Ultimate analysis and heating value prediction of straw by near infrared spectroscopy.

Ultimate analysis and heating value determination are two of the most important routine analyses for exploiting agricultural wastes for energy conversion. The use of near infrared spectroscopy (NIRS) was investigated as an alternative method to predict the carbon, hydrogen, and nitrogen content and the heating value of straw. A total of 222 straw samples, collected from 24 provinces of China, were used for NIRS calibration and validation in this study. The R(v)(2) and standard error of predictions in independent validation were, respectively, 0.97 and 0.37% for C, 0.77 and 0.17% for H, 0.87 and 0.10% for N and 0.96 and 181 J/g for heating value. A multiple linear regression (MLR) model was also built to predict the heating value from the contents of C, H and N. The MLR equation gave good prediction (standard error of prediction=224 J/g) when evaluated using the same validation set as the NIRS. Therefore, rapid analysis of straw can be achieved through the constructed equations, saving analytical time and cost.