Coal beneficiation

Coal processing workshop, the original design washing capacity of 300,000t/a, after many technical modifications, especially after the modification of heavy media sorting process, the washing capacity has reached 750,000t/a. The production process adopts the combined process of desliming with pressurised three-product cyclone sorting - slurry flotation, tailing filter recovery and washed water closed-circuit recycling process, which is mainly used for selecting coal and raw coal from coal mines. With the continuous improvement of coal mining mechanisation, the content of pulverised coal in raw coal is increasing, and the amount of flotation concentrate accounts for about 30% of the total amount of concentrate, so the high efficiency and stability of the flotation process is crucial to the whole washing process. The original process design of the first workshop of coal dressing adopts 2 sets of PG58-6 disc vacuum filter for dewatering and recovering flotation fine coal, with a total filtration area of 116 m2 and a total processing capacity of l0~16 t/h.filter pressThe moisture of filtered cake is 30% to 33%, and the dewatering capacity cannot meet the needs of flotation process. The water content of the filter cake is 30 per cent to 33 per cent,

Problems with floating concentrate dewatering systems

(1)The efficiency of flotation coal dewatering system equipment is low.PG58-6 disc vacuum filter is aging, large maintenance, low vacuum (only 0.025 MPa), poor suction effect, coupled with the flotation of coal in the fine particles in the content of more (a 0.074 rain mass fraction of more than 40%), resulting in cake moisture as high as 30% to 33%, filtrate quality concentration of about 50 g/L. The fine coal is lost with the filtrate in the coal slurry. The quality concentration of the filtrate is about 50 g/L, and the fine coal is lost in the slurry with the filtrate. When the amount of flotation coal is large, especially when the content of fine particles is large, the filter has poor suction, low processing capacity, resulting in less selection or stopping the selection, which reduces the yield of fine coal.

(2) Affected by the high moisture of flotation coal, the moisture of comprehensive coal is around 11%, which brings a series of unfavourable impacts to the coal processing plant:

(1) Unable to meet customer demand, resulting in loss of sales. Although the exported refined coal was dewatered in warehouses and on the road, it was still unable to meet the demand of selling refined coal with moisture less than 8 per cent. According to the statistics, from June 2009 to May 2010, the users gave feedback that the moisture content of refined coal exceeded the standard by 16,000 tonnes;

(ii) Increase production costs. Due to the high moisture content of fine coal, a large amount of antifreeze needs to be added when loading trucks in winter, which increases the cost;

(iii) Loss of tonnage due to excess moisture in refined coal, which increases the cost of ineffective transport and transport expenses. According to the annual plan to transport 360,000t of refined coal, the freight cost of refined coal is calculated according to 88.62 shirts t, and the contract requires that the moisture is less than 8 per cent, and the extra freight cost due to ineffective transport is calculated as 360,000t X (11 per cent to 8 per cent) × 88.62 shirts t = 95.71 million yuan per year;

(4) Impact on site production management. After mixing the flotation fine coal with the heavy medium fine coal, due to high moisture, it causes accidents such as belt slip, deviation and flow channel blockage in the transport process, which affects the normal operation of production;

Loading is unfavourable. The high moisture of fine coal, after entering the silo, it often has the phenomenon of sticking to the wall, blocking the material and not stopping the material, which causes difficulties in loading and affects the speed of loading.

Modification of floatation dewatering process system

Without affecting the production, the new KZG500/1500×2000-U high-efficiency quick-opening diaphragm filter presses were added to replace the original two high-energy-consuming PG58-6 disc vacuum filter presses by dismantling and replacing them one by one. Two KZG500/1500×2000-U high-efficiency quick-opening diaphragm filter presses with an area of 150 m2 were arranged parallel to each other in the east-west direction on the first floor of a workshop, and two scraper conveyors were laid under the filter presses, with their tails perpendicular to the original floatation fine scraper conveyors. The filter cake passes through the two scraper conveyors. The filter cake is transferred to the original floating concentrate scraper conveyor through the chute, and the filtrate is discharged from the collecting trough through the pipeline to the circulating pool for circulating water.

2.2 Characteristics of the quick-opening diaphragm filter press The quick-opening diaphragm filter press adopts a series of optimised designs, such as high-pressure and strong-liquid feeding and dewatering, diaphragm pressure dewatering, and strong airflow through-flow cake dewatering. Compared with the vacuum filter, the main features of the quick-opening diaphragm filter press are as follows:

(1) Large production capacity. Optimised design of filter plate surface, large flow area of coal slurry, low liquid resistance, smooth discharge of filtrate and large flow rate. Under the same production process conditions, the production capacity of diaphragm filter press is 4-8 times higher than that of vacuum filter.

(2) Low moisture of filter cake. Quick-opening diaphragm filter press stops feeding after filtration, and the further dehydration of filter cake adopts compressed air to fill the diaphragm, and the two-dimensional pressure generated by the deformation of the diaphragm destroys the arched bridge formed between the particles, and squeezes out the filtrate remaining in the interstices between the particles; and the capillary water in the filter cake is discharged through the penetrating displacement by the strong airflow, so that the moisture of the cake can be reduced to the greatest extent possible.

(3) Low energy consumption. Compared with vacuum filter press, diaphragm filter press reduces electricity consumption by about 50 per cent under the same production capacity, and the production cost is obviously reduced.

(4) Low filtrate quality concentration. The filtrate is clean, usually with a concentration of 5-10 g/L, and can be used directly as recycled water, simplifying the process.

(5) Low noise. The noise is only 62.5 dB. (6) Fully automatic operation. The whole machine (including some auxiliary machines) is controlled by computer, centralised control of equipment start and stop, automatic monitoring and control of liquid level and material level, fault alarm and safety protection devices, real-time detection, display and recording of production process parameters. The production process parameters are detected, displayed and recorded in real time.

Application effects

High-efficiency fast-opening diaphragm filter press has been put into operation, and the production practice shows that the equipment has been used with good effect and has achieved the expected purpose.

(1) Reducing the moisture of refined coal and meeting the demand of users After the transformation, the moisture of floating refined product can be controlled below 23%, which is nearly 7% lower, and after blending refined coal products, the moisture of the refined coal for sale reaches below 8%, which meets the demand of users, and no longer generates tonnage loss and quality disputes, and eliminates the negative impacts of the storage, loading and transportation process.

(2) Increased floatation capacity and refined coal yield After the renovation of the floatation dewatering system, the floatation processing capacity has been increased. The original filter processing capacity was 70-80 t per shift, but after the use of fast-opening diaphragm filter press, the processing capacity was as high as 105-115 t per shift, an increase of 35 t, and the net amount after water refraction was 28 t, accounting for 1% of the amount of raw coal washed, i.e., the output rate of refined coal was increased by 1%. in June-January 2010, the first workshop washed raw coal of 405.4 million tonnes, and the selling price of refined coal was 1525 shaped tonnes, generating additional efficiency: 405.4 million tonnesxl%. The efficiency gained: 40.54 million txl%x1525 yuan t./t=618,240,000 yuan.

(3) Reducing the concentration of filtrate and the load on the coal slurry water system The filtrate from the fine coal quick-opening diaphragm filter press after the modification is basically clear water, which can be directly used as the recycling water for coal washing, reducing the load on a series of segments of the filtrate after it carries coal slurry into the coal slurry water system for thickening, clarification and recycling, and dismantling the slag washing segment of the original system, thus simplifying the system.

(4) Fully recover the fine coal in the coal slurry and improve the ash content of the coal slurry The operation of the fine coal fast-opening diaphragm filter press eliminates the disadvantage of insufficient flotation dewatering capacity, ensures the normal continuous production of flotation, and improves the ash content of the tailings under the premise of guaranteeing the quality of the flotation fine and improves the ash content of the coal slurry from less than 35% to about 40%.

(5) Improve the working environment and reduce the labour intensity of workers After the transformation of refined coal dewatering system, the dewatering workshop is spacious and bright, the working environment is greatly improved, automatic control and remote operation are realized, and the labour intensity is greatly reduced. After the transformation of flotation coal dewatering system of Xinzhi Coal Processing Plant, the water content of refined coal products has been reduced, the process link has been optimised, and the assessment and supervision of the data with scales have been carried out; the quality points have been selected, and the management system and operation procedure of the quality points of the process have been revised; and the quality management drivers have been evaluated for their quality of work.

Implementation of mass balance management

Training of process quality controllers in the theory of quantity and quality balance; formulation of production planning and technical indicators for production, and testing of quantity and quality balance. If the raw coal is not converted to moisture, and the comprehensive yield is set at 97% based on the raw coal quantity (the converted moisture of refined coal and middle coal washed products for export is 7%), the amount of washed gangue should be less than 7% (the moisture of washed gangue is about 5%). If all the data are converted into dry basis, the comprehensive yield will be changed from 97% to about 95%, and the amount of gangue will be changed from less than 7% to about 5%. Specific implementation measures for the management of quantity and quality balance are as follows: the Quality Control Section, Production Technology Section and Measurement Section provide relevant quantity and quality data, starting from the ten-month and monthly quantity and quality balance, and find out the problems through theoretical calculations; the process quality officer goes into the field to study the working condition of the quality management points, and puts forward the improvement suggestions for the management system and operation procedures to ensure the relative accuracy of the data, and at the same time puts forward the preliminary improvement suggestions for the selection of the quality management points; Conduct tracking investigation on the relevant quality data and make preliminary calibration determination; find out the balanced data by comparing the calculated data with the actual data and make basic determination; study with the relevant departments providing quality data, find out the problems, determine the relevant data, put forward preliminary opinions on rectification, and make rectification on a deadline after tracking and observation.

concluding remarks

The quality balance management starts from the bulk raw materials and products, namely raw coal, export products, and then the floating washing system, heavy media system, and finally the transition to the operating unit system. Strengthening the management of the number and quality balance of the production process and analysing the reliability of the measurement data can identify the problems of the production and operation systems and improve the operation and management level and economic efficiency of the enterprise.

Problems of the original flotation fine coal dewatering system in the first workshop of coal processing, the flotation fine dewatering system has been renovated, introducing two sets of l(zG500/1500×2000 a u-typeHigh-efficiency quick-opening diaphragm filter pressReplaced the original disc vacuum filter. After the quick-opening diaphragm filter press was put into operation, it reduced the moisture of fine coal and the concentration of filtrate, increased the yield of fine coal and the ash content of coal slurry, improved the operation environment and reduced the labour intensity of employees.