Prediction and Validation of Performance of an Entrained Flow Gasifier Model

Computational fluid dynamics (CFD) simulation of a single stage, dry-feed entrained flow gasifier is carried out to predict several physical and chemical processes within the gasifier. The model is developed using a commercial software package FLUENT. The CFD model is based on an Eulerian-Lagrangian framework, where the continuous fluid phase is modeled in Eulerian approach and the particle flow trajectory is simulated in Lagrangian frame. The two phases are coupled by appropriate source terms in the conservation equations. The gasification process can be divided into the following sub-processes, which are inert heating, moisture release, coal devolatilization, char gasification and gas phase reactions. Discrete Phase Model (DPM) is used to model the coal particles and coupled with heterogeneous particle surface reactions in Species Transport module. The interaction between reaction chemistry and turbulence is described by Finite-rate/Eddy dissipation model. The simulation provides detailed information of temperature field and species concentration profile inside the gasifier. The temperature distribution clearly indicates the three different reaction zones for devolatilization, gasification and reduction. Steady state model predictions are compared with benchmark experimental data from literature. The trend of the predicted species mole fraction distribution is in good agreement within error bound of the experiment. The model thus provides a validated set of model parameters along with an insight to the underlying flow physics and chemical reactions of gasification process that can be employed to improve design of experiments. This study also develops the basis to achieve further accuracy incorporating complex effects such as detailed reaction kinetic mechanisms, proper devolatilization models, effect of ash-slag transition and particle deposition.