Valorization of Mexican biomasses through pyrolysis, combustion and gasification processes

Pyrolysis, combustion and gasification processes of six different types of biomass, which were obtained from Mexico (Castor husk, Castor stem, Agave bagasse, Coffee pulp, Opuntia stem and Pinus sawdust) were investigated by means of thermogravimetric analysis coupled with mass spectrometry (TG-MS). The selection of biomass, for each thermochemical process, depended on its main physico-chemical properties (moisture content, volatile matter, fixed carbon, ash content, calorific value, mineral content, etc.). For pyrolysis processes, the desirable characteristics of biomass are high volatile matter and low ash content. For combustion processes, the biomass has to show high low heating value (LHV) and low ash content. In the case of gasification processes, the biomass ought to have high fixed carbon. Pinus sawdust had the highest volatile matter and the lowest ash content, Castor stem showed the highest LHV and Coffee pulp had the highest fixed carbon content. The pyrolysis process was divided in three main stages (dehydration, devolatilization and char formation). Moreover, for Agave bagasse two more peaks at high temperature were found due to the decomposition of lignin and cellulose but it could also be related to its high mineral content. On the other hand, three main different stages (dehydration, devolatilization and char oxidation) for the combustion process were found. It is noticeable that Coffee pulp showed one more peak than other studied biomasses, which is related to its high lignin content. Due to its high heat released, Castor husk could be considered as the best candidate for combustion process. However, Pinus sawdust can be considerate more suitable for this process because of its low amount of NO_xreleased. In addition, for gasification process the effect of the gas flow was studied. Coffee pulp resulted to be the most suitable for gasification process due to the amount and quality of the fuel gas produced.