Thermoelectric power generation from Biogas+H2 flames: Influence of Flame-Wall Interaction

In this paper, the viability of using laminar premixed Biogas + H2 flames in conjugation with a Thermoelectric generator (TEG) for direct heat-to-electricity conversion was evaluated in a side-wall configuration. The influence of different fuel blends and flame work conditions in TEG power and efficiency are discussed. Methane and two Biogas (BG) blends without and with added H2 were considered in the study. It has been found that power and efficiency optimization are closely related with the heat transfer from flame and burnt gases to the TEG. The interaction process of the flame with the wall was therefore studied in detail from the perspective of the side-wall quenching (SWQ). For this purpose, gases velocity field, flame quenching distance dq and heat release rate (HRR) were analyzed via Particle Image Velocimetry (PIV) and the chemiluminescence of excited OH* and CH* radicals. Even in small amounts (up to 20% in volumetric ratio), we found that H2 addition to BG improved both TEG operation (with power yield increasing by 10%) and flame stabilization (quenching distance reduced by 18%, to levels typical of methane flames). The impact of H2 was more significant for the lower BG grades (higher CO2 content). Flame quenching was governed by heat losses and it was found that HRR (derived from OH* chemiluminescence) is strongly correlated with dq. The results obtained revealed that convection contributes in the same order of magnitude as conduction for heat transfer in the quenching region.