Non-coking Coal Research Articles

Dissolution Kinetics of Iron from Low-Grade Mn Ore and Optimization Using Response Surface Methodology

In this study an attempt has been made to increase Mn/Fe ratio in dump Manganese ore fines so that it can be used for the production of ferromanganese. For this purpose non-coking coal was used as reductant and dilute hydrochloric acid as leaching medium for the roasted ore. The effects of acid strength, leaching time, leaching temperature, stirring speed, ore particle size and pulp density have been studied. The dissolution of iron follows the kinetic model 1 − 2x/3 − (1 − x)2/3 = kdt. Thus product layer diffusion is the controlling mechanism and the activation energy has been determined to be 26.23 kJ/mol at 40–95 °C. Another set of experiments have been conducted according to 23 full factorial design, and regression equation for iron dissolution has been developed.

Chemical and mineralogical composition of Kathara Coal, East Bokaro Coalfield, India

Utilisation of any coal primarily depends on its organic constituents. However, the inorganic constituents i.e., mineral matter present in the coal can decide its end uses. Therefore, the study of mineral matter in coal is an inevitable and such type of studies in India is very scanty. In this paper, we present the characters of a relatively low-ash non-coking coal from Kathara mines, East Bokaro coalfield, India with emphasis on its inorganic constituents and mineral matter. The coal is characterised by 22.56wt% ash (dry basis), 28.78wt% volatile matter (dry basis), and 48.66wt% fixed carbon (dry basis). Modal analysis by optical microscopy revealed 53.6vol% vitrinite, 38.3vol% inertinite, 8.1vol% liptinite on the mineral matter free basis (mmf), and 25.1vol% mineral matter. The minerals present in this coal are dominantly clay, quartz and siderite with a minor quantity of hematite, magnetite, goethite and pyrite. Electron micro-probe studies revealed trace presence of sphalerite, baddeleyite, and some altered magnesium silicate. The total sulphur content of this coal is found to be 1.16wt% on dry ash free basis (daf). Since the majority of the minerals, although fine in size, occur as independent phases with distinct and weak grain boundaries with the macerals, the coal shall be susceptible for beneficiation and the cleaner product can find applications in metallurgical industries for partial substitution in coke making because the mean vitrinite reflectance of this coal is 0.70%.

Microstructural relation of macerals with mineral matter in coals from Ib valley and Umaria, Son-Mahanadi basin, India

Coal petrology provides significant inputs for the industrial utilisation of coal and for broad understanding the coal formation and diagenesis. The present paper entails the results of the investigations carried out on the selected coal samples, from Ib valley and Umaria coalfield, using scanning electron microscope (SEM) and X-ray diffraction (XRD) to study the surface microstructures and minerals present in them and the relationship of the finely dispersed mineral matter with the organic constituents. This would further help in evaluating the distribution and chemical character of the mineral matter occurring within the maceral types. Ib valley and Umaria coals are typical Indian (Lower Gondwana) non-coking coals and only scanty data is available on SEM study of these coals. Under SEM examination, it manifests that, the mineral matters of these coal occur as deep intergrowth, massive impregnation, superficial mounting, filling and depletion of micropores, mechanical cavity filling and fusinitic cavity filling.

Selection of Coals for Making High Quality Metallurgical Coke at Ajaokuta Steel Company Limited

The objective of this paper is to describe the process and the need to select coals for making high quality metallurgical coke for use in the Blast furnace of the Ajaokuta Steel Company Limited. The selection process of these coals for the production of quality iron and steel will apparently reduce the dependence and huge financial burden that might be incurred by Government in the production process. This paper will therefore focus on the various methods of selecting coals for blend, the options of incorporating the locally available non-coking coal in the charge. Some other parameters, classification of coals and their functions were also highlighted

Study on the differences in the oxidation characters of two chinese coals

The adiabatic oxidation test indicates that the self-heating rate of candle coal (YM) is higher than that of non-coking coal (DFS) in the initial stage, whereas it is lower than that of DFS coal in the later stage.

Kinetic studies on the reduction of iron ore nuggets by devolatilization of lean-grade coal

An isothermal kinetic study of a novel technique for reducing agglomerated iron ore by volatiles released by pyrolysis of lean-grade non-coking coal was carried out at temperature from 1050 to 1200°C for 10–120 min. The reduced samples were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and chemical analysis. A good degree of metallization and reduction was achieved. Gas diffusion through the solid was identified as the reaction-rate-controlling resistance; however, during the initial period, particularly at lower temperatures, resistance to interfacial chemical reaction was also significant, though not dominant. The apparent rate constant was observed to increase marginally with decreasing size of the particles constituting the nuggets. The apparent activation energy of reduction was estimated to be in the range from 49.640 to 51.220 kJ/mol and was not observed to be affected by the particle size. The sulfur and carbon contents in the reduced samples were also determined.

Behavior of three non-coking coals from Iranian’s deposits in simulated thermal regime of tunnel kiln direct reduction of iron

The behavior of three types of non-coking coals from Iranian’s deposits in thermal regime of tunnel kiln direct reduction of the iron (TKDRI) process has been investigated. The heating condition of raw materials in tunnel kiln was simulated in a vertical TGA for three different non-coking coals. For non-isothermal devolatilization of coals from room temperature to 1100°C, the heating rates of 1.5, 3 and 7°C/min were chosen. Coal mass and volumetric changes during devolatilization were observed by TGA and dilatometry analysis. XRD and scanning electron microscopy of raw coals and chars were used to analyze coal structural changes. In non-isothermal low heating rate pyrolysis of coal, most of the volatiles leave the sample between 400 and 800°C. In this temperature range swelling observed in all coal samples, especially for high volatile coal in which swelling increased in higher heating rate and also remains even after cooling the sample to room temperature. In addition, the lower the heating rate of coal pyrolysis, the most reducing agents are available in preheating zone of TKDRI process. Devolatilization up to 1100°C broadened graphite peaks of coals which assumed to be related to rearrangement of crystalline clusters. Surface morphology of coal samples revealed more cracks and porosities after devolatilization. Low volatile coal samples seemed to be suitable for TKDRI process as their lower swelling, making less turbulence in charge bed despite the fact that high volatile coal will probably provide a more reactive bed for intermediate iron oxide layer.

Effect of Coal Cleaning on Ash Composition and its Fusion Characteristics for a High-Ash Non-Coking Coal of India

ABSTRACTIndian coals are usually blended or beneficiated prior to being fed to utility boilers. These coals often satisfy the heat-value requirement of the boilers but may not be ideal from an ash-composition perspective. The ash compositions of beneficiated coals can significantly differ from that of the original coals thereby affecting the fusion characteristics. To have a better understanding of the variation of ash compositions due to coal cleaning, the present investigation focused on the study of ash composition in different size and density fractions of a high-ash non-coking coal. A run-of-mine coal (58.5% ash) was crushed to -75 mm and screened into six size fractions. The individual size fractions and the composite coal -75 +0.5 mm were subjected to density separation. The ash composition and ash fusion characteristics of size and density fractions were determined. The basic components of ash enriched in the lower density fractions while acidic oxides concentrated in the higher density fractions. Ash-fusion temperature and gross calorific value showed linearity with density. No such variations were observed for the size fractions. The results also indicated that cleans (20% ash) and middlings (42% ash) may be efficiently utilized for direct reduction of iron and pulverized coal power generation, respectively.

Beneficiation of an Indian non-coking coal by column flotation

Beneficiation of non-coking coal is gaining ground in India. It not only reduces the volume of inert content to be transported to the power plant and also lowers the wear in the boiler houses. For special applications such as the fuel for integrated gasification combined cycle plant (IGCC), the ash content in the coal should preferably be below 15 %. Indian coals are characterized by high inter-grown ash content mainly due to ‘drift origin’ of Gondwana formation in Permian age. This warrants fine grinding of non-coking coal in order to liberate the ash forming minerals from coal macerals. A non-coking coal sample of vitrinite type from India was ground to 44 µm (d80) and subjected to column flotation to improve its quality. The non-coking coal analyzing 34.6 % ash, 26.2 % volatile matter, 1.3 % moisture and 37.9 % fixed carbon could be upgraded to a concentrate/froth of 14.83 % ash at 72.18 % yield by optimizing collector and frother dosages and flotation column operating parameters, namely, froth depth, superficial feed velocity and superficial air velocity. The concentrate produced by this process is suitable as fuel for IGCC in coal-to-electricity route.

Pre-combustion removal possibility of hazardous trace elements from Indian high-ash coal by coal preparation technologies

ABSTRACTMany of the potentially hazardous air pollutants listed in the 1990 Clean Air Act are elements commonly found in trace amounts in coal. When coal is burned, these elements release into the environment. An option for controlling the release of these elements into the atmosphere is to remove them before combustion. Conventional physical coal cleaning processes are effective in reducing the concentration of many of these trace elements in coal. In addition, advanced cleaning processes directed toward reduction of various elements may perform better than conventional processes. Therefore, current research focuses on the advanced coal cleaning technology which is directed toward reduction of mineral matter and various toxics elements as well. Results of recent studies indicate that the degree to which a specific trace element can be reduced by coal cleaning depends on its distribution in the coal. To quantify the capabilities of a gravity-based coal cleaning process for removing these hazardous air pollutants, a detail study was conducted on a coal sample collected from one mine of Talcher area. Careful analysis of the experimental data indicates that most of the trace elements of greatest environmental concern are strongly associated with the organic matter of the investigated coal, thus during beneficiation these elements are concentrated in the clean coal fraction. Therefore, it makes the situation more complex and the expected pre-combustion removal of these trace elements seems to be not possible for the high-ash non-coking coals of Talcher coal field.

Statistical optimization study of jigging process on beneficiation of fine size high ash Indian non-coking coal

Non-coking coal is used for metallurgical and cement industries apart from generating energy. Indian non-coking coals are high in ash content because of drift origin. These high ash coals require beneficiation before being used. Jigging is one of the unit operations used for beneficiation of coal. Beneficiation by jigging is carried out for the coarser size of particles. Jigging of fine size coal is limited. However, in present study two fine non-coking coal samples having sizes −3+2mm and −2+1mm were used for jigging study. In present study jigging experiments were performed using laboratory Denver mineral jig by varying feed size, water rate, and feed rate. 23 full factorial experimental design was used to study the performance of jigging operation. The performance of jigging was judged by statistical analysis; where ash content and combustible recovery of concentrate were considered to be responses. In addition to statistical analysis, optimization study was also carried out by Nelder–Mead multidimensional pattern search method. Statistical models developed in the present study could predict ash content and yield of the concentrate accurately. At optimized condition, it was possible to achieve 22.6% ash content with 64.15% combustible recovery.

Effect of briquette composition and size on the quality of the resulting coke

Five briquettes were prepared using sawdust, a non-coking coal and a binder. Industrial coal blends were used to study the influence of the type of sawdust (pine and chestnut), the binder (coal tar and coal-tar sludge) and the size of the briquettes on the quality of the cokes produced from mixtures containing up to 15wt.% of the five briquettes. The effect of the briquettes and briquette components on the fluidity of the industrial coal blends was investigated. It was found that biomass and non-coking coal produced a decrease in fluidity, whereas the binders increased it. The combined effect of both types of additive had the global effect of decreasing fluidity. Mixtures of the briquettes with the industrial coal blends were carbonized in a 17kg movable wall oven in order to assess their influence on the quality of the cokes produced. Their cold mechanical strength (JIS DI150/15 index), reactivity to CO2 (CRI index) and post-reaction strength (CSR index) were also tested. The composition of the ash of the sawdusts and the reactivity of the briquette components were used as an indication of the effect on coke reactivity. The effects on cold mechanical strength and post-reaction strength were different in some cases.

Study of the pyrolysis kinetics of Datong coal using a sectioning method

shortage of good-quality coking coal, the COREX process was designed as a new ironmaking technology, attracting wide attention (Fang et al., 2005). In this process, lump coal and a small quantity of coke are directly charged into the melter-gasifier, where a high-quality reducing gas is generated for the reduction of the iron ore (Kumar et al., 2009). In contrast to the conventional blast furnace (BF) process, non-coking lump coal is used as the reducing agent and as the energy source, and the iron charge consists of lump ore and/or pellets, which results in the elimination of the coke oven and sintering plant as well as a decrease in investment (Kumar et al., 2009; Liu et al., 2012). Although the COREX process has made great progress, in current production practice the energy consumption greatly exceeds that of the BF, and it requires a certain amount of coke to maintain permeability of the semi-coke bed (Wang et al., 2008). In addition, the process consumes a lot of good-quality lump ore and lump coal. The pyrolysis of coal is the first step in most coal conversion processes, such as carbonization, gasification, and combustion (Aboyade et al., 2013). The reaction behaviour of lump coals in the COREX melter-gasifier is crucial, as it determines energy utilization and gas composition, as well as the metallurgical properties and particle size of the semi-coke produced (Prachethan et al., 2011; Zhang et al., 2014). In order to optimize the process and improve its competitiveness, the pyrolysis kinetics of Datong coal used in Baosteel’s COREX C-3000 facility was studied. Generally, the Coasts-Redfern method (Xu et al., 2010), ‘model-free’ method (Xu et al., 2010), and DAEM method (Tang et al., 2005) are used to investigate the kinetics of coal pyrolysis. In the Coasts-Redfern method, commonly used mechanism functions are inserted into the non-isothermal kinetic equation to fit the experimental data one-byone. The mechanism function with the largest correlation coefficient is selected as the best (Zhang et al., 2013). In this process, the reaction order is often replaced by the apparent reaction order to obtain the best fit (Zhang et al., 2014). However, the physical and chemical meanings of the reaction model are ignored. In the ‘model-free’ method (or DAEM method), the activation energies under different conversion rates can be calculated. However, there is no way to calculate the kinetic mechanism functions and the related parameters (Xu et al., 2010; Tang et al., 2005). Therefore, based on the previous research, a sectioning method was proposed to study the kinetics of coal pyrolysis. The kinetic parameters at different heating rates were Study of the pyrolysis kinetics of Datong coal using a sectioning method by R. Du*†, K. Wu*†, X. Yuan*†, D. Xu*†, and C. Chao*†

Effect of crushing on near-gravity material distribution in different size fractions of an Indian non-coking coal

remove physical impurities as effectively and economically as possible. The beneficiation process includes various operations on the asmined coal to make it more suitable for enduse application without destroying the physical identity of the coal. There are several coal beneficiation processes, but gravity-based separators remain the most efficient unit operation for removing the undesirable gangue material from run-of-mine coal. These separators exploit the difference in density between coal particles and gangue particles to effect a separation. The feed is introduced into an aqueous suspension of ultrafine magnetite with a particular density. The feed particles with a relative density less than that of the suspension (clean coal) float to the top surface of the suspension, whereas particles denser than the suspension density (gangue material) sink to the bottom. When the difference in density between the particle and the aqueous suspension is large, the separation is easy, but when this difference is less the separation becomes much more difficult since the settling velocity of the particles is very low. This lower settling velocity increases the probability that particles that should report to floats report to sinks, and vice versa, hence increasing the amount of misplaced material. Therefore, the degree of difficulty in beneficiating a typical coal at a particular specific gravity depends on the amount of material occurring within ±0.1 specific gravity range. This is known as ‘neargravity’ material, also termed ‘near-dense’ material, at that particular specific gravity of separation. As coal is heterogeneous in nature, the density of a daughter coal particle depends on the nature of the parent coal particle from which it has been produced and the fracture patterns involved during crushing, as shown in Figure 1. As the fracturing of particulate material is a random process and many factors contribute to the fracturing of any single particle, the result is never exactly predictable. Particles of the same material and similar in size and shape show a wide variation in individual fracture patterns. Therefore, when a bigger heterogeneous particle of particular density is subjected to crushing a broad spectrum of particles of various sizes and densities is produced. Similarly, when run-ofmine coal is crushed, a wide variety of smaller particles are generated, which alters the amount of near-gravity material present in a particular density class and accordingly changes the degree of difficulty in washing. Therefore, it is imperative that the change in mass of the near-gravity material at a particular specific gravity on crushing should be determined accurately. The difficulty in washing a particular coal can be interpreted from the steepness of the ‘characteristic curve’, which is derived from the sink-and-float data (Corriveau and Effect of crushing on near-gravity material distribution in different size fractions of an Indian non-coking coal

Organo-refining of high-ash Indian coals at bench scale

Organo-refining is a process of solvent extraction through which organic matters are extracted from coal using organic solvents. Indian coals have high mineral matter content ranging from 25 to 45wt.% (dry basis). The ash in coal is highly disseminated, which makes it difficult to remove by physical beneficiation. Thus, chemical beneficiation is needed to remove the mineral matter. This study was conducted for high ash Indian coals at bench scale. The capacity of the bench scale plant was 40kg/batch feed basis. Coking coal, washery discards and thermal coals of bituminous origin were used as feed material. The mineral matter of these coals varied in the range of 27–36wt.% (db). The feed size of the particle was below −0.5mm. N-methyl-2-pyrrolidone (NMP) and ethylenediamine (EDA) were used as main solvent and co-solvent respectively. The extraction was done at 200°C with 1:6 coal to solvent ratio (by mass, wt./wt.) for 60min. Extraction was followed by solid–liquid separation, solvent recovery and washing of products. The feed and product materials were subjected to proximate analysis, ultimate analysis, and Free Swelling Index (FSI) tests. Organo-refining process produced clean coal yield in the range of 30–45% and clean coal mineral matter was less than 10% for coking as well as non-coking coals. Free Swelling Index (FSI) also improved from 1–5 range for feed coals to 7–8 for product clean coals. Two types of filter (basket and centrifuge) were also tried for separation of solid and liquid from different types of slurries. It was observed that cake moisture can be reduced by 6–12% points for these slurries using decanter centrifuge. The cake moisture reduced to 70% from 76% for clean coal slurry and 60% to 48% for reject slurry. The clean coal yield increased by 5 units (from 35% to 40%) with decanter centrifuge filter. In order to have better filtration and precipitation, the extraction was carried out by mixing of two different raw coals (TL and TC) in a certain ratio (1:1 to 1:3). Also, the extraction was done separately for TL and TC coals and then the clean coal extracts were mixed in 1:1 to 1:3 proportions. Mixing of two raw coals gives better results (36wt.% yield with 6.4% ash clean coal) than mixing of their extracts (30wt.% yield with 6.7% ash clean coal).

Evaluation of the Characteristics of As-received and Washed Low Grade Indian Coals for Their Industrial Applications

Coal is the most widely used source of global energy. With the fast depletion of coal quality in India, utilizing the abundantly available low grade coals through appropriate technologies for meeting the energy demands is the need of time. During the various industrial application of coal, its characteristics are crucial. Five as-received low grade coals from Rajapur, Rajrappa, Kargali, Kedla, and Kathara coal mines of Jharkhand (India) and corresponding washed coals/clean fractions were characterized. These are low moisture-low volatile-low sulphur non-coking coals, except Rajapur coal, which is medium volatile poor coking. Rajapur and Rajrappa coals have medium ash, whereas other coals have high ash. Rajapur coal has the highest C and calorific value followed by Rajrappa, Kedla, Kargali, and Kathara coals; the variation of H and N content is insignificant. After washing, Rajrappa and Kargali are poor coking and Rajapur, Kedla, and Kathara are medium coking. For power generation, as-received coals of Rajrappa and Kedla, and washed coals of Kargali and Kathara can be used; for directly reduced iron purpose, Rajrappa as-received coal can be used. For coke making, washed coals of Rajapur and Kathara coals and stamp charging; Kedla and Rajrappa washed coal with the blend of low ash medium volatile coal and good coking coal, respectively, in conjunction with stamp charging, may be significant. Also, Kargali and Rajrappa washed coals can be used to make formed coke. The rejects from coal washing comprising a substantial amount of coaly matter together with higher ash can be used for power generation using fluidized bed combustion.

The effect of volatile matter of non-coking coal on the reduction of iron oxide at non-isothermal condition

The effect of volatile matter of non-coking coal on the reduction of iron oxide at non-isothermal condition

A Novel Devolatilization Technique of Pre-reduction of Iron Ore Using Lean Grade Coal

The problem of properly utilizing non-coking coals in alternative iron making processes dates back to long ago. Lean grade coals with higher ash and volatile matter content (e.g. boiler grade coals) have always challenged the metallurgists to develop a suitable process for their utilization. The aim of this work is to achieve an energy efficient method for the reduction of briquetted iron ore fines using ‘SYNGAS’—which is the gaseous product (enriched with reducing agents) generated by pyrolysis of coal along with fine sized carbon particles produced during pyrolysis. A laboratory scale reduction furnace with pyrolysis facility has been designed and fabricated after in depth thermo-gravimetric analysis (TGA), differential thermal analysis (DTA), and gas chromatograph (GC) studies. A particular temperature profile has been maintained inside the furnace to achieve the optimum reduction temperature. The briquettes are reduced in the pyrolysis furnace and the extent of reduction has been calculated from the weight loss. The reduced specimens are characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX), field emission scanning electron microscope (FESEM), and chemical analysis method. It is observed that iron ore can be significantly reduced to metallic iron by using the devolatilization product of lean grade coal.

Low temperature pyrolysis properties and kinetics of non-coking coal in Chinese western coals

Chinese western low-rank coals known as for its favorable characteristics play a key role in the production of coal oil. In this work, based on the changes in element occurrence during low-temperature pyrolysis of coal, the kinetic and thermodynamic characteristics of coal at 400–500 °C temperatures with 10 °C/min heat rate were studied, which resulted in the drastically cracking of aliphatic groups. However, a significant amount of oxygen-containing functional groups were also found during coal pyrolysis at low temperature followed pseudo-first-order kinetics. According to the low-temperature thermal kinetics analysis of different coals, the activation energy of coking coal is higher than that of non-coking coals, and the activation of non-coking coals is relatively low under the same pyrolysis conditions. The objective of this work is to provide theoretical data about the pyrolysis characteristics of non-coking coal at low temperature and increase the non-coking coal proportion in coking proceeding.

A Comparative Study of Manual Wagon-Top Sampling and Auto Mechanical Sampling of 200 mm Size Coal with Respect to Stopped-Belt Sampling of Thermal Coal at Indian Thermal Power Plants

ABSTRACTThe majority of the power plants in India are fed with non-coking coals where the coals are dispatched from their respective mines via wagons loaded by a rapid loading system or pay loader. The usual top size of coal is 200 mm and sampling is carried out manually from wagons. The manual method of wagon-top sampling of large size raw coal is not only difficult but also violates some of the fundamental principles of sampling. As per sampling requirements, samples are to be drawn from the full depth of the wagons, which is impossible to be done manually. Since the ash distribution in the different size fractions is not homogeneous, the results from the samples, which do not reflect the true size distribution of the lot, are likely to be biased. More importantly, sample collection by shovel from the top is a function of human discretion and not governed by the equiprobability rule. In another case, the sample has been collected by a cross-belt type auto mechanical sampler for 200 mm size coal at one of the super thermal power stations. Test analysis shows that coal collected using a cross-belt type mechanical sampler also has significant deviations from stopped-belt coal samples of 200 mm size due to size segregation. Studies carried on wagon-top sampling through specially designed experiments reveal some interesting features. The presence of bias in wagon-top sampling is apparent when compared with the “stopped-belt” sample. In this article, a comparative study between manual wagon-top sampling/auto mechanical sampling with respect to stopped-belt sampling has been conducted for coal of size 200 mm and also precision studies have been performed for wagon-top sampling/mechanical sampling for Indian thermal power plants.