Development of High Performance Filtration System Using Composite Bed Filter and Multi-element Structured Array
Type of DegreeDissertation
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A composite nonwoven (CNW) material, activated carbon fiber enhanced microfibrous entrapped sorbent (ACF-MFES) , was prepared by incorporating micro sized (100-500µm) sorbent particulates into the blended microfiber (10-20µm bicomponent polymer fiber and ACF) webs via wet-lay process. This novel fibrous sorbent media is characterized by its small particulates, high voidage and uniform structure. The manufacturing process of ACF-MFES is similar with the industrial nonwovens production and thereby it can be readily scaled up. The application of ACF-MFES nonwovens materials in the air cleaning systems can provide considerable advantages over traditional packed bed design; these advantages include higher single pass removal efficiency, lower pressure drop, higher bed utilization and lightweight. The first part of this work is the development of ACF-MFES, including the formation of recipe and process optimization. For the recipe, self-bonding bicomponent fiber, activated carbon fiber, sorbent particulates and various process additives was used. For the process optimization, each process step, including the fiber selection, wet-end chemistry, web formation technology, and web bonding technology, was optimized. In this study, for the first time, ACF was added to create a blended fiber web; it was found that only small portion of ACF effectively improved the nonwoven’s quality including the softness, strength, resilience, and the homogeneity of particle distribution. The second part is the performance test of ACF-MFES. Hexane adsorption is used to demonstrate the media’s adsorption rate and capacity; the performance is compared with traditional granular packed bed sorbent. Bench scale experiments were firstly conducted in a 2.54cm (1.0”) diameter stainless steel pipe setup, and then full scale tests were conducted in a 24x24” HVAC filter test rig. The hexane breakthrough curve showed that the ACF-MFES media has much faster adsorption kinetics compared to packed bed sorbent. This enhancement in adsorption rate is resulted from ACF-MFES media’s high contacting efficiency due to its small particulates and high surface area. The third part is the kinetics study of adsorption in ACF-MFES. Hexane adsorption onto activated carbon is a strong physisorption process, which is usually in mass transfer control rather than in intrinsic reaction control. Therefore, the kinetics study of adsorption is actually the study of mass transport between fluid and solid. The mass transfer of hexane molecule from the bulk of fluid to the specific adsorption site on the interior surface of activated carbon involves two steps: external mass transport and internal mass transport. The external mass transport mainly carried out through film diffusion, whereas the internal mass transport is more complicated because some different mechanisms are involved in this step, including molecular and Knudsen diffusion in the fluid phase, and surface diffusion in the solid phase. In this work, these four mass transfer coefficients are lumped into one overall mass transfer coefficient kG by analogy to the electrical resistance model.