Prime Coking Coal Research Articles

Bio-coke: A sustainable solution to Indian metallurgical coal crisis

Coal is the predominant global energy source, where its consumption as metallurgical coke from fast-depleting prime coking coal is vital. In India, the complete depletion of prime coking coal and ultimate dependence on low-grade low-volatile coking coal reserves are the primary concern, so the need to explore alternative fuels, preferably with less climatic concern. Accordingly, a process for the synthesis of bio-coke, a novel product, using varying blending ratios (90:10, 80:20, 70:30, 60:40, and 50:50) of such inferior grade coal and biochars (derived at 550°C) of coconut shell (CSC), groundnut shell (GSC), sawdust (SDC), and sugarcane bagasse (SBC) in the presence of starch and molasses binders was developed via carbonization (at 800–1100°C). Obtained bio-cokes from coal and biochars with molasses possess better strength and plastic properties for metallurgical applications than those prepared with starch, and can be a sustainable substitute for metallurgical coke.

Natural gums as a novel, potent, and natural additive towards coke making: a preliminary feasibility study

ABSTRACT The present investigation entails delineating the implications of using a novel and naturally sourced additive for coke making. In particular, the focus of this study was to understand the extent to which such natural gums could induce plasticity and strength to non-coking coals without inclusion of any prime coking coal, emphasizing on the importance of thermal pre-treatment as an important parameter. Experimentally, the non-coking coal was pre-treated with xanthan gum (300°C for 1 h), followed by carbonization at 600°C for 1 h. Addition of water as an additive was deduced to be beneficial in enhancing the bulk density of the coal blend. The coal blend, including non-coking coal with natural gums (10–20%) and water (10 mL in 20 g scale), produced F grade coke when treated under low-temperature Gray King (LTGK) assay conditions at 600°C. A comparative XRD and Raman analysis of raw coal and coke demonstrated the presence of graphitic content in the resultant coke only. FTIR results showed the absence of small molecular fragments, thus substantiating semi-coke formation during the re-solidification stage. The present invention holds significant industrial viability toward production of coke from non-coking coal without inclusion of any prime coking coal.

Impact of bedding planes, delay interval and firing orientation on blast induced ground vibration in production blasting with controlling strategies

Traditional techniques of production blasting and delay timing patterns are restructured to minimise ground vibrations for the geological setting of Jharia coal field, a prime coking coal belt with densely covered habitat. Blasting techniques based on delay pattern and bench face orientation are proposed in this paper to protect the structures within a distance of 100 m from active bench face while maintaining daily production and charge per delay. Seventeen single representative blast holes (signature waveforms) were detonated in the last hole at the series of production blasts. When blast vibration was monitored in the opposite direction of the firing sequence and compared to the values in the same direction and behind the bench face, it was observed that the PPVs wereless than 10 mm/s at 55 m radial distance. Also, when blast monitoring is setup near structures, across the strike of rock bed, blasting range can be designed 65 m away from structures rather than along the strike. The signature hole waveforms were generated using electronic delay detonators, and PPV values were controlled by maintaining delay intervals of 25 ms and 67 ms between holes and rows, respectively. Monte Carlo simulation (MCS)was used to generate the probabilistic data, and 5000 simulations helped to evaluate the volatility arising in the investigated blasting techniques, and it was concluded that the modified bench face design technique in 80 % of the cases generates PPV which is lower than the threshold value of 10 mm/s. The contribution to variance (CTV) and correlation coefficient (CC) approaches were used for the sensitivity analysis and it was observed that the bedding plane strike direction and radial distance are the two most critical factors impacting PPV. The proposed equation has shown high coefficient of determination (R2 = 0.85) and low root mean square error (RMSE = 4.42) as compared to other four standard equations. Suggested blasting techniques can be of immense use for conducting production blasting in a safe and productive manner.

Use of organic polymers for improvement of coking potential of poor coking coal

ABSTRACT As the reserve of prime coking coal is low, there is a good amount of research going on worldwide to improve the coking potential of non-coking coal. Researchers have revealed the importance of hydrogen generation/transfer to improve the coking potential of coal. Based on this hypothesis, in this paper, the authors have tried to improve the coking potential of non-coking coal by adding different polymers. The polymers are derived from formaldehyde and phenol derivatives. Coking potential has been tested through conventional tests like crucible swelling number. Thermogravimetric mass spectroscopy (TG-MS) has been used to get an idea of plasticity and hydrogen generation in the plastic zone. High-temperature microscopy has also been used to evaluate the swelling of coal. Results indicate that the addition of polymers in a small percentage has an effect on hydrogen generation in the plastic zone, and thus, it can improve the coking potential of non-coking coal.

Difference in structural chemistry of non-coking and coking coal using acid treatment demineralization technique

ABSTRACT Recently, the structural information about non-coking and coking coal has attracted pronounced interest for sustainable utilization of poor coking coal in different industries specifically for steel industry like Tata Steel. In the present work, demineralization techniques via acid treatment (HCl-HF) are effective to remove mineral phase from coal. The difference in carbon chemistry of non-coking (CDPCI), weakly coking (Curragh SS), and prime coking coals (Illawarra and Jamadoba) has been studying through advanced characterization methods like petrography, TGA-DTG, FTIR spectroscopy, X-ray diffraction, Raman, 13C solid-state NMR, FESEM, and TEM. These advanced characterization techniques offer comparative structural information of different coal through the distribution of individual coal maceral and mineral grains with their rank (petrographic study), functional group study along aliphatic-aromatic structural relationship measurement (FTIR), crystalline/graphitic nature of carbon (XRD & Raman) with oxygenated carbon skeletal structural information (Solid State 13C NMR), aromatic-aliphatic cross-linking behavior (FESEM) and their orientation toward lattice fringe structure (TEM).

DETECTION AND DELINEATION OF SUBSURFACE COAL MINE FIRE FROM SPACEBORNE THERMAL INFRARED DATA IN JHARIA COALFIELD, DHANBAD, INDIA

Abstract. Coal fire has been found to be a major problem worldwide in coal mining areas. The surrounding areas get hugely affected, and significant amount of reserves are wasted due to the burning of coal. This severely affects the environment condition, which leads to a rise in temperature of the region, which is a major reason for climate change. Greenhouse gases like CO2 SO2 NO CH4 are also emitted from the cracks and fissures. Large masses of the burning of coal also causes land subsidence and collapse. Underground coal fires ignited by natural causes or human error leads to atmospheric pollution, acid rain, land subsidence, and increased coronary and respiratory diseases. They consume a valuable energy resource, destroy floral and faunal habitats, and promote human suffering because of heat, subsidence, and pollution. Jharia Coalfield, Jharkhand, India, is well known for being the storehouse of prime coking coal and for accommodating the maximum number of coal fires among all the coalfields in the country. In this paper, some of the important issues of coal fire mapping from satellite thermal infrared data have been addressed in particular reference to Jharia Coalfield. Namely, these are: retrieval of spectral radiance from raw digital satellite data using scene-specific calibration coefficients of the detectors from metadata, thermal emissivity of surface to obtain kinetic temperature at each ground resolution cell of satellite data, field-based modelling of pixel-integrated temperature for differentiating surface and subsurface fire pixels in Landsat 8 thermal IR data, identification of surface coal fire locations from infrared data and lateral propagation of coal fire.

Impact of underground coal fire on coal petrographic properties of high volatile bituminous coals: A case study from coal fire zone No. 3.2 in the Wuda Coalfield, Inner Mongolia Autonomous Region, North China

The Wuda Coalfield located in the Inner Mongolia Autonomous Region, North China is known as one of China's major source of prime coking coals and a site of well-researched and well-documented underground coal fires. The underground coal fire at the coal fire zone No. 3.2 is situated in the active coal mine of Suhai-Tu, located in the north westerly part of the Wuda Coalfield.The present paper investigates the impact of the underground coal fire on the coal seam No. 10 by application of coal petrographic methods, including detailed characteristic of macerals and other coal components, maceral analysis, microstructural analysis, and vitrinite reflectances performed on (1) coal grains lacking impurities, microfractures, dark oxidation rims, (2) on dark-rimmed vitrinite, as well as (3) on low-temperature semi-coke. The investigated coal seam No. 10 represents a high volatile A bituminous coal and is dominated by vitrinite, followed by inertinite with minor amounts of liptinite and by non-isotropic low-temperature semi-coke. The microstructure of the oxidatively and thermally altered coals is represented by (1) extensive non-tectonic microfissures and non-tectonic microfractures i.e., shrinkage microfractures, leading to defragmentation of coal grains, (2) dark oxidation rims observed at grain margins, non-tectonic microfissures and microfractures, and by (3) devolatilisation micropores. Random vitrinite reflectances measured in (1) coal grains lacking impurities, microfractures, and dark oxidation rims, and in (2) dark-rimmed vitrinite at non-tectonic microfissures and fractures reveal significant lateral variations. The presence of low-temperature semi-coke and its marked lower reflectance values are indicative of thermal alteration induced by the underground coal fire in the coal fire zone No. 3.2. The results obtained from the performed analyses of organic matter point to both low-temperature oxidation and low-temperature-pyrolysis processes. The applied coal petrological approach revealed characteristic changes to the coal's microstructure, its petrographic composition, as well as to optical properties induced by the underground coal fire.

Statistical modelling and optimization study for beneficiation of Indian high ash semi-coking coal using allflux separator

Coking coals are used for metallurgical purposes and the majority of it being used for iron and steel making. In India, there is a limited resource of prime coking coal, because of which these low-grade high ash semi-coking coals may be used for the coke making after beneficiation. The objective of the present investigation was to study the beneficiation of semi-coking coal using allflux separator that uses the principle of liquid–solid fluidization for separating the particles. The experiments were performed based on Box Behnken experimental design. The semi-coking coal in the size range of −1000 to 100μm with feed ash content of 33% was used for the study. Statistical analysis was performed to understand the significance of the effect of different operating parameters and their interaction effects on the performance of allflux separator. In addition to this statistical model was developed and the optimization study was carried out. It was found that course set point has a significant effect on both ash content and yield of the concentrate.

Effect of mass fraction of long flame coal on swelling pressure and microstructures of cokes

Long flame coal are abundant and widely distributed in China, but the resource utilization is quite low, the production efficiency is not high. Stamp-charging coke making technology can bend some long flame coal, which can reduce production cost and expand the coking coal resources. The long flame coal of different mass fraction is added into prime coking coal including fat coal from Longhu, 1/3 coking coal from Xinjian and coking coal from Didao in experiment. The swelling pressure is tested on-line detection using pressure sensor in coke making process, and the pores are observed by scanning electron microscopy. The results show that, the swelling pressure first increase and then decrease with the temperature increased and the maximum swelling pressure reduces gradually with mass fraction of the Long flame coal from Shenmu increased in coke making process. The SEM images of resultant coke display that the coke get more and more loose and the amount of pores is increased with mass fraction of the long flame coal from Shenmu increased. The amount pores and the pore diameter both is minimum for coking coal from Didao as prime coking coal under the same fraction of long flame coal.

Mapping Land Subsidence Related to Underground Coal Fires in the Wuda Coalfield (Northern China) Using a Small Stack of ALOS PALSAR Differential Interferograms

Coal fires have been found to be a serious problem worldwide in coal mining reserves. Coal fires burn valuable coal reserves and lead to severe environmental degradation of the region. Moreover, coal fires can result in massive surface displacements due to the reduction in volume of the burning coal and can cause thermal effects in the adjacent rock mass particularly cracks and fissures. The Wuda coalfield in Northern China is known for being an exclusive storehouse of prime coking coal as well as for being the site of occurrence of the maximum number of known coal fires among all the coalfields in China and worldwide, and is chosen as our study area. In this study, we have investigated the capabilities and limitations of ALOS PALSAR data for monitoring the land subsidence that accompanies coal fires by means of satellite differential interferometric synthetic aperture radar (DInSAR) observations. An approach to map the large and highly non-linear subsidence based on a small number of SAR images was applied to the Wuda coalfield to reveal the spatial and temporal signals of land subsidence in areas affected by coal fires. The DInSAR results agree well with coal fire data obtained from field investigations and thermal anomaly information, which demonstrates that the capability of ALOS PALSAR data and the proposed approach have remarkable potential to detect this land subsidence of interest. In addition, our results also provide a spatial extent and temporal evolution of the land subsidence behavior accompanying the coal fires, which indicated that several coal fire zones suffer accelerated ongoing land subsidence, whilst other coal fire zones are newly subsiding areas arising from coal fires in the period of development.

Investigation of the Role of Fire Retardants in Preventing Spontaneous Heating of Coal and Controlling Coal Mine Fires

Mine fire is a major problem for the Indian coal mining industry and exists since beginning of the mining. A huge amount of the prime coking coal reserves of different coalfields are blocked due to existence of fire and thus cannot be extracted without extinguishing it. Many approaches have been attempted in this direction to minimize this socio-technological problem. Use of chemical retardants to inhibit smouldering combustion phenomenon is an important method, which can be adopted to prevent or delay its occurrences. In this situation, it may sometimes be necessary to use fire retardants for reducing the intensity of fire so that the coal production will not be hampered. This paper presents the impact of chemical additives on coal oxidation process, studied from the mechanistic perspective aiming to search effective retardant materials to prevent and control coal self-heating phenomenon. A numbers of chemicals and combinations along with coal, which are moderately prone to smouldering combustion, were studied to determine its efficacy to prevent and combat it. In the process CPT, IPT and DSC study of coal samples and chemicals were observed. Based on the results, suitable retardants were selected and mixed with coal samples. The mixtures were further analysed for above properties. Finally, the best suitable combination of inhibitors were determined and applied in the field, which gave desired results.

The Effect of Biomass on Fluidity Development in Coking Blends Using High-Temperature SAOS Rheometry

The addition of biomass to coking blends has the potential benefits of reducing the amount of expensive coking coals and reducing carbon emissions. However, there is little research in the use of biomass as additive in coking blends. The easily available biomass samples pine wood, sugar beet, and miscanthus have been chosen to study the effect of these additives on the fluidity properties of coal. High-temperature small-amplitude oscillatory-shear (SAOS) rheometry was used to determine the fluidity of the samples as a function of temperature. TGA and solid-state 13C NMR were also used to determine the thermal stability and compositional changes in the samples during pyrolysis. Sugar beet can be added in coking blends up to 5 wt % without altering the viscoelastic properties of the coal, whereas pine wood and miscanthus reduce the fluidity even with 2 wt % additions. No solid–solid interactions were observed in the blends, but there were differences in viscoelastic behavior that were attributed to gas–solid interactions. Fast heating (i.e., 180 °C/min) can facilitate the incorporation of pine wood and miscanthus in coking blends. The use of fast heating increases the fluidity of the coal and preserves the fluid material in the biomass at higher temperatures. As a result, the biomass acts as a regulator of fluid material development in the coal, and the viscoelastic properties of the blend are identical to those of prime coking coals. Although fast heating could also be used to produce good coking blends by combining biomass with high volatile matter, high fluidity coals, the amount of biomass required (>5 wt %) is expected to be detrimental for coke strength.

FLOATABILITY CHARACTERISTICS: A CASE STUDY WITH THREE TYPICAL INDIAN PRIME COKING COALS

Three types of prime coking coals (coals A, B, and C) from Jharia coalfield, India, were investigated for the variations in their floatability characteristics. Among the three coals studied, coal A showed the least floatability. However, its floatability improved to some extent at higher dosages of collector and frother. Other two types of coal, i.e., coals B and C, showed almost similar flotation performance, which was much better as compared to coal A. The studies revealed that coal showed the least floatability characteristics, primarily due to the least concentration of vitrinite and liptinite content and a high percentage of inertinite and mineral matters in the coal. Also, the lower type of vitrinite (V7–V9) was present in the coal in greater proportion as compared to the other two coals and the proportion of ultra fines (− 0.053 mm) in coal A was higher as compared to the other two coals.

Binderless briquetting of some selected South African prime coking, blend coking and weathered bituminous coals and the effect of coal properties on binderless briquetting

The binderless briquetting of some selected South African prime coking and blend coking coals, as well as the effects of weathering on the binderless briquetting of some inertinite-rich bituminous coals, were investigated in the laboratory. Selected properties of these coals were determined and the coals were briquetted at various moisture contents and pressures. Based on the results obtained in this study, binderless briquetting was found to be most successful in the cases of the fresh, vitrinite-rich coking and blend coking coals and satisfactory in the fresh inertinite-rich Witbank coals. However, the bonding process seemed to be adversely affected by weathering. The negative impact on bonding could be ameliorated to some extent by the presence of a significant kaolinite content when the percentage ash reports in the order of more than 15% (air-dry basis). It should, however, be noted that kaolinite may reduce the water resistance of the briquettes.

Exploration drilling optimisation using geostatistics: a case in Jharia Coalfield, India

Drill hole optimisation using geostatistics has been used in many parts of the world in respect of various mineral deposits including coal. The present paper is an attempt to provide a means to maximise the information to cost ratio for optimisation of exploration drilling in the Jharia coalfield, which is the only source of prime coking coal in India. Exploration in Jharia Coalfield that has led to the generation of a huge exploration database has been carried out by various governmental and non-governmental agencies. But because of lack of importance and an obvious application towards exploration modelling, the database had not been utilised to its fullest extent. In the present study, an attempt has been made to derive geostatistical models of various proximate coal constituents of selected seams in respect of nine opencast mine blocks of the coalfield. This experimental study, employing geostatistical volume–variance relationships, revealed that an exploration grid density of 16 drill holes per square kilometre with a grid spacing of 300 × 300 m within an exploration area of 1 × 1 km is adequate for maximisation of information in respect of the Jharia Coalfield. Until now, the density of exploration drilling in the coalfield has been considered as per Indian Standard Procedure (ISP) norms solely based on past experience and proposed mining methods. The present study of exploration drill hole optimisation using the concept of kriging variance is associated with an objectively defined mathematical basis and therefore may be applied for exploration optimisation in other coalfields in India and other countries, which occur in similar geological settings.

Coal fire mapping from satellite thermal IR data – A case example in Jharia Coalfield, Jharkhand, India

Coal fire has been found to be a serious problem worldwide in coal mining processes. Coal fire burns valuable coal reserve and prevents access to proven reserve in the affected area. Moreover, it leads to severe environmental degradation of the region by an overall increase of the ambient atmospheric temperature, by the emission of obnoxious gases (e.g., SO 2, NO, CO, CH 4) along fissures and cracks and by causing land subsidence and collapse. Jharia Coalfield, Jharkhand, India, is known for being the exclusive storehouse of prime coking coal as well as for hosting the maximum number of known coal fires among all the coalfields in the country. In this paper, some of the important issues of coal fire mapping from satellite thermal IR data have been addressed in particular reference to Jharia Coalfield. Namely, these are: retrieval of true spectral radiance from raw digital data using scene-specific calibration coefficients of the detectors, thermal emissivity of surface materials to obtain kinetic temperature at each ground resolution cell of satellite data, field-based modelling of pixel-integrated temperature for differentiating surface and subsurface fire pixels in Landsat TM thermal IR data, identification of surface coal fire locations from reflected IR data and lateral propagation of coal fire.

Effect of Rapid Preheating on the Coking Behavior of Bituminous Coals: Retrogressive Reactions and Extract Yields

Mechanisms underlying observed changes in the plastic properties and swelling ability of weakly coking coals, induced by rapid heating to 400−450 °C, have been investigated. The enhanced softening would allow the shifting of coke blend compositions toward weakly coking coals. A surge in extractables content was observed at heating rates of >500 °C/s. After rapid heating, 25%−28% more of the mass of the weakly coking coal could be extracted. At these low temperatures (∼400−450 °C), repolymerization rates of solvent-extractables seem to be negligible. Increases in the extractables content that were determined by rapid heating clearly improve coke strengths via the related increase in thermoplasticity. However, when a “prime coking coal” was tested under similar conditions, no measurable effect of heating rate on the extractable contents was observed. A third “coking” coal showed behavior that was intermediate between these two cases. Taken together, the data strongly suggest the sequential occurrence of (i) fast retrogressive recombinations between reactive free radicals formed during thermally induced covalent bond cleavage reactions during the heat-up process, and (ii) slower repolymerization/recombination reactions occurring between the more-stable free radicals, observable at >450 °C. The example of the prime coking coal suggests that more of the reactive free radicals might be stabilized (quenched) by locally available hydrogen, irrespective of the heating rate. Liquefaction in the presence of hydrogen donors shows that high conversions to extractables are possible during slow heating. However, for transitional coals (between weakly coking coal and prime coking coals), pyrolysis yields are clearly sensitive to changes in heating rate. Transitional coals thus seem to be those that are marginally deficient in donatable hydrogen.

99/03548 Manufacture of complex carbonaceous materials from a mixture of non-coking coals: Strakhov, V. M. et al. Koks Khim., 1998, (9), 22–26. (In Russian)

Solvent refined coal (SRC) prepared from high-ash Indian non/weakly coking coals, as reported earlier (S.B. Choudhury, B.B. Brahamachari, S.R. Dwivedi, A.K. Roy, P.K. Dasgupta, M. Chakraborty, R. Hague, Solvent refined coal from high-ash non-coking coals/washery middlings for use in metallurgical coke making: part I, Fuel Processing Tech., USA, June '96, pp. 203–213), when blended in small doses (8–12%) with substandard coking blends and carbonised, yields coke with increased anisotropy as well as hot and cold strengths. This is reflected by positive improvement in the values of the Micum indices (M40 and M10), coke reactivity index (CRI) and the coke strength after reaction with CO2 (CSR) and also the optical texture of the resultant coke as reported in this paper. The authors confirmed, by pilot scale carbonisation tests (250 kg/batch) that SRC produced by the technology developed (S.B. Choudhury, B.B. Brahamachari, S.R. Dwivedi, A.K. Roy, P.K. Dasgupta, M. Chakraborty, R. Hague, Solvent refined coal from high-ash non-coking coals/washery middlings for use in metallurgical coke making: part I, Fuel Processing Tech., USA, June '96, pp. 203–213) can help in substituting high-fluid low ash prime coking coals (PCC) to the extent of 30% (by weight). The use of SRC can thus accommodate additional quantum of medium coking coals (MCC) in the coking blends of the major Indian steel plants. The large reserves of indigenous medium coking coals, especially low volatile medium coking coals (LVMC) after beneficiation can also be used in the blends for making blast furnace grade coke thereby conserving scarce prime coking coals.

98/02750 Primary study on sulfur fixing in combustion of coal briquets promoted by Fe 2O 3: Zhang, L. et al. Huanjing Kexue, 1997, 18, (1), 65–67. (In Chinese)

The binderless briquetting of some selected South African prime coking and blend coking coals, as well as the effects of weathering on the binderless briquetting of some inertinite-rich bituminous coals, were investigated in the laboratory. Selected properties of these coals were determined and the coals were briquetted at various moisture contents and pressures. Based on the results obtained in this study, binderless briquetting was found to be most successful in the cases of the fresh, vitrinite-rich coking and blend coking coals and satisfactory in the fresh inertinite-rich Witbank coals.However, the bonding process seemed to be adversely affected by weathering. The negative impact on bonding could be ameliorated to some extent by the presence of a significant kaolinite content when the percentage ash reports in the order of more than 15% (air-dry basis). It should, however, be noted that kaolinite may reduce the water resistance of the briquettes.

98/02743 Method of promoting carbonization at coke oven port: Kunimasa, H. and Inoe, K. Jpn. Kokai Tokkyo Koho JP 09 48,973 [97 48,793] (Cl. C10B21/22), 18 Feb 1997, Appl. 95/219,754, 3 Aug 1995, 9 pp. (In Japanese)

The binderless briquetting of some selected South African prime coking and blend coking coals, as well as the effects of weathering on the binderless briquetting of some inertinite-rich bituminous coals, were investigated in the laboratory. Selected properties of these coals were determined and the coals were briquetted at various moisture contents and pressures. Based on the results obtained in this study, binderless briquetting was found to be most successful in the cases of the fresh, vitrinite-rich coking and blend coking coals and satisfactory in the fresh inertinite-rich Witbank coals.However, the bonding process seemed to be adversely affected by weathering. The negative impact on bonding could be ameliorated to some extent by the presence of a significant kaolinite content when the percentage ash reports in the order of more than 15% (air-dry basis). It should, however, be noted that kaolinite may reduce the water resistance of the briquettes.