Comparison of Charcoal, Ceramics and Dolomite as a Bed Material in Two-Stage Pyrolytic Processing of Wood Waste into the Synthesis Gas

Abstract

This document explains the advantages and disadvantages of three types of bed materials used in two-stage pyrolytic processing of wood waste into the synthesis gas. The process combines pyrolysis and subsequent high-temperature heterogeneous cracking of volatiles in the carbon residue fixed bed (obtained by raw material pyrolysis), the inert material (aluminum oxide ceramics) or dolomite. Experimental data characterising the dependence of the gas yield, its chemical composition, the calculated lower heating value and tar content on the process parameters are presented. The optimisation of parameters and the bed material mostly depends on the process purpose: a large-volume inert material bed is preferable for using in burners in the cracking zone, it allows to obtain the most calorific gas with a lower calorific value up to 13 MJ / m3; whereas a carbon residue at a temperature of above 1,010 °C is a preferable bed material in gas engines (when the tar content is less than 50 mg/m3); and a carbon residue at a temperature less than 1,000 °C is the best for the synthesis of liquid fuels (H2 to CO ratio reaching its maximum). Using dolomite turned up to be impractical because of its thermal instability and high amount of both CO2 and H2O in the gas product.