Using cellulose as a representative feedstock composition, estimates of the enthalpy changes for some of the primary reactions that take place in biomass gasification systems are shown in Table 9.1. Although many stoichiometries are possible, as alluded to in this table, most of the hypothetical steam gasification reactions listed are endothermic at 300 and 1000 K. If methane is produced, along with the concomitant formation of C02, the process becomes progres­sively more exothermic. The partial oxidation reactions, as expected, are exo­thermic except at low oxygen levels. The degree of endothermicity and exother — micity of the pyrolysis reactions depends upon the product distributions. As carbon monoxide formation decreases and methane and carbon formation increase, the trend is toward more exothermic processes. It is evident that if fuel gases of higher energy content are desired, the gasification process should be operated to maximize methane and other light hydrocarbon products be­cause their heating values are considerably greater than those of the other fuel components, carbon monoxide and hydrogen, as shown in Table 9.2. As will be shown later, pyrolysis and steam gasification of biomass can be self­sustaining under certain conditions. These types of conversions have each been demonstrated in large facilities.