Combustão do biogás e do natural com elevadas concentrações de H2S e CO2 em caldeira de queimador poroso

Abstract

The use of biogas and natural gas (GN) with high concentrations of carbon dioxide (CO2) and hydrogen sulfide (H2S) through conventional combustion thermal systems can result in reaction instability or flame front quenching, under risk of irreversible damages to the physical structure of a piece of equipments, due to corrosive acids remaining from reaction. Furthermore, high concentrations of these contaminants favor the occurrence of high pollutant levels in the products, like carbon monoxide (CO) and unburned hydrocarbon (HC), among others. Therefore, an experimental study was performed with basis on the application of a non conventional combustion technology, Filtration Combustion, in order to deal with these low-quality fuels. The experimental apparatus employed in this research consists of a reciprocal flow porous boiler, in which its burner is completely filled by ceramic spheres of alumina (Al2O3), forming an inert porous matrix, which involves boiler’s heat exchangers. The burning process of both the fuels was investigated under extreme operation conditions, in terms of ultra-lean fuel-air mixtures. As support for interpretation of the process phenomena, a numerical simulation model was applied, which takes in account the methane oxidation mechanism in a porous medium, adapted to identify the chemical effects of a high CO2-concentration on the reaction. The influence of the main operation parameters, equivalence ratio and gas flow velocity, on combustion products and on reaction stability was studied theoretically and experimentally. The results have shown excellent boiler operation stability with ultra-low emissions of NOx and CO, less than 1 ppm for equivalence ratios inferior to 0.6, and with the H2S-burning efficiency overcoming 99%.