Gas turbines and other conventional internal combustion engines can combust landfill gas (LFG), which is an important renewable energy source, to generate electricity. However, the corrosion and damage that can be caused by its impurities may reduce the operating life of these combustion engines when operating on LFG. One class of major impurities present in LFG is Siloxanes. In our research, the decomposition of Hexamethyldisiloxane (also referred to as L2) present in LFG is experimentally investigated in order to provide a better knowledge of the way it is degraded during the combustion of LFG. Several experimental techniques were utilized in order to study premixed flat flames, and to gain a better understanding about the durability of L2 in the flame environment and the kinetics of its decomposition. In our experiments, we have utilized the counterflow technique, which allows one to accurately probe and analyze the mechanisms leading to the formation of silica microparticles resulting from the decomposition of L2. We also applied laser extinction techniques for the in situ monitoring of particle formation, as well as GC-MS techniques for measuring the kinetics of siloxane decomposition.
It was found that microcrystalline silica particles were generated during LFG combustion, leading to a rapid coverage of the surface of Ni/Cr sheets placed in the flame environment, and forming a light white layer of solid particles, whose surface was analyzed by atomic force microscopy (AFM). The size of these particles was then estimated using SEM/EDAX. The effect of L2 concentration on its conversion along the flame was found for a number of different feed concentrations. Volume fractions of particles within the flame were also measured via the laser extinction method indicating a linear relationship between the concentration in the fuel and the corresponding volume of particles in the flue-gas. The temperature profile has been measured experimentally in order to identify the kinetics of burning of the siloxane compounds. This fundamental insight is important in terms of being able to accurately determine the maximum allowable siloxane content for biogas that is safe to use without leading to deposits and microparticle formation.