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Influences of Physical and Thermochemical Properties on the Exergy of Cereal Straws

Ghaly AE, Yaning Zhang, Bingxi Li

Exergy is a measurement of how far a material deviates from a state of equilibrium with the environment. The exergy values of the barley, oat, rye and wheat straws were determined and the influences of LHV, moisture content, ash content, S, C, O, H and N on the exergy of cereal straws were evaluated. The moisture content of the four cereal straws varied from 10% (oat straw) to 17% (rye straw). The moisture related exergy value of the four cereal straws varied from 283.954 kJ/kg (oat straw) to 479.747 kJ/kg (rye straw), accounting for 1.376-2.275% of the total exergy of cereal straws. A positive linear relationship between the exergy value and moisture content of cereal straws was observed. The ash content of the four straws varied from 1.635% (rye straw) to 4.554% (oat straw). The ash related exergy value varied from 25.912 kJ/kg (rye straw) to 111.061 kJ/kg (oat straw), accounting for 0.123-0.538% of the total exergy of cereal straws. A negative linear relationship between the exergy value and ash content of cereal straws was observed. The S content of the four straws varied from 0.058% (rye straw) to 0.144% (oat straw). The S related exergy value varied from 5.626 kJ/kg (rye straw) to 13.944 kJ/kg (oat straw), accounting for 0.027-0.068% of the total exergy of cereal straws. A negative linear relationship between the exergy value and S content of cereal straws was observed. The results showed that the combined contribution of the exergy values of moisture, ash and S contents to the total exergy of cereal straws (1.982-2.424%) is very small and can be neglected. The O/C, H/C and N/C atomic ratios varied from 0.7184 to 0.7780 (8.30%), from 1.4214 to 1.5457 (8.74%) and from 0.0026 to 0.0254 (876.92%), respectively. The correlation factors varied from 1.133 to 1.142 (0.8%). The exergy values of the four cereal straws varied from 20.631 MJ/kg (oat straw) to 21.156 MJ/kg (wheat straw). They were mainly determined by the correlation factors and the LHVs. A positive linear relationship between the exergy value and LHV of cereal straws was observed.