CH4-CO2 Fuel Mixture Combustion and Emission Characteristics in a Combi Boiler Combustor

Biogas can be obtained from agricultural, animal, and waste, replacing natural gas in heating systems. Because of that, studying its combustion characteristics will be valuable. This study investigates biogas combustion characteristics in a natural gas-powered heating system. Various CH4-CO2 biogas fuel mixtures were analyzed experimentally and numerically for a thermal power of 13 and 31 kW. In the experimental part of the study, the fuel mixtures were burned, and the temperature and the NOX were measured. The standard k-ε turbulence model and Eddy Dissipation Concept were used in the present study's numerical part. The model was validated with the measured data. The modeling results are in agreement with the measurements. Various fuel mixtures were then modeled to seek varying inlet temperature and O2 concentration effects on the combustion characteristics of the biogas fuel mixtures studied. It was concluded that as the amount of CO2 in the fuel mixture was increased the flame temperature decreased linearly from about 1900 K to 1775 K. NOx concentrations in the combustion product decreased from about 10 ppm to below 2 ppm. It was also concluded that air preheating and change in O2 concentration in the oxidizer affected the flame temperatures and NOx considerably.