Process overview
The pilot-scale coal preparation plant includes appropriate equipment to handle and process coal through various coarse, fine and ultra-fine circuits. The plant does not wash all fractions concurrently as in a typical wash plant. After separating the coal into the required size fractions, the coarse, fine and ultra-fine coals are processed individually through stand-alone circuits. This allows for greater control of the sample processing stages.
The following provides guidance on the processing of a coal and the equipment available within the pilot-scale coal preparation plant.
- The raw coal is initially processed through a 15 tonne feed hopper with static grizzly and a variable speed conveyor. The coal then passes through a double rolls crusher which can accept coal up to 200 mm top-size and can crush from 150 mm to 25 mm nominal top-size
- Separating the received coal into the coarse, fine (and ultra-fine feed material) is initially performed by passing the coal over a sloping vibrating screen with the aperture of the screen deck set to the size required by the customer. This can accept screens between 35 mm and 0.5 ww mm. Typically, the screen deck has a throughput of approximately 6 tonnes/hour
- The very coarse size fraction, typically between –120 mm +31.5 mm, is processed through a dense medium drum. This can process coal at up to 10 tonnes per hour
- The coarse size fraction, typically within the size range -31.5 mm +0.5 mm, is processed through a 330 mm dense medium cyclone. The cyclone has a capacity of approximately 10 tonnes per hour at 30 mm nominal top-size.
- A sieve bend and low head vibrating screen is used for the drain and rinse process.
- Typically for thermal coals, the fine size fraction -1.0 ww mm is processed through a set of spirals or a 300 mm reflux classifier. The spirals and the reflux classifier have throughput capacities of approximately 1 tonne per hour
- For coking coals the fines fraction reporting to the spirals or reflux classifier might be -1 ww +0.250 mm. In this case the ultra fines, i.e. material less than –0.250 mm, would be processed through mechanically agitated cells (2 banks of three cells) or a column flotation cell. These components have capacities of approximately 1 tonne per hour.
- Classification of fines and ultra-fines is performed using 150 mm classifying cyclone and a 1200mm vibrating screen to guarantee maximum sizing efficiency.
Control systems
The plant contains appropriate control systems including nuclear density gauge, a full suite of density tracers, and automatic medium density control based on CITEC SCADA system. There are also two 10 tonne product bins, 1,200 mm and 600 mm Kasson screens, horizontal vacuum belt filter, water recovery and recycling systems. An on-site cold room allows for sample storage to reduce the degradation of the coal’s properties.,
Laboratory support
If there is limited coal washability information on the plant feed, ALS Coal is able to collect a sample to conduct a full washability analysis which can be used to identify the target densities to meet yield and target ash values. Each of the pilot plant products are typically dried, weighed and subsampled for ash percent. This provides guidance on the product ash and yield. A simulated overall plant product can be targeted by proportional blending of the product streams
Finally, comprehensive coal characterisation is provided on simulated product by sub-sampling the products and rejects and processing the coal through ALS’ extensive laboratory network.
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