JPH0626679B2 - Wet mill operation control method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an operation control method for a wet mill for producing coal / water slurry, and more particularly to an operation control method for a wet mill suitable for operation at startup.

[Background of the Invention]

Fuel used in combustion equipment such as boilers is heavy oil or LNG.
There are liquid fuels such as and solid fuels such as coal. In recent years, a coal / water slurry prepared 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 during transportation and storage.

When this coal / water slurry (hereinafter referred to as CWM) is supplied to the burner of the boiler and directly burned, the coal concentration is about 6
High concentration of 0% (wt%) or more, and its particle size is 2
The passage amount of 00 mesh is adjusted to about 70 to 80%. Furthermore, in this case the CWM must be a stable, low viscosity liquid to allow pumping. As described above, in order to produce a stable CWM having a high slurry concentration, a low viscosity and a stable CWM, the packing density of particles is increased due to an error in a wide particle size distribution to increase the concentration, and the addition of a dispersant is added. Therefore, it is necessary to form a water film on the surface of the particles, charge the particles, and disperse the particles to reduce the viscosity. A continuous wet ball mill is usually used to manufacture such a CWM.

FIG. 4 is a system diagram of a CWM manufacturing facility using a continuous wet ball mill. In the figure, A is coal, B is water, and C is an additive liquid. 1 is a bunker for storing coal A, 2 is a coal feeder for feeding coal from the bunker 1, and 3 is a wet mill. 4 is a tank for storing the water B, S is a tank for storing the additive liquid C, 6 is a pump for supplying the water in the tank 4 into the wet mill 3, and 7 is a tank for storing the additive liquid C in the tank 5 in the wet mill 3. It is a pump that supplies to. 8 is a slurry adjusting tank for receiving the slurry produced by the wet mill 3, 9 is a pump for sending the slurry from the slurry adjusting tank 8, and 10 is a coarse particle separator for separating coarse particles in the slurry supplied from the pump 9. is there. 11 is a screen in the coarse particle separator 10, 12 is an outlet for discharging the slurry D that has passed through the screen 11 as CWM, 13 is an outlet for discharging coarse particles that have not passed through the screen 11, 14
Is a coarse particle slurry recovery pipe for returning the coarse particles discharged from the discharge port 13 into the wet mill 3. The coarse particles recovered through the coarse particle slurry recovery pipe 14 are re-ground in the wet mill 3.

CWM is continuously produced by the above-mentioned equipment, but as described above, in order to produce stable CWM having a predetermined particle size, high concentration and low viscosity, an appropriate slurry is prepared in the wet mill 3. It is necessary to maintain the concentration and to appropriately grind the residence time of the coal particles in the wet mill 3. However, conventionally, a method of producing a large amount of low-concentration and low-viscosity slurry (waste slurry) at the time of starting the wet mill 3 is adopted, and the amount of this waste slurry is 2 to the ball porosity in the wet mill 3. This is an amount corresponding to three times the volume. This will be described with reference to the drawings.

FIGS. 5 (a) and 5 (b) are characteristic diagrams of respective values when the conventional starting method is used. FIG. 5 (a) shows the amounts of coal and water supplied to the wet mill 3, with the horizontal axis representing time and the vertical axis representing the respective amounts. Further, FIG. 5 (b) shows the flow rate, viscosity, coal concentration and the amount of coal particles passing through 200 meshes produced by the wet mill 3, and the horizontal axis shows time on the same scale as in FIG. 5 (a). Each value is plotted on the vertical axis. The starting method in this case is to fill water and additives in the wet mill 3 in advance, and start a start of the wet mill 3 with a predetermined amount of coal, water,
And the method of supplying additives. According to this method, since the wet mill 3 is already filled with water at the time of start-up, even if coal is supplied, the slurry produced will reach the predetermined coal concentration by the time shown in FIG. 5 (b). As you can see, it takes about 8 hours. During the 8 hours, as shown in FIG. 5 (b), the wet mill 3 discharges a low-concentration slurry having an extremely low coal concentration, and this slurry is immediately separated into water and coal. , Coal particles settle. For this reason, not only is it difficult to handle the waste slurry, but it is unavoidable to support the slurry production.

A start-up method for reducing such defective slurry (waste slurry) has been separately proposed. FIGS. 6 (a) and 6 (b) are characteristic diagrams of respective values when this starting method is used, and are shown in the same manner as in FIGS. 5 (a) and 5 (b). The starting method in this case is a method of supplying a predetermined amount of coal and water with the inside of the wet mill 3 being emptied in advance (the state where only the balls are filled) at the time of starting. According to this method, as shown in FIG. 6 (b), the slurry is started to be discharged from the wet mill 3 about 2.5 hours after the start, and after about 4 hours, a predetermined slurry flow rate of 95% is reached.
Reach%. In this case, the coal concentration reached a predetermined concentration (about 66%) as shown in the figure when the slurry flowed out, but the coal particle size (200 mesh passage amount) was as high as 82%. this is,
This is because the retention time of the coal particles in the wet mill 3 increases at the time of startup. That is, the average retention time of the coal particles in the wet mill 3 in the high-concentration coal / water slurry is about 1.5 to 2.0 hours in a steady state (depending on the nature of the coal), but in the above method, before starting Since the inside of the wet mill 3 is empty, it takes about 1.5 to fill it with slurry.
Needs 2.0 hours. Thus, the retention time of the coal particles fed into the wet mill 3 at the beginning of startup is almost 2 in the steady state.
It is considered that the coal is over-crushed and the particle size of the coal is increased, and the slurry viscosity is also increased.

After all, it is unavoidable that a large amount of slurry (waste slurry) deviating from the predetermined particle size and viscosity is generated by any of the above-mentioned conventional methods, and it takes 4 to 8 hours until a steady state is reached after startup. It also has the drawback of requiring a long time.

[Object of the Invention]

An object of the present invention is to solve the above-mentioned problems of the prior art, prevent the generation of waste slurry at the time of starting the wet mill, and control the operation of the wet mill that can reach a steady state in a short time. There is a way to provide.

[Outline of Invention]

In order to achieve the above object, the present invention sets the amount of coal supplied at the time of starting the wet mill to 2 to 3 times the set amount of coal supplied in a steady operation state, and the average retention time of the coal particles in the wet mill. The feature is that the coal supply amount is gradually reduced so as to reach a predetermined coal supply amount later.

Example of Invention

 Hereinafter, the present invention will be described based on the illustrated embodiments.

FIG. 1 (a) is a characteristic diagram showing the supply of coal and water in the operation control method according to the embodiment of the present invention, and FIG. 1 (b) is the first diagram.
It is a characteristic view of each value when the supply method shown in FIG. In FIGS. 1 (a) and 1 (b), the horizontal axis shows time on the same scale, and the vertical axis shows each value. As aforementioned,
In the conventional method, when the wet mill 3 is started, the wet mill 3 is filled with water in advance and a predetermined amount of coal or water is supplied thereto, or the wet mill 3 is emptied in advance. ,
Although a method of supplying a predetermined amount of coal and water to this was adopted, in the method of the present embodiment, as shown in FIG. It supplies about 3 times the specified amount. That is, the predetermined slurry viscosity (about 1000c
P), the coal supply amount (predetermined amount) needs to be about 33 kg / h in order to obtain a predetermined particle size (200 mesh passing amount 72%). It supplies three times as much coal. Then, in order to keep the coal concentration in the wet mill 3 constant, the amount of water supplied is about three times the predetermined amount. In this embodiment, after that, as shown in FIG.
As shown in (a), the amount of coal and the amount of water are gradually reduced, and the amount of coal supplied and the amount of water are set to predetermined amounts approximately 1 hour and 30 minutes after startup. By adopting such a method, as shown in FIG. 1 (b),
Slurry begins to flow out from the wet mill 3 about 1 hour and 30 minutes after starting, and the slurry satisfies predetermined values for slurry viscosity, coal concentration and 200 mesh passage amount. That is, a slurry having a slurry viscosity of about 1000 cP, a coal concentration of about 65%, and a grain size of 200 mesh passing 71% was obtained, and these values are always stable after the slurry flows out.
Then, the slurry flow rate of such a slurry reaches a steady state in about 2 hours after starting. This is because the method of the present embodiment can prevent the generation of over-pulverization by averaging the retention time of the coal particles in the wet mill 3, and the slurry discharged from the wet mill 3 has a predetermined quality. Satisfactory, no generation of waste slurry. Further, in the conventional method, it took about 4 hours or more after starting to reach the steady state, whereas in the method of this embodiment, the steady state is reached in about 2 hours after starting, and the required time is greatly shortened. .

FIG. 2 shows a graph modeling this embodiment. In the figure,
The horizontal axis represents time, and the vertical axis represents coal supply. θ is the average staying time, and F ₁ is the predetermined coal supply amount. In the case of the above embodiment, the coal supply amount at the time of start-up at time 0 is 3F ₁ , but in this figure, the coal supply amount is not necessarily limited to the value 3F ₁ , and the value 2F ₁ and the value 3F _1.
It is shown that it should be between F ₁ and it. At startup,
The coal supply amount selected within the range of the values 2F _{1 to} 3F ₁ is gradually reduced to the predetermined coal supply amount F _{1 in} the average staying time θ, and thereafter the predetermined coal supply amount is continuously supplied. .
The line showing the reduction of the coal supply amount is within the range shown by the hatching in the figure.

Here, the basis for calculating the average residence time in the wet mill 3 will be described. Now, each value is represented as follows.

V: Volume in the wet mill J: Ball filling rate ρ _s : Slurry density: Coal concentration W: Coal amount At this time, the coal amount W is as follows.

W = 0.4 × (1.5 to 2.0) ρ _s ·· V · J where 0.4 indicates the void ratio of the ball, and 1.5 to
2.0 is a value indicating the hold-up amount of the slurry under the operating condition and is a value calculated from the experimental result. And
When the amount of coal supplied is F, the average retention time θ of coal particles in the wet mill can be expressed by θ = W / F 2.

FIG. 3 (a) is a characteristic diagram showing the supply of coal and water in the operation control method according to another embodiment of the present invention, and FIG. 3 (b) is the supply method shown in FIG. 3 (a). It is a characteristic view of each value in the case. The method of this example is different from the method of the previous example, whereas the method of the previous example reduces the coal supply amount and the water amount linearly after starting, whereas the method of the present example. Differs in that these are gradually reduced,
Other points are the same. As is clear from comparison between FIG. 3 (b) and FIG. 1 (b), in this case, the characteristics of the slurry flowing out from the wet mill 3, the outflow start time and the steady state arrival time Is the same as in. Therefore, the effect of this embodiment is the same as the effect of the previous embodiment.

In addition, in each of the above-described embodiments, an example in which the coal supply amount at the time of start-up is about three times the coal supply amount at the steady state is shown, but this is three times as described in the description of FIG. However, it is not limited thereto, and can be selected to be about 2 to 3 times.

〔The invention's effect〕

As described above, in the present invention, at the time of starting the wet mill, the amount of coal supplied is 2 to 3 times the amount of coal supplied in the steady state, and reaches the amount of coal supplied after the average retention time of coal particles. Since it has been gradually reduced, it is possible to prevent the generation of waste slurry at the time of starting the wet mill.
Moreover, the steady state can be reached in a short time.

[Brief description of drawings]

1 (a) and 1 (b) are views showing the method according to the embodiment of the present invention and the characteristics of the slurry produced thereby, and FIG. 2 is a model of the coal supply method according to the embodiment of the present invention. Figure showing,
FIGS. 3 (a) and 3 (b) are diagrams showing characteristics of a method according to another embodiment of the present invention and slurry produced thereby, and FIG. 4 is a system diagram of a CWM manufacturing facility using a wet mill, Fig. 5
(a) and (b) are figures showing the characteristics of each value when the conventional starting method is used, and FIGS. 6 (a) and (b) are the values when each other conventional starting method is used. It is a figure which shows a characteristic. 1 …… Bunker, 2 …… Coal feeder, 3 …… Wet mill, 8 ……
Slurry adjusting tank, 10 ... Coarse grain separator.

Claims (1)

[Claims] 1. In a wet mill for supplying coal and water and crushing the coal to produce a coal / water slurry, the supply amount of coal at the start-up of the wet mill is set to 2 of a set supply amount of coal in a steady operation state. A method for controlling the operation of a wet mill, characterized in that the supply amount of the coal is gradually reduced so as to reach a predetermined coal supply amount after an average retention time of the coal particles in the wet mill.