Development of kinetic model for supercritical water gasification and dynamic characteristics investigation on tubular reactor

Abstract

Supercritical water gasification (SCWG) technology is considered as a potential technology to realize resource utilization of biomass waste. Both experimental and modeling researches are performed to guide the development and scale-up of this technology. Among these researches, dynamic study of the reactor is an important aspect. However, related published literature is relatively limited. In this study, a one-dimensional dynamic model was developed, and a kinetic model of soybean stem containing detailed reaction pathway of biomass was established based on the lumped parameter method. It was calculated through fitting experiment data (obtained at 600, 650, and 700℃ three temperatures and pressure of around 25 MPa), after which it was applied to the tubular reactor for further analysis. Sensitivity analysis of the reactor displayed that H2 mole fraction was most sensitive to the inlet temperature, which increased or decreased by around 10 % when the temperature had a ± 5 % fluctuation. Dynamic simulation results showed that the gasifier responds quickly under a transient change of concentration. Gasification efficiency decreased from 83.8 % to 41.9 % at 500 s, kept constant for 240 s, and then increased to 83.4 % and stabilized at this value. Total response time was 900 s. Molar fraction of CO, CO2 and CH4 increased by 0.8 %, 0.66 %, 3.08 % respectively. While that of H2 decreased by 4.54 % within 660 s. As for fluctuation of flowrate, gasification efficiency increased by 3.4 % when residence time increased from 527 s to 584 s. Mole fraction of H2 and CO2 increased with time, while that of CH4 and CO decreased, and response time was 900 s.