Study On Gasification Of Biochar In CO₂/H₂O Atmosphere

Zero carbon emission is one remarkable feature of biomass energy.The development of biomass energy to partially replace fossil energy is of great significance to Chinese carbon emissions reduction.Biomass gasification technology can produce high calorific value syngas,such as CO,H₂,CH₄,etc.,which can be used as fuel or chemical raw materials,and it is one of the main ways of biomass utilization.In the actual process of biomass gasification,the CO₂/H₂O reacts with biomass char at the same time.The gasification mechanism of biomass char in the mixed atmosphere of CO₂ and H₂O is not clear.Besides,the effect of inorganic matter in biomass on its gasification behavior is also controversial.In this paper,a variety of biomass gasification experiments were carried out on a simultaneous thermal analyzer and a micro-fluidized bed.The gasification reaction rate of each biomass char under different atmospheres was measured,and contribution of reactions between the char-CO₂ and char-H₂O under different conditions were quantitatively analyzed.Besides,the influence of the inorganic matter in the biomass on the gasification behaviors was explored.The gasification experiments of beech and poplar char were carried out in a simultaneous thermal analyzer,and the gasification model of biomass char under CO₂/H₂O atmosphere was built.At 1273K,the reaction of char CO₂ and char H₂O occurred in the same active site,and the react rate under the condition of mixture of CO₂/H₂O atmosphere is larger than that of reaction in single atmosphere.When the H₂O partial pressure increased to a certain extent（P=1/3）,the reaction of char-H₂O was independent of char-CO₂ reaction,and it was not affected by the partial pressure of CO₂.The char-H₂O reaction was competive with the char CO₂ reaction,and the reaction priority of char-H₂O was higher.The gasification experiments of five kinds of biomass chars were carried out in a micro-fluidized bed.The gasification behavior of jatropha seed shell char,cotton stalk char and melon seed shell char were suitable for the volume model,while sawdust char and corncob char were suitable for the shrinking core model.Ca and Mg can promote the gasification of biochar,while Si and Al can inhibit the gasification of biochar,and the catalytic index M was proposed,which can describe the relationship between gasification reactivity and the types and contents of inorganic matter.