|Rotz, Clarence - Al|
Submitted to: Transactions of the ASABE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2010
Publication Date: 12/1/2010
Citation: El-Mashad, H.M., Zhang, R., Rumsey, T., Hafner, S.D., Montes, F., Rotz, C.A., Arteaga, V., Zhao, Y., Mitloehner, F.M. 2010. A mass transfer model of ethanol emission from thin layers of corn silage. Transactions of the ASABE. 53(6):1903-1909. Interpretive Summary: Volatile organic compounds are an important component in the production of ground level ozone, a pollutant that causes respiratory problems. Ozone is produced when these volatile organics and nitrogen oxides react in the atmosphere on clear summer days creating smog. Some volatile organic compounds are emitted from fermented animal feeds with ethanol being a major compound emitted. The San Joaquin Valley in California is an area with a high concentration of dairy farms, and previous estimates indicate that these dairies are a major contributor of the volatile organic compounds found in the atmosphere in the valley. Little quantitative information exists though for accurately estimating feed emissions. A method was developed to predict the emission of ethanol from corn silage, an important feed source on dairy farms. Based on wind tunnel measurements, a relationship was developed that relates ethanol emission rates to air speed and ambient temperature. This relationship was then found to adequately predict ethanol emissions measured from silage in a large environmentally controlled chamber. Predictions obtained indicate that ethanol emission rates are high immediately after silage is exposed to air and then rapidly decline. Over 95% of the ethanol present in silage can be emitted in the first 8 hours after exposure to moving air. Further development of this model will provide a tool for estimating the emissions of volatile organic compounds from farms and evaluating the potential reductions obtained through mitigation practices.
Technical Abstract: A mass transfer model of ethanol emission from thin layers of corn silage was developed and validated. The model was developed based on data from wind tunnel experiments conducted at different temperatures and air velocities. Multiple regression analysis was used to derive an equation that related the effective mass transfer coefficient to temperature and air velocity. Evaluation of the model was done using data collected from experiments conducted in a controlled environmental chamber. Ethanol emission was determined by measuring ethanol concentration in the environmental chamber exhaust over a 24 hour period using a photoacoustic gas analyzer. Silage ethanol concentration was also monitored throughout the duration of each experiment. Predicted ethanol emission rates were strongly correlated (R2 = 0.94) with measured values in the environmental chamber. A high correlation (R2 = 0.96) was also found between predicted and measured ethanol concentrations in the silage. The model was used to estimate ethanol emission rates from thin layers of loose silage under typical weather conditions for a California dairy farm. Model predictions indicate that over 95% of the ethanol present in silage could be emitted in the first 8 hours after exposing the silage to ambient air temperature (18 to 35 deg C) and air velocity (0.1 to 2.0 m s-1)