Entrained flow gasification: Experiments and mathematical modelling based on RANS

Entrained flow gasification of biomass has become one of the promising technologies for the production of fuels and chemicals in a closed carbon cycle economy. Due to the complexity of the conversion of low-rank fuels to high-quality synthesis gas and due to the lack of experimental data inside entrained flow gasifiers, there is still a need for a better understanding of the physical and thermo-chemical processes during entrained flow-gasification. In order to close this gap, the bioliq process has been constructed at Karlsruhe Institute of Technology (KIT). In parallel, the research network Helmholtz Virtual Institute for Gasification Technology (HVIGasTech) has been established. Its primary focus is the development of a numerical model for the description of the entrained flow gasification of biomass at both atmospheric-pressure and high-pressure conditions.
This paper focuses on the recent experimental and numerical results of four campaigns carried out at the atmospheric research entrained flow gasifier REGA. The two first campaigns (REGA-glycol-T1, REGA-glycol-T2) used ethylene glycol as model fuel; the two others (REGA-slurry1-T2, REGA-slurry2-T2) applied model slurries (90 % ethylene glycol + 10 % wood-char and 70 % ethylene glycol + 30 % wood-char). ... mehrIn each of these campaigns, radial profiles of gas phase composition ($\text{CH}_4$, $\text{CO}$, $\text{CO}_\text{2}$, $\text{H}_2$) and gas phase temperature were measured at burner distances of 300 mm and 680 mm. The experimental data sets have been used for the validation of the RANS based numerical model. The model assumes a steady state and includes turbulence-chemistry interaction described by the Eddy Dissipation Concept (EDC) in combination with one of two global reaction mechanisms for the entrained flow gasification of ethylene glycol: the HVI1 mechanism and the extended Jones-Lindstedt mechanism. Reaction rates for the devolatilisation and the heterogeneous reactions of wood-char with $\text{CO}_\text{2}$ and $\text{H}_\text{2}\text{O}$ are derived from measurements.
The numerical results concerning the entrained flow gasification of ethylene glycol show that both global mechanisms predict the gas phase compositions well and overpredict the gas phase temperatures slightly. The model based on the HVI1 mechanism has advantages in the near-burner region and in computing time. The numerical results for the entrained flow gasification of slurry deviate from the experimental results concerning the gas phase composition. Experimental results suggest a higher carbon conversion of wood-char than predicted. Sensitivity studies also emphasize that higher reaction rates concerning the heterogeneous reactions are required for the numerical model. In addition to that, numerical errors in balance of elements are a significant source of error. Therefore, further research has already been initiated to reinvestigate and to improve both the numerical accuracy and the heterogeneous kinetics.