JPH0323115B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coal-water slurry production apparatus, and more particularly to an apparatus for producing a highly concentrated coal-water slurry by wet-pulverizing coal using a continuous ball mill. In recent years, against the background of the world energy situation, oil and
Coal, which has abundant reserves and is inexpensive, is being reconsidered as an alternative fuel to liquid fuels such as LNG and LPG. However, since coal is solid, it has the disadvantage that handling such as storage and transportation is troublesome. As a technology to overcome this problem, the use of fluidized coal has recently been considered. One example is COM (Coal
−Oil Mixtures) and coal-water slurry CWM (Coal
−Water Mixtures) or CWS (Coal−Water
Slurries). COM has an oil dependence rate of 50~
Currently, coal-water slurry (hereinafter referred to as CWM) is attracting attention because 60% of them are economically unsatisfactory. The conditions for direct combustion and pump transportation of this CWM are as follows: 74μm standard sieve (JIS Z8801)
The coal particles in the CWM have a fineness that allows about 60 weight percent or more of the coal particles to pass through, and the coal concentration in the CWM is high, about 60 weight percent or more, and the viscosity of the CWM is about 2000 cp or less. That's true. In order to achieve this, (1) adjust the particle size distribution to a wide range and increase the packing density to achieve high concentration, and (2) add appropriate additives such as bulk particles and PH regulators. It is necessary to reduce the viscosity by adjusting the surface potential of the particles, repelling the particles, and stably dispersing them. When continuously manufacturing CWM with such high concentration, a wet ball mill is generally used.
Figure 1 shows the process using a general wet ball mill.
FIG. 2 is an explanatory diagram showing the configuration of an apparatus for manufacturing CWM.
A ball mill basically consists of a horizontally rotating cylinder filled with cast iron balls, and as the mill rotates, the balls are lifted along the inner wall and allowed to fall freely or roll down the surface of the contents. 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 friction or impact. In Fig. 1, coal A, which has been roughly pulverized to about 3 to 5 mm or less, is adjusted together with an additive liquid (water B and additive C) so that the coal concentration is about 60% by weight or more, and is placed in a coal bunker 1. from the feeder 2 to the inlet of the ball mill 3,
In the mill 3, the coal particles are pulverized and mixed as described above, and CWM having a 74 μm standard filter passing amount of about 60 to 85 weight percent and a viscosity of about 100 to 2000 cp is produced, and the CWM is discharged from the outlet of the mill 3. . In addition,
4 is an additive liquid supply pipe line. Generally, once the grinding capacity of a ball mill is determined, how to determine the mill diameter D and length L becomes important. That is,
According to the studies of the present inventors, the relationship between the powder capacity Q, the mill diameter D, the length L, and the volume V is expressed by the following equation. Q∝VD ^0.3~0.5 ∝π/4D ² LD ^0.3~0.5 Therefore, when the mill diameter D or length L is determined, the other is uniquely determined, so L/
D. It is necessary to decide. Looking at the various aspects of L/D, in a cement finishing mill that requires ultrafine grinding in which 99% of the ground material passes through an 88 μm standard sieve, L/D is
A mill with a D of 2.5 is used. ("On-site experience of 3500kw closed circuit ball mill operation", crushing,
Proceedings of a Symposium on Grinding and Its Applications, Japan Society of Materials Science, 1972) A mill with L/D = 2 to 3 is used for fine grinding in the production of CWM and COM. For CWM, (Coal−
Water Slurry as Utility Boiler Fuel, EPRI−
For CS-2287, March, 1982, COM,
Technical Results of EPDC's COM R&D,
(See STEP1 Laboratory Tests, March 1978). In addition, since fine coal particle size is required as a necessary condition for CWM, the conventional general idea is to increase the length of the mill (increase L/D) in order to increase the residence time. The idea was that In fact, according to the conventional example, coal with a coal crushability index (JIS Z8801) of HGI = 50 was used, and the coal concentration was
570mmφ×1710mmL (L/D=3) as equipment for manufacturing 70% by weight CWM at 100Kg/h.
If a ball mill is selected and milled so that the amount passing through a 74μm standard sieve is 70% by weight, the slurry concentration is 69% by weight and the viscosity is
CWM with a high concentration of 70% by weight or more and a viscosity of 2000cp or less, which can only be obtained at 2400cp (see conventional examples in Table 1 below), with HGI≦50.
It was very difficult to produce, and as mentioned above, it was unsuitable for direct combustion. Generally, the coal used in power plant boilers has a grindability index (HGI)
Most of them are around 50, so when putting CWM into practical use, it is necessary to use products with higher concentration and lower viscosity.
It is desired to establish a technology that can economically manufacture CWM. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a coal-water slurry that eliminates the above-mentioned drawbacks of the prior art and provides CWM with high concentration and low viscosity. In short, the present invention adjusts a wider particle size distribution than the conventional technology by selecting a ball mill with a ratio of length L to inner diameter D of less than 2, and achieves CWM with high concentration and low viscosity. This makes it possible to manufacture Embodiments of the present invention will be described below with reference to the general device configuration shown in FIG. In FIG. 1, as a ball mill 3, its L/D is 1≦L/D<2, preferably 1.2 to 1.99.
The configuration is the same as the conventional one, except that the The mill is filled with balls of, for example, about 75 to 50 mm or less. A slurry tank 5 is arranged at the outlet of the mill 3, and CWM is discharged from this tank 5 to the next process by a slurry pump 6. Coal that has been roughly pulverized to about 5 mm or less is supplied in a fixed amount from a bunker 1 to a mill 3 via a feeder 2. Adjusted additives (surfactants and PH regulators) at predetermined concentrations
The liquid is supplied to the mill 3 from the additive liquid supply pipe 4 so that the coal concentration becomes a predetermined value. The coal particles are efficiently pulverized and mixed in the ball mill 3, resulting in a coal concentration of approximately 65-80% by weight and a viscosity of approximately 2000 cp.
The following CWM is produced and discharged continuously from the outlet of mill 3. Based on the above embodiment of the invention, the inner diameter is 650 mm;
Using a ball mill with a length of 1250 mm (L/D = 1.92), HG150 coal was pulverized to a slurry concentration of 70 weight percent and a 74 μm standard sieve passing rate of 70 weight percent.
Shown in the table. In addition, for comparison in the table, inner diameter 550mm,
The results of conventional operation using a ball mill with a length of 1650 mm (L/D=3) are also shown. Moreover, the viscosity distribution of the obtained slurry is shown in FIG. In the figure, numeral 11 indicates the first embodiment of the present invention, and 10 indicates the conventional method.

[Table] As is clear from the table, even though the coal concentration in the slurry increased by 1% by weight,
We were able to reduce the viscosity by 650 cp. this is,
As shown in Figure 2, the amount of passage through a 74μm standard sieve is 70
This is because when grinding to weight percent, the present invention provides a wider particle size distribution than the conventional method, resulting in an increased packing density of the particles and achieves high concentration and low viscosity. . In order to explain the above results, we conducted the following study. For the two mills mentioned above, the tracer was dissolved in 50 c.c. of additive liquid, this additive liquid was introduced into the mill inlet for a short period of about 1 second, samples were taken intermittently at the mill outlet, and tracer was dissolved in 50 c.c. The concentration was analyzed and the residence time distribution in the mill was determined. Figure 3 shows
This shows the residence time distribution of the tracer in the mill.
The horizontal axis plots the dimensionless time, which is the elapsed time divided by the average residence time, and the vertical axis plots the frequency of discharge from the mill. From Figure 3, L/D of the conventional method =
The residence time distribution 13 in the mill of No. 3 is close to the distribution 16 of the extrusion flow (4 piston flow), and the residence time distribution 14 of the mill with L/D = 1.92 in the example of the present invention is close to the distribution 15 of complete mixing. I understand. (Chemical Engineering, p91-94, Tokyo Kagaku Dojin, 1965). In addition,
When we actually measured the residence time distribution of a mill with L/D = 2.1, it was similar to 15 in the case of complete mixing in Figure 3, and as L/D = 1.92 to 2.1, the residence time distribution rapidly approached the extrusion flow. I found out that Also, L/D = 1 mill (800mm diameter x 800mm
When the residence time distribution of the sample (long) was measured, it almost coincided with the distribution 15 for complete mixing in FIG. When a similar test was conducted on a mill (850 mm diameter x 700 mm length) with L/D = 0.82, the residence time distribution was almost complete mixing, but the discharge rate of coarse particles increased.
When using CWM as boiler fuel, coarse particles can clog the burner chip.
Even if the L/D is different, it is necessary to remove coarse particles with a strainer or the like and recirculate coarse particles with a size of 500 to 840 μm or more. When 1≦L/D<2, the coarse particles were 1 to 2% or less, but when L/D was 0.8, the coarse particles increased to 5 to 10%, which was found to be undesirable. The number of times a particular coal particle is crushed in a mill is proportional to the particle's residence time. Therefore, from FIG. 3, for example, L/D=1.92 in the embodiment of the present invention.
In this mill, the pattern approaches perfect mixing, so
Particles that leave the mill faster than their average residence time also
In addition, particles that stay in the mill longer than the average residence time and come into contact with more opportunities for pulverization are also found to be pulverized more times than in the case of a mill with L/D = 3, which is close to the piston flow of the conventional method. Ta. Therefore, the particle size distribution of the coal particles discharged from the mill with L/D=1.92 in the embodiment of the present invention is the same as that of the conventional method with L/D=1.92.
The width is wider than the 3 mil. As mentioned above, one of the conditions necessary to produce CWM with high concentration and low viscosity is to obtain a wide particle size distribution, so even mills with the same grinding capacity have low L/D values. It has become clear that a small mill, ie a mill with a large internal diameter and a short length, is suitable. From the above study results, it is clear that L/D in the present invention
The range is L/D<2, preferably 1≦L/D≦
1.99, more preferably 1≦L/D≦1.8. Next, Figure 4 shows high concentration using a wet ball mill.
An example of a process for manufacturing CWM with lower viscosity and at lower cost is shown. In FIG. 4, the ball mill 3 is divided into two chambers by installing a porous partition plate 7, and the ratio of the length L to the mill inner diameter D is 2.
A raw coal feeder 2 is connected to the inlet of the smaller ball mill 3, and an additive liquid supply pipe 4 is introduced from the inlet of the mill 3 into the first chamber of the mill 3. The first chamber of the mill 3 is filled with balls with a large diameter, and the second chamber is filled with balls with a small diameter, and a second additive liquid supply pipe 8 is introduced from the outlet side of the mill 3. has been done. A slurry tank 5 is installed below the outlet of the mill 3, and a pump 6 for transporting slurry is connected to the tank 5. Coal that has been coarsely crushed to a size of approximately 10 mm or less is transported to feeder 2.
A fixed amount is supplied to mill 3. Coal concentration is about 70~
85% by weight, additive amount is coal (dry coal standard)
so that it is about 0 to 0.3 weight percent of
Water and additive liquid are fed into the first chamber of the mill 3 in a controlled manner. In the first chamber, the particles are crushed in a more concentrated atmosphere and with larger diameter balls, so a wider particle size distribution is produced. The slurry that has passed through the partition plate 7 is efficiently crushed by small-diameter balls in the second chamber, and the newly added additive liquid adsorbs the slurry to the particle surface without waste.
CWM with high concentration and low viscosity can be produced. In this example, additives are added as new particle surfaces are generated by pulverization, and two-stage addition is performed so that the additives are evenly and wastefully adsorbed onto the particle surfaces, so that the total additive The amount can be significantly reduced. Example 2 in Table 1 and 12 in Figure 2 have an inner diameter of 650 mm and a length of
Using a 1250mm ball mill, HG150 coal is crushed to a final slurry concentration of 70% by weight and 74μm.
A high concentration of 70% by weight passes through a standard sieve.
The results of manufacturing CWM are compared with the conventional method and the first embodiment of the present invention. As can be seen from these results, according to this example, the coal crushing capacity was increased by about 7% compared to the conventional method, and the viscosity was reduced despite the amount of additive used being 40% of the conventional method.
1000cp can also be reduced, and the particle size distribution is
It can be seen that the area is wider than the conventional method. According to the present invention, by using a ball mill in which the ratio of the length L to the mill inner diameter D is smaller than 2, that is, L/D<2, a low viscosity, high concentration coal-water slurry suitable for direct combustion is produced. efficiently,
Moreover, it can be manufactured by reducing the amount of additive liquid by half or less.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a high-concentration coal-water slurry manufacturing apparatus according to a conventional method and a first embodiment of the present invention;
The figure is an explanatory diagram showing a comparison of CWM manufacturing test results according to the conventional method and the present invention. Fig. 3 is an explanatory diagram showing the residence time distribution of particles in a ball mill. Fig. 4 is an explanatory diagram showing another example of the present invention. FIG. 1...Coal bunker, 2...Feeder, 3...Ball mill, 4...Additive liquid supply pipe, 5...Slurry tank, 6...Slurry pump, 7...Porous partition plate, 8...Additive liquid supply pipe.

Claims (1)

[Scope of Claims] 1. In a coal-water slurry production apparatus for wet-pulverizing coal using a continuous ball mill to obtain a highly concentrated coal-water slurry, the ratio of length L to diameter D of the ball mill (L/D ) is in the range of L/D<2. 2 In claim 1, the L/D
A coal-water slurry manufacturing apparatus characterized in that L/D is in the range of 1≦L/D≦1.99. 3 In claim 1, the L/D
A coal-water slurry production apparatus characterized in that L/D is in the range of 1≦L/D≦1.8. 4. The coal-water slurry manufacturing apparatus according to claim 1, wherein the mill is a multi-chamber mill divided into two or more chambers.