Process simulation of the co-gasification of biomass and polythlene

Abstract

The aim of this study was to determine the effects of the feedstock composition, such as biomass, polyethylene and their respective blend ratios, -gasifying agents and operating conditions on the product gas composition, H2/CO ratio of the syngas and on the Lower Heating Value (LHV) of the syngas. The synergistic interaction between the polyethylene and biomass was also evaluated. The co- gasification of biomass (pine sawdust) and polyethylene (low- density polyethylene) was conducted using an equilibrium model in Aspen Plus. The co- gasification of biomass and polyethylene (75% PE + 25% biomass) showed that a H2 composition of 56% was achieved at equivalence ratio (ER) equals to 0.1 from the use of oxygen, and a H2 composition of 54.5% was achieved at ER equals to 0.34 and steam to fuel ratio (SFR) equals to 0.6 from the use of oxygen – steam mixture. High CO of 54% was achieved at ER equals to 0.22 from the use of oxygen as a gasifying agent and 52% was achieved at ER equals to 0.22 and carbon dioxide – to- carbon ratio (CO2/C) ratio of 0.6 for the use of oxygen – carbon dioxide mixture as a gasifying agent. The recommended H2/CO ratio of 2 was attained from the use of various gasifying agents and a Lower Heating Value of 10.7 MJ/Nm3 was achieved at ER equals to 0.2 and Steam to Fuel Ratio (SFR) equals to 0.6 was attained from the use of oxygen – steam mixture and for an oxygen – carbon dioxide mixture as a gasifying agent, a Lower Heating Value (LHV) of the syngas of 9.2 MJ/Nm3 was attained at ER equal to 0.1 and CO2/C ratio of 0.6. The co- gasification of biomass and polyethylene results indicated that an increase in the polyethylene percentage in the blended mixtures also has shown positive influence on the H2 composition in the product gas, the H2/CO ratio of the syngas and also on the Lower Heating Value (LHV) of the syngas. The blend ratio of (75% PE + 25% biomass) produced a high H2 composition in the product gas and a blend ratio of (25% PE + 75% biomass) produced a high CO composition in the product gas. An increase in the polyethylene percentage in the blend mixture, using oxygen-steam mixture as a gasifying agent, increases the gas yield (GY), cold gas efficiency (CGE) and the extent of the synergistic effect. The results from this study have shown that the co-gasification of biomass and polyethylene can be a feasible study that can be used to alleviate challenges associated with a syngas of biomass with low H2 composition, and low energy content.