Renewable Fuels from the Gasification of Food Agricultural Wastes

In this idealized, stoichiometric equation, cellulose (represented as C,H,,O,) reacts with water to produce hydrogen and carbon dioxide, mimicking the commercial manufacture of hydrogen from methane by catalytic steam reforming chemistv. More realistically, a practical technology must be able to convert the cellulose, hemicellulose, lignin, and extractive components of the biomass feedstock to a gas rich in hydrogen and carbon dioxide, including some methane and carbon monoxide. Unfortunately, biomass does not react directly with steam to produce the desired products. Instead, significant amounts of tar and char are formed, and the gas contains higher hydrocarbons in addition to the desired light gases (Antal, 1978, 1983, 1985). The recent work of Corella and his colleagues (Herguido et al., 1992) nicely illustrated this situation. In a fluid bed operating at atmospheric pressure Corella's group observed yields of char from thc steam gasification of wood sawdust in the range of 20 to I O wt %, and yields of tar decreasing to 4 wt % as the temperature of the bed increased from 650 to 775 "C. But at the highest temperature, only 80% of the carbon in the feedstock is converted to gas. By employing a secondary, fluidized bed of calcined dolomite operating at 800 to 875 "C, Corella and his co-workers (Delgado et al., 1997) were able to convert almost all of the tar to gas. Nevertheless, the char byproduct was not converted and represents an effective loss of gas. The objective of this work is to define conditions which enable the steam reforming of biomass feedstocks such as food and agricultural wastes to produce renewable fuels.