Pressure Swing Adsorption Process Research Articles

Bed configurations in CO vacuum pressure swing adsorption process for basic oxygen furnace gas utilization: Experiment, simulation, and techno-economic analysis

CO is a primary component of basic oxygen furnace gas (BOFG) and can be used for producing fuel and various value-added chemicals. It can be typically obtained from steel mill gases via separation. Herein, suitable bed operation configurations for vacuum pressure swing adsorption (VPSA) were determined based on the desired CO product purity (PURCO,P) when separating CO from simulated BOFG (CO:CO2:N2:CH4 = 65:20:10:5 mol%) using a numerical model validated with experimental data. By changing the operation steps, one case of two-bed, four-step (2-bed), one case of three-bed, five-step (3-bed), and two cases of four-bed, six-step (4-bedbase and 4-bedmod) operation configurations were considered at a setting temperature of 60 ℃, desorption pressure of 0.13 kgf cm−2, and adsorption pressure in the range of 2.5–4.0 kgf cm−2. The sensitivities of these four operation configurations were evaluated to compare the separation performance and economic benefits of each operation configuration. In the 2-bed case, the PURCO,P demonstrates a separation limit (92.1–92.7 mol%). When targeting PURCO,P ≥ 99.00 mol%, the 3-bed case presents the most favorable CO recovery values (RECCO,P; 92.97–94.13 %) and unit production costs of CO (UPCCO; 0.252–0.357 US$ Nm−3), whereas the 4-bedmod case presents optimal RECCO,P (82.06–91.65 %) and UPCCO values (0.273–0.406 US$ Nm−3) when targeting PURCO,P ≥ 99.99 mol%, under the same operating conditions. These results indicate cost-effective CO-VPSA process configurations for enriching CO from BOFG, based on the target PURCO,P.

Handling model uncertainty in control of a pressure swing adsorption unit for syngas purification: A multi-model zone control scheme-based robust model predictive control strategy

The application of a robustly stabilizing model predictive control (MPC) strategy to a pressure swing adsorption (PSA) unit, hitherto unexplored in the literature, is addressed in this work. Here, a set of linear models to handle model uncertainties describes the PSA nonlinear dynamic behaviour. Each model represents a different operating condition of the PSA, generating a multi-model uncertainty description. In addition to incorporating the multi-model uncertainty, the proposed MPC control law deals with a controlled output zone tracking scheme to systematically accommodate typical cyclic steady states of a PSA process. From the industrial standpoint, economic targets on process variables (controlled outputs, manipulated inputs, or both) are also incorporated into the robust control method. A Real-Time Optimizer usually defines these targets, making up a two-layer control scheme. The effectiveness of the robust MPC is evaluated in a syngas purification process via a single bed, six-step PSA unit composed of a porous amino-functionalized titanium terephthalate MIL-125-type MOF adsorbent.

Enhanced ammonia adsorption performance of MgCl2-loaded activated carbon in pressure swing adsorption

Ammonia, which decomposes to N2 and H2, is considered an excellent hydrogen storage material because of its high capacity. However, undecomposed ammonia can cause corrosion and catalyst poisoning, thereby necessitating its removal from the effluent stream. One of the methods used to separate H2, N2, and residual NH3 gases after ammonia decomposition is pressure swing adsorption (PSA). In this study, activated carbon (AC) loaded with MgCl2 was used as an adsorbent for PSA. High-pressure adsorption and breakthrough experiments showed that the optimum Mg loading amount is 4 wt% Mg and the optimum operating temperature is 40 °C. Under these conditions, a balance between the adsorption and desorption performance (in terms of adsorption capacity and desorption time, respectively) was achieved. The optimal MgCl2-loaded AC had an average adsorption capacity of 6.48 mmol NH3/g, which was higher than that of AC by 93%. This adsorbent maintained its high adsorption capacity throughout 15 cycles of adsorption–desorption and performed well in breakthrough experiments simulating either the removal or enrichment of ammonia. Thus, MgCl2-loaded AC is a promising adsorbent that can be potentially applied for both ammonia removal and enrichment in industrial PSA processes for hydrogen extraction.

Model-Based Analysis of a Highly Efficient CO2 Separation Process Using Flexible Metal–Organic Frameworks with Isotherm Hysteresis

To realize large-scale CO2 separation to prevent global warming, energy and space saving separation technologies are required. Flexible metal–organic frameworks (flexible MOFs) with gate-opening properties have been found to be promising adsorbents, but the unconventional sigmoidal shapes and hysteresis of the isotherms have hindered quantitative evaluation of their applications in separation processes. This paper is the first to evaluate ELM-11, a flexible MOF that exhibits sigmoidal isotherms with hysteresis, in a process model and quantify its advantages over a conventional adsorbent. Based on the experimental uptake data, isotherm models for adsorption and desorption were developed, and their parameters were estimated. The resulting isotherm models are incorporated into a rigorous dynamic model of partial differential algebraic equations (PDAEs) to simulate a vacuum pressure swing adsorption (VPSA) process to evaluate the process performance. Numerical challenges to solve the PDAEs, including sigmoidal and hysteresis isotherm models, were resolved with the proposed numerical approaches. Sensitivity analysis for feed pressure and temperature was performed to identify the optimal operating strategy. A comparison with a conventional adsorbent, zeolite 13X, showed that high selectivity and sigmoidal isotherms of ELM-11 give higher productivity and CO2 product purity exceeding 99% without rinse and purge operations as well as lower power consumption for the compressor and vacuum pump.

Performance evaluation of gas fraction vacuum pressure swing adsorption for CO2 capture and utilization process

• A simple 2-column gas fraction VPSA process without a rinse step is proposed. • The performance of gas fraction VPSA has been evaluated by simulations and experiments. • This simple operation allows flexible adjustment of CO 2 purity and recovery, which can produce low-cost CO 2 at a moderate purity. Pressure swing adsorption (PSA) is widely used in various gas separation processes. Many PSA operations have been proposed that require multiple beds having a rinse step in order to obtain a product gas of high purity. This operation may cause re-adsorption of desorbed gases on the adsorbent depending on the process design, which leads to a decrease in the productivity and energy efficiency. In this work, a simple vacuum type PSA (VPSA) process without a rinse step is proposed and demonstrated experimentally for CO 2 separation. The proposed VPSA process fractionates the outlet gas from the bed, which allows flexible adjustment of the purity and recovery of the product gas exploiting isotherm nonlinearity. To investigate the performance of the proposed process, a dynamic VPSA simulation was conducted. The performance of this gas fraction VPSA was evaluated also experimentally at the laboratory scale to analyse the trade-offs amongst purity, recovery, productivity and energy efficiency. In our experiment, the highest CO 2 recovery of 68.7% was obtained by the newly designed 2-column gas fraction VPSA at the feed gas volume of 76 NL-feed/kg-adsorbent/cycle, which is about 60% higher than 3-column VPSA with a rinse step. The CO 2 separation energy estimated from experimental results with assumptions on the efficiency of the compressor and vacuum pump also indicated the possibility of further cost reduction at moderate CO 2 purity.

Methane recovery from low-grade unconventional natural gas by the integrated mode of the conventional/improved vacuum pressure swing adsorption processes

There is a strong challenge for the CH4 recovery from nitrogen-rich low-grade unconventional natural gas by the existing adsorption separation technologies to obtain the high-purity methane because of the similar properties between CH4 and N2. Therefore, the developments of both novel sorbents and advanced adsorption processes for the high-efficient separation of CH4/N2 are greatly significant. In this article, the integrated mode of the conventional/improved vacuum pressure swing adsorption (VPSA) processes was developed to capture and upgrade the low-concentration CH4 from N2-rich streams for high-purity CH4 production. The improved VPSA process represented the conventional adsorption process run with the simulated moving bed (SMB) mode to enhance the separation of CH4/N2. To evaluate the feasibility and effectiveness of the integrated VPSA processes, the commercial coconut shell activated carbons (ACs) were used as the tested sorbents for experimental demonstrations, since the ACs were microporous materials widely used in industry. Experiments with one-column and eight-column unit were performed for CH4 recovery from 10% to 50% CH4/N2 feed gas, and the experimental results of the improved VPSA process were compared with the conventional adsorption process. The experimental results confirmed that 10% CH4/N2 feed gas could be enriched and upgraded successfully to 99.0% CH4 product gas by the integrated VPSA processes even if the commercial activated carbons were used as sorbents.

Integrated Process Design and Life Cycle Assessment of Carbon Monoxide Provision from Basic Oxygen Furnace Gas

AbstractVacuum pressure swing adsorption (VPSA) processes are promising separation technologies to recover valuable compounds from industrial off‐gases. In this work, the separation of CO from basic oxygen furnace gas (BOFG) with a three‐bed VPSA process for high‐purity applications using a dynamic process model is analyzed. The analysis evaluates technical operating ranges for providing 99.9 % pure CO and assesses system‐wide environmental impacts using life cycle assessment. The results show that CO from BOFG as feedstock for chemicals reduces greenhouse gas (GHG) emissions by about 10 % for Germany's current grid mix regardless whether the VPSA process operates at maximum productivity (0.18 Nm3h−1kg−1ads) or maximum recovery (95.7 %). Further reduction in GHG emissions by up to 68 % can be achieved using renewable energy albeit increasing other environmental impacts such as mineral and metal depletion. Overall, VPSA offers a viable, short‐term solution for providing low‐carbon CO from BOFG.

A multicolumn vacuum pressure swing adsorption biogas upgrading process for simultaneous CO2 and N2 separation from methane: Exergy and energy analysis

Adsorption is commonly used as an industrial process for biogas upgrading through elimination of unwanted species to obtain high quality biomethane. While several studies have addressed individual removal of CO2 and N2 from raw biogas, limited attention has been paid to their simultaneous removal due to the complexities involved. This works presents the results of design, modeling, and numerical simulation of a novel vacuum pressure swing adsorption (VPSA) process for upgrading a model raw biogas containing 40 and 10 vol% CO2 and N2, respectively, to increase CH4 purity to 98% and with less than 2 % N2. The proposed process is comprised of 4 columns including two columns of carbon molecular sieves (CMS) and two others with zeolite Sr-ETS-4 as the selective adsorbents for removal of CO2 and N2, respectively. Two configurations are evaluated and compared in terms of CH4 purity, CH4 recovery, productivity, energy consumption, and 2nd law efficiency. For the best configuration, an energy consumption of 24.9 kJ/mol CH4, productivity of 3.38 mol h−1 kg−1, CH4 purity of 98.2 mol%, and CH4 recovery of 73.8 mol% were achieved. 15% improvement in CH4 recovery in comparison to the basic configuration is obtained. The findings highlight the importance of adsorbent selection and process configuration for achieving high separation performance.

Methane enrichment for biogas purification using pressure swing adsorption techniques

Biogas is a highly potential renewable fuel source substituting fossil-based natural gas. To commercialize biomethane, biogas purification systems via selective removal of CO2 are a crucial step for the production of biomethane. Technologies based on pressure swing adsorption (PSA) are widely used and achieve promising results, such as water scrubbing, membrane separation, cryogenic processes, chemical absorption, and physical absorption. This review describes the potential of PSA as a technology to separate CO2 from biogas to purify biomethane. PSA is an efficient technology for biogas purification having a low energy penalty, low cost and a safe operation. Nowadays, different biomethane purification technologies are operated, such as cryogenic separation, membrane operations and absorptive separation. The PSA process, as one of the main technology, and its concepts are described. Then, the main process engineering approaches for efficient biogas purification are analyzed. Different adsorbents are compared and key process performance variables are evaluated. Next, the results of different studies on adsorption materials and the yield of real examples as well as the current research trends and improvement potentials are presented and discussed.

Integrated vacuum pressure swing adsorption and Rectisol process for CO2 capture from underground coal gasification syngas

An integrated vacuum pressure swing adsorption (VPSA) and Rectisol process is proposed for CO2 capture from underground coal gasification (UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly designed to pre-separate and capture 74.57% CO2 with a CO2 purity of 98.35% from UCG syngas (CH4/CO/CO2/H2/N2 = 30.77%/6.15%/44.10%/18.46%/0.52%, mole fraction, from Shaar Lake Mine Field, Xinjiang Province, China) with a feed pressure of 3.5 MPa. Subsequently, the Rectisol process is constructed to furtherly remove and capture the residual CO2 remained in light product gas from the VPSA process using cryogenic methanol (233.15 K, 100% (mass)) as absorbent. A final purified gas with CO2 concentration lower than 3% and a regenerated CO2 product with CO2 purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·kg–1 of the single Rectisol process to 1.008 MJ·kg–1 of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO2 capture from UCG syngas. Additionally, the high-value gas (e.g., CH4) loss can be decreased and the effects of key operating parameters on the process performances were detailed.

Computational-cost-efficient surrogate model of vacuum pressure swing adsorption for CO separation process optimization

We present a computational-cost-efficient surrogate model to optimize the separation of carbon monoxide (CO) from steel-mill off-gas when adsorbent material and the vacuum pressure swing adsorption process are used. We use a mathematical model to generate the full-factorial design data points, then use them to train, validate, and test the surrogate model, which we then use to suggest the best prediction algorithm for CO separation. The extra-tree regressor was selected by considering the test R2 score, and purity and recovery were well predicted (R2 = 0.999 for both). The optimized condition was 3.94 bar for the adsorption, and 0.05 bar for the desorption, which gave 99.99% purity and 71.3% recovery. Analysis of cost sensitivity of electricity price and CO selling price showed how the optimal conditions were moved from the base case; these results were consistent with the phenomenological knowledge which favors a large difference in pressure between the adsorption and desorption steps. Also, Pareto-front solutions of the productivity and purity implied that compared to a previous study, the productivity can be increased by 9.4% when the target purity is 90%, and by 7.5% when it is 99%.

Adsorbents selection for the enrichment of low-grade methane coal mine emissions by temperature and pressure swing adsorption technologies

This work evaluates the feasibility of common adsorbents (carbonaceous materials, zeolites and metal-organic frameworks) for the adsorption and further methane upgrading of the ventilation air methane (VAM) emissions from underground coal mining (0.57% CH4). Concentration was achieved by adsorption through two different operational procedures based on fixed bed configurations: temperature swing adsorption (TSA) and pressure swing adsorption (PSA). All the combinations have been simulated using a rigorous mathematical model implemented in a commercial simulation package. The main purpose is to evaluate the performance of the different combinations of adsorption technique and adsorbent material, as well as establishing a valid mathematical model able to test a wide range of materials. The comparison has been fulfilled with an economic evaluation of the different combinations. Results show that carbonaceous materials provide the highest concentration factors (C/C0 = 5), with low total methane recoveries (30%) and the lowest cost per kmol of methane recovered (1.5 €/kmol). MOFs can retain substantial amounts of methane, but with lower CH4/N2 selectivities than carbonaceous materials and lower methane concentration factors (C/C0 = 2.6). For this type of materials, a high recovery of methane is achieved, but at expense of the highest costs (80 €/kmol). Finally, zeolitic materials present the lowest methane concentration factor (C/C0 = 2), with intermediate both methane recoveries (58%) and costs (25 €/kmol). Concerning the adsorption technique, TSA has shown higher final methane concentrations for carbonaceous materials and some MOFs, whereas PSA overperforms for zeolitic materials. In addition, TSA is cheaper in all cases than PSA processes. On the other hand, PSA allows higher total methane recoveries and adsorption capacities for all materials, highlighting the high dependence on adsorption pressure, especially in carbonaceous materials (PSA/TSA = 18.3, in the case of Maxsorb).

Vacuum pressure swing adsorption for producing fuel cell grade hydrogen from IGCC

In this work, a vacuum pressure swing adsorption (VPSA) process was developed for the fuel cell grade hydrogen purification from H2-rich syngas of an integrated gasification combined cycle (IGCC) plants, where activated carbon, 5 A zeolite, and Cu(I)AC were used as adsorbents. Two kinds of cycle configurations were proposed and evaluated to achieve a higher process performance based on ten bed VPSA process. Meanwhile, the effects of key operating parameters on the performance of the VPSA process with different cycle configurations were investigated. The results demonstrated that the impact of argon content in the feed gas on the process performance was significant, and the hydrogen purity in the light product stream would decrease from 99.9902% to 99.9119% when the argon content in feed gas varied from 1000 ppm to 10,000 ppm. Moreover, the cycle configuration 2 of VPSA process with a receive purge step achieves much better process performances compared with the cycle configuration 1 of VPSA process just with a blowdown step and vacuum step. Although the energy consumption of cycle configuration 2 is approximately 2–3 times that of cycle configuration 1, it's close to 90% hydrogen recovery and high productivity make it more competitive.

Optimization and Recovery of a Pressure Swing Adsorption Process for the Purification and Production of Bioethanol

Today, there are new technologies to produce bioethanol: one of them is the Pressure Swing Adsorption (PSA) process. This process has displaced other separation technologies due to the use of natural adsorbents and its methodology to obtain high purities with a lower energy cost. The aim of this work focuses on the optimization of the PSA process (experimental case) to obtain a higher recovery and production of bioethanol using lower energy consumption. The results are favorable since the energy cost is reduced to a range of 60% and 62%, obtaining purities above 99% wt of ethanol and recovery between 75% and 77.41%. The bioethanol produced and purified in the different scenarios meets international standards to be used as a fuel or oxygenating additive.

A comparative study of multi-objective optimization with ANN-based VPSA model for CO2 capture from dry flue gas

A 3-bed-7-step vacuum pressure swing adsorption (VPSA) process was developed for carbon capture from dry flue gas with a silica gel adsorbent. The VPSA process is simulated based on a series of detailed models. This paper aims to solve the multi-objective optimization problem of the VPSA process. A trained artificial neural network (ANN) model with double hidden layers was established to optimize the process performance through the metaheuristic algorithm (NSGA-II, MOPSO, MOEA/D, and NSGA-III). Subsequently, the diversity and convergence performance of the metaheuristic algorithm were analyzed and compared. The optimization results show that on the one hand, the purity of CO2 could reach 80.94% with recovery of 90.61%; and on the other hand, the productivity could reach 0.5233 mol/h/kg with energy consumption of 1004.14 kJ/kgCO2 with the constraint of 70% purity and 90% recovery. The results indicate that, the ANN model can predict the performance metrics and dynamic performance of the VPSA process with very high accuracy. Meanwhile, the NSGA-II can obtain a comprehensive set of trade-off alternatives from different optimization problems, which can be used as a powerful reference for the operation of the carbon capture process.

Simulation and State Feedback Control of a Pressure Swing Adsorption Process to Produce Hydrogen

One of the separation processes used for the production and purification of hydrogen is molecular sieve adsorption using the Pressure Swing Adsorption (PSA) method. The process uses two beds containing activated carbon and a sequence of four steps (adsorption, depressurization, purge, and repressurization) for hydrogen production and purification. The initial composition is 0.11 CO, 0.61 H2, and 0.28 CH4 in molar fractions. The aim of this work is to bring the purity of hydrogen to 0.99 in molar fraction and implement controllers that can maintain the desired purity even in the presence of the disturbances that occur in the PSA process. The controller design (discrete PID and state feedback control) was based on the Hammerstein–Wiener model, which had an 80% fit over the rigorous PSA model. Both controllers were validated on a virtual plant of the PSA process, showing great performance and robustness against disturbances. The results obtained show that it is possible to follow the desired trajectory and attenuate double disturbances, while managing to maintain the purity of hydrogen at a value of 0.99 in molar fraction, which meets the international standards to be used as a biofuel.

Simulation and optimization of VPSA system based on pseudo transient continuation method

AbstractIn order to address the challenge of optimization of pressure swing adsorption systems, an optimization framework based on pseudo transient continuation method was used and a corresponding library with several models was established for simulation of more complex processes. Then, two vacuum pressure swing adsorption processes for oxygen and nitrogen production were considered as case studies and the results based on the single discretization and pseudo transient method were compared and analyzed in detail. Besides, a new strategy was proposed for the stability and efficiency of simulation. Finally, reduced successive quadratic programming and time relaxation algorithm were used for the optimization of the two systems, respectively, and the results showed that the time relaxation algorithm based on the pseudo transient framework has a strong advantage in saving optimization time cost compared with the former.

Intensification of Temperature Swing Adsorption

Temperature swing adsorption (TSA) is an energy intensive process as it needs heat for regenerating the adsorbent bed. Beds are regenerated and saturated simultaneously and are used cyclically. While one bed is undergoing adsorption, other is regenerated and vice versa. Regeneration of bed can be carried out by changing pressure or temperature. Former is called pressure swing adsorption (PSA) and later TSA. Heat is supplied for regeneration to desorb the impurities. Temperature required to regenerate the gas is high. Cycle time can be reduced and the process can be intensified by facilitating faster heat transfer in the bed. Normally the heat transfer coefficient of the adsorbent material is low which affects the cycle time. Better heat transfer can be obtained by increasing the heat transfer through packing by adding metal wires, strips or composite materials. Thus, metal fillings with good conductivity can be used in the bed. Technologies like TEPSA (Thermally Enhanced Pressure Swing Absorption) and TPSA (Temperature Pressure Swing Absorption) are developed for air pre-purification. TEPSA is a PSA process and TPSA is a TSA process. TEPSA is improved by addition of heat while in TPSA, adsorbate is removed by unheated regeneration gas. It is possible to make 20-60% power savings by moving to a TPSA cycle compared to TSA system. TPSA reduces not only cost of vessel but also pipe work involved in process. TPSA has a major advantage which is, without decreasing cycle time, thermal energy can be saved. This article explores various methods for intensification of Temperature swing adsorption. By combining advantages of pressure and temperature swing adsorption, solution to the problem of high energy demand and cycle time can be obtained. Proper selection of adsorbent material can be helpful in building economic process. Selection of adsorbent materials is based on various factors like cross-sectional area, strength, chemical inertness, etc. of the adsorbents. For TSA, thermal properties of adsorbent materials become significantly important while selecting the adsorbent.

A Review of Numerical Research on the Pressure Swing Adsorption Process

The pressure swing adsorption (PSA) process has been considered a promising method for gas separation and purification. However, experimental methods are time-consuming, and it is difficult to obtain the detailed changes in variables in the PSA process. This review focuses on the numerical research developed to realize the modelling, optimization and control of the cyclic PSA process. A complete one-dimensional mathematical model, including adsorption bed, auxiliary devices, boundary conditions and performance indicators, is summarized as a general modelling approach. Key simplified assumptions and special treatments for energy balance are discussed for model reliability. Numerical optimization models and control strategies are reviewed for the PSA process as well. Relevant attention is given to the combination of deep-learning technology with artificial-intelligence-based optimization algorithms and advanced control strategies. Challenges to further improvements in the adsorbent database establishment, multiscale computational mass transfer model, large-scale PSA facility design, numerical computations and algorithm robustness are identified.

Application analysis of layered pressure swing adsorption method for offshore floating natural gas purification

In view of the particularity of offshore operations, a new layered pressure swing adsorption (PSA) method for natural gas purification was proposed. CH4 is enriched in the three-component CH4/CO2/N2 crude mixed gas. The pressure swing adsorption process is based on the traditional method. The adsorption bed is divided into two layers, which are the first layer with activated carbon as the adsorbent to remove CO2 impurities, and the second layer with molecular sieve as adsorbent to remove N2 impurities. The process of PSA was simulated by Aspen Adsorption software. The simulation results show that after the process of double layered PSA, the purity of the product gas CH4 reached 98.7%, and the recovery rate of gas production was 89%. The concentration of CO2 was successfully reduced to 0.23% in the activated carbon layer, and the concentration of N2 was reduced to 1.2% in the molecular sieve layer of the first Tower.