• Korean Chemical Engineering Research
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• v.53 no.5
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• pp.653-662
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• 2015

In general, the coal gasification has to be operated under high temperature ($1300{\sim}1400^{\circ}C$) and pressure (30~40 bar). However, to keep this conditions, it needs unnecessary and excessive energy. In this work, to reduce the temperature of process, alkali catalysts such as $K_2CO_3$ and $Na_2CO_3$ were added into Cyprus coal. We investigated the kinetic of Cyprus char-$CO_2$ gasification. To determine the gasification conditions, the coal (with and without catalysts) gasified with fixed variables (catalyst loading, catalytic effects of $Na_2CO_3$ and $K_2CO_3$, temperatures) by using TGA. When catalysts are added by physical mixing method into Cyprus coal the reaction rate of coal added 7 wt% $Na_2CO_3$ is faster than raw coal for Cyprus char-$CO_2$ gasification. The activation energy of coal added 7 wt% $Na_2CO_3$ was calculated as 63 kJ/mol which was lower than raw char. It indicates that $Na_2CO_3$ can improve the reactivity of char-$CO_2$ gasification.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.1
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• pp.89-96
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• 2016

The mechanism for laminar dust flame propagation can only be elucidated from a comprehensive mathematical model which incorporates conduction and radiation, as well as the chemical kinetics of particle devolatilization and gas phase and char reaction. The mathematical model for a flat, laminar, premixed coal-air flame is applied to the atmospheric coal-air mixtures studied by Smoot and co-workers, and comparisons are made with their measurements and predictions. Here the principal parameter for comparison is the laminar burning velocity. The studies of Smoot and co-workers are first reviewed and compared with those predicted by the present model. The effects of inlet temperature and devolatilization rate constants on the burning velocities are studied with the present model, and compared with their measurements and predictions. Their measured burning velocities are approximately predicted with the present model at relatively high coal concentrations, with a somewhat increased inlet temperature. From the comparisons, their model might over-estimate particle temperature and rates of devolatilization. This would enable coal-air mixtures to be burned without any form of preheat and would tend to increase their computed values of burning velocity.

• Clean Technology
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• v.21 no.1
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• pp.53-61
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• 2015

In this study, we have investigated the kinetics on the char-CO₂ catalytic gasification reaction. Thermogravimetric analysis (TGA) experiments were carried out for char-CO₂ catalytic gasification of an Indonesian Kideco sub-bituminous. Na₂CO₃ and K₂CO₃ were selected as catalysts which were physically mixed with coal. The char-CO₂ catalytic gasification reaction showed a rapid increase of carbon conversion rate at 850 ℃, 60 vol% CO₂, and 7 wt% Na₂CO₃. At the isothermal conditions ranging from 750 ℃ to 900 ℃, the carbon conversion rates increased as the temperature increased. Four kinetic models for gas-solid reaction including the shrinking core model (SCM), random pore model (RPM), volumetric reaction model (VRM), and modified volumetric reaction model (MVRM) were applied to the experimental data against the measured kinetic data. The gasification kinetics were suitably described by the MVRM for the Kideco sub-bituminous. The activation energies for each char mixed with Na₂CO₃ and K₂CO₃ were found 55-71 kJ/mol and 69-87 kJ/mol.

• Journal of the Korean Society of Combustion
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• v.22 no.4
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• pp.19-26
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• 2017

This study investigates the gasification of coal char by $CO_2$ under high pressures in a drop tube furnace(DTF). The rate constants are derived for the shrinking core model using the conventional method based on the set reactor conditions. The computational fluid dynamic(CFD) simulations adopting the rate constants revealed that the carbon conversion was much slower than the experimental results, especially under high temperature and high partial pressure of reactants. Three reasons were identified for the discrepancy: i) shorter reaction time because of the entry region for heating, ii) lower particle temperature by the endothermic reaction, and iii) lower partial pressure of $CO_2$ by its consumption. Therefore, the rate constants were corrected based on the actual reaction conditions of the char. The CFD results updated using the corrected rate constants well matched with the measured values. Such correction of reaction conditions in a DTF is essential in deriving rate constants for any char conversion models by $H_2O$ and $O_2$ as well as $CO_2$.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.69-72
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• 2015

Computational fluid dynamics (CFD) modeling of large-scale coal-fired boilers requires a complicated set of flow, heat transfer and combustion process models based on different degrees of simplification. This study investigates the influence of coal devolatilization, char conversion and turbulent gas reaction models in CFD for a tangential-firing boiler at 500MWe capacity. Devolatilization model is found out not significant on the overall results, when the kinetic rates and the composition of volatiles were varied. In contrast, the turbulence mixing rate influenced significantly on the gas reaction rates, temperature, and heat transfer rate on the wall. The influence of char conversion by the unreacted core shrinking model (UCSM) and the 1st-order global rate model was not significant, but the unburned carbon concentration was predicted in details by the UCSM. Overall, the effects of the selected models were found similar with previous study for a wall-firing boiler.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.5
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• pp.413-420
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• 2013

Effect of inherent volatile matters in fuels on electrochemical reactions of anode was investigated for a single direct carbon fuel cell (DCFC). Raw coals used as power source in the DCFC release light gases into the atmosphere under the operating temperature of DCFC ($700^{\circ}C$) by thermal decomposition and only char remained. These exhausted gases change the gas composition around anode and affect the electrochemical oxidation reaction of system. To investigate the effect of produced gases, comparative study was conducted between Indonesian sub-bituminous coal and its char obtained through thermal treatment, carbonizing. Maximum power density of raw coal ($52mW/cm^2$) was appeared higher than that of char ($37mW/cm^2$) because the gases produced from the raw coal during thermal decomposition gave additional positive results to electrochemical reaction of the system. The produced gases from coals were analyzed using TGA and FT-IR. The influence of volatile matters on anodic electrolyteelectrode interface was observed by the equivalent circuit induced from fitting of impedance spectroscopy data.

• Korean Chemical Engineering Research
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• v.52 no.4
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• pp.544-552
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• 2014

In this study, We have investigated the kinetics on the char-$CO_2$ gasification reaction. Thermogravimetric analysis (TGA) experiments were carried out for char-$CO_2$ catalytic gasification of an Indonesian Roto lignite. $Na_2CO_3$, $K_2CO_3$, $CaCO_3$ and dolomite were selected as catalyst which was physical mixed with coal. The char-$CO_2$ gasification reaction showed rapid an increase of carbon conversion rate at 60 vol% $CO_2$ and 7 wt% $Na_2CO_3$ mixed with coal. At the isothermal conditions range from $750^{\circ}C$ to $900^{\circ}C$, the carbon conversion rates increased as the temperature increased. Three kinetic models for gas-solid reaction including the shrinking core model (SCM), volumetric reaction model (VRM) and modified volumetric reaction model (MVRM) were applied to the experimental data against the measured kinetic data. The gasification kinetics were suitably described by the MVRM model for the Roto lignite. The activation energies for each char mixed with $Na_2CO_3$ and $K_2CO_3$ were found a 67.03~77.09 kJ/mol and 53.14~67.99 kJ/mol.

• Clean Technology
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• v.19 no.3
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• pp.306-312
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• 2013

We investigated the effects of the concentration of carbon dioxide on the char-$CO_2$ gasification reaction under isothermal conditions of $850^{\circ}C$ using the Drayton coal. Potassium carbonate was used to improve the low-temperature gasification reactivity. The enhancement of carbon dioxide concentration increased the gasification rate of char, while gasification rate reached a saturated value at the concentration of 70%. The best $CO_2$ concentration for gasification is determined to be 70%. We compared the shrinking core model (SCM), volumetric reaction model (VRM) and modified volumetric reaction model (MVRM) of the gas-solid reaction models. The correlation coefficient values, by linear regression, of SCM are higher than that of VRM at low concentration. While the correlation coefficients values of VRM are higher than that of SCM at high concentration. The correlation coefficient values of MVRM are the highest than other models at all concentration.

• Korean Chemical Engineering Research
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• v.49 no.1
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• pp.114-119
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• 2011

Thermogravimetric analysis(TGA) was carried out for pyrolysis and char-$CO_2$ gasification of low rank Indonesian ABK coal and China lignite. The pyrolysis rate was successfully described by a two-step model adopting the modified Kissinger method. The shrinking core model, when applied to char-$CO_2$ gasification gave initial activation energy of 189.1 kJ/mol and 260.5 kJ/mol for the ABK coal and China lignite, respectively. Thus, the char-$CO_2$ gasification has been successfully simulated by the shrinking core model. In particular, the activation energy of char-$CO_2$ gasification calculated in this work is similar to the results on the anthracite coal, but considerable difference exists when other models or coal types are used.

• Journal of Energy Engineering
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• v.11 no.2
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• pp.166-177
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• 2002

The present study is described of the flame structure of one-dimensional, flat, premixed, laminar, coal-air flame with some addition of methane for the flame stability. A low pressure burner operating at a combustion pressure of 0.3 arm was employed in order to extend the reaction zone. Predicted results from the models considered in the present study are compared with experimental results. Comparisons are included gas temperatures, species concentrations, char analysis and measured burning velocity. Among the models, Model II $I^{*}$-d, which specified devolatilization rate constants and a char surface area factor S=4, resulted in good agreement within the present experimental ranges. The results of char analysis suggest that the extent of the reaction occurring on the panicle might be underestimated in the model so that the char surface area should be increased. A value of 4 for this factor was given by sensitivity analysis of change in char surface area. Again, model II $I^{*}$-d gave satisfactory predictions of burning velocities over most of the experimental range studied. It has been clearly shown that the particle diameter appreciably affects the rates of devolatilisation and char oxidation through the effects of thermal lag and volumetric reactive surface area, consequently laminar burning velocity.ity.