JPH0761454B2 - Operation method of high concentration coal-water slurry mill - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for operating a mill for high-concentration coal-water slurry, and particularly to the operation of the mill without producing a bad slurry when the mill is stopped. On how to do.

[Prior Art] Fuels used in combustion devices such as boilers include fluid fuels such as heavy oil and LNG, and solid fuels such as coal. A coal-water slurry obtained by suspending coal with an additive such as a surfactant and water to form a slurry has attracted attention as a boiler fuel because it facilitates handling of transportation and storage. This coal-water slurry is generally called CWM and has a coal concentration of about 60 when burned directly.
%, The particle size is about 7 when passing through 200 mesh.
Adjusted to 0-80%. Also in this case the CWM must be a pumpable and stable low viscosity liquid. Conditions for producing a stable CWM having a high slurry concentration, a low viscosity, and the following conditions (1) and (2). That is, (1) the packing density of particles is increased by adjusting a wide particle size distribution to increase the concentration, and (2) a water film is formed on the surface of particles by addition of a dispersant to be charged to disperse the particles, thereby lowering the viscosity. Down. When continuously manufacturing such CWM,
A method using a continuous wet ball mill is generally used.

Figure 2 shows a system diagram of the CWM manufacturing facility using a continuous wet ball mill. Coal A is supplied from the bunker 1 to the inside of the mill 3 via the coal feeder 2, and the water B and the additive liquid C are supplied from the respective tanks 4 and 5 to the inside of the mill 3 from the respective pumps 6 and 7. The CWM produced in the mill 3 is discharged to the slurry adjusting tank 8 and the coarse particle separator 10 is pumped by the pump 9.
Can be supplied to. A screen 11 is installed in the coarse particle separator 10 and a slurry having a predetermined particle diameter is taken out as a product D from an outlet 12. The coarse particles separated by the coarse particle separator 10 are returned to the inside of the mill 3 through the discharge port 13 and the coarse particle slurry recovery pipe 14 and are pulverized again.

[Problems to be solved by the invention]

When CWM is continuously produced in this way, in order to produce stable CWM having a predetermined particle size, high concentration and low viscosity, the inside of the mill 3 is maintained at an appropriate slurry concentration and coal is It is necessary to properly control the residence time of the particles in the mill and to grind. However, in actual operation of the mill, it is conceivable that start and stop will occur frequently. Especially when stopped, a large amount of slurry in the mill flows out of the system. This is because the mill is operating with the hold-up amount of slurry in the mill increasing. The hold-up amount of slurry in the mill depends on the rotation speed and viscosity of the mill, but as shown in Fig. 3, the hold-up amount is 1.5 to 2.0.
I understand that it is big. Here, the hold-up amount Us of the slurry in the mill can be expressed by the following equation (1).

Us = V _mill × J × 0.4 (1) V _mill : Mill internal volume (m ³ ) J: Ball volume filling rate (-) 0.4: Ball space rate (-) Hold-up amount during operation is 1.5 to 2.0 Therefore, the amount of slurry that flows out when the mill is stopped is around 0.6
Equivalent to 1.1. This amount of slurry is the amount of slurry for about 1 hour during steady operation of the mill, and neither viscosity nor particle size satisfy the predetermined properties. 4 and 5 show an example of slurry outflow characteristics and properties when the mill is stopped. Mills and feeds (water, coal, additives)
Stop, the flow from the mill increases and after the mill stops,
The slurry flow rate becomes zero in a few minutes. That is, it can be seen that the hold slurry in the mill flows out of the system when the mill stops. However, it is found that the slurry at the time of outflow does not satisfy the predetermined particle size and viscosity. As shown in Fig. 6, the particle size of 200 mesh is about 7-9.
%, And the viscosities are almost the same as shown in FIG. 5, but the stability of the slurry is poor because a large amount of coarse particles are mixed in the slurry. That is, there is a drawback that sedimentation is fast. In any case, such an outflow slurry when the mill is stopped cannot be used as a product, so a method of treating it as waste slurry is adopted.

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

[Means for solving problems]

The present invention has a coal concentration of 60% by weight or more of high-concentration coal-when the mill is stopped from the steady operation of the mill when producing water slurry, after stopping the supply of coal to the mill, water and additives, The operation time of the mill, which is 1/2 to 1/4 of the average residence time of the coal particles in the mill, is set, and the operation of the mill is stopped after this operation time has elapsed.

[Action]

After stopping the supply of coal, water and additives supplied during the steady operation of the mill, and then operating the mill with the same rotation speed of the mill as during the steady operation, the flow rate of the slurry flowing out from the mill gradually decreases. To 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 to stop the supply of raw material to the mill
Optimum setting of T ₁ and time T ₂ for stopping the operation of the mill, that is, by setting the operation time of the mill to be 1/2 to 1/4 of the average residence time of coal particles in the mill, The slurry that flows out can be made into product slurry without being made into waste slurry. This set time is for the production of high-concentration coal-water slurry with a coal concentration of 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 represents time and the vertical axis represents each physical quantity. That is, the coal, water,
In order to clarify the amount of additive, the flow rate of slurry, and the stop time of the mill, the rotation speed of the mill is shown. In FIG. 1, when shifting from the steady operation of the mill to the stop of operation, first, the supply of coal, water, and additives required for slurry production into the mill is stopped. As shown in FIG. ₁ , a state of steady operation is shown from time T ₀ to time T ₁ , and at time T ₁ , the supply of coal, water and additives is stopped. However, even at time T _2, the mill is operated at the same rotational speed as between T ₀ -T _1. During that time, the flow rate of the slurry flowing out from the mill gradually decreases after time T ₁ . This is coal, which is a raw material for slurry production,
This is because water and additives were stopped at time T ₁ . The slurry flow rate decreases, and at time T ₂ , the hold-up amount of the slurry in the mill (see FIG. 3) is high, so that the slurry flows out of the mill again, and at time T ₃ , the amount becomes zero. In the above stop characteristics, the amount of slurry flowing out of the mill after time T _{1 or} T ₃ is 10 to 15 times the inner volume of the mill as shown in Table 1.
Equivalent to%. 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 similar to the target values.

Next, the optimum conditions of the time T ₁ when the supply of the raw material to the mill was stopped and the operation stop time T ₂ of the mill were examined. Since during the time T ₂ -T ₁ before stopping the mill raw material is stopped, is ground in a mill have been made, this time due to the properties of the slurry (particle size, viscosity). Therefore we investigated the properties of the slurry at the time of changing the T ₂ -T _1. The results are shown in Table 2.

From Table 2, assuming that the average residence time of coal in the mill is Θ, the time T ₂ −T ₁ is 1/2 to 1/4 Θ, which is the value closest to the target value (property during steady operation). I understand. If this time (T ₂ −T ₁ ) is larger than 1/2 to 1 / 4Θ, the grain size (200 mesh pass) is 73% of the target value due to over-milling in the mill.
%, Increased by 7%, and the viscosity reaches 2200 cP.
Conversely, when the time (T ₂ −T ₁ ) is short, (T ₂ −T ₁ <1 /
4Θ) The grain size of the slurry is coarse and the 200 mesh pass amount drops to 68%.

By optimizing the time T ₁ for stopping the supply of the raw material to the mill and the time T ₂ for stopping the operation of the mill as described above,
It can be seen that a large amount of slurry that flows out when the mill is stopped can be used as a product.

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

When the volume V in the mill, the ball filling rate J, the slurry density Ps, and the coal concentration ζ are used, the coal amount W in the mill can be expressed by the following equation (2).

W = 0.4 × (1.5 to 2.0) PsζVJ …… (2) where 0.4 is the porosity of the ball. 1.5 to 2.0 are values indicating the hold-up amount of the slurry under operating conditions, which are calculated from the experimental results.

Therefore, the average residence time Θ of coal particles in the mill is given by the following equation (3), where F is the amount of coal supplied. Can be expressed as

〔The invention's effect〕

As described above, according to the present invention, it is possible to prevent waste slurry from being generated from the mill during steady operation of the mill and when the mill is stopped. Therefore, it is possible to always treat the slurry with stable properties and to easily handle the slurry. Becomes

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing an example of an operating method of a CWM mill according to the present invention, FIG. 2 is a system diagram of a wet tube mill, and FIG. 3 is a relation between a hold-up amount in a mill and a mill rotation speed. Graphs, FIGS. 4 and 5 are characteristic diagrams of a conventional tube mill stopping method, and FIG. 6 is a particle system distribution of outflow slurry when the conventional mill is stopped and a slurry particle system distribution during steady operation. It is a graph which shows and compares. 1 ... Bunker, 2 ... Coal feeder, 3 ... Ball mill, 4,5 ... Tank, 8 ... Slurry adjusting tank, 10 ... Coarse grain separator, 11 ... Screen.

Claims (1)

[Claims] 1. A method for operating a mill for producing a coal-water slurry having a coal concentration of 60% by weight or more from continuously supplied coal, water and an additive, which is stopped from a steady operation.
After stopping the supply of each of coal, water and additives that are being supplied during steady operation of the mill, set the operating time of the mill that is 1/2 to 1/4 of the average residence time of coal particles in the mill. ,
A method for operating a mill for high-concentration coal-water slurry, which is characterized in that the operation of the mill is stopped after this set time.