Analysis of biogas content influence on the flame properties

Abstract

The paper has examined the combustion of gas with variable methane content where it was supplied separately from the air. The analytical one-dimensional model of the diffusion straight-flow flame in the unrestricted and restricted space and a numerical three-dimensional model of the turbulent flame in a swirled airflow were used in this research. It has been established that in furnaces (in a restricted space) the maximum flame temperature depends only on the methane content in fuel and in average lower than the temperature of clean methane combustion by 20-70°C for conventional biogas and by 100-200°C for biogas with low methane content. The methane content decrease in gas leads to the diffusion flame length decrease in comparison with clean methane combustion by approximately two-fold for conventional biogas and fourfold for combustion of biogas with low methane content. For the turbulent flame in a swirled air flow, the flame length decrease is insignificant and is around 10% for conventional biogas and around 40% for biogas with low methane content. It can be concluded that by changing the methane content in biogas the heating plant operating mode can be stable on the condition that the biogas flow rate is controlled to ensure constant heat production during its combustion and turbulent flame with a swirled airflow. Combustion, in this case, can be done using the same burner.