(496c) A Study of Trace Ammonia Impurities in Renewable Natural Gas and Their Impact on Its Potential Utilization

Renewable natural gas (RNG), produced from biogas upgrading, is an important alternative to fossil fuels for power generation. Unfortunately, RNG contains several trace contaminants. One such contaminant is NH₃, of particular concern for RNG produced from farming operations. The presence of NH₃ in RNG can have serious consequences. These can range from damage to the NG infrastructure, to corrosion of analytical and end-user equipment and added pollutant formation during combustion. We have previously reported in the area of pollutant emissions, where we tested several common end-user equipment. They were all operated with NG injected with NH₃ concentrations ranging from 0 to 500 ppm_v. Emissions studied included unburned hydrocarbons (UHC), CO, and NO_X, the latter being of particular concern. The presence of NH₃ resulted in increased NO_X emissions for all equipment.

In this talk our focus is on NH₃-induced corrosion in materials relevant to the NG infrastructure with the goal to identify various (bulk and surface) species potentially forming, their rates of formation, and their dependence on the operating conditions. The tested materials included components made of steel and brass, and a variety of polymer gaskets. They were exposed to both dry and humidified NH₃/NG mixtures with 0-500 ppm_v of NH₃ for periods, under each concentration, ranging from 400-1200 hours. NH₃-induced changes in the materials were identified via direct weight change measurements and optical observations, SEM-EDS, ICP-OES and microhardness testing. For the metal components, corrosion phenomena were observed, particularly for the higher NH₃ concentrations under humidified conditions. We also report here the impacts of NH₃ on Gas Chromatographs used for customer billing. NH₃ has a detrimental impact on the instrument the severity depending on exposure length. The results of the study are concerning, indicating the need for thorough purification of the RNG prior to its potential injection into the NG network.