Temperature Vacuum Swing Adsorption Research Articles

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.

Process-performance of solid sorbents for Direct Air Capture (DAC) of CO2 in optimized temperature-vacuum swing adsorption (TVSA) cycles

The process performance of three amine-functionalized chemisorbents (TRI-PE-MCM-41, SI-AEATPMS, APDES-NFC-FD-S) and two physisorbents (SIFSIX-18-Ni-β and NbOFFIVE-1-Ni) was evaluated for direct air capture (DAC) of CO2 in temperature-vacuum swing adsorption (TVSA) and steam-assisted temperature-vacuum swing adsorption (s-TVSA) cycles. Rigorous process optimizations were performed to evaluate the trade-off between energy consumption and productivity. Thermal energy consumption, with main contributions arising from desorption of CO2 and H2O, sensible heat of solids, is higher than electrical energy. While steam purge generally improves productivity at the cost of energy, an exception was noticed where it was also found to reduce energy. For the sorbents studied, minimum energy and maximum productivity ranged between 6.25–30.4 MJth/kgCO2, and 0.01–0.15 TPD of CO2/m3 of sorbent, respectively. For all the sorbents, while target CO2 purity (≥95%) can be achieved with moderate vacuum pressure (≈0.30 bar), low regeneration pressures (≈0.050 bar) can lower energy demand and increase productivity. A new ambient pressure temperature swing adsorption cycle is introduced. This cycle achieves target purities, albeit at higher energy consumption compared to those that use vacuum. The study showed that physisorbents, generally not studied for DAC, can be promising. Parametric studies revealed that the lack of multi-component thermodynamic and kinetic data impedes the objective evaluation of DAC processes.

Experimental study of CO2 capture from air via steam-assisted temperature-vacuum swing adsorption with a compact kg-scale pilot unit

Reactor design and process performance evaluation.

Design and assessment of a novel mobile carbon capture system: Energy and exergy analyses

In this work, we designed a mobile carbon capture (MCC) system that can effectively capture CO2 from the exhaust gas of diesel engines for applications in commercial vehicles. We present the results of energy and exergy analyses conducted on this system, which includes an energy recovery unit, a cooling unit, CO2 adsorption and desorption units, and a CO2 liquefaction unit. Three processes were considered to capture CO2: temperature vacuum swing adsorption (TVSA), vacuum pressure swing adsorption (VPSA), and vacuum swing adsorption (VSA). Energy is produced using turbines and generators, which supply the necessary power to run the MCC system, thus overcoming the limitation of mobile devices, i.e., lack of energy source. The energy requirement for each process was found to be in the order of VPSA > TVSA > VSA. In terms of specific energy consumption (SEC) and exergy efficiency, VSA was the most suitable process. As an MCC system, the VSA process consumes a small amount of energy in the designed system, and CO2 can be captured, liquefied, and stored by utilizing the energy contained in the exhaust gas. Because the TVSA process is expected to operate with less additional energy input, it can be used as an MCC system to improve the efficiency of each process unit. Our study can serve as a basis for advancing carbon capture technologies that can be implemented in commercial vehicles to reduce the greenhouse effect and help control global warming.

Adsorption-based post-combustion carbon capture assisted by synergetic heating and cooling

Adsorption carbon capture has shown its superiority in energy consumption and cost investment when compared with common amine scrubbing technologies. However, high regeneration energy demand of adsorbents is still a challenge for large-scale application. This paper proposes a temperature vacuum swing adsorption system integrated with auxiliary heating and cooling technology. Absorption chiller and double-stage absorption heat transformer (DAHT) are introduced from the perspective of adsorption and desorption process of CO2 capture system. Results indicate that when the duration of each step increases from 25 min to 45 min, the CO2 recovery rate decreases from almost 100 %–75.7 %, and CO2 purity increases slightly from 89.6 % to 91.1 %. Considering the temperature grade of waste heat, heat consumption of the absorption chiller assisted system is lower than that of DAHT for original and adjusted cases at a generation temperature of 58 °C. If the desorption temperature decreases from 120 °C to 100 °C, heat consumption of the absorption chiller decreases from 1.90 GJ·ton−1 to 1.76 GJ·ton−1, but the average capture capacity decreases from 306.3 ton·ton−1ad to 272.1 ton·ton−1ad. It is demonstrated that both absorption chiller and absorption heat transformer could be promising solutions to reducing the energy consumption of CO2 capture system. Absorption chiller has a priority over DAHT in regions with low temperature heat sources. Moreover, a tradeoff between adsorbent loss and heat consumption should be found when choosing the appropriate heat pump for practical application.

Amine-functionalized MIL-101(Cr) fibers for direct air capture at cold temperatures using rapid temperature vacuum swing adsorption

Given that most of the world shows annual temperatures lower than 25 °C and some regions exhibit a large diurnal temperature difference in a single day, it is desirable to explore the CO2 sorption behavior of materials not only at ambient (25 °C) but also at cooler, “sub-ambient” conditions (defined here as < 25 °C). These cold temperatures may offer advantages for DAC such as higher gas adsorption capacities and lower absolute humidity, reducing concomitant water adsorption. Here, amine-functionalized MIL-101(Cr) fibers are evaluated at cold temperatures using rapid temperature vacuum swing adsorption (RTVSA). MIL-101(Cr)/cellulose acetate fibers loaded with macromolecular amines are evaluated as practical gas–solid contactors. As spun MIL-101(Cr) fibers show desirable properties for use as structured contactors such as high permeance and low pressure drop. Breakthrough and RTVSA experiments are conducted in the presence of humidity at sub-ambient temperatures to understand the CO2 adsorption and desorption behavior of the sorbent/contactor under conditions approaching practical operation. With optimized amine loading, the PEI-MIL-101(Cr) fibers give CO2 capacities comparable to the powder form of the sorbent, as well as sharp breakthrough curves at fast flow rates (1.4 m/s superficial velocity) suggesting the system is not limited by additional mass transfer resistances under the tested conditions. RTVSA shows fast desorption kinetics (14.4 mmol of CO2/g of fiber/h) at moderate desorption conditions, at 0.1 bar vacuum with temperatures below 80 °C. The entire cycle during RTVSA finishes in ∼ 25 min with ∼ 76 mol% CO2 purity as the product in this initial, modestly optimized study.

Solar-assisted temperature vacuum swing adsorption for direct air capture: Effect of relative humidity

Direct air capture (DAC) has emerged as a promising tool to address the sizeable non-point sources of CO2 emissions. However, energy penalty of its regeneration process is extremely high due to the low CO2 concentration in the atmosphere. This paper aims to explore the potential of a temperature vacuum swing adsorption (TVSA) system for DAC which utilizes solar energy and condensation heat recovered from air conditioners. The effect of indoor environmental parameters especially for relative humidity (RH) is targeted for carbon removal processes. It demonstrates that 40% RH is the optimal value with regard to the minimum heat consumption of 12.16 MJ/kg. Then four representative cases with different energy supply methods for the regeneration processes, i.e., solar-assisted condensation heat recovery, solar energy, condensation heat, and electricity, are compared and analyzed in terms of techno-economic aspects to seek the best system configuration. The effects of various indoor environmental conditions, e.g., temperature, RH, and CO2 concentration are also counted. The results demonstrate that the levelized cost of DAC (LCOD) and the cost calculated via net present value (NPV) increase with the increased temperatures and the reduced CO2 partial pressure. Due to a tradeoff between the increased adsorption capacity and regeneration heat in the presence of water, a minimum value of economic performance could be obtained at 30% RH. It reveals a novel and cost-effective TVSA combined system for DAC, which may bring more merits to approach carbon mitigation shortly.

Improving adsorption-based direct air capture performance through operating parameter optimization

Direct air capture (DAC) of CO2 through adsorption is a promising technology for mitigating climate change, but its high cost presents a significant challenge to large-scale implementation. To address this issue, this study presents a dynamic fixed-bed model of the closed-inlet temperature-vacuum swing adsorption (TVSA) process and investigates the impact of various operating and model parameters on DAC performance via dynamic simulation. The results indicate that optimizing the durations of the adsorption and regeneration phases is crucial for improving cyclic DAC performance. Maximizing the working capacity by driving both phases towards near-equilibrium conditions generally leads to the lowest specific energy requirement (SER), while cutting the adsorption phase earlier increases the CO2 productivity. Additionally, appropriate choices of operating parameters, such as feed gas velocity and vacuum pressure, can significantly improve DAC process performance. Furthermore, placing the DAC unit in a location with favourable temperature and humidity conditions, affordable heat source, and elevated CO2 concentration can greatly enhance the process and its cost-effectiveness. These individual approaches have the potential to multiply productivity and decrease SER by increasing the working capacity, shortening the cycle duration, and minimizing the absolute energy consumption. However, optimizing the DAC process necessitates careful consideration of trade-offs between productivity, SER, and various constraints. These insights, along with the developed model, can provide a valuable basis for further advancement of DAC technology.

Temperature-vacuum swing adsorption for direct air capture by using low-grade heat

Direct air capture (DAC) is a promising carbon mitigation technology and will likely be part of extensive carbon removal portfolio. Adsorptive DAC is an appropriate option for carbon capture to utilize low-grade heat because of its desirable regeneration temperature and adaptability to be integrated with renewables. Building indoor environment with CO2 concentrations above 1000 ppm provides another suitable scenario for DAC. Herein, DAC using temperature-vacuum swing adsorption (TVSA) is presented and analyzed by integrating various low-grade heat sources in buildings. An amine-functionalized metal organic framework is selected for process simulation, and the performance is compared with those using other sorbents. It indicates that amine-functionalized material has advantages in CO2 productivity and purity. A techno-economic analysis is carried out to explore the benefit of the proposed DAC in buildings. The results show that regeneration by heat pumps at 373 K is the most competitive solution and has 176.7 $·tCO2−1 of the levelized cost of DAC (LCOD). Compared with conventional energy supply, solutions with low-grade heat utilization in buildings could achieve lower carbon intensity and increase by 5.2–25.0% in net LCOD. These results will provide practical guidelines for DAC application with lower energy penalties and costs.

Analysis on temperature vacuum swing adsorption integrated with heat pump for efficient carbon capture

Carbon capture and storage (CCS) is gathering the momentum to achieve the ultimate target of carbon neutrality. Temperature vacuum swing adsorption (TVSA) has uncovered its superiority due to large working capacity, CO2 purity and recovery rate. However, high energy demand in the regeneration process of adsorbent leads to the loss of net efficiency of coal-fired power plant (CFPP) after retrofitted. This paper initially proposes and evaluates an integrated system which is composed of an adsorption carbon capture unit (ADCCU) and a single-effect absorption heat transformer (SAHT). Then a general concept of sorption carbon capture integrated with heat pump could be introduced. Results indicates that CO2 purity and recovery rate of the integrated system vary from 91.20 % to 92.75 % and from 95.62 % to 98.11 % when flowrate range from 48 NL·min−1 to 60 NL·min−1. Under the condition of 140 °C regeneration temperature of ADCCU and 80 °C generation temperature of SAHT, exergy efficiency of SAHT achieves the maximum value of 85.28 %. Moreover, a vapor compression heat pump (VCHP) system is coupled to provide moderate temperature heat for SAHT when waste heat of CFPP is inadequate. The effect of waste heat and electricity consumed on performance of CFPP is also taken into consideration. When recovery rate is lower than 27 %, performance of the proposed integrated system is more favorable than that using steam evacuated from the turbine. It is demonstrated that heat pump assisted adsorption capture for CFPP may be a promising solution to reduce energy consumption in the near future.

Hybrid induction vacuum swing adsorption, a rapid and fully electrified carbon capture process

In this study, a fully electrified temperature vacuum swing adsorption (TVSA) was experimentally investigated for adsorbent regeneration in post-combustion carbon capture. To this purpose, consecutive adsorption/electrified-desorption steps were carried out in a fixed bed, packed with composite extrudates of 13X zeolite and Fe3O4 powder, where the heating was performed electrically via induction. Different strategies of simultaneous and sequential heating and evacuation, as well as only heating (TSA) or evacuation (VSA), were applied for adsorbent regeneration. The adsorbate loading, bed pressure, bed temperature, and mole fraction of CO2 at the outlet were chosen as performance indicators. Using only vacuum evacuation, it took 23 times longer (regeneration time) to reach a 90% regeneration level compared to the inductive TVSA process, using one minute of heating at an electrical current of 74.1 A, either before subsequent evacuation or during the beginning of this evacuation. A series of three-minute adsorption-regeneration experiments, in particular VSA and TVSA, were performed to assess the effect of omitting the long cooldown and partial bed regeneration on the subsequent adsorption steps. Over 66% of the total bed capacity could be maintained as working capacity with very short (1 min) heating and (2 min) evacuation times. These are amongst the shortest reported times for thermally assisted regeneration methods of extruded adsorbents.

Process analysis of temperature swing adsorption and temperature vacuum swing adsorption in VOCs recovery from activated carbon

• The adsorption process of TSA and TVSA for VOCs in waste gas was studied, and the parameters of process purification and recovery of VOCs were discussed. • The dynamic adsorption experiment was completed,The adsorption isotherm of benzene on activated carbon was determined. • A mathematical model was established to simulate the process of TSA and TVSA. • The initial range of the optimal hot-cold purge ratio is determined. • The influence of vacuum step on adsorption and desorption step is discussed. • Under the condition of low grade heat source, TVSA will be an environmental protection process. In order to better guide the design of industrial process for purification and recovery of VOCs, Temperature swing adsorption (TSA) and Temperature vacuum swing adsorption (TVSA) process for VOCs purification and recovery were studied systematically with activated carbon adsorbent. The adsorption and desorption behaviors of benzene on activated carbon in above two processes were investigated systematically. Effects of operating parameters on process performances were further analyzed, including as regeneration temperature, purging feed ratio and hot-cold purging ratio. The results showed that the increase of hot-cold purging ratio (HP/CP) could obtain the same regeneration effect as the increase of desorption temperature. Increasing the feed purge ratio without increasing the hot-cold purging ratio is not conducive to bed regeneration, because a large number of cold purge gases cannot utilize the residual heat of temperature wave, thus reducing the desorption effect of the cooling step on the bed. In addition, the vacuum step can enhance the regeneration ability of hot nitrogen to the bed at the same regeneration temperature, making the bed regeneration of TVSA process more thorough. Temperature in the middle and lower part of the bed in TVSA process was higher and the regeneration was more thorough. In conclusion, TVSA has more obvious advantages than TSA in terms of energy consumption, hot or cold purge volume and bed regeneration.

Process-informed adsorbent design guidelines for direct air capture

Direct air capture using solid adsorbents is a proven technology critical to reducing our net greenhouse gas emissions to zero and beyond. Currently, academic research into the technology mainly focuses on the development of new adsorbents. However, there is a discord between the adsorbent design and process performance. Many materials scientists focus on maximising metrics such as the CO2 capacity of their adsorbent. Here, we combine detailed process modelling, machine learning, and extensive global sensitivity analysis, which entails varying all of the model parameters together, on a direct air capture process to show that the dry CO2 adsorption capacity does not influence process performance for an amine-functionalised adsorbent operating in a temperature vacuum swing adsorption (TVSA) process, while it is important in a steam-assisted TVSA (S-TVSA) process. In fact, adsorption kinetics, density, and thermal conductivity are all critical attributes to obtaining a low energy penalty and reduced costs. The analysis also highlights the importance of heat transfer, directing process engineers to (alternative) adsorber designs that maximise this. By an in-depth evaluation of how process performance indicators are affected by materials properties and process operating parameters, this work provides guidance to both material scientists and process engineers towards the design of a “unicorn adsorbent” and intensified DAC processes. This will improve the performance of solid adsorbent direct air capture and help drive down the costs of this vital technology to avert the worst impacts of climate change.

The potential of direct air capture using adsorbents in cold climates.

Global warming threatens the entire planet, and solutions such as direct air capture (DAC) can be used to meet net-zero goals and go beyond. This study investigates using DAC in a 5-step temperature vacuum swing adsorption (TVSA) cycle with adsorbents' Li-X and Na-X, readily available industrial zeolites, to capture and concentrate CO2 from air in cold climates. From this study, we report that Na-X in cold conditions has the highest known CO2 adsorption capacity in air of 2.54mmol/g. This combined with Na-X's low CO2 heat of adsorption, and fast uptake-rate in comparison to other benchmark materials, allowed for Na-X operating in cold conditions to have the lowest reported DAC operating energy of 1.1 MWh/tonCO2. These findings from this study show the promise of this process in cold climates of Canada, Alaska, Greenland, and Antarctica to be part of the solution to global warming.

Thermodynamic study on two adsorption working cycles for direct air capture

• Thermodynamic performance of VPSA and TVSA cycle in DAC is explored. • Working capacity of adsorbents are determined using temperature-dependent modelling. • N 2 H 4 /Mg-MOF-74 in TVSA proves to be the best combination for DAC. • A graphical method is presented to assess the minimum separation work intuitively. Direct capture of CO 2 from air, i.e. DAC, is considered as a potential solution to address anthropogenic climate change in the near future. This work provides a comparative assessment of DAC by using five adsorbents, i.e. SIFSIX-3-Ni, NbOFFIVE-1-Ni, N 2 H 4 /Mg-MOF-74, TRI/PE-MCM-41 and DETA/PPN-6, based on equilibrium working capacity and exergy efficiency analysis. Vacuum-pressure swing adsorption (VPSA) and temperature-vacuum swing adsorption (TVSA) cycles are compared by adjusting working parameters. Adsorption temperature/pressure, desorption temperature/pressure and CO 2 concentration are analyzed. For working capacity, SIFSIX-3-Ni can achieve 1.08 mmol·g −1 at 6 mbar adsorption and 1 mbar desorption partial pressure in VPSA cycle. N 2 H 4 /Mg-MOF-74 performs the most outstanding working capacity in TVSA cycle. The results show that raising pressure of air is an unsatisfactory choice to increase working capacity due to the large amount of energy demand of compression process. Thus, TVSA is a promising process applied in DAC. When desorption pressure is 4 mbar and adsorption temperature is 25 °C, the maximum exergy efficiency among these adsorbents is 50.9% of DETA/PPN-6. Amine-modified adsorbents have an excellent performance above two metal–organic frameworks (MOFs) in most situations. These findings can provide helpful guides when choosing appropriate adsorbents and cycles for DAC.

High purity CO2 from direct air capture using a single TVSA cycle with Na-X zeolites

The capture and concentration of 0.04% CO2 from a dry ambient air stream by temperature vacuum swing adsorption (TVSA) was investigated in order to produce high purity CO2. Initial investigation into the pure gas adsorption included the determination of CO2, N2, O2, and Ar adsorption isotherms with Na-X zeolite and their fit to the temperature dependent Toth isotherm model equation. These studies allowed for the evaluation of the TVSA cycle and showed the potential of reducing the pressure and/or elevating the temperature during the blowdown step in order to produce high purity CO2. Fixed bed adsorption desorption breakthrough curves for TVSA cycle were obtained to investigate the pressure and temperature effects on the blowdown step. High purity CO2 was experimentally produced between a concentration of 99.5% and 99.96% by lowering the blowdown pressure. By controlling the blowdown temperature, the concentration of the product was increased from 99.8% to 99.95%, however with a significant loss of CO2. This effect of N2, O2, and Ar desorbing during the blowdown step with CO2 desorbing during the evacuation step is shown graphically by measuring the concentration and flow rate of the exiting gas species. The results from this study show the potential for producing a valuable product of high purity CO2 from atmospheric concentrations, which can be used in many applications, particularly ones where CO2 infrastructure does not exist or where there is a burden in utilizing a CO2 cylinder.

Energy and Cost-Efficient Temperature Vacuum Swing Adsorption Processes for CO2 Capture in a Rotating Column Reactor

Energy and Cost-Efficient Temperature Vacuum Swing Adsorption Processes for CO2 Capture in a Rotating Column Reactor

An Optimization Framework for a Temperature-Vacuum Swing Adsorption Direct Air Capture Process

An Optimization Framework for a Temperature-Vacuum Swing Adsorption Direct Air Capture Process

Correction to: Analysis of direct capture of CO2 from ambient air via steam-assisted temperature–vacuum swing adsorption

Correction to: Analysis of direct capture of CO2 from ambient air via steam-assisted temperature–vacuum swing adsorption

Process optimization of a fixed bed reactor system for direct air capture

The extraction of CO2 directly from the atmosphere (Direct Air Capture) is commonly employed using supported-amine sorbents. This adsorption technology is under rapid development with novel sorbent materials emerging and with processes being demonstrated on increasingly larger scale. Optimization of such processes requires accurate knowledge on sorbent characteristics and knowledge on how operational variables affect process performance. This study primarily focuses on the latter, where we aim to quantify the influence of operational parameters on the energy duty and CO2 productivity. In addition, we examine the influence of weather conditions on the adsorption rate. For this, we develop a dynamic model of the complete temperature-vacuum swing adsorption cycle (TVSA). This model was validated by experimental results on a kg-scale direct air capture system. The impact of selected operational variables was assessed by two-dimensional sensitivity analyses. We show that desorption temperature is preferably high, limited by the chemical stability of the sorbent material in this particular case. In addition, the sorbent working capacity should be high when opting for an optimization towards energy duty, whereas it reaches a clear optimum in terms of CO2 productivity. Finally, we conclude that weather conditions and diurnal variations can significantly affect the performance of a direct air capture process and should certainly be considered during design and operation. With these insights and the developed model, this study provides a sound basis for further process development and optimization of direct air capture using fixed bed technology combined with solid amine sorbents.