ARS | Publication request: A mass transfer model of ethanol emission from thin layers of corn silage

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: March 26, 2010
Publication Date: September 13, 2010
Citation: El-Mashad, H.M., Zhang, R., Mitloehner, F.M., Arteaga, V., Rumsey, T., Zhao, Y., Hafner, S.D., Montes, F., Rotz, C.A. 2010. A mass transfer model of ethanol emission from thin layers of corn silage. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE). Paper No. 711P0510cd.

Technical Abstract: Dairies may be important emission sources for volatile organic compounds (VOCs). Reactive organic gases (ROG) emissions from dairy farms are the second largest source responsible for ozone formation in the California’s San Joaquin Valley. Animal feed was found to be a major ROG emission source on dairies in several recent studies. Ethanol represented 70-80% of the VOC mass emitted from silages. The objective of this research was to develop and validate a mathematical model for estimating ethanol emission rates from corn silage under different temperatures and air velocities. A first-order boundary layer mass transfer model was developed. The developed model was validated using data collected from experiments conducted in a controlled environment chamber (10.5 m×4.4 m×2.8 m). A 100 kg mass of corn silage was kept inside the environmental chamber that was ventilated at an air flow rate of 2100 cubic meters per hour. Ethanol emissions were measured every minute, over one day, using a photoacoustic gas analyzer. Ethanol concentration in the silage was monitored over the experimental time using a gas chromatograph. Experiments were also conducted to calculate the effective mass transfer coefficient of ethanol under different temperatures and air velocities using a wind tunnel. A multiple regression equation was derived that correlated the effective mass transfer coefficient with temperature and air velocity. Predicted ethanol emission rates were well correlated with measured values. A high correlation was also found between predicted and measured ethanol concentrations in the silage. The model was further applied to determine ethanol emission rates from thin layers of loose silage under selected weather conditions of a dairy farm in California. The model results showed that over 95% of the ethanol present in silage could be emitted in the first 8 hours after exposing the silage to ambient air with temperature ranging from 18 to 35 C and velocity ranging from 0.1 to 2 meters per second.