JPH0637626B2 - Method for preparing coal slurry - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for preparing a coal slurry containing ground coal, limestone, and water, respectively.

(Prior art) When using coal as a fuel, in order to facilitate handling such as transportation and storage of this coal, and deashing as necessary to improve quality,
BACKGROUND ART Coal slurry is prepared by adding a proper amount of water and a small amount of additives (dispersing agent, stabilizer, etc.) to coal, pulverizing and mixing the coal.

In the above coal slurry, the pulverized coal concentration is 65% by weight.
In order to maintain good slurry characteristics in terms of fluidity, stability, etc. over a long period of time when a high concentration of about -80% is used, this coal slurry has a special pulverized coal particle size composition. Required. That is, pulverized coal is required to be distributed in a wide range in terms of particle size, and moreover, not only those having a large particle size to a minute particle size but also the packing density of the coal to be used is increased in order to increase the packing density. Depending on the type, for example 3 μm
Ultrafine powder of less than 3 to 15% is extremely required.

(Problems to be Solved by the Invention) By the way, in general, coal is harder than other minerals, requires a large amount of power for crushing, and has a disadvantage that the parts of the crushing device are severely worn. Therefore, if it is attempted to obtain a large amount of ultrafine powder by pulverization as described above, the above-mentioned inconvenience will occur remarkably. For example, regarding the pulverization power, it depends on the type of coal, the pulverization system, etc., but on average, 30 to 50 kwh is required for 1 ton of coal (dry basis), which is considerably large as the production cost of the coal slurry. It is a thing.

On the other hand, when burning the coal slurry, there are the following disadvantages apart from the above. That is, since coal contains sulfur, when the coal is burned, the sulfur is combined with oxygen in the combustion air to form sulfur oxides (SOx), and if this is released into the atmosphere, It will be accompanied by pollution problems. Therefore, conventionally, exhaust gas from a heat exchange device that uses combustion gas after coal combustion has been treated by a desulfurization device. However, in this case, there is an inconvenience that the facility cost for desulfurization and the operating cost are high, especially in the case of small-lot application.

(Object of the Invention) The present invention has been made by paying attention to the various circumstances as described above, and when a desired coal slurry is to be obtained, it is possible to use a small grinding power and to burn the coal slurry. Occasionally, it is intended to suppress the generation of sulfur oxides at low cost.

(Structure of the Invention) In order to maintain high-concentration coal slurry with good slurry characteristics in terms of fluidity and stability, it is necessary to make a part of the coal into ultrafine powder. The gist of the present invention is to reduce the proportion of pulverized coal in the above ultrafine powder, and to that extent, limestone (calcium carbonate) that easily produces fine powder by pulverization.
The limestone fine powder can be used for desulfurization during combustion.

(Example) Hereinafter, the Example of this invention is described.

In general, limestone has a characteristic that fine powder is more likely to be generated by pulverization due to its crystallographic structure, and the abrasion property given to a pulverizer is smaller than that of coal.

That is, even when limestone is pulverized into fine powder of substantially 44 μm or less, for example, pulverized into fine powder in which the amount passing through the 44 μm sieve is about 95%, it can be easily pulverized by a pulverizing system using a roller mill as a pulverizer. The crushed limestone with such a particle size contains about 30% of ultrafine powder finer than 3 μm. The power required for crushing is 1 to 1 limestone.
It is about 30 to 40 kwh per n, and it is small compared to the amount of fine powder, and it is only about half of the power required for pulverizing pulverized coal having the same particle size. Further, the amount of wear of the crusher parts is only about 1/5 to 1/10 of the case of crushing coal.

Therefore, in crushing coal and limestone, when the overall particle size is given a predetermined distribution, both are crushed so that the particle size of limestone is smaller than the particle size of coal, that is, in the coal slurry. If the proportion of pulverized coal in the fine powder is reduced and the amount of limestone fine powder is increased by that amount, the overall power required for pulverization will be reduced, and the abrasion of the parts of the pulverizer will be less. .

When the limestone is crushed as described above, the limestone may be preliminarily crushed and the preliminarily crushed limestone may be crushed together with coal to obtain a desired fine powder. Alternatively, coal and limestone may be crushed separately, and then both crushed may be mixed with each other. Further, the crushing of coal may be performed wet, while the crushing of limestone may be performed dry.

In any of the above methods, the same effect as described above can be obtained by making the particle size of limestone smaller than that of pulverized coal.

On the other hand, when burning the coal slurry, the sulfur content in the coal tends to become sulfur oxides, but since fine powdered limestone was added, this is heated and decomposed during the combustion,
Combines with the sulfur content in the combustion gas to exert a desulfurization effect.

At this time, most of the limestone is pulverized into ultrafine powder or fine powder, and the contact area with the combustion gas is significantly increased, so even if the amount of limestone is small, the reaction with the sulfur content in the combustion gas is effective. The desulfurization to a predetermined concentration is performed more reliably. For example, calcium in limestone is sufficient if the molar ratio to the sulfur content in coal requiring desulfurization is about 1.5 to 2 or more, and in this case, per 1% sulfur content in the coal requiring desulfurization. The amount of limestone is equivalent to 4-6% or more of the amount of coal by weight.

Therefore, when using the above-mentioned fine pulverized limestone whose content passing through the 44 μm sieve is about 95%, the amount of ultrafine powder finer than 3 μm is contained around 1.5% of the amount of coal, and this amount in the coal slurry The amount of ultrafine powder of coal can be reduced.
In addition, when the sulfur content in coal is large, it is effective to increase the amount of finely powdered limestone mixed in and to further finely grind the particle size of limestone.

Further, in the combustion of coal slurry, the decomposition reaction of limestone is accompanied by heat absorption, so that the combustion temperature is lowered and the nitrogen oxide (NOx) in the combustion exhaust gas is also reduced.

It should be noted that, as fine powder limestone, the amount passing through the 44 μm sieve is 80 to 90%
The use of limestone with a particle size smaller than a certain degree is not preferable because of the stability of the coal slurry.

Next, more specific examples for preparing a coal slurry will be described.

(First Specific Example) FIG. 1 shows a first specific example. In the figure,
The limestone 1 washed with water and drained is supplied to a preliminary crusher 2 and preliminarily crushed by a dry method, and then a coarse powder 4 is crushed by an air classifier 3.
And fine powder 5, and coarse powder 4 is returned to the preliminary crusher 2 and crushed again. Since the limestone 1 is easily pulverized into fine powder, the preliminary pulverization can easily make the limestone 1 fine on an industrial scale.

The fine powder 5 of the classified limestone 1 is supplied to the crusher 9 together with the coal 7, and both of them 5 and 7 are crushed and mixed by a low-concentration wet method using water 10 separately supplied to the crusher 9. It The pulverized product is supplied to a wet classifier 11 such as a liquid cyclone and classified into a coarse powder 12 and a fine powder 13, and the coarse powder 12 is returned to the pulverizer 9 and re-pulverized.

In the crusher 9, since the limestone 1 which has already been made into the fine powder 5 is supplied, this is easily pulverized by the crusher 9 to become ultrafine powder, and accordingly, the amount of the ultrafine powder of the coal 7 is increased accordingly. Can be reduced.

The low-concentration slurry containing the fine powder 13 crushed to a predetermined particle size together with the limestone 1 is supplied to the dehydrator 14 and adjusted to a predetermined water content. Further, this is mixed with an additive 17 by a stirrer (or a kneader) 16, and at the same time, a necessary concentration of water is adjusted to form a high-concentration coal slurry 18 having a predetermined fluidity. Not transported to storage process.

(Second Specific Example) FIG. 2 shows a second specific example. In the figure,
Limestone 1 is pulverized by a pulverizer 20 in a dry manner and fine powder 21
Is obtained. On the other hand, coal 7 is crusher 22 separately from this.
The pulverized coal 23 is pulverized by a wet method, and the low-concentration slurry-like pulverized coal 23 thus obtained is supplied to the dehydrator 14 and adjusted to a predetermined water content. And, fine powder 21 of limestone 21 coal 7
The additive 17 is added to the fine powder 24 and the fine powder 24 are mixed with the stirrer 16.

Further, the pulverized coal 23 from the classifier 11 is made into a slurry or cake-like pulverized coal 24 of high concentration by the dehydrator 14, and at this time, the dehydrated wastewater 25 is returned to the crusher 22 for reuse. It has become.

According to the above configuration, the limestone 1 and the coal 7 are crushed individually, so that it is easy to adjust the particle size of each of the fine powders 21 and 24. Further, according to this method, since the high concentration pulverized coal 24 from the dehydrator 14 and the dry limestone powder 21 are mixed, the pulverized coal 24 may have a high water content. Therefore, there is an advantage that the dehydration work in the dehydrator 14 is easy and the power consumption for dehydration is small.

In this embodiment, the number of the stirrers 16 is one, but two stirrers 16 are arranged in series, and the additive 17 is added to the first stirrer 16 to provide the high-concentration pulverized coal 24 from the dehydrator 14. The second stirrer 16 may be used to mix the pulverized limestone 21 into the pulverized coal 24 with the second stirrer 16.

In addition, in the first and second specific examples described above, the high-concentration coal slurry 1 is obtained by dehydrating the low-concentration slurry produced by the pulverizers 9 and 22 as the coal pulverizing system with the dehydrator 14.
The method for obtaining 8 is described above.
Alternatively, the additive may be supplied together with water 10 to perform high-concentration pulverization to directly obtain a high-concentration slurry.

The crusher for coal 7 may be a combination of a primary crusher and a secondary crusher as appropriate. Furthermore, the crushing system for the limestone 1 can be freely selected,
In addition, the type of the crusher for the coal 7 and the limestone 1, the type and mixing ratio of the limestone 1 or the additive 17, the addition position of the additive, the presence or absence of a deashing step, and the like are also free.

Further, a storage tank may be provided at an appropriate place during the manufacturing process.

(Effect of the Invention) According to the present invention, when preparing a coal slurry composed of crushed coal, limestone, and water, respectively, crush these coal and limestone so that the particle size of limestone becomes smaller than the particle size of coal. As a result, the proportion of pulverized coal in the ultrafine powder of the coal slurry can be reduced, and limestone, which can be easily crushed, can be supplemented in the form of fine powder by that amount. Therefore, in preparing the coal slurry, the required power for pulverization is reduced as compared with the conventional one, and at the same time, the abrasion of the components of the pulverization device is also reduced.

Moreover, when burning the coal slurry, the sulfur content in the coal tends to become sulfur oxides, but since fine powdery limestone was mixed in the coal slurry, it was heated and decomposed during the combustion, and Effectively combines with sulfur to exert desulfurization effect. Therefore, the desulfurization device conventionally required is not required, so that the sulfur oxide can be suppressed in a simple structure and at a low cost.

The technique of the present invention is not only particularly effective for coal species with a high sulfur content, but pulverized limestone has no risk of explosion in the process of production and storage as compared with pulverized coal, and is easy to handle. is there.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is a process drawing showing the first embodiment, and FIG. 2 is a process drawing showing the second embodiment. 1 ... Limestone, 2 ... Preliminary crusher, 7 ... Coal, 9 ...
Crusher, 10 ... Water, 17 ... Additive, 18 ... Coal slurry, 20 ... Crusher, 22 ... Crusher.

Claims (5)

[Claims] 1. A coal slurry characterized by crushing coal and limestone so that the particle size of limestone is smaller than the particle size of coal when preparing a coal slurry composed of crushed coal, limestone, and water, respectively. Preparation method of. 2. A method for preparing a coal slurry according to claim 1, wherein limestone is preliminarily ground, and the preliminarily ground limestone and coal are ground together. 3. The method for preparing a coal slurry according to claim 1, characterized in that coal and limestone are separately crushed and then the crushed both are mixed with each other. 4. The method for preparing a coal slurry according to any one of claims 1 to 3, wherein the crushing of coal is carried out by a wet method while the crushing of limestone is carried out by a dry method. . 5. The method for preparing a coal slurry according to any one of claims 1 to 4, wherein limestone is crushed to substantially 44 μm or less.