Gas Stream Research Articles

A mass transfer study of CO2 absorption in aqueous solutions of isomeric forms of sodium alaninate for direct air capture application

Direct air capture (DAC) of CO2 is a critical emerging technology required to achieve ambitious net-zero emissions. Aqueous amino acid absorbents are ideal candidates for DAC and this work describes the investigation of the CO2 absorption performance of sodium salts of β- and α-alaninate under relevant conditions for DAC by utilising synthetic CO2 gas streams at concentrations levels found in the atmosphere (200–600 ppm). The effects of solution concentration, temperature, gas flowrate, liquid flowrate, and dissolved CO2 concentration (i.e., CO2 loading) on CO2 mass transfer coefficients were investigated. The overall mass transfer coefficient was found to be independent of the gas and liquid flowrates, with larger values determined for β-alaninate solutions (0.75–1.16 mmol m−2 s−1 kPa−1) than that of α-alaninate (0.65–0.87 mmol m−2 s−1 kPa−1), under similar experimental conditions. The results showed that the overall mass transfer coefficient increases with increasing temperature, conversely decreasing steadily with increasing CO2 loading. The maximum CO2 loading capacity of the 5.0 M solutions was ∼10 % higher for β-alanine (0.651 mol CO2/mol alaninate) than α-alanine (0.607 mol CO2/mol alaninate) at 25.0 °C. Precipitation was found to play an important role in the CO2 absorption processes here. Interestingly, beyond CO2 loadings >0.12 mol CO2/mol α-alaninate, the 5.0 M solution of α-alaninate begins to develop precipitate(s) while precipitation in the β-alaninate solution is only initiated at much higher CO2 loadings >0.52 mol CO2/mol β-alaninate. This study provides valuable insights into the suitability of β-alanine and α-alanine for CO2 capture directly from the ambient air.

Multi-scale simulation of particle density effects on hydrodynamics in dense gas-solid fluidized beds

Gas-solid fluidization has gained prominence in chemical engineering, particularly for processes involving high-density particles. However, a notable dearth of research on the fundamental fluidization of high-density particles exists, distinct from the well-studied low-density particles. This knowledge gap presents significant challenges in designing and operating fluidized beds for such processes. In this study, we employ the CPFD scheme to comprehensively investigate how particle density affects hydrodynamics. Simulation results consistently align with experiments for pressure drop and minimum fluidization velocity, underscoring the model reliability. Importantly, typical empirical correlations for predicting minimum fluidization velocity display substantial inaccuracies, particularly for high-density particles. Additionally, we identify marked disparities in fundamental fluidization behavior between high and low-density particles, with increasing density leading to deteriorating fluidization performance, characterized by larger bubbles, defluidized regions, gas streaming, and reduced bed expansion ratios. Investigating high-density particle gas-solid fluidization systems promises valuable theoretical insights, bridging the gap between theory and practice.

Constructing oxygen vacancy-enriched Fe3O4@MnO2 core–shell nanoplates for highly efficient catalytic oxidation of H2S in blast furnace gas

The rational design of catalyst structures holds paramount significance for realizing efficient catalytic reactions. In this study, an Fe3O4@MnO2 core–shell catalyst was successfully synthesized using a facile one-pot method and applied in the selective oxidation of H2S in blast furnace gas. The introduction of the MnO2 shell suppressed the further growth and aggregation of Fe species, leading to outstanding catalytic stability. Simultaneously, abundant oxygen vacancies facilitated the adsorption and activation of oxygen, thereby enhancing H2S oxidation. Experimental results revealed that the Fe3O4@MnO2 catalyst (Fe/Mn = 4:1) displayed 100 % H2S conversion and 95.7 % sulfur selectivity at 150 °C in a humid gas stream containing O2 and CO. Remarkably, no discernible decline in catalytic activity was observed after 170 h of operation, indicating the promising industrial prospects of this catalyst. This study provides an effective strategy for designing efficient and stable desulfurization catalysts.

Study of eco-friendly static gas-solid centrifugal separator

Gas-solid separation is a common process in many industries, including transport and power engineering. A static centrifugal multivortex device has been developed for effective separating fine particles from gas streams. The work aims to numerically study the efficiency and pressure drop of the separator. It was found that a choice of the turbulence model does not affect the pressure drop. The efficiency of the static centrifugal separator is 64.3% at the input gas velocity of 7 m/s. The sloped blades located above the apertures made in the internal pipe results in the improvement of separation efficiency. Moreover, changing the slope of the blades does not affect the efficiency of the separator. The hydraulic resistance coefficient of the developed device is on average 20.6, with a Reynolds number from 11400 to 38000. The low pressure drop provides reduced energy cost, which promotes decarbonization efforts.

Microwave study of the effect of cold argon plasma on functional state of rat’s skin

The purpose of this study was a comparative study of the dielectric parameters of rat skin when treated with argon and argon cold plasma. The experiment was performed on 40 male Wistar rats divided into 4 equal groups. The first group of animals (n=10) was a control (intact). The rats of the remaining groups (n=10 in each) were treated daily with a pre-epilated area of the skin of the back (area = 1x1 cm). The duration of the course for all experienced groups is 10 procedures. Animals of the second group were treated with a non–ionized argon stream (the duration of one procedure was 1 minute), rats of the third and fourth groups were treated with argon cold plasma (1 and 2 minutes, respectively). Cold plasma generation was performed using a device using the principle of microwave ionization of a gas stream. Argon of high purity (99.99%) was used as the latter. The dielectric parameters of the skin of animals in the treated area (in control group rats – at a similar point in the back) were evaluated upon completion of a full course of exposure. For this purpose, a specialized software and hardware complex was used, providing near-field resonant microwave probing of biological tissues. It was found that the course treatment of the skin of the back of rats with gas streams with different ionization causes the formation of a specific functional-metabolic and morpho-structural response. Its character is determined by the parameters of the gas flow used: non-ionized argon significantly reduces the dielectric parameters (permeability and conductivity), and the result of the action of cold argon plasma depends on the exposure. During one-minute treatment, tissue permeability was observed to remain intact with a moderate decrease in conductivity. In the case of an increase in the exposure time to 2 minutes, the dielectric constant increased, and the conductivity remained unchanged.

Dry desulphurisation of gas streams using KCC-1 mesoporous silica functionalised with deep eutectic solvents.

Sulphur dioxide, a toxic gas pollutant, is mainly generated by the combustion of fossil fuels and the smelting of sulphur-bearing mineral ores. Removal of SO2 gas or desulphurisation can be accomplished in industries using a variety of processes; the most efficient is wet flue gas desulphurisation (FGD). However, wet FGD has challenges, such as the requirement for wastewater treatment, excessive water usage, and the necessity for chloride protective coating. Despite having a lesser adsorption capacity than wet FGD, dry FGD can efficiently remove SO2 from the effluent gas stream and avoid the issues associated with wet FGD, provided that the sorbents are modified and regenerable. An alternative dry desulphurisation strategy by using fibrous mesoporous silica (KCC-1) modified with deep eutectic solvents (DES), choline chloride-glycerol (DES1) and choline chloride-ethylene glycol (DES2) is studied in this paper. KCC-1 modified with DES1 is found to increase SO2 adsorption capacity to 4.83 mg g-1, which is 1.73 times greater than unmodified KCC-1 and twice higher than KCC-1 modified with DES2 attributed to the sorbent's high porosity. Increasing reaction temperature and SO2 concentration reduce the adsorption capacity to 1.73 mg g-1 and 2.73 mg g-1, respectively. The Avrami kinetic model and the Toth isotherm model best reflect SO2 adsorption on the modified KCC-1, indicating that SO2 molecules are adsorbed exothermically in multilayer adsorption on a heterogeneous surface through a combination of physical and chemical processes. The higher SO2 adsorption capacity of the modified KCC-1 suggests that choline chloride-glycerol can provide additional sites for SO2 adsorption in dry FGD technology.

Numerical analysis of single SC-50-800 and SC-50-500x2-x4 group centrifugal cyclones: efficiency comparison

Centrifugal cyclones are important devices used to separate solids or liquids from gas streams using centrifugal forces. They are widely used in various industrial processes and air and gas purification systems. In this work, numerical modeling and study of the efficiency of cyclones of various configurations are carried out: single cyclone SC-50-800, group cyclones SC-50-500x2 and SC-50-400x4. To conduct the study, the engineering software package Comsol Multiphysics 6.1 was used with the addition of the Flow Simulation module, specialized for modeling hydrodynamic processes. To simulate turbulent flows, the v2-f model was chosen, which is often used in the case of swirling flows. The computational experiment was carried out at a constant air flow rate of 4500 m3/h. Based on the obtained numerical data, an analysis of the effectiveness of various cyclone configurations was carried out. The results of the study show that the operating efficiency of group cyclones significantly exceeds the efficiency of single cyclones. This is confirmed by analysis of separation parameters and comparison of performance indicators of various cyclone configurations. The data obtained can be useful for the design and optimization of gas stream purification systems in various industrial and environmental applications.

Numerical studies on the propagation of iron dust flames in confinement

Iron powder is a promising alternative fuel owing to its high energy density, non-volatile combustion, and recyclability using green hydrogen. For the safe storage, transportation, and use of iron powder as a reactive energy source, the physical mechanisms behind pressurising dust flames in explosions must be understood. Here, we study the propagation of one-dimensional iron dust flames in confinement using an Euler–Lagrange framework with reflective adiabatic boundary conditions. The gas phase is described by the compressible Navier–Stokes equations, and heterogeneously burning iron particles follow the parabolic rate law for solid-phase oxidation, and diffusion-limited combustion during liquid-phase combustion. We demonstrate that the pressurisation in a closed vessel leads to an increase in unburnt gas density, decelerating flame propagation via a decrease in thermal diffusivity. Flames through dust suspensions at concentrations above the thermodynamic limit are quenched, while for concentrations near the quenching limit, flames are quenched before re-ignition. The trajectories of particles and gas parcels demonstrate that particles are strongly entrained in the gas streams, causing fluctuations in local dust concentrations. The transient evolution of flame speeds in confinement is used to inform a pressure-rise model, which predicts the time to peak pressure in a 20-L vessel with good agreement to experimental measurements. Our insights provide mechanistic understandings about dust flame propagation under pressurising conditions, particularly relevant to the informed design of explosion protection measures.

Freon-CO2-assisted purification of single-walled carbon nanotubes.

With the rapidly growing applications, efficient purification of single-walled carbon nanotubes (SWCNTs) has become one of the key problems. This paper proposes Freon-CO2-assisted purification of SWCNTs, where CO2 can oxidize the graphitized carbon layer to expose iron (Fe) impurities, while the chlorine from Freon can react with the Fe impurities to form low-boiling-point metal chlorides that can be eliminated in a gas stream. After an acid washing with a very small amount of hydrochloric acid, the last remaining metal impurities are removed and highly pure SWCNTs are produced. Compared with traditional strong-acid-oxidation purification or high-temperature-vacuum purification, this method can maintain the structure and length of the SWCNTs. Raman spectra show that an I G/I D ratio of more than 100 can be obtained. This purification method can maintain the microstructure and excellent properties of SWCNTs and provide a solution for the preparation of high-quality SWCNTs to exert their properties.

Optimization of the vinyl-monochloride recovery process for the reduction of costs and environmental impact

Reducing environmental impacts in the production processes is the focus of large industries. In the PVC production process, the loss of vinyl monochloride (VCM) through an incineration stream of inert materials is a point of attention due to emission of greenhouse gases. VCM is lost as part of the stream of uncondensed gases from the VCM recovery unit. The optimization of the VCM recovery process was carried out by modelling the industrial system and running it using a process simulator. The unit model and simulation results have been verified through plant operating data. Sensitivity analyses were performed to identify which independent variables improved the VCM condensation rate. Based on plant operating experience, three independent variables were selected and their influence on the VCM recovery flow rate was verified: pressure, composition of the input stream and utility water flow rate. After the sensitivity analysis, the plant operating pressure was selected for optimization, resulting in the additional quarterly recovery of 7.5 tons of VCM and a reduction of more than 5 tons of natural gas fuel, that is, an annual reduction of 23 tons of fuel, which represents 53 tons of CO2eq. Overall, the annual savings amount to US$15,000, US$1,060 by reducing the consumption of fuel gas alone. Therefore, by ensuring greater VCM recovery, competitiveness improves by reducing production costs, and greenhouse gas emissions are reduced due to the decrease in gas incineration.

Bibliometric Analysis of the Modelling of LowQuality Biomass Pellets Combustion

Abstract Diversification of energy resources is a current objective that several countries want to achieve, including in northern Europe. Demand for wood fuels is increasing in Latvia, which is reflected in consumer expenditure. Using low-quality biomass (LQB) to produce fuel pellets for market stabilisation and diversification is possible. LQB pellets can theoretically and practically be used in low-capacity solid fuel boilers to provide different types of individual heating systems with an alternative energy source. Before starting mass production of LQB fuel pellets, it is necessary to clarify the properties of the raw materials. Any fuel study shall be divided into two phases: determination of the parameters of the fuel or raw material (calorific values, moisture content, and ash content) and analysis of the combustion process. The combustion process can be studied in two ways: experimentally and by mathematical modelling. Knowing the parameters that would need to be clarified during the study of the LQB fuel pellets combustion process (thermodynamics, gaseous emissions, particulate matter emissions, bottom ash, and slag), the authors have set the goal of clarifying the software applied to mathematical modelling of these parameters. A bibliometric analysis method was chosen to identify the software. The bibliometric analysis was carried out in the Scopus database. As a result, two software were identified: ANSYS Fluent software is suitable for modelling thermodynamic processes and gaseous emission streams. At the same time, XDEM software is the most suitable for modelling particle streams and ash/slag generation. This software will be used in future studies.

Latest technological advances and insights into capture and removal of hydrogen sulfide: a critical review

Hydrogen sulfide is an extremely toxic, poisonous and flammable gas often found in natural gas streams and crude oil reservoirs.

Deformation and aerobreakup of RP-2 droplets from hypersonic shock waves

The shock-induced atomization and burning of liquid fuel droplets are paramount for hypersonic propulsion and detonation-based combustion systems. The present work experimentally explores the atomization and aerobreakup of liquid RP-2 droplets in a hypersonic shock tube. The shock tube is operated with normal shocks propagating between Mach 5–10 interacting with RP-2 droplets with diameters between 200 and 300 µm. The droplet deformation and breakup dynamics are characterized by ultra-high-speed 5 MHz shadowgraph imaging diagnostics. For all hypersonic shock-droplet interactions, the droplets first undergo structural deformations with subsequent breakup occurring from a shear-stripping mechanism along the periphery of the droplet. The structural changes and droplet deformation rate are found to be self-similar among all cases, and the rate of deformation collapsed to a unified non-dimensional timescale. The complete breakup time of the fuel droplets were analyzed, and theoretical scaling arguments were used to quantify the effects of the Mach number, Weber number, and Ohnesorge number. The experimental data is then used to develop a modified boundary layer stripping model to estimate the breakup time of liquid drops. The model leverages the concept of displacement and momentum thickness to provide a numerical solution to estimate droplet breakup times when exposed to a high-speed gas stream. The model is compared to the experimental RP-2 data and water data available in the literature. The model predicts the breakup time for a range of droplet sizes between 200 and 2000 µm within a reasonable accuracy. The results can be used to optimize liquid fuel injection for hypersonic and detonation-based combustion systems.

Скоростные напоры и их соотношения за стационарными маховскими конфигурациями ударных волн, распространяющихся в потоке газа

We analyzed the parameters of gas streams, which form after the triple shock configurations occurring in Mach reflection with normal Mach shock (so called stationary Mach configuration). We suppose that this stationary Mach configuration moves in a counter flow with arbitrary velocity (and corresponding Mach number). Analyzing relations of the dynamic pressures across the contact discontinuity, which emanates from the triple point of the Mach reflection, we have shown that the streams after the triple shock configuration differs much in their translational action on surrounding objects.

Evaluation of amine-based ionic liquids as potential solvents for hydrogen sulfide absorption using COSMO-RS: Computational and experimental validation

Ionic liquids (ILs) is an effective way to convert and remove hydrogen sulfide, H2S from natural gas streams. Amine-based ILs have recently been discovered due to their efficiency of removing H2S due to their excellent characteristics. However, the selection of potential amine-based ILs from a wide range combination of cations and amine-based anions are rather challenging if performed experimentally. Conductor-like Screening Model for Real Solvents (COSMO-RS) was used for the prediction of liquids thermodynamics such as activity coefficient at infinite dilution, selectivity, capacity and performance index (PI) values to evaluate the performance of each amine-based ILs and determine the most efficient ILs for H2S absorption without requiring any experimental data. A total of 42 previously unexplored ionic liquids, amine-based ILs from a combination of 7 amine cations and 6 anions were screened by COSMO-RS model. The findings from COSMO-RS prediction results revealed that ILs without aromatic rings displayed higher efficiencies compared to ILs with aromatic rings. Moreover, N,N,N′,N′-tetramethyl-1,3-propanediamine chloride, [TMPDA][Cl] cation-anion combinations displayed the highest PI value of 52.55 among the screened ILs thus, predicted as the most efficient ILs for H2S absorption. The experimental results obtained validated the COSMO-RS predictions with an approximation of ± 4.51% discrepancies between predicted and experimental data. Hence, it is concluded that COSMO-RS can be used for a reliable pre-experimental prediction and amine-based ILs approach has a huge potential for effective H2S absorption in industrial applications.

Parametric study and optimization of an acid gas enrichment plant with outlet streams and energy usage consideration

Acid gas enrichment (AGE) is a new method to increase the H2S conversion in conventional Clause process. In this paper effect of methyl diethanolamine (MDEA) flow rate, MDEA temperature, acid gas flow rate, and AGE tower pressure on the outlet H2S and CO2 concentration and energy consumption have been studied. A novel procedure based on enthalpy of combustion in the reaction furnace and incinerator is conducted for energy consumption calculations. By changing MDEA and inlet acid gas flow rates, a maximum H2S concentration in the enriched stream could be attainable. Increasing MDEA temperature will decrease maximum H2S concentration and enriched acid flow rate; also, CO2 concentration in off-gas will be decreased. By increasing AGE pressure, maximum H2S concentration in the enriched stream will be diminished. At higher MDEA flow rates, lower AGE pressures will bring higher H2S concentration in enriched acid gas stream. According to flame temperature simulation in the reaction furnace, energy consumption is directly related to H2S concentration in the sulfur recovery unit (SRU) feed stream. Results show that maximum H2S concentration in the enriched acid gas stream has the best conditions from energy point of view. At optimum conditions, H2S concentration in enriched acid gas is 62.45 mol%, which has been increased by 24.8%, compared with existing plant conditions, and energy consumption has been decreased by 25.05 GJ/h, and CO2 concentration in off-gas is 94.94 mol%.

Additive Manufacturing of Ti-6Al-4V with laser-wire DED and local shielding gas protection

Additive Manufacturing of titanium has the need of protecting the hot metal from atmospheric gases like oxygen using a shielding gas. The paper shows a possibility to realize this during laser-wire-DED with a local shielding gas stream and without the need of a chamber. A simple nozzle design together with a welding strategy of using short seams in the range of the nozzle diameter exhibits only minor discolorations. Tensile stress tests have been performed showing a significant deviation of the mechanical properties regarding the direction. The vertical results, which are perpendicular to the layer, are much better compared to the horizontal results in the layer plane. The vertical tests show an average of the tensile strength of 1215.8 N/mm² and an average elongation of 3.97%.

Aspen HYSYS’ Simulation of Ammonia Synthesis from Stranded Gas

Companies have been finding ways stranded gas can economically be used or marketed rather than flaring it. The issue of gas flaring is being frowned upon by many regulatory bodies; hence most oil and gas operators are advised to find a better alternative. A high rate of gas flaring threatens our environment as it reduces the oxygen content in the atmosphere resulting in health issues and waste of our natural resources. However, this paper aims to simulate ammonia production from stranded gas (gas flare stream). A simulation approach was adopted using Aspen HYSYS V10 (Version 10). Three basic processes were employed during the simulation: steam reforming, carbon capturing and ammonia synthesis. The data used for the simulation were obtained from a marginal field operator in the Niger Delta region of Nigeria. Upon simulation, it was observed that the gas stream flowing at a rate of 484.13MMscf/day, with a pressure of 568.9 psig, yielded high ammonia gas of0.810829276 mole fraction at a low temperature of 30oC and pressure of 298.62 bar. High purity of hydrogen and 0% yield of carbon (IV) oxide were obtained by passing the syngas through carbon capture unit which made of absorber and desorber of packed column and MEAmine solvent for removal of CO2. In a nutshell, the result obtained from the simulation proved to be environmentally friendly as little to no greenhouse gases were expended.

What is behind a gas stream scrubbing liquid? Monoethanolamine/water mixtures as seen by dielectric relaxation spectroscopy.

High-quality dielectric data for monoethanolamine (MEA)/water mixtures covering the entire miscibility range are presented. For MEA concentrations c1 ≥ 1 M the obtained complex permittivity spectra, covering the frequency range from 0.05 to 89 GHz, are best described by a sum of four Debye relaxations. Modes at ∼3 GHz and ∼10 GHz are solute-specific. Whilst the first can be assigned to MEA aggregates, the second is a composite arising from "free" MEA dipoles with dynamically retarded water hydrating them. The relaxations at ∼18 GHz and ∼200 GHz essentially reflect the cooperative H-bond fluctuations of more-or-less unperturbed "bulk" water, albeit with minor solute contributions. Evaluation of the bulk-water amplitude reveals that in water-rich mixtures (c1 ≤ 3.5 M) Zt = 3.5 ± 0.2 H2O molecules hydrate a MEA molecule. Then Zt drops linearly, reaching zero for neat MEA. Supported by the literature, this concentration dependence suggests that only H2O molecules H-bonded to the NH2 and OH groups of MEA contribute to Zt. At concentrations beyond hydration shell overlap (c1 ≥ 3.5 M) these H-bonds are gradually eliminated, while new interactions with neighboring MEA molecules are formed. From the evaluation of the MEA-specific amplitudes we conclude that for c1 ≥ 2 M, including neat MEA, ∼35% of the solute molecules are in aggregates, where breaking the intermolecular NH⋯O hydrogen bond determines the dynamics.

Thermodynamic limits of the depolymerization of poly(olefin)s using mechanochemistry.

Mechanochemistry is a promising approach for chemical recycling of commodity plastics, and in some cases depolymerization to the monomer(s) has been reported. However, while poly(olefin)s comprise the largest share of global commodity plastics, mechanochemical depolymerization of these polymers in standard laboratory-scale ball mill reactors suffers from slow rates. In this work, the observed reactivities of poly(styrene), poly(ethylene) and poly(propylene) are rationalized on the basis of thermodynamic limitations of their depolymerization by depropagation of free radical intermediates. In addition, subsequent phase partitioning equilibria for the removal of monomers from the reactor via a purge gas stream are discussed for these polymers. For poly(styrene), a typical vibratory ball mill supplies just enough energy for its depolymerization to be driven by either thermal hotspots or adiabatic compression of the impact site, but the same energy supply is far from sufficient for poly(propylene) and poly(ethylene). Meanwhile, removal of styrene from the reactor is thermodynamically hindered by its lower volatility, but this is not an issue for either propylene or ethylene. The implications of these thermodynamic limitations for mechanochemical reactor design and potential for mechanocatalytic processes are highlighted.