Ultrahigh temperature steam gasification of biomass and solid wastes

Experimental results are presented on the gasification of several waste products using high-temperature steam as the gasification media. Four cellulose-rich surrogate waste products (paper, cardboard, and wood pellets) were gasified with high-temperature steam at different temperatures in the range of 700 to 1,100 C. Gasification is an efficient method for clean conversion of waste to hydrogen-rich syngas having moderate heating value, and producing negligible soot and tars during its conversion. Although gasification is a relatively old technique, it has not been examined at ultrahigh gasification temperatures. Paper, cardboard, and other cellulose-rich waste products represent a majority share of municipal solid waste. Basic chemistry of gasification and main reactions propelling the process are presented here. The experimental facility used provided pure steam or steam-oxygen mixtures from the combustion of hydrogen and oxygen at very high temperatures. The role of the chemical composition of the feedstock, the gasifying agent flow rate and temperature, and the steam/feedstock ratio are examined. The results obtained are compared with the equilibrium calculations using Equil software (a part of Chemkin software) at discrete temperatures close to the experimental range examined. The experimental results for hydrogen and carbon monoxide yield are compared with the calculations. The results clearly reveal the role of input and operational parameters on the enhanced yield of hydrogen from the cellulose-rich wastes. The results showed a high hydrogen yield of over 36% at 1,000 degrees C gasification temperatures using paper. At higher gasification temperatures the yield of hydrogen decreased due to its dissociation. For other biomass waste, only 24% hydrogen was obtained at 900 degrees C. The heating value of the gases produced was high at higher gasification temperatures for all waste. The experimental results showed good trends with the calculations. The experimentally determined values for hydrogen and CO were somewhat less than the calculations because of the lack of mixing between steam and waste in experiments and diffusion limitations in the experimental results.