Performance Study On Gasification And Char Combustion Of Hydrogen Production By Chemical-Looping Gasification Process

As the main energy source in China, coal causes the great pollution during the utilization. So the new technology for coal utilization must be provided to improve efficiency and reduce pollution. Hydrogen has broad prospects in future because of high efficiency and free of pollution. In this thesis, hydrogen production by chemical-looping gasification process with CO₂ capture unit was presented. The new process had great attraction to relieving energy crisis owing to producing highly pure hydrogen and realizing near zero emission of pollutants. Based on the correlated research in world and combined with characteristics of the two reactors, the following investigations are made in this thesis:The gasification performance of this process under atmospheric pressure was investigated by the HSC Chemistry. The influence of different parameters including temperature, H₂O/C, CaO/C on syngas products were studied. The efficiency of hydrogen production were calculated for Lingnancang bituminite, Xiwujiang anthracite and Shanxi lignite under the optimum gasification condition, which proved that high efficiency could be also got under atmospheric condition. Besides, it was found that syngas characteristics changed with different parameters with similar trend to these three coals, and the main difference was caused by their diverse total gross and composition of volatile. Without regard to the coal reactivity, the higher coal rank was, the higher the efficiency of hydrogen production was. Furthermore, the high gasification efficiency was also achieved even under atmospheric pressure.On the basis of simulation results, the corresponding gasification experiments were finished in the tube furnace. The syngas composition under different conditions tested by the GASBOARD-3100P gas analyzer showed: for Lingnancang bituminite, more CaO would promote the gasification reaction. Hydrogen yield was the highest when CaO/C mole ratio was 1.5. Then keeping increasing CaO could inhibit reaction owing to reducing the effective contact area between coal and steam. High temperature could promote pyrolysis and gasification when reaction temperature was less than 800℃. However, rising temperature above 800℃inhibited the forming of CaCO₃, and was disadvantageous to the gasification. Hydrogen yield was determined by volatile and fixed carbon together. And, compared with the previous simulation results, less H₂ was produced in the experiment because of physical conditions.The combustion performance of gasification char was investigated using thermal balance. By comparing TG/DTG curves, ignition temperature, burnout temperature, activation energy and so on, influence of some factors on the performance were analyzed. The lower gasification temperature was, the better combustion performance of char was. But less hydrogen were produced because of the lower gasification temperature. As the heating rate increased, char would be subjected to intense thermal shock, which could contribute to its burning. Besides, oxygen of high concentration would also favor burning, because more oxygen contacted with char and improved its combustion reactivity.