(443a) Modeling Adsorption of Organics-Laden Air from Wood Drying Using the Virtual Moving Bed Model

Air leaving a wood dryer contains organics which must be removed before the air can be released to the atmosphere. The current state-of-the-art in wood drying is the regenerative thermal oxidizer (RTO), which reduces the organics to carbon dioxide over a packed bed of ceramics (and sometimes iron catalyst) at high temperatures. [1,2] Sustainability and economic pressures suggest a more passive mode of capture, where the organics are condensed and recovered instead of burned. Captis Aire has developed a moving bed thermal adsorption process which can recover organics from air using a fluidized bed adsorber. However, models for such a process are lacking in commercial process simulators. Developed as a general shortcut model for cyclical adsorption processes, the virtual moving bed model previously developed can be also used to model the continuous flow unit and provide insights into its performance [3,4,5] using the concept of adsorption efficiency proposed by Smith and Westerberg. [6] Pure component adsorption of representative compounds were modeled with both the Langmuir-Freundlich and thermodynamic Langmuir (tL) isotherms, [7] which were extended to mixtures using their multicomponent counterparts: the empirical loading ratio correlation (LRC) [8] and real adsorbed solution theory (RAST-aNRTL). [9,10] These isotherm predictions are used in the virtual moving bed model using the one-efficiency model, with unity bed-state efficiencies for some components, to make predictions of the performance of the fluidized bed adsorber system.

Works Cited:

1. Milota, M. R., and Western Dry Kiln Association. (2000). Regulation and Control of Air Emissions.
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3. Sees, M.D., Kirkes, T., and Chen, C.-C. (2020). A Simple and Practical Process Modeling Methodology for Pressure Swing Adsorption. submitted.
4. Sees, M.D. (2018, October). “Novel Steady-State Process Modeling Methodology for Pressure Swing Adsorption.” Paper presented at the 2018 Annual Meeting of the American Institute of Chemical Engineers, Pittsburgh, PA.
5. Sees, M.D. (2020, November). “Modeling of Gas Separations by Pressure Swing Adsorption Using a Novel Steady-State Methodology.” Paper presented at the 2020 Annual Meeting of the American Institute of Chemical Engineers, San Francisco [virtual], CA.
6. Smith, O.J. and A.W. Westerberg. Eng. Sci., 1991, 48(12), 2967 – 2976.
7. Chang, C.K., Tun, H., and Chen, C.-C. (2020). An Activity-Based Formulation for Langmuir Adsorption Isotherm. Adsorption, 2020, 26(3), 375 – 386.
8. Yang, R. T. (1997). Gas Separation by Adsorption Processes(Vol. 1). World Scientific.
9. Kaur, H., Tun, H., Sees, M.D., and Chen, C.-C. (2019). Local Composition Activity Coefficient Model for Mixed-Gas Adsorption Equilibria. Adsorption, 25(5), 951-964.
10. Tun, H., and Chen, C.-C. (2020). Prediction of Mixed‐Gas Adsorption Equilibria from Pure Component Adsorption Isotherms. AIChE Journal, 1 – 9.