JPS6257883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of combustion of slurry fuel, and more particularly to a method of combustion that can reduce the amount of fly ash in combustion exhaust gas.

In view of the recent fuel situation, there is a rapid increase in the development of slurries made by mixing liquids such as water and solid fuels such as coal pulverized to a certain particle size.
However, in the combustion of slurry, problems arise due to the combustion of solid content (hereinafter referred to as "coal") contained in the slurry. That is, a large amount of fly ash is contained in the exhaust gas due to the combustion of coal, which causes the following problems. First, as the exhaust gas containing this fly ash passes through, it causes wear and thinning of the heat transfer tubes of various devices installed in the combustion equipment, such as superheaters, reheaters, and economizers if the combustion equipment is a boiler. I will do it. Furthermore, in order to collect a large amount of fly ash, the dust collector placed in the flue must be large and have a large capacity. Therefore, depending on the conventional combustion method, it becomes necessary to take measures such as limiting the amount of slurry burned and reducing the mixing ratio of coal to slurry.

An object of the present invention is to provide a combustion method capable of eliminating the above-mentioned drawbacks of the prior art and reducing the amount of fly ash in the combustion exhaust gas.

In short, the present invention is characterized by burning the slurry in a reducing atmosphere to make the main component of the ash a substance with a low melting point, thereby melting and solidifying the ash and recovering it as slag.

Embodiments of the present invention will be described below with reference to the accompanying drawings. The slurry will be explained below using a water slurry as an example.

First, the constituent substances of coal ash produced by combustion of coal contained in water slurry are as follows. Namely Fe ₂ O ₃ (ferric oxide) CaO (calcium oxide) MgO (magnesium oxide) Na ₂ O (sodium oxide) Al ₂ O ₃ (aluminum oxide) TiO ₂
It is composed of (titanium dioxide), K ₂ O (potassium oxide), SiO ₂ (silicon dioxide), etc. Among these, those with a high acidic content have a high melting point; for example, SiO ₂ has a high melting point.
1700℃, Al ₂ O ₃ is over 2000℃. In contrast to this
Those with a high basic content such as Fe ₂ O ₃ , Na ₂ O, and K ₂ O have low melting points. By the way, Fe ₂ O ₃ is about 1550℃, K ₂ O is about
The temperature is 350℃. Here, basic substances are produced by combustion in a reducing atmosphere, and conversely, the production of substances with a high acid content is reduced. That is, the melting point of ash generated by combustion in a reducing atmosphere is lowered. The inventors have confirmed that the melting point of ash generated by burning coal in a reducing atmosphere is approximately 40-160°C lower than the melting point of ash generated in a non-reducing atmosphere.

FIG. 1 shows an embodiment of the method according to the present invention constructed based on the facts confirmed above. In the figure, a plurality of burners 2 (hereinafter simply referred to as "burners") for burning water slurry are arranged for a boiler 1. Of these, the two burners 2a and 2b located at the upper stage are reduction burners. In other words, the wind boxes 3a and 3b of these two burners are independent from the wind boxes of other burners, and combustion exhaust gas is introduced into these wind boxes via the exhaust gas fan 4. Combustion air preheated by an air preheater 5 is supplied to the burner 2 located below the reduction burners 2a and 2b in an amount that is approximately the same as the theoretical air amount or slightly less than this. 6 is an air fan that supplies combustion air. Also, the reduction burner 2a,
In step 2b, the air supply amount is reduced and exhaust gas is introduced to perform low-oxygen combustion to create a reducing atmosphere in the entire boiler furnace. As a result, the ash whose melting point has been lowered is melted and solidified, adhering to water cooling walls and the like. After the solidified ash grows to a certain size (usually grows in the shape of an icicle), it is destroyed by a gas flow or the like, falls into a slag hopper 7 placed at the bottom of the furnace, and is then discharged to the outside. On the other hand, in the afterburner 17, combustion air in an amount greater than the theoretical amount is supplied to burn incombustibles generated by combustion in a reducing atmosphere.

In the illustrated case, exhaust gas is introduced into only a certain burner to form a reduction burner, but the exhaust gas may be introduced into all burners.

According to this invention, most of the ash that should become fly ash can be melted and recovered as slag, so wear and thinning of heat exchanger tubes, etc. can be suppressed, and a small-capacity dust collector is sufficient.

Furthermore, since the combustion temperature is lowered, the concentration of nitrogen oxides in the exhaust gas can also be lowered.

[Brief explanation of the drawing]

FIG. 1 is a sectional side view of a boiler for carrying out the method according to the invention. 1...boiler body, 2...burner, 2a...reduction burner.

Claims (1)

[Claims] 1. A slurry combustion method characterized by lowering the melting temperature of the ash by burning the slurry in a reducing atmosphere, allowing the molten ash to adhere to and solidify on the furnace wall surface, etc., and further collecting the solidified ash as slag. .