JPH0315956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a highly concentrated coal-water slurry, and particularly to a method for producing a coal-water slurry using a wet ball mill.

Coal, which is a solid fuel, is difficult to handle during storage and transportation, but it becomes easier to handle if it is made into a slurry with water. According to the studies of the present inventors, the conditions for a stable and directly combustible slurry are that the particle size is about 70% by weight passing through a 200 mesh;
and the coal concentration is approximately 60% by weight or more and the viscosity is approximately
It is less than 2000 cp. To achieve this, it is necessary to (1) prepare a wide particle size distribution and increase the packing density to achieve high concentration, and (2) reduce the viscosity by adding appropriate additives.

When continuously producing such a highly concentrated coal-water slurry, a wet ball mill is generally used. A ball mill basically consists of a horizontally rotating cylinder, and the inside is filled with steel balls of 75 to 50 mm or less. By rotating the mill, the balls are lifted along the inner wall of the mill and rolled down to impact the coal. It is something to do. At this time, the coal particles are caught between the balls or between the balls and the inner wall of the mill, and are crushed by the impact. In a typical conventional operation, coal coarsely pulverized to about 5 mm or less has a coal concentration of about 60% by weight together with the surfactant liquid.
It is adjusted so that it is above, and is supplied to the inlet of the mill, and flows toward the mill outlet while being pulverized and mixed in the mill, and the amount passing through 200 meshes is approximately 60 to 85% by weight
A coal-water slurry having a viscosity of about 100 to 2000 cp is produced and discharged from the overflow outlet of the mill. At this time, the rotational speed of the mill is generally about 65 to the critical speed (the speed at which the balls rotate together with the mill along the mill wall when centrifugal force and gravity are balanced).
It is 80%. Here, the critical speed Nc is defined by the following equation.

Nc=42.3/√− rpm Where D is mill inner diameter (M), d is ball diameter (m)
It is.

It is generally accepted that the optimum rotational speed for dry or wet grinding ball mills is 65-80% of the critical speed (e.g., RHPerry and CHChilton,
Chemical Engineers' Handbook, 5th Edition,
P8-26, McGraw-Hill Book Co., 1973).

However, according to the studies conducted by the present inventors, it has been found that at the above rotation speed, the production capacity of coal-water slurry is low, the power consumption rate is high, and it is not possible to obtain a slurry with a lower viscosity.

An object of the present invention is to provide an operating method for reducing the power consumption of the mill and obtaining a slurry with higher concentration and lower viscosity when producing a highly concentrated coal-water slurry by crushing coal with a wet ball mill. It's about doing.

The present invention uses a continuous ball mill to improve coal concentration.
When producing a highly concentrated coal-water slurry by wet-pulverizing coal under conditions of 60% by weight or more, the ball mill is operated at a critical speed of 45 to 64% (preferably 50 to 60%), which is unprecedented in the past. It is characterized by operating at rotational speed.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

FIG. 1 is an explanatory diagram of a wet crushing apparatus for carrying out the present invention. In Figure 1, the mill volume is 35
A feeder 2 for supplying raw coal is connected to the inlet of the mill 1, which is occupied by balls with a diameter of 50 to 20 mm.
Further, an additive liquid supply pipe 3A is introduced into the mill from the mill inlet. The mill 1 is driven by a gear drive system, and the rotation speed is made variable by a continuously variable speed motor 4. A slurry tank 6 is provided directly below the mill outlet, and the obtained slurry is transported to the next step by a pump 7.

In the above configuration, coal coarsely pulverized to about 5 mm or less is supplied in a fixed amount from the bunker 3 to the mill 1 by the feeder 2 for supplying raw coal. Additive liquid is simultaneously supplied to the mill inlet so that the coal concentration is 65-80% by weight and the additive amount is about 0.7% of the coal amount. Mill 1 is operated at a rotational speed of 45-60% of the critical speed;
Coal particles are crushed by the rolling of the balls, and the resulting coal-water slurry is stored in a slurry tank 6 from the mill outlet. The particle size distribution curve of the coal-water slurry produced in this manner is shown in FIG. 3B. In the figure, A is the case of normal wet pulverization with a coal concentration of 50% by weight. From the results shown in FIG. 3, it can be seen that high-concentration wet pulverization produces a wider particle size distribution including ultrafine powder than normal low-concentration wet pulverization.

Next, Figure 2 shows the hard globe grindability index (HGI) of a continuous ball mill with a diameter of 650 mm and a length of 1250 mm.
JIS-M8801) 50 coal is pulverized at a high concentration with a coal concentration of 72% by weight, and the coal feed amount, added liquid amount, and mill rotation speed are changed according to the rotation speed to obtain the particle size distribution shown in Figure 3. , 200 This shows the data when operating so that the amount of meshes passed was 70%.
These results show that in the optimal rotational speed range (65 to 80% of Nc) for conventional low-concentration wet and dry grinding, the slurry production capacity is low, the power consumption is large, and the viscosity does not decrease much. It can be seen that by setting the rotation speed in the range (45 to 64% of Nc, preferably 50 to 60%), the slurry production capacity becomes about 80% or more, and the power consumption and viscosity are also reduced.

Figure 4 shows high concentration coal using a wet ball mill.
This shows another example of an apparatus for producing water slurry at a lower cost.
By operating at a rotation speed of ~64%, it is possible to further reduce costs and increase or decrease the concentration of the slurry. In the apparatus shown in FIG. 4, a feeder 2 for supplying raw coal is installed at the entrance of a mill 1 which is divided into two chambers by installing a partition plate 8 such as a screen.
are connected, and a water supply pipe 3A and an additive liquid supply pipe 4 are introduced into the first chamber from the mill inlet. The first chamber of mill 1 is filled with large diameter balls, the second chamber is filled with small diameter balls, and the second chamber is filled with small diameter balls.
An additive liquid supply pipe 5 is inserted into the chamber. A slurry tank 6 is installed directly below the mill outlet, and the slurry is transported from the tank 6 to the next process by a pump 7.

In the apparatus configured as described above, the raw coal coarsely pulverized to about 10 mm or less is fed in a fixed amount from the bunker 3 to the mill 1 by the feeder 2, and the coal concentration is about 75 to 85% by weight and the amount of additives is 0 to 0.3% by weight. Water and additive liquid are regulated and fed into the first chamber of mill 1 so that In the first chamber, the coal slurry is pulverized with a higher concentration and with a larger diameter ball, so that a coal slurry containing finer powder and having a wider particle size distribution is produced. The slurry that has passed through the screen 8 is efficiently pulverized by small-diameter balls in the second chamber, and at the same time, the particle surfaces are efficiently wetted with the newly added additive liquid, thereby reducing the viscosity. Even in the operation of such a wet ball mill, by setting the rotational speed to 45 to 64% of the critical speed, the power consumption can be further reduced and the viscosity of the coal-water slurry can be reduced.

As described above, according to the present invention, when producing a high-concentration coal-water slurry by a high-concentration wet pulverization method using a ball mill with a coal concentration of 60% by weight or more, the operation of the ball mill during conventional dry or wet pulverization is By operating the ball mill at an unprecedented rotational speed of 45-64% of the critical speed, the power consumption is reduced by more than 10% compared to manufacturing at the conventional operating range of 65-80% of the critical speed. It is possible,
Furthermore, the viscosity of the slurry can be reduced by several hundred cps or more.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the high concentration coal-water slurry manufacturing apparatus used in the present invention, Fig. 2 is an explanatory diagram showing the influence of the rotational speed of the ball mill on the power unit and slurry viscosity, and Fig. 3 is FIG. 4 is an explanatory diagram showing the particle size distribution of a high concentration coal-water slurry, and FIG. 4 is an explanatory diagram of a coal-water slurry manufacturing apparatus showing another embodiment of the present invention. 1...Ball mill, 2...Feeder for raw coal supply,
3...raw coal bunker, 5...additive liquid supply pipe, 6...slurry tank, 7...slurry tank, 8...middle partition plate.

Claims (1)

[Claims] 1. When producing a highly concentrated coal-water slurry by wet-pulverizing coal under conditions where the coal concentration is 60% by weight or more using a ball mill, the ball mill is operated at a rotational speed of 45 to 64% of the critical speed. A method for producing a highly concentrated coal-water slurry, characterized by: