| Biogas, which is produced from sludge biodegradation in wastewater treatment plants (WWTP), and landfill gas (LFG), which is generated from solid waste in landfills, are potentially important renewable fuels. Gas turbines and conventional internal combustion engines can combust LFG (or biogas) to generate electricity. Aside from their main components, such as methane and carbon dioxide, biogas and LFG may also contain undesirable contaminants. A particularly bothersome such trace constituent is a class of compounds known as siloxanes. The corrosion and damage that can be caused by these impurities may reduce the operating life of power and electricity generation equipment. In this research, the decomposition of siloxanes present in simulated renewable natural gas (RNG), which is LFG (or biogas) after its methane content has been upgraded to meet natural gas (NG) pipeline standards, is experimentally investigated in order to provide a better knowledge of their fate during RNG combustion. In the study, individual siloxanes and their mixtures in trace amounts were introduced into RNG flat flames. The counter-flow experimental technique was utilized which allows one to accurately probe and analyze the mechanisms leading to the formation of silica micro-particles resulting from the decomposition of the siloxanes.;In order to probe the nature of deposits formed on surfaces in proximity to the RNG flames, flat Ni/Cr metal strips were placed downstream of a Bunsen flame. The chemical composition, morphology, and structure of the solid particles formed were investigated by scanning electron microscopy (SEM), energy dispersive analysis by X-ray (EDAX), and atomic force microscopy (AFM). It was found that microcrystalline silica particles were generated during RNG combustion, leading to a rapid coverage of the surface of Ni/Cr strips placed in the flame environment, and forming eventually a light white layer of solid particles. The size of these particles was estimated using SEM/EDAX.;The effect of siloxane concentration on its conversion along the flame was studied via the use of the GC-MS technique for a number of different feed concentrations. Volume fractions of particles within the flame were 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 was measured experimentally to help identify the kinetics of the 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 micro-particle formation. |
