Gasification Characteristics Of Biomass-derived Hydrochar

Biomass can be converted into large quantities of gas by gasification.However,the large volume,high water content and low energy density of biomass limit the large-scale utilization of biomass.The application of biomass quality improvement technology is very important.Hydrothermal carbonization can improve the fuel characteristics,fixed carbon content and energy density of biomass,and reduce the corrosion of alkali metal in biomass gasification reactor.In this thesis,the effects of hydrothermal carbonization and co-hydrothermal carbonization on gasification characteristics were studied by using different kinds of biomass,hydrochar and co-HTC as raw materials through TGA and downdraft fixed bed gasification under CO₂ atmosphere.The main conclusions are as follows.（1）The experimental platform of hydrothermal carbonization was set up.Using sawdust（SD）,rice stalk（RS）,lotus petiole（LP）and their mixture with PVC（mass ratio9:1）as raw materials,sawdust hydrochar（SHC）,rice stalk hydrochar（RHC）,lotus petiole hydrochar（LHC）,sawdust co-HTC（SPC）,rice stalk co-HTC（RPC）and lotus petiole co-HTC（LPC）were prepared by hydrothermal carbonization at 260°C.The effect of hydrothermal carbonization on the physicochemical properties of samples was studied.The results showed that hydrothermal carbonization reduced the volatile content of biomass and increased the fixed carbon content and the lower heat value（LHV）of biomass.Which also increased the stacking density of SD（0.14～0.18 g/cm³）.The ash in biomass could be removed effectively by biomass and PVC co-hydrothermal carbonization.At the same time,due to the high volatile characteristics of PVC,the volatile content of hydrochar was increased,which was conducive to improving the gasification efficiency of hydrochar.（2）Based on TGA and fixed-bed gasification experiment,the weight loss behavior and gasification characteristics of different biomass were studied.The results are as follows.Lignin-based SD required the highest temperature for volatiles escape and had the highest weight loss rate.The gasification reactivity of LP was higher than that of SD and RS.The gas yield of the three kinds of biomass increased with increasing temperature,which of SD was higher than that of RS and LP.In the gas product were mainly composed of CO,H₂and CH₄.It is accompanied by a small amount of C_mH_n production at 500～700°C,and C_mH_n undergoes reforming reaction to generate CO and H₂ at 800～900°C.When the same mass of biomass（ad）has gasified,SD had the highest gas production efficiency and cold gasification efficiency（78.92%）.The gas production effect of SD with the same volume was not as good as RS and LP,and LP had the best gas production effect（3322 MJ/m³）.（3）Experimental results of TGA and gasification of hydrochar showed that dehydration and decarboxylation of biomass in hydrothermal process resulted in the decrease of water content of hydrochar and affected the maximum dehydration rate of hydrochar.The hydrothermal carbonization process will lead to the hydrolysis and carbonization of biomass,which will reduce the catalytic activity and pyrolysis activity of the hydrochar with the enhancement of the carbonization degree.The hydrothermal carbonization process promoted the breaking of chemical bonds in the sample and the cracking of functional groups in the tar,thus promoting the generation of gas in the gasification reaction.Which also could reduce the tar production rate of biomass in the process of high-temperature gasification,and improved the conversion rate of resources.It could also increase the density of biomass and play a positive role in biomass gasification,and RHC has the largest increase（13.43～26.53 MJ/kg）.The gas production and LHV of hydrochar were lower than those of biomass.SHC and LHC have better gasification effect,and LHC had the highest cold gasification efficiency（43.99%）,while RHC was the least suitable for gasification.（4）The TGA and gasification results of co-hydrothermal carbon were processed and compared with the analysis results of biomass and hydrothermal carbon.Co-hydrothermal carbonization of biomass and PVC could improve the gasification reaction activity and carbonization degree of raw materials.The char yield of co-hydrothermal carbon in gasification was lower than that of hydrochar.The gas yield and LHV of hydrochar were lower than that of biomass,but the co-HTC was better than that of hydrochar.Through the multi-angle analysis of the gas yield and LHV of the co-HTC,it could be seen that the co-hydrothermal carbonization had a positive effect on the gas production of gasification,which also could effectively improve the LHV of the gas production of SD in the low temperature section,RS and LP in the high temperature section.LPC had the highest LHV（11.67MJ/kg）.The hydrothermal carbonization process improved the reactivity of hydrochar in the gasification process,and promoted the gasification reaction of char,tar cracking and reforming reaction.It also had a qualitative effect on biomass.Which had a positive effect on improving the LHV of gas production of materials（ad）.Among them,SPC and LPC had obvious effect on improving quality.