(115g) Dynamic Adsorption Process Simulator: Evolution of the Energy Balance on the Approach to Periodicity

Authors: 
Ebner, A. D., University of South Carolina
Ritter, J. A., University of South Carolina

The dynamic adsorption process simulator (DAPS) developed over the past fifteen years has slowly transformed into a very rigorous, very robust and very useful adsorption process simulator. It has been used and is being used to develop and study countless cyclic adsorption processes including but not limited to air separation, air purification, air revitalization, hydrogen purification, solvent vapor recovery, gasoline vapor recovery, natural gas purification, refinery gas upgrading, ammonia purification, isotope separation, etc. DAPS is capable of simulating the most complex PSA cycle schedules including the 12-bed 13-step hydrogen purification process, which utilizes 3 to 4 layers of different adsorbents in a column. It can handle multiple input and output flows along the column, not just at the ends. DAPS can also equalize bed-to-bed or bed-to-tank-to-bed, depending on the demands of the cycle schedule. Finally, it can be coupled with a reactor, either as a layered or mixed bed of adsorbent and catalyst.

DAPS accounts for mass, energy and momentum changes throughout every step of every cycle of a pressure swing adsorption (PSA), temperature swing adsorption (TSA) or concentration swing adsorption (CSA) process until the periodic state is reached. It utilizes many assumptions, like all process simulators; but, DAPS still accounts for velocity changes due to adsorption, temperature, and pressure changes along the column. It accounts for mass transfer effects via a liner driving force expression and heat transfer effects via an overall heat transfer coefficient. To ensure accuracy, the mass and energy balances are checked for closure from cycle to cycle during the approach to periodic behavior.

The energy balance closure looks at the energy in the input and output flows, the energy accumulated in the gas and adsorbed phases, the energy gains and losses due to adsorption and desorption, and the energy losses and gains through the wall of the bed. This cycle to cycle energy balance closure reveals some surprising dynamics that appear in the first cycle and the then they change from cycle to cycle until they finally disappear at the periodic state after many ensuing cycles. Because these energy balance closure dynamics are real and thus exist in actual cyclic adsorption processes, they reveal very interesting features about the energy changes that take place within the column during the approach to periodicity. They also are a much more stringent check on the energy balance closure within DAPS because much more information is available to analyze compared to that at the periodic state. This presentation will provide an overview of DAPS, with particular emphasis on the cycle to cycle energy balance closure dynamics.