Experimental Study On Biomass Catalytic Pyrolysis And Reactivity Of Char

A lot of research has proved that biomass gasification process includes two steps, firststep is pyrolysis at relatively low temperature and the second step is process of chargasfication at high temperature. Based on these two steps, further research on biomassgasification was carried out systematic by this thesis.To understand different characteristics of different reaction steps in biomassgasification process, the pyrolysis gasification in vapor experiments of typical biomassagricultultural straw and wood were done on TGA test bed. The results proved thatcompared with pyrolysis process in pure nitrogen, pyrolysis gasification in vapor showsdifferent characteristics in high temperature reaction step in which char gasfication wasactive. Rate of reaction of char gasfication became higher and E became lower with thepartial pressure of vapor goes bigger. The reaction processes of pyrolysis gasification invapor of the4kinds of biomass samples are similar, however, due to different physical andchemical properties the characteristic parameters of gasification are different.To understand influence mechanism of pyrolysis process and reactivity of char onbiomass gasification, the pyrolysis experiments were carried out with different kinds ofbiomass samples at different temperatures on the fixed bed which is capable of continuousfeeding. By applying GC,GC-MS,FTIR, the physical and chemical properties of pyrolysisreaction products were analyzed to explain the mechanism of biomass pyrolysis. And then,gasification experiment of char was carried out in TGA to show the influence on chargasfication process of sample type, temperature and gasification medium. Results show theproportion of noncondensable gas and combustible gas including H₂,CH₄,CO becamelarger; liquid products are acids, alcohols, aldehydes and other substances；The soild char isdecrease, but the fixed carbon is increase. Char gasfication is the process of reactionbetween fixed carbon and gasification medium. Rate of gasification reaction and activitydecrease with the temperature goes high, and the TG and DTG of char steam gasification ismore high than char CO₂gasification. By analyzing the physical and chemical propertiesof pyrolysis reaction products, it can be concluded that the pyrolysis process of biomass was finished at temperature of900℃.On the base of conventional gas product of pyrolysis, catalyzed pyrolysis experimentswere carried out with4kinds of biomass samples at700℃and900℃. Investigation wasdone to determine influence of different kinds of catalyst（Calcined limestones,Al2O3,Fe2O3and MgO） on productivity of H₂and CH₄, and how catalyst influence reactivity of biomasschar in CO₂atmosphere. Experiments results show the exist of catalyst increases theproductivity of noncondensable gas and char and decreases the produce of biomass oil.Among the referred4kinds of catalyst, Calcined limestones has the most prominentinfluence on product distribution. The quality of gasification product was improvedobviously by applying catalyst, the proportion of CH₄can be increased by15%at700℃and productivity of H₂can be increased,even more remarkably, about by40%.