Computational fluid dynamics modeling of ventilation of confined-space manure storage facilities: applications.

Fatalities associated with entry into on-farm confined-space manure storage tanks occur each year The fatalities are due to asphyxiation or poisoning by exposure to high concentrations of hydrogen sulfide, methane, and carbon dioxide. Forced ventilation has been shown to be an effective way to reduce concentrations of these noxious gases to levels that are safe for human entry into these storage tanks. Hydrogen sulfide (H2S) was used as an indicator gas to investigate the effectiveness of forced ventilation strategies for eliminating the toxic and oxygen-deficient atmospheres in confined-space manure tanks. Validated computational fluid dynamics (CFD) modeling protocols were used to simulate H2S evacuation from fan-ventilated manure tanks. The simulation studies were conducted for rectangular and circular manure tanks, and the effects of pollutant source, inter-contamination (process by which a portion of exhausted contaminant gas enters a ventilated confined airspace through the fresh air intake), storage size (i.e., length, diameter), and air exchange rate on H2S removalfrom fan-ventilated manure tanks were investigated. For the same air exchange rate, as the size (i.e., length, diameter) of the tank increased, the rate of evacuation of the H2S from the confined space decreased. For rectangular and circular manure tanks, the higher the air exchange rate, the higher the rate of evacuation of the H2S from the confined space. For the rectangular tank geometries and ventilation system layouts simulated, evacuation times decreased exponentially with air exchange rate. Evacuation times for the circular tanks simulated decreased linearly with air exchange rate.