Preliminary investigation to characterize deposits forming during combustion of biogas from anaerobic digesters and landfills

The objectives of this study were to compare composition and morphological characteristics of the deposits forming in engines operated with biogas from anaerobic digesters and from landfills. Engine deposit samples were collected from biogas to energy facilities in Florida, USA. The deposit samples were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Similarities and differences between the deposit samples collected from the engines operated with biogas from anaerobic digesters and biogas from landfills were analyzed in terms of chemical composition and morphology. The sample obtained from the anaerobic digester gas did not contain potassium while calcium and zinc were present at a higher ratio. Relatively high levels of carbon were present in the crystalline deposits forming during the combustion of biogas. C:O:Si ratios were about 5:7:1 in the deposits obtained from the engines operated with biogas from the anaerobic digesters and 2:3.5:1 in the deposits from the engines operated with landfill gas. In general, the silicon content from deposits found in facilities utilizing biogas from anaerobic digesters was lower than those operated with landfills gas. The difference was made up with higher phosphorus, sulfur and calcium content in the deposits from the engines operated with digester gas.