M.K. Mohanty

Performance optimization of jameson flotation technology for fine coal cleaning

Abstract A performance optimization study has been conducted using a laboratory Jameson Flotation Cell, which resulted in the development of empirical models for four key response parameters, such as product ash content, product total sulfur content, combustible recovery and separation efficiency. The empirical models were utilized to identify an appropriate experimental region to achieve a target set of metallurgical performances from the treatment of a flotation feed sample. The separation performance obtained from the treatment of three additional coal samples used in this investigation indicate that a high positive bias factor of about 0.6, which translates to a wash water ratio of 2.5, is required to produce superior quality coal especially from the treatment of high ash coals. The separation performance obtained using the same orifice—downcomer combination with various size separation chambers indicate that the diameter of the separation chamber of the Jameson Cell can be potentially reduced without affecting the separation performance. In other words, more number of downcomers can be used with the same size cell, which will significantly improve the throughput capacity of the Jameson flotation technology without sacrificing the separation performance.

Coal maceral separation using column flotation

Abstract Recent studies have found that coal macerals have properties which may allow their use as high-valued products. A conceptual approach for the production of individual maceral concentrates utilizing column flotation is presented in this publication. Before maceral separation,the coal was ground to the particle size corresponding to near complete liberation of the macerals, which was approximately 4 gmm for an Illinois No. 6 seam coal. The production of maceral concentrates using flotation was based on the differences in the flotation rates among the various macerals, which was manipulated by adjustment of the medium pH. An increase in pH from 8 to 11 resulted in an order of magnitude reduction in the flotation rate of the vptinite maceral group while the corresponding reduction for the inertinite group was about 50% . On the other hand, the kinetic rate for the vitrinite group remained unchanged. By using pH control and column flotation, the inertinite content was increased from 7.5 % to 50% . Although the upgrading of the other two maceral groups was not as significant, it was evident that the success of the maceral enrichment for a given coal is dependent on the maceral liberation characteristics and the magnitude of the flotation kinetic rate differences among the macerals.

Enhanced column flotation performance for fine coal cleaning

Abstract Past studies have found that the froth flotation process is efficient in recovering heavy middling particles, which negatively affects the recovery-grade curve achieved for fine coal recovery. Experimental and theoretical results indicate that the recovery of middling particles can be reduced from 25% to 10% using flotation columns in a multi-stage cleaning approach, thereby improving the overall separation performance. Tests conducted on a −48 mesh coal sample found a 7% improvement in mass yield using a rougher-cleaner column circuit while producing a flotation concentrate containing 8% ash. Similarfindings were obtained from the treatment of a −65 mesh coal sample using a different flotation column technology. To fundamentalty evaluate the use of multi-stage cleaning, a continuous column model has been developed which incorporates selective and non-selective froth drop-back, and feed component flotation kinetics. For kinetic rate limiting conditions, separation performance was found to substantially improve with the use of multi-stage cleaning, which agrees with the experimental findings. Under carrying capacity conditions, the improvement is a function of the degree of selectivity in the detachment process. Economic justification of the use of multi-stage column treatment must be based on enhancements in product grade and/or mass yield.

A comparative evaluation of the leading advanced flotation technologies

Abstract A comparative evaluation has been conducted using three leading advanced flotation technologies, which utilize different types of bubble-particle attachment environment. Based on a statistical evaluation of the test data the Packed-Column technology, which provides a near plug-flow flotation environment due to the presence of corrugated packing material in the cell, produced the best separation performance due to its ability to support an extremely deep froth zone. However, because of the absence of an air sparging system and the consequent larger bubbles, the froth carrying capacity was the mininum with the Packed-Column technology. On the other hand, the throughput capacity achieved by the Jameson Cell technology, which has a self air-inducing co-current system that provides an intimate bubble-particle attachment environment characterized by an extremely high air fraction and ultrafine bubbles, was found to be maximum. The Microcel ™ technology achieved its maximum carrying capacity while providing a high energy recovery with a reasonably low reagent consumption.

Altair jig: an in-plant evaluation for fine coal cleaning

Abstract Coal preparation plants treat a majority of the run-of-mine coal using various gravity processes, which are known for their low cost and high process efficiency values. Due to the inefficiencies of conventional gravity-based processes in treating −1 mm coal, froth flotation processes are traditionally employed at a relatively high cost. To address cost and separation performance issues, several enhanced gravity separation technologies have been developed and evaluated which may allow effective gravity-based separation to particle sizes as small as 25 μm. The Altair centrifugal jig is an enhanced gravity technology, whose suitability for fine coal cleaning has been demonstrated through an in-plant study as reported in this publication. A relatively low specific gravity cut-point of 1.50 with a probable error value of 0.11 over a wide particle size range 1 mm ×45 μm is indicative of the excellent separation performance achievable from the Altair jig. Tests performed with and without ragging material were performed with the goal that the latter would provide enhanced throughput capacities. However, although the performance was close to the theoretical limits over the broad range of product grades generated, the no-ragging experiments resulted in a significant loss in coal recovery under the given conditions. Overall, the centrifugal jig achieved 80% ash rejection and 50% total sulfur rejection while recovering nearly 80% of the combustibles.

Coal Flotation Washability: Development of an Advanced Procedure

A modified coal flotation characterization procedure, referred to as the Advanced Flotation Washability (AFW) technique, has been developed which, compared to traditional procedures, provides a more accurate prediction of the optimum separation performance achievable by a froth flotation process. The AFW procedure uses a batch-operated flotation column packed with corrugated plates which provides enhanced selectivity among particles of varying degrees of hydrophobicity due to a selective bubble-particle detachment mechanism. This mechanism is more pronounced in a flotation column operating under carrying-capacity limited condition with a deep froth zone. In addition, the plug-flow environment resulting from the apparent high length-to-diameter ratio provides an improved performance over the near perfectly-mixed conventional cells used in the traditional procedures. The separation performance provided by the AFW procedure was superior to that obtained from multiple stage cleaning provided by commercially-a...

Development of a characteristic flotation cleaning index for fine coal

Cleaning index values provide valuable information for assessing the ability to concentrate a mineral in an ore using a given physical property and for selecting the appropriate separation technology. In response to the recent developments of advanced froth flotation technologies and flotation characterization procedures, a flotation index (FI) has been developed which can be utilized to quantitatively assess the flotation cleaning potential of a given coal sample. Along with an overall FI value, two separate FI values have been determined for each coal to separately characterize the negative selectivity effects caused by the presence of mixed-phase particles and the suppressed recovery rates caused by a lower degree of hydrophobicity of the coal particles. Separate FI values have been determined for ash and sulfur cleaning, which indicate the superior ash cleaning and relatively inferior sulfur cleaning performances achievable by froth flotation.

Fine coal screening performance enhancement using the Pansep screen

Abstract Size separation inefficiency in the fine particle size range of 150 μm and finer has been a perennial problem in coal preparation plants. A close examination of many plant data indicate that both quantity and quality of the clean coal product from the fine circuit of a plant may be significantly increased by improving the efficiency obtained for the size separations at 150- and 45-μm particle size. Thus, this investigation has concentrated in optimizing the fine size separation performance of a newly developed screening technology, known as the Pansep Screen. Statistically designed factorial experiments have been conducted to obtain the optimum size separation performance from the Pansep screen at d 50c sizes of 150 and 45 μm. The results of this study indicate that near-perfect size separation efficiency of nearly 98% is achievable from the Pansep screen in comparison to below 60% obtained from the classification technologies conventionally used in the preparation plants. High oversize product throughput capacity of 7 and 5 tph/m 2 were achieved for efficient 150- and 45-μm size separations, respectively.

Evaluation of the Altair Centrifugal Jig for Fine Coal Separation

A significant effort has been made during the past decade to develop gravity separators for treating fine particles. As a result, several enhanced gravity separators have been developed and commercialized. The Altair Centrifugal Jig is an enhanced gravity separator that provides relatively efficient separations on +25 μm size fractions. An experimental program conducted on −600 μm coal found that the Altair Jig reduced the ash content of the 600×44 urn material from about 30% to 10% with an 86% combustible recovery value. The pulse water pressure, feed volumetric rate and ragging volume were found to be the key operating parameters affecting the separation performance indices obtained from the process. A low density cut point of 1.55 with a probable error value of 0.09 was indicative of the high process efficiency values achievable by the Altair Jig.

Trace Element Reductions in Fine Coal Using Advanced Physical Cleaning

Studies show that pre-combustion physical cleaning can substantially reduce the trace element contents of a given coal. Using an advanced fine coal cleaning circuit comprised of an enhanced gravity separator (EGS) and a flotation column, over 80% of the Hg and Se contents of a −250 μm Illinois No. 6 coal sample were rejected while achieving an energy recovery of 80%. According to a statistical correlation evaluation, this performance was achieved due to a strong affinity of the Hg and Se with the ash forming and coal pyrite particles, which were rejected at rates of 84 and 83%, respectively. However, Cr was found to have a moderate affinity with the organic material, which limited its rejection to 62%. Treatment of a pre-cleaned pulverized coal combustion boiler feed sample originating from the same Illinois No. 6 coal seam provided an additional reduction in total sulfur and trace element contents. Overall, the EGS-Column circuit was found to be effective in reducing the amounts of three trace elements f...