The difference in the physical properties, particularly the water resistance or wet strength, of the binderless coal briquettes produced from flotation feed and concentrate was investigated using six bituminous coals from two collieries in the Witbank Coalfield. The coal samples were analyzed for their proximate, petrographic, and mineralogical properties. The presence, in the flotation concentrates, of the reagents used during the froth flotation process was also investigated using gas chromatography. Pillow-shaped binderless briquettes were produced from coal samples at various moisture contents and a pressure of approximately 17 Mpa using a Komarek B-100A double-roll press. The briquettes were tested for some physical properties (i.e., dry- and wet-compressive strengths), which were thereafter compared with the properties determined for the coal samples. The binderless briquettes produced from the flotation concentrates were more water-resistant than those produced from the flotation feed. The flotation feed and concentrates of the coals tested were found to have similar petrographic properties. As expected, the ash and kaolinite contents were found to be lower in the flotation concentrates than in the flotation feed. Flotation reagents were detected in the flotation concentrates from both collieries. From the results obtained it is concluded that the increased water resistance of the binderless briquettes produced from flotation concentrates of the coals tested is due to a combination of the fineness of the coal particles, assisted by the amount of reactive macerals (most particularly vitrinite) with the lower ash and kaolinite contents, together with the presence of the flotation reagents, particularly the collector, in the flotation concentrate.

ABSTRACT The nonevaporative brown coal dewatering technologies, Mechanical Thermal Expression (MTE) and Hydrothermal Dewatering (HTD), are being evaluated in an attempt to increase the efficiency of coal drying compared with current evaporative methods. Product waters from each of the three major Latrobe Valley mines were prepared under both MTE (200°C and 15 MPa mechanical pressure) and HTD (300°C and 12 MPa) conditions. Comparison of the relative abundance of individual inorganic components across the two processes generally reflected their form (dissolved, exchanged, or mineral) in the parent coals. For MTE the data were complicated by leaching of rig components (principally bronze). MTE-derived waters contained greater amounts of Ag, As, Cd, Cr, Cu, Hg, Mo, Ni, Sn, and Zn. HTD waters had greater amounts of Al, B, Ba, Ca, Fe, K, Mg, Mn, Na, Pb, Se, Sr, Tl, and V. Dissolved organic carbon was five times higher in the HTD products as a result of the higher processing temperature employed. Many species (Al, Ag, As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, V, Se, and Zn) were found to be above acceptable guidelines for discharge to the environment.

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.

Indian coals, which are of Gondwana origin, contain high ash wherein the extraneous material was intimately mixed in the coal matrix during the formation stage, causing a high level of impurities in the run-of-mine (ROM) material. These coals possess difficult to very difficult washability characteristics. Beneficiation of high-ash noncoking coals of India has become the prerequisite for improving the overall economics and efficiency of power generation. This article describes the washability characteristics of a typical noncoking coal from the Ib Valley Coalfields aiming at 34% ash level in the clean coal as per the stipulations laid by environmental gazette notification of the Government of India. Conventional float-and-sink testing was used to determine the yield of clean coal of 58% at 34% ash content.

This article evaluates frother performance by studying a two-phase gas-liquid system. Surface tension, foamability, foam stability, and bubble-size distribution were measured as a function of frother type, frother dosage, and solution pH. Variation of bubble size with respect to frother concentration was used for predicting the critical coalescence concentration (CCC) of selected alcohol and polyglycol ether family frothers. An inverse relationship was found between critical coalescence concentration and dynamic foamability index (DFI). Frothers DF-1012 and PPG were found to be more powerful in terms of stability, foamability, and CCC than frothers belonging to the alcohol family. Frother effectiveness was found to be relatively better in alkaline pH.

At the West Bokaro Washery of Tata Steel, India, the coarse coal is dewatered in a vibrating basket centrifuge and fine clean coal is dewatered in a screen bowl centrifuge. Due to the higher amount of fine fraction (0.038 mm) treated in the flotation circuit of the washery (about 9% of ROM), the moisture content of the clean coal fines is high. A polyacrylate surfactant reduced the fine coal moisture content by 8% and it was found to be the best among the various reagents tested in the laboratory. The chemical was found very effective for dewatering the coarse clean coal. Laboratory and plant trials showed that through treating only the coarse clean coal by the surfactant, the moisture in the composite clean coal could be reduced from 12.0% to 9.8%. The optimum dosage of the reagent was 0.24 kg/t dry coal. Laboratory-scale filtration using coagulant and surfactant increased filtration rate of centrifuge centrate. Also, the final moisture content was found to be 10% less than that obtained without addition of any reagents. For improving the clarity of thickener overflow, anionic polyacrylate based flocculant was found better than present plant flocculant based on polyamide. The optimum dosage of the recommended flocculant was 0.012–0.016 kg/t of dry fine coal.

Fine coal (− 0.5 mm) is treated in a flotation circuit at Bhelatand washery of Tata Steel. The average ash content of the flotation feed, the fine clean coal, and the tailings of the flotation circuit are 18.5%, 12.5%, and 36%, respectively. The yield of clean coal from the flotation circuit is about 72%. However, the performance of the circuit in terms of clean coal yield is not satisfactory. The feed to the flotation contains 15–20% of oversize (+ 0.5 mm) fraction because of the inefficiency of the desliming screens. These oversize materials, which are of high carbonaceous value, are not efficiently recovered through the flotation process. Hence, the major challenge is to improve the flotation kinetics of the coal fines, especially the oversize particles. The way flotation reagents are distributed down a flotation bank can positively influence the flotation response of oversize particles. Hence, two-stage reagent distribution, with extra amount of reagent in the second stage, was studied in the laboratory. Results of laboratory-scale studies showed an improvement in yield of clean coal of 10–12% with a marginal increase of clean coal ash content. Based on encouraging laboratory findings, the idea was implemented in the plant, which showed a substantial improvement in the yield of clean coal from 74% to 84% with marginal increase in clean coal ash content.

Thermal coal, which is the mainstay of India's power generation, contains as high as 50% ash. To meet the rapidly growing demand for thermal power, the transportation facilities need to be significantly expanded. Major routes of Indian Railways are currently saturated. Creation of transport infrastructure is expensive. Beneficiation of coal is known to improve its quality and consistency. The present work examines the impact of beneficiation on thermal coal transportation by railways and finds that it would considerably improve the loading capacity of wagons, their life and also “release” carrying capacity on the saturated rail network.

The Knelson concentrator has found wide acceptance in the gold processing industry to recover fine free gold particles from the milling circuits. Several case studies have recently been reported to extend its applications for processing various mineral fines with limited success. A few empirical models have also been developed, but there has been hardly any attempt to understand the basic particle separation mechanism inside this equipment. An attempt has, therefore, been made to understand the separation characteristics of coal fines in a Knelson concentrator. The entire exercise has revealed that this equipment can produce a clean coal ash content of 17% from a feed coal ash content of around 36%. The hydrodynamic analysis provided will also help in understanding the roles of centrifugal force and the fluidization water to process various other mineral fines using a Knelson concentrator.