JPH0254397B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a coal-water slurry, and more specifically, to a method for producing a coal-water slurry, and more particularly, to a method for producing a coal-water slurry.
This invention relates to a method for producing coal-water slurry using a ball mill consisting of more than one chamber. Since coal is a solid, it is much more difficult to store, transport, and handle than fluid fuels such as oil or gas, but if coal is slurried with water, it becomes easier to handle. It is also possible to directly burn the coal-water slurry;
Coal particle size is 200 mesh passing amount (74μm or less)
is approximately 70% by weight (hereinafter simply referred to as % in the present invention), and the slurry concentration is at least approximately 70% by weight.
It is desirable to have a high concentration of 60% or more (on a dry basis) and a low viscosity that allows transport. Figure 1 is a schematic diagram of the manufacturing process and slurry structure of a highly concentrated coal-water slurry.
When producing water slurry D, the challenges to producing stable coal-water slurry D with high concentration and low viscosity are: (1) increasing the packing density by adjusting the particle size distribution of the crushed coal particles A1; (2) By adding an appropriate dispersant C, coal particles A1
Forming a water film B1 on the surface and charging it, coal particles A
The purpose is to reduce the viscosity by repelling and dispersing the comrades. To continuously produce such a highly concentrated coal-water slurry, a continuous wet ball mill is generally used. FIG. 2 is a system diagram of a conventional coal-water slurry production apparatus using a continuous wet ball mill. The conventional ball mill 1 basically consists of a horizontally rotating cylindrical body 2 and a cylinder filled with
For example, it is composed of a steel ball 3. As the cylindrical body 1 rotates in the direction of the arrow as shown in FIG. It appears on the surface and then rolls down the surface. Ball 1B falling and rolling like this
Among them, coal A is mainly caught between the balls 3 when they collide with each other, and is crushed by the impact. In order to prevent the ball 3 from slipping on the inner wall of the cylindrical body 2 and to make lifting and rolling of the ball 3 smooth, the inner wall of the cylindrical body 2 is often covered with a liner 2A. Ball 3 is usually
Several types of balls with different diameters are mixed and used, and they are almost completely mixed inside the ball mill 1. During long-term operation of the mill 1, the balls 3 are worn and have a reduced diameter, and are discharged through the grate 2D at the mill outlet 2B. Therefore, balls 3 with the largest diameter are introduced from the mill inlet 2C to compensate for the decrease in balls due to wear and discharge. In this way, the distribution of the diameters of the balls 3 in the mill 1 reaches an equilibrium. The distribution of the diameter of ball 3 in an equilibrium state is as follows: dm is the maximum ball diameter,
If the weight fraction of the ball smaller than the ball diameter d is M, it is expressed as M=(d/dm) ^3.8 ...(1) (FCBond, “Crushing and
Grinding Calculations”, Allis―Charmers
Publication 07R9235B, 1961). A conventional method for producing coal-water slurry using the conventional ball mill 1 described above will be explained with reference to FIG. The coal A in the raw coal bunker 5, which has been coarsely crushed to about 3 to 5 mm or less, has a coal concentration (dry coal standard) of about 60 to
From coal supply feeder 4 so that it is 75%,
Further, the dispersant C is adjusted to be approximately 1 part by weight per 100 parts by weight of dry coal, and is supplied together with water B to the mill inlet 2C, and inside the ball mill 1, approximately 1 part by weight is added.
It flows toward the mill outlet 2B while being pulverized and mixed by a group of balls 1B of 50 to 75 mm or less. Therefore,
The particle size distribution of the coal particles A1 in the ball mill 1 changes from large to small from the mill inlet 2C side to the mill outlet 2B side. In this way, a coal-water slurry with a viscosity of about 100 to 2000 cp and a 200 mesh passing rate of about 60 to 85% is produced, which is flowed out from the overflow type mill outlet 2B of the ball mill 1, passed through the adjustment tank 6, and pumped. 7 to be transported to the next process. However, in the above case, if the hard globe grindability index (hereinafter referred to as HGI) of the coal is large and it is easy to grind, a highly concentrated coal-water slurry can be obtained, but the grinding efficiency is low and the grinding efficiency is low. (50% or less), the power consumption will be larger. On the other hand, if the coal has a low HGI and is difficult to crush, a highly concentrated slurry cannot be obtained. Furthermore, in the case of the conventional method described above, the viscosity of the slurry obtained from coal with an HGI of less than 50 is as high as 2000 cp or more at a slurry concentration of 70%, making it unsuitable for direct combustion. Furthermore, in the conventional method described above, a method is adopted in which a dispersant is added at the inlet of the mill 1, and the required amount of addition is as large as about 1% by weight. The purpose of the present invention is to provide a production method that eliminates the drawbacks of the above-mentioned prior art, efficiently pulverizes coal, reduces the amount of dispersant used, and provides a coal-water slurry with low viscosity even at high concentrations. It is in. In order to achieve the above object, the present inventor conducted the following studies. In general, if the particle size distribution of a coal-water slurry produced in a wet ball mill is determined using the Andreasen pipette method, the cumulative weight percent (y) of coal particles smaller than the coal particle diameter x is calculated using the Rosin-Ramler equation: y= 100 {1-exp(-x/a) ^m } ...(2) Or, it is approximated by the Godin-Schuman formula: y=100(x/b) ⁿ ...(3). Here, a and b are constants, and n and m are distribution coefficients. If we focus on a small range of coal particle diameters, equation (2) can be approximated and reduced to equation (3), where m=n. Figure 4 shows HGI50 coal with a diameter of 650 mm and a length of
The results are plotted on a double-logarithmic scale using a 1200 mm continuous wet ball mill with two slurry concentrations, 50% and 70%, and a 200 mesh passing rate of 70%. It is understood that a linear relationship holds true for the particle size range of 20 to 30 microns or less, and the above equation (3) holds true. And in this example,
In the range where the above linear relationship holds true, the slurry concentration is 50
When milling at a slurry concentration of 70%, n = 0.95, and at a slurry concentration of 70%, n = 0.62, indicating that milling at a higher concentration can achieve a wider particle size distribution required for the production of a highly concentrated coal-water slurry. Ru. In addition, in general, the factors that influence the particle size and shape of the particle size distribution of coal particles produced by pulverization are the particle size distribution caused by single crushing of each particle (single particle crushing) and the shape of the particle size distribution. It's speed. Fifth
The figure shows the particle size distribution (particle size
(d) The following weight fraction (y) and particle size before crushing (do)
(Relationship with the ratio (x) of the particle diameter (d) after crushing to
is shown on a logarithmic scale. The slope γ of this plot is approximately equal to n in equation (3) representing the particle size distribution described above, and the value of γ determines the breadth of the particle size distribution. In ball mill grinding, the fifth
As shown in the figure, good crushability (large HGI)
The higher the slurry concentration during pulverization of coal and the larger the ball diameter, the smaller the value of γ, and therefore the wider the particle size distribution. on the other hand,
Figure 6 shows the relationship between the grinding speed of a single particle, the particle size, and its influencing factors, and coal with good grindability (high HGI) is better than coal with a lower slurry concentration during grinding. However, the grinding speed is high. Furthermore, as shown in Figure 6, for a given ball diameter, there is an optimal particle size that maximizes the crushing speed, and as the particle size becomes smaller than the optimal particle size, the crushing speed decreases. , and the grinding speed decreases as the particle size becomes larger. This optimum particle size also increases as the ball diameter increases, as shown by the broken line in the figure (LG
Austin, K. Shoji and PTLuckie. “Effect of
Ball Size on Mill Performance，”Powder
Technoloqy, 14 (1976) 71–79). From this, small balls are used to crush coal particles with small particle diameters.
It was found that a large ball is suitable for grinding coal particles with a large particle size. Furthermore, as mentioned above, the particle size of the coal particles in the ball mill becomes finer from the mill inlet 2C side to the mill outlet 2B side. Exit 2B
It was found that pulverization efficiency was improved by placing small diameter balls on the side. In addition, in the conventional method, the balls are distributed in a substantially completely mixed state in a ball mill having only one chamber. This causes poor pulverization efficiency and increased power consumption. In addition, in the conventional method, a large amount of dispersant was required at the mill entrance where the coal was not yet pulverized.
Since the entire amount of the dispersant was added in step C, the dispersant adsorbed to the ash in the hydrophilic coal before the new surface, which was hydrophobic in nature, created by the coal grinding, was wetted with water. It is thought that the required addition amount becomes large in order to lower the slurry viscosity. Based on the above-mentioned study results, and in order to achieve the above-mentioned object of the present invention, the present invention provides a ball mill consisting of two or more consecutive chambers in coal-water continuous wet ball milling, each chamber having one group. The diameters of the large number of balls gradually change from large to small starting from the first chamber on the mill inlet side, and adjacent chambers are separated by a porous intermediate partition plate with a hole diameter slightly smaller than the predetermined diameter of the smallest ball on the upstream side. Coal, water and a portion of the total amount of dispersant are supplied to the first chamber of the ball mill,
It is characterized in that the remaining amount of the dispersant is supplied to at least one chamber after the second chamber for pulverization. In the present invention, in order to obtain a highly concentrated coal-water slurry by pulverizing the coal so as to distribute the particle size of the coal over a wide range and increase the packing density, the ball diameter is gradually changed from large to small. Ball milling is carried out continuously, and the addition of the dispersant is carried out over time in two or more divided times: the first time and one or more times thereafter. In this case, the ball wears out at each stage and its particle size becomes smaller, but in order to maintain the initial ball diameter at each stage,
Balls smaller than the predetermined diameter of the smallest ball in each of the above stages are transferred to the next stage through the holes in the partition plate. In addition, especially poor grinding speed (low HGI)
In the case of coal, by adding limestone and grinding it, a highly concentrated and low viscosity coal-water slurry can be obtained. Hereinafter, the present invention will be explained in detail using the drawings. FIG. 7 is a system diagram of a coal-water slurry manufacturing apparatus showing an embodiment of the present invention. In the figure, numbers 1~
7 is the same as in the case of FIG. In the figure, a cylindrical body 2 of a ball mill 1 is connected to a first chamber 2 by a partition plate 8 using a screen or grate.
A feeder 4 for supplying raw coal is located at the mill entrance 2C on the side of the first chamber 2E.
The water supply pipe 9 and the first dispersant liquid supply pipe 10 are inserted into the first chamber 2E through the mill inlet 2C. The first chamber 2E of the ball mill 1 is filled with a group of balls 3 having a diameter within a predetermined range (for example, approximately 64 to 41 mm), and the second chamber 2F is filled with balls 3 having a diameter within a predetermined range smaller than the balls in the first chamber 2E. A group of balls 3 with a diameter of (for example 40-12 mm) are filled. The diameters of the numerous holes in the middle partition plate 8 are slightly smaller (for example, 40 mm) than the minimum diameter of the ball diameter range determined for the first chamber 2E (41 mm in the above example). . Further, the grate 2D of the mill outlet 2B is provided with holes having a diameter slightly smaller (for example, 11 mm) than the minimum particle diameter similarly determined for the second chamber 2F. Also, the second room 2F
A second dispersant liquid supply pipe 11 is introduced through the mill outlet 2B. Below the mill exit 2B,
A regulating tank 6 is installed, and a pump 7 transports the product slurry to the next process. In the apparatus having the above configuration, coarsely crushed coal A
(for example, particle size of about 5 to 10 mm or less) is supplied in a fixed amount to the first chamber 2E of the ball mill 1 by the feeder 4 for supplying raw coal. Next, the coal concentration (dry coal standard) is adjusted to a predetermined high concentration (for example, about 75 to 85%), and the amount of dispersant C added is a part of the predetermined total weight part to 100 parts by weight of coal A (dry coal standard). (e.g. 0.3 parts by weight or less)
Water B and dispersant C are supplied to the first chamber 2E from the water supply pipe 9 and the first dispersant supply pipe 10, respectively. Dispersant C may be in liquid or powder form, and may even be diluted with water to facilitate measurement of the amount to be added. In the first chamber 2E of the ball mill 1, the slurry D
The high coal concentration and the use of large-diameter balls 3 produce a wide particle size distribution including small particle sizes (see FIG. 5). Furthermore, since the large-diameter balls 3 are used, coarse particles including larger coal particles (for example, 5 to 10 mm) can be more efficiently pulverized than in the conventional method. Moreover, the new surface created by the crushing is wetted with water before reaching the second chamber 2F. The coal particles thus crushed by the large-diameter balls in the first chamber 2E move through the holes in the partition plate 8 to the next second chamber 2F. In the second chamber 2F, the remaining amount (for example, 0.3 parts by weight or less) of the dispersant obtained by subtracting the amount added in the first chamber 2E from the total weight part of the dispersant per 100 parts by weight of the coal is supplied from the second dispersion supply pipe 11. It is added and acts efficiently on wet coal particles, reducing the viscosity of the slurry. The coal particles in the second chamber 2F, which have a smaller particle size,
It is efficiently crushed by the small diameter balls 3. As described above, during long-term operation of the ball mill 1, the diameter of the balls 3 decreases due to wear. In the present invention, the balls 3 that have been worn in the first chamber 2E and have become smaller than the hole diameter of the intermediate partition plate 8 naturally move through the holes to the second chamber 2F, and are worn out in the second chamber 2F and become smaller. The balls 3 are naturally discharged from the mill 1 through the mill exit grate 2D. Therefore, in order to compensate for this amount of wear loss, if balls 3 with the largest diameter are introduced from the mill entrance 2C of the first chamber 2E, the diameters of the balls 3 in each chamber will form a distribution according to the above formula (1),
control automatically. This stabilizes the expression of the crushing effect in the present invention. According to the above embodiment, the particle size of the coal particles A1 at the mill outlet 2B is 70 to 85% when 200 meshes are passed through.
Viscosity is less than 2000cp, coal concentration is approximately 70 on dry coal basis
~80% higher concentration coal-water slurries can be produced with about 50% less dispersant and about 5-10% less mill power costs than conventional methods. When producing highly concentrated coal-water slurry, the fifth
As shown in Fig. 6, the particle size distribution of coal with poor crushability (low HGI) is determined by the slope γ of the particle size distribution after single crushing, even when crushed at a high concentration, and therefore the distribution coefficient n. If the value is large (that is, the width of the particle size distribution is narrow), it may be difficult to increase the concentration of the slurry. In the conventional method, if coal with an HGI of 50 or less is used, it is not possible to produce a slurry with a solids concentration of 700% or more and a viscosity of 2000 cp or less. FIG. 8 is a system diagram of a coal-water slurry production apparatus suitable for producing a high-concentration, low-viscosity coal-water slurry from the above-mentioned coal with poor grindability. This apparatus is the same as the apparatus shown in FIG. 7 except that it is provided with a limestone feeder 12 for supplying limestone E to the first chamber 2E of the ball mill 1. In the figure, coal A, water B,
The dispersant C is supplied to the first chamber 2E in the same manner as in the case of FIG. ) is supplied to the mill inlet 2C, for example, about 0.1 to 5 parts by weight,
After being mixed with coal and pulverized, a highly concentrated and low viscosity product slurry flows out from the mill outlet 2B. The reason for using limestone is as follows. That is, as shown in FIG. 9, the gradient of the particle size distribution of limestone powder produced by high-concentration wet ball milling is about 0.4 or less, compared to about 0.4 or more for coal.
In addition, limestone has good crushability and is extremely friable compared to coal. Therefore, when coal, which has poor crushability, is wet-pulverized at a high concentration, if a small amount of limestone is added and the mixture is crushed, limestone can be crushed. Fine powder is generated and fills the voids between coal particles, increasing the packing density and making it possible to increase the concentration and lower the viscosity of the slurry. In this case, for example, a slurry with a concentration of 700% and a viscosity of 2000 cp or less can be obtained from coal with an HGI of 50 or less. According to the above example, in addition to the effects of increasing concentration, lowering viscosity, and lowering the power consumption unit, the unique effects of limestone as a particle size distribution regulator, that is, the effects of increasing concentration and lowering viscosity, can be obtained. Furthermore, the limestone in the coal-water slurry has the advantage of acting as a desulfurization agent during direct combustion of the coal slurry. In the above embodiment, limestone is supplied to the first chamber 2E, but limestone may be supplied by connecting the limestone feeder 12 to the second chamber 2F in FIG. 8. Generally, limestone may be supplied to the first chamber or at least one chamber after the second chamber.
Note that limestone may be supplied in the form of limestone-water slurry. In addition, although FIG. 7 and FIG. 8 both show the ball mill 1 consisting of two chambers, the ball mill 1 may consist of three or more chambers, and in this case, the slope gradually decreases from the inlet to the outlet of the ball mill. The coal particles can be crushed with balls having a particle size more suitable for each stage of particle size. In addition, the coal-water slurry flowing out from the outlet of the ball mill is classified using a classifier such as a vibrating sieve, and the slurry consisting of coal particles coarser than a predetermined particle size is returned to the first chamber of the ball mill, and the slurry consisting of coal particles coarser than a predetermined particle size is If the operation is carried out so that slurry is extracted as a product, there will be no waste of coal and product efficiency can be increased. Specific examples of the present invention will be shown below. Example 1 In the apparatus shown in FIG. 7, a cylindrical body 2 with an inner diameter of 650 mm and a length of 1200 mm, with a partition plate 8 provided at a distance of 50 cm from the mill inlet 2C, was used as the mill 1, and HGI50 was produced according to the method of the present invention. of coal is pulverized to a high concentration, the final slurry concentration is 70%, and the amount of passing through 200 meshes.
A highly concentrated coal-water slurry of 70% was produced. On the other hand, a coal-water slurry having the same concentration and particle size was produced by the conventional method using the same apparatus as above except that it did not have the partition plate 8 and the second dispersant supply pipe 12. The production volume per hour, amount of dispersant used, power unit, and product slurry viscosity in the above two cases are
In addition, the particle size distribution (weight distribution under the sieve) of the product slurry is shown in the table and in FIG.

[Table] As seen from Table 1, according to the method of the present invention,
Compared to the conventional method, the slurry production amount per hour, that is, the amount of coal pulverized per hour, increased by about 7%, and as a result, the power consumption rate was reduced by about 7%. Furthermore, although the amount of dispersant used was only about 40% of the amount used in the conventional method, the viscosity could be reduced by 15%. Furthermore, as is clear from FIG. 10, according to the method of the present invention, the particle size distribution is wider than that of the conventional method. Example 2 Using various coals having HGI other than the coal used in Example 1 as raw materials, a coal-water slurry with a final concentration of 70% was produced by the method of the present invention and the conventional method in the same manner as described above. Figure 11 shows a comparison of the results of both methods regarding the relationship between slurry viscosity and power unit consumption with respect to HGI of coal. When producing a coal-water slurry with a final concentration of 70% as shown in FIG. 11, according to the method of the present invention, compared to the conventional method,
Power consumption is reduced by approximately 7%, and slurry viscosity is approximately 15%.
It can be seen that it decreases by ~20%. As shown in Figure 11, which shows the distribution coefficient of coal particles in the slurry in the case of the conventional method, in the case of coking coal with a low HGI (less than 50), even if it is pulverized at a high concentration (70%), the distribution coefficient is low. It can be seen that the coefficient is large and a wide particle size distribution cannot be obtained. Example 3 A manufacturing apparatus equipped with a limestone feeder in the same manner as shown in FIG.
A slurry with a coal concentration of 70% was produced in the same manner as in Example 1 except that 1 part by weight of limestone was added to 100 parts by weight. When this coal was made into a slurry using the conventional method, the viscosity of the slurry with a coal concentration of 70% was approximately 2300 cp, as shown in the results of Example 2.
By using limestone as described above, the slurry viscosity was 1900 cp. Note that point P in FIG. 11 indicates the viscosity of the slurry of this example. As described above, according to the method of the present invention, a highly concentrated coal-water slurry suitable for direct combustion can be produced extremely efficiently, with a reduction in power consumption, and the amount of dispersant used can be reduced by more than half. Moreover, low viscosity can be obtained. Furthermore, even when coal, which has poor crushability, is used as a raw material, by adding limestone, it is possible to obtain a slurry with sufficiently high concentration and low viscosity for direct combustion.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the manufacturing process and slurry structure of highly concentrated coal-water slurry, Figure 2 is a system diagram of a conventional coal-water slurry manufacturing equipment, and Figure 3 is a diagram of the structure of the balls and particles in the ball mill. FIG. 4 is an explanatory diagram showing the influence of the pulverized slurry concentration on the particle size distribution; FIG. 5 is an explanatory diagram showing the particle size distribution caused by crushing a single particle and its state of change; FIG. 6 is an explanatory diagram showing the relationship between the crushing speed of a single particle, the particle diameter, and its influencing factors, and FIG. 7 is an illustration of the coal-water slurry manufacturing apparatus used in the present invention.
Fig. 8 is an equipment system diagram showing another example, Fig. 9 is an explanatory diagram showing a comparison of particle size distribution of coal and limestone, and Fig. 10 is an equipment system diagram showing another example. A graph showing the undersieve weight distribution of coal particles in the slurry, FIG. FIG. 3 is an explanatory diagram showing the relationship between sex indexes. 1... Ball mill, 2... Cylindrical body, 2B... Mill outlet, 2C... Mill inlet, 2E... First chamber, 2F... Second
Chamber, 3...Ball, 4...Raw coal supply feeder, 8...
Partition plate, 9... Water supply pipe, 10... First dispersant supply pipe, 11... Second dispersant supply pipe, 12... Coal stone supply feeder, A... Coal, B... Water, C... Dispersant, D
...coal-water slurry, E...limestone.

Claims (1)

[Scope of Claims] 1. In continuous wet ball milling of coal-water systems, a ball mill consisting of two or more consecutive chambers, in which the diameter of a group of many balls in each chamber is from the first chamber on the mill inlet side. Coal, water, and a dispersant are placed in the first chamber of a ball mill, which is partitioned by a porous intermediate partition plate that changes from large to small in order, and the adjacent chambers have a hole diameter slightly smaller than the predetermined diameter of the smallest ball on the upstream side. A method for producing a coal-water slurry, which comprises supplying a portion of the dispersant, and supplying the remaining amount of the dispersant to at least one chamber after the second chamber for pulverization. 2. In claim 1, further supplying limestone or limestone-water slurry to the first chamber,
A method for producing a coal-water slurry, which comprises mixing and pulverizing coal with coal. 3. The method for producing a coal-water slurry according to claim 1, characterized in that the limestone-water slurry is further supplied to at least one chamber after the second chamber, and mixed and pulverized with the coal. 4. In any one of claims 1 to 3, the coal-water slurry flowing out from the ball mill is classified using a classifier, and the slurry consisting of particles coarser than a predetermined particle size is returned to the first chamber of the ball mill. , a method for producing a coal-water slurry, characterized in that it is extracted as a slurry product consisting of fine particles with a predetermined particle size or less.