Biogas combustion on reciprocal flow porous burner with energy extraction

Abstract

This research has the purpose of demonstrating the effectiveness of "Filtration Combustion" (CF) to deal with fuels of low heat content, like biogas. CF is a non-conventional technology capable of producing ultra-low emissions of carbon monoxide (CO), unburned hydrocarbons (HC) and nitrogen oxides (NOx). A reciprocal flow porous burner was experimentally utilized, constituted of ceramic spheres (alumina) that fill the combustion chamber, where heat exchangers are inserted at the porous matrix ends. The burner is equipped with a reciprocating system that provides a periodical alternation of the gas flow direction, allowing operating with several fuels and providing a stable combustion process with temperature distribution on trapezoidal profile, with temperature peaks between 1300 and 1600 K. The focus of this analysis is the fuel-air mixture flammability limit as function of CO2 concentration and equivalence ratio, taking the technical methane as the reference gas. The results have pointed out significant benefits of the reversal on the combustion process, allowing operation in a wide equivalence ratio range (0.10<Φ<1) and achieving energy extraction efficiencies above 90%, with ultra-low CO and NOx emissions (below 1 ppm). However, when the burner operates on only flow direction, it is possible to realize a drastic reduction of the flammability limit, as the CO2 content in the biogas composition is increased.