10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Ultrafine Particle Emissions from the Combustion of Natural Gas, Biogas, and Biomethane
Jian Xue, Yin Li, Joshua Peppers, Peter Green, Thomas Young, MICHAEL KLEEMAN, University of California, Davis
Abstract Number: 1037 Working Group: Combustion
Abstract Biogas and biomethane (=upgraded biogas) are major renewable fuels in the evolving energy economy. Biogas and biomethane burn cleanly but they do produce ultrafine particles (UFPs) which have greater toxicity than fine particles. The factors that control UFP emissions rates from biogas/biomethane combustion should be understood before these fuels are widely adopted.
Here we measure UFPs emissions from the combustion of biomethane and/or biogas produced from five different representative sources: two food waste digesters, two dairy waste digesters, and one landfill. Combustion exhaust for each of these biomethane/biogas sources is measured from representative sectors including electricity generation, motor vehicles, water heaters, and cooking stoves. Results show that basecase emissions of UFPs are a strong function of the sulfur content in the fuel. Sulfur content greater than 2 ppm caused a strong increase in UFP emissions. Increasing dilution during source tests caused UFPs emitted from water heaters and cooking stoves to evaporate, suggesting that these particles are semi-volatile. This may reflect the lack of ammonia in the dilution air used during the tests leading to the semi-volatile behavior of the UFPs composed mostly of sulfuric acid. UFPs from electricity generation and motor vehicles were non-volatile possibly because these particles were exposed to sufficient ammonia to produce ammonium sulfate. Photochemical aging of biomethane combustion exhaust in a representative urban “surrogate” atmosphere did not significantly alter secondary UFP formation compared to natural gas tests.
The results of the current study highlight the importance of fuel sulfur content and ammonia concentration in the background air as controlling variables for the UFP emissions rate from the combustion of natural gas, biogas, and biomethane. Future biomethane production facilities should ensure that fuel sulfur content remains below 2 ppm so that widespread adoption of biogas/biomethane does not significantly increase ambient concentrations of UFPs relative to natural gas combustion.