Experimental Study On The Use Of Compression Molding Technology On Biomass Fuels Of Sawdust,leaves And Wheat Straw

Biomass energy is a renewable clean energy source.Biomass compression molding is one of the effective ways to convert biomass into biomass energy.In this paper,sawdust,leaves and wheat straws were used as raw materials for normal temperature and pressure molding.The sawdust,leaves and wheat straws were compressed into pellet fuels with a hydraulic press powder pelletizer.The following studies were carried out on the compression molding process of biomass fuels.(1)The main factors influencing compression molding of biomass were studied based on the density,size stability and compression strength of biomass fuels.Results showed that the moisture content,molding pressure and particle size of the raw materials had a significant effect on the physical properties of the three types of the biomass fuels.The optimal molding parameters for the sawdust were: moisture content of 5%,molding pressure of 12 MPa,and particle size less than 0.315 mm.The optimal molding parameters for the leaves were: moisture content of 5%,molding pressure of 10 MPa,and particle size of 0.63~2mm.The optimal molding parameters for the wheat straws were: moisture content of 5%,molding pressure of 12 MPa,and particle size of 0.315~0.63 mm.(2)Based on the above research results on the main influencing factors of the biomass molding process,the effects of additives(bentonite,cassava starch and waste paper fiber)on the physical properties of the three types of biomass fuels made from sawdust,leaves and wheat straws were studied.Results showed that the addition of waste paper fibers had the most significant effect in improving the physical properties of the three types of biomass fuels.Compared with the control group,when 15% of waste paper fiber was added,the density,size stability and compression strength of sawdust pellet fuels were significantly improved,and the compression strength was increased by 37.98%.When 10% of waste paper fibers were added,the leaves pellet fuel showed the highest density,best size stability and highest compression strength,and compression strength was increased by 22.74%.When 15% of waste paper fibers were added,the density and strength of the wheat straw-molded fuel increased significantly,while the size stability decreased.(3)The effects of pretreatment techniques(dry torrefaction and wet torrefaction)at different temperatures on biomass and biomass pellet fuel were further studied.The results showed that dry torrefaction and wet torrefaction are two effective heat treatment methods for biomass fuels of sawdust,leaves and wheat straws.As torrefaction temperature increases,the energy densification ratio of the three types of biomass also increases while mass yield decreases.In addition,dry torrefaction and wet torrefaction also improved the higher heating values and thermal degradation characteristics of the biomass fuels.Compared with the untreated biomass pellet,the compression strength of the dry-torrefied biomass pellet fuel was significantly reduced.At the same torrefaction temperature,the compression strength of the wet-torrefied biomass pellet fuel was significantly higher than that of the dry-torrefied biomass pellet fuels.In addition,the hydrophobicity of these three types of biomass pellet fuels was significantly increased at certain torrefaction temperatures.(4)Considering the higher heating value,compression strength and hydrophobicity of the biomass pellet fuels,additives(such as waste paper fibers)were combined with pretreatment methods in the preparation of biomass pellet fuels.Results showed that additives reduced the negative effects of torrefaction,such as increasing the density,strength and size stability of the biomass pellet fuels.