Assessment of auto-oxidation cum self-heating tendency of Indian coals by DRIFT studies

52-56Coal self-heating, due to low temperature oxidation of coal, is generally considered to be the primary cause of spontaneous ignition. With the purpose of having a more definitive quantization of this subtle stage of coal oxidation, study on proneness to coal towards auto-oxidation, vis-à-vis self-heating phenomenon, has been carried out. Various methods like crossing point temperature (CPT), diffuse reflectance infrared fourier transform spectroscopy (DRIFT), differential scanning calorimetry-thermogravimetric analysis (DSC-TGA) and wet oxidation method has been used for comparative study. It is observed that though CPT values alone are adequately indicative and are consistent with actual field experience, the combination of CPT and DRIFT data complements each other very well to provide greater information for better prediction of proneness to auto-oxidation vis-à-vis self-heating phenomenon of coals. Other methods tried are found to be comparatively inadequate

Using Rock-Eval S4Tpeak as thermal maturity proxy for shales.

The Rock-Eval pyrolysis-stage derived parameters such as free hydrocarbons (S1), heavier pyrolysis-hydrocarbons (S2), pyrolyzable carbon (PC) and pyrolysis Tmax (from S2 curve) have received considerable interest for source-rock screening and thermal maturity assessment. On the other hand, the Rock-Eval oxidation-stage S4CO2 curve, which gives the amount of residual carbon (RC), only recently has received some interest. While the pyrolysis-stage S2 temperature-peak (Tmax) is conventionally used as a maturity proxy, in this work we show that the temperature-peak of S4CO2 curve (S4Tmax) can also be used as a thermal maturity proxy for shales. For overmature and low-TOC shale samples, showing asymmetric S2 shape and concomitantly producing doubtful Tmax, the S4 curves showed symmetric nature and consequently the S4Tmax was observed to be a reliable thermal maturity estimate. While the S4Tmax clearly resolved immature and overmature shales, for the early mature and peak mature shales the S4Tmax showed overlapping values. S4Tmax of pre-pyrolyzed and pyrolyzed masses showed good positive correlation with differential scanning calorimetry temperature-peak (DSCTpeak), and consequently indicated its applicability as a thermal maturity proxy. When early mature pre-pyrolyzed samples were directly analyzed using the Rock-Eval oxidation stage, the S4 curves showed formation of two sub-peaks, and consequently the Tmax was observed to decrease. It is recommended that analysts and interpreters should thoroughly cross-check S2 curves before reporting data, and in case of asymmetric or unreliable S2 curves, the S4Tmax can be used as a maturity proxy

Pyrolysis and combustion behavior of few high-ash Indian coals

In this study, three high-ash Indian sub-bituminous coals of different thermal maturities from three different open cast mines of Raniganj basin, eastern India, were studied to understand their combustion and pyrolysis behavior. The combustion analyses were performed under three different heating rates (5°C, 10°C, and 15°C/min). From the thermograms of TG-DTG pyrolysis curves, it was observed that the overall pyrolysis reaction can be deduced into four different temperature regions with each region showing unique properties, and those regions are inherent moisture loss, prior to primary pyrolysis, primary pyrolysis, and secondary pyrolysis regions. The main pyrolysis reaction occurs in the primary pyrolysis region for all the samples but a significant devolatilization has also been seen for the early oil window mature noncoking coal in the secondary pyrolysis region. The kinetic parameters were also evaluated for both combustion and pyrolysis analysis. X-ray diffraction revealed that this sample consists of a significant amount of siderite and pyrite, and consequently showed distinct behavior. It was observed that the pyrolysis properties and kinetics were closely related to their complex mechanisms and reactions. Rock-Eval pyrolysis also confirmed the presence of siderite in the sample, which decomposed simultaneously with the organic-matter during pyrolysis