Pressure Swing Adsorption Performance Research Articles

SOFC-VPSA System for Power Generation with CO2 Separation

Solid Oxide Fuel Cell (SOFC) has attracted huge scientific attentions lately, as it is a promising power production technology that can reduce user’s dependency on electricity-grid. SOFC system can generate electricity by using liquid or gaseous fuels. Small volume and external fuel storage make SOFC technology more compatible, and it can easily be adjusted for different industry power plant scales. Moreover, SOFC operates at high temperature (700 0C), and it cogenerates high-quality heat or steam, which can be used as a heat source within the system. As maximum fuel utilization for SOFC is around 85%, a burner is required for the combustion of unconverted fuels. The burner provides additional heat to the SOFC system, at the same time, it generates more CO2.In order to meet “net zero” emission target for greenhouse gases in the year 2050, it is essential to introduce Carbon Capture and Storage (CCS) technology that can retrieve most of the produced CO2 from emission intensive activities and store it permanently in nature (e.g, sequestration and mineralization), leading to an almost carbon neutral activity. The stored CO2 can also be used in methanation process, to convert it into green methane. By integrating an existing CCS technology with SOFC, and using biofuels as energy source, SOFC system can be considered as a carbon negative technology. The most common and widely used CCS technology is Chemical Absorption (CA). The CA process presents good retrofitting options. However, corrosion and degradation are major issues.The high efficiency of SOFC system is however penalised by the fact that the flue gases contain typically a mix of CO2 and N2, which makes it difficult and expensive to separate/capture the produced CO2. There is a possibility of directly injecting pure oxygen to the burner. For industrial scale, cryogenic distillation is commonly used air separation technology for producing O2. Cryogenic distillation is an energy intensive technology, and it is not suitable for small scale O2 production. In the recent times, other technologies such as Pressure Swing Adsorption (PSA) and membrane have evolved for O2 production from air. The non-cryogenic technologies for air separation are preferred to their lower operating cost and easier integration with other processes. PSA is usually suited for medium-range production capacity, and it can produce O2 with 94 % purity. However, it is still necessary to improve performance by reducing energy consumption. The energy consumption is 3.211 MJ/kg-O2 for PSA to produce oxygen. In the oxygen production process, energy consumption accounts for more than 90% of the operating cost.This study considers integration of a SOFC system with PSA, which consists of a SOFC stack, balance of plant components for SOFC system, PSA bed and auxiliary components for PSA. The PSA produces O2 from air, that is injected to the combustion chamber (or burner). In the integrated system, the energy needed for the PSA directly comes from SOFC system. The right amount of oxygen is used to complete the oxidation of the unconverted fuel from the anodic side of SOFC, and CO2 is separated automatically after water condensation. Figure 1 shows layout of integrated system. The performance of PSA is explored for different materials, different pressure ratio and temperature, to achieve minimum energy consumption. Moreover, heat integration has been studied for SOFC system, the integrated system has waste heat available, especially at the downstream of the burner. In order to valorize the waste heat of the system, a steam cycle has been integrated for producing extra amount of electricity, to improve the overall efficiency of the system. Finally, the performance of integrated system has been optimized for maximization of electrical efficiency and minimization of exergy distraction, via multi-objective optimization.In this study, the net electricity output from SOFC-PSA system is around 9 kW. The SOFC produces 9.8 kW electricity, and about 8% electricity is consumed by the PSA for producing O2 that is required for the combustion of unconverted fuel. The integrated system has an overall efficiency of more than 55%. A steam cycle has been integrated for producing extra amount of electricity, and it produces additional 2.5 kW of electricity. Hence, the overall efficiency of the integrated system reaches above 70% with automatic CO2 separation. Figure 1

Scale-up analysis of a twin-bed PSA pilot plant

Small-scale pressure swing adsorption (PSA) plants, also referred to as pilot plants, are commonly exploited for studying separation processes in favour of the development of mathematical models and scale-up strategies. The applicability of a lately presented mathematical model, which was developed based on experimental data acquired from a high-purity twin-bed N2-PSA pilot plant, is verified in this paper for the design of large-scale systems by an analysis of the mass transfer zone development at different PSA cycle times. Effects of the PSA scale-up factor, adsorber aspect ratio, packed-bed density, and flow resistances along the piping system on the process performance are studied numerically. These considerations are particularly relevant for the scale-up of bank-type PSA units as well as for skid-mounted systems fitted to local space limitations, where the standard scale-up concept of keeping the gas velocity constant often cannot be fully realised. It is demonstrated that the sensitivity of the PSA performance to studied factors increases along with the required product purity level. Therefore, recommendations for adequate dimensions of pilot plants depending on the desired gas purity level can be derived. Limitations of the gas velocity through the adsorber shall be observed to generate reliable simulation data. The agreement between experimental results obtained from an industrial-scale system on one hand, and the outcome of a dynamic simulation on the other hand, is confirmed—provided that realistic pressure profiles are generated by a proper adjustment of flow resistances along the piping.

Effect of adsorption–desorption on hydrogen purity and recovery in non-adiabatic pressure swing mediated by microporous palm kernel shell adsorbent

The adiabatic cylindrical columns, which are commonly used in the pressure swing adsorption (PSA), do not recuperate the heat energy effectively from the adsorption–desorption processes, resulting in energy waste to the surrounding and degradation of the PSA performance over time. In this work, a non-adiabatic PSA mediated by an amorphous microporous palm kernel shell activated carbon demonstrated effective CO2 capture and hydrogen purification from syngas surrogate. The hydrogen recovery was improved by delaying the adsorption through a non-adiabatic pressure swing, in which transfer of the heat was allowed between the two plate columns. The improved hydrogen recovery, however, was achieved at the expense of decreasing hydrogen purity. Hydrogen recovery of 98.7% and purity of 97.5% were obtained at 3 min of adsorption whereas, hydrogen recovery of 99.3% and purity of 92.5% were obtained at longer adsorption of 5 min. Although desorption during blowdown did not affect the purity and recovery of hydrogen significantly, it revealed a noticeable trade-off between carbon dioxide purity and recovery at increasing blowdown time. The non-adiabatic plate PSA is promising in improving the hydrogen recovery that might be challenging using the conventional adiabatic cylindrical column PSA.

Effect of Adsorption Duration and Purge Flowrate on Pressure Swing Adsorption Performance

The effect of the duration of the adsorption step and purge flowrate on the performance of a demand-driven pressure swing adsorption unit (PSA) was investigated. These two operating parameters were varied and examined by simultaneously varying the requested total productivities (demand) using a model for biogas upgrading. The considered biogas PSA application uses a FAU zeolite (13X) to separate CH4 and CO2. The performance is tracked by three key performance indicators (KPIs): purity, recovery and total productivity. Depending on the selected KPI and constraints, an optimum emerges for the adsorption duration and purge flowrate. The breakthrough of carbon dioxide and insufficient purging are key elements limiting the performance for adsorption durations above and below the optimum, respectively. The complex interplay among the KPIs for the PSA process is visualized using a three-dimensional representation. Here, the various operating parameter settings (duration of the adsorption step and purge flow) define curves on the 3D surfaces, visualizing the effect of the PSA settings on all KPIs simultaneously. From such graphs, contour plots are extracted to highlight Pareto frontiers for a constant productivity or purity constraint.

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

This paper introduces a novel Coke Oven Gas (COG) hydrogen purification/compression system based on the technologies of Pressure Swing Adsorption (PSA) and Electrochemical Hydrogen Purification and Compression (EHP/C). As the EHP/C tolerates O2, N2 and CH4 impurities, PSA can be utilized solely for CO and CO2 removal (other COG impurities were not considered in this work). A relaxation of PSA hydrogen purity could significantly enhance its recovery rate. In this study, the suitability of traditional hydrogen PSA as part of the hybrid PSA/EHP/C approach was investigated. Aspen Adsorption and Matlab were used to model the PSA and EHP/C systems, respectively. The effect of adsorption pressure, purge-to-feed-ratio (P/F-ratio) and adsorption time within cycle on PSA performance is reported. This study found that breakthrough of non-detrimental components is typically accompanied with poisonous CO. Hence, the CO removal with traditional H2-PSA resulted into high purity product. In a two-bed PSA, 36.3% of hydrogen was recovered at 99.9988% purity and 0.18 ppm CO. Subsequently, as a result, the EHP/C purification capability was merely utilized, but polished this hydrogen to >99.999% purity. Simultaneously, hydrogen was isothermally compressed to 20 MPa, consuming a marginal 2.42 kWh/kg. Compared to mechanical compression, this is 31.6% more energy efficient. Recovering hydrogen from by-product COG was found to save 0.5 kg CO2/kg H2 compared to hydrogen produced from natural gas. Conventional hydrogen PSA, utilizing 70% Activated Carbon and 30% Molecular Sieve 5A, was found not to be effective to target the removal of CO specifically. To increase synergy between PSA and EHP/C, the PSA requires adequate design and operation using appropriate adsorbents and cycle steps to target elimination of CO. An increased EHP/C catalyst tolerance for CO also contributes to higher flexibility.

Evaluation of simplified pressure swing adsorption cycles for bio-methane production

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.

Artificial neural network based optimization for hydrogen purification performance of pressure swing adsorption

A pressure swing adsorption (PSA) cycle model is implemented on Aspen Adsorption platform and is applied for simulating the PSA procedures of ternary-component gas mixture with molar fraction of H2/CO2/CO = 0.68/0.27/0.05 on Cu-BTC adsorbent bed. The simulation results of breakthrough curves and PSA cycle performance fit well with the experimental data from literature. The effects of adsorption pressure, product flow rate and adsorption time on the PSA system performance are further studied. Increasing adsorption pressure increases hydrogen purity and decreases hydrogen recovery, while prolonging adsorption time and reducing product flow rate raise hydrogen recovery and lower hydrogen purity. Then an artificial neural network (ANN) model is built for predicting PSA system performance and further optimizing the operation parameters of the PSA cycle. The performance data obtained from the Aspen model is used to train ANN model. The trained ANN model has good capability to predict the hydrogen purification performance of PSA cycle with reasonable accuracy and considerable speed. Based on the ANN model, an optimization is realized for finding optimal parameters of PSA cycle. This research shows that it is feasible to find optimal operation parameters of PSA cycle by the optimization algorithm based on the ANN model which was trained on the data produced from Aspen model.

Pressure Swing Adsorption for Biogas Upgrading with Carbon Molecular Sieve

This work focuses on the study of a pressure swing adsorption (PSA) process for biogas upgrading using a carbon molecular sieve adsorbent. Adsorption equilibrium and diffusion data of pure components were used to predict the multicomponent behavior. To validate the prediction of multicomponent adsorption at different concentrations, breakthrough curve experiments were performed for a gas mixture at different pressures (0.25, 0.5, 1, and 5 bar). Based on basic information, a model was used to predict the performance of a two-column PSA unit. The mixture used as feed was 60% CH4 and 40% CO2 with pressure swings between 5 bar in adsorption mode to 0.1 bar in blowdown. Experimental data demonstrated that the model could describe the PSA performance with good accuracy. We have evaluated the influence of different feed times in the biomethane recovery and purity. Biomethane purity higher than 97.5% with recovery higher than 90% was obtained.

Machine learning model and optimization of a PSA unit for methane-nitrogen separation

In this work we study the separation of N2/CH4 in a bed packed with silicalite. Pressure swing adsorption (PSA) is a competitive technology for this task. Predicting PSA performance is a time consuming computational intensive problem. Direct optimization of the system of differential algebraic equations (DAE) describing the phenomena takes an impractical amount of time. We then analyze the suitability of using artificial neural networks (ANN) as a surrogate model to predict and optimize the PSA performance. Using the ANN surrogate model, optimization time decreased from 15.7h to 50s. We demonstrate that the PSA cycle proposed can achieve an optimized 99.5% nitrogen purity stream from an 85% inlet stream and a 50% purity stream from a 10% inlet stream. We also show that nitrogen recovery can be at most 90%. We further carry out a multi-objective optimization to demonstrate the tradeoff curve between nitrogen purity and recovery.

Combined Flue Gas Cleanup Process for Simultaneous Removal of SOx, NOx, and CO2—A Techno-Economic Analysis

Flue gas cleanup often requires the removal of SOx, NOx, and CO2 in separate units before being emitted into the atmosphere. This stepwise treatment process incurs significant cost and energy penalty to the electricity production. A combined adsorption process based on pressure swing adsorption (PSA) by which these impurities are removed is envisioned as an efficient means of flue gas cleanup that can be applied relatively easily. In this study, the technological and economic feasibilities of a combined separation process in which SOx, NOx, and CO2 are simultaneously removed from flue gas streams are assessed. Capital and operating costs are estimated based on sizing the equipment items and utilities needed, and the potentials for increased energy efficiency are determined in relation to the required PSA performance. The energy saving potential for the adoption of 2-bed and 4-bed PSA cycles is compared with conventional FGD, SCR, and amine scrubbing units needed to clean up flue gas in a stepwise fashion....

The effect of number of pressure equalization steps on the performance of pressure swing adsorption process

Cycle sequence has an important effect on the performance of pressure swing adsorption (PSA) processes. Pressure equalization steps influence significantly the purity and recovery of product, and therefore, may be properly designed to improve the performance of PSA processes. Open literature lacks of a systematic study on the effect of cycle sequence design on the performance of a specific PSA process as a controlling parameter. In this work, the results of recent studies on different cycle schedule design strategies have been used as a basis for comparing various cycle schedules (proposed by the authors of this work) on the performance of a six-bed PSA process for hydrogen purification. Three different cycle sequences have been designed, the pressure equalization and idle steps consisting the main controlling parameters. Simulation results showed that designs with more pressure equalization steps result in higher product recovery and those with less pressure equalization steps result in higher product purity. The proper performance of a PSA process is a tradeoff between product recovery and product purity. In this view, a target function has been developed that enables us to lump the latter performance parameters into one function for comparing the performance of the different cycles employed.

Pressure Swing Adsorption Process for Recovering H2 from the Effluent Gas of a Melting Incinerator

A two-bed pressure swing adsorption (PSA) process using activated carbon was studied to recover hydrogen from the effluent gas (H2/CO/CO2, 39.3:35.4:25.3 vol.%) of a melting incineration process. The adsorption dynamics of the activated carbon bed were investigated by breakthrough experiments. Since the product purity needs depend on demands of the incinerator site, various PSA operating conditions, such as purge to feed (P/F) ratio, adsorption (AD) step time, adsorption pressure, and feed flow rate, were investigated to recover H2 with a wide range of purities. The purity varied with P/F ratio, and the recovery varied with AD step time asymptotically because bed purification by H2 product purge approached a limitation. On the other hand, the variations in purity and recovery with P/F ratio, AD step time, and adsorption pressure were almost linear or only slightly curved. The variation in purity with feed flow rate was similar to the variation with P/F ratio while the recovery trend was more similar to the variation with the AD step time. Because the propagation velocity was significantly different for CO and CO2, the PSA performance was mainly affected by CO propagation, but the contribution of the CO2 heat of adsorption to the bed should be considered. The PSA process in this study produced hydrogen with a purity of 75.43–99.99% and a recovery of 90.99–49.29%. When a syngas (H2 and CO) is needed, the PSA process can result in high recovery and productivity because the major impurity in the product is CO.

Performance Comparison of Different Separation Systems for H2 Recovery from Catalytic Reforming Unit Off‐Gas Streams

AbstractThe performance of pressure swing adsorption (PSA), membrane separation, and gas absorption systems for H2 recovery from refinery off‐gas stream was studied by simulation‐based data. The PSA process was simulated using adsorbents of silica gel and activated carbon for removing heavy and light hydrocarbons. The mole fraction profiles of all components and the relationship between hydrogen purity and recovery as a function of feed pressure were examined. The solution‐diffusion model was applied for modeling and simulation of a one‐stage membrane process. The gas absorption process with a tower tray was simulated at sub‐zero temperature and the correlation between hydrogen purity and recovery as a function of tower pressure and temperature was evaluated at different solvent flow rates.

Advances in Pressure Swing Adsorption for Gas Separation

Pressure swing adsorption (PSA) is a well-established gas separation technique in air separation, gas drying, and hydrogen purification separation. Recently, PSA technology has been applied in other areas like methane purification from natural and biogas and has a tremendous potential to expand its utilization. It is known that the adsorbent material employed in a PSA process is extremely important in defining its properties, but it has also been demonstrated that process engineering can improve the performance of PSA units significantly. This paper aims to provide an overview of the fundamentals of PSA process while focusing specifically on different innovative engineering approaches that contributed to continuous improvement of PSA performance.

A comparison of the CO2 capture characteristics of zeolites and metal–organic frameworks

Considerable progress has been made in recent years on the development of novel adsorbents for CO2 capture. Pressure swing adsorption (PSA), using a packed bed of adsorbents is one of the leading contenders for use in technological applications. The candidate adsorbents are often structured micro-porous materials such as metal organic frameworks (MOFs), zeolitic imidazolate frameworks (ZIFs), and zeolites. The most common method of screening and selecting adsorbents is on the basis of adsorption selectivity. Besides adsorption selectivity, the performance, and economics, of a PSA unit is governed by a number of other factors, notably the working capacity. The main objective of this study is to investigate the relative importance of selectivity and capacity on PSA performance. Breakthrough characteristics of a packed bed adsorber packed with a number of zeolites (MFI, JBW, AFX, NaX), and MOFs (MgMOF-74, MOF-177, CuBTTri-mmen) were investigated for CO2 capture from a CO2/N2 mixture. These breakthrough calculations demonstrate that high capacities could have a dominant influence on the overall performance of PSA units. Our studies indicate that MgMOF-74 is the best adsorbent for post-combustion CO2 capture.

Propane/Propylene Separation by Pressure Swing Adsorption Using Zeolite 4A

In this work we have studied Pressure Swing Adsorption (PSA) process for separation of propane/propylene mixtures using zeolite 4A extrudates (CECA) as an alternative to distillation. Purified propylene is withdrawn in the blowdown step at 10 kPa because is the most adsorbed compound. The cycle used comprises five steps: pressurization, feed, purge with product, depressurization to intermediate pressure and counter-current blowdown for propylene recovery. Two mixtures with different propylene/propane ratios (54−46 and 85−15 diluted to 50% with nitrogen) corresponding to different sources of propylene production (steam cracking and Fluid Catalytic Cracking) were studied. The effects of the different step times in the performance of the PSA unit were evaluated. PSA performance was also studied using different operating conditions: process temperature and feed pressure. Also, the removal of inert from the process was studied. The simulation of the PSA unit was performed in gPROMS using a bi-LDF approximati...

Solvent Recovery by PSA, an Experimental and a Simulation Study

Solvent recovery by pressure swing adsorption (PSA) with resin adsorbent or high silica zeolite was tried and was related with characteristics of each adsorbent, i.e., the adsorption isotherms and the rates of adsorption and desorption. CH2Cl2 vapor was chosen as adsorbate. The performance by each adsorbent, shown in terms of the yield against purity of the product gas, was discussed. The high silica zeolite gave better performance than the resin adsorbent in a small-scale experiment, as expected from their isotherms (Chihara et al., 2004). Computer calculations were carried out to simulate the experimental results using the Stop-Go method to show the calculated results coincide well with experimental results. The method is useful to predict the performance of a solvent recovery system operated by PSA. The performance of Dual Reflux PSA which is the new type of PSA method (Wakasugi et al., 2002) was also simulated by this method.

Layered Pressure Swing Adsorption for Methane Recovery from CH4/CO2/N2 Streams

In this paper we discuss the performance of Layered PSA (Layered Pressure Swing Adsorption) for methane/carbon dioxide/nitrogen separation for methane upgrading from contaminated natural gas. A four-step PSA cycle was defined using extrudates of zeolite 13X (selective for carbon dioxide) and CMS 3 K (nitrogen selective) in a layered packed bed. Ternary breakthrough curves are reported as well as PSA experiments using a stream composition of 70% CH4–20% CO2–10% N2. Purity of methane of 92% with no carbon dioxide contamination and 43.5% recovery was obtained.

Pressure swing adsorption processes to purify oxygen using a carbon molecular sieve

Four different pressure swing adsorption (PSA) cycles using CMS for oxygen purification were developed to produce high-purity oxygen of over 99% with a high level of productivity. The cyclic performances such as purity, recovery, and productivity of the four different PSA cycles were experimentally and theoretically compared under non-isothermal conditions. In addition, one binary (O 2/Ar; 95:5 vol%) and two ternary (O 2/Ar/N 2; 95:4:1 and 90:4:6 vol%) mixtures were used to study the effects of feed composition. The PSA cycles with two consecutive blowdown steps produced oxygen with 98.0–99.9% purity and 56–66% recovery. The PSA cycle with oxygen generation in the second blowdown step produced oxygen with a higher level of purity and productivity. Also, the cycle introducing a pressure equalization step instead of a pure step produced oxygen with about 99.8% purity and 78% recovery. The period for the cyclic steady state of the ternary feed with 1% N 2 was slightly longer than that of the binary feed, while the PSA performance of the ternary feed was similar to that of the binary feed without nitrogen. However, in the ternary feed with 6% N 2, the purity of the O 2 in the purification cycles decreased by up to 97.3%. Therefore, nitrogen played a key role in producing high-purity oxygen in the CMS PSA instead of argon.

Effects of Nonisobaric and Isobaric Steps on O2 Pressure Swing Adsorption for an Aerator

The effects of nonisobaric and isobaric steps on a two-bed O2 pressure swing adsorption (PSA) packed with zeolite 5A were investigated. In addition, the operating conditions in the O2 PSA were studied to supply the various O2 concentrations to the oxygen aerator efficiently. Because the velocity variation along the bed and the related Mass Transfer Zone (MTZ) shape at the isobaric and nonisobaric steps were affected by the diffusion rate, the concentration-dependent rate parameter in a modified linear driving force (LDF) model was evaluated from the Darken equation related to the loading ratio correlation isotherm model. The LDF coefficients had a significant effect on the prediction of the O2 purity and recovery at the low flow rate region. However, the higher the feed flow rate, the lower the LDF parameter effect. It was also noted that the effects of each step time in the isobaric and nonisobaric steps on the PSA performance were subtle in the O2 purity and recovery except for the blowdown step. Also, there was the optimum step time to maximize the O2 purity and recovery in the adsorption and pressurization steps, while the increase of O2 purity and recovery with the pressurization equalization step time showed asymptotic curvature. The idle time at the pressurization step had a negative effect on the PSA performance, while the short idle time at the pressure equalization step led to improved product purity. However, it was negligible for the effect of the idle time at the blowdown step on the PSA performance. The successive variation between high and low P/F ratios caused the continuous variation of O2 purity and recovery to nearly the same extent as the results under each constant P/F ratio condition. Therefore, to save the operating cost of the oxygen aerator system, the desired oxygen concentration for the aerator can be supplied simply by controlling the feed rate or purge rate.