A mixed computational and experimental approach to improved biogas burner flame port design

Anaerobic digestion is a well-known and potentially beneficial process for rural communities in emerging markets, providing the opportunity to generate usable gaseous fuel from waste resources. With recent developments in low-cost digestion technology, communities across the world are gaining affordable access to the benefits of anaerobic digestion derived biogas. For example, biogas provides a more efficient and cleaner burning alternative to biomass (wood, charcoal, dung), effectively reducing harmful emissions and fuel consumption. This study sought to develop and test a design approach for optimizing flame port geometry for household biogas-fired burners. The approach consists of a multi-component simulation that incorporates three-dimensional CAD designs with simulated chemical kinetics and computational fluid dynamics. The simulated flame port designs included an array of circular and rectangular geometries using a widely available biogas burner. The three highest performing designs identified were manufactured and tested experimentally to validate model outputs and to compare against a baseline port geometry. In the experiment, each of the three designs suggested improved thermal efficiency relative to the baseline. A configuration of four millimeter circular ports resulted in a 7.17% improvement, raising an average thermal efficiency of 53.0% to 56.8%. The results indicated that hydraulic diameter, velocity and mixture density are relevant factors in port geometry design to improve the thermal efficiency of a biogas burner. Conversely, the emissions predictions made by the model were found to be unreliable and incongruent with laboratory experiments.