CFD analysis of the downdraft gasifier using species-transport and discrete phase model

Abstract

In the present study, a 2-D axisymmetric steady-state computational fluid dynamics (CFD) model has been developed for biomass gasification in a fixed bed Imbert downdraft gasifier. A discrete phase model (DPM) based on the Euler-Lagrangian approach with species transport is applied to the gasifier having the capacity of ≈ 5 kW. The use of DPM for the particle-continuous phase interaction leads to capture more realistic gasification phenomena. The proposed model is an effort to carry forward the CFD technique by implementing an alternative chemical kinetic scheme to study the various gasification parameters. The model is validated at different values of equivalence ratios (0.19–0.33) for producer gas composition and found to be in better agreement with the experimental values reported in the literature. The standard estimated error for the present model is 6.64, 7.55, 2.92, and 5.28 % for carbon monoxide, hydrogen, methane, and carbon dioxide, respectively. Moreover, the calculated standard deviation is 0.44 only. The biomass feed and airflow rates vary from 3.43 to 5.82 kg/h and 2.41–8.02 Nm3/h, respectively. It has been found that an equivalence ratio in the range of 0.25 to 0.30 is the most appropriate condition in the present operating range of the gasifier. The proposed scheme allows accurate prediction under various operating conditions, which may enable the designer to optimise the operating conditions. The model predictions would help to design the process integration of gasification with any existing commercial energy-producing unit based on conventional fuels. Hence, it deliberates significant contribution and value addition in the current literature for the CFD modelling of biomass gasification. The present study not only helps to improve the overall performance of the gasifier but also provides the profiles of essential design variables across the length of the gasifier.