Researches On High Temperstur Stam Gasticationo Of Biomas To Produce Hydrogen-rich Gas

Hydrogen is recognized as the ideal energy in the 21st century. Biomass gasification to produce hydrogen-rich gas is considered as one of the most promising hydrogen production technology. However, there are a few defects existing in the process of biomass gasification, mainly low content of H2 fuel gas, high tar content and low calorific value. High temperature steam used as gasification agent can improve hydrogen yield, reduce tar content and improve the quality of fuel gas. In this study, experiments of biomass high temperature steam gasification were carried out in a benchscale fixed bed reactor without catalyst, with regard to hydrogen yield maximization in the fuel gas. Sawdust and ricehusk were used as biomass feedstock.Pyrolysis is an important reaction step of biomass gasification. By the study of pyrolysis process, theory guidances can be provided for high-temperature steam gasification. Firstly, the effects of temperature(750~1050℃) on the pyrolysis process were determined. The results showed that high temperature could accelerate reactions rate, and be conducive to the formation of hydrogen-rich gas.The results also showed that: with the temperature increasing from 750℃to 1050℃, hydrogen yield of sawdust and ricehusk increased from 8.30 g/kg biomass (dry basis) to 20.64 g/kg biomass (dry basis), and from 4.28 g/kg biomass (dry basis) to 14.72 g/kg biomass (dry basis) respetctively. The LHV of fuel gas ranged from 13 to 14.50 MJ/Nm~3, and decreased with the rise of the temperature.Secondly, high temperature steam gasification was completed at bed temperature ranged from 750℃to 1050℃, a steam flow rate of 0.32~1.50 g/min. The results showed that both high gasification temperature and introduction of proper steam led to higher hydrogen yield and gas yield,obviously higher than the pyrolysis process.As the gasification temperature was 1000℃and steam flow rate was 1.02 g/min,the hydrogen content of fuel gas produced by sawdust reached the maximum,up to 51.03 %.Meanwhile,the maximum hydrogen yield was 71.08 g/kgBiomas(sdry basis),which was 41.32 % of the theoretical maximum hydrogen yield. As the gasification temperature was 1050℃and steam rate was 1.02 g/min,the hydrogen content of fuel gas produced by ricehusk reached 44.58 %,and the maximum hydrogen yield of ricehusk was 57.05 g/kgBiomass(dry basis),which is 32.52 % of the theoretical maximum hydrogen yield.Over the range of the experimental conditions,the LHV of the fuel gas was between 11 MJ/Nm~3 and 13 MJ/Nm~3.The optimal value of steam flow rate at 850℃was 1.02 g/min.Finally, the tar produced by pyrolysis and high temperature steam gasification process was determined by GC-MS.The analysis showed that tar content of fuel gas decreased with the rise of temperature and the steam flow rate. When the steam flow rate was 1.02g/min at 1050℃,the tar content was 17.30 g/Nm~3 and it was the lowest we could attend.In this study, hydrogen-rich gas was produced by the method of biomass high temperature steam gasification avoiding the defects of using the catalyst. The hydrogen content of the hydrogen rich gas was more than 45% and LHV was above 11 MJ/m~3. This study provided the basis data and fundamental idea on the theory for the practical application of biomass high temperature gasification.