Tower mill

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The barrel of the agitating mill is equipped with a blade type stirring device and a ball medium (ceramic ball, glass ball, steel ball, etc.), and the stirring device rotates to rotate the ball medium, thereby generating impact, shearing and grinding action to grind the material. .
According to the structural characteristics of such a sail, it can be divided into a tower type, a stirring tank type, a flow tube type and a ring type, and the like can be used as an ultrafine mill, a stirring mixer or a dispersing machine. According to the production method, it can be divided into dry and wet. In dry grinding, the pressure strength of the material particles increases, the surface energy of the particles increases, and the particles form agglomeration, which tends to adhere to the inner wall of the mill barrel. When wet grinding, the particle dispersion performance is good, resulting in particles. The surface energy is reduced to prevent coagulation between the particles, so wet grinding is better when superfine grinding.
First, the tower mill tower mill is actually a vertical cylinder vertical ball mill . The mill is composed of a vertical cylinder, a spiral agitating blade, a classifying device and a driving device. The specifications of the tower mill are expressed in terms of the inner diameter and height of the cylinder, that is, D × H.
Tower mills are also available in both dry and wet types. Figure 1 is a diagram of a closed-circuit production system of a wet tower mill. A spiral stirring blade (or agitator) is mounted on the main (vertical) shaft in the vertical cylinder, and is driven by the driving device of the motor.


Figure 1 Wet tower mill production system
1. Vertical circular cylinder; 2. Electric drive part; 3. Screw stirrer; 4. Classifier;
5, 7. sand pump pool; 6, 8. sand pump; 9. hydrocyclone

The rapid rotary motion is used to force the grinding medium and the material to be ground in the mixing drum to rotate strongly, so that the material is pulverized by grinding. The pulverized product flows into the classifier by the mill, and is classified by a hydrocyclone. The overflow is the grinding product, and the coarse particles are returned to the mill through the pipe and then ground.
In addition to the wet separation system, the dry tower mill has the same air separation system as the wet scrubber. The mill barrel, the spiral mixing blade and the spindle drive are exactly the same as the wet tower mill.
The basic grinding action of the tower mill is to strip and not impact, so the feed size can not be too large, generally less than 3 mm. The vertical installation of the grinding cylinder is mainly based on the following considerations: (1) The medium rotates in the horizontal plane under the action of the agitator, instead of acting in the vertical direction and parabolic motion like in the horizontal grinding machine, so that the grinding medium does not overcome Gravity works to save energy; (2) The tower mill has a small diameter and a large height, which increases the pressure between the grinding media, and increases the grinding force on the material when the grinding medium rotates; therefore, this The equipment is suitable for fine grinding and ultra-fine grinding of materials. The pressure of the grinding medium has a suitable range in which the grinding efficiency is high and the power consumption is low; when it exceeds this range, the grinding efficiency can no longer be increased; therefore, the height-to-diameter ratio (H/D) of the tower mill There should be a suitable value. The tower mill is mainly used for grinding and stripping, so the size of the grinding ball should not be too large. Generally, the maximum ball diameter is about 25 mm. When it is ultra-fine grinding, the size of the grinding media should be smaller.
This type of mill first appeared in 1953 and was used to replace the ball mill as a medium mine re-grinding. Laboratory and industrial tests have been carried out on tower mills at home and abroad. U.S. e.g. copper plant in New Mexico (Copper Flars) installation of a tower mill for regrinding molybdenum concentrate. Marcassa, Ontario, Canada installed a 200 kW tower mill to simultaneously pulverize and leach the tailings of the gold . The mill's production capacity for the tailings is 12.2 tons / hour, the tailings Bond's work index is about 14.5 kWh / ton, the tailings in the 325 mesh content is 45%, grinding to a 325 mesh accounted for 95% . The production test shows that the tower mill saves more than 60% of the electric energy compared with the general ball mill, and the investment is similar. The tower mill requires a small foundation and saves space, so the installation cost is much lower than that of the ball mill. [next]

Table 1 Product Size of Tower Mill 1 Superfine Grinding

Material name
Feeding average particle size, μm
Product average particle size, μm
talc
Silica
Barite
limestone
limestone
Pure iron sand
9
37
2.8
-74
-4000
-1680
1.9
1.7
1.55
3.1
2.4
2.0
1Kw-3 tower type grinding machine.

Table 1 shows the fineness of the product obtained by grinding different materials with a tower mill.
Table 2 shows a comparison of the results when using a ball mill and a tower mill to grind uranium ore. From the test results, it can be seen that the tower mill is more than twice as high as the ball mill, based on the energy consumed to produce one ton of material less than 200 mesh.

Table 2   Comparison of indicators between tower mill and ball mill when grinding uranium mine
project
Ball mill
Tower mill
Mill specifications, mm
Mill power, kW
Auxiliary equipment power, kW
Grinding medium weight, kg
Feeding size, mm
Grinding efficiency by production - 200 mesh, t / / kW
Power consumption by production - 200 mesh, kW.h/t
Φ600 × 200
2.24
0.75 (classifier)
Steel ball 250
-3
0.006~0.011
95.6~169.9
Φ400 × 2000(H)
3.7
2.24 (pump)
Uranium ore 230
-3
0.020~0.021
48.8~50.1
Table 3 shows the comparison of the working performance of the tower mill and the ball mill provided by a certain subsidiary of Kopper Corporation of the United States. In the table, examples A and B are laboratory test results; C is the result of the mill operation of the southern McKegen flue gas desulfurization system; and D is the application in the re-grinding circuit of the Raka Mining Company of the Klander Lake. Based on the company's test results, the following insights are obtained:
Table 3 Comparison of operating data between tower mill and ordinary ball mill
project
A
B
C
D
Tower mill model
Processing material
Work index, kW·h/t
Loop
Grading machine
Feeding size, mm
Tower mill net power consumption, Kw.h/t
F80,mm
P80, mm
Ball mill net power consumption, kW.h/t
Energy saving, %
kW-20
Aragon
>10
Closed circuit
Hydrocyclone 9.2%+4.76
41.64
0.56
0.026
51.72
19.5
kW-20
limestone
10
Closed circuit
Hydrocyclone
-4.76
39.22
1.825
0.011
51.83 1
24.3
kW-100
limestone
10
Closed circuit
Hydrocyclone
-12.7
20.52
6.44
0.028
23.14
11.4
kW-200
Gold mine
16
Closed circuit
Hydrocyclone
45%-0.044
6.48
0.105
0.035
14.22
54.44
1 Bond work index calculated value.
Tower mills cannot replace conventional cylindrical mills, which are mainly used for re-grinding of mines. In addition, it can be used in the preparation of limestone slurry in flue gas desulfurization process, lime ripening, grinding and leaching in gold leaching circuit, water "mixing of coal and kerosene, superfine grinding of coal or other materials. Tower mill feeding" It should not be more than 5 mm, otherwise the processing capacity and efficiency of the equipment will decrease. When the feed size is suitable and the product size is less than 74 microns, the energy consumption is much less than that of the ordinary mill. When the product size is required to be coarse, for example, 74 μm At the time, the general tower mill does not save energy than the ball mill.
The MQL-500 spiral stirring tower mill developed by the relevant units in China is also divided into dry and wet type. Wet tower mill in 1984, more than half of industrial tests carried out in Dashihe iron ore processing plant, and then later used as a flotation mill gold mine in Jinchang Yu gold, cyanide leaching step to meet the requirements under the plant. The plant uses a tower mill to grind 65.84% of the gold flotation concentrate less than 350 mesh to less than 350 mesh, accounting for 99.74%, and the mill utilization factor is 0.485 ton/ m3 . When the power consumption is 13.45 kW. / ton, steel consumption is 4.65 kg / ton. Industrial test indicators for the MQL-500 tower mill and ball mill are listed in Table 4. [next]
Table 4 Comparison of MQL-500 tower mill treatment gold flotation concentrate and ball mill
project
Tower mill
Ordinary ball mill
Equipment specifications, mm
Equipment weight, t
Processing capacity, t/h
Loading amount, t
Effective volume, m 3
Motor power, kW
Floor area, m 3
Utilization factor (-200 mesh), t/m 3 .h
Noise intensity, sB
Power consumption (by -200 mesh), kW.h/t
Equipment price, ten thousand yuan
500 × 1950
2.84
0.5~1.3
1.35
0.275
5.5
2.89
1.25~1.72
<85
11.64~13.86
4.8
900 × 900
3.8
0.16~0.48
0.67
0.45
17
4.5
0.6~0.8
>90
~20
6.6
In general, the advantages of tower mill and ball mill are: (1) suitable for superfine grinding; (2) simple structure, accounting for less plant area, no need for huge equipment foundation, saving installation Cost; (3) can be opened, closed, dry and wet, open circuit grinding can also obtain very fine products, which simplifies the process and operation; (4) smooth operation, low vibration, low noise, general Below 85 decibels, and ball mills are mostly in the range of 95 to 100 decibels; (5) the process of grinding and leaching of materials can be completed simultaneously in the tower mill, simplifying the process and improving the efficiency; (6) low.
The disadvantage of tower grinding is that the feed size is not too large and therefore not suitable for ore or coarse. In addition, as the height of the mill increases, the pressure between the grinding media increases, and the grinding efficiency increases, but the wear of the agitating members and the lining plate becomes a prominent problem. This limits the large-scale and large-scale application of tower mills.
Table 5 lists the series of tower mills produced in Japan, and lists the treatment capacity (ton/hour) for which the feedstock has a feed size of less than 3 mm and an average particle size of 10 μm.
Table 5 Type and processing capacity of tower mill
model
Processing capacity, t/h
Mill power
kW
Dry
Wet
Dry
Wet
KD-10
KD-20
KD-50
KD-100
KD-150
KD-200
KD-300
KD-500
KD-600
KD-800
KD-1000
KW-10
KW-20
KW-50
KW-100
KW-150
KW-200
KW-300
KW-500
KW- 600
KW-800
KW-1000
0.08
0.26
1.0
2.8
4.6
6.4
9.8
17.6
21.6
29.0
36.0
0.2
0.65
2.5
7.0
11.5
16.0
24.0
44.0
54.0
72.0
91.0
7.5
15
37
75
110
150
220
370
450
600
750

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