(90a) Modeling Adsorption of Organics-Laden Air from Wood Drying Using Equilibrium Approaches

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 concentrator (FBC). A process model was developed in AVEVA Simulation which models the FBC as a series of equilibrium adsorption stages, as well as modeling the downstream desorption and condensing operations. While a traditional analysis using Murphree tray efficiencies to account for discrepancies is certainly possible, the recently proposed virtual moving bed model (VMB) suggests a different efficiency based on the equilibrium loading is also available. [3] The behavior of both types of efficiencies are reviewed. Additionally, the adsorption of α-pinene, a representative compound for a collection of terpenes, was modeled with two different isotherm forms: The Langmuir-Freundlich (Sips) isotherm and the thermodynamic Langmuir (tL) isotherm. [4–7] The capability of each model to represent the data is contrasted and recommendations are made for their use in commercial process simulators.

Works Cited:

1. Milota, M. R., and Western Dry Kiln Association. (2000). Regulation and Control of Air Emissions.
2. Zhang, Z., Jiang, Z., and Shangguan, W. (2016). Low-temperature Catalysis for VOCs Removal in Technology and Application: a State-of-the-Art Review. Catalysis Today, 264, 270 – 278.
3. Sees, M.D., Kirkes, T., and Chen, C.-C. (2020). A Simple and Practical Process Modeling Methodology for Pressure Swing Adsorption. Computers & Chemical. Engineering, 2021, 147, 107235.
4. Chang, C.K., Tun, H., and Chen, C.-C. (2020). An Activity-Based Formulation for Langmuir Adsorption Isotherm. Adsorption, 2020, 26(3), 375 – 386.
5. Yang, R. T. (1997). Gas Separation by Adsorption Processes(Vol. 1). World Scientific.
6. 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.
7. Tun, H., and Chen, C.-C. (2020). Prediction of Mixed‐Gas Adsorption Equilibria from Pure Component Adsorption Isotherms. AIChE Journal, 1 – 9.