriched air 5
The use of 0 and nitrogen-enriched air 52a promotes and stabilizes the ignition of pulverized coal,
In the first-stage combustion zone, rapid reactions occur and the temperature becomes high, and reductive combustion progresses at high temperatures.
_NOX generation is suppressed, and the combustion reaction of unburned gas and unburned particles progresses in the two-stage combustion zone. In this way, the combustion reaction of the pulverized coal is significantly promoted and completed, so that the amount of unburned matter remaining in the ash can be reduced. Therefore, high combustion efficiency can be obtained even in the combustion of pulverized coal with a high fuel ratio and low fuel properties, and in addition to the _NO Since combustion is possible, the effect of suppressing _NOx can be obtained.

In the coal pulverizer 14, the coal 58 is pulverized under the introduction of heated nitrogen-enriched air, so that the coal 58 is pulverized at a sufficient flow rate in an inert atmosphere. This prevents the accumulation of pulverized coal and spontaneous combustion, resulting in a high level of safety.

In the pulverized coal burner 12, the pulverized coal is injected into the furnace 10 using nitrogen-enriched air with a low oxygen ratio, which facilitates combustion in a reducing atmosphere, and further reduces the occurrence of flame recession. The turndown ratio of the pulverized coal burner 12 can be significantly increased.

FIG. 2 shows the structure of another embodiment of the present invention, and shows the case of a storage combustion type. The redundant explanation of the parts in FIG. 2 that are common to FIG. 1 will be omitted.

60 is pulverized coal, which is manufactured by a pulverized coal machine (not shown). Pulverized coal 60 is stored in a pulverized coal silo 62, and is discharged at a constant flow rate from a feeder provided at the bottom of the pulverized coal silo 62.
Further, in the mixer 68, the nitrogen enriched air 52
are mixed to form a mixed flow, which passes through the pulverized coal transport pipe 16a and is ejected from the pulverized coal burner 12 to the furnace 10. Additionally, the branched nitrogen-enriched air 52a
is supplied from the secondary air port 56 and the tertiary air port.

Further, a portion of the nitrogen-enriched air 52 is supplied to the blower 70.
The pressurized nitrogen-enriched air 52b is connected to the pulverized coal silo 62 via the storage tank 72, and the pressurized nitrogen-enriched air 52b is supplied to the pulverized coal silo 62 while maintaining a predetermined pressure. The pulverized coal silo 62 is sealed to form an inert atmosphere, and is pressurized compared to atmospheric pressure, thereby preventing outside air from entering the pulverized coal silo 62 and disturbing the inert atmosphere. In this way, a sufficient inert atmosphere is formed, and spontaneous combustion of the pulverized coal within the pulverized coal silo 62 can be prevented.

In both embodiments, nitrogen-enriched air and oxygen-enriched air are used at the same time, and nitrogen-enriched air is used in systems such as pulverizers, pulverized coal silos, pulverized coal transport pipes, and pulverized coal burners. Pulverized coal combustion is carried out by making the atmosphere inert and complete, forming a reducing atmosphere in the first stage combustion area, and oxygen-enriched air is introduced from the pulverized coal burner and second stage combustion air port to produce a wide variety of combustion conditions. By burning coal, it is possible to control the combustion efficiency to a high level and suppress _NOx emissions. Therefore, when burning pulverized coal under safe production, storage, supply, and transportation of pulverized coal, unburned losses can be reduced, making it possible to improve boiler thermal efficiency.

Furthermore, since the turndown of the pulverized coal burner can be significantly increased, it becomes possible to cope with large load fluctuations when using the pulverized coal combustion boiler.

It should be noted that the embodiments of the present invention are of course not limited to the above-mentioned embodiments;
Many embodiments of _NOx burners and similar combustion devices can be employed.

〔Effect of the invention〕

As is clear from the upper air embodiment, the present invention simultaneously utilizes nitrogen-enriched air and oxygen-enriched air separated by an oxygen-enriched membrane unit to burn pulverized coal using nitrogen-enriched air. It is possible to safely produce pulverized coal in a machine, store pulverized coal in a pulverized coal silo, and transport pulverized coal in a pulverized coal transport pipe.

In addition, it is possible to easily burn pulverized coal in a reducing atmosphere using oxygen-enriched air, and it is possible to perform optimal combustion control and _NO This has the great effect of improving the turndown ratio.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a pulverized coal combustion boiler according to one embodiment of the present invention, and FIG. 2 is a schematic block diagram of a pulverized coal combustion boiler according to another embodiment of the present invention. 10...furnace, 12...pulverized coal burner, 14...
... Pulverized coal machine, 16 ... Pulverized coal transport pipe, 18 ... Secondary air port, 20 ... Tertiary air port, 30 ... Air port for two-stage combustion, 46 ... Oxygen enrichment membrane unit, 50
...Oxygen-enriched air, 52,52a...Nitrogen-enriched air.

Claims (1)

[Claims] 1 An oxygen-enriched membrane unit that separates air into oxygen-enriched air and nitrogen-enriched air, and transports a mixed flow of nitrogen-enriched air supplied from the oxygen-enriched membrane unit and pulverized coal from a pulverizer. A pulverized coal transport pipe, a pulverized coal burner attached to a furnace for burning the pulverized coal transported by the pulverized coal transport pipe, and supplying nitrogen-enriched air to the first stage combustion air port of the pulverized coal burner. a single-stage combustion air pipe and another single-stage combustion supplying oxygen-enriched air supplied from the oxygen-enriched membrane unit to another single-stage combustion air port of the pulverized coal burner and a second-stage combustion air port of the furnace; A pulverized coal combustion boiler characterized by comprising an air pipe for combustion and an air pipe for two-stage combustion.