Process simulation of gasification of various feedstocks.

Abstract

Gasification is the reduction waste to energy method, which converts organic waste types into syngas fuel, which then can be used for energy and in chemical production. In this work, ASPEN Plus software was used for modelling and simulation of the gasification processes. The investigation was carried out for three waste feedstock: palm kernel shell, meat and bone meal, and wood pellets to forecast the produced syngas using air gasification. These fuels were characterized based on their ultimate and proximate analysis. A fluidized bed gasifier was selected based on its ability to accept different types and sizes of feedstock, making them possible for commercial uses on a large scale. The circulating fluidized bed gasifier was simulated to reproduce its actual behaviour using a non-stoichiometric equilibrium model. It employed the use of minimization of Gibbs free energy to estimate the chief syngas composition (CO, H2, CO2 and CH4). The operational parameters studied were the gasification temperature, gasifier pressure and equivalence ratio. The sensitivity analysis on ASPEN Plus was carried out to understand the influence of operating parameters on syngas composition, yield and lower heating value and gasifier performance parameters. Other selected parameters were carbon conversion efficiency and cold gas efficiency. The equilibrium model was able to estimate the gasifier performance and examine the operational parameters' behaviour in the gasification process. The results from the sensitivity analysis pointed out that gasification temperature and equivalence ratio influence the gasifier performance more than gasifier pressure. An increase in equivalence ratio or gasification temperature increased the syngas yield and carbon conversion efficiency. When increasing gasifier pressure, it was found to decrease the syngas yield, increases the syngas lower heating value, cold gas efficiency and carbon conversion efficiency. Increasing equivalence ratio reduce lower heating value and cold gas efficiency. An increase in temperature increases the cold gas efficiency. This study found that the optimal equivalence ratio is controlled from 0.2 to 0.4. The gasification temperature is controlled between 800 and 950°C and gasifier pressure is controlled between 0.1 and 2 MPa. Meat and bone meal gasification is the promising feedstock that provides higher hydrogen to carbon monoxide ratio of close to 2.0, which can be used for chemical and energy production.