Comprehensive Investigation into the Exergy Values of Six Rice Husks

Exergy is a measurement of how far a certain system or material deviates from a state of equilibrium with the environment and it is a useful tool for improving the efficiency of energy-resource use. Based on the previous work, the exergy values of six rice husks were investigated in this study. The effects of physical and chemical properties were also detailed. These included moisture content, ash content, S, C, O, H and N contents. The moisture related exergy of the six rice husks ranged in 241.432-290.304 kJ per kg rice husk, accounting for 1.563-1.758% of the exergy of rice husks. An exponential relationship between exergy value and moisture content was observed. The exergy of ash varied between 37.419 kJ per kg rice husk and 61.217 kJ per kg rice husk, making up 0.233-0.401% of the exergy of rice husks. An exponential linear relationship between exergy value and ash content was observed. The S related exergy ranged from 1.217 kJ per kg rice husk to 2.993 kJ per kg rice husk, accounting for 0.007-0.018% of the exergy of rice husks. The O/C, H/C and N/C atomic ratios varied in ranges of 0.592-0.662, 1.404-1.730 and 0.008-0.011, respectively, whereas the correlation factors varied slightly in the range of 1.118-1.127. The exergy values of the six rice husks ranged in 15.053-18.407 MJ/kg. They were mainly determined by the correlation factors and the LHVs. A positive linear relationship between exergy value and LHV was observed.