It is generally known that the environmental pollution becomes one of the most serious problems in China. The contradiction between the energy demand and environment protection has become increasing apparent with society development and population growth. To solve this problem, it is essential to develop the renewable energy in China. The biomass energy, which is a kind of renewable energy, has aroused great attention in China for its abundance and environmental friendliness. Biomass gasification technology has been considered to be the most promising way for power, heat generation and various biofuels synthesis. In order to overcome the constraints of using biomass, it is recommended to be pretreated by torrefaction. Larch wood and corn stalk, as the representative of forest residue and agriculture residue, were studied in this research.
Under the optimal condition, the solid product after wet torrefaction was analyzed with the proximate analyses, ultimate analyses, heating values, organic functional groups, SEM, BET and so on. The wet torrefaction was effective to improve the fuel properties of Larch wood and corn stalk. The wet torrefaction was compared with the dry torrefaction to find the best pretreatment method. It was found that the wet torrefaction had the features of lower temperature and shorter reaction period. As a result, the wet torrefaction was selected in this research.
The ‘‘Torrefaction–Gasification’’ two-stage gasification flow chart was put forward. The raw biomass and wet torrefied biomass samples were both gasified with the gasifying agents of steam and CO2. The syngas production during gasification was mainly analyzed to testify the effect of wet torrefaction. During steam gasification, H2 and CO production during gasification of the wet torrefied biomass samples were higher than that of raw biomass samples, showing the superiority of the wet torrefaction. During CO2 gasification, CO is the main product, and the CO production was also significantly improved by wet torrefaction.
The gas-solid reaction models were used to study the kinetics of gasification process, including VRM, SCM and RPM. The RPM proved to be the most suitable model for the gasification of biomass in this research. The structure change during gasification process was explained successfully by the RPM. . The results showed that the wet torrefaction pretreatment could reduce the activation energy of gasification compared with that of raw biomass, which was also found in CO2 gasification.
