Gasification of Pruned Peach Tree Branches in a CO₂/O₂ Atmosphere in the Presence or Absence of Steam: Effect of Gas Media Composition on Product Gas, Reactivity, and Kinetics

Pruned peach tree branches (PP) are widely and thinly distributed in comparison to cedar, a typical planted forest species in Japan, making them a promising small-scale local energy source. However, their low carbon conversion rate restricts their use as fuel for small-scale gasification in combined heat and power plants. Moreover, kinetic studies required to inform the design of gasifiers are lacking. Thus, in the current study, the gasification of PP using mixed CO2 and O2 gasifying media was evaluated using a laboratory-scale gasification apparatus. Thermogravimetric and differential thermal analyses were performed to elucidate the characteristics of product gas and reaction kinetics. In the absence of steam, higher CO2 or O2 concentrations in the media led to higher CO yields and carbon conversion to gas (CCG) rates. However, when steam was added, the H2/CO yield and CCG were higher under conditions with higher O2 and lower CO2 gasifiers. This suggests that the char–O2 and char–steam reactions do not compete. Moreover, analysis of the CO2/O2 gasification reactivity of PP and timber waste (mainly containing cedar) chars revealed that the effect of O2 was low during the early reaction stages and increased as the reaction progressed. Collectively, these results can be used to design gasifiers and gasification processes for PP char.