Design and Simulation Model of a Gasifier for the Production of Syngas

Abstract

Production of syngas by gasification of locally available coal in the moving bed gasifier is one of the most economical and promising options to produce high calorific value gaseous fuel. Syngas contains significant amounts of C1—C4 hydrocarbons. Regarding the current situation of energy crisis and increase in the cost of conventional fuels (i.e. furnace oil) biomass and coal seems to be a cheap and accessible fuel in this part of the world. In these prevailing circumstances, syngas from surface mined coal gasification could be suitable alternate for limited natural gas. A moving bed gasifier designed by Aspentech in 2010 has been used to get some important results using local lignite coal samples, which are helpful in analyzing the potential of this conventional fuel. For this study, Aspen-Plus V8.0 has been utilized to simulate the performance of gasifier. The gasifier can withstand the temperature of 950°C and a pressure of 3.5MPa. Several numbers of RCSTRs are used to specify gasifier in the model, which utilizes 5 kg/s of coal after drying and pyrolysis. In this study steam is used as a gasifying medium. The R-yield reactor is used for pyrolysis in the modeling. Particle size distribution (PSD) is not considered in the model and coal feed is assumed to be pretreated to remove excessive moisture to 5 % in the proximate analysis for the simulation in gasifier. Fortran Subroutine codes built in the model were used for obtaining the mass and energy balances for the different process steps within the syngas production process. Sensitivity analysis and process optimization is done by considering pyrolysis temperature and S/C ratio as input variables. Based on this investigation, critical process steps for process heat integration and syngas yield are identified.