Energy and exergy analysis of gas production from biomass intermittent gasification

Abstract

In this paper, thermochemical biomass intermittent gasification was performed in a fluidized-bed reactor with pure steam as gasification agent. A single fluidized bed two-stage gasification process, also known as intermittent gasification process, which involves the time segregated hybridization of coal-combustion and steam biomass-gasification stages in the same vessel, was employed. This research aims to explore the influences of gasification temperature (T) and steam-biomass ratio (S/B) on composition, energy and exergy distribution, as well as energy and exergy conversion efficiencies of the product gas (biomass-gas). Over the ranges of the test conditions used, the total concentration of H2 and CO in the biomass-gas varies between 57.9% and 80.8%, and the exergy and energy efficiencies of the biomass-gas are in the ranges of 54.61%–35.52% and 82.91%–60.78%, respectively. The results show that the chemical exergy values of the biomass-gas are 13.50 to 17.71 times as the corresponding physical exergy values, whereas the chemical energy values are 6.91 to 9.45 times as the corresponding physical energy values. The total energy values of the biomass-gas are higher than the corresponding exergy values, this result in higher energy efficiencies of the biomass-gas. Higher temperature contributes to higher CO and H2 content, physical and chemical energy values, physical and chemical exergy values, as well as energy and exergy efficiencies of the biomass-gas. The steam to biomass ratio is optimal in the intermediate levels for maximal energy and exergy efficiencies of the biomass-gas.