Washability Characteristics Research Articles

Determination of washability characteristics of anthracite coal by index of washability and near gravity material index – a case study

ABSTRACT This paper summarizes the results of determination of the washability characteristics of anthracite coal from Vrska Cuka coal mine, Serbia. The effect of different coal size fractions has been studied through washability studies. In this study, float-sink experiments were carried out with the anthracite coal samples on (−19 + 9.5) mm, (−9.5 + 4.75) mm, (−4.75 + 2.36) mm, and (−2.36 + 0.6) mm size fractions. Two washability parameters, Index of Washability (IW) and Near Gravity Material Index (NGMI), were calculated and the results were compared. The IW and NGMI values indicated that the washability of different size fractions of anthracite coal was easy to relatively difficult to wash. The obtained values of IW showed that the order of coal washing ability by size fractions was as follows: (−9.5 + 4.75) mm, (−4.75 + 2.36) mm, (−2.36 + 0.6) mm, and (−19 + 9.5) mm. The NGMI values decreased with increasing specific gravity and decreasing particle size fractions. The minimum values of NGMI were achieved at density of 1650 kg/m3 and these values were 0.1322, 0.0695, 0.0677, and 0.0240, respectively. The results presented in this study indicate that washability of the anthracite coal is relatively easy and should be washed at a specific density of 1650 kg/m3.

Studies on Washability Characteristics of Low-Volatile Indian Coking Coal by Differential Crushing

The effect of differential crushing on liberation characteristics has been studied for a low volatile coking coal of Indian origin through washability studies. Two parameters, namely “Index of Washability” (IW) and “Near Gravity Material Index” (NGMI), are used to describe the ease of washability. The ROM Coal is crushed to four different top sizes namely, 75mm, 25mm, 13mm and 6mm.On the basis of calculated IW it is observed that relative ease of washability increases with decrease in top size. From calculated IW values it may be said that this coal can be economically beneficiated using gravity process after crushing to -6mm size. From the calculated NGMI values, the critical specific gravities have been estimated and the values for crushing to -75 mm, -25mm, -13mm and -6 mm are 1.65, 1.68, 1.53 and 1.58 respectively. These critical specific gravity values suggest the separation at this specific gravity range is most difficult task using gravity methods. From NGMI analysis, it may be said that the NGMI values for coals crushed to -25 mm & -6mm are identical (≈ 0.18) at 17% clean coal ash content. This suggests that with similar degree of difficulty, clean coal of 17% ash can be produced from these two different crushing sizes. In order to increase the yield for the clean coal of 17% ash, the decision on blending these two size coals may need to be taken.

Methodology for predicting the washability of apatite ores (Kirovsky mine, Kola Peninsula)

A statistical approach has been proposed that allows strictly defining the structure of a rock (ore), isolating fields of various structures in barycentric diagrams, and comparing them with the processing results. An original method is proposed for predicting the washability defined as the separation of apatite grains from polymineral aggregations at the crushing and flotation stages. It develops and formalizes the current approach that combines the mineral composition of ores, their structures and textures into a multifactor semiquantitative model. The method is based on the calculation of the probabilities (frequencies) of all types of intergranular contacts recorded in a symmetric matrix under a microscope in petrographic thin sections. Its canonical diagonal shape allows identifying the rock (ore) structure type. The algebraic theory of quadratic forms is used to demonstrate that the structure identified using this method corresponds to one of the types of n-dimensional nondegenerate quadratic surfaces, where n is the number of minerals in the rock (ore). The structure is invariant for a certain fluctuation in the probabilities of intergranular contacts. The calculated probabilities uniquely identify the imaging point in the corresponding barycentric diagram. The Hardy–Weinberg boundary is important as it corresponds to the ideal uniform mixing of minerals and the balance of various intergranular contacts for any modal composition of rocks (ores). It allows distinguishing fields of different structures in barycentric diagrams. The method proposed offers a means to identify ores with different washability characteristics at early exploration stages.

Nonlinear Control of Refuse Discharge in a three-product Coal Jig

The paper presents the results of simulation tests of the dynamic characteristics of a three-product jig for coal separation and control systems for refuse discharge. The changes in the position of the stratified bed layers and the density of the separation layer in the product discharge zone as well as the static characteristics of the zone in two compartments of the jig were investigated. It was assumed that the main disturbance occurring in industrial systems are changes in the flow rate and the feed washability characteristics. The simulation model was verified in industrial tests in two coal preparation plants. An analysis of the effects of the control of the bottom product discharge system for nonlinear PI controllers and adaptive radiometric density meters with variable measurement time was carried out. The aim of control was to stabilize the density of the separation layer at the desired level. The parameters of the nonlinear PI controller depended on the direction of changes in the feed flow rate. The control effects were compared with linear control systems and meters with a constant measurement time commonly used in industry. Proposed system improves product quality and reduces product losses in waste compared to conventional systems.

Beneficiation of difficult-to-wash Indian low volatile coking coal fines by Falcon concentrator

ABSTRACT The fast depleting reserves of high-grade Indian coking coal and its resultant dependence on import makes the emerging situation a fit case for exploring innovative and high efficacy techniques such as non-conventional gravity-based systems for clean coal recovery viz., advanced centrifugal gravity separators like Falcon concentrators for fine and ultra-fine coal particles processing using enhanced gravitational force. The above methodology has been adopted for low volatile coking (LVC) coal due to the high ash content associated washability characteristics and high near gravity material content. Attempt was made using laboratory Falcon SB40 concentrator for cleaning the LVC coals assaying 32.6% ash. Considering the physical properties, coal petrography and washability studies, as received coal was ground to three size fractions of –500 μm, –250 μm and –150 μm and subjected to separation in Falcon separator. Experiments were conducted using Design Expert software to evaluate the effects of four significant process variables such as feed size, pulp density, gravitational force value and water pressure. The relationship between the response functions (ash content, combustible recovery and separation efficiency) and process variables is presented as empirical model equations. Under the optimum operating conditions, LVC coal was cleaned to 18.4% ash content with 57.8% combustible recovery using Falcon concentrator.

Metal-Free Combination Tanning with Replenishable Polyphenols and Marine Oil

In line with the resurgence of natural products in the global manufacturing industry, the leather industry is also relooking the increased use of organic materials. To exploit the benefits of the vegetable tanning materials and to couple with suitable organic material for overcoming the inherent shortcomings of vegetable tanning materials, studies were undertaken. Tanning materials like raw fish oil have advantageous properties to impart on leather such as softness, lightweight, and washability characteristics. Hence studies were undertaken on polyphenol-fish oil combination tannages.
 The quantities of wattle and fish oil and process conditions were standardized. The study indicated that the oxidation of fish oil could take place in the presence of vegetable tannins. The leathers tanned by this combination tanning system could be converted into garment leathers of rich shades and possessed good strength and physical properties. Propelled by encouraging results, investigations were also made on the nature of interaction between vegetable tannins and fish oil with collagen. It was also observed that the vegetable tannins probably do not hinder the oxidation of oil. To sum up, the study leads to the development of a viable, versatile organic tanning system to gain eco-acceptability for the leather manufacturing process.

Selective screening of coal to improve the washability characteristics at different levels of size reduction

ABSTRACT In coal beneficiation, ash content is the main focus area as it plays a vital role in controlling the yield and quality of the washed clean coal. Indian sub-bituminous and bituminous coals are of low-grade with intrinsically distributed ash-bearing minerals, which makes it difficult to segregate the low ash coal. Different stages of crushing and grinding techniques have been used to produce the desired feed size of coal washeries, i.e., −13 mm. During blasting and crushing, cracks propagate through the weaker interfaces within the coal particles. Petrographic analysis suggests the formation of good amount of naturally liberated maceral-rich particles of −13 mm size at different stages. These particles generated at mine site and primary crusher are subjected to further crushing during subsequent stages of secondary and tertiary crushing, resulting in more fine generation and higher energy consumption. Hence, an attempt has been made to check the washability characteristics of coals at different stages of crushing and effect of prescreening of coarse (−13 + 0.5 mm) and fine (−0.5 mm) fraction on washability characteristics of coal and overall clean coal yield. It was observed that −13 mm particles generated at early stage of crushing show good washability characteristics compared to the crushed lump coal (+13 mm) for the separation of 17.8–18% ash clean coal; and hence, prescreening of −13 mm prior to tertiary crushing improves the process efficiency.

Assessment of coal sortability and washability using dual energy X-ray transmission system

ABSTRACT Sorting coal using x-ray transmission sensors has been explored since 1972 by Jenkinson et al. Coal sortability is assessed using washability derived from dual-energy X-Ray transmission (DE-XRT) system. Coal sorting is considered to be dry separation of coal that can be carried out before coal is send to the processing plant. It can act as deshaling/destoning process or it can also be used to selectively mine shallow coal seams to avoid overburden contamination hence dilution. There are a few commercial concepts in the coal industry which utilizes the XRT sensors to sort the coarse particle coal. In order to define final product quality in terms of ash as well the efficiency of any separation based on density such as yield, washability is used to determine the separation process parameter such as density of separation, e.g. specific gravity. Washability characteristics have been traditionally assessed using the float-sink (washability) tests. These analyses determine how much of coal can be separated from associated rock (mineral matter) in liquids of different densities. However, the test work requires a wet processing where organic liquids, referred to as heavy liquids are used. The test work is very time consuming as it requires significant amount of time to complete full washability for a wide spectrum of coal particles. To avoid using toxic chemicals and save time, the DE-XRT can easily become an alternative method to assess the washability of coarse coal before the coal is processed by sorting to establish separation parameters and obtain information about the yield of clean coal of desired quality in terms of ash content. In this project in order to assess effectiveness of DE-XRT for sorting and at the same time to derive the washability data for the coarse coal, the test work has been designed to test various lithotypes identified from coarse coal sample. As a result, the test work included classification of coal lithotypes (larger pieces of coal of certain petrographic composition), density measurement using both DE-XRT and float-sink tests and ash analysis. The results are compared to float-sink tests for coarse coal fractions obtained by proxy washability analysis derived from pycnometry. Similar to float-sink tests, the DE-XRT can estimate a relative density by measuring the attenuation of x-rays from two different energy levels. The paper explains the basics of the DE-XRT analysis and its data processing methods to determine the relative densities and how to derive washability curves and density of separation for coal sorting. The basic principle of dual-material decomposition is adopted from Dual-Energy CT in the medical industry where the sum of each vector provides a proportion of the two material.

Comprehensive performance characterization of conductive fabric made of reduced graphene oxide (rGO)

AbstractIn this study, the production and comprehensive characterization of graphene based electrically conductive textile products, which will allow lower processing costs, such as, low temperature and short process times, and known textile production processes without losing their flexibility, lightness, permeability, and washability characteristics of textile products. Reduced graphene oxide (rGO) was applied with a single step process by impregnation to woven fabrics and various properties of fabrics related to performance and comfort were analyzed besides electrical conductivity. The results obtained in the study have shown that it is possible to produce flexible and soft conductive textiles with low resistance values below 100 kΩ, resistant to mechanical deformations, such as, bending, rubbing, and stretching (cyclic test). In addition, the findings indicated that the fabrics applied rGO with the one‐step production process will provide significant advantages to the electronic textile market in terms of wearability, cost‐effectiveness, and applicable processes.

Nonlinear Control of Coal Separation in a Jig

Abstract Discussion on nonlinear control of coal separation in a jig using a float or, more recently introduced in the industry, radiometric density meters applied to measure the density of the separation coal layer, have been presented. The main signals describing the separation process are: the flow rate of the discharged refuse as the control signal, the density of the separation coal layer as the output signal and the raw coal feed rate and its washability characteristics as disturbances. A jig is a highly nonlinear control element for changes in all input signals, however, in most industrial float control systems usually there can be found linear P controllers in order to achieve stable operation and avoid frequent oscillations. There has been presented a comparison of effects of various nonlinear strategies of control, using a developed simulation model of coal separation process, which was verified during industrial tests. The analysis showed a distinct advantage of systems with a radiometric meter over systems with a float measuring the stabilized density of the coal separation layer and advantage of nonlinear PI controllers over commonly applied P or PI linear controllers.

Utilization of High Ash, Low Volatile Coking Coals of Jharia Coalfield, India for Coke Making

India is having limited resources of coking coal, an essential input for production of iron and steel especially through blast furnace route. The coking coal sources are presently from the lower seams of Jharia coalfield, which are high in ash content and low in volatile matter and difficult to wash. This paper describes the washability characteristics of a typical coking coal from the Eastern and Western Jharia coalfields aiming at 18% ash level in the clean coal mainly to meet the specifications of coke making for blast furnace use. Conventional float-and-sink testing was used to determine the yield of clean coal for the coarser fraction, while the coal fines was subjected to flotation. The theoretical recovery of clean coal for the coal tested from Eastern and Western Jharia coalfields are 27% and 19.7% at the stipulated ash content. The coking propensities and the petrographic analysis of the clean coal strongly support its use for coke making either directly or as a blend with imported coal.

Dry processing of high ash Indian coal by air fluidized vibrating deck

ABSTRACT Processing of noncoking coals in India is limited due to the high cost involved in wet processing. In the present study, dry beneficiation of two high ash Indian non coking coal samples from two different coalfields, namely, Talcher (coal-A) and Ib Valley (coal-B) having diverse characteristics are studied using an air fluidized vibrating deck separator. Washing characteristics of two coal samples indicate that coal-A was easy-to-wash and coal-B was difficult to wash. The near-gravity materials (NGM) present in coal-B were higher than coal-A due to different geographical origin. The responses of dry separation of two coal samples studied under varied process variables were found to be dependent on the washability characteristics and the operating parameters used for achieving the desired product. The performance of dry beneficiation is described by the recovery of combustibles, ash rejection, ash recovery in clean coal (R A/cc), Ecart probable error (Ep), and organic efficiency. It is found that Ep of the dry process was 0.17 for easy-to-wash coal (coal-A) and 0.23 for difficult-to-wash coal (coal-B). The organic efficiency of coal-A was 91% and 80% for coal-B at optimum condition. The prospective of dry separation of high ash Indian coal using air fluidized vibration technology was found to be effective for achieving product with 34% ash content.

Laboratory-Scale Tests for the Utilization of High Ash Non-Coking coal in Coke-Making Process

India has vast coal resources all over the country; however, the presence of high ash content makes them invulnerable for industrial usage. To compensate for the rapid depletion of high-quality coking coals and to compensate for the demand for coal in iron and steel sectors, coal cleaning or beneficiation and blending techniques have come into limelight for the usage of low-quality coal. In this paper, laboratory-scale experiments were performed on the utilization of Indian high ash non-coking coal (NCC) and imported semi-coking coal (SCC) for the coke preparation. At first, washability characteristics of Indian high ash coal were investigated by using jigging, spiral concentration, and sink and float density separation methods. The optimum cut-off density NCC and SCC coals were blended and sent for the caking properties analysis. Proximate and ultimate analysis, vitrinite reflectance, crucible swelling number, and caking index or roga index have been taken as the measure for the caking ability of coal blends.

Efficient utilization of Indian Coking Coal: Opportunities and challenges

The preservation of coking coal and the reduction of coke cost are gaining much importance in iron and steel industry. An effort is being made worldwide to maximize the use of inferior quality of coking coal in cokemaking without sacrificing the coke quality to minimize the coke cost. In general, Indian coking coals contain lower content of vitrinite (≤ 50%) and higher content of ash (≥ 15%) as compared to imported coking coal. Indian coking coals have poor washability characteristics also. Therefore, for making coal blend for coke making, selection of an appropriate proportion of Indian coking coals with imported coking coals is a major challenge for Indian steel industries. Proper selection of Indian coal not only reduces the coking coal import but also minimizes the coal blend cost with added benefits of the increase in the captive mine life. This paper touches the opportunities and challenges for efficient utilization of Indian coking coal as a component in the coal blend to produce the desired quality of coke.

Refining of Indian coals to obtain super clean coals having insignificant amounts of deleterious elements under milder conditions

ABSTRACT Indian coals have difficult to formidable washability characteristics. Presently, five Indian coals were subjected to solvent extraction under ambient pressure conditions using N-methylpyrrolidone (NMP) containing a small amount of Ethylenediammine (EDA) (termed as e,N solvent system). The coals and their solvent refined super clean coal (SCC) products obtained after solvent extraction have been extensively characterised for calorific value, ATR-FTIR spectral analysis, XRD measurements and ICP-MS analysis. The organo-refining of coals through the use of e,N extraction resulted in the production of Super clean coals (SCCs) having 0.2–1.5% ash. Studies have been carried out for the first time to analyse the concentration of minor elements in super clean coal. However, the ATR-FTIR analysis, XRD measurements and ICP-MS analysis also revealed the reduction of major elements such as Na, K, Al, Mg, Ca and Fe. The ATR-FTIR and XRD studies of SCC clearly demonstrated deashing of coals. As high as 94% improvement in calorific value in one of the high ash coals, Pandra coal could also be achieved on extraction with e,N solvent system.

Effect of Quaternary Ammonium Salt Addition to Conventional Biodiesel Production Process

Biodiesel on a commercial scale is largely produced by transesterification using a conventional homogeneous catalyst like KOH and NaOH. The major problem associated with conventional homogeneous transesterification process is that it is prone to water & FFA content. This problem can be mitigated with some process modification using quaternary ammonium salts. In the present study, the reaction between waste palm oil & methanol was carried in a batch reactor at 65oC & various molar ratios of oil to methanol. Further, the effect of various dosages of tetramethylammonium bromide (TMAB) addition to this reaction was studied. Results show that there is a strong influence of TMAB (a phase transfer catalyst) on the methanol requirement during the reaction and also on the washability characteristics of the produced biodiesel. It was observed that there is a considerable decrease in the molar ratio of methanol to oil requirement during the reaction. Moreover, the addition of TMAB has enhanced the washability of the final biodiesel product by forming less foam. This has a direct advantage of decreasing the water requirement during the purification process.

Design of experiments to optimize the extraction parameters of a power grade Indian coal

Low grade high ash coals with difficult physical washability characteristics require chemical cleaning techniques such as solvent extraction to obtain super clean coal with lower ash contents. Kedla, an Indian low grade coal has ash content around 44%–50% and there is a need to maximize its solvent extraction yield so as to make this power grade coal industrially useful. This paper highlights the use of definitive screening design and response surface methodology to extract the maximum organic matter from Kedla coal using ethylenediammine (EDA) and N-methyl pyrollidone (NMP) as solvents under mild atmospheric pressure conditions. The coal was pre-treated with acetic acid before extractions were carried out. The parameters such as the acid pre-treatment time, acid concentration, particle size, the co-solvent concentration and the solvent concentration were optimized in this paper. With this design of experiments technique about 40% of the organic matter with minimal ash (less than 2%) content was rendered extractable unlike the already postulated designer solvent system—e, N system (i.e. NMP containing small amount of EDA) that uses coal to solvent ratio as 1:17 (wt/vol) and coal to co-solvent ratio as 1:1(wt/vol) thus only giving 19% extraction yield. Therefore, the present design of experiments technique helps in conserving the number of experiments for process intensification.

Development of simple techniques for determining the extent of coal cleaning-part 2: Estimating coal washability characteristics and separator performance

ABSTRACT The extent of coal cleaning is primarily dependent upon three core factors; (1) coal liberation, (2) coal washability, and (3) separator performance. The first factor has been dealt with in part 1. This part focuses on the second and third core factors. Coal washability data are typically generated by the standard float-sink test. Many researchers have proposed different washability indices based on float-sink data to describe coal amenability to washing, but most of these involve cumbersome mathematical calculations while relying on an error-prone graphical technique. Probable error (Ep) is generally used to represent coal separator efficiency but its calculation requires float-sink analysis of both feed and separator products. This paper proposes a simple equation for quantitative estimation of the degree of coal washing based on the feed coal washability data, clean coal yield, and ash. The proposed equation was applied to quantify and compare the washability characteristics of coals from different countries and provides an alternative method for measuring separator efficiency (in percentage).

Application of high-resolution X-ray microcomputed tomography for coal washability analysis

Float and sink testing is the standard laboratory method for determining the coal washability characteristics using heavy liquids. In this paper, we describe an alternative technique for determining coal washability using High-Resolution X-ray Microcomputed Tomography (HRXMT). Specifically, the application of HRXMT and specialized software have enabled us to determine the particle characteristics of coal samples with the considerable details needed for building washability analysis. Coal samples taken from the feed streams to the dense medium circuits at two plants in Australia were obtained, characterized and used in the analysis. The coal samples were fractioned into the size and density fractions using sieves and heavy liquids as per the Australian Standard AS 4156.1-1994. The fraction-averaged densities were determined using helium gas pycnometry. The float and sink results were obtained for calibration and validation of the HRXMT results. Our results show that HRXMT can be used to perform coal washability analysis. It provides a new methodology for non-destructive and non-toxic determination of coal washability data. It is safe and fast. Significantly, the successful applications of X-ray computed tomography to perform coal washability analysis would allow for developing an on-line coal washability monitoring system, which would not be achievable with the traditional float-and-sink analysis.

Effect of Crusher Type and Crusher Discharge Setting On Washability Characteristics of Coal

Natural resources have been serving the life of many civilizations, among these coals are of prime importance. Coal is the most important and abundant fossil fuel in India. It accounts for 55% of the country’s energy need. Coal will continue as the mainstay fuel for power generation. Previous researches has been made about the coal feed size and coal type had great influence on the crushing performance of the same jaw crusher and amount of fines generated from a particular coal depends not only upon coal friability but also on crusher type. Therefore, it necessitates crushing and grinding the coal for downstream process. In this paper the effect of crusher type and crusher discharge setting on washability characteristics of same crushed non-coking coal has been studied. Thus four different crushers were investigated at variable parameters like discharge settings, different capacities and feed openings. The experimental work conducted for all crushers with same feed size and HGI (Hardgrove Grindability Index). Based on the investigation the results indicate that the four crushers which has been involved for the experimental work shows that the variation in not only the product size distribution and also reduction ratio. Maximum breakage has been occurred at coarsest size fraction of irrespective of crusher type and discharge setting.