Simulation of the gasification of animal wastes in a dual gasifier using Aspen Plus®

Abstract

The gasification of an animal waste biomass (manure) in a dual gasifier was studied using the software Aspen Plus®. For this purpose, a model based on a Gibbs free energy reactor was considered. Effects of the gasification temperature, the gasifying/biomass ratio and the use of steam and CO2 as the gasifying agents on the composition and the low heating value (LHV) of the produced syngas were evaluated. In this sense, the H2/CO ratio and the LHV were the parameters calculated to stablish the best operating conditions for the production of either hydrocarbons via Fischer-Tropsch or energy. Furthermore, the CO2 net emissions generated by the gasification process were also important in the selection of the best operating conditions from an environmental point of view. The obtained results showed that for both gasifying agents the H2 and CO production was favoured at high temperatures whereas the production of CH4 and CO2 was favoured at low ones. On the other hand, the H2 production was higher when steam was used as the gasifying agent and the formation of CO was enhanced when CO2 was considered as gasification agent. An increase of the gasifying agent/biomass ratio had a negatively influence on the production of CH4, leading to a decrease of the LHV. Therefore, steam as the gasifying agent and high temperatures favoured the obtaining of a syngas suitable for the Fischer-Tropsch process whereas CO2 and low gasification temperatures enhanced a syngas with a high LHV which could be used for energy production. Finally, the net CO2 emissions were estimated to be lower when CO2 was again used as the gasifying agent.