A nonisothermal thermogravimetric analysis technique was used to evaluate the effect of CO2 concentration on the overall reactivity of Indian coal chars during CO2/O2 combustion. The study was carried out for the drop tube furnace derived chars of three Indian sub-bituminous coals from different sources. The selected coal char samples were combusted in different CO2/O2 molar volume combinations, namely, 80:20, 60:40, 40:60, 20:80, and 0:100 (pure O2) so that the effect of the concentration of CO2 on the overall reaction rate could be quantified. The Arrhenius constants (E and A) were determined using the random pore model. The concept of weighted mean activation energy was used to account for the multi-Arrhenius linearities. Empirical equations were proposed to evaluate the Arrhenius constants in terms of the mole fraction of CO2 for the overall reaction rate. © 2011 American Chemical Society.

Sreenivas Jayanti

Department Of Chemical Engineering

ARRHENIUS CONSTANTS

Coal chars

DROP TUBE FURNACES

Effect of co

Empirical equations

Mole fraction

NONISOTHERMAL THERMOGRAVIMETRIC ANALYSIS

OVERALL REACTIONS

Random pore model

SUBBITUMINOUS COAL

Weighted mean

Activation energy

Atmospheric composition

Bituminous coal

Coal combustion

Drops

Rate constants

Thermogravimetric analysis

Carbon dioxide

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Industrial and Engineering Chemistry Research

The present study investigates the enhancement of CO2 gasification reactivity of coals due to the presence of catalytic elements in biomass such as K2O, CaO, Na2O and MgO. Co-gasification of three Indian coal chars with two biomass chars has been studied using isothermal thermogravimetric analysis (TGA) in CO2 environment at 900, 1000 and 1100 °C. The conversion profiles have been used to establish synergetic or inhibitory effect on coal char reactivity by the presence of catalytic elements in biomass char by comparing the 90% conversion time with and without biomass. It is concluded that both biomasses exhibit synergistic behavior when blended with the three coals with casuarina being more synergetic than empty fruit bunch. Some inhibitory effect has been noted for the high ash coal at the highest temperature with higher 90% conversion time for the blend over pure coal, presumably due to diffusional control of the conversion rate. © 2016 Elsevier Ltd.

Bioresource Technology

Synergetic and inhibition effects in carbon dioxide gasification of blends of coals and biomass fuels of Indian origin

Gasification of solid fuels such as coals, lignite and biomasses has been studied using isothermal and non-isothermal thermogravimetric analysis (TG) with CO2 as gasifying agent. Non-isothermal TG of three Indian coals (two bituminous and one sub-bituminous coal), one lignite and two biomass fuels (Casuarina and empty fruit bunches) at a constant heating rate of 20 °C min-1 in the temperature range from 25 to 1200 °C showed a clear separation of DTG peaks associated with pyrolysis and CO2 gasification. Based on these studies, isothermal TG experiments were conducted in the temperature range from 900 to 1100 °C for coals and from 800 to 1000 °C for biomass fuels. These results show that the CO2 gasification rate follows coal rank for the three coals and the lignite. The two biomasses have significantly higher reactivities than the three coals. The higher reactivity of one coal is attributed to the presence of calcium-containing minerals in its inorganic matter. The kinetic parameters for each fuel were extracted from the isothermal TG results using the volumetric reaction model for the coals and a zeroth-order model for biomass fuels. Biomass and lignite are found to have a much higher reactivity index and much lower conversion time than the three coals under identical conditions. © 2015 Akadémiai Kiadó, Budapest, Hungary.

Journal of Thermal Analysis and Calorimetry

Evaluation of CO2 gasification kinetics for low-rank Indian coals and biomass fuels

Studies on the growth of three-dimensional cavity geometries in underground coal gasification (UCG) are important in exploiting the large fraction of coal that is present in underground coal seams. In the present study, the cavity formation in UCG has been simulated using experiments carried out in three configurations: (i) sublimation experiments in camphor simulating primarily the heat transfer aspects, (ii) bore hole combustion in Acacia nilotica wood bringing in chemical reaction into play, and (iii) bore hole combustion a coal block bringing into consideration the effect of ash on the cavity formation. In all the three cases, the time-evolution of the cavity shape has been monitored under constant oxygen flow rate conditions by measuring the cavity shape and size at periodic intervals. Results show that the cavity formation rates as well as the shape of the cavity are significantly affected by the oxidant flow rate. The importance of the ash present in the coal on the cavity growth has also been brought out. A fair amount of gasification leading to the formation of H2, CO and CH4 was observed; this is shown to depend both on the inherent moisture as well as on the reaction zone temperature. © 2011 Elsevier Ltd.

Energy

Simulation of cavity formation in underground coal gasification using bore hole combustion experiments

Oxy-fuel combustion is one of the emerging technologies to capture and store CO2 emissions generated from thermal power plants. Research programs are in full swing to find out the possibility of retrofitting existing coal fired power plants with oxy-fuel mode combustion. Most of the Indian thermal power plants are pulverized coal based and use sub-bituminous Indian coals. These coals differ from the foreign coals in respect of maceral composition, ash content and combustion kinetics. It is imperative to understand the burning characteristics of Indian coals in oxy-fuel environment to evolve the suitable design for the retrofit of Indian boilers with oxy-fuel mode for the efficient and economic carbon capture without losing thermal efficiency. The present study involves the assessment of the kinetics of pyrolysis and char oxidation of three different Indian coals with varying ash contents viz. 33 to 44% in normal air and in oxy-fuel environment with three different CO 2/O2 concentrations (60:40, 70:30 and 80:20) by Thermo Gravimetric method (TGA). The results are compared in respect of weight loss pattern, peaking temperatures and weighted mean activation energy. The results have shown that the combustion kinetics of the selected high ash Indian coals in normal air combustion is more comparable with 70:30 and 80:20 than 60:40 CO2/O2 concentrations. The methodology adopted in the present study is found useful for comparing the combustion kinetics of various types of coals in normal air and oxy-fuel environment. Copyright © 2008 by ASME.

ASME International Mechanical Engineering Congress and Exposition, Proceedings

Burning profile of high ash Indian coals in oxy-fuel environment

Asia-Pacific Journal of Chemical Engineering

Kinetic study of the gasification of an Australian bituminous coal char in carbon dioxide

Fuel

Properties of high ash coal-char particles derived from inertinite-rich coal: II. Gasification kinetics with carbon dioxide

Reaction kinetics of pulverized coal-chars derived from inertinite-rich coal discards: Characterisation and combustion

Combustion characteristics of coal in a mixture of oxygen and recycled flue gas

Evaluation of the effect of the concentration of CO2 on the overall reactivity of drop tube furnace derived Indian sub-bituminous coal chars during CO2/O2 combustion

Journal	Industrial and Engineering Chemistry Research
ISSN	08885885
Open Access	No