Study on gasification mechanism of biomass waste in supercritical water based on product distribution

Supercritical water gasification technology is widely applied to convert organic waste into valuable substances as a clean and efficient method. Biomass gasification in SCW is a complex process and complicated chemical reactions like decomposition and poly-condensation take place, thus, reaction mechanism of real biomass needs to be further investigated. In this paper, experimental study on cornstalk gasification in SCW was conducted at the temperature of 500–800 °C, reaction time of 1–15min and feedstock concentration of 1–9%. The effects of various operating parameters on evolution of gas, liquid and solid products were conducted. It was discovered that pore structure and carbon microspheres appeared successively on the surface of solid residue. Mechanism study showed that the biomass was first depolymerized into monomer and its derivatives, then cracked and poly-condensed into a nuclear to generate carbon microspheres as its concentration reached the critical concentration. As the reaction proceeds, reduction reaction, coke combustion and secondary reaction occurred, thus carbon microspheres decreased. The results indicated that higher reaction temperature, longer reaction time and lower feed concentration were conducive to improving reaction performance of biomass. Finally, it was discovered that carbon gasification efficiency reached 99% at the temperature of 700 °C, reaction time of 15 min and biomass concentration of 3%.