Exergetic study of beech wood gasification in fluidized bed reactor using CO2 or steam as gasification agents

Abstract

The study of energy and exergy balance in the gasification of beech wood was performed using a pilot-scale fluidized bed reactor at different operation conditions. The temperature range studied was from 600 °C to 900 °C, with the use of CO2 and steam as gasification agents and biochar and sand as bed materials. The singularity of this work was the combination of an experimental work and a complete evaluation of the exergy distribution of beech wood gasification based on strict use of the same experimental set-up, but varying the operating conditions. Also, a detailed analysis of pyrolysis products was taken into consideration. Temperature increase had a negative influence on exergy destruction. When sand was used as the bed material, the exergy destruction rate increased from 9 to 13% of the total exergy entering the system. Comparing pyrolysis and gasification with CO2 under the same conditions, it was found that the pyrolysis reaction destroyed more exergy than gasification. Steam showed lower exergy destruction rate than CO2 gasification when biochar was used as bed material for tar cracking. This means that more exergy was conserved in steam gasification reaction, even though syngas efficiency was to 65% for both set-ups.