Vacuum Pressure Swing Adsorption Unit Research Articles

Techno-economic analysis of vacuum pressure swing adsorption process for a sustainable upgrading of biogas

Vacuum pressure swing adsorption (VPSA) has demonstrated promising features for the upgrading of biogas to biomethane. In this study, a biogas upgrading plant, comprised of a hybrid of an N-column VPSA unit (2 ≤N ≤ 6) with a combined heat and power (CHP) engine, was developed and its techno-economic characteristics were assessed via a mathematical approach. Moreover, the techno economic analysis was used for the state-of-the-art VPSA configuration (a sophisticated configuration) and compared with the developed hybrid process. The prominent parameters including feedstock transport, biogas production, desulfurization, drying, upgrading, combustion, and grid injection were considered in the analyses of the plant for the upgrading capacity in the range of 100–6500 Nm3/h. Sensitivity analysis of the most influencing parameters, i.e., electricity price, gas price, and feed processing revenues, was conducted for the developed models. Beside comparing upgrading cost of the sophisticated VPSA with other upgrading technologies, a detailed comparison with the best available membrane unit for biogas upgrading was conducted. The limitations of adsorption process and VPSA in reducing the upgrading cost were also investigated. The results showed that in the absence of subsidies and requirements for CO2 capture, the hybrid plant outperforms the sophisticated VPSA units. Also, higher market price of natural gas or feedstock processing revenues were necessary in order to render the plant profitable. The results showed that, at flowrates larger than 175 Nm3/h, the sophisticated VPSA unit required a lower investment cost than the membrane unit for identical outputs. The results also show that even at the most idealistic conditions in the adsorption process, the upgrading is not economically favorable without subsidies. The findings of this study shed light on the importance of process design for biogas upgrading.

Optimization of hydrogen purification from biomass‐derived syngas via water gas shift reaction integrated with vacuum pressure swing adsorption for energy storage

AbstractBiomass is one of the promising sources to produce green H2, which can be considered an energy storage medium. To produce high‐purity H2 from biomass‐derived syngas, this study implemented a two‐stage H2 purification process. In the first stage, a water gas shift reaction (WGSR) was performed to enhance the H2 concentration in the syngas. The Taguchi method was employed to analyze the influence of the operating conditions and maximize the H2 concentration in the water gas shift reaction product. The results suggested that reaction temperature is a more dominant factor for enhancing the H2 concentration than the molar steam/carbon monoxide (S/CO) ratio. In the second stage, vacuum pressure swing adsorption was employed to obtain the high‐concentration H2 using the product from the water gas shift reaction having the optimum H2 concentration. Using the adsorption pressure as the primary parameter, it was found that high H2 purity and recovery could be obtained from vacuum pressure swing adsorption operated at low adsorption pressures. Based on this study's results, the vacuum pressure swing adsorption unit's best outcome occurs during an adsorption pressure of 2 kg·cm−2 and a flow rate of 17 L·min−1. Under these conditions, 93.61% H2 purity, 31.63% H2 recovery, 4.86 mol H2·(kgads·h)−1 productivity, and 448.14 kJ·(kg H2)−1 energy consumption are obtained.

Techno-economic analysis of plastic wastes-based polygeneration processes

To address the plastic waste reduction and reutilization, three designs of mixed plastic wastes-based polygeneration processes are named Designs 1–3. Designs 1 and 2 produce MeOH and electricity simultaneously by using the cryogenic air separation unit (CASU) and the vacuum pressure swing adsorption unit (VPSA), respectively. To increase the capacity of capturing CO2, the calcium looping process (CaLP) is involved in Design 3 to produce the products of H2 and CO2 and recover waste heat for power generation. The complicated CaLP dramatically increases the total costs of Design 3, although the carbon capture ratio of Design 3 is superior to other designs. If the cumulative carbon revenue is counted into the total annual income according to the emission trading scheme, the economic evaluation shows that Design 3 has a higher net present value (NPV), or a higher internal rate of return (IRR), or a shorter dynamic payback period (DPP) than other designs.

Utilization of Two-Stage Vacuum Pressure Swing Adsorption Units for CHF3/CHClF2 Separation and Recovery

Trifluoromethane (CHF3) is a ubiquitous by-product of chlorodifluoromethane synthesis (CHClF2) and is regarded as one of the most potent greenhouse emissions. Despite the adverse effects on the environment, CHF3 is the general method of exhaust gas incineration and is used for other purposes, for example, as a coolant and in plasma etching. This project establishes a flexible and efficient two-stage vacuum pressure swing adsorption (VPSA) process to generate pure CHF3 and CHClF2 simultaneously, improving the product’s recovery rate. The first-stage VPSA unit loading activated carbon is developed to obtain CHF3 with the purity of 99%. CHClF2 of 99.5% purity is obtained from the second-stage VPSA unit with NaX zeolite. The process simulation predicts that the two-stage coupled VPSA separation system can obtain CHF3 and CHClF2 simultaneously. Under the best process parameters, the purity of CHF3, the recovery rate of CHF3, the purity of CHClF2, and the recovery rate of CHClF2 are 99, 77.71, 99.5, and 72.13%, respectively. In all, our research demonstrates that the two-stage VPSA system is a practicable and worthy prospect for research and development. In addition, it can recover and purify CHF3 and CHClF2 through an efficient and cost-effective method.

Multi-technique integration separation frameworks after steam reforming for coal-based hydrogen generation

Coal-based H 2 generation has abruptly increased in recent years. The PSA-VPSA-SC process is the matured and standard framework for H 2 purification and CO 2 capture in many existing plants, including normal and vacuum pressure swing adsorption units in series (PSA-VPSA), and shallow condensation unit (SC). However, this standard process is frequently subjected to low H 2 recovery ratio and high purification cost. In this work, H 2 -selective and CO 2 -selective membrane units, i.e. , HM and CO2M, are attempted to support the standard process and ameliorate constraints. In the beginning, HM unit is arranged after VPSA to enhance H 2 recovery from the decarbonized stream, i.e. , the PSA-VPSA-SC/HM process. As a result, H 2 recovery ratio can be enhanced significantly from 83% to 98%. In the following, VPSA is replaced with CO2M unit to reduce investment and operation cost, i.e. , the PSA-CO2M-SC/HM process. Accordingly, the specific purification cost is diminished from 33.46 to 32.02 USD·(10 3 m 3 H 2 ) −1 , saved by 4.3%, meanwhile the construction cost is falling back and just a little higher than that for the standard process. In the end, another CO2M unit is launched before PSA, i.e. , the CO2M-PSA-CO2M-SC/HM process, which could unbundle CO 2 enrichment partially from H 2 purification, and then save more investment and operation cost. In comparison with the standard process, this ultimate retrofitted process can be superior in all the three crucial indices, i.e. , recovery ratio, investment, and specific purification cost. On the whole, coal-based H 2 generation can be ameliorated significantly through high efficient H 2 -selective and CO 2 -selective membrane units.

Biomethane production by adsorption technology: new cycle development, adsorbent selection and process optimization

Gas separation by adsorption processes such as pressure swing adsorption (PSA) presents an attractive alternative for upgrading biogas to biomethane. A new vacuum pressure swing adsorption (VPSA) cycle is proposed for a unit designed to purify pre-cleaned biogas (40% CO2 and 60% CH4) in industrial conditions (feed flow rate more than 500 Nm3/h and large-volume equipment). The process simulations performed to optimize the VPSA unit consider the kinetic separation of the feed components by using an appropriate carbon molecular sieve (CMS) adsorbent having a high kinetic separation selectivity for CO2 with respect to CH4. The designed VPSA unit is composed of five columns that perform three equalization steps. Minimizing methane losses during the regeneration steps necessitates injecting part of the off-gas rich in CO2 at the bottom of the column during the production step to push the CH4 forward. The produced biomethane meets the specification (97% CH4) of grid injection purity. The developed cycle allows a CH4 recovery of 92% to be obtained with a specific energy consumption of 0.35 kWh/Nm3, thus meeting the initial requirements for industrial exploitation of VPSA technology for biomethane purification from biogas sources.

Application of metal-organic frameworks in VPSA technology for CO2 capture

One of the technologies that may find application in the reduction of CO2 emissions from both energy and other industrial plants is the adsorption method. Among all adsorption techniques, the Vacuum Pressure Swing Adsorption (VPSA), seems to be the most effective for the separation of CO2 from flue gases, because flue gas is at low pressure. The development of the adsorption method in recent years has been favoured by the intensive development of efficient adsorbents, including metal-organic frameworks (MOFs). Owing to their unique sorption properties and high selectivity, these compounds provide a chance for a considerable reduction of the adsorbent volume, should CO2 be needed to be removed from a huge volume of flue gas. In order to evaluate the possibility of using MOFs, besides zeolites and activated carbon, for CO2 adsorption in large-scale VPSA units, investigations of these compounds in bench-scale and pilot VPSA adsorption units are necessary. In this paper, its authors have carried out investigations into the use of MIL-53(Al) in a bench-scale VPSA installation.. The tests of CO2 separation from a simulated combustion gas mixture on a MIL-53(Al) and on activated carbon and zeolite 13X, respectively, have been carried out in a two-column VPSA installation, which enables adsorbent regeneration in a vacuum. The study also analyzes the effects of adsorption/regeneration time and desorption pressure on CO2 purity and CO2 recovery. The presented results provide new insights into the behaviour of MOFs in the VPSA installation.

The pilot dual-reflux vacuum pressure swing adsorption unit for CO2 capture from flue gas

The results of carbon dioxide separation from real flue gas using the dual-reflux vacuum pressure swing adsorption (DR-VPSA) technology have been presented. The mobile pilot CO2 separation plant consists of two containers: a processing container and a control container. The processing container includes a flue gas treatment section (which comprises dust removal, cooling, deSOx, deNOx, gas drying and compression units), as well as a CO2 adsorptive separation unit. The adsorption unit is made up of four fixed-bed columns, each divided into two sections, operating in a dual-reflux vacuum pressure swing adsorption mode. Two kinds of activated carbon in the total amount of 540 kg were used as the beds filling. The results from the 8-step reference process with no partition of the adsorbers into the upper and lower sections (as one-step separation process with partial product recirculation), and from the 9-step DR-VPSA process (as two-step separation process) with a division of the adsorbers are presented. In the measurement campaign three different feed gas flow rates and five different times of adsorption step were selected to assess their influence on separation results. The results show the optimal parameters of 100 Nm3/h for feed gas flow rate and 300 sec for adsorption step time for both mentioned processes. The 87.5% of purity, 44.6% of recovery, 11.4 kg/(m3 h) of productivity and 978 kWh/MgCO2 of energy demand for gas compression and vacuum evacuation in the case of optimal parameters of 9-step DR-VPSA technology were obtained. Additionally the results from measurement campaign were compared with those reported by other researchers.

Vacuum Exhaust Process in Pilot-Scale Vacuum Pressure Swing Adsorption for Coal Mine Ventilation Air Methane Enrichment

Recovery and treatment of methane from coal mine ventilation air methane (VAM) with cost-effective technologies have been an ongoing challenge due to low methane concentrations. In this study, a type of coconut shell-based active carbon was employed to enrich VAM with a three-bed vacuum pressure swing adsorption unit. A new vacuum exhaust step for the VPSA process was introduced. The results show that the vacuum exhaust step can increase the methane concentration of the product without changing adsorption and desorption pressure. Under laboratory conditions, the concentration of product increased from 0.4% to 0.69% as the vacuum exhaust ratio increased from 0 to 3.1 when the feed gas concentration was 0.2%. A 500 m³/h pilot-scale test system for VAM enrichment was built rendering good correlation with the laboratory results in terms of the vacuum exhaust step. By using a two-stage three-bed separation unit, the VAM was enriched from 0.2% to over 1.2%.

CO2 capture from flue gas by two successive VPSA units using 13XAPG

With the development of novel adsorbent material and adsorption process, adsorption technology has become a potential tool for the CO2 removal from flue gases. The reduction of carbon dioxide emissions from flue gases with two successive vacuum pressure swing adsorption (VPSA) units, using 13XAPG as the adsorbent, was investigated both theoretically and experimentally. A 3-bed 5-step VPSA process was designed to capture CO2 from flue gases, which included feed pressurization, adsorption, rinse, blowdown and counter-current purge. It was found that was difficult to achieve both high CO2 purity and high CO2 recovery by one VPSA unit when capturing CO2 from flue gases at atmospheric pressure. After the verification of one-column VPSA experiment for further concentrating CO2 stream from one VPSA unit to above 95 % purity, two successive VPSA units were designed, composed of 3-bed 5-step cycle for the first unit and 2-bed 6-step cycle for the second unit, and the effects of operating parameters on the separation behaviors were investigated by simulation. With the proposed VPSA process, a CO2 purity of 96.54 % was obtained with recovery of 93.35 %. The total specific power consumption of the two successive VPSA units was $528.39\mbox{~kJ/kg}_{\mathrm{CO}_{2}}$ , while the unit productivity was $0.031\mbox{~kg}_{\mathrm{CO}_{2}}\mbox{/kg\,h}$ .

Two-Stage VPSA Process for CO2 Capture from Flue Gas Using Activated Carbon Beads

Carbon dioxide removal from flue gas with a two-stage vacuum pressure swing adsorption (VPSA) process, which uses activated carbon (AC) beads as the adsorbent, was investigated both theoretically and experimentally. First, single-column VPSA experiments were studied for CO2/N2 separation with high CO2 feed concentration. Then, a two-stage VPSA process composed two columns for each stage was designed, and the effects of different parameters were investigated. The first-stage VPSA unit operates with a four-step Skarstrom cycle, which includes feed pressurization, adsorption, blowdown, and counter-current purge with N2. For the second-stage VPSA process, a cycle with feed pressurization, adsorption, pressure equalization, blowdown and pressure equalization was employed. With the proposed two-stage VPSA process, a CO2 purity of 95.3% was obtained with 74.4% recovery. The total specific power consumption of the two-stage VPSA process is 723.6 kJ/kg-CO2, while the unit productivity is 0.85 mol-CO2/kg·h.

Capture of CO2 from flue gas by vacuum pressure swing adsorption using activated carbon beads

Vacuum pressure swing adsorption (VPSA) for CO2 capture has attracted much research effort with the development of the novel CO2 adsorbent materials. In this work, a new adsorbent, that is, pitch-based activated carbon bead (AC bead), was used to capture CO2 by VPSA process from flue gas. Adsorption equilibrium and kinetics data had been reported in a previous work. Fixed-bed breakthrough experiments were carried out in order to evaluate the effect of feed flowrate, composition as well as the operating pressure and temperature in the adsorption process. A four-step Skarstrom-type cycle, including co-current pressurization with feed stream, feed, counter-current blowdown, and counter-current purge with N2 was employed for CO2 capture to evaluate the performance of AC beads for CO2 capture with the feed compositions from 15–50% CO2 balanced with N2. Various operating conditions such as total feed flowrate, feed composition, feed pressure, temperature and vacuum pressure were studied experimentally. The simulation of the VPSA unit taking into account mass balance, Ergun relation for pressure drop and energy balance was performed in the gPROMS using a bi-LDF approximation for mass transfer and Virial equation for equilibrium. The simulation and experimental results were in good agreement. Furthermore, two-stage VPSA process was adopted and high CO2 purity and recovery were obtained for post-combustion CO2 capture using AC beads.

Vacuum Pressure Swing Adsorption to Produce Polymer-Grade Propylene

We have evaluated the Vacuum Pressure Swing Adsorption (VPSA) technology to separate propane–propylene streams to produce polymer-grade propylene. Zeolite 4A is used as kinetic adsorbent since propylene diffuses much faster than propane. A single VPSA process is able to produce propylene with purity higher than 99.6%. However, propylene recovery is only 67% and therefore a second stage is used. In this VPSA unit, zeolite 4A with smaller crystal radius is employed to reduce kinetic limitations. The second VPSA (tail unit) produces purified propane and recovers propylene that is recycled to the feed of the first VPSA (front unit). Linking these two VPSA units allows us to produce polymer-grade propylene (PGP) recovering 95.9% of the propylene. Comparing the performance of this process with distillation, there is a significant decrease in the separation volume. However, further efforts are necessary to reduce the power consumption of VPSA which is still slightly higher than for distillation.