JPH0315677B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a low-viscosity coal-water slurry, and particularly to a method for producing a low-viscosity coal-water slurry without reducing the coal concentration. Coal, which is a solid fuel, is cheaper than liquid fuels such as oil, has large reserves, and is produced in various countries around the world, so its supply is stable. It has the disadvantage that it is complicated. Therefore, as seen in heavy oil-coal slurry (COM), methanol-coal slurry (CMM), and highly concentrated coal-water slurry (CWM), it is necessary to slurry coal with a liquid medium to make it fluid. Technology development is being actively promoted. Among the above slurries, COM is a coal slurry that uses heavy oil as a fluidizing medium, but from the viewpoint of transportation resistance, the proportion of heavy oil is 50% (weight,
(the same applies below), it is difficult to reduce the
Therefore, it has the disadvantage of requiring a large amount of heavy oil. Furthermore, CMM is a coal slurry that uses methanol as a fluidizing medium, but methanol itself has the disadvantage of being expensive under current production technology, and has not been put into practical use. on the other hand,
Since CWM is a coal slurry that uses water as a fluidizing medium, thermal loss due to water supply is a problem in boilers, etc., but if it is a highly concentrated water slurry containing more than 65% coal, It is said that these problems will also be reduced. In other words, in the case of conventional boilers that use coal as fuel, the raw coal used already contains about 10 to 30% water, and the desulfurization tower that removes sulfur dioxide gas from exhaust gas requires a wet method. This is common, and considering that a large amount of water evaporates and causes heat loss, if the water content in the coal-water slurry can be suppressed to about 35% or less, the thermal It can be said that losses are not that much of an issue. By using CWM, there is no risk of spontaneous ignition of pulverized coal or fire, which was a problem during conventional coal storage, and the storage area can be reduced because it can be stored in tanks or transported through pipes. Since there is no pollution, it is possible to build a safe and non-polluting system. Although CWM has various advantages as described above, on the other hand, as the concentration of coal increases, the viscosity of the slurry increases, resulting in an increase in pressure drop during pipe transportation, which is a major problem. Therefore, there is no problem of viscosity increase,
In order to create a high-concentration CWM with a coal concentration of 65% or more, preferably 70% or more, without the influence of thermal loss, even smaller coal particles are inserted between the coal particles, thereby increasing the coal concentration. It has been desired to produce a slurry having such a wide particle size distribution as shown in Fuller's particle size distribution, and containing a large amount of fine powder. In order to obtain such a slurry, it is currently necessary to set up a complex system such as combining several types of crushers, but even in this case, it is necessary to create a continuous particle size distribution with a wide width. requires more complex control. An object of the present invention is to provide a method for producing a low-viscosity coal-water slurry, which eliminates the drawbacks of the prior art described above and can reduce the viscosity of the slurry while maintaining a high coal concentration with simple operations. be. The present inventors have discovered that when wet pulverizing coal is carried out in the presence of a high concentration of coal, the rate of attrition increases, and as a result, the rate of fine powder production increases and the width of the particle size distribution increases. It has been experimentally found that expansion can be achieved. The present invention has been made based on the above findings, and includes a method for producing a coal-water slurry by wet-pulverizing coal. Water is added to a concentrated coal-water slurry to obtain a product coal-water slurry with a low viscosity suitable for handling such as transportation and storage. In the present invention, the reason why coal is pulverized with a high concentration of coal is as follows. That is,
In order to obtain a coal-water slurry with high concentration and low viscosity, it is said to be effective to widen the particle size distribution of pulverized coal and to increase the proportion of fine powder. By the way, when coal is crushed in a mill according to the conventional method, the crushing mechanism is broadly divided into impact crushing and attrition, but in order to achieve a wide particle size distribution and increase the proportion of fine powder, It is desirable to increase the rate of attrition. In order to increase this grinding ratio, as is clear from the experimental results shown in FIG. 1, it is most effective to keep the coal at a high concentration of about 75 to 80% when grinding. Possible reasons for this are as follows. That is, in a wet ball mill, when the casing is rotated, the balls in the follower mill are lifted up and then dropped, which is repeated. At that time, in the area of impact fracture shown in Figure 1, there may be a large amount of moisture, or
Alternatively, the viscosity of the slurry in the mill is low because the slurry is in a low state, so as shown in Figure 2A, the ball 2 that was lifted up as the mill (casing) 1 rotates drops with force, and the impact at this time causes the coal to explode. Since it is crushed, the crushing is mainly caused by impact. Therefore, the particle size distribution width of the coal in the slurry is narrow and the proportion of fine powder is also reduced, making it impossible to produce a highly concentrated coal-water slurry. Meanwhile, increase the concentration of coal to 75-80%
As the viscosity inside the mill becomes high when the concentration is increased to a certain degree, the viscosity inside the mill becomes high, and as shown in Fig. 2B, the lifted ball 2 causes a movement that slides down the inner wall of the mill 1, causing the grinding to become the center of the grinding. As a result, pulverized coal with a large proportion of fine powder and a wide particle size distribution can be obtained. Furthermore, it has been found that by adding water to the highly concentrated coal-water slurry obtained above, a significantly lower viscosity can be achieved than when the slurry is wet-milled to the same concentration after adding water. This water addition is generally at a concentration level of 70
It is sufficient to do this up to about %. Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that % in each example means % by weight unless otherwise specified. Example 1 Coal was crushed and water was added to the crushed slurry under the conditions shown in Table 1, and the slurry of the present invention (Example 1) and the slurry based on the conventional method, each having a coal concentration of 70% at the mill outlet, were prepared. (Comparative Example 1) was obtained. Although the coal concentration of the obtained slurry was 70% in both cases,
The slurry viscosity of Example 1 was 80 cp, and that of Comparative Example 1
It is clear that the viscosity is significantly lower than that of 1500op.

[Table] When the cumulative ratio of coal particle diameter was determined for each slurry obtained in Example 1 and Comparative Example 1, the results shown in FIG. 3 were obtained. In the figure, A indicates Example 1, and B indicates Comparative Example. From this figure, it was found that the coal particles in the slurry obtained in Example 1 had a wider particle size distribution than those in Comparative Example 1. This is because the coal concentration in the mill was higher in Example 1, and it was ground under conditions more suitable for grinding.
it is conceivable that. Example 2 Coal was pulverized while varying the coal concentration during pulverization within the range of 60 to 75%, and changes in slurry viscosity were determined when water was added after pulverization to change the slurry concentration. As for the former, a ₁ , b ₁ , c ₁ , d ₁ and e ₁ on the solid line shown in FIG. 4, and for the latter on the broken line a ₁ to a ₅ , b ₁ to b ₃ and c ₁ to
It became like c ₃ . From the results shown in Figure 4, the viscosity of slurry pulverized with a coal concentration of 70% or higher, preferably 73% or higher, and when water is added to the slurry to a concentration of around 70%, the viscosity decreases significantly, making it difficult to transport, store, etc. It was found that it is suitable for handling. As described above, according to the present invention, coal is first pulverized in the presence of water containing coal at a high concentration, and then water is added to the obtained high concentration coal-water slurry, thereby producing a large amount of fine powder. A pulverized coal slurry with a wide particle size distribution, that is, a low viscosity coal-water slurry suitable for handling such as transportation and storage, can be obtained by a simple operation.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the influence of the coal concentration in the mill on the coal crushing mechanism, Figure 2A is a cross-sectional view of the mill explaining the behavior of the balls during impact crushing, and Figure B is a diagram explaining the influence of the coal concentration in the mill on the coal crushing mechanism. FIG. 3 is a cross-sectional view of the mill explaining the behavior of the balls during crushing, and FIG. 4 is a diagram explaining the effects of the embodiment of the present invention together with a comparative example.
It is a figure explaining the relationship between the density|concentration and viscosity of various coal-water slurries obtained by this invention. 1...mil, 2...ball.

Claims (1)

[Claims] 1. In a method for producing a coal-water slurry by wet-pulverizing coal, the above-mentioned coal is first pulverized in a high-concentration coal-containing state, and then the resulting high-concentration coal-water slurry is A method for producing a low viscosity coal-water slurry, which comprises adding water to the slurry. 2. The method for producing a low-viscosity coal-water slurry according to claim 1, characterized in that the coal concentration during coal pulverization is 70 to 80% (by weight). 3. The method for producing a low-viscosity coal-water slurry according to claim 1, characterized in that the coal concentration of the coal-water slurry is made 65 to 70% (by weight) by adding water.