Effect Of The Sawdust Hydrothermal Carbonization On Pellets' Properties And Aldehyde/Ketone Formation From Wood Pellets

Biomass pellets are the solid fuels,making of agriculture and forestry waste,through drying,crushing,mixing and extrusion process,which has the potential alternatives to traditional fossil energy.However,due to the time difference between production and consumption of pellets,it inevitably needs to storage and transport in a closed environment.During storage,not only the qualities of the pellets will change,but it also forming hazardous gases,due to the reaction of the chemical compounds in pellets.Moreover,these hazardous gases threaten the health of producers and users.This paper focus on the effect of the sawdust hydrothermal carbonization(HTC)on pellets' properties and aldehyde/ketone formation from wood pellets during storage.The effect factors included the HTC temperature(200-260 ?),environment temperature(30-70?)and relative humidity(RH,30-70 ?)during storage.This paper analyzed the appearance,composition,combustion characteristics and pelletization energy consumption of raw sawdust and hydrochars.Meanwhile,properties of pellets and the emission of aldehyde/ketone from pellets during storage were also analyzed.The effects of various factors on pellets' properties and aldehyde/ketone formation from wood pellets during storage were identified.The results of this study are as follows:(1)After HTC,the color of samples became darker,greener and bluer.As HTC temperature increasing,the contents of ash,volatile,cellulose and hemicellulose in sawdust were decreased,while the contents of fixed carbon and lignin were increased,resulting in an increase of higher heating value.Meanwhile,the pelletization energy consumption,pellets density and Meyer hardness were increased.The results indicated that the color of samples,to some extent,could reflects the difference of its composition and properties.HTC of sawdust could improve the qualities of pellets,and is conducive to the subsequent storage and transportation of wood pellets.(2)The emissions of aldehyde/ketone from pellets were increased with raising HTC temperature,environment temperature and RH during storage,while the pellets'properties(dimension,density,Meyer hardness and moisture content)were reduced.Pellets produced from hydrochar show less hydroscopicity and stable properties during storage.The emission of aldehyde/ketone were significantly affected by the pellets properties and the oxidation of unsaturated fatty acids.The results indicated that higher temperature and RH have a negative effect for pellets in keeping its qualities during storage.The interaction between pellets' properties variation and unsaturated fatty acid oxidation was revealed,which affected the aldehyde/ketone emissions.HTC could improve the ability of pellets to keep its properties stable during storage.However,HTC would accelerate the aldehyde/ketone emission from pellets during storage.