JPH0543925B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulverized coal combustion boiler, and relates to a device that can control combustion efficiency according to the type of coal and ensure the safety of a pulverized coal cyclo.

[Conventional technology]

In pulverized coal combustion boilers, when burning pulverized coal,
It is desired to be able to burn a wide variety of coals without significantly changing the boiler structure, burner structure, etc., and to suppress NO _x emissions with high combustion efficiency. There is a strong demand for safety measures against spontaneous combustion of pulverized coal in pulverized coal silos.

In pulverized coal combustion, its combustion efficiency and
NO _x emissions are greatly influenced by the coal type, which has unique coal properties.

Combustion efficiency is influenced by coal combustion mode, pulverized coal particle size, combustion reaction time, etc., and coal combustion mode is indexed by combustion ratio corresponding to coal carbonization degree, and pulverized coal particle size The combustion reaction time is influenced by the furnace temperature, oxygen concentration in the atmosphere, pulverized coal particle size, fixed carbon and volatile content properties, etc. ing.

In pulverized coal combustion, pulverized coal is burned in a furnace and discharged from the furnace after a certain residence time. Therefore, it is necessary to complete the combustion reaction within the residence time, and if the combustion reaction time is longer than the residence time depending on the type of coal, unburned matter remains in the ash and the combustion efficiency (carbon reaction rate).

In large-capacity pulverized coal-fired boilers, it is possible to secure a relatively long residence time in the furnace, but in medium- and small-capacity pulverized coal-fired boilers, it is difficult to secure a long residence time due to structural constraints. Therefore, it was difficult to improve combustion efficiency.

On the other hand, in terms of suppressing NO _x emissions, NO _x generated during pulverized coal combustion can be divided into thermal NO _{x and} fuel _{NO x} is generated from N compounds such as N in coal. Staged combustion methods such as low air ratio combustion and two-stage combustion have been put into practical use as combustion technologies to suppress NO _x . (For example, the new edition of the Fuel Handbook (expanded), page 798) Furthermore, in the storage combustion method, pulverized coal stored in a pulverized coal silo is transported by primary air and burned in a furnace. During storage, spontaneous combustion, explosion, flame, etc. may occur, and a number of safety measures have been proposed as safety measures, such as inertizing the atmosphere inside the pulverized coal silo and preventing temperature rise through forced cooling of the pulverized coal. has been done.

[Problem that the invention seeks to solve]

However, in the above conventional pulverized coal combustion boiler, it is not possible to easily adjust and control an appropriate oxygen atmosphere in the furnace according to a wide variety of coal types, and it is not possible to maintain high combustion efficiency. Since air is sometimes used for combustion, thermal NO _x is generated, and along with fuel NO _x , there is a problem in that it is difficult to suppress NO _x using combustion technology. In order to inert the atmosphere inside the pulverized coal silo, it is necessary to use a gas source separate from the boiler, and there is a problem in that it is difficult to easily use inert gas.

The present invention solves these conventional problems by forming a strongly reducing atmosphere in which the pulverized coal is highly concentrated at a high flame temperature using oxygen-enriched air during pulverized coal combustion. , control to achieve high combustion efficiency according to a wide variety of coal types,
The purpose of the present invention is to provide an excellent pulverized coal combustion boiler that can suppress NO _x emissions and at the same time inert the atmosphere inside the pulverized coal silo to ensure safety.

[Means for solving problems]

In order to achieve the above object, the present invention includes a separation device that separates air into nitrogen and oxygen, and a mixed flow transport pipe of pulverized coal and temporary air supplied from a pulverized coal silo, which is connected to a pulverized coal burner, and a furnace. The tertiary air pipe is connected to the tertiary air port, the nitrogen supply pipe is connected to the pulverized coal silo, and the oxygen supply pipe is connected to the mixed flow transport pipe, secondary air pipe, and tertiary air pipe. A control device is installed to form oxygen-enriched air, and a control device is provided to control the amount of oxygen supplied according to the type of coal, and the fuel atmosphere at the outlet of the pulverized coal burner is made into a high-temperature, strongly reducing atmosphere using the oxygen-enriched air. In this method, pulverized coal is combusted, and the combustion atmosphere after the tertiary air port is made into an oxidizing atmosphere using the oxygen-enriched air.

[Effect]

The present invention has the following effects due to the above configuration. That is, air is separated into nitrogen and oxygen in a separator, and the pulverized coal from the pulverized coal silo is supplied to the furnace together with combustion air to perform pulverized coal combustion. The above-mentioned oxygen is supplied to the pipe and the tertiary air pipe, and the oxygen flow rate is controlled according to the type of coal.

Therefore, an oxidizing agent having a substantially high oxygen ratio and low nitrogen ratio is used as the combustion air, that is, oxygen-enriched air is formed.

This oxygen-enriched air means a mixture of the above oxygen and air with an oxygen ratio of 21% or more (volume ratio).In a furnace, pulverized coal and an oxidizer, that is, oxygen-enriched air, Staged combustion is carried out by supply, and following the rapid ignition and temperature rising process under the above-mentioned adjustment of the supply amount, a strong reducing atmosphere is formed in the first stage combustion, and oxidation occurs in the second stage combustion area from the tertiary air inlet onward. The atmosphere is controlled. At the outlet of the pulverized coal burner, the pulverized coal is ignited and heated under a combustion atmosphere by an oxidizing agent, which promotes and stabilizes ignition, and oxidizes the combustion atmosphere in the first stage combustion zone under a high flame temperature. A strongly reducing atmosphere is created in which the pulverized coal is enriched, which is different from the atmosphere, and a combustion reaction of unburned gas and unburned particles progresses in the second stage combustion.

In this way, the combustion reaction of the pulverized coal is significantly promoted and completed, resulting in less unburned _matter remaining in the ash and high combustion efficiency. , can be significantly actively promoted and the generation of NO _x can be significantly suppressed.
Furthermore, by controlling the amount of oxygen-enriched gas supplied according to the type of coal, the amount of oxygen in the atmosphere can be adjusted and controlled. flammability,
Optimal combustion control according to the N content and the above-mentioned occurrence
It becomes possible to suppress the generation of NO _x by promoting the decomposition reaction of NO _x .

The above-mentioned nitrogen supply pipe is connected to the pulverized coal silo, and the nitrogen separated in the separation device installed in the boiler equipment is directly used to inert the atmosphere inside the pulverized coal silo. It becomes possible to prevent occurrences such as spontaneous combustion.

〔Example〕

FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, 1 is a boiler furnace, 2 is a pulverized coal burner, 3 is a pulverized coal silo, and 5 is an air preheater. 4 is a feeder installed at the bottom of the pulverized coal silo 3, and air 8 passes through a forced air blower 9, is heated by an air preheater, passes through an air pipe 11, is pressurized by a primary blower 12, and passes through a primary air pipe 13. The mixed flow is mixed with pulverized coal from the feeder 4, passes through the mixed flow transport pipe 13a, and is ejected from the pulverized coal burner 2 to the furnace 1.

A secondary air pipe 1 is connected from the air outlet side of the air preheater 5.
0 is provided and connected to the pulverized coal burner 2 to supply secondary air necessary for pulverized coal combustion. In the furnace 1, a pulverized coal burner 2 forms a first stage combustion zone. Further, a tertiary air port 16 is provided in the furnace 1,
Tertiary air pipe 14 from the air outlet side of the air preheater 5
A blower 15 is used to supply the tertiary air necessary to form the second stage combustion zone.
Exhaust gas from the furnace 1 and a steam generator (not shown) passes through an air preheater 5 and is discharged to the outside of the system via a pipe 7 by an induced fan 6.

20 is a separation device for separating air into nitrogen and oxygen, 21 is air, 23 is a nitrogen supply pipe, 24
indicate the oxygen supply pipes, respectively. The separation device 20 separates air into nitrogen gas and oxygen gas using a chemical adsorption method that has a simple structure and consumes less energy, unlike a liquefaction separation method. The nitrogen supply pipe 23 is connected to the pulverized coal silo 3, and the pulverized coal silo 3 is filled with nitrogen gas while maintaining a predetermined pressure to create an inert atmosphere, and the pulverized coal silo 3 is in a pressurized state compared to atmospheric pressure. This prevents outside air from entering the pulverized coal silo 3 and disturbing the inert atmosphere. In this way, a sufficient inert atmosphere is formed to prevent spontaneous combustion of the pulverized coal within the pulverized coal silo 3.

25 is an oxygen tank, 25a, 25b, and 2
5c are oxygen supply pipes. Oxygen supply pipe 2
4 connects the separation device 20 and the oxygen tank 25. In addition, oxygen supply pipes 25a, 25b and 25
c is provided with regulating valves 26a, 26b, and 26c and mixers 27a, 27b, and 27c, respectively, and is connected to the mixed flow transport pipe 13a, the secondary air pipe 10, and the tertiary air pipe 14, respectively. . Furthermore, the output signal of the control device 30 operates the regulating valves 26a, 26b, and 26c to control the amount of oxygen gas supplied according to the type of coal. The above control can also be performed using a manual regulating valve. Thus, the fuel air flowing through the mixed flow transport pipe 13a, the secondary air pipe 10, and the tertiary air pipe 14 has different oxygen concentrations, and the oxidizing agent having a high oxygen ratio and a low nitrogen ratio, that is, oxygen It becomes enriched air. In the furnace 1, the above-described staged combustion is performed, and the amount of oxygen in the atmosphere in the first and second combustion zones is controlled.

During the pulverized coal ignition and temperature raising process at the pulverized coal burner 2 outlet, the above process proceeds rapidly under the combustion atmosphere caused by the oxidizer, promoting and stabilizing ignition, and improving the combustion atmosphere in the first stage combustion zone. At a high flame temperature, a strongly reducing atmosphere is created in which the pulverized coal is enriched, which is different from an oxidizing atmosphere, and a combustion reaction of unburned gas and unburned particles proceeds in the second stage combustion zone. In this way, the combustion reaction of the pulverized coal is significantly promoted and completed, so that less unburned matter remains in the ash. Therefore, high combustion efficiency can be obtained even in pulverized coal combustion of coal with a high fuel ratio and low combustibility, and the decomposition reaction of generated NO _x is significantly promoted under high temperature conditions, resulting in the above-mentioned
In addition to being able to significantly suppress the generation of NO _x , combustion can be performed using an oxidizing agent with a low nitrogen ratio during staged combustion, so the NO _x suppressing effect can be further achieved in coordination with the NO _x suppressing effect described above. It will be done. ” Thus, as is clear from the above examples, in pulverized coal combustion, it is possible to burn a wide variety of coal types and control the combustion efficiency to high.
_NOx emissions can be suppressed. Thus,
As is clear from the above example, the nitrogen gas and oxygen gas separated by the separator are used at the same time, and the nitrogen gas inerts the atmosphere inside the pulverized coal silo and burns the pulverized coal. Under the safe storage and supply of oxygen gas, various types of coal can be combusted using oxygen gas, and combustion efficiency can be controlled to high and NO _x emissions can be suppressed.

Therefore, when burning pulverized coal under safe storage and supply of pulverized coal, it is possible to reduce unburned losses, improve boiler thermal efficiency, shorten the combustion time of pulverized coal, and reduce the combustion flame. Since the length can be shortened and the amount of combustion gas can be reduced, the furnace can be made smaller, and the pulverized coal combustion boiler can be made smaller.

Furthermore, since the amount of combustion gas can be reduced, it is possible to reduce the size and size of processing containers such as blowers, air preheaters, dust collectors, etc., which are boiler gas processing equipment.

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 above embodiments, the present invention simultaneously utilizes nitrogen gas and oxygen gas separated by a separator to safely store and supply pulverized coal in a pulverized coal silo using nitrogen gas for pulverized coal combustion. By controlling the amount of oxygen gas supplied under
Since the amount of oxygen in the combustion atmosphere from the start to the completion of the combustion reaction can be adjusted and controlled, the combustion atmosphere at the outlet of the pulverized coal burner can be changed to oxygen-enriched air without significantly changing the boiler structure, burner structure, etc. It is possible to create a strongly reducing atmosphere with a high concentration of pulverized coal under high flame temperatures, and it is also possible to perform optimal combustion control according to the combustibility of the coal type and N content.
The decomposition reaction of NO _x is significantly promoted under high temperature conditions, and NO _x generation can be significantly suppressed.
Furthermore, the effects of improving boiler thermal efficiency, reducing the size of the boiler, and reducing the processing capacity and size of equipment related to gas processing of the boiler are significant.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a pulverized coal combustion boiler according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Furnace, 2...Pulverized coal burner, 10...Secondary air pipe, 13...Primary air pipe, 13a...Mixed flow transport pipe, 14...Tertiary air pipe, 16...Tertiary air port, 20 ... Separation device, 21 ... Air, 23 ...
...Nitrogen supply pipe, 24...Oxygen supply pipe, 25a, 2
5b, 25c...Oxygen supply pipe, 30...Control device.

Claims (1)

[Claims] 1. A separation device that separates air into nitrogen and oxygen;
A mixed flow transport pipe of pulverized coal and temporary air supplied from a pulverized coal silo is connected to a pulverized coal burner, and a tertiary air pipe is connected to a tertiary air port of the furnace.
The nitrogen supply pipe is connected to the pulverized coal silo, and the oxygen supply pipe is connected to the mixed flow transport pipe, the secondary air pipe, and the tertiary air pipe to form oxygen-enriched air;
A control device is provided to control the amount of oxygen supplied according to the type of coal, and the combustion atmosphere at the outlet of the pulverized coal burner is made into a high-temperature strongly reducing atmosphere using the oxygen-enriched air, and the pulverized coal is burned. A pulverized coal combustion boiler characterized in that the combustion atmosphere thereafter is an oxidizing atmosphere using the oxygen-enriched air.