Investigation on indgenous biomass feedstock upgradation as solid fuel/

Abstract

Biomass, a lignocellulosic material, has a potential to act as an alternative solid fuel in the energy generation processes and offers a viable solution for energy shortfall in developing countries as it is cheap source and easily available. However, some of the raw biomass inherent properties, such as high moisture content, slagging nature, low mass and energy densities which hinder its commercial utilization. Among various proposed pretreatment solutions, demineralization and torrefaction are promising pretreatment processes for converting raw biomass into an efficient and suitable solid fuel. In demineralization process, minerals causing slagging are leached out of biomass using different acid solutions and torrefaction, also known as slow pyrolysis, is defined as the thermolysis of agricultural residue in the temperature range of 200-300 °C while maintaining an inert environment to improve its higher heating value (HHV) and hydrophobic nature. Different leaching agents, including HCl and H2SO4, were used for the demineralization of the biomass with varying residence time. After the acid treatment, HHV of the agricultural residue increases and ash content decreases. The specimen leached with 5 wt. % H2SO4 solution with 120 min residence time showed 7.10% improvement in HHV and its ash content was decreased by 34.20% when compared to raw biomass. The demineralized samples were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). A slight change in the peak intensities of O-H, C-H, C=O and C=C stretching vibrations was noted through FTIR. The increased surface erosion and fuzziness through SEM confirms that few particles were leached away by the acid solutions. The shifting of shoulders in the thermal degradation (DTG) curve towards high temperature indicated that the treated specimen are showing more resistance towards their thermal degradation. Torrefaction was performed to assess the improvement in the elemental composition, hydrophobic behavior and HHV of the biomass. The carbon content of thermolyzed biomass was raised to 48.46% from 32.45%. The hydrogen and oxygen contents showed a decline thus improving the hydrophobic behavior as higher oxygen content increases the moisture adsorption capability of the biomass and reduces its shelf life. The water uptake of torrefied samples decreased 92% from 307% due to which the ignition temperature of the treated samples reduces and stability and durability increases. The calorific value of the treated samples was also increased to 4913 cal.g-1 compared to raw biomass having HHV 3939 cal.g-1. The torrefied samples were also characterized by SEM and FTIR to observe the physio-chemical changes and surface morphology and their thermal degradation was also studied. The results confirmed that the most affected fraction of the lignocellulosic material is hemicellulose. Torrefaction of the acid treated samples was also studied to evaluate the fuel properties of the specimen. For assessment of compositional changes, X-ray Fluorescence (XRF), ultimate and proximate analysis were performed. The XRF analysis confirms the removal of alkali and alkaline earth metals (AAEM) thus reducing the slagging nature of treated samples. The pretreatment processes upgrade the carbon content from 32.45% to 43.10%, hence also improved the HHV from 3939 cal.g-1 to 4356 cal.g-1. The reduction in the oxygen and hydrogen content is observed from 45.92% to 36.08% and 5.44% to 4.30%, respectively which improves the hydrophobic behavior as water uptake of the treated samples reduces by 55%.