CO2 Concentration Profiles Research Articles

Large Scale CO2 Releases for Dispersion Model and Safety Study Validation

Abstract The second phase of the CO2PIPETRANS Joint Industry Project (JIP) aims to fill knowledge gaps associated with the safe and reliable pipeline transport of CO2. The JIP has three main focus areas and technical work packages designed to address these. The work packages collect experimental data and experience on dense phase CO2 release model validation data, pipeline fracture arrest, and corrosion. This paper presents an overview of results and conclusions from the work package focusing on collection of data for validation of release models. The JIP consists of 15 partner organisations, who are: Arcelor Mittal, BP, DNV GL, Endesa, ENI, E.on Ruhrgas, Gassco, Gassnova, Health and Safety Executive (HSE) UK, Maersk Oil, Petrobras, Petroleum Safety Authority (PSA) Norway, Shell, V&M Tubes, and Vattenfall. The objective of the CO2 release model validation data work package was to collect and make available data for validating release and dispersion models for dense phase CO2. This involved releasing dense phase CO2 from large inventories through orifices ranging in size 6 mm to 150 mm onto a suitably sized array of instruments to measure the CO2 concentration and temperature profiles. The condition of the CO2 being released was up to 150 barg and 150 °C with release durations up to 10 minutes. Most of the releases were in a horizontal orientation 1m above the ground but during some of the tests the orientation was changed to be upwards, downwards to impact the ground, or into an enclosure. In addition to the CO2 releases described above, the work package also undertook rapid depressurisation of a long horizontal pipe containing 100 barg CO2 in order to collect data, amongst other aspects, on shock wave propagation. These experiments used a 200m long, 50 mm diameter pipe mounted on load cells with an orifice plate and explosive initiated bursting disk at one end. In addition to measuring data within the pipe during the rapid depressurisation tests, dispersion and temperature data was also recorded downstream of the release for release model validation purposes. The paper presents an overview of the frontier experimental work mentioned above along with discussion on the output of the data review that was subsequently completed during which recorded data was compared with model predictions. Validation of dispersion models and safety studies reduces the uncertainty and hence conservatism required in these studies thereby making design and implementation of CO2 pipelines safer and more cost effective.

Soil CO2 concentration in biological soil crusts and its driving factors in a revegetated area of the Tengger Desert, Northern China

Biological soil crusts (BSCs) are an important cover in arid desert landscapes, and have a profound effect on the CO2 exchange in the desert system. Although a large number of studies have focused on the CO2 flux at the soil–air interface, relatively few studies have examined the soil CO2 concentration in individual layers of the soil profile. In this study, the spatiotemporal dynamics of CO2 concentration throughout the soil profile under two typical BSCs (algae crusts and moss crusts) and its driving factors were examined in a revegetated sandy area of the Tengger Desert from Mar 2010 to Oct 2012. Our results showed that the mean values of the vertical soil CO2 concentrations under algal crusts and moss crusts were 600–1,200 μmol/mol at the 0–40 cm soil profiles and increased linearly with soil depth. Daily CO2 concentrations showed a single-peak curve and often had a 1–2 h time delay after the maximum soil temperature. During the rainy season, the mean soil CO2 concentration profile was 1,200–2,000 μmol/mol, which was 2–5 times higher as compared to the dry season (400–800 μmol/mol). Annually, soil moisture content was the key limiting factor of the soil CO2 concentration, but at the daily time scale, soil temperature was the main limiting factor. Combined with infiltration depth of crusted soils, we predicted that precipitation of 10–15 mm was the most effective driving factor in arid desert regions.

Impact of thermal convection on CO2 flux across the earth–atmosphere boundary in high-permeability soils

Quantifying earth–atmosphere gas exchange is a challenging, yet important problem that is made more complicated by the large number of mechanisms that contribute to this process. This work investigates one mechanism controlling non-diffusive gas transport from high-permeability media that is driven by natural diurnal thermal gradients in the upper vadose zone. We quantified CO2 migration through 1-m long columns packed with two different permeability values: sand and large soil aggregates – both dry to eliminate chemical reactions. The bottom ends of the columns were exposed to 2000ppm CO2-enriched air and the CO2 concentration profiles along the columns was continually monitored. The columns were exposed to two different thermal regimes: isothermal conditions and a range of typical nighttime thermal gradients that are known to lead to unstable gas density profiles. Under isothermal conditions, and regardless of the matrix air-permeability, diffusion was the major mechanism for surface–atmosphere gas exchange. Under nighttime conditions, the prevailing mechanism depended upon matrix air-permeability: diffusion controlled CO2 transport in the low permeability matrix, whereas thermal convection dominated transport in the high permeability matrix. Venting by thermal convection caused a CO2 flux of up to two orders of magnitude higher than the diffusive flux. Such a mechanism may be implicated in a number of environmental settings. In soil, thermally driven convection can contribute to soil aeration influencing root respiration and microbial activity, and is likely one of the mechanisms associated with rapid CO2 exchange that is commonly noted to follow tillage. With respect to the global CO2 output, thermal convective venting is shown to be a permeability-limited mechanism with high gas exchange potential and a continuous diurnal presence. Its characteristic spatial scale could include, geologic sources via fractured rock surfaces, soil cracks, mine tailings, and rock-fill embankments.

Analysis and predictive correlation of mass transfer coefficient [formula omitted] of blended MDEA-MEA for use in post-combustion CO2 capture

The mass transfer performance of the absorption of CO2 in aqueous blended MDEA-MEA solutions was evaluated experimentally in a lab-scale absorber packed with high efficiency DX structured packing over MDEA-MEA concentrations of 27/3, 25/5, and 23/7%wt under atmospheric pressure using a premixed feed gas containing 15% CO2 balanced with N2. The absorption performance was presented in terms of overall mass transfer coefficient (KGav) and CO2 concentration profile. The results showed that the mass transfer performance increased as ratio of MEA in the blended solution, temperature, and liquid flow rate increased but decreased as CO2 loading increased. In addition, it was found that the cyclic capacity and relative solvent regeneration ability decreased as the ratio of MEA in the blended solution increased. Based on mass transfer performance, cyclic capacity, and relative solvent regeneration ability, 23/7%wt MDEA-MEA was found to be the most effective blend ratio among the three ratios investigated in the present work. Also, the correlation for predicting KGav for CO2 absorption into aqueous blended MDEA-MEA was successfully developed with an AAD of 21.8%.

Shock tube study of methanol, methyl formate pyrolysis: CH3OH and CO time-history measurements

Methanol and methyl formate pyrolysis were studied by measuring CH3OH and CO concentration time-histories behind reflected shock waves. In the study of methanol pyrolysis, experimental conditions covered temperatures of 1266–1707K, pressures of 1.1–2.5atm, and initial fuel concentrations of 1% and 0.2% with argon as the bath gas. Detailed comparisons of CH3OH and CO concentration profiles with the predictions of the detailed kinetic mechanism of Li et al. (2007) [8] were made. Such comparisons combined with sensitivity analysis identified the need to include an additional methanol decomposition channel, CH3OH↔CH2(S)+H2O, into the mechanism. Pathway and sensitivity analyses for methanol decomposition were performed, leading to rate constant recommendations both for CH3OH unimolecular decomposition and H-abstraction reactions with improved model performance. In the study of methyl formate pyrolysis, methanol concentration time-histories were measured at temperatures over the range of 1261–1524K, pressures near 1.5atm, and initial fuel concentrations of 1% with argon as the bath gas. Our current work, and CO time-histories from previous work, indicates that the Dooley et al. (2010) [3] model is able to accurately simulate most species concentrations in shock tube experiments at early times. However, model improvement is still needed to match the CH3OH and CO time-histories at later times. Incorporation of the modified rate constants in the methanol sub-mechanism leads to good predictions of the full methanol time-histories at all temperatures. The kinetic implications of some aspects of the CO time-histories and suggestions for further improving the predictive capabilities of these mechanisms are discussed. The current results are the first quantitative measurements of CH3OH time-histories in shock tube experiments, and hence are a critical step toward understanding of the chemical kinetics of oxygenates.

Various air distribution modes on commercial airplanes—Part 2: Computational fluid dynamics modeling and validation

Both experimental test and numerical modeling can be used to investigate air distribution on commercial airplanes. Numerical modeling by computational fluid dynamics has gained popularity; however, current computational fluid dynamics modeling efforts are concentrated primarily on the mixing-air distribution mode. To fully evaluate computational fluid dynamics modeling for different air distribution modes, the flow, heat transfer, and pollutant species transport in a twin-aisle aircraft cabin mockup is modeled. Three air distribution modes, namely the mixing, under-aisle displacement, and personal air distribution modes, are studied. The steady renormalization group k-ϵ model together with the standard wall function has been employed for turbulence modeling and the near-wall treatment. The experimental data in terms of the velocity field, temperature, and CO2 concentration profiles are applied to validate the numerical models. This study finds that the renormalization group k-ϵ model is able to solve major air distribution parameters in reasonable agreement with the measured values. When carrying out the steady computational modeling by resolving the Reynolds-averaged Navier-Stokes equations, it should be noted that the models may underestimate the turbulent mixing effect.

Multi-points scanning method for wavelength locking in CO2 differential absorption lidar

Differential absorption lidar (DIAL) is a promising technique for retrieving atmospheric CO2 concentration profiles, which help researchers gain an insight into the carbon cycle. The slight CO2 absorption line center frequency shift caused by pressure and temperature change causes reduced accuracy when using the DIAL technique. The ground-based DIAL performances, aimed at retrieving the vertical atmospheric CO2 concentration distributions, are markedly deteriorated by such interferences. The multi-points scanning method is presented and investigated to handle this problem. Experiments show that a transmitted laser can be locked at the desired ON wavelength with an average accuracy of 0.0956 pm and variance of 4.13E-8 pm at various altitudes ranging from 1000 to 9000m using this proposed method.

Modeling mass transfer of CO2 in brine at high pressures by chemical potential gradient

To investigate long-term CO2 behavior in geological formations and quantification of possible CO2 leaks, it is crucial to investigate the potential mobility of CO2 dissolved in brines over a wide range of spatial and temporal scales and density distributions in geological media. In this work, the mass transfer of aqueous CO2 in brines has been investigated by means of a chemical potential gradient model based on non-equilibrium thermodynamics in which the statistical associating fluid theory equation of state was used to calculate the fugacity coefficient of CO2 in brine. The investigation shows that the interfacial concentration of aqueous CO2 and the corresponding density both increase with increasing pressure and decreasing temperature; the effective diffusion coefficients decrease initially and then increase with increasing pressure; and the density of the CO2-disolved brines increases with decreasing CO2 pressure in the CO2 dissolution process. The aqueous CO2 concentration profiles obtained by the chemical potential gradient model are considerably different from those obtained by the concentration gradient model, which shows the importance of considering non-ideality, especially when the pressure is high.

Variability of CO2 concentrations and fluxes in and above an urban street canyon

The variability of CO2 concentrations and fluxes in dense urban environments is high due to the inherent heterogeneity of these complex areas and their spatio-temporally variable anthropogenic sources. With a focus on micro- to local-scale CO2-exchange processes, measurements were conducted in a street canyon in the city of Basel, Switzerland in 2010. CO2 fluxes were sampled at the top of the canyon (19 m) and at 39 m while vertical CO2 concentration profiles were measured in the center and at a wall of the canyon. CO2 concentration distributions in the street canyon and exchange processes with the layers above show, apart from expected general diurnal patterns due mixing layer heights, a strong dependence on wind direction relative to the canyon. As a consequence of the resulting corkscrew-like canyon vortex, accumulation of CO2 inside the canyon is modulated with distinct distribution patterns. The evaluation of diurnal traffic data provides good explanations for the vertical and horizontal differences in CO2-distribution inside the canyon. Diurnal flux characteristics at the top of the canyon can almost solely be explained with traffic density expressed by the strong linear dependence. Even the diurnal course of the flux at 39 m shows a remarkable relationship to traffic density for east wind conditions while, for west wind situations, a change toward source areas with lower emissions leads to a reduced flux.

Dynamic Adsorption of CO2 from Methane: Studies on Mass and Heat Transfer

AbstractThree‐dimensional computational fluid dynamics studies related to dynamics adsorption of CO2 from natural gas is found to be limited. 3D analyses for dynamics adsorption are substantially crucial to give a better prediction on the adsorption process by considering the actual fluid flow behavior within the packed‐bed porous media. A kinetic adsorption model has been integrated in a commercial fluid dynamics simulator to simulate the 3D hydrodynamics and adsorption phenomenon in a zeolite‐filled packed column for a CO2‐methane separation system. The effects of various parameters such as Reynolds number, CO2 feed concentration, feed temperature, and column dimension on CO2 adsorption efficiency have been investigated. A correlation for adsorption efficiency based on the CO2 concentration profiles has been developed and validated.

Modeling CO2 Absorption and Desorption by Aqueous Monoethanolamine Solution with Aspen Rate-based Model

Nineteen data sets of CO2 absorption by aqueous monoethanolamine solution (0.3g/g monoethanolamine in water) from the recent pilot plant studies at the University of Kaiserslautern have been simulated with Aspen rate-based model. The simulation study was performed with both the rigorous rate-based model and the traditional equilibrium- stage model. The results show the rate-based model yields reasonable predictions on all key performance measurements including CO2 removal percentage in the absorber, temperature and CO2 concentration profiles in the absorber and the desorber, and the desorber reboiler duty. In contrast, the equilibrium-stage model fails to reliably predict these key performance variables.

Concentration profiles of CH4, CO2 and N2O in soils of a wheat–maize rotation ecosystem in North China Plain, measured weekly over a whole year

Agricultural soils are main sources and sinks of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The source–sink function depends on soil characteristics, climate and management. Emission measurements usually quantify the net result of production, consumption and transport of these gases in the soil; they do not provide information about the depth distributions of the concentrations of these gases in the soil. Here we report on concentrations of CO2, CH4 and N2O in air of 300cm deep soil profiles, at resolutions of 30–50cm, over a full year. Gas samples were taken weekly in a long-term field experiment with an irrigated winter wheat–summer maize double cropping system, and four fertilizer N application rates (0, 200, 400 and 600kgNha−1year−1). The results showed distinct differences in CH4, CO2 and N2O concentrations profiles with soil depth. The concentrations of CO2 in soil air increased with soil depth and showed a seasonal pattern with relatively high concentrations in the warm and moist maize growing season and relatively low concentrations in the winter-wheat growing season. In contrast, CH4 concentrations decreased with depth, and did not show a distinct seasonal cycle. Urea application did not have a large effect on CH4 or CO2 concentrations, neither in the topsoil nor the subsoil. Concentrations of N2O responded to N fertilizer application and irrigation. Application of fertilizer strongly increased grain and straw yields of both winter wheat and summer maize, relatively to the control, but differences in yield between the treatments N200, N400 and N600 were not statistically significant. However, it significantly increased mean N2O concentrations peaks at basically all soil depths. Interestingly, concentrations of N2O increased almost instantaneously in the whole soil profile, which indicates that the soil had a relatively high diffusivity, despite compacted subsoil layers.In conclusion, the frequent measurements, at high depth resolutions, of concentrations of CH4, CO2 and N2O in soil air under a winter wheat–summer maize double crop rotation provide detailed insight into the production, consumption and transport of these gases in the soil. Concentrations of CH4, CO2 and N2O responded differently to management activities and weather conditions.

Estimating a Lagrangian Length Scale Using Measurements of CO2 in a Plant Canopy

Analytical Lagrangian equations capable of predicting concentration profiles from known source distributions offer the opportunity to calculate source/sink distributions through inverted forms of these equations. Inverse analytical Lagrangian equations provide a practical means of estimating source profiles using concentration and turbulence measurements. Uncertainty concerning estimates of the essentially immeasurable Lagrangian length scale (\({\mathcal{L}}\)), a key input, impedes the operational practicality of this method. The present study evaluates \({\mathcal{L}}\) within a corn canopy by using field measurements to constrain an analytical Lagrangian equation. Measurements of net CO2 flux, soil-to-atmosphere CO2 flux, and in-canopy profiles of CO2 concentration provided the information required to solve for \({\mathcal{L}}\) in a global optimization algorithm for 30-min time intervals. For days when the canopy was a strong CO2 sink, the optimization frequently located \({\mathcal{L}}\) profiles that follow a convex shape. A constrained optimization then fit the profile shape to a smooth sigmoidal equation. Inputting the optimized \({\mathcal{L}}\) profiles in the forward and inverse Lagrangian equations leads to strong correlations between measured and calculated concentrations and fluxes. Coefficients of the sigmoidal equation were specific to each 30-min period and did not scale with any measured variable. Plausible looking \({\mathcal{L}}\) profiles were associated with negative bulk Richardson number values. Once the canopy senesced, a simple eddy diffusivity profile sufficed to relate concentrations and sources in the analytical Lagrangian equations.

Model for growth of bubbles during proofing of viscoelastic dough

A model for growth of bubbles during proofing of bread dough is presented for infinitely dilute as well as finite volume fraction gas dispersions. The model accounts for diffusion of CO2, produced by fermentation, along with the resistance to bubble expansion by the viscoelasticity of the dough as described by Oldroyd-B constitutive equation. The model predicts evolution of bubble size, bubble growth rate and the profiles of CO2 concentration and normal stresses in the vicinity of the gas bubble. The growth of bubbles exhibits a lag time followed by an exponential growth phase. The lag time is found to be smaller for larger dough relaxation time, larger surface tension, smaller dough viscosity, higher temperature, higher gas volume fraction and higher CO2 production rate. The bubble growth rate is larger for smaller bubbles resulting in crossover of bubble size at longer times.

Comprehensive mass transfer and reaction kinetics studies of CO2 absorption into aqueous solutions of blended MDEA–MEA

In the present work, the reaction kinetics and mass transfer performance of CO2 absorption into aqueous solutions of blended MDEA–MEA solutions were comprehensively studied. The reaction kinetics was investigated using a laminar jet absorber in terms of a second order reaction rate constant and enhancement factor. The mass transfer performance was evaluated experimentally in a lab-scale absorber packed with high efficiency DX structured packing in terms of CO2 concentration profile and over all mass transfer coefficient (KGav). The experiments were conducted over the MDEA/MEA concentrations of 27/3, 25/5, and 23/7wt% MDEA/wt% MEA (which equivalent to MDEA–MEA molar ratios of 2.3/0.5, 2.1/0.8, and 1.95/1.16M, respectively). It was found that kMEA was successfully extracted and can be expressed as: kMEA=(5.127×108)exp-3373.8T. The results also show that the operating parameters (i.e., MDEA–MEA blended ratio, temperature, and CO2 loading) affect both the reaction kinetics and mass transfer performance significantly. Lastly, the MDEA–MEA blended ratio of 1.95/1.16 provided the highest reaction kinetics and mass transfer performance among the three concentrations investigated in this study.

Numerical Simulation of Natural Convection in Heterogeneous Porous media for CO2 Geological Storage

We report a modeling and numerical simulation study of density-driven natural convection during geological CO2 storage in heterogeneous formations. We consider an aquifer or depleted oilfield overlain by gaseous CO2, where the water density increases due to CO2 dissolution. The heterogeneity of the aquifer is represented by spatial variations of the permeability, generated using Sequential Gaussian Simulation method. The convective motion of the liquid with dissolved CO2 is investigated. Special attention is paid to instability characteristics of the CO2 concentration profiles, variation of mixing length, and average CO2 mass flux as a function of the heterogeneity characterized by the standard deviation and the correlation length of the log-normal permeability fields. The CO2 concentration profiles show different flow patterns of convective mixing such as gravity fingering, channeling, and dispersive based on the heterogeneity medium of the aquifer. The variation of mixing length with dimensionless time shows three separate regimes such as diffusion, convection, and second diffusion. The average CO2 mass flux at the top boundary decreases quickly at early times then it increases, reaching a constant value at later times for various heterogeneity parameters.

Detailed Modeling of NOx and SOx Formation in Co-combustion of Coal and Biomass with Reduced Kinetics

In the paper, the numerical simulation program coupled with the detailed chemical reaction mechanism and computational fluid dynamics software was applied to calculate the concentration profiles of CO, NOx, and SOx during co-combustion of coal and biomass. The predicted data are compared to experimental results in an entrained flow combustion reactor to validate the numerical method for pulverized coal combustion. The characteristics of pollutant emissions in co-combustion with coal and three typical kinds of biomasses (Swedish wood, Danish straw, and sewage sludge) are also investigated. NO formation is significantly affected by the reactor temperature, and an increasing temperature obviously enhances the NO concentration. In the range of the calculated temperature, the final SO2 emission level is not obviously influenced by the temperature. Co-combustion technology could effectively reduce the pollutant emissions, and the effect is proportional to the blending ratio of biomass. The biomass with low contents of nitrogen and sulfur and a high volatile content and lower heating value is an ideal co-fired fuel to reduce NO and SO2 emissions.

合肥上空大气二氧化碳Raman激光雷达探测研究

Raman lidar is used as an effective tool for detection of the atmospheric compositions and characteristics.A complicated Raman lidar system was developed by Anhui Institute of Optics and Fine Mechanics of Chinese Academy of Sciences for measuring the low-tropospheric temporal and spatial distribution of CO2 in the atmosphere.And a series of observations and comparative analysis were performed.A wavelength of 355 nm UV laser was applied as the light resource in this system and the N2 and CO2 Raman backscattering signals were acquired by a dual-channel photon-counting card.Li-7500 H2O/CO2 analyzer was employed to compare with the detection results to make system calibration and then to retrieve the atmospheric CO2 volume mixing ratio in the horizontal and vertical direction.And the spatial temporal variation of a whole night atmospheric boundary layer CO2 profile was measured at Hefei area.The observations have a good agreement in the trend of change with the Li-7500 H2O/CO2 analyzer.The results show that atmospheric CO2 has relatively homogeneous concentration and the Raman lidar is capable of continuous measuring efficiently the temporal and spatial distribution of CO2 in the atmosphere.

合肥上空大气二氧化碳Raman激光雷达探测研究

合肥上空大气二氧化碳Raman激光雷达探测研究

拉曼激光雷达探测低对流层大气二氧化碳分布

拉曼激光雷达探测低对流层大气二氧化碳分布