Effective Pretreatment of Corn Straw Biomass Using Hydrothermal Carbonization for Co-Gasification with Coal: Response Surface Methodology–Box Behnken Design

Abstract

In this study, hydrothermal carbonization was adopted as a promising approach for the improved management and better use of agro waste. The response surface methodology- Box Behnken design (RSM-BBD) approach was applied to investigate the individual and interactive effects of operating parameters (temperature, particle size and residence time) on hydrochar properties. From the results, carbon mainly retained in solid fraction, while oxygen content in hydrochar decreased from 48.83 % to 23.32 % as the temperature increased from 180°C to 240°C. In addition, O/C and H/C were also decreased from 0.8 to 0.2 and 1.8 to 1, specifying higher degree of coalification. The maximum hydrochar yield, energy yield and higher heating value of the hydrochar were 67.46 %, 77.64% and 19.71 MJ kg -1 , respectively. The response surface of process parameters and their combine effects showed that, the decline of hydrochar and energy yield was due to the increase of temperature (>200°C) and residence time. Particle size showed mild effect over the range studied. From ANOVA test, temperature was found the most significant parameter, followed by particle size and residence time, respectively. By comparing the experimental and calculated rate values, the synergy effect of co-gasification of hydrochar and coal was much more significant than that of co-pyrolysis. However, the co-gasification synergy decreased as the addition of severe HTC hydrochar in blends. The application of RSB-BBD for diagnosis of HTC parameters for hydrochar production seems to be an appropriate step for technological scalability.

Keywords: Agricultural biomass, hydrochar, optimization, co-gasification, coal