Study On The Co-pyrolysis/gasification Characteristics Of Coal And Biomass And The Interactions

Co-gasification of coal and biomass is a promising technology which can highly-efficient and cleanly make full use of the energy.The smooth development and application of the highly-efficient co-gasification technology of coal and biomass,depends on the systematic study on the key issues such as the interac and its influence mechanism during the co-pyrolysis/gasification,the further utilization of the co-gasification residual char,and the influence of catalyst on the co-gasification,however,so far,the relevant research is not very thorough.Therefore,in this study,firstly,the influence of critical factors including feedstock type?coal type,biomass type?and biomass mass ratio on the products characteristics and the interactions during the co-pyrolysis/gasification of coal and biomass are investigated;then,the mechanisms of the synergy are revealed from two perspectives,including the volatiles-char interactions and the migration of the inorganic mineral elements between coal and biomass;after this,the structural characteristic and reactivity of the co-gasification residual char are analyzed to provide the theoretical basis for its further utilization and the“zero emission”gasification technology;at last,the influence of the catalysts on the co-gasification of coal and biomass are systematically studied to provide a new way to the development of highly-efficient co-gasification technology of coal and biomass.The research in this study should be helpful for a full understanding of the mechanism of the highly-efficient co-gasification of coal and biomass,and improve and push forward its development.Influence of feedstock types?coal type,biomass type?and biomass mass ratios on co-pyrolysis characteristics of coal and biomass are investigated in a fixed-bed reactor,the results show that:the interactions at all biomass mass ratios promotes the gas yield but inhibites the formation of the liquid products.The interactions at about 50%biomass mass ratio during the co-pyrolysis of coal and biomass is stronger.The HLH coal,SM coal,ZD coal and Rice straw blends have a higher gas yield during co-pyrolysis.The interactions between biomass and coals with different metamorphic degrees promotes the liquid products converting into the gas products,the coals with middle and low metamorphic degree and higher organic matter content such as HLH coal,SM coal,and ZD coal show the stronger interactions.The Poplar wood,Camphor wood,Cotton straw and SM coal blends have a higher gas yield during co-pyrolysis.The interactions between coal and different biomass promotes the formation of the volatiles products.The biomass with higher H content such as poplar wood,camphor wood,cotton straw,and cotton husk show the stronger interactions.The interactions of biomass pyrolysis volatiles-nascent coal char and coal pyrolysis volatiles-nascent biomass char are studied in a two-stage fixed-bed reactor,the results show that:the presence of char promotes tar conversion into non-condensable gases during the volatiles-char interactions between the coal and biomass.For biomass volatiles with coal char interaction,the gas products are CO₂,CH₄,and CO whose concentrations decrease,and H₂,whose concentration increases.Concerning the liquid products,the ketones,esters,phenols,and furans contents increase,whereas the aromatics content decreases.However,for coal volatiles with biomass char interaction,the concentrations of CO₂ and H₂ in the gas products and the content of furans in the liquid products showe the opposite trend.In addition,in the presence of biomass or coal volatiles,the larger aromatic ring systems?with?6 fused aromatic rings?in coal or biomass char grows,resulting in a decrease in the gasification reactivity.The volatiles-char interactions have a stronger influence on decreasing the reactivity of coal char than biomass char.Influence of feedstock types?coal type,biomass type?and biomass mass ratios on co-gasification characteristics of coal and biomass are investigated in a fixed-bed reactor,the results showe that:the interactions between coal and biomass at all biomass mass ratios promotes the total gas yield.The interactions at 50⁷5%biomass mass ratios during the co-gasification of coal and biomass is stronger.The ZD coal and Rice straw blends has a higher total gas yield during co-gasification.The interactions between biomass and different coals promotes the formation of gas products,the coals with higher ash content such as HLH coal,JZ coal show the stronger interactions.The poplar wood,corn straw and SM coal blends have a higher total gas yield during co-gasification.The interactions between coal and different biomass promotes the formation of the gas products.The biomass with higher K content in ash such as corn straw shows the stronger interactions,while the biomass with lower K content in ash and lower H content such as rice straw and corn cob shows the weaker interactions.The interactions between coal and biomass in their co-gasification and the physic-chemical structural characteristics and gasification reactivity of the residual char are studied in a fixed-bed reactor,the results show that:conversion of the residual char and tar into gas is enhanced due to the synergy between coal and biomass.The physical structure of residual char showes more pores and inorganic salts particles on coal char when more biomass is added during the co-gasification.The migration of inorganic elements between coal and biomass is found,the formation and competitive role of K₂SiO₃,KAlSiO₄,and Ca₃Al₂?SiO₄?₃is a mechanism behind the synergy.The graphization degree is enhanced but size of graphite crystallite in the residual char decreases with biomass mass ratio increasing.The gasification reactivity of the residual char decreases with the biomass mass ratio increasing.The TGA result also strongly suggests the big difference in the reactivity of chars derived from coal and biomass in spite of influence from co-gasification.Influence of catalysts on the co-gasification of coal and biomass are invesitigated in a TGA with steam and a fixed-bed reactor respectively,the results show that:As for the catalysts of different types,Ni-based catalyst Ni?AC?₂ and the alkali K-based catalyst K₂CO₃showe stronger catalytic role in both the co-pyrolysis stage and the mixed char gasification stage during co-gasification,while the Fe-based catalyst Iron ore and the Ca-based catalyst CaO only showe a weaker catalytic role in the co-pyrolysis stage and no any significant catalytic role in the mixed char gasification stage.K₂CO₃ and Ni?AC?₂ promote the H₂ yield,while the Iron and CaO showe an inhibition role.As for the potassium salt catalysts with different anions,execpt the KCl catalyst only in co-pyrolysis stage,K₂CO₃,KAC,and K₂SO₄showed catalytic role in both co-pyrolysis and mixed char gasification stage.K₂CO₃,K₂SO₄,and KAC promote the H₂ yield significantly.All catalysts promote the carbon conversion significantly during the co-gasification of coal and biomass.When K₂CO₃ is used as a catalyst,the maximum H₂ yield is obtained at 2.5%adding amount,and the maximum carbon conversion is obtained at 5%adding amount,while the maximum calorific value of gas products is obtained at 10%adding amount.