CO2 Mass Fraction Research Articles

A general probabilistic approach for the quantitative assessment of LES combustion models

The Wasserstein metric is introduced as a probabilistic method to enable quantitative evaluations of LES combustion models. The Wasserstein metric can directly be evaluated from scatter data or statistical results through probabilistic reconstruction. The method is derived and generalized for turbulent reacting flows, and applied to validation tests involving a piloted turbulent jet flame with inhomogeneous inlets. It is shown that the Wasserstein metric is an effective validation tool that extends to multiple scalar quantities, providing an objective and quantitative evaluation of model deficiencies and boundary conditions on the simulation accuracy. Several test cases are considered, beginning with a comparison of mixture-fraction results, and the subsequent extension to reactive scalars, including temperature and species mass fractions of CO and CO2. To demonstrate the versatility of the proposed method in application to multiple datasets, the Wasserstein metric is applied to a series of different simulations that were contributed to the TNF-workshop. Analysis of the results allows to identify competing contributions to model deviations, arising from uncertainties in the boundary conditions and model deficiencies. These applications demonstrate that the Wasserstein metric constitutes an easily applicable mathematical tool that reduce multiscalar combustion data and large datasets into a scalar-valued quantitative measure.

A numerical study of the impurity effects on CO2 geological storage in layered formation

The effects of two kinds of common impurities (i.e., N2 and H2S) on CO2 geological storage in layered formations were investigated by numerical simulations. This study was focused on the migration behaviour and spatial distribution of CO2 plume. The effects of capillary pressure on the spread of CO2 plume in the layered formations were examined first. The results suggested that the capillary pressure was a minor influence when injecting, but it affected the migration and distribution of CO2 plume significantly during post-injection period in which, the contact area between CO2 plume and formation brine became smaller with increased capillary pressure, leading to a decrease of dissolved CO2 mass fraction. In the case of co-injection of CO2 with N2 impurity, it was found that as the N2 concentration rose up, the horizontal migration distance of CO2 plume extended, and the plume inclined to accumulate below the impermeable caprock. The phenomena were due to the enhancement of buoyance effect of CO2 plume and accordingly, the contact area between the CO2 plume and the formation brine enlarged, resulting in an increase of dissolved CO2 mass fraction. However, the effects of H2S impurity were less obvious compared with N2, by showing an inconspicuous shrinkage of CO2 plume spread.

Encapsulation of passion fruit seed oil by means of supercritical antisolvent process

Large quantities of passion fruit seeds are wasted after juice production. Heat and light can cause loss or reduction of seed oil biological activities including antioxidant and antimicrobial. Thus, co-precipitation with polymers by Supercritical AntiSolvent (SAS) process could be used to preserve seed oil compounds. This work aimed to apply SAS process to produce passion fruit seed oil particles encapsulated with a biopolymer, PLGA (poly(lactic-co-glycolic) acid). The phase behavior of the seed oil in dichloromethane with and without PLGA in CO2 was studied to support to determine the best SAS processing conditions. The static synthetic method was applied for the phase equilibrium assays with different CO2 compositions (60–98.8wt%) and different temperatures (35–55°C). Liquid-vapor, liquid-liquid and liquid-liquid-vapor phase transitions were observed. Based on phase behavior, the selected SAS encapsulation conditions were: 35 and 45°C, CO2 mass fraction of 92.5 and 95.0%, and pressures of 90 and 110bar. Microscopy images showed that pressure affected PLGA+passion fruit seed oil particles morphology and size, which varied from spherical shape at low pressure (90bar) to irregular shape at high pressure (110bar). The particle size ranged from 721 to 1498nm and the oil encapsulation efficiency varied from 67.8 to 91%. According to differential scanning calorimetry results, all SAS conditions produced particles with encapsulated oil. The oil release consisted of an initial burst, raising gradually (until 24h), followed by a uniform release up to 72h. The amount of oil released reached 88% of total entrapped material. This study shows the potential of using green methods to aggregate value to agroindustrial waste materials.

Smoke Clearance in an Underground Car Park using the Jet Fan System

Fire propagation and control in underground car parks are of an important safety issue. This paper investigates the effect of the jet fan system on the smoke clearance in an underground car park using CFD simulations. Two fire locations were considered under a steady state fire source of 4 MW. The consideration of the fire zone was also studied. The underground car park used in this study is 5,290 m2 in area with a height of 3.7 m. A comparison between CFD results and analytical correlations for the fire modeling was made. The ANSYS FLUENT 14.0 software was used for all simulations. The results showed that the temperature is limited to the zone, where the fire is detected, and it is within an accepted range. The CO2 mass fraction was presented and showed how the jet fans contribute in reducing the smoke density and hence improve the visibility. It was found that dividing the car park into zones is highly recommended and should be taken in the design of the jet fan system.

Numerical study of hydrogen enrichment effects in oxy-flame turbulent of three separated jets

The development of oxy-fuel combustion in a burner with separated jets presents a promising technology ensuring higher thermal efficiency, better flame stability and more safety compared to premixed combustion. This paper presents a numerical investigation of burner of 25kW power consisting of a central methane and hydrogen jet surrounded by two oxygen jets. This study aims to evaluate the effect of hydrogen on the dynamics, the distribution of temperature, the stability of the flame, the variation of species mass fraction (CO, CO2…) and the radiative heat flux. Results show that the addition of hydrogen has a considerable effect on the dynamic behaviour and flame temperature. Indeed, using hydrogen increases the temperature maximum, accelerates the fusion of three jets, and favours the mixing between them. Therefore, it ensures the flame stabilization. Moreover, the results show that the mass fraction of CH4, CO and CO2 are highly reduced with the addition of hydrogen. Furthermore, adding hydrogen attenuates the radiative heat flux.

Calculation of pressure- and migration-constrained dynamic CO2 storage capacity of the North Sea Forties and Nelson dome structures

This paper presents a numerical simulation study of CO2 injection into the Forties and Nelson dome structures in the North Sea. The study assumes that these structures are fully depleted of their remaining hydrocarbon and brine has replaced their pore space, and therefore the structures can be treated as saline aquifers. Under this assumption, the objective is to calculate the dynamic CO2 storage capacity of the Forties and Nelson structures and design an injection scenario to enhance storage utilisation. In doing so, first, a detailed geological model of the dome structures and their surrounding aquifer is developed to represent the lithological facies associations and attribute them with petrophysical properties. The geological model is calibrated in terms of the surrounding aquifer support using the hydrocarbon production data. The dynamic storage capacity is subsequently estimated by numerical simulation of the two-phase (brine and CO2) process. Key performance indicators (KPIs), such as the pressure build-up and regional mass fraction of CO2, are used to constrain the injection scenarios that consequently result in the best capacity utilisation of the storage structures. In our model of fully brine saturated dome structures, based on specific constraints, namely <0.1% of the total gaseous CO2 outside the dome into an upper pressure unit and 66% of the initial hydrostatic pressure as the allowable increase in the bottom-hole pressure, we obtained a dynamic capacity of 121 million tonnes for the Forties structure and 24 million tonnes for the Nelson structure. These values are subject to change when a three phase model of residual oil, gas and water is considered in simulations.

Large eddy simulation of methane diffusion jet flame with representation of chemical kinetics using artificial neural network

Chemical kinetics modeling within the numerical simulations of turbulent reactive flows is a critical issue. In this study, first a large eddy simulation of a non-premixed planar methane jet flame with artificial neural network -based chemical kinetics is performed. To consider the effects of turbulence on the evolution of the thermo-chemical state space, the artificial neural network training patterns are obtained by solving the unsteady reaction-diffusion equations of linear eddy mixing sub-grid combustion model. The optimization procedure for selecting the optimum neural network architecture is discussed in detail. A flow field analysis and a comparison between a non-reactive jet with the same velocity boundary conditions with the flame jet are performed. It is shown that the non-reactive jet is more turbulent and vortical structures of the non-reactive jet occur closer to the jet exit compared to the flame jet. Second, in a first attempt to quantify the influence of different chemical kinetics methods, large eddy simulation computations are performed with other methods used to represent the chemical kinetics such as direct integration and look-up table. A comparative study is performed between the averaged, instantaneous and fluctuation profiles of the scalar field and flame structures obtained by each method. Although all large eddy simulation results are very close to each other, the main discrepancy is observed for CO mass fractions obtained by artificial neural network and look-up table-based chemical kinetics simulations. It is also shown that the averaged scalar field and the conditional averaged values of the flame are overestimated by look-up table based chemical kinetics large eddy simulation computations. Moreover, the potential savings of artificial neural network in computational costs in comparison with other chemistry approaches are illustrated.

Trace Element Contents in Bone Affected by Osteomyelitis

To clarify the role of trace elements in the etiology and the pathogenesis of the osteomyelitis, a nondestructive neutron activation analysis with high resolution spectrometry of long-lived radionuclides were performed. The silver (Ag), cobalt (Co), chromium (Cr), iron (Fe), mercury (Hg), rubidium (Rb), antimony (Sb), selenium (Se), and zinc (Zn) mass fraction were estimated in normal bone samples from 27 patients with intact bone (12 females and 15 males, aged from 16 to 49 years), who had died from various non bone related causes, mainly unexpected from trauma, and in samples, obtained from open biopsies or after operation of 10 patients with osteomyelitis (3 females and 7 males, 9 to 21 years old). The reliability of difference in the results between intact bone and bone affected by osteomyelitis was evaluated by Student’s t-test. In the bone affected by osteomyelitis the mass fractions of Co, Cr, Fe, Se, and Zn are significantly higher than in normal bone tissues. In the inflamed bone tissue many correlations between trace elements found in the control group are no longer evident. In bone affected by osteomyelitis the trace element homeostasis is significantly disturbed.

Smoke Clearance in an Underground Car Park using the Jet Fan System

Fires in underground car parks are an important issue. This paper investigates the effect of the jet fan system on the smoke clearance in an underground car park using CFD simulations. Two fire locations were considered with a steady state fire source of 4 MW. The consideration of the fire zone was also studied. The underground car park used in this study is 5290 m2 in area with a height of 3.7 m. A comparison between CFD results and analytical correlations for the fire modeling was made. The ANSYS FLUENT 14.0 software was used for all simulations. The results showed that the temperature is limited to the zone, where the fire is detected, and it is within an accepted range. The CO2 mass fraction was presented and showed how the jet fans contribute in reducing the smoke density and hence improve the visibility. It was found that dividing the car park into zones is highly recommended and should be taken in the design of the jet fan system. Keywords: ANSYS FLUENT, CFD, jet fan, smoke clearance, smoke density, underground car park.

Optimization of a cascade refrigeration system using refrigerant C3H8 in high temperature circuits (HTC) and a mixture of C2H6/CO2 in low temperature circuits (LTC)

This paper discusses the multi-objectives optimization of a cascade refrigeration system using refrigerant C3H8 in high temperature circuits (HTC) and a mixture of C2H6/CO2 in low temperature circuits (LTC). The evaporator temperature, condenser temperature, C2H6/CO2 mixture condensation temperature, cascade temperature differences, and the CO2 mass fraction are chosen as the decision variables. Whereas cooling capacity, cold space temperature, and ambient temperature are taken as the constraints. The purpose of this research is to design a cascade refrigeration system whose optimum performance are defined in terms of economics and thermodynamics. Accordingly, there are two objective functions that should be simultaneously optimized including the total annual cost which consists of the capital and operational cost and the total exergy destruction of the system. To this aim, the optimum operating temperature of the system and CO2 fraction should be determined so that the system has minimum exergy destruction and annual cost. Results show that, the optimum value of the decision variables for this system can be determined by trade-off between annual cost and exergy destruction.

High Energy Efficiency Plasma Conversion of CO2at Atmospheric Pressure Using a Direct-Coupled Microwave Plasma System

Energy and conversion efficiencies of the carbon dioxide (CO2) dissociation process at atmospheric-pressure conditions are investigated using a direct-coupled continuous microwave plasma system (MPS). Gas chromatography and mass spectrometer measurements were performed on the gas mixture postplasma treatment, over a range of specific energy inputs (SEIs) (0.06–0.6 eV mol $^{-1})$ , in order to determine species mass fractions of CO2, carbon monoxide, and oxygen. In this region of SEI, energy efficiency is maximized at the cost of conversion efficiency. The corresponding maximum observed quantities for conversion efficiency and energy conversion efficiency (ECE) occurred at conditions close to the end of the test range and are, respectively, 9% and 0.0048 L min $^{-1}\text{W}^{-1}$ . The maximum throughput of CO2 converted was 0.59 L min $^{-1}$ , at an SEI of 0.1 eV mol $^{-1}$ and an ECE of 0.004 L min $^{-1}\text{W}^{-1}$ . Optical emission spectroscopy was used to approximate the rotational and vibrational temperatures of the plasma system to be in the range of 7000–8000 K. This paper suggests that an MPS is the most energy efficient method in dissociating CO2 under atmospheric pressure and, therefore, most suitable to be used in a CO2 recycling setup, which can further increase conversion rates.

Scalar structure of turbulent stratified swirl flames conditioned on local equivalence ratio

In a recent paper (Kamal, et al., 2015), we reanalyzed single shot species and temperature measurements from non-swirling flames stabilized on the Cambridge/Sandia stratified burner by conditioning measurements on the local equivalence ratio, and found that the state space structure of the flames was closely approximated by that of a laminar flame at the given equivalence ratio. In the present communication, we show that the same state space relationships remain robust for species CH4, O2, H2O, and CO2 in premixed and stratified flames under high swirl. Conditioned mass fractions of CO and H2 in the stratified swirl flame show a greater effect of stratification than was observed in the non-swirling cases, and this is attributed to larger gradients in equivalence ratio that occur with the addition of swirl. Aside from this modest effect of stratification, major species mass fractions in the swirling flame are also closely approximated by laminar flame results at the local equivalence ratio.

Condensation of steam with high CO2 concentration on a vertical plate

The effect of a non-condensable gas on steam condensation has been studied. From experimental and theoretical studies to date, clear evidence of significant heat transfer deterioration by the non-condensable gas can be seen. The deterioration varies with the concentration of the non-condensable gas, geometric parameters, system pressure, etc. However, these data and correlations may be unreliable due to the high concentration of CO2 in the vapor mixture and lack of verification through experiments. In this paper, a systematic investigation has been conducted for film-wise condensation using a vapor mixture of steam and a high concentration of CO2. Some data were obtained on a vertical plate, with the average vapor velocity of 1.2m/s, CO2 mass fraction of 20%—94% and a pressure of 1atm. The effects of CO2 concentration and surface sub-cooling on heat transfer characteristics have been investigated. Moreover, the relevant parameters such as gas/liquid film resistance were included in the description of the condensation phenomenon. The developed correlation for steam and a high concentration of CO2, based on experimental results, has a standard deviation of less than ±20%.

Measurement of trace element content in bone samples using long-lived neutron activation products and high-resolution gamma-ray spectrometry

A nondestructive instrumental neutron activation analysis with high-resolution gamma-ray spectrometry of long-lived radionuclides was developed and used for measurement of trace element contents in samples of bone to determine health and diseases. Using this method, the silver (Ag), cobalt (Co), chromium (Cr), iron (Fe), mercury (Hg), rubidium (Rb), antimony (Sb), selenium (Se), and zinc (Zn) mass fractions were estimated in bone samples from 27 patients with intact bone (12 females and 15 males, aged from 16 to 49 years) who had died from various non-bone-related causes, mainly unexpected traumas, and from 5 patients with chondroma (2 females and 3 males, 15–42 years old), obtained from open biopsies or after operation. The reliability of the differences in the results between intact bone and bone affected by chondroma was evaluated by a parametric Student’s t test and a nonparametric Mann–Whitney U test. It was found that in the bone affected by chondroma, the mean mass fractions of Co, Cr, Fe, Se, Sb, and Zn were significantly higher than in normal bone tissues. In the neoplastic bone, many correlations between trace elements found in the control group were no longer evident. This work revealed that there is a significant disturbance of the trace element metabolism in bone affected by chondroma.

Phase behaviour of sesame (Sesamum indicum L.) seed oil using supercritical CO2

ABSTRACTNew experimental data were measured for phase transition of the binary system CO2 + black sesame oil. A variable volume cell was employed using the static synthetic method in a temperature range of 303–333 K, pressures up to 20 MPa, and CO2 mass fractions between 0.12–0.39 g/g. For mass fractions &gt; 0.39, phase transition data were not measured due to pressure limitations of the high‐pressure system used. Vapour‐liquid transitions (VLE) of bubble point (BP) were determined. Phase transition data of CO2 + black sesame oil were compared to reported data from the literature involving CO2 and similar oils. The trend of the phase transition behaviour between all systems compared was similar. Phase equilibrium data obtained experimentally were successfully modelled with the Peng‐Robinson equation of state (PR‐EoS) combined with the van der Waals mixing rule (PR‐vdW2) and Wong‐Sandler mixing rule (PR‐WS).

On the use of molecular-based thermodynamic models to assess the performance of solvents for CO2 capture processes: monoethanolamine solutions.

Predictive models play an important role in the design of post-combustion processes for the capture of carbon dioxide (CO2) emitted from power plants. A rate-based absorber model is presented to investigate the reactive capture of CO2 using aqueous monoethanolamine (MEA) as a solvent, integrating a predictive molecular-based equation of state: SAFT-VR SW (Statistical Associating Fluid Theory-Variable Range, Square Well). A distinctive physical approach is adopted to model the chemical equilibria inherent in the process. This eliminates the need to consider reaction products explicitly and greatly reduces the amount of experimental data required to model the absorber compared to the more commonly employed chemical approaches. The predictive capabilities of the absorber model are analyzed for profiles from 10 pilot plant runs by considering two scenarios: (i) no pilot-plant data are used in the model development; (ii) only a limited set of pilot-plant data are used. Within the first scenario, the mass fraction of CO2 in the clean gas is underestimated in all but one of the cases, indicating that a best-case performance of the solvent can be obtained with this predictive approach. Within the second scenario a single parameter is estimated based on data from a single pilot plant run to correct for the dramatic changes in the diffusivity of CO2 in the reactive solvent. This parameter is found to be transferable for a broad range of operating conditions. A sensitivity analysis is then conducted, and the liquid viscosity and diffusivity are found to be key properties for the prediction of the composition profiles. The temperature and composition profiles are sensitive to thermodynamic properties that correspond to major sources of heat generation or dissipation. The proposed modelling framework can be used as an early assessment of solvents to aid in narrowing the search space, and can help in determining target solvents for experiments and more detailed modelling.

Phase Behavior of a United Arab Emirates Stock-Tank Oil and Carbon Dioxide at Reservoir Conditions: Experiments and Thermodynamic Modeling

Injection of a soluble gas like CO2 into an oil reservoir reduces the interfacial tension and oil viscosity and contributes to oil swelling, which together, in turn, enhance the oil mobility and relative permeability. In this work an experimental phase equilibrium setup for the recombination of live oil (stock-tank oil and first-stage separator gas) and measurement of the corresponding phase behaviors of CO2/live oil mixtures is described. In the recombination process, the vapor-to-oil molar ratio was adjusted until the composition of the original reservoir fluid was obtained. The average of the absolute error (AAE) in composition was about 0.77% and 1.09% for the two reservoir fluids under test (named here wells A#22 and A#33, respectively). The optimum vapor-to-oil molar ratio for zero deviation in the methane composition in the live oil (recombined) was about 0.42 for both wells. In addition, the PVTi simulator was used to reproduce the live oil (by combining the first-stage separator gas and the stock-tank oil) and also to predict the recombined oil characteristics at the reservoirs’ saturation pressure and bottom hole temperature. On the other hand, the PVTpro simulator was used to investigate the oil swelling rate and establish the relationship between saturation pressure and the injected CO2 mass fraction. The average of the absolute relative error (AARE) between experimental and predicted saturation pressures was 7.78% for well A#22 and 5.38% for well A#33.

Numerical investigation of counter-flow diffusion flame of biogas–hydrogen blends: Effects of biogas composition, hydrogen enrichment and scalar dissipation rate on flame structure and emissions

This study addresses numerically the influence of several operating conditions on the structure and NO emissions of a biogas diffusion flame. The analysis is conducted at atmospheric pressure in counter-flow configuration and mixture fraction space. CO2 volume in biogas is varied from 25% to 60%, H2 enrichment from 0% to 20% and the scalar dissipation rate from near equilibrium to near extinction. Particular attention is paid to CO2 chemical effect. CO2 contained in biogas can have chemical effects when it participates in chemical reactions and thermal effects when it acts like a pure diluent. Chemical effects of CO2 are elucidated by using the inert species technique. Flame structure is characterized by solving flamelet equations with the consideration of radiation and detailed chemistry.It is observed that flame properties are very sensitive to biogas composition, hydrogen addition and scalar dissipation rate. CO2 increment decreases flame temperature, mass fraction of chain carrier radicals and NO emission index. Blending biogas with hydrogen increases the mixture heating value and makes the fuel more reactive. Hence, chain carrier radicals and NO index emission are all increased. The chemical effect of CO2 is found to be present overall scalar dissipation rate values where it reduces the maxima of temperature and OH mass fraction and increases the maxima of CO and NO mass fractions. H2 enrichment has a weak influence on CO2 chemical effect. Hydrogen-rich biogas flames produce less NO at high scalar dissipation rates.

Analysis of a time dependent injection strategy to accelerate the residual trapping of sequestered CO2 in the geologic subsurface

A time dependent injection strategy for greatly accelerating the immobilization of geologically sequestered CO2 is proposed and analyzed. The injection of high density CO2 into a brine aquifer is followed by brine flooding facilitating residual trapping and dissolution of the CO2 on time scales much shorter than those that would occur by natural processes. One-dimensional kinematic wave equations are derived for the two-phase flow of brine and CO2 and for the transport of dissolved CO2. A solution of these equations using the method of characteristics reveals that brine flooding is most effective when the kinematic wave speed of CO2 saturation is higher than the propagation velocity of a shock wave separating the two-phase flow from the native brine. Finite volume simulation using the reservoir simulator TOUGH2 with PetraSIM interface are generally in good agreement with the one-dimensional model, but show that gravitational overriding of the CO2 can become important if the duration of the injection process is too long. Both methods show that brine flooding is able to reduce the mass fraction of mobile CO2 to less than 10% using a volume ratio brine:CO2 of less than 2.75 on time scales comparable to that of the CO2 injection.

Near wall combustion modeling in spark ignition engines. Part B: Post-flame reactions

Reduced fuel consumption, low pollutant emissions and adequate output performance are key features in the contemporary design of spark ignition engines. Zero-dimensional numerical simulation is an attractive alternative to engine experiments for the evaluation of various engine configurations. Both flame front reaction and post-flame processes contribute to the heat release rate. The contribution of this work is to highlight and model the role of post-flame reactions (CO and hydrocarbons) in the heat release rate.The modeling approach to CO kinetics used two reactions considered to be dominant and thus more suitable for the description of CO chemical mechanism. Equilibrium concentrations of all the species involved were calculated by a two-zone thermodynamic model. The computed characteristic time of CO kinetics was found to be of a similar order to the results of complex chemistry simulations. The proposed model captured the ‘freezing’ effect (reaction rate is almost zero) for temperatures lower than 1800K and followed the trends of the measured values at exhaust. However, a consistent underestimation of CO levels at the exhaust was observed. The impact of the remaining CO on the combustion efficiency is considerable especially for rich mixtures. For a remaining 0.4% CO mass fraction, the impact on combustion inefficiency is 0.1%.Unburnt hydrocarbon, which have not reacted within the flame front before quenching, diffuse in the burnt gas and react. In this work, a global reaction rate models the kinetic behavior of hydrocarbon. The diffusion process was modeled by a relaxation equation applied on the calculated kinetic concentration. The relaxation time was calculated by the reduction of a general hydrocarbon diffusion equation. This modeling approach enabled the final part of combustion to be simulated. The HC consumption predicted by the model is consistent with the HC measurements at the exhaust. The hydrocarbon consumption at the final combustion stage varied from 1% to 6% depending on the operating point.