Energy & Fuels, Vol.33, No.6, 4877-4889, 2019
Effects of Char and Volatiles Extraction on the Performance of Dual Bed Pyrolysis Gasification System
The molar ratio of H-2/CO (R-HC) and high heating value (HHV) for gasification syngas are the crucial parameters for a chemical synthesis process. Except for the conventional method by changing the ratios of O-2/coal and H2O/coal, is it feasible to improve the quality of syngas by controlling the elemental components of the given coal fed into the gasifier? To investigate this hypothesis, we focused on the dual bed pyrolysis gasification (DBPG) technology and proposed the operation of char and volatiles extraction to change the elemental mass fraction fed into a gasifier. A two-step model coupling the chemical percolation devolatilization (CPD) model for pyrolysis and the Gibbs free energy minimum model for a gasifier is raised to evaluate the performance of DBPG system, and the properties of the syngas are compared with those of the one-step gasification process. The results show that under a certain strategy for oxygen and steam feeding, if 50% of char or volatiles is extracted, the HHV of gasifier syngas can be affected slightly, while the R-HC will increase by 17.13 or 9.10%, respectively. However, the unit yield of available syngas will reduce due to the extraction of char and volatiles.