1 Introduction

In recent years, a series of large-scale cyclone-static microbubble flotation columns (Φ1.5m, Φ2m, Φ3m, 3.0m×6.0m) and their supporting processes have been developed mainly by China University of Mining and Technology, and have been established in seven provinces of China. dozens of selected coal plant has been widely used and achieved remarkable economic and environmental benefits.

Flotation column was invented in the 1960s, its unique structure and movement pattern makes it a beginning by many countries, coal preparation and beneficiation plants of all ages. However, due to the unreasonable structure of the early flotation column and the instability of motion, its development is slow. In recent years, with the deepening of the research on flotation column, with the bubble generator as a breakthrough, a number of unique flotation columns have been developed. These flotation columns are relatively early from the reliability of the equipment to the stability of operation. The flotation column is greatly improved. According to the characteristics and sorting needs of China's slime, China University of Mining and Technology developed a cyclone-static microbubble flotation column that combines the principle of flotation with the principle of re-election, taking into account the accuracy and yield of flotation. A coal slime sorting equipment that has reached the international advanced level.

Under the same operating conditions, when the clean coal ash is the same, the yield of the cyclone-static microbubble washing column is higher than that of the flotation machine; when the yield is the same, the clean coal ash is lower than the flotation machine, generally lower 1 to 2 percentage points. At the same time, in terms of investment, operating costs, etc., the new process of sorting the cyclone-static microbubble flotation column also has great advantages.

2 Sorting new process of flotation column and sorting process of conventional flotation machine

2.1 Conventional flotation machine sorting process

The conventional flotation process (Fig. 1) sends the slime water to the flotation machine through the slurry pretreatment device, and the clean coal sorted by the flotation machine is filtered by a disc vacuum filter. The process is complicated, especially the vacuum filter is equipped with vacuum pump, gas water separator, filtrate pump, cooling water system, softened water device and other equipment. In addition, the process generally requires 2 to 3 floors, and the civil construction cost is relatively large. . Therefore, the characteristics of the process are: large investment, large equipment, large power consumption, complicated process, large maintenance, and high operating cost. However, due to the application of this technology in China for many years, it has accumulated rich experience and is the most widely used flotation process in China.

2.2 Flotation column—the new process of sorting the chamber filter press

Flotation column—Floor filter press flotation process (Fig. 2) is a new type of slime flotation process system developed by China University of Mining and Technology with cyclone-static microbubble flotation column as the core. The process adopts a direct flotation process, and the coal slurry water is adjusted by a mixing tank and sent to a flotation column for sorting, and the sorted clean coal is filtered by a box filter press. Compared with the previous process, the process is much simpler, with less investment, less power consumption, less maintenance, lower operating costs, and the adaptability of the process to slime due to the inherent advantages of the flotation column. Sorting accuracy and yield are higher than conventional flotation machines. In addition, the process makes full use of the advantages of the high discharge port of the flotation column and adopts the ground arrangement, which greatly saves the civil construction investment.

3 Economic comparison of two flotation processes

The economic process comparison of the two process systems is based on the scale of the 600,000 t/a coal preparation plant.

The main technical indicators are as follows:

The annual coal processing capacity of the coal preparation plant: 600,000 tons;

The amount of coal sludge treated in the flotation year: 150,000 tons;

Clean coal ash: 7.0% to 12.5%;

Clean coal yield: 65%;

Clean coal production: 97,500 tons;

Working system: 300d/a, 14h/d.

The project investment details, construction investment comparison and unit operating expenses are shown in Tables 1 to 3.

Table 1 Comparison of investment plan for coal slurry flotation process in 600,000 t/a coal preparation plant

Table 3 Composition of unit operating expenses (yuan/t clean coal)

Note: 1) The conventional flotation process has a capacity of 35 persons, the flotation column process has a capacity of 15 persons, and the per capita salary is calculated at 5,000 yuan/d; 2) the electricity fee is calculated at 0.45 yuan/kW; 3) the chemical consumption is 1.0 kg/t. For dry coal slime calculation, the price of the chemical is calculated at 3,000 yuan/t; 4) the depreciation period of the equipment is 15 years, and the depreciation period of the building is 30 years.

The above comparison results are analyzed as follows:

(1) Equipment investment. The same processing volume of flotation machine and flotation column price are similar, the main difference of investment lies in the clean coal dewatering system, the investment of this system accounts for 60% of the flotation machine sorting system, and the flotation column sorting process In the system, this part only accounts for 40% of the equipment investment.

(2) Civil construction investment. Conventional flotation machine sorting process Because of the choice of disc vacuum filter, it is generally required to adopt a three-story design, which not only increases the building area, but also costs a unit volume, while the flotation column process system uses a box filter press. Dewatering greatly reduces the floor space. At the same time, due to the full advantage of the column height of the flotation column, the floor space is used to reduce the cost per unit volume. The latter is 18% of the former.

(3) Electricity and wages. Because the disk vacuum filter dewatering system and the flotation machine itself consume a large amount of electricity, the electricity cost of the flotation machine sorting system is 3.43 times that of the flotation column sorting system; the conventional flotation machine sorting process has many equipments. The system is complex and the number of people used is much higher than that of the flotation column sorting system. The total salary is 2.3 times. The electricity bill and wages account for nearly 70% of the main operating costs of the conventional flotation machine process system, so these two factors are the main reasons for the high operating costs of the conventional flotation machine sorting process system.

4 Conclusion

From the above analysis, the conventional flotation machine sorting system has a investment of 1.61 times compared with the flotation column process sorting system, the installed capacity is 3.43 times, and the main operating cost is 2.06 times. It can be seen that the various economic indicators of the cyclone-static microbubble flotation column flotation process are much better than the conventional flotation machine flotation process. With further improvement in practice, it will be more widely used.

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