Experimental and numerical evaluation of electrothermal–swing adsorption for capture and recovery or destruction of organic vapors

Electrothermal Swing Adsorption (ESA);Activated Carbon Fiber Cloth (ACFC);Electrothermal Heating;Adsorption;Volatile Organic Compounds (VOCs);Steady-State Tracking (SST);Desorption;Modeling;Organic Vapors;Acetone;Toluene;Methyl Ethyl Ketone (MEK);Hazardous Air Pollutants (HAPs)

Emamipour, Hamidreza

关键词: Electrothermal Swing Adsorption (ESA);    Activated Carbon Fiber Cloth (ACFC);    Electrothermal Heating;    Adsorption;    Volatile Organic Compounds (VOCs);    Steady-State Tracking (SST);    Desorption;    Modeling;    Organic Vapors;    Acetone;    Toluene;    Methyl Ethyl Ketone (MEK);    Hazardous Air Pollutants (HAPs);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/15584/2_Emamipour_Hamidreza.pdf?sequence=4&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Emissions of hazardous air pollutants (HAPs) and volatile organic compounds (VOCs) to the atmosphere are serious environmental issues. There were 0.53 billion kg of HAPs and 15 billion kg of VOCs emitted to the atmosphere from anthropogenic sources during 2004 and 2002, respectively. Eighty-nine percent of those HAPs were emitted from point sources that can be readily captured by techniques such as adsorption. The cost to meet regulations for VOC control during 2010 was estimated at $2.3 billion/yr. Environmental regulations encourage the development of new technologies to more effectively remove HAPs/VOCs from gas streams at lower cost. Electrothermal Swing Adsorption (ESA), as described here, is a desirable means to control these emissions as it allows for capture, recovery and reuse or disposal of these materials while providing for a more sustainable form of technological development.The Vapor Phase Removal and Recovery System (VaPRRS or ESA-R)) was initially evaluated for possible improvements. An automated bench-scale adsorption device using activated carbon fiber cloth (ACFC) was designed and built to study effects of select independent engineering parameters on the ability of the system to capture and recover an organic vapor (e.g., methyl ethyl ketone, MEK) from air streams. Factors that can increase the adsorbate liquid recovery with low energy costs were investigated using sequentially designed sets of laboratory experiments. Initially, the screening experiments were conducted to determine significant factors influencing the energy efficiency of the desorption process. It was determined that “concentration of organic vapor”, “packing density”, and “maximum heating temperature” are significant factors while “nitrogen flow” and “heating algorithm” are insignificant factors in the ranges of values that were evaluated. Experimental data provided from this work were then used as inputs by Kaldate (2005) to complete a response surface methodology using Central Composite Design to optimize the operation of the ESA system in a region where efficient liquid recovery can be achieved. These results were used by Kaldate (2005) to reduce the amount of power applied per unit mass of ACFC in the vessel and provide a scale-up model of the ESA system.A comparison between experimental bench-scale VaPRRS and a pilot-scale VaPRRS was also completed as part of this research. Results from this effort demonstrated that both the bench-scale and pilot-scale ESA systems had removal efficiencies of MEK > 98%. The average electrical energy per unit mass of recovered liquid MEK was 4.6 kJ/g and 18.3 kJ/g for the bench unit and pilot unit, respectively. A new concentration controlled desorption device, known as ESA-Steady State Tracking (ESA-SS) desorption, was also designed and built as a bench-scale laboratory device as part of this research. This new system was demonstrated to operate over a wide range of conditions (i.e., type of organic vapor, concentration of organic vapor, ratio of desorption/adsorption cycle gas flow rates, fixed and dynamic desorption concentration set-points, constant and variable inlet concentration of organic vapor, batch and cyclic modes, and with dry and humid gas streams). It was shown that concentration of organic vapor that is generated during regeneration cycles can readily be controlled at concentration set-points for three organic compounds (MEK, acetone, and toluene). The average absolute errors (AAEs) were < 5% when comparing the set-point and the measured outlet vapor concentrations. This is the first time that such performance has been demonstrated and this performance is not possible with other current technologies. Such capability of the system allows a secondary control device to be optimized for select constant concentrations and much lower gas flow rates (e.g., 5% of the gas flow rate during the adsorption cycle) that is not possible without such pretreatment.An ESA-Concomitant Adsorption and Desorption (CAD) system was also developed as part of this research to readily control its outlet organic vapor concentration as the entire inlet gas stream passes through the CAD system. This bench-scale system adsorbed organic vapor from a gas stream and simultaneously heated the adsorbent using direct electrothermal energy to desorb the organic vapor at user-selected set-point outlet concentrations. CAD achieved a high degree of concentration stabilization with a mean relative deviation between set-point concentration and measured outlet vapor concentration of 0.3 % to 0.4 %. The CAD system was also evaluated to treat a humid gas stream (inlet relative humidity = 85%) that contained a variable organic vapor concentration. CAD operated successfully at high inlet relative humidity conditions because the water vapor did not adsorb but penetrated through the adsorbent because of local warming of the adsorbent.Computational fluid dynamics was used for the first time to model the three-dimensional (3-D) pressure drop, flow patterns, and heat transfer in an adsorption vessel with annular cartridges of ACFC. It was demonstrated that pressure drop and velocity contours are very uniform (e.g., within 5%) in the porous zones of the ACFC cartridges within the vessel. The main pressure drop across the vessel is due to the ACFC cartridges. It was also demonstrated that electrothermal heating is much more energy efficient than heating with hot inert gas such as air. These results support the use of1-D or 2-D modeling regarding mass and energy transfer in the ACFC while achieving sufficient accuracy.A fundamental mathematical model for simulation of ESA was also developed and evaluated. The model consists of: a) material balances for organic vapors in the adsorption vessel and b) energy balances for the adsorbent, carrier gas, vapor, and fittings. The model predicts outlet vapor concentrations, temperature profiles, power requirements, voltage requirements, and current requirements for ESA desorption cycles. The model is very helpful in the initial stages of design of an ESA system to reduce cost and time and to more effectively evaluate experimental results pertaining to energy and material balances.Future work that should occur includes the development and testing of VaPRRS, SST, and CAD at the full-scale. Results from these tests can then be used to compare these technologies to existing air quality control technologies and to evaluate these new systems under more realistic field conditions that exist in the laboratory. CFD simulations can also be developed and implemented to consider mass transfer within the adsorption vessels and to consider new adsorbent geometries, such as pleated cartridges in rectangular enclosures.ESA VaPRRS/SST/CAD should also be developed for indoor air quality control applications. Such technologies have the potential to remove particulate matter, organic gases, and biological materials from indoor air streams.