JPS63296850A - Method for grinding high concentration coal aqueous slurry - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention discloses a method for reducing the crushing power required when producing a highly concentrated coal-water slurry using a ball mill, tube mill, or the like.

[Conventional technology]

The coal-water slurry targeted by the present invention is coal and water.

It is a mixture consisting of additives such as a surfactant and an alkaline substance, the coal concentration in the slurry is 60 wt% or more, preferably 65 wt% or more, and the viscosity is 4000 cp or less, preferably 2000 cp or less.

Such a highly concentrated and highly fluid slurry (Coal
The requirements for manufacturing Water Mxture (hereinafter referred to as CWM) are specified in Japanese Patent Publication No. 56-501.568.
．． Special Publication No. 58-501.183 and Special Publication No. 54. -1.
651.1. The content is to adjust the particle size of coal particles so that they have a specific particle size distribution. Its particle size distribution has a maximum particle size of 1180 μm or less and a minimum particle size of 0.0! Since it has a wide range of 5 μm or more and contains many fine particles, fine pulverization is necessary to produce CWM by this method. Therefore, there is a drawback that the crushing power becomes high. This patent does not include any description of the method for reducing the grinding power disclosed in this patent.

The amount of pulverization for CWM production is JP-A-57-96090.
has been disclosed. The method involves producing coarse particles and fine particles separately, adding water and a dispersant to them, and then applying high shear force to mix and disperse them. Although it is possible to manufacture CWM using this method, it requires two pulverizers and a high-shear mixing/stirring device, which adds a new mixing power in addition to the pulverizing power, reducing the slurry production cost from 1 to 1.
It has the disadvantage of being high.

One common manufacturing method for CWM currently being carried out in Japan and abroad is to use a tube mill (also called a ball mill) with coal and water.
Continuous pulverization is performed while supplying additives such as surfactants and alkaline substances.

The weight ratio of coal and water supplied to the mill ranges from 6:4 to 8:2.
CWM can be produced in one mill by simultaneously pulverizing the particles and dispersing them in water in the mill.

In a tube mill, grinding balls and the material to be crushed are put into a cylindrical container, and the balls are scraped up to a high height by the rotation of the container, and the grinding proceeds by the impact and friction caused by the natural fall of the balls. Therefore, in order to reduce the crushing power as the object of this patent, it is important to improve the crushing effect of the balls in the mill and increase the crushing performance of the mill.

A method for improving the crushing efficiency of a tube mill is disclosed in JP-A-53-416561.54-2568. The first two players throw balls of different sizes into the mill,
Furthermore, a mill is disclosed in which a lifter is provided on the inner wall. According to this invention, balls of different sizes can be separated by the lifter, so that only large balls are located at the mill inlet and only small balls are located at the mill outlet. For this reason, the material to be crushed introduced from the mill inlet is coarsely crushed by large balls, and then finely crushed by small balls while moving toward the mill outlet. This mill has the function of simultaneously performing coarse and fine pulverization in one unit, and is considered to be effective in adjusting a wide particle size distribution suitable for CWM.

[Problem that the invention seeks to solve]

However, the mill disclosed in JP-A-53-116561.54-2568 is considered to have the same effect as the conventional two-chamber tube mill.

In conventional two-chamber mills, large balls are placed in the first chamber near the mill inlet, while small balls are placed in the second chamber near the mill outlet. Even in such a mill, the material to be crushed is coarsely crushed by large balls in the first chamber, then moved to the second chamber through the partition wall, and then finely crushed by small balls.

As a result, the present inventors have already confirmed through experiments that the produced slurry contains coarse particles and fine particles together, resulting in a wide particle size distribution suitable for CWM. However, although both mills are suitable for producing a wide particle size distribution,
It does not have the function of reducing the grinding power of the mill itself. In other words, reducing the mill grinding power means grinding under conditions that maximize the grinding efficiency. Said patent (JP-A-53-11.6561.54-2568)
Although the girder lid and mill structure are specified, there is a problem in that the maximum grinding efficiency cannot be obtained only by specifying the girder lid and mill structure.

An object of the present invention is to provide a method for reducing the crushing power when producing CWM with high concentration and high fluidity by wet crushing coal together with a third substance such as water, a surfactant, and an alkaline substance. .

[Means for solving problems]

The basic concept of the CWM manufacturing process according to the present invention is shown in FIG.

The raw coal stored in the hopper 1 is supplied to the tube mill 5 by the feeder 2. -Power water and additives are in tank 3
is supplied to the tube mill 5 by the pump 4.

After the coal is wet-pulverized together with additives in a tube mill 5, it becomes a highly concentrated coal-water slurry. The slurry overflows from the mill outlet and is temporarily stored in a tank 6, then supplied to a filter 8 by a pump 7 to remove coarse particles, and then stored in a tank 9 as a product. On the other hand, the coarse particles separated by the filter 8 are returned to the mill 5 and re-pulverized.

The distribution of the grinding balls in the tube mill 5 is adjusted according to the following equation.

R= (D"Ds") / (r)+, +Ds")
X 100...(1) D: Arbitrary ball diameter (■) DL: Maximum ball diameter (am) Ds: Virtual minimum ball diameter (cm) n: Particle size distribution index (-) R: Under-sieve cumulative weight ratio (wt%) The distribution index is n=0.4 to 3.5, and the maximum ball diameter is 40 to 60 nlIn.

The crushing power of a tube mill is generally expressed by the following formula.

-T Wccm ... (2) W: Grinding power consumption (K VJ hr / ton Coa
l,) N: Rotation speed (rpm) T: Torque (kgf-m) Q: Coal processing amount (ton/hr) The power required for a tube mill is the power required to crush 1 ton of crushed material, that is, the power Shown in basic unit. Reducing this unit consumption is connected to reducing power, which is the objective of the present invention.

From equation (2), it is clear that in order to reduce the basic unit W, it is sufficient to reduce N·T or increase Q.

There is a correlation between the mill rotation speed N and the torque T, and NT in equation (2) is constant under constant grinding conditions. Therefore, in order to reduce the crushing power, it is sufficient to increase the throughput Q according to equation (2).

In order to increase the throughput under constant grinding conditions, it is necessary to improve the grinding efficiency of the mill. Therefore, the present researchers considered the behavior of the grinding balls, which are thought to have a large effect on the grindability of the mill.

Figure 2 shows a model of the behavior of the balls during wet grinding. In general, a tube mill rotates a cylindrical main body 2 to scrape up the grinding balls 22 filled in the main body above the mill, and then progress the grinding by impact and friction when they fall. It is something. In the case of dry pulverization, the coal is pulverized by the impact when the balls are scraped up in two directions and fall to the bottom of the mill.

On the other hand, in high-concentration wet grinding for CWM production, the CWM medium has a high viscosity of about 1000 cp, so the movement of the grinding balls is suppressed. Therefore, as shown in FIG. 2, it is thought that pulverization mainly occurs due to friction on the ball surface.

This frictional pulverization mainly occurs in the tube mill used to manufacture the CWM that is the subject of this patent, and therefore, it is effective to increase the number of times the balls rub against each other as a way to improve the efficiency of wet pulverization. It is expected that To this end, it is considered that the ball distribution should be adjusted so that the number of contact points between the balls that cause friction is large. In order to increase the number of contact points, the system can be tightly packed.

Here, the inventors believe that if the particle size is adjusted so that the balls are in a tightly packed system when they are stationary, the balls will be close to a tightly packed state even during wet grinding, and therefore the number of contact points will be large. It was thought that the pulverization efficiency would be increased.

The method of tightly packing particles has been studied for a long time, and F
Urnas formula (Furnas, C, C, Gradin
gaggregates.

I-Mathematj, ca], relatj, o
ns for beds of broken,
i, ds of maxj, mum densj, ty
, Ind, Eng, Chem, 23.9pp1052~
1058(], 931)) are typical. Furna
The s-formula is mathematically equivalent to the formula (1). According to Furnas, the closer Ds to 1-+ is to O in the equation (), the more closely packed the particles become. Therefore, when we measured the number of contact points of the ball when changing the distribution index n as Ds”O, we found that n
It was experimentally clarified that the smaller the number of contact points, the more the number of contact points increases. From this, it is considered that wet grinding using balls adjusted to reduce the value of n improves the grinding efficiency.

In order to verify this, domestic coal A was continuously wet-pulverized at a high concentration according to the flow shown in Figure 1. Tube mill has an inner diameter of 5
00φ and length looonw+ was used. The feed rates of coal and surfactant solution were controlled such that the coal concentration in the CWM was 63 wt% in the mill. Further, as a surfactant, anionic Naphthalene sulfonate Na was added in an amount of 0.5 wt% based on the weight of the coal.

Four types of grinding balls with different diameters were used, and the distribution was adjusted in advance so that n was 0.1 to 3.8 according to equation (1). Table 1 shows the grinding ball diameter and filling amount when n=0.1 to 3.8. Total filling amount is 325-32
The weight is 6kg, but this is because the ball filling volume is approximately 35vo1% of the mill volume.
These are commonly used filling conditions. Here, the particle size distribution index was determined by setting DS=O in equation (1).

Table 1 Ball filling amount (kg) Ds”O was chosen because the higher Ds is, the higher the ball filling rate is and the number of contact points between the ball and the pusher increases.
This is because it is thought that the pulverization efficiency is improved. C.W.M.
Manufacturing experiments were conducted for each of the five ball combinations shown in Table 1. 2. of the coal particles in the obtained CWM. OOm
FIG. 3 shows the relationship between the amount of e and sh passes and the distribution index.

In normal coal combustion thermal power, coal is pulverized and burned so that the amount of 2.00 mesh passes is 70-80 wt%.

It is thought that the same standard is required for CWM, so in this experiment, 2 Q Qme was used as an index of pulverization efficiency.
The sh pass amount was used.

From Figure 3, when the distribution index is 0.4 to 3.5, 200
It is clear that the mesh pass amount increases and the grinding efficiency becomes higher. The reason why the crushing ability decreases when n<0.4 is due to the number of balls having a small diameter. As can be seen from Table 1, when n=0.1, the number of balls with a diameter of 26.4I or less is extremely large compared to the number of balls with a diameter of 26.4r@ or more. Such a small diameter ball is 1
Since the weight per piece is small, frictional movement is suppressed in high viscosity media. Therefore, it is considered that the pulverization efficiency decreased when n = O, 1. As described above, there is an appropriate value for the distribution index n, and this patent discloses this. In the past, the distribution index was empirically adjusted to about 3.8, but according to this patent, the atomization efficiency of the conventional pulverization method can be greatly improved.

In Figure 3, the particles in the crushed slurry are atomized when n = 0.4 to 3.5.
If the balls are adjusted to , the amount of pulverization Q to obtain slurry of the same particle size can be increased, and the required pulverization power can be reduced from equation (2).

The present inventors have discovered that the grinding performance of the mill can be improved by adjusting the ball distribution within the tube mill as described above,
This disclosed a method for reducing the crushing power in the CWM manufacturing process.

[Example 1] C, W MH production experiments were conducted using domestic coal A coal.

The mill used was a tube mill with an inner diameter of 50Qφ and a length of 1000+ nm. The manufacturing flow was as shown in FIG.

Raw coal was previously coarsely pulverized into 8 fields or less, temporarily stored in a hopper 1, and continuously fed into a mill using a screw feeder 2. The surfactant solution was supplied to the mill simultaneously with the coal using a metering pump 4. The feeding rate of coal and surfactant solution is
The coal concentration of CWM in the mill is 63 wt%, and the particle size of CWM overflowing from the mill outlet is 20 mesh bus 7
It was adjusted to be 0%. The surfactant was added in an amount of 0.5 Wt% based on the coal.

The rotation speed of the mill was kept constant at 25 rpm. The ball filling rate was 35vo]% (total filling amount: 325 kg). Grinding experiments were conducted using five types of ball distribution shown in Table 1.

The evaluation of the crushing test was based on the CW overflowing from the mill outlet.
I followed M.

The right side of equation (2) was used as the grinding power unit.

For this purpose, the torque of the mill was measured. Furthermore, the pulverization throughput Q on the right side of equation (2) was taken as the CWM outflow rate from the mill outlet.

In Figure 4, using each ball distribution in Table 1, 200mes
Pulverization processing amount Q when manufacturing CWM with h pass amount of 70%
The power intensity was shown. Conventionally, the distribution index was adjusted to approximately 3.8, so in order to compare with this, n, = 3.
When a ball distribution of , 8 is used, the power unit required to manufacture the CWM is set to 1.

It was confirmed that by adjusting the distribution index n to 0.4 to 3.5, the basic unit could be reduced to 70 to 90% of the conventional value.

[Example 2] Until now, it was possible to improve the pulverization efficiency by adjusting the distribution index n, but the present inventors also increased the contact points by reducing the maximum ball diameter D +, thereby increasing the atomization efficiency. I thought.

In equation (1), Ds ”O, n = 2, the maximum ball diameter Dt
When the number of contact points was measured when changing , from 30 to 80 nwn, the number of contact points increased as DL became smaller. Therefore, the crushing throughput and power unit ratio of the tube mill when the maximum ball diameter was changed were determined using the same method as in Example 1.

Table 2 shows the conditions for adjusting the balls tested. The ball distribution was set to Ds = O and n = 2 according to equation (1).

Table 1 Ball filling amount (kg) Figure 5 shows the relationship between the maximum ball diameter, crushing processing amount, and power consumption ratio.There is an appropriate value for the maximum ball diameter, and this should be 40 to 60 mm. It can be seen that the crushing power can be reduced.

〔Effect of the invention〕

According to the present invention, the crushing power required to manufacture CWM can be reduced, and manufacturing costs can be reduced. Further, with the same crushing power, finer CWM particles can be produced, and the maximum particle size of coal in CWM can be easily controlled (7).

[Brief explanation of drawings]

Fig. 1 is a basic conceptual diagram of the present invention, Fig. 2 is a behavior model of grinding balls in wet pulverization, and Fig. 3 is a pulverized coal
A diagram showing the relationship between the mesh pass amount and the ball particle size distribution index, Figure 4 is a diagram showing the relationship between the crushing throughput and the crushing power unit, and the particle size distribution index, and Figure 5 is a diagram showing the relationship between the crushing throughput and the crushing power unit and the particle size distribution index. FIG. 3 is a diagram showing the relationship between the grinding power unit and the maximum diameter of the ball. 1-...Hopper, 2...Feeder, 3...Additive tank, 4...Pump, 5...Tube mill, 6
...Tank, 7...Pump, 8...Filter, 9...
・Product tank, 21...Tube mill body, 22...
・Crushing ball, 23・Slurry.

Claims (1)

[Claims] 1. A step of supplying raw coal to a tube mill together with a third substance such as water, a surfactant, and an alkaline substance, a step of wet-pulverizing the coal in the tube mill, and a step of discharging the overflow from the tube mill. In a process consisting of a classification step to remove coarse particles contained in coal-water slurry, the particle size distribution of the grinding balls in the tube mill is determined by the particle size distribution index n in the following formula: R = (D^n - D_S^n)/ (D_L^n-D_S^
n)×100D: Arbitrary ball diameter (cm) D_L: Maximum ball diameter (cm) D_S: Virtual minimum ball diameter (cm) n: Distribution index R: Cumulative weight ratio under the sieve (wt%) 0.4 to 3. 5. A pulverization method for highly concentrated coal-water slurry. 2. Maximum ball diameter D_L in claim 1
60 mm or less, preferably 40 to 60 mm.