Design of a Top-Lit Up-Draft Micro-gasifier Biomass Cookstove by Thermodynamic Analysis and Fluent Modeling

Abstract

In this work the complete thermo-mechanical design of a biomass top-lit up-draft (TLUD) cookstove is presented. A design methodology which is based on mass and energy balances, geometry relations among the main dimensions of the cookstove, and fluent modeling is proposed. Three models were designed, sized, and simulated through computational fluid dynamics (CFD) conducted in ANSYS Fluent 15.0.7. These designs allowed analyzing the effect of cookstove design, primary and secondary air inlets (diameter and air supply setup) required in the gasification and combustion processes, respectively. Simulations indicated that compressed air is not a suitable way to supply the air flow for gasification and combustion stages, due to the poor velocity distribution across the grate and secondary holes. Therefore, the final stove design will operate with axial fans to favor a good mixture between biomass and the air in the gasification stage, and between producer gas and the air in the combustion zone. Operation with axial fans, in the final cookstove design, allowed obtaining a low standard deviation of air velocity through the grate holes and through secondary air ring holes (±0.13 m/s, and ±0.45 m/s, respectively), which entails a better cookstove performance. This air supply system, also presented combustion air velocities through the secondary ring holes according to the ones reported in the literature (3.02 m/s), which is important for the suitable air and producer gas mixing.