Exprimental Study On The Hydrogen Production From Biomass Gasifiction In Supercritical Water

In this paper, the experimental equipment of supercritical biomass gasification with batch operation is setted up. Aimed at hydrogen production with the glucose as the model compound in the sub-supercritical or the supercritical water, the experimental study is carried on with this equipment. The CaO is chosen as the removing solvent for CO2. The effects of reaction temperature, reaction pressure, stay time, initial concentration of the glucose and Ca/C molar ratio on the decomposing rate of the glucose are studied. The chamical oxygen demand (COD) value is used to determine the decomposing rate of the glucose, and the gas chromatography is employed to analyse the gas outcome from the experiments quantitatively.At first, the experiments are run in the pure supercritical water. The results show that the temperature and the stay time are the main parameters of the experiments. As the temperature rising in the experimental range, the proportions of hydrogen and methane in the gas outcome from the reactor increase, the proportion of the CO decreases, and the decomposing rate of the glucose decreases. The stay time of the reaction have a great effect on the composition of the gas outcome. The decomposing rate of the glucose decreases as the increasing of the stay time of the reaction. The pressure also has the effect on the composition of the gas outcome at the critical point. The methane proportion increases as the intital concentration of the glucose increases.The ideal reaction parameters of the hydrogen production in the pure supercritical water are as following: temperature about 500℃, pressure above critical point (22.5MPa), concentration between 2.5% and 5.0%, the stay time of the reaction within 3min⁵min.Secondly, in order to increace the proportion of the hydrogen and the decomposing rate of the glucose, the CaO is added in the experiments. In this case, the temperature and the stay time of the reaction are still the main parameters greatly effecting on the results of the experiments. The pressure has certain effect on the gasification and the decomposing rate of the glucose at the critical point. The decomposing rate rises a lot as the concentration increases with CaO, when the intital concentration of the glucose is more than 5%.The ideal reaction parameters of hydrogen production with CaO are as following: the temperature about 500℃, the pressure above the critical point (22.5MPa), the concentration between 2.5% and 5.0%, the stay time of the reaction within 3min⁵min, the molar ratio of Ca/C between 0.4-0.5.At last, on the foundation of the experimental results in this paper and the results from other studies, the reaction mechanism and the reaction path are analyzed. After comparing, the technology of hydrogen production from biomass gasification in supercritical water with CaO as the removing solvent for the CO₂ is comfirmed. The new technology is able to raise the output of the hydrogen and increase the decomposing rate of the biomass.