Application of an Intelligent Optimization Method Based on Aspen Adsorption in the Purification Process of Helium Via Pressure Swing Adsorption

Simulation of integrated novel PSA/EHP/C process for high-pressure hydrogen recovery from Coke Oven Gas

Simulation of CO2 capture for amine impregnated activated carbon - palm kernel shell (AC-PKS) adsorbent in pressure swing adsorption (PSA) using Aspen Adsorption

Optimization of steam-methane reforming process using PSA off gas

Pressure swing adsorption (PSA) is a promising technology for gas separation and purification, receiving considerable attention in the past decades. Existing studies on simulating PSA involving a vacuum pump, the vacuum (pressure) swing adsorption [V(P)SA] process, typically estimate vacuum pump energy consumption using an approximate constant energy efficiency or an empirical energy efficiency correlation, leading to inaccurate representation of realistic vacuum pump performance. In this work, we propose an enhanced computational approach for simulation and optimisation of V(P)SA processes through simultaneous incorporation of realistic vacuum pump performance prediction models and adsorption bed fluidisation limits. The vacuum pump performance prediction models are developed using data-driven modelling techniques with realistic vacuum pump performance data. The enhanced computational approach more accurately accounts for the V(P)SA performance, without relying on an estimated vacuum pump efficiency and assumed pressure/flow rate boundary conditions at the vacuum pump end of the adsorption bed. Furthermore, the impact of bed fluidisation on optimal PSA design is addressed. The computational results show that the developed prediction models accurately represent the actual performance curves of the vacuum pump. It is also demonstrated that incorporating the vacuum pump performance models and fluidisation constraints in PSA optimisation leads to significantly different optimal solutions compared to when these factors are not considered.

Biogas is a renewable and environmentally friendly energy source with a strong potential to replace fossil-derived natural gas. However, it must be upgraded to methane purities of >95% to meet fuel-quality standards. This study reports, for the first time, the application of a Pebax-supported ZIF-67 nanosheet composite as a structured adsorbent for biogas upgrading via a pressure swing adsorption (PSA) process combined with response surface methodology (RSM) optimization under industrially strict conditions. The composite adsorbent was synthesized and characterized using HR FE-SEM, FTIR, X-ray diffraction, and N2 adsorption–desorption analyses. Breakthrough experiments with CO2 and CH4 were conducted to evaluate adsorption selectivity and were used to validate a dynamic PSA model developed in Aspen Adsorption. A systemic parametric study examined the effects of length-to-diameter (L/D) ratio, operating pressure, and adsorption time on the separation performance for a biogas feed of 500 m3 STP h–1 containing 40% CO2 and 60% CH4. RSM analysis revealed strong interactions among these parameters and enabled the identification of optimal operating conditions. The optimal conditions were an L/D ratio of 5.1, an adsorption pressure of 7.8 bara, and an adsorption time of 62 s. Under these conditions, the PSA cycle achieved a biomethane purity of 98.67% with a recovery of 91.20%, exceeding the minimum pipeline specification of 95% CH4, with a compression energy requirement of 8.674 kJ mol–1 (75% efficiency). These results establish the fundamental feasibility and process-level advantages of the Pebax-supported ZIF-67 nanosheet composite for high-performance biogas upgrading, providing a new pathway for integrating anisotropic MOF-based composites into industrial PSA systems.

Experimental verification of hydrogen isotope enrichment process by dual-column pressure swing and temperature swing adsorption

This report summarizes the work performed under the Department of Energy’s National Energy Technology Laboratory (DOE-NETL) Advanced Energy Systems Program award number DE-FE0026163 Improving Energy Efficiency of Air Separation via Hollow Fiber Sorbents. The overall objective of the project was to develop technology to produce oxygen for use in coal gasification processes at a significantly lower cost than that of the commercial state-of-the-art technology. The focus of the project was development and optimization of hollow fiber sorbents for use in a pressure swing adsorption (PSA) process for producing oxygen from air. The key technical advancement under this program was the development of a hollow fiber sorbent capable of producing oxygen in a PSA process. PSAs produce oxygen by using a beaded zeolite material (typically lithium exchanged zeolites or LiX) that selectively adsorb nitrogen over oxygen. For a fiber to adsorb nitrogen, LiX needed to be integrated into a polymer fiber and then activated at over 350C to remove residual moisture. After screening multiple materials and process techniques, Matrimid/LiX hollow fibers were produced that were able to withstand the activation and had crystalline nitrogen capacity close to pure LiX crystals. The fibers were dual layer fibers with a barrier layer isolating the hollow bore from the LiX embedded layer. The barrier layer was formed from an Ultem® based solution. The hollow bore was intended for encapsulating phase change materials to ensure isothermal PSA operation. Modeling work from the project suggested that the benefits of this additional complexity were marginal, thus the team fabricated non-hollow fibers comprised of Matrimid and LiX. The Matrimid/LiX fibers were loaded into a module and tested on a bench scale PSA unit. The fibers were able to separate oxygen from air, but the purity and recovery were lower than expected and lower than traditional beaded LiX zeolites, although modeling results suggested that the bed sizes for fiber sorbents could be half the size of a beaded LiX bed. Additional work will be needed to understand the shortfall and to produce fiber sorbent modules with performance equal to the targets set for this program. In addition to producing fibers, modeling work was carried out at both the fiber level and process level to guide both fiber sorbent development and to determine the optimal process conditions for a PSA using fiber sorbents. A 2D hollow fiber model was developed in gPROMS Model Builder. This model was based on literature data for mass transfer and other parameters. This model used a basic single bed PSA process to determine important fiber properties and process conditions for achieving high oxygen recovery. The preliminary 2D fiber model was a valuable tool, however, for step-out technologies, such as a PSA process with fiber sorbents, intelligent optimization and plant control was needed to effectively determine minimum power designs. Therefore, a gPROMS Process Builder-based optimization tool was developed with an “Automated Cycle Optimizer” model that was able to determine optimal cycle conditions for a fiber sorbent PSA. The results from the optimizer were used in the final power analysis. Flow sheet analysis and techno-economic analysis (TEA) was carried out to determine a lower power solution versus the baseline case. The original project scope suggested that the fiber sorbent PSA could be used to debottleneck a cryogenic air separation plant (cryo-ASU) with the combined plant having lower power than a standalone cryo-ASU. However, early flowsheet analysis showed that the PSA/cryo-ASU concept would not lead to a lower power solution. However, further flowsheet analysis suggested that an oxygen PSA combined with a nitrogen PSA could have lower power versus state-of-the-art air separation technology. Work concluded with the TEA showing a fiber sorbent oxygen PSA combined with an advanced nitrogen PSA could be up to 8% lower power versus the base case cryo-ASU. Overall, there is significant potential remaining for the zeolite hollow fiber sorbent concept, and this project successfully identified -- and ultimately remedied -- many technical challenges associated with scale-up.

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.

Simulation and experimental results of a PSA process for production of hydrogen used in fuel cells

The growing concerns over CO2 emissions have led to the development of various methods for CO2 capture. CO2 capture by amine-based sorbents has been achieved by temperature (thermal) swing adsorption (TSA) process, pressure swing adsorption (PSA) process, and temperature pressure or vacuuming swing adsorption (TPSA or TVSA) process for CO2 capture. Amine sorbents for energy-efficient TSA, PSA, VSA, TPSA or TVSA CO2 capture should possess a capability which allow adsorbed CO2 to desorb and amine sorbent to be regenerated at low temperatures or low vacuums. Development of such amine sorbents would significantly decrease energy consumption and sorbent degradation during the regeneration step. The objective of this project is to develop a low vacuum swing adsorption (VSA) process for the capture of CO2 from air. The focus is on the development of amine sorbent which allows CO2 to adsorb in the form of weakly adsorbed CO2. The weakly adsorbed CO2 species can be collected from the sorbent by applying a low vacuum at ambient temperature. Specifically, no heating (i.e., thermal energy) is needed for regeneration of amine sorbents. This novel sorbent allows VSA to be operated at ambient temperature without a significant energy demand. This process eliminates the energy-intensive heating and cooling process in temperature swing adsorption (TSA) process. Ambient temperature operation could prolong the lifetime of sorbent and minimize the maintenance cost. Extensive sorbent studies with in-situ infrared spectroscopy have revealed the modifications of conventional amine sorbents with additives can increase the fraction of weakly adsorbed CO2. The amine sorbents with loaded CO2 can be regenerated in part by the following approaches: (i) mild heating to temperatures below 70 oC, (ii) flowing purging gas over modified amine sorbents at temperatures below 40 oC , (iii) vacuuming at pressure below 0.2 atm and temperatures below 40 oC. The performance of these modified amine sorbents has been tested in a 60 grams VSA unit at ambient temperatures. The results show that weakly adsorbed CO2 which can be desorbed from modified amine sorbents with purging gas at 100 cc/min can also be evacuated at a vacuum of 1 psia at room temperature. A preliminary techno- economic analysis indicates the major cost of the VSA process with modified amine sorbents stems from the operation of vacuum pumps. Thus, developing an excellent sealing with minimum leakage for the VSA unit is the most critical task for further the development of this VSA technology.

Adsorptive separations have gained considerable importance in process industry. A generic simulator has been developed in this work for Pressure Swing Adsorption (PSA) processes. Several simple and complex, conventional and unconventional PSA cycles have been studied using this simulator. Distinction has been made between PSA processes where a raffinate stream richer in the weakly adsorbed component as compared to the feed is the desired product as against processes where extract stream richer in the strongly adsorbed component is the desired product. These are termed as raffinate PSA and extract PSA respectively. Extract PSA is an unconventional process variation. The studies include several simple and complex PSA cycles for raffinate and extract PSA of industrial importance. The studies are aided by a generic simulator for all PSA process variations developed for the purpose. The simulator is equally applicable to Vacuum Swing Adsorption (VSA), Pressure Vacuum Swing Adsorption (PVSA), rapid cycle PSA processes, etc.

Semianalytical solution for multicomponent PSA: application to PSA process design

Activated carbon for gas separation and storage

Fixed bed adsorption processes such as pressure swing (PSA) and temperature swing (TSA), unlike other chemical engineering separation processes, are dynamic processes which do not produce a continuous or steady flow of either the adsorbate or lean (non-adsorbed) phase. Instead, they operate with multiple vessels in a cyclic operation. These processes, therefore, pose additional challenges which include amuch larger array of input parameters that control the individual steps within each PSA or TSA cycle. This work proposes an Aspen AdsorptionTM based Multi-Objective Optimisation (MOO) framework for PSA systems. The PSA systems can be optimised against different step times and process parameters suchas, blow down pressure, feed pressure, valve co-efficients etc. The proposed framework is demonstrated by considering an example of a PSA based Carbon Capture and Sequestration (CCS) unit, for the removal of CO2 from an entrained flow gasifier synthesis gas stream, downstream of the Water Gas Shift Reactors. The two objective functions maximise the CO2 capture rate and minimise the specific energy penalty associated with CO2 capture. A novel feature of this study is the purification of the CO2 produced by the PSA by condensing it, thereby, allowing it to be pumped up to a pressure of 100 bar. The off-gas from the separation has been constrained to have the same composition as that of the feed, which may be recycled to the PSA process or used for a different purpose. The MOO Pareto curves provide information on the most important variables for both the PSA and the refrigeration system.

The objective of this three-year project was to study new pressure swing adsorption (PSA) cycles for CO{sub 2} capture and concentration at high temperature. The heavy reflux (HR) PSA concept and the use of a hydrotalcite like (HTlc) adsorbent that captures CO{sub 2} reversibly at high temperatures simply by changing the pressure were two key features of these new PSA cycles. Through the completion or initiation of nine tasks, a bench-scale experimental and theoretical program has been carried out to complement and extend the process simulation study that was carried out during Phase I (DE-FG26-03NT41799). This final report covers the entire project from August 1, 2005 to July 31, 2008. This program included the study of PSA cycles for CO{sub 2} capture by both rigorous numerical simulation and equilibrium theory analysis. The insight gained from these studies was invaluable toward the applicability of PSA for CO{sub 2} capture, whether done at ambient or high temperature. The rigorous numerical simulation studies showed that it is indeed possible to capture and concentrate CO{sub 2} by PSA. Over a wide range of conditions it was possible to achieve greater than 90% CO{sub 2} purity and/or greater than 90% CO{sub 2} recovery, depending on the particular heavy reflux (HR) PSA cycle under consideration. Three HR PSA cycles were identified as viable candidates for further study experimentally. The equilibrium theory analysis, which represents the upper thermodynamic limit of the performance of PSA process, further validated the use of certain HR PSA cycles for CO{sub 2} capture and concentration. A new graphical approach for complex PSA cycle scheduling was also developed during the course of this program. This new methodology involves a priori specifying the cycle steps, their sequence, and the number of beds, and then following a systematic procedure that requires filling in a 2-D grid based on a few simple rules, some heuristics and some experience. It has been tested successfully against several cycle schedules taken from the literature, including a 2-bed 4-step Skarstrom cycle, a 4-bed 9-step process with 2 equalization steps, a 9-bed 11-step process with 3 equalization steps, and a 6-bed 13-step process with 4 equalization steps and 4 idle steps. With respect to CO{sub 2} capture and concentration by PSA, this new approach is now providing a very straightforward way to determine all the viable 3-bed, 4-bed, 5-bed, n-bed, etc. HR PSA cycle schedules to explore using both simulation and experimentation. This program also touted the use of K-promoted HTlc as a high temperature, reversible adsorbent for CO{sub 2} capture by PSA. This program not only showed how to use this material in HR PSA cycles, but it also proposed a new CO{sub 2} interaction mechanism in conjunction with a non-equilibrium kinetic model that adequately describes the uptake and release of CO{sub 2} in this material, and some preliminary fixed bed adsorption breakthrough and desorption elution experiments were carried out to demonstrate complete reversibility on a larger scale. This information was essentially missing from the literature and deemed invaluable toward promoting the use of K-promoted HTlc as a high temperature, reversible adsorbent for CO{sub 2} capture by PSA. Overall, the objectives of this project were met. It showed the feasibility of using K-promoted hydrotalcite (HTlc) as a high temperature, reversible adsorbent for CO{sub 2} capture by PSA. It discovered some novel HR PSA cycles that might be useful for this purpose. Finally, it revealed a mechanistic understanding of the interaction of CO{sub 2} with K-promoted HTlc.