Prediction of higher heating values of biochar from proximate and ultimate analysis

Higher heating value (HHV) is one of the most important properties for biochars as biofuel. In this manuscript, the HHV of ten different kinds of biochars were measured, and two empirical correlations based on proximate analysis and ultimate analysis were proposed for predicting HHV of biochars. The correlation was developed by stepwise multiple linear regression and multiple nonlinear regression methods. The correlation based on ultimate analysis was HHV = 32.9C + 162.7H - 16.2O - 954.4S + 1.408, and the average absolute error (AAE) and average bias error (ABE) of this correlation were 1.12% and 0.05% corresponding to the measured value of HHV, respectively. The correlation based on proximate analysis was HHV = -30.3FC(2) + 65.2Ash(2) + 55.4FC - 48.5Ash + 9.591. The correlations AAE and ABE were 2.59% and 0.08%, respectively. Both equations were validated by the reported data and the predicted HHV values were accurate in comparison with experimental values, which proved their universality in biochar HHV prediction. The aim of establishing the correlations was to accurately predict the HHV of different types of biochars by using proximate or ultimate analytical data, saving experimental costs, and providing a theoretical basis for modeling biochar combustion, pyrolysis processes and thermochemical conversion.