Study of Ammonia Emissions in a Ventilated Pig Pen

Pig productions cause a wide emission of odors, such as ammonia (NH3), hydrogen sulfide (H2S), and methane (CH4). Ammonia is one of the most important emissions for evaluating the air quality either in animal buildings or atmospheric environment. In studies of ammonia emission from animal buildings reported in literature, little effort has been made to investigate the accuracy of current Henry’s law constant for modeling ammonia mass transfer process and study ammonia emissions in a full scale pig pen from fluid dynamics by CFD simulations. This will be the main objectives of this study.

The ammonia emission rate was measured in a wind tunnel under different airflow and ammonium solution temperatures. This investigation provides a general understanding for the influence of velocity, turbulence intensity and temperature on the ammonia emissions. The relationship between ammonia emissions and boundary layer thickness of velocity are shown linearly under different ammonium solution temperatures.

Using the experiment data measured in the wind tunnel including velocity, concentration and temperature profiles and emission rate, this study adopts computational fluid dynamics (CFD) to investigate the accuracy of Henry’s law constants to determine the ammonia concentration in the air through the air-liquid interface. None of the present Henry’s law constant models provide a respectable agreement between simulated and measured results. A simplified model to determine the ammonia concentration in the air through the air-liquid interface is suggested from vapor-liquid equilibrium properties of ammonia water. Furthermore, the effects of airflow and temperature on ammonia mass transfer coefficient are also analyzed under different concentration boundary conditions determined by various Henry’s law constant models and vapor-liquid equilibrium properties.

The simplified model to determine the ammonia boundary condition on the emission surface has been further used to study the ammonia emissions in a full scale pig pen under different ventilation systems and slatted floor opening ratios as well as various solution temperatures. The results show that the diffusive ceiling ventilation system can provide a relative low velocity in the pig pen and decrease ammonia emissions from the pig pen, but this ventilation system causes high ammonia concentration distribution in the animal occupied zone. Further, our study shows the effects of slatted floor opening ratios and solution temperature on ammonia emissions and analyzes the influence of those factors on the ammonia mass transfer coefficient.