Master of Science (MS)
Civil and Environmental Engineering
Dynamically varying waste gas concentrations pose challenges to the operation and design of air pollution control techniques such as biofilters. Although design approaches are becoming well established for biofilters treating gases containing VOC concentrations that are constant as a function of time, many industrial processes emit gas streams contaminated with volatile organic compounds at concentrations that fluctuate with time. Application of an effective load equalization technique could eliminate some challenges associated with fluctuating pollutant concentrations. Recent research has demonstrated that granular activated carbon (GAC) can serve as a passively controlled system to provide load-equalization as a pre-treatment prior to biofiltration. Research described in this thesis was conducted to evaluate the effect of cycle length and fraction of time of contaminant loading on the degree of load equalization achieved by GAC columns subjected to intermittent pollutant loading. Columns filled with Calgon BPL 4 x 6 mesh GAC were experimentally tested with influent toluene concentrations of 250 ppmv and 1000 ppmv at cycle lengths as short as 6 hours and as long as 48 hours. The fraction of time that toluene was loaded to the columns ranged from 1/2 to 1/6 of the total cycle length. During non-loading intervals, contaminated-free air flowed through the columns at the same rate as contaminated air was supplied during loading intervals. Results revealed that passively operated GAC columns could provide effective load equalization by temporarily accumulating toluene during periods of high loading and subsequently desorb toluene during periods of no loading. Results also showed that the degree of load equalization increased as cycle length decreased, the fraction of time toluene was loaded decreased, and the influent contaminant concentration decreased. A pore and surface diffusion model (PSDM) was used to simulate the degree of load dampening achieved by GAC columns under various discontinuous loading conditions. The PSDM was able to predict the degree of load equalization achieved by each experimentally tested cyclic loading scenario within a reasonable degree of accuracy.
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Collins, Kodi L., "Pre-treatment of dynamically varying waste gas concentrations using activated carbon prior to biofiltration: effect of cycle length on degree of load equalization" (2007). LSU Master's Theses. 3242.
William M. Moe