Processing of coal fines in a water-only cyclone.

It is reported in the literature that a water-only cyclone (WOC), a centrifugal gravity concentrator, is an alternative to froth flotation to treat coal fines (below 0.5 mm). This unit overcomes the inherent limitations of froth flotation and the dense–medium cyclone techniques as it requires no chemicals or artificial medium. The literature dealing with WOC performance to treat coal fines is also limited and as a result it is not well established how the design variables affect the performance of a WOC while treating coal fines. Therefore, an attempt has been made to develop regression models based on factorial design of experiments to quantify the effects of major design variables of a WOC on the beneficiation characteristics of a typical coal fine sample. Further attempts have been made to provide possible explanations on the observed trends of the data based on simple hydrodynamic analyses

Development of new coal washability index

A new coal washability index, termed as ‘near gravity material index (NGMI)’, has been developed based on the sink-float data. This new index incorporates the effect of ash distribution in the near gravity material at various specific gravities of separation. The optimum specific gravity of separation of a particular coal may be determined by plotting NGMI as a function of various specific gravities of separation or the desired clean coal ash content. The concept and the method of calculation of this index have been discussed in detail. Using some published float-sink analytical data, a quick comparison of the washability characteristics of several different coals is demonstrated utilizing the NGMI curves for these coals

Separation Characteristics of Coal Fines in a Knelson Concentrator – A Hydrodynamic Approach

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

The "fish-hook" phenomenon in centrifugal separation of fine particles.

The literature on “fish-hook” in hydrocyclones is growing and so an attempt has been made to provide a mechanistic argument supporting its occurrence in all centrifugal separators

Modeling of coal flotation in a batch and continuous cell operation Coal Preparation

Detailed kinetic analyses of various size fractions of coal in a batch and continuous flotation operation have been presented. It is shown that the recoveries of non-ash and ash forming materials of individual size fractions during flotation in both batch and continuous cells can be described adequately by first order kinetic equations. A methodology has been proposed to predict the kinetic parameters in continuous flotation using suitable correction factors to batch flotation data

Applicability of a Dense Medium Cyclone and Vorsyl Separator for Upgrading Non-Coking Coal Fines for Use as a Blast Furnace Injection Fuel

Replacement of metallurgical coke by high injection rates of thermal coal into the blast furnace is an important technology as it reduces the cost of hot metals significantly. However, one of the main problems that prevents the use of thermal coals is their high mineral-matter contents. Although, the ash content of coals to be injected in a blast furnace should be as low as possible, a maximum of 16% ash is acceptable. A non-coking coal sample from Chhattisgarh area, India, having a feed ash content of around 27% was collected for beneficiation studies to a grade acceptable for the injection purposes.A series of experiments were conducted in a 76-mm diameter dense-medium cyclone (DMC) and a Vorsyl separator (VS). It is observed that a clean coal having around 16% ash can be produced using both the cyclones if the variables are properly optimized. Further, it is observed that at the same ash level the yield of clean coal was 5%–6% more in VS than in DMC. It has also been demonstrated that at the same ash level, the magnetite medium stability in a VS was better than a DMC

Development of a New Proximate Analysis Based Correlation to Predict Calorific Value of Coal

The experimental determination of higher heating value (HHV) of solid fuels is a cost intensive process, as it requires special instrumentation and highly trained analyst to operate it, where as proximate analysis data can be obtained relatively easily using an ordinary muffle furnace. Therefore, to simplify the task and to reduce the cost of analysis many correlations were developed for determining HHV from proximate analysis of solid fuels. An attempt has been made in this paper to evaluate the applicability of these correlations with a special focus on Indian coals. It has been observed that the developed correlations are either complex in nature or by-pass the effect of important variables like moisture and ash contents of coals. An effort has, therefore, been made to develop a simple correlation based on proximate analysis data for predicting HHV of coal (as-received basis). The model presented here is developed using analyses of 250 coal samples and its significance lies in involvement of all the major variables affecting the HHV. The developed model appears to be better than the existing models and has the following form

Studies on Kelsey jig treating Indian coal fines

The key operating parameters in a Kelsey jig have been identified based on the understanding of its operating principle. Empirical models have been developed to predict the performance of the Kelsey jig while treating typical Indian coal fines at a given operating condition. Empirical models developed have also been validated with some random experimental data generated within the range of the parameters studied