Biomass Pelletization In Combination With Torrefaction:Characterization And Analysis Of Pellets Prepared From Different Biomass Sources

Use of renewable energy particularly biomass is getting increasing popularity worldwide nowadays.Global pellet production and consumption are expected to grow and dependency on few biomass sources and sustainability issue urged the researchers towards finding other renewable energy sources(e.g.sewage sludge,furfural residue,agricultural residues etc.)to meet future pellet demands.Pellet industry can face challenges such as limitation of raw materials due to growing global pellet production and consumption.Finding new energy sources become significant to maintain the consistency of feedstock supply and sustainability of pellet production.We performed detailed research studies using different biomass materials.The key findings of these studies are described below1)This study was conducted to investigate the feasibility of furfural residue for the production of clean,high energy dense,uniform sized and shape solid fuel(e.g.pellet)and to compare the quality of furfural residue pellets(FRPs)with wood pellets(WPs).For FRPs made from particles of 0.25-0.5 mm,the highest particle density of 1.430 g/cm3,strength of>8 MPa and hardness of 438.5 N/mm2 were achieved at temperature of 130℃ and pressure of 160 MPa.Correspondingly,highest particle density of 1.433 g/cm3,strength of 5.56 MPa and hardness of 350.2 N/mm2 were found for FRPs made from particles of 0.5-1.41 mm.FRPs made from both particle sizes were 14.8-16.8%denser,52-74.12 and 54.2-59.6%stronger and 109-227.8 and 88-216%harder than WPs made at temperature of 70-160℃ and pressure of 70-160 MPa.Energy consumption of FRPs at temperature of 130℃ were found lowest and were 4.2-16.3%(0.25-0.5 mm)and 16.6-31%(0.5-1.41 mm)lower than WPs made at temperature of 130-160℃.Energy consumption of FRPs were lowered by 12.8-18.78%and 10-13.8%for particle size of 0.25-0.5 and 0.5-1.41 mm,respectively using synthetic resin as a binder.For MC of 5.5%,pellets made at temperature of 200℃ were found water resistive and the highest percentage of water resistivity was found as 97.80%.2)Co-pelletization of sewage sludge(SS),furfural residue(FR)and corn stalk(CS)was performed to characterize and analyse the quality of pellets under different pelletizing conditions and blending ratios.Addition of SS in ratios of 20-40%to FR did not demonstrate any enhancement in particle,relaxed and true densities of furfural residue sludge pellets(FRSPs).However,mixing SS in ratio of 20-80%with CS resulted in improvement of corn stalk sludge pellets(CSSPs)characteristics i.e.higher density,strength and hardness.The highest strength of 7±0.22 and 13.4±0.12 MPa were found for FRSPs-20 and CSSPs-40.The highest hardness of 508±28.1 and 392±5.96 N/mm2 was found for FRSPs-20 and CSSPs-80.Pelletizing at higher temperature(e.g.200℃)improved the mechanical characteristics of FRSPs and CSSPs.Energy consumption of pellets decreased markedly with increasing sludge ratio and lowest were found at 130℃ and 200℃ for FRSPs and CSSPs.Heating values of mixed pellets were higher than sewage sludge pellets.Compression models well evaluated the compaction behavior of FR,SS,CS and their corresponding mixture with R2≥0.9.Using SS in lower proportion(e.g.20%),smell during pelletizing and even smell in pellets was tolerable.The results showed that co-pelletizing SS with FR and CS enhanced the characteristics of pellets and reduced the energy consumption.3)However pelletization enhances the quality of pellets,there are still certain problems related to biomass pellets(e.g.energy density and hydrophobicity).Torrefaction subsequent to pelletization can address these issues.Recently,torrefaction integrated with pelletization has gained increasingly interest as it enhances the characteristics of fuel pellets(e.g.hydrophobicity and energy density).Torrefaction integrated with pelletization has gained increasingly interest as it enhances the characteristics of fuel pellets(e.g.hydrophobicity and energy density).In current study,torrefaction of furfural residue pellets(FRPs)and sawdust pellets(SPs)was performed by employing tubular reactor furnace,and quality of pellets was compared.The characteristics of both types of pellets were significantly improved with increasing torrefaction temperature from 200℃ to 300℃ and residence time from 15 min to>30 min.The highest lower heating value of 23.78 MJ/kg and energy density ratio(1.27)for torrefied furfural residue pellets(TFRPs)and 26.76 MJ/kg and 1.46 for torrefied sawdust pellets(TSPs)were achieved at 300℃ and 120 min.Increasing torrefaction temperature and residence time,the volumetric energy densities of TFRPs increased from 25.69(at 200℃ and 15 min)to 27.59 kJ/m3(at 300℃ and 120 min),while those of TSPs correspondingly decreased from 20.81 to 16.69 kJ/m3.The highest true densities(i.e.2.40 and 1.85 g/cm3)and porosities(i.e.52 and 65 v%)of TFRPs and TSPs were achieved at 300℃ and 120 min,much higher than those of un-torrefied pellets.Moisture uptake of TFRPs and TSPs at 300℃were only 1.4 wt.%and 2.0-2.8 wt.%,respectively,showing strong water-resistant ability.The crystallinity of cellulose in FRPs was found higher than that of SPs,while the crystallinity of cellulose in TFRPs was found lower than that of TSPs at same process conditions.FTIR showed that O-H bond was destroyed after torrefaction for both FRP and SP.4)Torrefaction and pyrolysis of furfural residue pellets(FRPs),sewage sludge pellets(SSPs)and furfural residue sewage sludge pellets(FRSSPs)was performed by employing tubular reactor furnace.Various characteristics were studied and quality of pellets were compared and analysed under the process conditions(e.g.temperature 200-850℃ and residence time 15-45 min).Mass yield and energy yields of FRPs,SSPs and FRSSPs dropped drastically with increasing torrefaction temperature.Higher heating value(HHV)of 24.91 MJ/kg torrefied FRPs and 26.76 MJ//kg for pyrolysed FRPs,22.54 MJ/kg torrefied FRSSPs and 23.72 MJ/kg pyrolysed FRSSPs were achieved at temperature of 300℃ and 850℃ respectively,indicating that torrefaction and pyrolysis processes enhance the HHV of pellets.However,the HHV of torrefied SSPs and pyrolysed SSPs were decreased slightly with increasing temperature.Particle density and strength of all pellets decreased with increasing temperature.Pellets remained dimensionally stable after water immersion test and storage time of 2 weeks,their relaxed densities and strength remained same as of initial particle density and strength.Volumetric energy density of torrefied FRPs(29.83 kJ/m3)and pyrolysed FRPs(30.35 kJ/m3)were higher than those of torrefied SSPs,FRSSPs and pyrolysed SSPs and FRSSPs respectively.Moisture absorbing(MU)capacity by torrefied pellets was lower comparing to pyrolysed pellets in all cases,indicating the strong water-resistant ability.Methylene blue and iodine adsorption capacity of torrefied and pyrolysed pellets were higher than those of raw pellets.Heavy metals in torrefied FRPs,FRSSPs and pyrolysed FRPs,FRSSPs respectively,were found in very less quantity,indicating the no or less risk to environment.