Vacuum Swing Adsorption Research Articles

Modeling and control of heating and heat circulation in direct air capture system

Direct air capture (DAC) is a critical technology for mitigating climate change. However, the high heat consumption of temperature vacuum swing adsorption (TVSA)-based DAC processes hinders its widespread deployment. This study focuses on developing a control strategy to optimize the energy efficiency of the TVSA heating phase. A novel adsorbent temperature estimation method, validated through experimental data, was integrated into a cascaded PI controller with a fuzzy gain scheduler (FGS). Experimental results demonstrate that the proposed control strategy effectively regulates the heating process, achieving a potential energy saving of up to 14%. This work contributes to enhancing the feasibility and sustainability of DAC technologies.

Analysis on temperature vacuum swing adsorption from wet flue gas carbon capture by using solid amine adsorbent with co-adsorption equilibrium models

Adsorption carbon capture has attracted extensive attention due to its low regeneration heat consumption, eco-friendly impacts and simplicity. However, there is a lack of comprehensive analysis of its energy consumption, economy and environment impact of adsorption carbon capture. This study aims to investigate the working performance using temperature vacuum swing adsorption (TVSA) from wet flue gas carbon capture utilizing co-adsorption equilibrium models for metal–organic framework (MOF) based amine materials. TVSA model is then carried out in terms of the continuous operational state, the dynamic changes in physical properties inside the bed, and the differences in properties at different positions within the bed layer. It is found that they often cannot simultaneously meet high CO2 recovery rates, productivity, and equivalent work. The analysis reveals that the optimal conditions, namely an adsorption temperature of 318 K and a CO2 component of 0.02 kmol during desorption, collectively result in reduced equivalent work and heightened productivity. The maximum productivity could reach 46.35 kg·m−3·h−1 for 5.6 v% water content and 308 K adsorption temperature. It is demonstrated that temperature vacuum swing adsorption for wet flue gas carbon capture using MOF based amine adsorbent is quite promising in terms of energy consumption and CO2 productivity in the future.

A numerical comparison of heavy‐purge and dual‐reflux strategies in pressure swing adsorption for methane enrichment

AbstractDual reflux pressure swing adsorption (DR‐PSA) has been regarded as a state‐of‐the‐art adsorption‐based process which can simultaneously obtain two streams of pure product gases with a narrow pressure window. However, the DR‐PSA has not yet been reported in industrial applications. Herein, a DR‐PSA and a heavy‐purge pressure vacuum swing adsorption (HP‐PVSA) were numerically investigated for the enrichment of 1%, 8% and 15% CH4 from N2 gas mixtures in pilot‐scale. Key separation indicators such as purity, recovery and energy cost of the two cycles were compared to analyze the limitations of the DR‐PSA process while scaling‐up. This study reveals the impact of heavy to feed (H/F) ratios on purity and recovery for both cycles and analyses the energy consumption of each process. For feed gas with 15% CH4, while DR‐PSA can achieve a slightly better purity and recovery (88.3% and 88.3%, respectively) compared to HP‐PVSA (87.5% and 80.3%, respectively), it also involves an order of magnitude higher energy consumption (181.6 versus 24.6 kJ/mol CH4 captured). DR‐PSA shows significantly superior performance than HP‐PVSA when the CH4 content in the raw feed gas is low. Under the investigated operating conditions, HP‐PVSA can only enrich 1% CH4 to 10% with 78.7% recovery while DR‐PSA can obtain 75.3% purity and 77.3% recovery. Results indicate that DR‐PSA exhibits superiority in enrichment of dilute gas, however, its high energy consumption, high capital expenditures and limitations in processing high throughput are the chief reasons hindering its industrial application.

Performance study of an electrified temperature vacuum swing adsorption cycle for post combustion carbon capture

The performance of a fully electrified temperature vacuum swing adsorption (E-TVSA) carbon capture process is investigated and compared with the performance of a VSA cycle as the reference case. A five-step process including (I) adsorption, (II) co-current heating, (III) counter-current evacuation, (IV) counter-current pressurizing, and (V) co-current closed loop cooling steps was devised and simulated. The adsorption time, electric heating power, and evacuation pressure were chosen as the independent variables for evaluating their impact on key performing indicators (KPI) of purity, recovery, productivity and energy consumption. In total 2717 cases were simulated to the cyclic steady state condition to provide 44 contours of the KPIs. From these contours it can be concluded that in E-TVSA carbon capture using 13X zeolite, a temperature rise of almost 50 degrees is necessary during the heating step, and the evacuation step should be continued to reach a pressure between 2.5 and 3 kPa. Under these conditions, a recovery and purity of more than 98 % were achieved with a production rate above 1.1 kg CO2/kg ads day and a specific energy consumption of 1.74 MJ/kg CO2 (0.61 MJ/kg CO2 for evacuation and 1.13 MJ/kg CO2 for heating). When comparing E-TVSA and VSA, it is noteworthy that the production rate and specific energy consumption of E-TVSA are in the same order as that of VSA. However, E-TVSA surpasses VSA in terms of purity and recovery rates. Further analysis of the transformation efficiency from electricity to heat revealed the transformation efficiency must be at least 50 % to keep the energy consumption below 3 MJ/kg CO2.

Exploring enhanced CO2 separation from blast furnace gas: A multicolumn vacuum swing adsorption approach with process design and experimental assessment

Excessive emissions of carbon dioxide (CO2) are a major driver of global warming. Blast furnace gas (BFG) represents a major source of CO2 emissions in the steel industry, accounting for approximately 30 % CO2 emissions among the industry sectors. Hence, effective CO2 capture from BFG is imperative. This study presents an approach utilizing the vacuum swing adsorption (VSA) technology to capture CO2 from BFG. A 6-column VSA rig was designed and constructed to separate CO2 from a simulated BFG (CO2/N2 = 20 %/80 %) using zeolite 13X as adsorbents. The VSA process involved steps of adsorption, desorption, heavy product purge, light product re-pressurization, and pressure equalization. Five different process modes, i.e., 1-column and 3-step, 2-column and 6-step, 2-column and 8-step, 3-column and 9-step, and 4-column and 16-step configurations, were implemented to evaluate the influence of various process design factors on the separation performance. Additionally, a 6-column and 36-step process was devised to conduct a parametric study of VSA cycles by varying the adsorption duration and desorption pressure. Results revealed the pivotal role of heavy product purge and pressure equalization on the separation performance. The six-column process achieved a CO2 purity and recovery of 94 % and 82 %, respectively, with a energy consumption of 0.76 GJ/tonCO2 when employing a desorption step duration of 240 s and pressure of 8 kPa. In addition, a method of process optimization based on the bed capacity ratio, C, was introduced in this study, which provides a dimensionless quantity of the utilization of the adsorption column. Moreover, capturing CO2 from BFG through the VSA cycle not only enhances its heating value but also yields substantial advantages in terms of mitigating CO2 emissions.

Design and Performance Evaluation of Multisorbent Vacuum-Swing Adsorption Processes for Postcombustion Carbon Capture

Design and Performance Evaluation of Multisorbent Vacuum-Swing Adsorption Processes for Postcombustion Carbon Capture

Upgrading low-concentration oxygen-bearing coal bed methane by dual-reflux vacuum swing adsorption

Fugitive methane (CH4) is a typical by-product of mining processes, which is commonly known as coal bed methane (CBM) or coal mine gas (CMG). The capture of these CH4 gases can simultaneously avoid greenhouse gas emissions and provide extra energy benefits. However, the explosion risk of low-concentration CBM (CH4 molar fraction ≤ 30%) requires strictly safe operating protocols to conduct the capture process. Dual reflux vacuum swing adsorption (DR-VSA) is a promising candidate with a vacuum operating condition which can lower the explosion risk and simultaneously reach CH4 enrichment and O2 removal targets in product and effluent streams. Herein, a low-concentration oxygen-bearing CBM (20% CH4, 16% O2 and 64% N2) can be upgraded to 69.7 mol% in the product gas while ensuring an effluent concentration of 2.5 mol% by the DR-VSA cycle using ionic liquidic zeolites (ILZ) as the adsorbents. A rigorous safety analysis has been conducted to investigate the explosion risk in the adsorption column and product tank, suggesting that the DR-VSA process is a safe technology for upgrading low-concentration oxygen-bearing methane.

Wood-structured carbon with reassembled pores showing high propylene adsorption rate for efficient separation of propylene/propane

Efficient separation of propylene/propane requires enhancing adsorption rates on adsorbents, while maintaining high adsorption capacity and selectivity, heavily relying on engineering pore structures within the adsorbents. Herein, we have prepared wood-structured carbon with reassembled pores by using wood frameworks incorporated with CuCl2 and a polymer coating. Upon carbonization, the wood framework transforms into microporous carbon, while the polymer coating converts into molecular sieving carbon. Notably, the evaporation of CuCl produced from the in-situ reduction of CuCl2 creates additional micropores in the molecular sieving carbon layer. This wood-structured carbon adsorbent exhibits a propylene diffusion constant of 0.011 min−1 at 0.5 bar, which is 4.1-fold higher than the sample without CuCl2. Additionally, this adsorbent shows a high propylene uptake of 2.38 mmol g−1 and a propylene/propane dynamic selectivity of up to 161 at 298 K and 1 bar. Aspen simulation suggests that a propylene purity of 99.9 % can be achieved with a 70 % recovery using a vacuum swing adsorption process. The enhanced performance is primarily attributed to the unique pore structures of the wood-structured carbon adsorbent.

Coke oven gases processing by vacuum swing adsorption: Carbon capture and methane recovery

Coke oven gas (COG), a by-product gas from the steel industry with great potential for chemical utilization, contains multiple high-value gases including H2, CO2, and CH4. Our previous work has successfully achieved hydrogen production from COG with a purity greater than 99.99 %. For further separation of COG-to-hydrogen tail gas, a two-phase vacuum swing adsorption (VSA) strategy for CO2 capture and CH4 upgrading was carried out in this study. The accuracy of the 4-bed 8-step and 4-bed 7-step cycles established in the in-house mathematical model was verified through a series of multi-component breakthrough and VSA experiments for the two-stage CO2 capture and CH4 upgrading processes employing zeolite NaY and activated carbon RB3, respectively. To achieve more excellent separation performance, several novel VSA cycles were designed and developed in terms of each stage, and the Pareto fronts of purity and recovery of CO2 or CH4 for each cycle were obtained through a multi-objective optimization framework. Based on this, the separation performance and energy consumption of the optimal cycle for each stage were parametrically analyzed under various feed gas concentrations, vacuum pressures, and feed velocities. Moreover, the CO2 product with a purity of 95.58 % and a recovery of 90.11 % can be obtained ultimately by using a 4-bed 8-step cycle for the first stage and a 4-bed 7-step cycle for the second stage of the CO2 capture process under 0.1 bar vacuum pressure. The CH4 upgrading process using a 4-bed 7-step cycle at 0.1 bar vacuum pressure produced a product with 92.07 % purity and 98.81 % recovery. The specific energy consumption was 32.17 kJ/mol and 1.80 kJ/mol for CO2 capture and CH4 upgrading, respectively. Recovery of high-purity CO2 and CH4 at such medium vacuum pressure and low energy consumption through a two-phase VSA strategy from COG has great application potential.

Optimizing medical oxygen concentrators: Efficiency, flexibility, and patient-centric solutions

Medical oxygen concentrators (MOCs) play a vital role in providing oxygen therapy to patients with respiratory diseases. This paper offers a comprehensive evaluation of different adsorbents, including 13X, LiLSX, 5A, CaX, Ag-ETS-10, and AgLiLSX, utilized in MOCs. Process modeling and multi-objective optimization are conducted to assess the effectiveness of these adsorbents using the Skarstrøm cycle, employing pressure swing adsorption (PSA), vacuum swing adsorption (VSA), and pressure vacuum swing adsorption (PVSA) processes. The optimization result indicates that LiLSX is the top choice, providing medical-grade oxygen at a total product flow rate exceeding 15 SLPM. Additionally, 13X and CaX are identified as economical alternatives, particularly suitable for employment in the PSA and VSA processes, respectively. This study highlights the significance of establishing a connection between the Medical and Chemical Engineering communities through the direct incorporation of medical performance indicators, such as the fraction of inspired oxygen (FIO2), into the optimization process. The findings serve as a guide for selecting an appropriate design based on the patient’s requirements and demonstrate LiLSX’s capability to meet a diverse range of treatments, achieving FIO2 values up to 0.75. Furthermore, we explore the flexibility of MOC designs in meeting the demands of multiple patients simultaneously and propose energy-efficient design options based on patient needs. Overall, this study provides valuable insights into optimizing MOCs, ensuring effective and reliable oxygen therapy for patients, while also addressing challenges like the COVID-19 pandemic and potential global lithium scarcity.

Lab-scale pilot for CO2 capture vacuum pressure swing adsorption: MIL-160(Al) vs zeolite 13X

Carbon capture is among the key technologies to quickly reduce anthropogenic CO2 emissions to a net zero emission by 2050. Among the different separation technologies, adsorption is one of the most promising. Several Vacuum and/or Pressure Swing Adsorption cycles have been developed and tested for CO2 capture using mainly zeolite 13X. Metal organic frameworks, due to their exceptional tunability, can improve the performance of adsorption processes. Nevertheless, there is a lack of experimental results for these materials at pilot scale. To address this gap, a versatile VPSA lab-scale pilot (3 columns of 1.1 L) has been developed to evaluate adsorbents at kilogram scale for CO2 capture in various adsorption process configurations. The metal organic framework MIL 160(Al), synthesized and shaped at 60 kg, was also studied on this installation and compared to zeolite 13X with a 3-bed 6-step VPSA cycle for the separation of a 15/85 %vol of CO2/N2 mixture between 0.1 and 2 bar. Results obtained reveal purity of 90 % and recovery of 92.7 % for the MIL-160(Al) while zeolite 13X only reaches 79.7 % of purity and 85 % of recovery, proving the efficiency of this material for CO2 capture. These results contradict conventional indicators and demonstrate the importance of testing a material in VPSA cycle at kg scale to fully assess its performance.

Balancing the Kinetic and Thermodynamic Synergetic Effect of Doped Carbon Molecular Sieves for Selective Separation of C2H4/C2H6.

Selective separation of ethylene and ethane (C2H4/C2H6) is a formidable challenge due to their close molecular size and boiling point. Compared to industry-used cryogenic distillation, adsorption separation would offer a more energy-efficient solution when an efficient adsorbent is available. Herein, a class of C2H4/C2H6 separation adsorbents, doped carbon molecular sieves (d-CMSs) is reported which are prepared from the polymerization and subsequent carbonization of resorcinol, m-phenylenediamine, and formaldehyde in ethanol solution. The study demonstrated that the polymer precursor themselves can be a versatile platform for modifying the pore structure and surface functional groups of their derived d-CMSs. The high proportion of pores centered at 3.5Å in d-CMSs contributes significantly to achieving a superior kinetic selectivity of 205 for C2H4/C2H6 separation. The generated pyrrolic-N and pyridinic-N functional sites in d-CMSs contribute to a remarkable elevation of Henry selectivity to 135 due to the enhancement of the surface polarity in d-CMSs. By balancing the synergistic effects of kinetics and thermodynamics, d-CMSs achieve efficient separation of C2H4/C2H6. Polymer-grade C2H4 of 99.71% purity can be achieved with 75% recovery using the devised d-CMSs as reflected in a two-bed vacuum swing adsorption simulation.

Process design and adsorbent screening of VSA and exchanger type VTSA for flue gas CO2 capture

Carbon capture, as a core technology for mitigating greenhouse gas emissions, the greatest challenge is the balance between separation performance and energy consumption. This study seeks to evaluate and screen the separation performance and energy consumption of four typical adsorbents (13X, Mg-MOF-74, activated carbon, and Lewatit VP OV 1065) in vacuum temperature swing adsorption (VTSA) and vacuum swing adsorption (VSA) through optimization approach, which will support in-depth research and decision-making on adsorption processes. A non-isothermal non-adiabatic numerical model was carried out to describe a novel 4-bed 10-step VTSA cycle developed on an exchange type adsorption unit (ETAU), and the model was validated by binary breakthrough and temperature swing experiments. A 4-bed 10-step VSA cycle was in turn established and investigated. Parametric analysis of the two cycles was performed by varying the operating variables including feed gas flow rate, recycle time, and purge-to-feed ratio. Process optimization of the multiplicative fraction evaluation function, simultaneously considering purity, recovery, and productivity, was achieved using a dual convergence algorithm. Results showed that all four adsorbents could achieve more than 90 % purity and recovery on the VTSA process employing the ETAU for post-combustion carbon capture, and the separation performance was substantially superior to that of the VSA cycle. Mg-MOF-74 obtained a CO2 product with 97.90 % purity, 98.48 % recovery, and 5.48 mol/kgads/hr productivity at a desorption temperature of 383.15 K; it has a specific heat consumption of 1.45 GJth/ton and a specific power consumption of 0.55 GJel/ton. The total energy consumption of 13X was slightly lower than that of amine adsorbents, giving 95.00 % purity, 97.60 % recovery, and 1.91 mol/kgads/hr productivity. Relatively low desorption temperature is expected to introduce ultra-low-grade waste heat for partial heat source substitution, contributing to the energy sustainability of adsorption carbon capture technology.

Effects of aluminium/Clay ratio on the adsorption selectivity of aluminium pillared clays for Biogas purification

Biogas, a sustainable energy source, is hampered by CO2 and N2. Commercially purifying it to biomethane involves pressure or vacuum swing adsorption. The efficiency and cost-effectiveness of these techniques pivot on the adsorption selectivity of the employed adsorbent material. This study examined the impact of varying metal/clay ratios in porous aluminium pillared clays on adsorption selectivity. Characterization techniques, including nitrogen adsorption/desorption, XRD, FTIR, SEM, and Raman spectroscopy, were employed. High-pressure adsorption capacity for CO2, CH4, and N2 was investigated up to 1000 kPa. Selectivity for CO2/CH4, CO2/N2, and CH4/N2 binary mixtures was calculated using IAST. Results indicate that changing the metal/clay ratio altered physiochemical properties, enhancing adsorption capacity and selectivity. AlPILC-4 demonstrated maximum surface area (158 m2∙g-1) and adsorption capacity (0.35–1.13 mmol∙g-1) for all gases, while AlPILC-2 exhibited the highest selectivity (11.85–1.85) at 100 kPa. The decrease in the surface area at higher metal/clay ratio apprehends to the saturation of swelling capacity of the parent clay. However, increase in the competitive adsorption with surface area resulted in a decrease in the selectivity of the samples. Working capacity of the modified samples calculated at two different regeneration pressures (100 kPa and 0.133 kPa) help comprehend the cost layout and efficiency of the prepared materials. Notably, the results mirrored the trends observed in adsorption capacity, with values nearly 200 % higher than those of the parent clay.

Rapid and Accurate Screening of the COF Space for Natural Gas Purification: COFInformatics.

In this work, we introduced COFInformatics, a computational approach merging molecular simulations and machine learning (ML) algorithms, to evaluate all synthesized and hypothetical covalent organic frameworks (COFs) for the CO2/CH4 mixture separation under four different adsorption-based processes: pressure swing adsorption (PSA), vacuum swing adsorption (VSA), temperature swing adsorption (TSA), and pressure-temperature swing adsorption (PTSA). We first extracted structural, chemical, energy-based, and graph-based molecular fingerprint features of every single COF structure in the very large COF space, consisting of nearly 70,000 materials, and then performed grand canonical Monte Carlo simulations to calculate the CO2/CH4 mixture adsorption properties of 7540 COFs. These features and simulation results were used to develop ML models that accurately and rapidly predict CO2/CH4 mixture adsorption and separation properties of all 68,614 COFs. The most efficient separation process and the best adsorbent candidates among the entire COF spectrum were identified and analyzed in detail to reveal the most important molecular features that lead to high-performance adsorbents. Our results showed that (i) many hypoCOFs outperform synthesized COFs by achieving higher CO2/CH4 selectivities; (ii) the top COF adsorbents consist of narrow pores and linkers comprising aromatic, triazine, and halogen groups; and (iii) PTSA is the most efficient process to use COF adsorbents for natural gas purification. We believe that COFInformatics promises to expedite the evaluation of COF adsorbents for CO2/CH4 separation, thereby circumventing the extensive, time- and resource-intensive molecular simulations.

Induction vacuum swing adsorption over magnetic sorbent monoliths and extrudates for ethylene/ethane separation

AbstractElectrification of adsorption processes is emerging as an adaptable solution for future gas separations. This study develops magnetic sorbent structures for use in induction vacuum swing adsorption (IVSA) process specifically designed for olefin/paraffin separation. Two sorbents, namely Fe3O4/ZIF‐7 (ethane‐selective) and Fe3O4/13X (ethylene‐selective) were developed and formulated into extrudates (Fe20/ZIF‐7‐P) and monoliths (Fe20/13X‐M), and tested under different regeneration scenarios, including simultaneous and subsequent induction‐evacuation, induction only, and evacuation only. The dynamic adsorption results demonstrated that regeneration under subsequent induction‐evacuation improves desorption rate and capability. Under this regeneration scenario, Fe20/ZIF‐7‐P achieved an ethane desorption rate of 0.24 mmol/g.min, representing a remarkable 37.5% enhancement over the induction‐only scenario. Similarly, Fe20/13X‐M exhibited an ethylene desorption rate of 0.35 mmol/g.min, indicative of a 34.2% enhancement. Moreover, the IVSA cyclic runs highlighted the excellent regeneration capability and stability of both Fe20/ZIF‐7‐P and Fe20/13X‐M with Fe20/13X‐M exhibiting ethylene purity, recovery, and productivity of 99.4%, 99.6%, and 39.9 mol/kg.h, respectively. Overall, these findings underscore the potential of the hybrid induction/vacuum process as an effective technique for achieving efficient regeneration of sorbents in olefin/paraffin separation.

Separation of hydrogen from 10 % hydrogen + methane mixtures using double-stage Vacuum Swing Adsorption (VSA)

Transportation of hydrogen by blending it into the existing natural gas infrastructure is one economical way of having a green future. After co-transportation of hydrogen this way, hydrogen deblending from natural gas is needed at various locations for different end-users. The hydrogen content in pipelines at the primary injection phase will be low (<20 %) which makes the separation challenging. The goal of the current study is to investigate the extraction of high purity hydrogen from a 10 % hydrogen + natural gas mixture using Vacuum Swing Adsorption (VSA). A four-bed VSA plant using activated carbon was used to conduct the experiments in our lab using a binary mixture of 10 % H2 + CH4 (% mol/mol). High purity hydrogen (99 %) was achieved at 102 kPa feed pressure. After validation of our simulation tool with experimental results, Aspen Adsorption software was used to assess the performance of producing 99 % hydrogen purity using a double-stage VSA process at small scale. Results revealed that achieving high-purity hydrogen using a double-stage VSA, by upgrading H2 from 10 % to 50 % in the first stage and then to 99 % H2 in the second stage leads to better separation performance and less energy consumption than a single stage VSA for the same separation target. Afterwards, a five-bed double VSA system at industrial scale was simulated using Aspen Adsorption, to produce high hydrogen purity from a representative 10 % hydrogen + natural gas mixture. High purity hydrogen (>99 %) along with high recovery (>82 %) were achieved at a feed pressure of 110 kPa.

Increasing of the unit capacity of MF process at Miike Smelter

MF (Mitsui Furnace) is a half shaft blast furnace developed by Mitsui Miike Smelter in the 1960’s to treat vertical retort residue. Currently MF mainly treats various secondary wastes (EAF dust, Secondary Fly Ash, etc.) and recovers zinc and lead as crude zinc oxide, copper and silver as matte, meanwhile other elements such as FeO, CaO, SiO2, Al2O3 are concentrated in slag.There are two steps in the MF process. The first step is pretreatment. In this process, various waste materials are blended in a certain proportion with reductant and dried adding binder in a rotary dryer, then grinded in a rod mill. The grinded materials are made into an oval briquette by briquetting machine. The second step is treatment process. The briquettes fed into the MF are smelted and reduced by blowing air through the tuyeres. By enriching the tuyere air with oxygen generated by the VSA (Vacuum Swing Adsorption) oxygen generator in 2005 and 2012, we have improved the throughput of wastes.By the improvement of oxygen enrichment in the MF, the unit capacity increased significantly. However shortage of the drying capacity in the pretreatment process became a problem. To ensure sufficient drying capacity, we installed one more rotary drier in series in 2016. Additionally in 2018, we installed a granulator after the rod mill to improve the bulk density in briquette. As a result of these efforts, the treatment amount in the whole MF process has increased.The MF can treat various kinds of materials containing various non-ferrous metal-valuables. Through these process improvements, we promote the treatment of wastes containing heavy metals and contributes significantly to the recycling of metal resources.

Ambient wind conditions impact on energy requirements of an offshore direct air capture plant

This study proposes an off-grid direct air (carbon) capture (DAC) plant installed on the deck of an offshore floating wind turbine. The main objective is to understand detailed flow characteristics and CO2 dispersion around air contactors when placed in close proximity to one another. A solid sorbent DAC design is implemented using a commercially deployed air contactor configuration and sorbent. The sorbent is assumed to undergo a temperature vacuum swing adsorption cycle. Computational fluid dynamics (CFD) is used to determine the local conditions entering each unit based on varying wind speed and angle. Two-dimensional (2D) simulations were used to determine the pressure drop through a detailed air contactor design considering the sorbents APDES-NFC, Tri-PE-MCM, MIL-101(Cr)-PEI-800, and Lewatit VP OC 106. Only APDES-NFC was explored for further analysis in the three dimensional (3D) CFD dispersion model. 3D simulations were used to model flow patterns and CO2 dispersion using passive scalars. A worst case scenario is analyzed for all DAC units in adsorption mode with fans running simultaneously. 2D simulations show an under utilization of contactor length, and quantify pressure loss curves for four common sorbents. One commercially deployed sorbent is considered for further analysis; a pressure drop of 390.62 Pa is experienced for a flow velocity of 0.73 m s−1 through a 1.5m×1.5m×1.5m contactor. Using 3D simulations, fan energy demands are computed based on flow velocities and applied pressure gradients. There is found to be a decrease in overall fan power demand as wind speed increases. High wind speeds can passively drive the adsorption process with fans shut off at certain wind directions. This occurs at an average contactor inlet velocity of 17.5 m s−1, correlating to a hub height (150 m) wind speed of 24 m s−1. Thermal energy demands are computed based on inlet CO2 concentrations entering downstream units. Thermodynamic work for desorption based on an assumed second law efficiency is compared to thermal energy for desorption computed using a simplified isotherm method, taking into account the impacts of humidity on CO2 adsorption. Going from 414.72 ppm to 300 ppm CO2 inlet concentration requires an additional 63.9 kWh (t- CO2)−1 using the 2nd law thermodynamic efficiency method and 25.9 kWh (t- CO2)−1 using the isotherm method. Contactor arrangement, wind angles, and wind speeds have a significant impact on flow patterns experienced, and resulting CO2 dispersion. High wind speeds assist in CO2 dispersion, resulting in higher inlet concentrations to downstream DAC units and decreased thermal energy requirement.

Improving energy estimation in VSA processes through integration of vacuum pump characteristics: A carbon capture case study

This study introduces a novel approach to enhance the precision of energy estimation in Vacuum Swing Adsorption (VSA) processes. To address this, a mathematical model was developed that incorporates the vacuum pump's characteristic curve, allowing for a more realistic representation of the VSA process. The model was rigorously validated against published data from a pilot plant study, where power consumption had been directly metered. Our results demonstrate that the isentropic work of gas compression, which is commonly used to estimate the evacuation energy, underestimates energy consumption by a significant factor, approximately threefold. The root cause of this divergence is the allocation of efficiency at a moderate vacuum (e.g. 20 kPa) to the entire range of evacuation pressure (below 10 kPa). A novel electromechanical efficiency factor (hereafter ηEM) that accounts for transforming power to the required shaft work was introduced. This factor, which incorporates vacuum pump characteristics into the calculations, not only rectifies the underestimation in energy consumption but also serves as a tool to evaluate the impact of the vacuum pump type on process performance.