Sensitivity Analysis and Optimization of Parameters for the Gasification of High Ash Indian Coal

摘要

Gasification of high ash coals and controlling resulting emissions is a challenging task. Effective utilization of these coals depends on proper selection of operating conditions. This paper is aimed at comprehensive analysis of effect of operating conditions on the gasification of a high ash Indian (Jharia) coal with two-fold objectives of maximizing syngas heating value and reducing CO_2 emissions. An ASPEN Plus model is developed to simulate the gasification process and simulation results are validated with experimental data available in literature. The simulated results are in good agreement with experimental results with less than 10% error. In the first stage the sensitivity analysis of four operating conditions viz., Equivalence Ratio (ER), Steam-to-Coal Ratio (SCR), Gasifier Temperature, and Gasifier Pressures is performed. A design specification Limiting Air Flow Rate (LAFR) is used for effective carbon conversion and reduced emissions. Gasification temperature is the most influencing parameter among all parameters, followed by ER and SCR. Gasification pressure has no significant effect on syngas composition. The results clearly indicate that a lower ER and SCR are favorable for formation of maximum amount of combustible gases (H_2, CO) and minimum amount of CO_2. Different combination of ER and SCR in the specified ranges were examined. In all cases, the maximum efficiency is attained in a temperature range of 600°C to 900°C. In the second stage these parameter are optimized with an objective of maximizing the heating value of syngas and minimizing CO_2 emissions. Both normal and constraint based optimization is performed. In constraint based optimization, a constraint of CO_2 mole fraction less than 1% is imposed. Optimum parametric domains for maximum efficiency are presented.