The mass transfer zone in nitrogen PSA columns

New cycle configuration to enhance performance of kinetic PSA processes

Approximation of a PSA process based on an equivalent continuous countercurrent flow process: Blow-up and blow-down representation

Performance and dynamic behavior of H2 layered-bed PSA processes using various activated carbons and zeolite LiX for steam methane reforming gas

Optimal startup operation of a pressure swing adsorption

Purification of hydrogen from natural gas/hydrogen pipeline mixtures

Both pressure swing adsorption (PSA) and vacuum swing adsorption (VSA) processes are often characterized by the slow evolution of temperature profiles to cyclic steady state (CSS). Perhaps most profound is the severe axial temperature profile that characterizes oxygen VSA occurring at the interface between a prelayer and the main adsorbent layer. This temperature profile or cold spot has been of much interest to the gas industry and adsorption researchers. Previous work (Wilson, S. et al. Ind. Eng. Chem. Res. 2001, 40 (12), 2701) has developed qualitative explanations of these temperature profiles. This paper describes a detailed experimental investigation of the process parameters that affect the axial CSS temperature profile in oxygen VSA. These experimental results are compared with a numerical model of the process and a simple predictive model. A conclusion of this work is that numerical models can accurately capture the CSS temperature profiles and that the simple model can account for some, but not all, of the observed effects. A better understanding of thermal profiles is necessary for the development of new thermal optimization strategies in oxygen VSA.

Tailoring activated carbons for the development of specific adsorbents of gasoline vapors

Simulation of breakthrough curves by a moving zone collocation method

Recent developments in the fuel cell industry have yielded an increase in expected demand for a pure hydrogen source; one attractive method for meeting this demand involves separating hydrogen from a hydrogen-methane mixture using pressure swing adsorption (PSA). In designing PSA systems, the selection of the adsorbent and operational flowsheet are the most important and limiting decisions; beyond this, implementing systematic methods to find optimal operating conditions and bed parameters is essential. These decision variables include flowrates, bed pressures, step times and bed dimensions. This research examines this PSA system via dynamic simulation and optimization; the primary purpose of the optimization is to maximize the recovery of the key components while meeting both the hydrogen purity and cyclic steady state requirements. In this study, the process model is formulated for this separation using gPROMS. The model discretizes the spatial domain, and binary variables are used to adjust the boundary conditions for the bed as the system runs through the four-step PSA cycle. Two alternative PSA cycles are simulated, optimized and compared to assess the best performance for this PSA separation.

Pressure swing adsorption (PSA) is a mature technique for biogas upgrading. However, it constitutes the most expensive step to obtain fuel-quality bio-methane, particularly in small-scale units. To reduce the cost of upgrading in small-scale plants, we have evaluated different PSA cycles with two and three columns (less than commercial units). An equalization tank was used to perform one asynchronous pressure equalization step and keep the process fed continuous even in the case of using two columns. The effect of the purge step was also evaluated. Carbon molecular sieve was used as adsorbent. The feed composition was 40% CO2/60% CH4 and pressure swinging between 5 and 0.1 bar in the adsorption and blowdown steps, respectively. Four performance indicators (methane purity and recovery, productivity and energy consumption) were used to evaluate the PSA cycles. The mathematical model could predict the experimental PSA performance. Bio-methane with purity higher than 97.5% (specification) and recovery higher than 90% was obtained experimentally using a PSA with two columns and an equalization tank. When a third column is used (implementing an additional pressure equalization), the recovery increases in approx. 4% showing the importance of pressure equalization to reduce the methane slip.

An equilibrium model for pressure swing adsorption (PSA) process with equalization step is developed by using the method of characteristics. The concentration profiles at the cyclic steady state are obtained by tracking the movement of wave fronts derived from the characteristic lines during the transient cycles. The results of this model compare quite well with the conventional finite difference method, but with less computational effort. Multiple waves in PSA processes are clearly demonstrated by this model. Effects of equalization step on PSA process performances are also analyzed using this model.

Pressure swing adsorption (PSA) is attractive for final separation in the process of water removal especially for fuel ethanol production. Despite many researches on simulation and experimental works on adsorption of water on 3A zeolite in a fixed bed, none have studied a process with the actual PSA system. The purpose of this research was to study the PSA process with two adsorbers and effects of several parameters. The research also included analysis of kinetic and thermodynamic data of ethanol-water adsorption on commercial 3A zeolites in a single fixed bed. A two-level factorial design experiment was used in this research work to preliminarily screen the influence and interaction among the factors. Effects of important parameters such as initial temperature, feed concentration and feed rate were investigated. It was proven that the Langmuir isotherm could best predict the experimental results. In the PSA pilot test, the principal factors, which had effects on the performance, were feed rate, feed concentration, adsorption pressure and the cycle time. Prediction of the process efficiency in terms of ethanol recovery and enrichment was proposed in the form of regression models. The results of the study in a fixed bed adsorber could help designing a pilot-scale PSA unit. The experiments proved to be successful in terms of producing high concentration ethanol with high percentage of ethanol recovery. With further simulation work the process could be scaled up for an industrial use.

Research was conducted to improve the system efficiency of a fuel-processing system combined with a hydrogen-purification system to supply hydrogen to a 10 kW residential building proton-exchange membrane fuel cell (PEMFC). The system consists of a steam-reforming reactor, a water–gas shift reactor, heat exchangers and a pressure swing adsorption (PSA) system, increasing the purity of the produced hydrogen by over 99.97%. Aspen Plus® and Aspen adsorption® simulators were used to optimize operating conditions by calculating thermal efficiency and hydrogen-production yield under various temperature and pressure conditions in the reformer. To optimize the hydrogen-production system, simulations were performed under conditions of 1 to 10 atm and 600 to 1000 °C, and simulations were also performed while maintaining the PSA pressure at 9 atm. The overall system efficiency was expressed as a function of methane conversion, and the methane conversion was expressed as a function of reformer temperature and pressure. The fuel-processing system showed the highest thermal efficiency of 82.40% at a pressure of 1 atm and a temperature range of 800 °C. For the combined system of a fuel-processing system and a hydrogen-purification system, the highest hydrogen-production yield was 43.17% at 800 °C and 1 atm.

Oxygen separation from air by PSA: modelling and experimental results

A two-bed pressure swing adsorption system on a commercial type of zeolite 13X adsorbent has been studied numerically over a wide range of operating conditions to helium separation from gaseous mixture. The model includes energy, mass and momentum balances. The coupled partial differential equations are solved using fully implicit forth order Rung-Kutta scheme in the simulation. The effects of adsorption step pressure, adsorption step time and feed flow rate on the helium purity and recovery were investigated. Results shown that as the adsorption step pressure increases the helium purity will be increased. In addition, the helium recovery increases, and the helium purity decreases when the feed flow rate increases. Finally, the simulation results indicated a very good agreement with some current literature experimentally work.