Determination of the Exergy of Four Wheat Straws

Exergy is a measurement of how far a certain materi al deviates from a state of equilibrium with the environment. It is a useful tool for improving the efficiency of energy-resource use. The exergy value s of four wheat straws (Absolvant, Max, Monopol and Vuka) were determined in this study. The effects of physical and chemical properties (moisture content, ash content, LHV and S, C, O, H and N contents) were evaluated. The moisture related exergy varied from 281.834 kJ kg -1 (Monopol) to 366.766 kJ kg -1 (Absolvant), accounting for 1.311-1.734% of the tot al exergy of wheat straws. A negative linear relationship between the exergy value and moisture content was observed. The ash related exergy varied from 53.468 kJ kg -1 (Absolvant) to 117.675 kJ kg -1 (Vuka), accounting for 0.253-0.556% of the total e xergy of wheat straws. A negative linear relationship bet ween the exergy value and ash content was observed. The S related exergy ranged from 6.817 kJ kg -1 (Max) to 11.077 kJ kg -1 (Vuka), accounting for 0.032-0.052% of the total exergy of wheat straws. A positive linear relationship between the exergy value and S conten t was observed. The O/C, H/C and N/C atomic ratios and the correlation factors varied in ranges of 0.7133-0.7537, 1.3475-1.5457, 0.0063-0.0225 and 1.133-1.138, respectively. The exergy values of the fo ur wheat straws were between 21.156 MJ kg -1 (Absolvant) and 21.503 MJ kg -1 (Monopol). They were mainly determined by the correlation factors and the LHVs. A positive linear relationship between the exergy value and LHV was observed. The combined contribution of ash, moisture and S related exergy to the total exe rgy was very small (1.694-2.212%) and can be neglected.