Phase Mass Transfer Research Articles

Coupling the fictitious domain and sharp interface methods for the simulation of convective mass transfer around reactive particles: Towards a reactive Sherwood number correlation for dilute systems

We suggest a reactive Sherwood number model for convective mass transfer around reactive particles in a dilute regime. The model is constructed with a simple external-internal coupling and is validated with Particle-Resolved Simulation (PRS). The PRS of reactive particle-fluid systems requires numerical methods able to handle efficiently sharp gradients of concentration and potential discontinuities of gradient concentrations at the fluid-particle interface. To simulate mass transfer from reactive catalyst beads immersed in a fluid flow, we coupled the Sharp Interface Method (SIM) to a Distributed Lagrange Multiplier/Fictious Domain (DLM/FD) two-phase flow solver. We evaluate the accuracy of our numerical method by comparison to analytic solutions and to generic test cases fully resolved by boundary fitted simulations. A previous theoretical model that couples the internal diffusion-reaction problem with the external advection-diffusion mass transfer in the fluid phase is extended to the configuration of three aligned spherical particles representative of a dilute particle-laden flow. Predictions of surface concentration, mass transfer coefficient and chemical effectiveness factor of catalyst particles are validated by DLM-FD/SIM simulations. We show that the model captures properly the effect of an internal first order chemical reaction on the overall respective reactive Sherwood number of each sphere depending on their relative positions. The proposed correlation for the reactive Sherwood number is based on an existing non-reactive Sherwood number correlation. The model can be later used in Euler/Lagrange or Euler/Euler modelling of dilute reactive particle-laden flows.

Experimental Study of Regularities in Suppression of Flame Combustion and Thermal Decomposition of Forest Combustible Materials Using Aerosols of Different Dispersiveness

This paper presents results of experimental studies on the heat and mass transfer and phase transformations in suppression of thermal decomposition and flame combustion of a group of typical forest combustible materials (leaves and needles used as examples) due application of water aerosol and a group of droplets of a fixed total volume. The main attention is paid to the experimentally found effect of aerosol dispersiveness (via variation in the concentration and size of droplets) on the integral characteristics of the heat and mass transfer processes and phase transformations. The effective irrigation density, the minimum (necessary and sufficient) volume, and the respective specific water consumption for complete termination of destruction of forest combustible materials are calculated. Three most typical schemes of sprayed liquid interaction with the surface of forest combustible material under intensive pyrolysis are considered with the aim of establishing conditions for inhibition, localization, and complete cessation of the process of destruction of forest combustible materials. Dependencies illustrating how the properties and structure of layers of forest combustible materials affect the characteristics of these processes are established.

Study on Macro Kinetics of the Desulfurization Processes of Heteropoly Compounds in Ionic Liquids and Aqueous Solutions

Ionic liquids and heteropoly compounds have been found to be effective systems for H2S removal due to their unique properties. This study, which investigated the absorption kinetics of these new systems, continues our earlier research. Specifically, the macro kinetic characteristics of the H2S absorption for three systems, viz., a [Bmim]3PMo12O40/BmimCl solution, an aqueous solution of peroxo phosphomolybdic acid and an aqueous solution of CuH2PMo11VO40, were determined using a gas-liquid reaction cell. The gas and liquid phase mass transfer coefficients were measured, and the activation energy was calculated. The H2S absorption for the [Bmim]3PMo12O40/BmimCl solution can be expressed as a macro kinetic equation: NH2S = 6.6 × 10–2∙[exp(–1064/T)]∙CH2S1.120∙C[Bmim]3PMo12O400.099. For the aqueous solutions of peroxo phosphomolybdic acid and CuH2PMo11VO40, the absorption can be expressed as NH2S = 2.68 × 10–6∙[exp(–790/T)]∙CH2S0.252∙CPHPMo0.131 and NH2S = 1.02 × 10–6∙[exp(607/T)]∙CH2S0.510∙CCuH2PMo11VO400.431, respectively.

A study on the use of existing pump as turbine

Cavitation is an abnormal physical phenomenon which occurs in relatively low–pressure regions in turbomachinery such as pumps and hydraulic turbines. A comparison between the pump and turbine cavitation behavior is a significant and essential process. The work investigates feasibility of turbineusing existing pump and a comparative study of the cavitation characteristics on a centrifugal pump asturbine numerically and experimentally. The current work adopted the Rayleigh–Plesset cavitation model as the source term for inter–phase mass transfer to predict cavitation characteristics.The experimental data were compared with the numerical results and were found to be in good agreement.Results of the comparative study showed that cavitation first occurred at the suction leading edge on the impeller blades and attached cavitation observed on the impeller blade at the lower suction head in pump mode; however, for the turbine mode, the development of vortex cavitation happened at the runner outlet near thetrailing edge on the impeller blades. Also, in the pump, the cavitation became largerfromshroud to the hub and the cavitation rapidly extended from the suction side to the pressure side. On the other hand in the turbine mode, as the cavitation number decreased more vapor bubbles are drawnup at the runner outlet near trailing edge on the blade suction side.

A Telescoping View of Solute Architectures in a Complex Fluid System.

Short- and long-range correlations between solutes in solvents can influence the macroscopic chemistry and physical properties of solutions in ways that are not fully understood. The class of liquids known as complex (structured) fluids—containing multiscale aggregates resulting from weak self-assembly—are especially important in energy-relevant systems employed for a variety of chemical- and biological-based purification, separation, and catalytic processes. In these, solute (mass) transfer across liquid–liquid (water, oil) phase boundaries is the core function. Oftentimes the operational success of phase transfer chemistry is dependent upon the bulk fluid structures for which a common functional motif and an archetype aggregate is the micelle. In particular, there is an emerging consensus that mass transfer and bulk organic phase behaviors—notably the critical phenomenon of phase splitting—are impacted by the effects of micellar-like aggregates in water-in-oil microemulsions. In this study, we elucidate the microscopic structures and mesoscopic architectures of metal-, water-, and acid-loaded organic phases using a combination of X-ray and neutron experimentation as well as density functional theory and molecular dynamics simulations. The key conclusion is that the transfer of metal ions between an aqueous phase and an organic one involves the formation of small mononuclear clusters typical of metal–ligand coordination chemistry, at one extreme, in the organic phase, and their aggregation to multinuclear primary clusters that self-assemble to form even larger superclusters typical of supramolecular chemistry, at the other. Our metrical results add an orthogonal perspective to the energetics-based view of phase splitting in chemical separations known as the micellar model—founded upon the interpretation of small-angle neutron scattering data—with respect to a more general phase-space (gas–liquid) model of soft matter self-assembly and particle growth. The structure hierarchy observed in the aggregation of our quinary (zirconium nitrate–nitric acid–water–tri-n-butyl phosphate–n-octane) system is relevant to understanding solution phase transitions, in general, and the function of engineered fluids with metalloamphiphiles, in particular, for mass transfer applications, such as demixing in separation and synthesis in catalysis science.

Mass Transfer of Anthocyanins during Extraction from Pre-Fermentative Grape Solids under Simulated Fermentation Conditions: Effect of Convective Conditions.

The colour of red wine is largely determined by the concentration of anthocyanins that are extracted from grape skins during fermentation. Because colour is a key parameter in determining the overall quality of the finished product, understanding the effect of processing variables on anthocyanin extraction is critical for producing a red wine with the desired sensorial characteristics. In this study, the effect of convective conditions (natural and forced) on the mass transfer properties of malvidin-3-glucoside (M3G) from pre-fermentative grape solids was explored at various liquid phase conditions representing stages of fermentation. A mathematical model that separates solid and liquid phase mass transfer parameters was applied to experimental extraction curves, and in all cases, provided a coefficient of determination exceeding 0.97. Calculated mass transfer coefficients indicated that under forced convective conditions, the extraction process was controlled by internal diffusion whereas under natural convection, both internal diffusion and liquid-phase mass transfer were relevant in determining the overall extraction rate. Predictive simulations of M3G extraction during active fermentation were accomplished by incorporating the current results with a previously developed fermentation model, providing insight into the effect of a dynamic liquid phase on anthocyanin extraction.

Modeling of atmospheric and vacuum petroleum residue hydroconversion in a slurry semi-batch reactor: Study of hydrogen consumption

In this work, Arabian light atmospheric residue and Safaniya vacuum residue were hydroconverted in a slurry phase semi-batch stirred tank reactor at 15 MPa for a wide range of temperatures (420–440 °C) and reaction times up to 4 h. Experimental data was used to develop a semi-batch reactor model including vapor-liquid equilibrium, gas-liquid mass transfer and gas phase hydrodynamics. Mass transfer and kinetic parameters were estimated by minimizing not only the total masses of products but also the outlet gas flow dynamics. Mass transfer and hydrogen consumption were compared against former studies using a batch reactor, a continuous stirred tank reactor and work by other authors, reported in the literature. Higher hydrogen consumption was achieved with the semi-batch reactor and no hydrogen mass transfer limitation was observed. Therefore, it was concluded that this setup is more suited and reliable for studying the chemical kinetics of slurry-phase hydroconversion of petroleum residues and permits improved representation of the role of hydrogen compared with current models.

An optimization framework to investigate the CO2 capture performance by MEA: Experimental and statistical studies using Box-Behnken design

The absorption of carbon dioxide gas by monoethanolamine (MEA) in the packed tower is the most common method for the CO2 capture. The present study describes the set-up and operation of a laboratory-scale CO2 capture unit in detail, as the closed cycle of the absorption/desorption process continuously operated at the different operating conditions. The effect of six independent variables was investigated on CO2 absorption in three levels. To analyse the results, Response Surface Box-Benhken design method was applied. The absorption unit was evaluated in terms of absorption percentage (Φ), the overall gas phase mass transfer coefficient (KGaV), and the specific heat duty of the reboiler (η).The results of the analysis indicated that the MEA concentration in the solvent had the most significance, whereas the input solvent temperature had the least effect upon the overall gas phase mass transfer coefficient.The response surface optimization was also carried out to determine the optimal operating conditions to maximize KGaV and minimize η. The results demonstrated that at an inlet solvent temperature of 45 °C, solvent flow rate of 1.25 L/min, gas flow rate of 100 L/min, reboiler heat load 1.4 kW, MEA concentration 30 wt.%, and the CO2 concentration of 15 vol.%, η was at the minimum value of 3.88 MJ/kg CO2, while KGaV was at the maximum value of 4.59 kmol/m3.h.kPa.

Creation of ZnO-based nanomaterials with use synergies of the thermal action and laser-induced vibrations

Synthesis of metallic-semiconductor nanocomposite based on ZnO nanowires under pulse-periodic laser action with a pulse frequency of 3 Hz was performed. By analyzing the results of the samples’ responses to the laser-induced vibroexcitation, it was found that the vibration rate increases in the case of frequencies that are divisible by the frequency of initial oscillation, during the amplitude decrease with the frequency increase. The determination of sample heating features by laser action was performed. Analysis of the X-ray diffraction image showed that thermal oxidation by the pulse-periodic laser treatment leads to the ZnO oxide formation on the substrate of porous Cu–Zn alloy. It is shown that a non-stationary local deformation, caused by a highly-powered external action, is a condition for the intensification of mass transfer in the solid phase of a metallic material. Thus, for the first time it is shown that the use of synergies of thermal effects and laser-induced vibrations in the sound frequency range of pulse-periodic laser beam allow the implementation of a new approach for the creation of structures of composite nanomaterials based on zinc oxide. Results of study are the basis for creating software to controlling laser systems.

Experimental study of gas phase mass transfer coefficients in gas condensate reservoirs

Gas condensate reservoirs as a proportion of worldwide gas reservoirs experiencing retrograde condensation throughout their production period have been consistently attracting research interests in recent decades. However, their compositional simulators usually consider local equilibrium assumption and neglect the non-equilibrium effect represented by gas phase mass transfer coefficients. Since no independent research has yet targeted mass transfer coefficients in gas condensate reservoirs, in this study, a series of flow tests were carried out using a novel experimental setup to address the issue. Correspondingly, separate empirical correlations were developed for methane and isobutane representing light and intermediate components respectively at two temperatures, thus two condensate saturation ranges. The results confirm the positive effect of pore gas velocity on gas phase mass transfer coefficients reported in NAPL volatilization related studies even in low gas flow rates. Also temperature, effective diffusion coefficient, condensate saturation, mean grain size and component types were shown to affect these coefficients.

Mass transfer performance for CO2 absorption into aqueous blended DMEA/MEA solution with optimized molar ratio in a hollow fiber membrane contactor

Combination N,N-dimethylethanolamine(DMEA) and monoethanolamine (MEA) may represent a potential absorbent for CO2 capture due to the high absorption rate, high cyclic CO2 capacity and low energy requirement for solvent regeneration. Both the absorption and regeneration performances for 2 kmol/m3 DMEA/MEA with molar ratios of 2.0:0.0, 1.5:0.5, 1.0:1.0, 0.5:1.5, and 0.0:2.0 were estimated in terms of the absorption rate, regeneration rate and cyclic CO2 capacity using an improved rapid screening method. The experimental results showed that the highest cyclic CO2 capacities (i.e. low energy requirement) for the cyclic reaction time of 30 min and 60 min were obtained both by 1.0 M DMEA + 1.0 M MEA solution, indicating the synergistic effects existing in CO2 absorption into DMEA/MEA solution. Additionally, the mass transfer performance of CO2 absorption into 1.0 M DMEA + 1.0 M MEA solution was investigated in a hollow fiber membrane contactor. The effects of key operational parameters such as liquid velocity, inlet gas flow rate, CO2 partial pressure, feed temperature range, CO2 lean loading, amine concentration and membrane contactor height on the CO2 flux and overall gas phase mass transfer coefficient were investigated. Furthermore, a developed correlation was successfully applied for the prediction of overall gas phase mass transfer coefficient (KG) for CO2 absorption into DMEA/MEA solution, with an average absolute relative deviation (AARD) of 8.31%. Thus, a potential absorbent (i.e. DMEA/MEA) for CO2 capture was proposed in this work.

Stability of vapor phase water electrolysis cell with anion exchange membrane

The production of renewable hydrogen gas with a vapor-fed solar hydrogen generator is an appealing strategy. In such all solid-state standalone device no liquid electrolyte is required. The use of an anion exchange membrane separating cathode and anode compartments is particularly advantageous and its performance matches the performance of liquid phase electrolysis. In this work, a vapor-fed water electrolyzer was investigated comprising a poly(vinyl alcohol) anion exchange membrane impregnated with 4M KOH solution and Ni-based catalysts. The performance was evaluated over time periods of hours to days. The vapor fed device showed similar initial activity as an electrolysis setup with the same electrodes immersed in 1M KOH liquid electrolyte. To sustain a current density of 10 mA/cm², it was observed that the required potential initially increased but eventually reached a steady state at ca. 1.9 V. From a D2O isotope labelling experiment of the vapor phase, it was noticed that the system initially consumed H2O absorbed in the membrane to produce H2. After this water of the membrane was consumed, water to be split is taken from the vapor phase and water mass transfer limitation starts occurring. Once water mass transfer and splitting reactions are matched, a steady state potential is reached. The results of this work are encouraging and pave the way to efficient stable operation of vapor-fed solar hydrogen generators.

Development and Application of the TUM-WelChem Cell Model for Prediction of Liquid Distribution in Random Packed Columns

Liquid maldistribution is, next to the prediction of interfacial phase area and mass transfer coefficients, one of the bigger uncertainties in random packed column design. In a joint project, “Cell Model for Packed Column and Liquid Distributor Design” supported by the Bavarian Research Foundation, liquid maldistribution experiments were conducted in three packed columns with diameters of 0.4, 1.2 and 2.0 m at Technical University of Munich (TUM), RVT Process Equipment GmbH and Linde AG. Experiments covered varying experimental and operating parameters – gas/liquid system, type of packing, packing height, type of liquid distributor, liquid load, and gas load. An evaluation of the acquired database provided insight into influencing factors on liquid distribution (Hanusch et al., 2017). In 2007, Wild and Engel first presented their WelChem Cell Model. The original model predicted liquid distribution in random packing from cell layer to cell layer based on directional dispersion coefficients, deduced from virtual 3D irrigation simulations with a CAD model of one random packing element (Wild and Engel, 2007). Further development at TUM included implementation of the influencing factors liquid load and gas load, considering local loading effects and increasing liquid dispersion. Wall effects were refined by distinction of packing elements and voids at the column wall. Liquid distribution profiles predicted with the TUM-WelChem Cell Model are in good agreement with experimental data.WelChem GmbH implemented the TUM-WelChem Cell Model in their column design software TrayHeart, thus making the research results directly accessible for TrayHeart users. Application of the TUM-WelChem Cell Model ranges from prediction of maldistribution in random packed columns, through liquid distributor design, considering interactions with random packing, to process simulation, considering maldistribution in parallel column models (Schultes, 2000).

Desorption of isobutyl acetate into air as a low-cost alternative system for the measurement of liquid phase mass transfer coefficients

CITATION: Lamprecht, J. H. & Burger, A. J. 2018. Desorption of isobutyl acetate into air as a low-cost alternative system for the measurement of liquid phase mass transfer coefficients. Chemical Engineering Transactions, 69:712, doi:10.3303/CET1869002.

Mass Transfer Rate Parameters of Sulzer EX Laboratory Scale Gauze Structured Packing

Sulzer EX packing is widely used in lab-scale separation studies owing to its high efficiency, low theoretical stage height and small pressure drop. In this work the three fundamental characteristic mass transfer parameters of this packing, effective gas-liquid contact area (ae) gas-film and liquid-film mass transfer coefficient (kG) and (kL) are measured in a 0.19 mm ID counter-flow absorption column using aqueous liquids. With end effects removed, the results show that the effective gas liquid contact area is independent of gas and liquid loads and reaches about 90 % of the geometric area of the packing. Correlations of the dimensionless gas and liquid phase mass transfer parameters are determined as ??hG = 0.048 ????G1.0 ????G0.33 and ??h L = 0.050 ????L0.4????L0.5.

When binaries keep track of recent nucleosynthesis

Context. Barium stars are s-process enriched giants. They owe their chemical peculiarities to a past mass transfer phase. During this phase they were polluted by their binary companion, which at the time was an asymptotic giant branch (AGB) star, but is now an extinct white dwarf. Barium stars are thus ideal targets for understanding and constraining the s-process in low- and intermediate-mass AGB stars. Aims. We derive the abundances of a large number of heavy elements in order to shed light on the conditions of operation of the neutron source responsible for the production of s-elements in the former companions of the barium stars. Methods. Adopting a recently used methodology, we analyse a sample of eighteen highly enriched barium stars observed with the high-resolution HERMES spectrograph mounted on the Mercator telescope (La Palma). We determine the stellar parameters and abundances using MARCS model atmospheres. In particular, we derive the Nb–Zr ratio which was previously shown to be a sensitive thermometer for the s-process nucleosynthesis. Indeed, in barium stars, 93Zr has fully decayed into mono-isotopic 93Nb, so Nb/Zr is a measure of the temperature-sensitive 93Zr/Zr isotopic ratio. Results. HD 28159, previously classified as K5III and initially selected to serve as a reference cool K star for our abundance analysis, turns out to be enriched in s-process elements, and as such is a new barium star. Four stars are characterised by high nitrogen abundances, and among those three have high [Nb/Zr] and [hs/ls] ratios. The derived Zr and Nb abundances provide more accurate constraints on the s-process neutron source, identified to be 13C(α, n)16O for barium stars. The comparison with stellar evolution and nucleosynthesis models shows that the investigated barium stars were polluted by a low-mass (M ∼ 2 − 3 M⊙) AGB star. HD 100503 is potentially identified as a high metallicity analogue of carbon-enhanced metal-poor star enriched in both r- and s-process elements (CEMP-rs).

Hydrogen Sulfide Removal from Biogas Using Digester Effluent Absorbent in a Continuous Vertical Column

HYDROGEN SULFIDE REMOVAL FROM BIOGAS USING DIGESTER EFFLUENT ABSORBENT IN A CONTINUOUS VERTICAL COLUMN. Gas-Liquid mass transfer is one of the most commonly used phenomena in the chemical process, such as absorbtion. This research evaluates the value of liquid phase mass transfer coefficient of hydrogen sulfide removal from biogas in a continous contactor column for digester effluent-biogas system. This study was carried out by contacting biogas at certain flow with digester effluent continously in a counter-current flow packed bed column. Samples were taken in steady state condition. This research used raschig rings, large balls, and small balls as packing materials with surface areas are 0.9269 m2/m3, 0.6279 m2/m3, and 0.2992 m2/m3 respectively at volumetric flow rates of biogas from 0.1109 m3/h to 0.8846 m3/h. The results show that the relationship between the variables and mass transfer coefficient gives following mathematical model This model is valid in the range of (As·dt) and (Vg/dt·DL) respectively from 0.03 to 0.09 and from 237,267.08 to 3,307,522.67. Average error is 17.85%.

The blue straggler V106 in NGC 6791: a prototype progenitor of old single giants masquerading as young

We determine the properties of the binary star V106 in the old open cluster NGC6791. We identify the system to be a blue straggler cluster member by using a combination of ground-based and Kepler photometry and multi-epoch spectroscopy. The properties of the primary component are found to be $M_{\rm p}\sim1.67 \rm M_{\odot}$, more massive than the cluster turn-off, with $R_{\rm p}\sim1.91 \rm R_{\odot}$ and $T_{\rm eff}=7110\pm100$ K. The secondary component is highly oversized and overluminous for its low mass with $M_{\rm s}\sim0.182 \rm M_{\odot}$, $R_{\rm s}\sim0.864 \rm R_{\odot}$ and $T_{\rm eff}=6875\pm200$ K. We identify this secondary star as a bloated (proto) extremely low-mass helium white dwarf. These properties of V106 suggest that it represents a typical Algol-paradox system and that it evolved through a mass-transfer phase which provides insight into its past evolution. We present a detailed binary stellar evolution model for the formation of V106 using the MESA code and find that the mass-transfer phase only ceased about 40 Myr ago. Due to the short orbital period (P=1.4463 d) another mass-transfer phase is unavoidable once the current primary star evolves towards the red giant phase. We argue that V106 will evolve through a common-envelope phase within the next 100 Myr and merge to become a single over-massive giant. The high mass will make it appear young for its true age, which is revealed by the cluster properties. Therefore, V106 is potentially a prototype progenitor of old field giants masquerading as young.

Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357)

IODP Expedition 357 used two seabed drills to core 17 shallow holes at 9 sites across Atlantis Massif ocean core complex (Mid-Atlantic Ridge 30°N). The goals of this expedition were to investigate serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. More than 57 m of core were recovered, with borehole penetration ranging from 1.3 to 16.4 meters below seafloor, and core recovery as high as 75% of total penetration in one borehole. The cores show highly heterogeneous rock types and alteration associated with changes in bulk rock chemistry that reflect multiple phases of magmatism, fluid-rock interaction and mass transfer within the detachment fault zone. Recovered ultramafic rocks are dominated by pervasively serpentinized harzburgite with intervals of serpentinized dunite and minor pyroxenite veins; gabbroic rocks occur as melt impregnations and veins. Dolerite intrusions and basaltic rocks represent the latest magmatic activity. The proportion of mafic rocks is volumetrically less than the amount of mafic rocks recovered previously by drilling the central dome of Atlantis Massif at IODP Site U1309. This suggests a different mode of melt accumulation in the mantle peridotites at the ridge-transform intersection and/or a tectonic transposition of rock types within a complex detachment fault zone. The cores revealed a high degree of serpentinization and metasomatic alteration dominated by talc-amphibole-chlorite overprinting. Metasomatism is most prevalent at contacts between ultramafic and mafic domains (gabbroic and/or doleritic intrusions) and points to channeled fluid flow and silica mobility during exhumation along the detachment fault. The presence of the mafic lenses within the serpentinites and their alteration to mechanically weak talc, serpentine and chlorite may also be critical in the development of the detachment fault zone and may aid in continued unroofing of the upper mantle peridotite/gabbro sequences.New technologies were also developed for the seabed drills to enable biogeochemical and microbiological characterization of the environment. An in situ sensor package and water sampling system recorded real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential (Eh), and temperature and during drilling and sampled bottom water after drilling. Systematic excursions in these parameters together with elevated hydrogen and methane concentrations in post-drilling fluids provide evidence for active serpentinization at all sites. In addition, chemical tracers were delivered into the drilling fluids for contamination testing, and a borehole plug system was successfully deployed at some sites for future fluid sampling. A major achievement of IODP Expedition 357 was to obtain microbiological samples along a west–east profile, which will provide a better understanding of how microbial communities evolve as ultramafic and mafic rocks are altered and emplaced on the seafloor. Strict sampling handling protocols allowed for very low limits of microbial cell detection, and our results show that the Atlantis Massif subsurface contains a relatively low density of microbial life.

Enhancement of char gasification in CO2 during chemical looping combustion

Three chars were gasified in CO2 in a fluidised bed of inert sand or Fe2O3 as an oxygen carrier (either derived from an ore or prepared in the laboratory). Rates of gasification were found to increase with temperature and the presence of active oxygen carriers. The observed change varied both with the chars’ and carriers’ reactivity. A numerical model was developed to simulate char gasification. It accounts for: intrinsic kinetics of gasification, intraparticle mass transfer in the char, external mass transfer in the particulate phase of the fluidised bed and CO combustion in the bed of Fe2O3. At 1223 K, CO was removed from the vicinity of the char on being oxidised by an oxygen carrier; this was accompanied by a simultaneous increase in CO2 concentration, reducing the limitation imposed by mass transfer. It was concluded that the acceleration of gasification by oxygen carriers is significant only if gasification is limited by mass transfer in the first place. In addition, an analytical solution has been proposed, to combine all the processes into one simplified expression for estimating the apparent gasification rate. The influence of the intraparticle resistance was introduced with the effectiveness factor; the gasification rate was linearized with a Taylor series; finally the processes in the particulate phase were described with an enhancement factor, based on the Hatta number. This simple analytical model allows one to predict the influence of an oxygen carrier on the gasification of char during chemical looping combustion. The proposed expression for the effective rate was used to construct a map of the enhancement expected for various kinetic characteristics of an oxygen carrier.