JPS62125891A - Treatment of fly ash - Google Patents

Abstract

PURPOSE:To decrease the carbon content in fly ashes by separating and capturing the fly ashes from the gas formed by the combustion of coal, conducting the fly ashes to a slag tap type combustion furnace and burning the fly ashes by air enriched with oxygen in said furnace. CONSTITUTION:The fly ashes are separated and captured from the gas formed by the combustion of coal and are conducted to the slag tape type combustion furnace where the fly ashes are burned by the air enriched with oxygen to decrease the carbon content in the fly ashes. As a result, the burned ashes of the coal which cannot be made into fly ash cement because of the unburned carbon contained the permissible threshold or above and with which a discarding treatment is difficult are thoroughly burned out to substantially decrease the unburned carbon in the ashes. The fly ashes are thereby made usable as heavy aggregate for concrete, etc. The pulverized coal is made into the coarse grains at least equivalent to the grain sizes of sand or larger, by which the remedy and handling of dust are made easy and economy is improved. The high fuel ratio carbon is made utilizable for a coal firing boiler, etc., by such effects.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for treating fly ash produced by combustion of coal, and relates to a method for treating fly ash produced by combustion of coal, and is applicable to coal-fired boilers, coal-water slurry-fired boilers, coal coke, petroleum coke combustion furnaces, and fluid flow furnaces. It is used in technology to process the residual combustion ash generated in bed-type coal gasifiers, etc.

Conventional technology The combustibility of coal is better as the degree of coalification is lower, and the fuel ratio (the ratio of the calorific value of fixed carbon to the calorific value of volatile matter in the coal) is lower; The higher the temperature, the more likely it is to burn, and the more likely it is that unburned matter will remain. Anthracite coals with the highest of these values are therefore difficult to burn in pulverized coal burners.

Furthermore, in the case of coal-concentrated water slurry (hereinafter abbreviated as CWM), which uses coal as a water slurry, the temperature of the ice flame rises due to the large amount of fire water (approximately 3 AM amount of coal). Unburned matter is more likely to remain in fly ash.

In Japan, the unburned content in the ash of coal-fired boilers is regulated to less than 5%, so in the case of CWM, compared to dry pulverized coal combustion, coal with a high degree of coalification and fuel ratio is used. The use of bituminous coal is more restricted, and much of the bituminous coal cannot be used up. However, with the exception of anthracite coal, coal with a high degree of carbonization and high fuel ratio makes it easier to produce high-quality CWM and easily becomes highly concentrated, resulting in higher boiler efficiency and greater economic effects. For this reason, there is a strong demand for countermeasures against unburned matter in fly ash produced when coal with a high degree of coalification and a high fuel ratio is combusted.

Similar requirements are also desired for measures against unburned matter in the combustion ash of fluidized bed boilers and fluidized bed coal gasifiers.

Problems to be Solved by the Invention The following measures have been taken to reduce the amount of unburned content in coal combustion ash, but these measures are insufficient, especially in the case of CWM.

(1) In the case of a pulverized coal boiler (al (same as Il-fal) (bl) When manufacturing CWM, coarse particles are removed at the outlet of the pulverizer using a salt sieve or filter, and returned to the inlet of the pulverizer. Re-grind.

In the case of dry grinding, sieving technology is relatively easy;
In the case of wet milling, which is easy to produce stable CWM, filtration techniques are difficult and incomplete.

Although improvements are being made to technologies such as TC+FAT and FBL, they are still insufficient, and the use of less combustible coal types will eventually have to be restricted or discontinued.

(3) Incineration treatment technology for combustion ash A technology that can be applied to both (1) and (2) above is to re-burn the ash collected in the boiler dust collector together with auxiliary fuel in an incinerator. There is a way to reduce unburned content.

If this method were successful technically and economically, the problem would be solved, but as described below, this has not been achieved with conventional techniques.

In other words, unburned matter is a highly condensed carbonaceous material that is inherently difficult to burn, so ordinary combustion cannot reduce unburned matter, so very high-temperature combustion technology is required, and depending on the conditions, storage may be carried out in the furnace. It adheres to walls and causes so-called tarinka trouble. In order to avoid this talinka trouble, it is necessary to maintain the flame temperature sufficiently high, completely melt the ash, improve its fluidity, and adopt the so-called slag tap method, which allows the ash to flow out from the bottom of the combustion furnace.

However, coal ash has a pour point of 1,500 to 1,700.
℃ or higher, and the restrictions on use based on the type of coal have not yet been resolved.

In addition, as a method of increasing the flame temperature, it is very effective to use oxygen or oxygen-enriched air instead of air during combustion, but in cryogenic separation plants for conventional oxygen production methods, the operating temperature is Since it is close to 'C, it takes time to start up, it cannot be stopped for a short period of time, and it has disadvantages such as the high cost of producing oxygen in small plants such as those for ash roasting furnaces.

Due to the above drawbacks, slag tap combustion treatment of fly ash has not received much attention.

Therefore, the present invention provides a method in which unburned ash generated in a coal-fired boiler, coal-water slurry-fired boiler, etc. is placed in a slag tap type combustion furnace using oxygen or oxygen-enriched air to melt and burn it. That is.

Means for Solving the Problems The present invention separates and collects fly ash from the gas produced by combustion of coal, guides it to a slag tap combustion furnace, and burns the fly ash with oxygen-enriched air in the furnace. Therefore, the carbon content in fly ash is reduced.

Effect: According to this method, fly ash containing unburned carbon, which is difficult to burn, is combusted at a high temperature to burn off the unburned carbon. In addition, when solidifying the slag-like stock that flows out of the furnace, it can be made into coarse particles or lumps, which solves another drawback of fly ash, which is in the form of a fine powder that easily generates dust and is difficult to handle. I can do something.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

A single diagram shows a system combining a coal-fired boiler and a slag tap fly ash processing furnace having a pressure swing adsorption separation (hereinafter abbreviated as PSA) type oxygen-enriched air production device.

In the figure, coal enters a coal feed processing device 2 through a coal feed line 1 . This coal feeding processing device is a coal pulverizer in the case of a pulverized coal-fired boiler, and is a CWM manufacturing device in the case of a CWM-fired boiler. The produced pulverized coal or CWM is passed through the fuel pipe 3 to the boiler 4.
and is burned in this boiler by a burner (not shown).

The combustion gas generated during this combustion enters a catalytic denitrification device 6 through a duct 5 with fly ash on it, and after nitrogen oxides are removed, it passes through a duct 7, an air heater 8, and a duct 9 to a dust collector 10. enter.

The fly ash is separated and collected from the combustion gas here, and the dust-free combustion gas enters the desulfurization equipment 2 through the duct 11, where it becomes completely clean exhaust gas and passes through the duct 13 and chimney 14 to the atmosphere. released inside.

Thus, in the boiler 4, the ash that melts during combustion, collides with each other, or collides with the furnace wall and becomes coarse, falls in the furnace and is discharged from the clinker hopper 15 to the outside of the boiler 4. This ash is substantially free of residual carbon since combustion is sufficient to completely dissolve the ash. Also,
Since its shape is so-called grainy, it is easy to handle.

On the other hand, the fly ash separated and collected from the combustion gas by the precipitator 10 is conventionally disposed of via a line 16' to an ash disposal site (not shown), or is temporarily stored in a fly ash storage tank (not shown). After that, it was transported out by fly ash carriers and freight cars.

In contrast, according to the present invention, this fly ash is sent via line 16 to a slag tap combustion furnace 17.

This transportation method includes air sent by a blower (not shown), exhaust gas sent from the duct 13, etc., or in some cases from the line 22 (described later) under conditions where there is no risk of spontaneous ignition. Airflow conveyance using oxygen-enriched air or the like sent through a branched line (not shown) is preferable.

The fly ash thus sent from line 16 can be used alone if its unburned carbon content is sufficient for slag tap combustion, or if it is insufficient, it can be sent as an auxiliary fuel, for example from line 18. The oxygen-enriched air is premixed with pulverized coal or CWM and led to the slag tap combustion furnace 17, where the oxygen-enriched air is sent to the furnace through line 22 to perform high-temperature combustion in the slag tap combustion furnace 17. be done.

The oxygen-enriched air used in the rice is air that has been pressurized to at least atmospheric pressure, at least 1.05 atm, by a forced draft fan or compressor 20 from line 19.
' to a PSA type oxygen-enriched air production device 21 using a nitrogen adsorbent, where nitrogen in the air is selectively adsorbed and removed. This PSA type oxygen-enriched air production device has good maneuverability, such as a start time of X or less, compared to a cryogenic separation type.

In addition, the nitrogen selective adsorbent used in the oxygen-enriched air production device 21 is, for example, sodium faudiasite represented by Na-X type zeolite, as described in Japanese Patent Application Laid-open No. 59-17927. A 60-70% Ca exchanger such as Na-A type zeolite is suitable.

When using sodium faugiasite, as described in the above-mentioned publication, in at least two adsorption towers filled with sodium faugiasite, air is blown into one tower at a temperature below room temperature above the atmospheric pressure plate. Nitrogen in the air is selectively adsorbed by flowing in at a pressure of 3 ata or more, and oxygen or oxygen-enriched air is flowed out from the outlet of the adsorption tower, and the other adsorption tower that previously adsorbed nitrogen is The pressure is reduced to 0.08 ata or more and 0.5 ata or less for regeneration, and the adsorption step and regeneration step are performed alternately or sequentially to continuously produce oxygen-enriched air.

On the other hand, when a Ca exchanger made of Na-A type zeolite is used, the adsorption and desorption rates of nitrogen at low temperatures are slow, so the temperature is room temperature, the adsorption pressure is above atmospheric pressure, and the desorption pressure is atmospheric pressure. In the following, and under the conditions of adsorption pressure/desorption pressure ≥ 3 ata, the adsorption-desorption process is performed alternately or out of phase in two or more adsorption towers, as in the case of sodium faudisite described above. Operated in sequential order.

In either case, the nitrogen discharged under reduced pressure during the desorption process is discharged from line 23 via vacuum pump 24 and line 23'.

In the slag tap combustion furnace 17, part of the ash in the oxygen-enriched coal and carbon-containing fly ash becomes molten slag and is discharged from the bottom of the furnace through the slag flow path 35 to the outside of the furnace, forming a sandy state. , made into grains or lumps. Since it is stored in storage, it may be made into large chunks or shaped.

On the other hand, in the combustion furnace 17, the other part of the ash is entrained in the combustion gas in the form of fine particles, cooled in the heat recovery furnace 2S to remove stickiness, and enters the cyclone 27 through the duct 26. Here, relatively coarse ash is collected. and,
This collected coarse ash is transferred to the line 32 and the blower 33.
, through line 34 to the slag tap type combustion furnace 17, where it is turned into slag again and discharged.

In this case, if the fine powder is fed into the furnace 17 from the line 34, the grains will not be coarsened, and a large proportion of the fine powder may return to the cyclone 27 through the duct 26 from the heat recovery furnace 25. It is also possible to provide coarse graining means such as rolling granulation in the middle of the process.

Alternatively, instead of directly feeding the fine particles from the line 34 to the slag tap type combustion furnace 17, the fine particles may be mixed and adsorbed with relatively coarse coal from the line 18 and then supplied to the slag tap type combustion furnace 17. .

The combustion gas from which the ash content has been roughly removed by the cyclone 27 enters the dust collector 29 through the duct 28, where the remaining fine ash is also collected. The dust collector 29 is preferably an electric dust collector, a granular bed filter, a bag filter, or the like.

The combustion gas from which fine ash has also been removed in the dust collector 29 is transferred to the line 30. It is returned to the front of the denitrification device 6 of the boiler 4 via the blower 31 and line 31'.

In this case, if the amount of nitrogen in the coal from line 18 is sufficiently low, it may be returned further downstream.

The fine fly ash collected by the dust collector 29 is well-calcined and has virtually no carbon content, so it is taken out of the system through lines 36 and 37' and used as a raw material for fly ash cement. I can do it. 1. Depending on the conditions, the ash collected in the cyclone 27 may also be taken out through the lines 32, 37, 37' and used as a raw material for fly ash cement.

However, if the pulverized ash collected by the dust collector 29 is not to be used as a raw material for fly ash cement, it is sent from the line 36 to the line 32 and mixed with the fly ash from the cyclone 27, and then sent again to the furnace 17. The slag is then discharged.

In any case, part of all fly ash is taken out as a raw material for fly ash cement, etc., and the other part is sent to the slag tap combustion furnace 17 for granulation processing or granulation as necessary. After processing,
It is fed into a slag tap type combustion furnace 17 and discharged from a line 35 using a slag tap type, where it is coarsened.

In the system described above, an oxygen adsorbent can also be used instead of the nitrogen adsorbent used in the PSA type oxygen-enriched air production device 21. As this oxygen adsorbent, as described in JP-A-56-163753,
It is desirable to use an oxygen adsorbent based on a two-component system of oxygen and nitrogen, which is obtained by dissolving iron having a valence of at least two or more in Na-A type zeolite, or a commercially available carbon molecular sieve.

In either case, from the line 19' shown in the figure to the adsorption tower 2
Since the air sent to 1 is adsorbed with oxygen and nitrogen passes through as is, line 22 serves as a nitrogen gas exhaust pipe, line 23 is a regeneration line, and vacuum pump 2
4. Since oxygen-enriched air comes out from line 23', this line 23' is connected to the slag tap type combustion furnace 17.

Effects of the Invention As detailed above, according to the present invention, coal combustion ash, which cannot be made into fly ash cement because it contains more than the permissible amount of unburned carbon and is difficult to dispose of, is burnt out, and the ash is Unburned carbon can be made sufficiently small, which allows it to be used as heavy aggregate for concrete, etc.

At the same time, the pulverized ash can be made into coarse particles at least as coarse as sand, making dust countermeasures and linkage easier, and economical efficiency can be greatly improved.

These effects allow high fuel ratio coal to be used in coal-fired boilers and CWM-fired boilers.

[Brief explanation of drawings]

A single figure shows one embodiment of the present invention, showing a coal-fired boiler plant and a slag tap combustion ash treatment system with an oxygen-enriched air production device for a seven-day treatment. 1. Coal feed line, 2. Coal feed processing device, 3..7 Knee 1/L/pipe, 4. Boiler, 6. Catalytic denitrification device, 8. Air heater, 10. Dust collector , 16... fly ash line, 17... slag tap type combustion furnace,
18...Auxiliary fuel supply line, 19...Air supply line, 21...Oxygen enriched air production device, 22...Oxygen enriched air supply line, 25...Heat recovery furnace, 27...Cyclone, 29Φ・collection Dust container, 32, 34, 36... Collection fly ash recirculation line, 35... Slag outlet path, 37
．． 37' fly ash extraction line. Sub-agent Masami Kimura (1 or 7 people)

Claims (1)

[Claims] Fly ash is separated and collected from the gas generated by coal combustion and guided to a slag tap combustion furnace, where the fly ash is combusted with oxygen-enriched air to reduce the carbon content in the fly ash. A method for processing fly ash, characterized by: