Computational Fluid Dynamics Simulation and Validation of H2S Removal from Fan-Ventilated Confined-Space Manure Storages

Abstract

Confined-space manure storage entry is a major safety concern in the agricultural industry. An oxygen-deficient atmosphere as well as toxic and/or explosive gases (i.e., NH3, H2S, CH4, and CO2) often results from fermentation of the stored manure and accumulation in confined areas. These gases may create very hazardous conditions for farm workers who may need to enter these confined-space manure storages to work or perform maintenance. 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 storages. The overall goal of this research was to develop and validate computational fluid dynamics (CFD) modeling protocols to simulate H2S removal from fan-ventilated confined-space manure storages. The CFD model was used to identify the time taken to reach the OSHA permissible exposure limit of H2S (Tpel). This article presents the CFD model simulations of evacuating H2S during forced ventilation for the best ventilation strategies identified in previous research for a typical rectangular on-farm manure tank with three cover types (i.e., solid, fully slotted, and partially slotted) and the validation of the CFD modeling protocols based on comparisons between simulated and measured H2S evacuation times. Simulated and measured evacuation times within the confined-space manure storages evaluated agreed within 10% at all measuring locations except those immediately adjacent to the ventilation fan jet for all three cover types for both high (5 AC min-1) and low (3 AC min-1) air exchange (AC) rates. Corresponding evacuation times agreed within 15% for all cover types and air exchange rates in the high-velocity gradient region of the ventilation fan jet.