JPS62247845A - Method of operating mill for high-concentration coal-water 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 Application Field] The present invention relates to a method for operating a mill for highly concentrated coal-water slurry, and particularly to a method for operating a mill without producing defective slurry when the mill is stopped. Regarding how to.

[Conventional technology]

Fuel used in combustion equipment such as boilers includes heavy oil and LNG.
There are liquid fuels such as coal, and solid fuels such as coal. Coal-water slurry, which is made by suspending coal in water and additives such as surfactants, is attracting attention as a boiler fuel because it is easy to handle during transportation and storage. This coal-water slurry is generally called CWM, and when directly combusted, the coal concentration is about 60% or more, and the particle size is 200 Mes
The amount of h passing through is adjusted to about 70-80%. In this case, the CWM must also be a pumpable, stable, low viscosity liquid. The following conditions (1) and (
There is a condition 2). In other words, (1) increasing the packing density of particles by adjusting a wide range of particle size distribution to achieve high concentration;
) By adding a dispersant, a water film is formed on the surface of the particles to accumulate electricity, thereby dispersing the particles among themselves and lowering the viscosity. CW like this
When manufacturing M continuously, a method using a continuous wet ball mill is common.

Figure 2 shows a system diagram of CWM manufacturing equipment using a continuous wet ball mill. Coal A is supplied into the mill 3 from the bunker 1 via the coal feeder 2, and water B and additive liquid C are supplied into the mill 3 from the respective tanks 4 and 5 through the respective pumps 6 and 7. . CWM manufactured in Mill 3
is discharged into a slurry adjustment tank 8 and supplied to a coarse particle separator 10 by a pump 9. The coarse particle separator 10 has a screen 1
1 is installed, and the slurry having a predetermined particle size is discharged through the discharge port 12.
It is taken out as a finished product. The coarse particles separated by the coarse particle separator 10 are returned to the mill 3 through the discharge port 13 and the coarse particle slurry recovery pipe 14, and are re-pulverized.

[Problems to be Solved by the Invention] When producing CWM continuously in this way, in order to produce stable CWM with a predetermined particle size, high concentration, and low viscosity, it is necessary to maintain proper slurry concentration,
It is necessary to properly control the residence time of coal particles in the mill for pulverization. However, in actual mill operation, starting and stopping may occur frequently. Especially when the mill is stopped, a large amount of slurry inside the mill flows out of the system. This is because the mill is operated with an increased hold-up amount of slurry in the mill.

The hold up amount of the slurry in the mill varies depending on the mill rotation speed, viscosity, etc., but as shown in FIG. 3, the hold up amount is as large as 1.5 to 2.0. Here, the hold-up amount Us of the slurry in the mill can be expressed by the following equation (1).

U s = V m1LL X J X 0, 4-
-----(ilVlliLL: Mill internal volume (n?) J: Ball volume filling rate (-) 0.4=Boll space ratio (-) Hold up amount during operation is 1.5 to 2.0 Because of the high temperature, the amount of slurry that flows out when the mill is stopped is held up.
This corresponds to 0.6 to 1.1. This amount of slurry is equivalent to approximately one hour's worth of slurry during steady operation of the mill, and the viscosity,
Neither the particle size nor the specified properties were satisfied. FIGS. 4 and 5 show an example of the slurry outflow characteristics and properties when the mill is stopped. When the mill and feeds (water, coal, additives) are stopped, the flow rate from the mill increases until the slurry flow rate reaches zero within a few minutes after the mill is stopped.

In other words, it can be seen that the ball slurry inside the mill flows out of the system when the mill stops. However, it can be seen that the slurry upon discharge does not meet the predetermined particle size and viscosity. As shown in Figure 6, the particle size is 200.
As shown in Figure 5, the viscosity is almost the same, but the stability of the slurry is poor because a large amount of coarse particles are mixed in the slurry. bad. In other words, it has the disadvantage of rapid sedimentation. In any case, the slurry that flows out when the mill is stopped cannot be used as a product, so a method is adopted in which it is disposed of as waste slurry.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, eliminate the generation of waste slurry when the mill is stopped, and eliminate the feed (
An object of the present invention is to provide a method of operating a mill for high concentration coal-water slurry, which can maintain a high amount of product slurry relative to the amount of water, coal, and additives.

[Means to solve the problem]

The present invention has the advantage that when the mill is in steady operation and when the mill is stopped, the properties of the slurry flowing out from the mill after stopping the supply of coal, water, and additives to the mill are almost the same as the properties of the slurry during mill operation. The operating time of the mill is set so that the operating time is reached, and the operation of the mill is stopped after this operating time has elapsed. Especially when the coal concentration is 60% by weight or more, the set time is 1/2 to 1/4 of the residence time of coal particles in the mill.
It is desirable to do so.

[Effect]

After stopping the supply of coal, water, and additives that are supplied during steady operation of the mill, if the mill is operated at the same rotation speed as during steady operation, the flow rate of slurry flowing out of the mill will gradually decrease. do.

At this time, if the coal is over-pulverized in the mill, the particle size becomes too small and the viscosity increases. Therefore, the time T for stopping the supply of raw materials to the mill and the time T2 for stopping the operation of the mill are set optimally, that is, they are set so that the properties of the slurry flowing out from the mill are the same as the properties of the slurry during steady operation of the mill. Then, the slurry flowing out from the mill can be used as product slurry instead of being used as waste slurry. This set time is set to 1/2 to 1/4 of the average residence time of coal particles when the coal temperature is 60% by weight or more.

〔Example〕

FIG. 1 is a characteristic diagram showing an example of the operating method of the present invention.

In this characteristic diagram, the horizontal axis shows time, and the vertical axis shows each physical quantity. In other words, the coal, water, and
Mill rotation speed is shown to clarify additive amount, slurry flow rate, and mill stop time. In FIG. 1, when the mill shifts from steady operation to shutdown, first the supply of coal, water, and additives necessary for slurry production into the mill is stopped. Time T as shown in FIG. The period from to T indicates a steady state of operation, and at time T, coal,
Stop water and additive supply.

However, even at time T2, Mill is T. - It is operating at the same rotation speed as during T1. Meanwhile, the flow rate of slurry flowing out from the mill gradually decreases after time T. This is because the raw materials for slurry production, such as coal, water, and additives, were stopped at time TI. The slurry flow rate decreases, and at time T2, since the hold-up amount of slurry in the mill (see FIG. 3) is high, the slurry flows out of the mill again, and at time T3, the amount becomes zero. In the above-mentioned stopping characteristics, the amount of slurry flowing out from the mill from time T to T3 corresponds to 10 to 15% of the internal volume of the mill, as shown in Table 1. However, in the operation example of the present invention, as is clear from Table 1, the properties of the slurry flowing out from the mill are equivalent to the target values.

Next, the time T+ when the supply of raw materials to the mill is stopped
We investigated the optimal conditions for the mill operation stop time T2. Since pulverization is performed in the mill during the time Tt T+ from when the raw material is stopped until the mill is stopped, this time is caused by the properties of the slurry (particle size, viscosity). So Tz”
The properties of the slurry were investigated when I'+ was varied. The results are shown in Table 2.

From Table 2, it can be seen that when the average residence time of coal in the mill is θ, the value closest to the target value (properties during steady operation) for time T2-T is obtained between 1/2 and 1/4θ. Recognize. When this time (T 2 T l ) is larger than 1/2 to 1/4 θ, the particle size (200 mesh bath amount) increases by 7% compared to the target value of 73% due to over-pulverization in the mill. , the viscosity reaches as high as 2200 cP. On the other hand, time (T
2 T 1) is short, (Tz-T, <1/
4θ) The particle size of the slurry is coarse, and the amount of 200 mesosie passes is 6
This decreases to 8%.

As mentioned above, the time ′r1 for stopping the supply of raw materials to the mill
It can be seen that by optimizing the time T2 for stopping the mill operation, a large amount of slurry flowing out when the mill is stopped can be sufficiently utilized as a product.

The method for calculating the average residence time of coal in the mill will be described below.

Volume inside the mill■, ball filling rate, workpiece, slurry density Ps'
-Coal concentration, in other words, the amount W of coal in the mill can be expressed by the following equation (2).

W = 0.4 X (1,5~2.0) P S ζ
V J, ------- (21 Here, 0.4 indicates the void ratio of the ball. 1.5 to 2.0 is a value indicating the hold-up amount of the slurry under operating conditions. This is calculated from the results.

Therefore, the average residence time θ of coal particles in the mill is expressed by the following formula (3), where F is the coal supply amount. Since waste slurry from the mill can be prevented from being generated when the mill is stopped, slurry with stable properties can be processed at all times, and the slurry can be easily handled.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing an example of the operating method of the CWM mill according to the present invention, FIG. 2 is a system diagram of a wet tube mill, and FIG.
The figure is a graph showing the relationship between the hold-up amount in the mill and the mill rotation speed, Figures 4 and 5 are characteristic diagrams of the conventional tube mill stop method, and Figure 6 is the outflow when the mill is stopped using the conventional method. It is a graph showing a comparison between the particle size distribution of slurry and the particle size distribution of slurry during steady operation. 1...Banka, 2...Coal feeder,
3...ball mill, 4.5...tank, 8...slurry adjustment tank, 10...
Coarse particle separator, 11... Screen.

Claims (3)

[Claims] (1) In an operating method in which a mill for producing a coal-water slurry from continuously supplied coal, water and additives is stopped from steady operation, the coal, water and additives that are supplied to the mill during steady operation are After stopping the supply of each agent, set the mill operation time so that the properties of the slurry flowing out from the mill are almost the same as the slurry properties during steady operation of the mill, and stop the mill operation after this set time. A method of operating a mill for highly concentrated coal-water slurry, characterized by: (2) The coal concentration of the highly concentrated coal-water slurry produced in the mill is 60% by weight or more.
) A method of operating a mill for highly concentrated coal-water slurry as described in item 2. (3) The method of operating a mill for high concentration coal-water slurry according to claim (1), wherein the set time is 1/2 to 1/4 of the average residence time of coal particles in the mill.