Coal Preparation Priorities
There are a range of high level issues facing the industry which, in the context of coal preparation research, translate to:
- Occupational health, safety and environmental improvement in coal processing.
- Supply, quality and usage rates of water.
- Response to pressure on margins by reducing capital and operating costs, increasing yield, and increasing throughput and run hours of existing equipment.
Specific occupational health and safety issues include finding workable alternatives to heavy organic liquids for float/sink testing. A project examining the most prospective water-based alternative methods is nearing completion, and another examining fine ferrosilicon suspensions is ongoing. Until these project are complete and the results have been assessed in detail, proposals to develop further alternatives are unlikely to be funded. Elimination of radioactive sources from plants remains a key issue for which proposals are sought.
Rejects disposal and tailings dams are also becoming problematic for the industry. Proposals addressing the challenges of fine rejects and stabilising tailings dams with a high proportion of clay minerals are sought. Proposals for final rehabilitation of tailings dams should be directed to the open cut committee. Availability of good quality water in sufficient volumes is becoming problematic. The challenge is to either reduce water consumption in coal preparation, or increase water recycling to reduce fresh water importation. Proposals that examine these aspects are encouraged. In the case of recycling, the effect of dissolved salt build up on plant, product quality and separation process are of particular interest. Pressure on margins is addressed by the three component strategy pursued in the past (identified below) which remains a priority. Consideration will also be given to projects focussed in the traditional areas of coal preparation improvement, such as yield maximisation, moisture reduction and cost reduction. Proposals to adapt technologies proven in other industries to solve problems in coal preparation plants will be well received.
The three strategic areas are as follows:
Increase Run Hours Of Existing Equipment
The challenge is to reduce scheduled maintenance frequency to one 12 hour shutdown every 3 months and to reduce the duration of shutdowns. Proposals are sought to increase the durability of key equipment items, improve the ability to predict their remaining useful life and improve equipment design integrity, eg for screens. Priority will be given to known short life items such as:
- Centrifuge baskets.
- Sieve bends.
- Conveyor idlers.
- Screening media.
Improved Recovery
The objective is to operate each circuit to minimise loss of product specification coal. Proposals will be considered to develop more efficient operating units and improve the operating efficiency of existing units. Proposals are also encouraged to address product quality issues, eg moisture. In particular, the following specific issues are of interest:
- A means for accurate sizing at 100 – 200 microns.
- Screen drain rate and efficiency determination.
- Dense medium cyclones;
- Optimum medium to coal ratio determination.
- Quantification/Elimination of the low density tail.
- Quantification/Elimination of the breakaway size.
Plant Capacity
The challenge is to operate the plant at the maximum possible feed rate while maintaining metallurgical performance. Coal preparation plants are designed around assumed steady state conditions, whereas actual performance is dynamic.
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