The coal industry is being subjected to increasing public scrutiny with regards to its effect on the environment and impact on public health and safety. Recently, disposal and storage of fine coal waste slurry has drawn considerable public attention. This article discusses the emerging paste thickening technology as a possible solution to the fine coal waste slurry disposal problem. Paste-thickening studies were conducted on thickener underflow slurry from a central Appalachia preparation plant. Initial experiments were conducted with a laboratory scale T-Floc apparatus to optimize flocculant dosages to obtain maximum settling flux and underflow solids concentration. Results showed that the addition of anionic flocculant (400 g/t) to the slurry followed by cationic flocculant (100 g/t) provided the highest settling flux (3.85 tonnes/hr/m2) and solids concentration (35% by weight). Pilot-scale paste thickening tests were conducted using a Dorr-Oliver Eimco Deepcone™ thickener. The thickener concentrated the solids from 10% to 50% by weight using about 450 g/t of anionic and 150 g/t of cationic flocculants. The thickened paste had a yield stress of about 165 Pa that is sufficiently low to allow transport using a conventional positive displacement pump to a disposal area. The clarity of the overflow stream was similar to that currently obtained with a conventional thickener.

A coal-blending model has been developed using relationships between coal and coke quality parameters. This coal-blending model gives a least-cost coal blend for the desired coal blend quality in terms of ash, volatile matter, mean maximum reflectance, and coke quality based on the coke strength and ash content. The model takes into account various constraints like coal availability, minimum and maximum permitted coal usage, etc. The model has been validated using actual plant data of coal drawn from different silos. The model is presently being used in plant as a process control tool. This model can also be used to evaluate a new coal or selection of a least-cost coal blend for a plant.

Coal properties are inherently variable even within a single coal seam due to reasons such as coalification history and mining method. Since nonconsistent coal characteristics negatively affect the efficiency and production cost of power plants as well as the profitability of the coal producer, special attention should be paid to control the variability of coal quality. In this paper, variations in coal properties delivered to the Tuncbilek Power Plant have been investigated by means of control charts. The control charts have mostly indicated that the variations in the properties of coal are significantly high. The considerable amount of off-design coal relative to coal contract specifications has been determined. Finally, the revenue of the coal producer has been examined by taking into account the blending operation; the aim of which is to minimize the variance of coal properties.

This study demonstrates a low-cost, high-efficiency filter press technology for dewatering minus 150 µm column flotation clean coal products from two coal mines. Pilot-scale in-plant demonstration of this technology at these two locations provided stable, trouble-free operation while achieving an excellent dewatering performance at a high throughput. At one location, filter cakes with residual total moisture contents in the 20–22% range were achieved. At the other location 25–27% residual total moisture contents were achieved. At the second location, lower cake moisture content in the range of 21–25% was achieved with the use of appropriate dewatering aids. For difficult to dewater coals with higher clay contents, the innovative use of hot water during the filtration process was found to reduce cake moisture content by two to three percentage points over the baseline conditions. Engineering economic evaluations indicated that a fine coal product can be produced using column flotation and the filter press at a cost of $5.95/t (dry basis) for one mine. With appropriate blending strategies, annual profitability can be shown to increase by $0.9 million ($US) for this 1.8 Mt/year mine. For the second 2.4 Mt/year mine, annual profitability was projected to increase by $2.5 million ($US).

The potential of using Air Dense Medium Fluidized Bed (ADMFB) separation for cleaning sub-bituminous coal was investigated. The effect of operating parameters such as the fluidizing air velocity and medium particle size on separation efficiency was determined with coal of various size fractions. Good separation efficiencies with raw coal in the 6 to 1 mm size fraction were achieved. Partition curves showed an E p value of 0.03 for coal in 5.6 to 3.35 mm size fraction. For the 1.00 to 0.42 mm size fraction, the separation efficiency deteriorated to an E p value of 0.10. To achieve an optimum separation efficiency, a separation medium with a narrow and distinct size fraction is needed to allow a superficial gas velocity sufficiently high to create a pseudo fluid medium bed while sufficiently low to avoid back mixing of fine coal and lifting of fine size mineral matter during fluidization.

The possibility of significant improvements in vacuum filtration of fine coal suspensions through the application of ultra-flocculation was studied. It was shown theoretically that even when present in quantities of a few percent, the ultrafine particles (<10 microns) highly contributed to the hydraulic resistance of the filter cake. The experiments showed that short-term hydrodynamic treatment of the coal suspension at relatively high medium velocity gradients (750 s−1) performed immediately upon the introduction of the flocculant resulted in significant improvements in the filtration process due to the effect of specifically binding the finest particles. This treatment decreased the hydraulic resistance of the cake on the screen vacuum filter by roughly 1.6 times, decreased the solids content in the filtrate by 4 times and decreased the flocculant consumption by 2 times.

ABSTRACT Experiments have been carried out to measure the effect of processing temperature on the moisture content of low rank coal upgraded by the hot water drying (HWD) method. The Berau coal from East Kalimantan, which was used for this investigation, is a sub-bituminous coal with a calorific value of 5324 kcal/kg and an inherent moisture content of 16.13% (air dried basis). Experimental results from this study indicate that at the processing temperature of 300°C the moisture content is reduced to 1.94% and the calorific value is increased up to 6312 kcal/kg (air dried basis). The change in functional groups determined by FTIR analysis and the change in combustion characteristics determined by DTA-TG are discussed for both the raw and upgraded coals.

ABSTRACT Laboratory testing was carried out to evaluate the performance of a wet-drum magnetic separator (WDMS) when treating magnetite dense-medium slurries containing fine bituminous coal refuse material. Test variables included slurry feed rate, magnetite-to-coal ratio, and size distribution of the coal refuse. The separations were carried out with and without the application of ultrasonic energy. The performance of the WDMS was evaluated based on the purity of the magnetic concentrate and recovery of magnetic material. As expected, the purity of the products depended on the operating conditions, whereas magnetic recovery was essentially independent of operating conditions. Moreover, under many conditions, the purity of the magnetic material increased slightly after ultrasonic treatment. For selected tests, the size distributions of the magnetic material were determined for both the magnetic concentrate and nonmagnetic streams. This analysis indicated that after demagnetization, the size distributions of the magnetic material in both the concentrate and nonmagnetic streams were similar.

ABSTRACT Recent test data have shown that the Knelson concentrator can provide a more efficient separation than froth flotation when cleaning coal in the 150 × 25 µm particle size range. To further improve the performance of this enhanced gravity separator, air bubbles were injected into the feed stream in an attempt to decrease the apparent density of the coal particles due to the formation of bubble-coal particle agglomerates. The test data showed that air injection had a significant impact on operating characteristics and separation performance. Coal recovery was increased by 10 to 20 absolute percentage points, while a 2 percentage point drop in the minimum product ash content was also achieved.