Gas-liquid Absorption Research Articles

Mass transfer of gas–liquid two‐phase flow in asymmetric parallel microchannels with liquid feed splitting

AbstractDue to size limitations, the gas–liquid absorption capacity of a single microchannel is limited, making it difficult to achieve large‐scale CO2 capture. Therefore, the parallel microchannels combining the advantages of high efficiency and large throughput stand out. However, when the operating condition is high gas–liquid flow rate ratio, the liquid phase between bubbles almost disappears after multiple distributions, which affects the amount of gas–liquid absorption. In this study, the numbering‐up of the asymmetric parallel microchannels in the gas–liquid absorption process was investigated by splitting the liquid feed stream in two. The flow patterns under different operating conditions were obtained. The flow and distribution of gas–liquid two‐phase flow were investigated, and the reason of the distribution deterioration caused by appearance of long slug bubbles was explained by the pressure drop distribution. The total liquid mass transfer coefficient and bubble residence time were derived and obtained, and the mass transfer was further discussed.

Understanding the performance of membrane for direct air capture of CO2

AbstractDirect air capture (DAC) of CO2 is becoming increasingly important for reducing greenhouse gas concentrations in the atmosphere. However, the cost and energy requirements associated with DAC make it less economically feasible than carbon capture from flue gases. While various methods like solid sorbents and gas–liquid absorption have been explored for DAC, membrane processes have only recently been investigated. The objective of this study is to examine the separation performance of a membrane unit for capturing CO2 from ambient air. The performance of a membrane depends on several factors, including the composition of the feed gas, pressure ratio, material selectivity, and membrane area. The single‐stage separation process with the co‐current flow and constant permeability flux model is evaluated using a commercial module integrated with a process simulator to separate a binary mixture of carbon dioxide and nitrogen to assess the sensitivity of selectivity on purity and recovery of CO2 in permeate, and power requirement. Additionally, three levels of CO2 reduction from the feed stream to the retentate stream (25%, 50%, and 75%) are studied. A trade‐off between purity and recovery factor is observed, and achieving high purity in permeate requires high concentration in the retentate.

Intensification of absorption rate of carbon dioxide and ammonia in a simulated packed (Stephens–Morris) column using pulsed gas phase under optimized parametric conditions

BackgroundReducing gas emissions is a significant challenge in our ecosystem. Gas-liquid absorption is used in chemical industry to remove components from gas streams. Stephens–Morris tube, known for liquid-liquid and gas-liquid systems, has gained attention for gas absorption columns utilizing disc-shaped packing elements to improve mass transfer by creating tortuous flow path. MethodsThis investigation focuses on physical absorption of CO2 and NH3 in gas-liquid systems based on various process parameters vis. liquid flow rate (0.24–0.60 L/min), gas flow rate (6–60 L/min), pulsation frequency (0–9.06 Hz), pulsation amplitude (0–26 mm), effect of solute gas concentration (0–100 %), and effect of varying the number of discs in the disc column (15, 20, 25, 33). Response Surface Methodology (RSM) was used to predict maximum absorption efficiency under optimized conditions. Significant FindingsPulsation frequency and amplitude proportionally increased absorption coefficient, while liquid flow rate affected it differently in pulsed and unpulsed absorption. In gas film-controlled system, mass transfer coefficient was proportional to the gas flow rate. RSM yielded R2 of 0.975 while relative error and dwill was 0.097 and 0.96, respectively. Understanding system characteristics and operations at optimal pulsation frequencies and amplitudes can maximize absorption effectiveness, particularly for low-solubility gases dominated by liquid phase resistance.

Upscaling of dispersion in gas-liquid absorption on an inclined surface.

We extend the Taylor-Aris dispersion theory to upscale the gas absorption into a viscous incompressible liquid flowing along an inclined surface. A reduced-order model of advection-dispersion-reaction is developed with the aid of Reynolds decomposition and cross-sectional averaging techniques. The upscaled model allowed evaluation of the dispersion, advection, and absorption kinetics as a function of the Peclet number (Pe) and the Damköhler number (Da). The transport and kinetics parameters for the limiting cases of nonabsorption and absorption dominant are also evaluated. The upscaled model is solved analytically, and the obtained solution is used to evaluate the upscaled mass transfer between the gas and liquid. The results for the overall Sherwood number identify three regions: (i) advection dominant, (ii) transition where both advection and absorption play a role, and (iii) absorption dominant. The scaling relation between the Sherwood number (Sh) and the Da for the last region was determined to follow Sh∼Da^{1/2}. It is also revealed that in the first two regions, the Sherwood number versus the Peclet number exhibits a bell-shaped (or Gaussian) behavior, suggesting an optimal Pe that maximizes mass transfer between gas and liquid in these regions. The model and insights presented have the potential to be applied in a wide range of industrial separation processes involving the interaction of a gas exposed to a liquid flowing downward on an inclined surface under gravity.

Insight into the enhancement effect of amino functionalized carbon nanotubes on the H2S removal performance of nanofluid system

By constructing nanofluid system, trace functionalized nanoparticles can significantly enhance the absorption performance of basic liquid. In this work, amino functionalized carbon nanotubes (ACNTs) and carbon nanotubes (CNTs) were introduced into alkaline deep eutectic solvents to build nanofluid systems and used for the dynamic absorption of H2S. The experiment results showed that the introduction of nanoparticles can significantly enhance the H2S removal performance of original liquid. When performing H2S removal experiments, the optimal mass concentrations of ACNTs versus CNTs were 0.05 % and 0.01 %, respectively. The characterization showed that the surface morphology and structure of the nanoparticles unchanged significantly during the absorption-regeneration process. A double mixed gradientless gas-liquid reactor was used to explore the gas-liquid absorption kinetics characteristics of the nanofluid system. It was found that the gas-liquid mass transfer rate increased significantly after the addition of nanoparticles. The highest total mass transfer coefficient of the nanofluid system of ACNTs was increased to more than 400 % of the value before the addition of nanoparticles. The analysis showed that the shuttle effect and hydrodynamic effect of nanoparticles play important role in the process of enhancing gas-liquid absorption, and the amino functionalization enhanced the shuttle effect of nanoparticles significantly.

Green hydrogen production from decarbonized biomass gasification: An integrated techno-economic and environmental analysis

Biomass gasification represents an effective and promising conversion technology to different energy carriers/chemicals. Biomass gasification with CO2 capture will give an energy conversion system with negative CO2 emissions. This work assesses the techno-economic and environmental implications of decarbonized green hydrogen generation using the biomass gasification. Several pre-combustion decarbonization technologies were evaluated: chemical and physical scrubbing (absorption), membrane, hybrid membrane - chemical scrubbing. All evaluated biomass gasification concepts have 300 MW hydrogen output (corresponding to 100,000 Nm3/h hydrogen with purity above 99.95% vol.) with 90% carbon capture rate. Different system engineering tools were employed for the integrated assessment. As an important novelty outcome of this work, the green hydrogen production from decarbonized biomass gasification has promising potential to deliver high energy conversion efficiency (in the range of 57–59%), lower energy and cost penalties for decarbonization (about 2.2–3.5 net points), negative carbon emissions (considering that the primary fuel - biomass - is of renewable source). Among various assessed decarbonization technologies, the membrane system shows better techno-economic performances than the gas-liquid absorption (e.g., reduced CAPEX and OPEX by 7% and 7–9% respectively, inferior hydrogen production cost by about 7% etc.).

Liquid-bridge flow on a vertical spiral spring and its mass transfer characteristics

Spiral liquid-bridge flows have significant potential for mass transfer and reactions. However, the spiral liquid-bridge formed by a circular-section spiral pipe column exhibits poor flow performance. Based on the characteristics of the liquid-bridge flow between the plates, the cross section of the spiral spring is optimized to be rectangular. We studied the hydrodynamic properties and mass-transfer performance of a liquid-bridge flow in detail. The flow pattern of the liquid-bridge was observed, and hydrodynamic data were measured. The results showed that the optimized spiral spring residence time and gas–liquid contact area increased. In the gas–liquid absorption experiment, the liquid mass-transfer coefficient, mass-transfer unit height, and pressure drop of the spiral spring were measured. The results showed that the spiral spring exhibited an excellent mass-transfer effect and a low pressure drop. In the experiment on CO2 capture by MEA, good performance was observed.

A new reactive absorption model using extents of reaction and activities. I. Application to Alkaline-salts-CO2 systems

CO2 absorption into basic aqueous solutions is widely used for CO2 separation from gas streams (e.g., for natural gas purification). CO2 loading and ionic strength increase significantly along industrial columns. In absorption modelling, deviation from ideality should then be considered. This study implements a general steady-state model for reactive gas–liquid absorption. Firstly, equilibrium relations, Nernst-Planck diffusion fluxes and reaction rates are written based on activities. Secondly, local fluxes are related by stochiometric constraints through extents of reaction. In a first case study, the model, together with an appropriate thermodynamic representation, was applied with the stagnant film theory (Whitman, 1923) to alkaline salts-water-CO2 systems. The following Arrhenius expression was found for the direct kinetic constant of reaction CO2 + HO– ↔ HCO3–: ln k (m3 mol−1 s−1) = 19.84–5248.8/T (K) – 12% overall AAD. This kinetic law can be used in any system involving this reaction (e.g., aqueous amine solutions). This part I paves the way to the further study of CO2 absorption into aqueous amine solutions.

Gas absorption in reactive solutions: Adapted instrumentation of a stirred cell for kinetic study and application to CO2/amine systems

The elimination of impurities from natural gas (water, CO2, H2S, mercaptans) is an obligation: in Europe, a max. of 20 mg/Sm3 in total sulfur (at 15°C and 1 atm) is allowed, as well as 2.5 vol% in CO2. It maximizes the calorific value of delivered gas and limits chemical risks (corrosion, toxicity) associated with this transition fuel to cleaner energy sources. Acid gas separation is commonly performed by reactive gas-liquid absorption. Raw gas and absorptive solution are brought into counter current contact in an absorber at 40-80°C and 30-80 bar. Then the acid-gas loaded solvent is sent to a stripper where acid gas desorption from the solvent takes place at T between 105 and 140°C and P ≤ 2.5 bar. The solvent is an aqueous base (e.g., amine) solution. A good solvent has a high reactivity with the dissolved gas during absorption and a low regeneration energy, hence the advantage of mixtures of two amines. Here we study an aqueous solution of a small amount of piperazine (PZ) added to methyldiethanolamine (MDEA). PZ reacts faster with CO2 than MDEA, and the major reaction product with CO2 is the hydrogen carbonate ion HCO3-, which lowers the solvent regeneration duty. This work aims at characterising the kinetics of the absorption of CO2 in an aqueous solution of MDEA-PZ. Indeed, no consensus has been found on the reaction mechanism of CO2 in this amine mixture; the synergies between MDEA and PZ observed in the literature remain poorly explained. However, its knowledge is essential to optimize solvent formulation and industrial unit design.

Hydrodynamics and mass transfer performance of gas–liquid microflow in viscous liquids

Mass transfer performance is markedly improved in microchannels compared with traditional gas–liquid chemical devices. The residence time is a crucial parameter for determining the mass transfer performance. However, investigation of the residence time in gas–liquid absorption systems remains insufficient, especially in viscous gas–liquid systems with obvious flow non-uniformity between the two phases. Herein, the microscale gas–liquid flow and mass transfer performance in viscous liquids (9.0–55.4 mPa·s) based on the true residence time are investigated. Owing to the broad operating conditions of the gas–liquid flow ratio (0.2–6.7), both Taylor flow and bubbly flow patterns were observed. The results show that the bubble velocity gradually decreases to the minimum value with increasing flow distance in the Taylor flow pattern owing to gas absorption. Subsequently, bubble velocity gradually increases under the bubbly flow pattern, and the dominant factor of bubble velocity is pointed out. The true bubble residence time initially increases and then gradually decreases compared to the superficial time as the gas holdup decreases, based on the superficial velocity using the initial flow rates. The transition point occurs at a gas holdup of 0.2. In addition, the turning point of the different rules of the pressure drop occurs at a gas holdup of 0.5. Finally, a new dimensionless equation was proposed to predict the mass transfer coefficient and reveal the equation differences between low- and high-viscosity liquids. This work enriches the understanding of microflow characteristics and mass transfer performance in viscous solutions and provides a reliable guide for microreactor design.

Utilization of steel slag as a highly efficient absorbent for SO2 removal at coal-fired power stations

• Steel slag was tried in wet flue gas desulfurization using a bubbling-bed reactor. • Kinetics of SO 2 absorption in steel slag slurry was studied. • The maximum SO 2 absorption capacity of the steel slag is 0.68g/g. • The Mn 4+ , Fe 3+ and Mg 2+ in steel slag promote the oxidation of SO 2 into SO 4 2− . • Mechanism of SO 2 absorption in steel slag slurry was also revealed. In this study, steel slag, a waste generated from steelmaking processes, was used as an absorbent for the removal of SO 2 in coal-fired flue gas. The results showed that SO 2 could be removed completely in the bubbling-bed reactor by the steel slag slurry under certain operating conditions. Effort was then made to study the kinetics of SO 2 absorption in steel slag slurry. It is found that the gas-liquid absorption model fits well with the experimental data and can be used to predict the SO 2 absorption process. Results also demonstrated that the maximum SO 2 uptake capacity of steel slag reaches 0.68 g, which is about 36 wt% higher than that of the traditional limestone-gypsum desulfurization process under similar conditions, while the SO 2 breakthrough time reaches the maximum of 951 min under a flow rate of 420 mL/min, an initial SO 2 concentration of 700 ppm, and a solid-liquid ratio of 1.5 g/100 mL. Moreover, it was found that SO 4 2− , was the main anions detected in the liquid phase after desulphurization and the pH of the solution decreased from 12.9 to 3.2. This study proved that steel slag is of the potential to replace limestone in the wet flue gas desulfurization process, which contributes to the mitigation of global CO 2 emissions and solves environmental problems associated with the disposal of steel slag.

Environmental impact assessment of post-combustion CO2 capture technologies applied to cement production plants

Decarbonizing the cement manufacturing sector presents an interesting and pressing challenge as it is one of the largest energy consumers in industry (i.e., 7%), emitting considerable amounts of anthropogenic carbon dioxide (i.e., 7%). This paper performs a technical and environmental assessment of decarbonisation of cement production through process modelling and simulation, thermal integration analysis, and Life Cycle Assessment (LCA). Integration of three post-combustion capture methods for a conventional cement plant with an annual productivity of one million tons and a carbon capture rate of 90% is evaluated in comparison to the reference case without carbon capture and storage (CCS). Mass and energy balances derived from simulations are used for the assessment of three innovative capture systems: reactive gas-liquid absorption using Methyl-Di-Ethanol-Amine, reactive gas-solid adsorption using calcium looping (CaL) technology and membrane separation. For the LCA study, a “cradle-to-gate” approach is carried out using GaBi software, according to the ReCiPe impact assessment method. The general conclusion is that integrating the CCS methods into the cement production process leads to a decrease in global warming potential (GWP) in the range of 69.91%–76.74%. Of the CCS technologies analysed, CaL technically outperforms the others as it requires 34% less coal and provides 1.6 times higher gross energy efficiency. From an environmental perspective, CaL integration ranks first, with the lowest scores in six of the nine impact categories and a GWP reduction of 76.74% compared to the baseline scenario without CCS.

Model analysis for development of piperazine activated sodium sarcosinate solutions for environmental sustainability

Model analysis for piperazine (PZ) activated sodium sarcosinate (Na-Sar) for CO2 capture and sequestration for environmental sustainability is challenging and required in-depth analysis. Here, we performed experiments and developed a model for correlating physical properties such as density, refractive index, surface tension, and viscosity of PZ activated Na-Sar for CO2 capture. Physical properties were investigated at different temperatures from 298.15 to 333.15 K and different mass fractions (w1 + w2) of aqueous blends of PZ + Na-Sar were used (0.02 + 0.10, 0.05 + 0.10, 0.10 + 0.10, 0.02 + 0.20, 0.05 + 0.20, 0.10 + 0.20, 0.02 + 0.30, 0.05 + 0.30, and 0.10 + 0.30). All physical properties decreased as temperature increased; however, as PZ in Na-Sar solutions increased, physical properties tended to increase. Refractive index, density, and surface tension showed a linear relationship, while viscosity showed an exponential behavior with the temperature. Empirical correlations were established for all measured properties as a function of temperature and solvent concentration. The correlations showed that the experimentally measured and correlated values were in good agreement. These properties are not available in the literature and are important for the designing of gas–liquid absorption systems. This work can be a useful contribution towards the global efforts to mitigate CO2 from various industrial streams.

Assessment of turbulent contact absorber hydrodynamics with application in carbon capture

Chemical gas–liquid absorption systems are one of the most employed technologies for CO2 removal from post-combustion processes, due to the high capture efficiency. This work presents a complex hydrodynamics model used to describe a novel CO2 capture technique that relies on the use of a three phase, gas–solid-liquid absorption column, in which the gas phase acts as the continuous phase, the liquid as the dispersed phase and the low-density solid particles are inert.To determine and analyze the hydrodynamic parameters of the process: minimum fluidization velocity, fluidized bed height, pressure drop, fluid retention, an air–water system was used. The developed hydrodynamics model was validated against experimental data from a pilot column (correlation coefficients above 0.97).For the study of the chemisorption process, the liquid phase consists of NaOH solution and the gas phase is a mixture of CO2 and air. The implementation of the hydrodynamic model along with the mass transfer model contributes to increasing the correlation coefficient for the outlet CO2 concentration to a value above 0.99. In this case, the increased value of the mass transfer area leads to a value up to 10 times higher of the transferred flow of carbon dioxide between the two phases, compared to regular packed bed columns.The model proves useful in the analysis of the influence of liquid phase and solid phase characteristics on the system’s performance. The results show that the capture rate is highly dependent on the fluidized bed height. Increasing the size or density of solid particles leads to a decrease in the height of the fluidized bed resulting in a 20 – 40% decrease in the carbon capture rate.

Assessment of bio-ionic liquids as promising solvents in industrial separation processes: Computational screening using COSMO-RS method

The use of organic solvents in the chemical industry for gas-liquid absorption or liquid-liquid extraction operations is still unavoidable. The search of “greener” solvents to replace fossil-based counterparts is a challenge for the scientific community. Biocompatible ionic liquids (bio-ILs) emerged as a sustainable approach for the development of greener processes. In this work, bio-ILs based on choline as common cation are evaluated as promising solvents in typical industrial separation processes such as gas absorption (refrigerants, CO2, H2S, NH3, or acetone) and liquid-liquid extraction (hydrocarbon separations, denitrogenation, desulfurization, and recovery of value-added compounds and/or contaminants from aqueous streams) by means of COSMO-RS method. Some bio-ILs show competitive behavior compared to the benchmark common ILs solvents for all the solutes evaluated. None of the solvents evaluated is predicted to form two liquid phases in aqueous solutions, so future work should be conducted on finding hydrophobic bio-ILs to perform these separations. On the other hand, bio-ILs in hydrocarbon separations by means of liquid-liquid extraction show competitive results in terms of selectivities (benzoate-based) and partition coefficients (bicarbonate-based) compared to benchmark sulfolane and common ILs previously tested.

Integration of membrane technology for decarbonization of gasification power plants: A techno-economic and environmental investigation

• Integration of membrane technology for decarbonization of gasification power plants. • Techno-economic and environmental assessment of decarbonized gasification plants. • Membrane-based CO 2 capture system increases the overall plant energy efficiency. • Membrane reduces capital cost (9%), operational cost (10%) and electricity cost (7%). • Decarbonized gasification plants are economic viable for current 75 €/t carbon tax. Membrane technology is one promising technology for CO 2 capture from industrial gases. The application of membrane system in gasification-based power plants is particularly appealing considering the elevated pressure of syngas subject to decarbonization resulting in lower energy and economic penalties for CO 2 capture. As key novelty element of this work, the membrane technology was evaluated in both alone and hybrid configuration with gas-liquid absorption in view of decarbonization of Integrated Gasification Combined Cycle power plants. Assessed decarbonized gasification-based power plant concepts produce about 450 MW net output with 90% CO 2 capture rate. An integrated techno-economic and environmental evaluation methodology (based on modelling, simulation and process integration) was applied to quantify the most important plant performance indicators. For comparison, similar IGCC designs without decarbonization feature or with decarbonization by chemical and physical gas-liquid absorption were also analysed. The overall conclusion is that the membrane technology has important techno-economic benefits in comparison to chemical and physical absorption e.g. greater overall net energy efficiency (up to about one net percentage point), lower specific capital investment costs (down to 9%), lower operational & maintenance costs (down to 10%), lower electricity production costs (down to 7%), lower CO 2 capture costs (down to 50%).

Design and analysis of Microcontroller based air scrubber using ANSYS CFD

The important part for human survival is air the and growing pollution in the environment is a major concern for mankind therefore there is a need for a device is that can remove the gaseous components in the air molecules. With the use of thermoplastic elements, gas-liquid absorption can occur. The concept of scrubber for the absorption of gases was introduced in late 1980 and with the growth of modern techniques, the gas liquids absorption and phase change is been studied for a very long time. A packed column is process equipment, and it is widely used in industries that produce toxic elements. Bed scrubber washing technique for removal of gaseous contaminants to a large extent bus stop with the use of a microcontroller for monitoring the emissions the basic idea of installing this machine in the end or environment for residential and commercial use is a need of the hour. The work relates to the design and performance of the back scrubber and the study of the practical approach results by using it in an indoor environment. The use of IoT in this process is enhancing its quality and we are adding a step towards optimizing the air pollution standards. As the government has taken a lot of efforts for halting the growth of air contaminants by implementing some loss on engine combustion so the work is innovation in the field of air pollution and control.

Enhanced gas-liquid absorption through natural convection studied by neutron imaging

Enhanced gas-liquid absorption through natural convection studied by neutron imaging

Techno-economic and environmental assessment of flexible operation for decarbonized super-critical power plants using reactive gas–liquid absorption

Reactive gas–liquid absorption is currently one of the most technological and commercial mature decarbonization solution for energy-intensive industrial applications. This decarbonization system is based on chemical absorption - desorption cycle using alkanolamine solutions. In this work, the reactive gas–liquid absorption was assessed from techno-economic and environmental perspective for decarbonization of super-critical power plants as well as to improve the plant time flexibility. The assessed coal and lignite plant concepts generate 1000 MW net output with 90% carbon capture rate. As benchmark cases, the plant designs without CO2 capture were also assessed to quantify the decarbonization energy and cost penalties. Detailed evaluations cover the following aspects: decarbonized power generation by chemical scrubbing with / without solvent storage facilities; set-up of an integrated assessment methodology; evaluation of main techno-economic and environmental performance indicators. A key novelty element of this work represents the usage of solvent storage to improve the flexibility of decarbonized power plant. Base-load operation and flexible part-load operation with lean & rich solvent storage were both evaluated to assess the flexibility impact on overall performance indicators. The time flexible solution based on solvent storage reduces the specific capital cost by about 11% and the levelized cost of electricity (LCOE) by about 7–9%.

Enhanced gas-liquid absorption through natural convection studied by neutron imaging

Heat release from absorption storage heat pump by means of absorption of water vapor into aqueous sodium hydroxide is limited by uptake kinetics affecting temperature gain, as well as power- and energy density of the method. Earlier studies pinpoint that natural diffusion alone is not sufficient to reach higher uptake rate, and that the surface to bulk exchange has to be enforced. In this paper, different technical solutions to this problem for the heat storage application are introduced and studied by neutron imaging, enabling visual observation of water vapor uptake and diffusion. The experiments brought to the fore that the buoyancy changes associated with water uptake may be utilized to markedly enhance kinetics. This concept was applied on a vertically installed spiral finned tube operating as heat and mass exchanger for the absorption storage heat pump, also referred to as sorption heat storage. By flooding the space between the spiral fin with absorbent, water absorption into the vertical surface leads to a buoyancy driven movement of the liquid, supplying unspent aqueous NaOH to the vertical surface and exchanging it with the diluted liquid. This is found to increase the rate of absorption markedly. Under realistic heat storage specific operating conditions, a temperature gain of 12.5 K, an active area specific power of 1.28 kW/m2 and an energy density of 243 kWh/m3 in respect to the volume of charged absorbent (greatest volume) is reached. It is proposed that carful design of the spiral finned tube to enhance buoyancy movement will further improve overall sorption heat storage performance.