Editor's note: This paper was published by Wang Haisheng and Shi Wenliang in the proceedings of 2015 national coal preparation academic exchange. The original title of the paper was "Application of FGX-24 composite dry coal separator in Donghuantuo Coal Preparation Plant". When selecting this platform, the content is deleted, and the drawing is selected according to the content. Here, I would like to thank the author of the article.

The coal preparation plant of Kailuan (Group) Donghuantuo mining branch, with a design production capacity of 1.5mt/a, is a mine type power coal preparation plant. Coal belongs to gas coal, which has the characteristics of soft reject hardness, large amount of fine coal, wet and sticky coal, not easy to screen, coal and reject are easy to muddy and not easy to settle. The original coal preparation method adopts 50-6mm dense medium separation. With the change of underground coal quality, the recovery rate has been less than 20%. Through the floating and sinking test of screening, it is found that the effect of separate heavy medium separation for particles below 30-6mm is better, and the recovery can reach more than 40%. Because there is lots of reject with particle size of more than 30mm, composite dry coal separation is adopted for materials with particle size of more than 30mm, and the reject is pre-arranged to improve the recovery rate of clean coal and economic benefits.

01.STRUCTURE OF FGX-24 COMPOSITE DRY COAL SEPARATOR

FGX-24 composite dry coal separator is composed of two FGX-12 composite dry coal separator. The main separation principles include: turnover stripping separation principle, separation principle of authigenic medium, segregation, etc. FGX-24 composite dry coal separator is composed of separating bed, vibrator, air chamber, frame, hanging device, receiving chute, etc. The vibrator is fixed on the separating bed motor frame by two vibrating motors, and the separating bed with vibrator is suspended on the frame by four steel wire ropes through damping springs.

The separating bed is composed of a right-angle trapezoidal bed surface full of air holes, a back plate, a grid, a discharge baffle and a reject gate. A number of air chambers are set at the lower part of the bed surface, which are connected with the centrifugal fan. Each air chamber is controlled by an air valve. The air chamber and the bed surface are fixed and integrated with the separating bed. 

02.COMMISSIONING PRACTICE OF FGX-24 COMPOUND DRY COAL SEPARATOR IN DONGHUANTUO COAL PREPARATION PLANT

In the commissioning process of Donghuantuo Coal Preparation Plant, the compound dry separator did not fully achieve the expected effect. The problems encountered mainly include the following:

(1) The phenomenon of reject sliming is serious. The coal slime circulates in the air duct. In the process of circulation, the air outlet of the screen bed is blocked, and the air volume cannot meet the requirements, affecting the separation effect. 

(2) There are many sundries such as plastic bags, textile bags and small wooden boards in the raw coal underground, which leads to the blockage of the air inlet of the screen bed and induced draft fan.

(3) After separation by the compound dry separator, the mismatch between clean coal and reject is caused due to the limited adjustment range of clean coal and reject.

(4) The selected 30-80mm raw coal contains a large amount of reject, mixed with more middings, and the coal content of reject is high.

(5) During the operation of the compound dry separator, due to the relatively fragile coal quality, the raw coal is transferred into the compound dry separator, resulting in a large amount of peripheral dust under the action of circulating air.

03.ANALYSIS OF FACTORS AFFECTING THE SEPARATION EFFECT OF COMPOUND DRY COAL SEPARATOR

3.1 Raw coal quality

Donghuantuo Coal Mine has large external moisture, which belongs to wet and sticky coal. In particular, the phenomenon of raw coal sliming is serious. In the process of dry coal separation, with the action of wind force circulating in the air duct, it will stick in the air duct after a certain time, paste the air duct, and reduce the air volume to a certain extent. Due to the strict requirements on air power for composite dry coal preparation, sticky coal has a great impact on wind separation.

3.2 Feed particle size

The feed particle size of the compound dry separator in Donghuantuo Coal Preparation Plant is mainly 30-80mm, and there are few fine-sized materials in the feed. The composition of pulverized coal and bed updraft cannot form a gas-solid two-phase mixed medium, i.e. authigenic medium. At the same time, the particle size of 30-80mm contains a large amount of reject. In the separation process, there are high requirements for the reject discharge capacity of the equipment.

3.3 reject content of raw coal

The raw coal of Donghuantuo Mine has a high reject content of 30-80mm particle size. When the underground coal quality is poor, the reject content exceeds 60%. In the process of using the compound dry coal separator, due to the large content of reject and the limited amount of reject at the reject discharge port, the content of clean coal mismatch is large, which seriously affects the quality of clean coal and reject.

3.4 other reasons

As the waste from underground production and living is mixed with raw coal along with the belt, the plastic bag enters the dry coal separation equipment, enters the bag filter and cyclone dust collector along with the circulating air, and enters the lower part of the separating bed along the pipeline, which seriously blocks the sieve hole of the separating bed, and the air volume cannot meet the requirements, affecting the separating effect.

04.OPTIMIZATION AND TRANSFORMATION OF PROCESS AND EQUIPMENT

4.1 Process optimization

(1) Pre crushing raw coal by 30-80mm

In the original design process, raw coal with particle size of 30-80mm directly enters the composite dry separator for separating. In the commissioning and production, the separating failed to achieve good results. Through the research and practice of the separation principle of the composite dry separator, the process flow is optimized. A counterattack crusher is designed to pre crush the 30-80mm particle size materials by 40mm. After crushing, the content of pulverized coal is increased. Due to the operation of authigenic medium, the separation effect is improved.

(2) Design and install 540 transfer belt

After 30-80mm dry coal separator is adopted in the original design process, the cleaned coal is sold as power coal. Due to the continuous change of underground coal quality, the calorific value of commercial coal is low when the coal quality is poor. 540 transfer belt is designed to mix the cleaned coal after dry coal separation with commercial coal to improve the quality of commercial coal. In addition, after simple reject discharge, the cleaned coal from dry coal separator can also be transferred into the heavy medium system through 540 belt to improve the recovery rate of cleaned coal from heavy medium washing.

(3) Adjust the dust cleaning time interval of bag filter

As the raw coal of Donghuantuo Mine is fragile, it leads to large dust in the periphery, which leads to the loss of clean coal on the one hand and affects the working environment of workers on the other hand. Therefore, by optimizing the ash cleaning PLC program, the original automatic ash cleaning time is changed from two hours to half an hour, and in the process of ash cleaning, it is transferred separately through the coal separator to avoid secondary dust caused by multiple belt transfer. After use, the amount of peripheral dust is significantly reduced.

(4)OPTIMIZED PROCESS FLOW

4.2 1) Add air duct maintenance and cleaning port

The original air duct does not consider the blockage of viscous coal on the air duct, and the maintenance and cleaning port is not set on the air duct. The blockage of the air duct seriously affects the air supply volume, thus affecting the separating effect and efficiency, and the quality of air separation cleaned coal products cannot be guaranteed. After the air duct maintenance cleaning port is added, the maintenance personnel are more convenient to clean and observe, ensure the smoothness of the air duct and improve the sorting effect.

(2) Add baffle for induced draft fan

The original induced draft fan only gives ideal consideration to the recovery of coal dust, and does not consider the situation that there are many sundries such as wet fine coal and plastic bags underground, which often blocks the air duct and sieve plate. After adding baffles, plastic bags and other domestic garbage can not be directly sucked into the induced draft fan, which plays a certain diversion role and indirectly ensures the smoothness of the air duct. 

(3) Extend the length of flap between chutes of each product

The two flaps between the original clean coal, medium coal and gangue are relatively short. When there is a mismatch between gangue and clean coal, the adjustment range is limited. When the calorific value of cleaned coal is higher than the production demand, the operator needs to adjust the cleaned coal turnover plate to expand the medium coal mixing rate. However, due to the short turnover plate, when the limit is reached, the cleaned coal still has a high calorific value, so the cleaned coal output is relatively reduced. The same is true when adjusting the amount of gangue. By extending the flap, the adjustment range of clean coal and gangue is expanded, and the operator can adjust the flap more flexibly, so that the quality control of clean coal and gangue is more accurate and the products are more competitive in the market.

(4) Increase opening of back plate of gangue section

Although the original sorting equipment takes into account the large amount of gangue, it also opens side waste discharge openings. The content of 30-80mm raw coal gangue in Donghuantuo Mine is large. When the coal quality is poor, the content of gangue is more than 60%. The amount of gangue Fed is far greater than the gangue discharge capacity of the equipment, resulting in more mismatches in clean coal. By increasing the back plate waste discharge port, the amount of waste discharge is increased to ensure the stability of cleaned coal products.

05. Application effect analysis

FGX-24 composite dry coal separator has been used in Donghuantuo Coal Preparation Plant for more than a year. After process improvement and equipment transformation, the equipment is in good operation. Through the application practice in Donghuantuo Coal Preparation Plant, its advantages compared with other separation equipment mainly include:

(1) Simple equipment

The compound dry coal separator has the advantages of simple structure, small floor area, few civil works and short construction and installation period has the advantages of simple structure, small floor area, few civil works and short construction and installation period. The FGX-24 composite dry separator purchased by Donghuantuo Coal Preparation Plant took only more than one month from equipment bidding procurement to commissioning and production, so as to ensure production and improve economic benefits.

(2) Low preparation cost

The raw coal in Donghuantuo Mine is fragile, and the content of reject in the particle size of 30-80mm is large. According to the original design process, the raw coal enters the main washing system. The recovery rate of clean coal with particle size of 30-80mm is low, and the pipeline is seriously worn due to the large amount of reject. By using FGX-24 composite dry separator, the calorific value of 30-80mm raw coal after reject discharge reaches more than 3900kcal / kg, the reject discharge rate is high, and the coal content of reject is less than 5%. Through comprehensive analysis, the cost per ton of heavy medium coal is about 18 yuan / T, the cost per ton of dry coal separation is about 4 yuan / T, the comprehensive cost is reduced by 14 yuan / T, and the economic benefit is obvious.

(3) Simple operation

Compared with heavy medium separation, the composite dry coal separator does not need strict density control, but only needs to adjust the turnover plate, screen front baffle or screen angle between product chutes. In addition, when the coal quality is poor, the amount of reject is large, and the back plate reject opening needs to be opened on site to increase the amount of gangue discharged. In the process of equipment operation, compared with heavy medium coal preparation, less on-site personnel are required to operate, and there is no need to set too high requirements for the quality of employees. Employees only need a short time of training to operate.

(4) The amount of overhaul and maintenance is small. 

The compound dry coal separator has simple equipment, few supporting equipment, stable equipment operation, small floor area and centralized equipment, so the amount of overhaul and maintenance is small.

06.EPILOGUE

After application of FGX-24 in Donghuantuo coal preparation plant, comparing with heavy medium preparation, it has greatly reduced the separation cost, with considerable economic benefits. The air separation process of Donghuantuo Coal Preparation Plant adopts 30-80mm particle size raw coal separation, which is characterized by large amount of reject and high external moisture of coal quality. Through the optimization and transformation of the original process and equipment, the operation of the equipment is stable, the production accidents are significantly reduced, and the production efficiency is significantly improved, which provides a reference for other coal preparation plants to use dry coal separation equipment to separate raw coal of similar coal quality.