Monitoring and control of electrothermal swing adsorption based on electrical properties of the adsorbent
Organic vapors and gases (e.g., toluene and isobutane, respectively) are used in industry to produce a variety of products (e.g., coatings and packaging materials). During production and use of these products, these vapors/gases are often emitted in dilute concentrations, causing adverse health effects and photochemical reactions that increase ground-level ozone concentration. Thermal oxidization is often used for vapor/gas disposal (ideal conversion to H2O and CO2). Capturing and recovering vapors/gases can reduce cost by providing feedstock for production and eliminate emissions from thermal oxidation. A bench-scale electrothermal swing adsorption (ESA) system that uses activated carbon fiber cloth (ACFC) to selectively remove vapors/gases from gas streams and electrothermal heating to regenerate the ACFC was previously developed. This system concentrates a vapor/gas to > 50 % by volume allowing for condensation for reuse as a liquid. Typically, the end of an ACFC-ESA adsorption cycle and the heating part of a regeneration cycle are determined based on measurements from hydrocarbon sensors, which have capital costs and require periodic maintenance. Also, regeneration heating and cooling requires direct-contact thermocouple measurements to determine when to apply power and when cooling is complete to initiate an adsorption cycle, respectively. However, these thermocouples can lose contact with the ACFC or create an electrical short circuit during regeneration that damages the system and/or adsorbent. For this research, a method was developed to monitor and control ACFC-ESA that eliminates the need for hydrocarbon and direct-contact temperature sensors. This method provides the ability to monitor the electrical properties of the ACFC and control adsorption cycles, regeneration cycles, and cyclic ESA based on these properties. This research is divided into five sections: 1) Characterize changes in ACFC electrical resistivity during adsorption for ACFC samples with select physical and chemical properties, 2) characterize the effect of varying temperature and applied power profiles on the ACFC regeneration energy efficiency, 3) develop and test a new method to control ACFC regeneration heating based only on electrical resistance measurements, 4) characterize and control cyclic ESA based only on electrical measurements, and 5) compare the ESA system to existing abatement systems using a life cycle assessment and a cost assessment. This method to monitor and control ESA based on the adsorbent’s electrical properties is an improvement over current methods because it provides real-time adsorbed mass during adsorption cycles resulting in improved vapor/gas recovery efficiency and does not require direct-contact temperature or hydrocarbon sensors, which periodically fail and need to be calibrated, maintained, and replaced, reducing system run time and increasing operating costs. This study provides a method to increase ACFC-ESA vapor/gas capture and recovery efficiency and reduce energy demand and vapor/gas emissions (and their corresponding health effects) to improve the sustainability of the system. The unique contributions of this research include: 1) characterization of parameters affecting ACFC electrical resistance, 2) evaluation of regeneration temperature and power profiles for their effects on regeneration energy efficiency, 3) control of regeneration cycles based on electrical properties of the ACFC, 4) control of cyclic ESA based on electrical properties of ACFC, and 5) evaluation (life cycle assessment and cost assessment) of cyclic operation with this novel method to control ACFC-ESA for vapor/gas abatement compared to typical volatile organic compound abatement systems (i.e., granular activated carbon system and regenerative thermal oxidizer).
Carbon, Activated Carbon Fiber Cloth (ACFC), Adsorption, Electrothermal Swing Adsorption, Resistivity, Electrical Resistivity
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign