Filtration is the technology most commonly used to remove particles from gas streams. Particles can be effectively removed by filtration mechanisms, such as diffusion, inertial impaction, interception, gravitational settling and electrostatic deposition. However, some concerns have been expressed that filtration efficiency of particles can be significantly reduced when particles approach nanometer size diameters. The purpose of this research was to assess the effect of inlet particle number concentration, superficial gas velocity, filtration time, and nanomaterial size on the filtration efficiency of a granular activated carbon (GAC) column to filter aerosols containing carbon and silica based engineered nanomaterials. A bench scale experimental system was designed and set up to quantify the granular filtration of silica nanoparticles (SNPs) and super activated carbon nanoparticles (SACNPs) using GAC. The experimental apparatus consisted of a compressed air supply system, an aerosol generation system, water-based condensation particle counter to measure number concentration of particles upstream and downstream of the filtration column, a scanning mobility particle sizer to obtain the particle size distribution, granular filtration system and a data acquisition system. A Magnehelic® differential pressure gauge was used to measure the pressure drop across the granular filter during the filtration tests. A granular filtration model was also developed to predict the filtration efficiency for individual particle sizes. The filtration model was based on mechanical collection mechanisms, such as diffusion, inertial impaction, interception and gravitational settling. Overall, the filtration efficiency of SNPs and SACNPs decreased about 1% to 20% as the superficial gas velocity increased by 6 cm/s. For SNPs, the filtration efficiency (99.7%) was the highest for the inlet particle number concentration of 120,000 #/cm3. For SACNPs, the filtration efficiency was the highest (99.2%) when the inlet particle number concentration was the highest at 300,000 #/cm3. In general, filtration efficiency gradually decreased from 2% to 47% within eight hours of filtration time. Experimental results were in best agreement with granular filtration model when the superficial gas velocity was 2.2 cm/s during the first four hours of filtration time. These results are encouraging to advance current filtration technologies and, thus, improve human health and the environment.
January 17, 2017
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