Effects Of Torrefaction On The Pyrolysis And Gasification Properties Of Typical Kitchen Waste

With the development of urbanization process in China,the transportation volume of municipal solid waste（MSW）is growing.Kitchen waste is the main component of China’s MSW.So more attentions are needed to the disposal of kitchen waste.Compared to incineration,pyrolysis and gasification technologies of MSW have low pollution and high efficiency.However,because of the high water content,high oxygen content and low heat value of kitchen waste,development of kitchen waste’s pyrolysis and gasification technologies is hampered.But torrefaction can effectively reduce moisture,the O/C value,and improve energy density.In view of this,this paper studied on the effect of torrefaction pretreatment on the characteristics of solid fuel,pyrolysis and steam gasification of typical kitchen waste.Cooked rice,Chinese cabbage leaves,soybean oil as the representatives of kitchen waste,were characterized and torrefied in a fixed bed bench at different temperatures.The results showed that the energy density and high heat value of torrefied rice and torrefied cabbage were improved significantly and the rates of O/C and H/C decreased after torrefaction.At last,270 ℃ is the more suitable torrefaction temperature for rice and cabbage.And oil is not suitable for torrefaction treatment.A non-isothermal thermogravimetric method was adopted to investigate the pyrolysis properties of torrefied typical kitchen waste.After 270 ℃ torrefaction,the initial decompose temperature of rice was lower significantly than the raw’s.The cabbage after torrefaction appeared the missing of hemicellulose/pectin decomposition peak and increase of the secondary cracking peak.When the torrefaction temperature got to 270 ℃,and 300 ℃,pyrolysis activation energy of rice was smaller than raw samples’.As torrefaction temperature increased,the pyrolysis activation energy of cabbage rose firstly and then fell.The raw samples and 270 ℃ torrefied chars of typical kitchen waste were pyrolyzed in a fixed bed bench at different temperatures.After torrefaction it was found that the solid yields of rice and cabbage were increased and the liquid yields were decreased.The GC-MS analysis showed that,in the pyrolytic tar of torrefied rice,the torrefaction had reduced the sugars,but enhanced the two dehydrated sugar,acetic acid,aliphatics,furan.In the pyrolytic tar of torrefied cabbage,torrefaction had reduced the content of alcohols,aldehydes,acids,and enhanced aromatics.The heat values of torrefied typical kitchen waste’s pyrolysis tar were significantly improved.Through the Raman spectroscopy,it was found that pyrolytic char of torrefied chars of typical kitchen waste became to more orderly,graphitized.A non-isothermal thermogravimetric method was adopted to investigate the steam gasification properties of torrefied typical kitchen waste.With the severity of the torrefaction,the rice’s reaction rate of gasification stage was faster,and the gasification temperature range expanded,but torrefaction had little effect on the cabbage’s.Rice after torrefaction had lower gasified activation energies,whereas cabbage had the opposite results.The raw samples and 270 ℃ torrefied chars of typical kitchen waste were gasified in steam atmosphere in the fixed bed bench.It was found that torrefaction of typical kitchen waste resulted in a significant increase in H2 production,and a reduction in CO₂.The volume ratios of H2/CO were enhanced.At 800/900 ℃gasification temperature,It was found that carbon conversion rates of torrefied typical kitchen waste decreased,however which were all close to 100% at 1000 ℃.The cold gas efficiencies of torrefied cabbage were higher than the raw sample at 800/900 ℃,whereas torrefied rice had the opposite results.