Editor's note: This paper was published by Wangwupeng in the Journal of coal processing and comprehensive utilization. The original title was "Application of zm400 mineral high efficiency separator in Yangquan Coal Group". The content of this platform is deleted, and the graphics are selected according to the content. Here, I would like to thank the author of this article.

The production capacity of commercial coal in the No. 5 coal preparation plant of Yangquan Coal Group is 6.8 million t/a, the main products are screening coal, washing medium block, washing small block, No. 3 injection coal, and the by-products are filter slime, dry slime, medium coal and gangue.

The coal preparation production process is as follows: jigging separation of raw coal less than 90mm; 0.5 ~ 0mm materials enter 3 angle cone tanks first. After classification by the classification cyclone, the underflow enters 4 sets of coal slime screens, and the overflow enters the primary thickener. After the primary thickener bottom flows through the classification cyclone for classification, the bottom flow enters 5 sets of high-frequency screens. Overflow of primary thickener is used as circulating water. The high-frequency screen water and the overflow of the classification cyclone enter the secondary thickener, and the underflow of the secondary thickener enters the filter press.

1. Problem analysis

1.1 raw coal quality deteriorates year by year

The mining areas of the five mines are concentrated in the south wing and the central area. With the significant changes in the mining area structure, the overall coal quality has further deteriorated. The south wing mining area accounts for 62%, the average ash content of the final coal is basically maintained at 36%, and the calorific value is 18.81mj/kg. When the amount of raw coal entering the existing washing system is large, the pressure filtration cycle time is increased from 45min to more than 90min, and there are problems such as mixed filter cake, high water content, deterioration of circulating water concentration, etc. It can be seen that the existing slime water system can not meet the production demand.

1.2 some raw coals have high moisture content, resulting in low screening efficiency

The normal moisture content of raw coal mined by Minmetals underground is 5% ~ 7%. When the underground watering operation is carried out to prevent dust, the moisture content of raw coal fluctuates, and the moisture content of raw coal exceeds 10% in some periods. At this time, the efficiency of raw coal classification screen decreases, and a large number of South Wing pulverized coal enters the washing system, resulting in a sharp increase in the load of slime water system and serious deterioration of circulating water.

1.3 low calorific value end coal cannot be loaded, transported and sold by railway

According to the environmental protection requirements and market demand, the final coal with calorific value of 18.81mj/kg cannot be sold on the railway. During the actual sales, in order to ensure the calorific value of power coal, clean coal products are added to reduce the economic benefits. The high-quality raw coal of the mine is decreasing year by year, and the washable coal available for blending is becoming less and less. It is urgent to select a reasonable production process to improve the quality of the coal.

2. Selection of washing process for fine coal

2.1 possibility of tapping potential by using existing washing system

Determine the existing washing capacity. The main washing system of the coal preparation plant: a single non graded (90 ~ 0mm) jigging main washing + jigging re washing process is adopted. Four skt-27 jigs are used in the "three in service and one standby" production mode. The designed processing capacity of a single machine is 270 ~ 500t/h. Affected by the coal quality, the actual processing capacity is 300t/h and the annual washing capacity is 4.752 million T. By extending the operation time, the jigging system actually washes 5.4 million t/a of raw coal, which has been overloaded. Without affecting the mine production, the potential of the processing capacity of the coal preparation plant has reached the limit. Slime water system: primary concentration of slime water system in coal preparation plant of Minmetals Corporation ? 3 sets of 30m thickeners, used for secondary concentration ? There are two 24m thickeners, and the washing water will deteriorate after the amount of fine coal in the south wing of the washing system increases; Therefore, without increasing the processing capacity of the concentration system, the amount of slime entering the system cannot be increased, and the processing capacity of raw coal cannot be increased.

The above shows that the existing jigging and washing system has run at full capacity, the treatment capacity of the slime water system can not meet the production requirements, and the potential to improve the existing washing capacity is limited. Tapping the potential of the existing system can not meet the actual production needs.

2.2 screening test of the last raw coal in the south wing mining area

See Table 1 for the screening test data of the last raw coal in the south wing mining area.

It can be seen from table 1 that the final raw coal ash is 36.17%, belonging to medium ash coal and sulfur is 1.5%, belonging to high sulfur coal. The distribution of each particle size in raw coal composition is uneven, and the ash content of each particle size basically decreases with the decrease of particle size, indicating that the coal is soft; The content of primary slime is high, and the yield is 14.99%. 

See Table 2 for the data of slime screening test in the south wing mining area.

It can be seen from table 2 that the ash content of coal slime increases with the decrease of particle size, and the content of particles smaller than 0.075mm is higher, accounting for 68% of particles smaller than 0.5mm, indicating that the coal slime is seriously slimed.

2.3 selection of wet and dry separation schemes

As the south wing mining area has become the main mining area of No. 5 coal mine, the end raw coal in the mining area is seriously slimed, so wet washing is not suitable. The original design of the washing system of coal preparation plant did not have a separate final coal washing system. In order to ensure the amount of lump coal, the raw coal entering the washing system can only produce clean coal products. However, after years of transformation, the equipment installation of the coal preparation plant is compact, and it is no longer possible to transform into a final coal gangue discharge washing system without affecting the existing production. 

Based on the above analysis, it is difficult to select the wet washing system for the quality improvement and separation process of fine coal in the coal preparation plant , and only the dry separation process can be used.

2.4 ZM high efficiency mineral separator

ZM mineral high-efficiency separator adopts modular design, with simple structure, good separation effect, high degree of automation and mature technology application. It has been certified as China's environmental protection product by China environmental protection product evaluation center and has been successfully applied in many coal preparation plants in China.

3. Principle and characteristics of zm400

3.1 principle of zm400

The materials are rotated in steps on the bed and separated repeatedly in the step sections. According to the composition of the materials, each step section forms a fluidized autogenous separation medium layer with different density; The thickness and fluidization degree of the fluidization separation medium layer are different, resulting in the difference of the buried depth of the separated materials in the medium layer of each step section. The materials with different densities realize the final separation in each step section. In the production system, the combined dust reduction measures of blanking point sealing, spray dust reduction and induced draft dust removal are adopted. The dust does not overflow, and the pulverized coal recovered by the dust collector is finally mixed into the cleaned coal products. 

The equipment adopts the step separation principle. The materials in each step section are fluidized and layered, and the impact force is increased to strengthen the layering effect of materials according to density. The low-density materials are discharged first through the overflow weir, and the remaining materials enter the next step section for sorting again until the sorting is completed and the heavy minerals are discharged.

3.2 performance characteristics of ZM separator

ZM separator used for dry separation of fine coal has the following characteristics:

(1) High sorting accuracy;

(2) Closed negative pressure operation of the whole system, no pollutant overflow, good environmental protection effect;

(3) The bed surface can be repaired and replaced;

(4) Secondary shock absorption design, the girder is shockproof, and no civil foundation is required;

(5) High degree of automation, which can be controlled by the centralized dispatching control system;

(6) The dust removal system with high dust concentration can discharge the purified air up to the standard after treatment.

4. Practical application of zm400 separator in the dry separation system of Minmetals fine coal

The dry separation system of fine coal can process 400t of fine raw coal per hour. Based on the annual production of 330D and 16h per day, it can process 2.1 million tons of fine raw coal per year.

4.1 composition and process flow of dry separation system

The dry separation system for fine coal consists of raw coal receiving system, air separation system, dust removal system and pulverized coal recovery system. The feeding particle size of the dry separator used by Minmetals is 0 ~ 13mm, and the processing capacity is 400t/h.

A set of raw coal receiving system is newly added in the South Coal platform of Minmetals. The raw coal is transported to the dry separation system through the coal receiving system. The dry separation system adopts modular design and installation, plus a steel structure cover, which is safe and environmentally friendly. Clean coal and tail coal products are separated in the dry separation workshop. The dry separation clean coal falls to the north coal platform through the belt conveyor and is loaded on the railway for outward transportation; The dry separation tailings are transported to the South Coal platform by belt conveyor, mixed with the coal in the jigging system and low-quality raw coal, and then transported to the gangue power plant; At the same time, the coal preparation plant is equipped with a separate gangue discharge channel. When the demand of the gangue power plant decreases, the gangue can be discharged separately.

The system adopts the combined dust reduction and dust removal process of blanking point sealing, spray dust reduction and induced air dust removal, so that the dust does not overflow and pollute the environment; The pulverized coal recovered by the dust collector can be discharged separately to reduce the impact on the environment.

4.2 characteristics of dry separation system

(1) Modular design, convenient installation;

(2) The raw coal has strong adaptability and is suitable for high-density gangue discharge;

(3) It does not increase the moisture content of power coal products, and there is no phenomenon that the coal ash and water in wet separation offset each other;

(4) Simple process, less equipment, simple management and high labor efficiency;

(5) Commercial coal products have low moisture content and are suitable for producing coal products with strict moisture requirements.

4.3 effect analysis of dry separation system

See Table 3 for industrial test report of dry separation system.

It can be concluded from table 3 that after the dry separation system is used to improve the quality of Minmetals' raw coal, high-quality coal with a calorific value greater than 21.54 mj/kg and low-quality coal with a calorific value less than 21.54 mj/kg are obtained, and the yields are 62.93% and 37.07% respectively. The high-quality end coal with a calorific value greater than 21.54 mj/kg is loaded on the railway for export. The low-quality end coal with a calorific value less than 21.54 mj/kg is mixed with medium coal, some low-quality end raw coal and some high-quality end raw coal to form mixed distribution Coal with a calorific value of 14.63 ~ 15.47 mj/kg for use in gangue power plants. 

4.4 the coal preparation plant realizes full washing of mine raw coal

(1) The dry separation system is combined with the jigging system to realize the full particle size separation of mine raw coal; The product quality of clean coal is improved, the quality of fine coal is stabilized, and the washing efficiency of lump coal and clean coal is improved.

(2) The combined process advantages of jigging and dry separation system include: first, the original water washing system is not changed, and each system operates independently; The second is to realize full size separation; The third is not to increase the moisture content of the fine coal; Fourth, reduce production costs; Fifth, the product structure is flexible, which improves the lump coal yield. 

4.5 environmental protection of dry separation system

(1) Dust control. Standardized dust removal system design meets the national dust emission standard; Sealed dust removal is adopted for plant, belt corridor, transfer point, etc; Single stage and multi-stage dedusting systems; Operation space purification and secondary dust removal; Strictly collect and control dust to prevent secondary pollution; Dust products are stored, transported and sold separately. 

(2) Noise control. The system is closed and the fan is isolated separately; The enclosed facilities shall be coated with sound insulation and noise reduction materials; The foundation of ZM separator and fan adopts shock absorption design.

(3) Explosion proof specification. Electrical explosion-proof design shall be carried out in strict accordance with coal mine safety production regulations and relevant specifications; Coal dust gathering facilities, such as enclosed plants and corridors, silos, dust collectors, silos, etc., are equipped with explosion-proof facilities.

4.6 product balance sheet

See Table 4 for the product balance table of Minmetals coal preparation plant after adopting the dry separation system. It can be seen from table 4 that the product structure is balanced. There are both high-quality end coal and clean coal to meet the railway transportation. There is no need to sell the end coal. The environmental protection benefit is good, and the average price of commercial coal has been increased.

4.7 social benefits

After the addition of the dry separation system for the final coal in the coal preparation plant of Minmetals Group, the resource recovery rate of Minmetals Group Co., Ltd. has been improved, the environmental pollution to the surrounding areas caused by the increase in the amount of gangue discharged has been reduced, and the policy requirements of the superior on environmental protection and governance have been complied with. It is an environmental protection project and benefit project in line with the current situation.

5. Conclusion

ZM mineral high efficiency separator is a kind of coal gangue separation equipment with mature technology. The final coal dry separation system has the characteristics of low investment and operation cost, high intelligence and separation efficiency, small floor area, fast assembly and production, modular design, convenient relocation, high efficiency and environmental protection. The system effectively improves the calorific value of the fine coal and the market competitiveness of the commercial coal. Yangquan Coal Group first introduced ZM mineral high-efficiency separator in the coal preparation plant of No. 5 coal mine and achieved success, which filled the blank of dry coal preparation in Yangquan Coal Group and achieved remarkable benefits. The project has good reference value and popularization significance for the technical transformation of other coal preparation plants of Yangquan Coal Group.