Impure Carbon Research Articles

Evaluation of Charcoal Usage and Its Influence on Deforestation in Makurdi Metropolis Benue State, Nigeria

Charcoal is the dark grey residue consisting of impure carbon obtained from vegetation substance and produced by pyrolysis, the heating of wood in the absence of oxygen. Charcoal is considered the major source of energy for the inhabitants of Makurdi metropolis. The study was conducted to assess the consumption of charcoal in Makurdi metropolis. Five council wards were selected purposively for data collection. The selected wards are noted for having large quantities of charcoal and consumers almost all year round. The wards selected are Agan, Fiidi, Wadata, Modern Market, and North Bank. From each council ward, 20 respondents were drawn using a random sampling technique. 100 respondents were selected and interviewed using a pre-tested checklist (questionnaire) to collect primary data. From the result, Prosopis africana was the highest used tree species for charcoal with 83.5% then Vitellaria paradoxa with 7.9%. Also, 88% of the respondents preferred charcoal for cooking in providing food for the family because of its affordability compared to other cooking energy sources. Therefore, it is inferred that charcoal has a positive impact on the lives of consumers since affordability is considered the main reason why the majority of households use charcoal. However, the continuous use of forest trees threatens the future of our forest estate and biodiversity leading to land degradation, endangering of species and enhancement of global warming. Therefore, Alternative energy sources should be encouraged for household fuel to ease the pressure on charcoal.

New models for estimating minimum miscibility pressure of pure and impure carbon dioxide using artificial intelligence techniques

CO2 miscible flooding stands out as one of the most-commonly employed and promising processes in enhanced oil recovery. The key factor for ensuring success in designing and executing CO2 injection projects lies in the precise determination of the Minimum Miscibility Pressure (MMP). Despite significant research endeavors in measuring and predicting the MMP through the use of empirical, analytical, numerical, and experimental approaches, the need for a comprehensive, accurate, efficient, and easy-to-use model remains. In response to this gap, our study developed various predictive models with 205 datasets, including well-established ones such as Artificial Neural Network (ANN), Random Forest (RF), and K-Nearest Neighbors (KNN) along with employing the Gradient Boosting Algorithm (GBA) with the Grid Search (GS) as a novel approach to predict the MMP of both pure and impure CO2. The performance of these models was validated by comparing them with previously published models, using relevant performance metrics such as R2 (coefficient of determination) and MAPE (mean absolute percentage error). Our results demonstrated that the GBA model with GS optimization exhibited remarkable superiority in terms of performance and accuracy in both scenarios, outperforming previously published models as well as the developed ANN, RF, and KNN models. For pure CO2, it achieved an impressive R2 value of 0.999 on the training set and a relatively high value of 0.910 on the validation set. Additionally, the model showed remarkably low MAPE values of 0.0705 % on the training set and 9.238 % on the validation set. Similarly, for impure CO2, the GBA model with GS optimization achieved an R2 value of 0.999 on the training set and a relatively high value of 0.865 on the validation set. The model also exhibited low MAPE values of 1.66 % on the training set and 6.798 % on the validation set. These findings highlight the potential of the GBA model with GS optimization as a valuable approach for accurately estimating the MMP, offering a cost-effective and efficient approach for designing and optimizing CO2 flooding operations in enhanced oil recovery processes.

Thermophysical evolution during different decompression of N2‐containing S‐CO2 pipelines

AbstractPipelines transporting impure supercritical carbon dioxide in the carbon capture, utilization, and storage (CCUS) chain exhibit varying decompression characteristics due to engineered emissions or accidental leakage, resulting in diverse temperature drops and heat transfer mechanisms in the media and pipe walls. Therefore, studying heat transfer characteristics during slow and instantaneous decompression is crucial to investigating pipeline operational risks. In this work, supercritical CO2 pipeline valve release and rupture disc release experiments were performed with a 1.5% molar ratio of N2 content in an experimental pipeline (16 m long, 100 mm inner diameter). The evolution of the medium and pipe wall's physical properties was measured and discussed. Two methods of depressurization were employed to analyze the phase changes and heat transfer processes in the pipe. The instantaneous decompression process has a shorter decompression time and undergoes fluctuating and stable decompression stages. The slow decompression process has a slower temperature drop rate, but the wall during the process can reach a lower minimum temperature. Both release methods cause a larger temperature drop and Nusselt number at the bottom of the pipe wall due to evaporation heat transfer compared to the middle and top. The slow decompression process demonstrates a higher peak Nusselt number at the bottom, resulting in superior heat transfer efficiency compared to the instantaneous decompression process. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Dehydration requirements for CO2 and impure CO2 for ship transport

CCS is expected to become an important contribution to the mitigation of carbon dioxide emissions. Transportation of CO2 from the capture site to the permanent storage reservoir plays a key role, and transportation by ship is now viewed as a relevant alternative for certain combinations of captured CO2 volume and distance.This paper presents experimental equipment, methods and new results for the water content of carbon dioxide and impure carbon dioxide in equilibrium with hydrates at temperatures between (-55 and -10)°C and pressures between (3 and 120) bar, hence in both vapour and liquid phases. The experimental data are compared with predictions from two thermodynamic models: the Cubic-Plus-Association equation of state and an approach using Multi-Fluid Helmholtz Energy Approximation (MFHEA) equations of state (EoS). In all cases, the hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw.

The high temperature degradation of ferritic stainless steel in solid carbon atmospheres

Stainless steel is widely used for many components and parts in coal-fired thermal power plants. AISI 430 ferritic stainless steel (FSS) is one common grade to combat the degradation at high temperatures in coal combustion atmospheres containing flue gas, coal ash, and soot (impure solid carbon particles). However, the effect of the solid carbon particles on the degradation of FSS needs to be clarified. Graphite powder was used to simulate solid carbon atmospheres for investigating the degradation of AISI 430 at high temperatures of 1150℃ to 1350℃ in coal-fired boilers. After the carbothermic reduction, the mass gain of a pre-oxidized sample at 750℃ was approximately 0.0793 mg⸳cm-2 and increased when increasing the reduction temperature. The peak of Fe2O3 and Cr7C3 were detected by X˗ray diffraction (XRD) after the oxidation and reduction test, respectively. Besides, the degree of sensitivity (%DoS) of the samples was measured by double loop electrochemical potentiokinetic reactivation (DL-EPR) technique and increased around 30 times after heating the pre-oxidized sample to 1150℃.

Numerical Simulation of Carbon Dioxide–Nitrogen Mixture Dissolution in Water-Saturated Porous Media: Considering Cross-Diffusion Effects

The possibility of impure carbon dioxide (CO2) sequestration can reduce the cost of these projects and facilitate their widespread adoption. Despite this, there are a limited number of studies that address impure CO2 sequestration aspects. In this study, we examine the convection–diffusion process of the CO2–nitrogen (N2) mixture dissolution in water-saturated porous media through numerical simulations. Cross-diffusion values, as the missing parameters in previous studies, are considered here to see the impact of N2 impurity on dissolution trapping in more realistic conditions. Homogeneous porous media are used to examine this impact without side effects from the heterogeneity, and then simulations are extended to heterogeneous porous media, which are a good representative of the real fields. Heterogeneity in the permeability field is generated with sequential Gaussian simulation. Using the averaged dissolved CO2 and dissolution fluxes for each case, we could determine the onset of different dissolution regimes and behaviors of dissolution fluxes in CO2–N2 mixture dissolution processes. The results show that there is a notable difference between the pure cases and impure cases. Additionally, a failure to recognize the changes in the diffusion matrix and cross-diffusion effects can result in significant errors in the dissolution process. At lower temperatures, the N2 impurity decreases the amount and flux of CO2 dissolution; however, at higher temperatures, sequestrating the CO2–N2 mixture would be a more reasonable choice due to enhancing the dissolution behavior and lowering the project costs. The results of the heterogeneous cases indicate that heterogeneity, in most cases, reduces the averaged dissolved CO2, and dissolution flux and impedes the onset of convection. We believe that the results of this study set a basis for future studies regarding the CO2–N2 mixture sequestration in saline aquifers.

Joint effects of production quality improvement of biofuel and carbon emissions towards a smart sustainable supply chain management

Controlling carbon emissions and improving biofuel generation are crucial for every manufacturer. The responsible managers’ primary concern is to increase profit and form a sustainable supply chain. Further, supply chain managers select appropriate combinations when dealing with minimizing waste, quality improvement of biofuel, and multi-mode transportation. The study’s objective is to show the combined effects of improved quality of biofuel and controlling carbon emissions in a smart three-echelon sustainable supply chain management. In this model, one-manufacturer, one-supplier, and multi-retailers are contemplated. When the supplier makes impure biofuel, it transports to the manufacturer for pure biofuel. A random production rate is applied through a smart production system; still, impure biofuel is produced. For that reason, a two-stage inspection policy with a variable manufacturing rate is considered to make the production process flexible such that the quantity of impure biofuel is reduced and impure biofuel treated as a waste. After production, the manufacturer transports pure biofuel to multi-retailers. A variable selling price-dependent demand is introduced for the maximization of profit. The carbon emissions are considered, which are associated with different operational activities of inventory such as preparation of setup of suppliers, manufacturers, transportation of products, and holding stock at manufacturers and the retailer’s end. The retailers keep up the actual order as on demand to the manufacturer to save from the excess holding costs. The model has been solved with a specific algebraic procedure to obtain the global optimum solution. Four numerical experiments are conducted to ensure the model’s effectiveness and profit maximization. The results indicate that these three echelons’ smart production significantly minimized impure biofuel and carbon emissions, positively impacting the environment and the finance, attached to the inventory. The proposed integrated system’s validity is illustrated with sensitivity analysis, numerical examples, and graphical representation. In addition, various worthy managerial insights based on the study are provided.

Modeling the density of acid gases at extensive ranges of pressure and temperature conditions

Carbon dioxide remains in the atmosphere for long time and has harmful effect on environment. Knowledge of the thermophysical properties of pure and impure carbon dioxide in this process can be very useful for monitoring this kind of processes. In this study, some intelligent models were developed to precisely predict the density of acid gases (i.e., carbon dioxide, hydrogen sulfide, and sulfur dioxide) under wide ranges of pressure (0.03–125.86 MPa), temperature, (220.204–450.052 K), mole fraction of carbon dioxide (50–100%), mole fraction of hydrogen sulfide (0–49%), and mole fraction of sulfur dioxide (0–5.2%). Two least square vector machine models optimized with harris-hawks optimization and coupled simulated annealing, two radial basis function neural network models optimized with harris-hawks optimization and cuckoo search algorithm, and a multilayer perceptron optimized with Levenberg-Marquardet algorithm were developed for the estimation of the density of acid gases based on 1911 experimental data points. Besides, by using the best models, a committee machine intelligent system was extended. Furthermore, seven equations of state were used to predict the density of the systems. The results revealed that the developed models present reliable prediction abilities. In addition, it was found that the committee machine intelligent system and multilayer perceptron are the fittest paradigms with coefficient of determination values of 0.985 for both paradigms. Lastly, the performance of the best-developed model was compared with equations of state. Although a good match between equations of state's predictions and experimental data was observed at low pressure, as pressure increased, the deviation between equations of state's prediction and experimental data increased. However, at all ranges of pressure, our best-developed model has good consistency with the experimental data. Trend analysis showed that our best model estimates the trend of variation of density as a function of pressure perfectly.

Origin of authigenic albite in a lacustrine mixed-deposition sequence (Lucaogou Formation, Junggar Basin) and its diagenesis implications

Authigenic albites occur widely in clastic reservoirs with important implications for diagenesis and reservoir formation. The middle Permian Lucaogou Formation in the Jimusaer Sag (Junggar Basin, NW China), where major exploration breakthroughs in shale oil have been achieved, reveals a new phenomenon that authigenic albites are abundant in unique mixed carbonate–volcanic–clastic sequences. This has not been reported in the literatures. To fill the knowledge gap, the origin of these authigenic albites and their relationship with dissolution pores (i.e. diagenesis implications) were investigated. Results show that two types (I and II) of authigenic albite were identified within the shale oil reservoirs. Euhedral Type I authigenic albites with 3–10 μm only occur in dolarenite intraclasts and are symbiotic with amorphous dolomite minerals with a pure chemical composition of >99% albite-end-member content. Larger Type II authigenic albites with 10–50 μm are widely distributed in reservoirs, primarily in dissolution pores, and coexist with authigenic dolomite minerals or dolomite overgrowths. Their chemical composition is less pure with anorthite-end-member contents that range from undetectable to 9.77%, with an average of 1.34%. A symbiotic relationship, pure chemical composition, size, and euhedral morphology indicate that Type I authigenic albites precipitated during syngenetic hydrothermal action. However, the morphology of dissolution pores, residual symbiotic “orthoclase”, impure chemical composition and carbon–oxygen isotope indicate that Type II were the products of the dissolution and reprecipitation of “perthite” crystal pyroclasts influenced by acid organic fluids in latter diagenesis. The differential dissolution of “orthoclase” and “albite” components in “perthite” crystal pyroclasts formed enormous intergranular secondary pores in the presence of dolomite minerals in the shale oil reservoirs.

Compositional modeling of multicomponent gas injection into saline aquifers with the MUFITS simulator

Reservoir simulations of the co-injection of natural gas, carbon dioxide, and other non-condensable gases into saline aquifers are in demand in many areas of subsurface utilization, ranging from excess energy and greenhouse gas storage to the substitution of cushion gas with CO2. We aim at extending our reservoir simulator MUFITS for modeling flows in porous media related to these applications. For the accurate prediction of phase equilibria in aqueous systems, we implement a modified method of Søreide and Whitson in the compositional module of the software. The modified equation of state (EoS) involves the most recent literature data on the binary interaction coefficients and several new correlations for volume shifts to improve the accuracy of the EoS for predicting the partial volume of dissolved gases. All the aggregated and developed correlations are built into the simulator to facilitate its usage by the scientific community. The extended software is validated against a benchmark study of pure CO2 injection into a saline aquifer. Furthermore, two more complicated studies concerning the co-injection of several gases are conducted to demonstrate the potential application areas of MUFITS. First, we simulate the injection of impure carbon dioxide into an aquifer and briefly discuss the influence of N2 impurity on the propagation of the gas plume. We show that the plume is significantly wider in the case of impure CO2 injection. Second, we simulate the injection of supercritical CO2 into a synthetic natural gas storage reservoir to substitute cushion gas. We show that the mechanical dispersion can cause a rapid CO2 spread into the wells used for natural gas production.

Highly efficient reduction of O2-containing CO2 via chemical looping based on perovskite nanocomposites

Abstract Purification/separation of CO2 stream from carbon capture or other carbon source is highly energy consuming process. However, oxidative impurity of O2 either deactivates catalysts in most carbon reduction systems, and thus reduces CO2 conversion efficiency. Here we report an effective method for splitting O2-containing CO2 into CO, through a chemical looping scheme with Cu (5 at%) doped LaFeO3 perovskites as efficient oxygen carriers. Up to 2.28 mol/kg CO yield was achieved with high stability in the presence of O2, five times higher than that with the state-of-the-art oxygen carrier, while pristine LaFeO3 perovskite only showed efficient capability of reducing pure CO2. Furthermore, the syngas productivity was doubled with Cu modification. Through experimental characterizations and ab initio calculations, we uncovered that the exsolution of metallic Cu on the surface of reduced perovskite was able to mitigate the competition between CO2 and O2 in the re-oxidation step. We envision that the efficient CO2 splitter with well-designed oxygen carriers have the potential to facilitate economical combination of impure carbon feedstock and carbon utilization system.

Investigation of carbon dioxide capture and storage by a novel LSSVM-GA method

Accurate knowledge about vapor–liquid equilibrium (VLE) and phase behavior of impure carbon dioxide has noticeable effect on designing carbon dioxide capture and storage (CCS) processes. In the current work, a novel computational method namely least square support vector machine (LSSVM) was used to predict VLE of binary system of carbon dioxide with nitrogen, hydrogen, oxygen, and argon. To this end, two models based on LSSVM were developed for vapor and liquid phases. The accuracy of predicting models was investigated by different methods. The results express that the proposed algorithms are dependable for the estimation of phase behavior of impure CO2.

DATA-BASED PREDICTION OF SOOT EMISSIONS FOR TRANSIENT ENGINE OPERATION

Global vessel traffic is one of the origins responsible for air pollution. Annex VI of the IMO International Convention for the Prevention of Pollution from Ships (MARPOL) focusses on air pollution. Air pollution accrues mainly from energy conversion in combustion engines especially during transient engine operation. One significant pollutant is soot. It represents impure carbon substances in various sizes due to an incomplete combustion of hydrocarbons. This paper focusses on the data-based modelling of soot for transient engine operation in order to predict air pollution in the context of a sophisticated manoeuvring assistance system. In a first step, a stationary approach is investigated and extended for transient engine operation. If one knows about the consequences of his actions, then the role of the human is enforced to decide on energy efficient and emission reduced ship operation, especially during ship manoeuvres.

Understanding gas-phase breakout with high H2 content in CCS pipeline gathering networks

An accurate understanding of the behaviour of impure carbon dioxide (CO2) during pipeline transport stage is required for commercial scale deployment of Carbon Capture and Storage (CCS) networks. Impurities in the CO2 stream modify phase behaviour and change the thermophysical and transport properties of the stream. CO2 streams containing hydrogen (H2) are a particular challenge due to the unique physical properties of H2. In a CCS gathering network where CO2 is sourced from processes such as pre-combustion capture or hydrogen production, H2 with a concentration of 2% mol can be expected to be present in the mixture.This paper describes foreseeable operating scenarios where gas breakout in single-phase CCS gathering networks might occur, leading to pockets of gas with high H2 concentration. Multiphase flow modelling of a CCS gathering network with impure CO2 containing H2 has been performed, demonstrating these operating scenarios and providing a basis for design. The H2 content of the gas breakout is shown to be >20% mol when the conditions are close to bubble point.High concentrations of H2 due to gas breakout must be considered as part of a single-phase CCS gathering network design, whenever H2 is present. This paper provides practical guidelines for understanding, quantifying and, managing the worst design cases for H2 exposure due to gas breakout. Specific recommendations for what must be included in the project design basis are presented. Potential mitigating factors and engineering measures that can be taken to manage high H2 concentration in a CCS system are also discussed.

Deposition of Carbon Thin Film by Means of a Low-Frequency Plasma Sputtering Using Battery Carbon Rods as a Target

Carbon rods of battery were utilized as a target in a plasma sputtering deposition of a carbon thin film. The rods were taken from unused battery waste containing some impurities. This study was intended to investigate the effect of the impurities on the resulted thin film. Furthermore, this work aimed to study the utilization of an unconventional sputtering technique to deposit the carbon film on glass substrates. A low-frequency plasma generator of 40 kHz was used to power the sputtering reactor. The plasma was generated from an Argon gas in a medium vacuum pressure. Two deposition parameters studied in this work were plasma power varied from 220 watts to 360 watts and substrate temperature varied from 25 °C to 202 °C. The carbon target in this research was also functioned as an electrode in the sputtering system. The deposition process was carried out for 1 hour to produce a reasonably thick carbon thin film. The resulted films were characterized using a Fourier Transform Infrared (FTIR) spectroscopy. The FTIR spectra showed a distinct peak around 1200 cm-1 and 1600-1700cm-1 related to the C-C and C = C vibration respectively. The relatively broad peak consisted of a doublet indicating a complex structure of the carbon film, presumably an amorphous carbon film. It was proven that impure carbon could be used as the target and successfully deposited on the glass substrate.

Non Destructive Methods (XRF and XRD) For Estimation of Impure Carbon and Heavy Metals in Printer Toner Ink Powder

Air pollution constitutes the largest among all of the environmental risks. Dust and soot fragments forms components of air particulates, which are released into the air as extremely small particles or liquid droplets. The basis of this research is to characterize toner ink powder and wood soot samples and the detection of metallic pollutants in wood soot (WS) and printer toner ink (PIS) for their physicochemical properties (pH, conductivity, bulk density and moisture content) and instrumental analysis using scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR). Two non- destructive analytical techniques; Dispersive X-ray Fluorescence Spectrometry (ED-XRF) and X-ray Diffraction (XRD) were adopted for heavy metals (elemental) composition and mineralogy respectively. The pH of printer ink and wood soot shows higher pH value which indicates that they are alkaline. Low conductivity values were reported with low moisture, indicating easy fragmentation and spreading. The bulk density values for samples shows that the soot can be easily spread by air current to the environment. The EDS analysis indicates that the soot particles to be composed of primarily impure carbon, thus pointing at potential organic pollutants. The IR spectra show characteristics signals at 749.2 cm-1, 745.5 cm-1, 738.0 cm-1 and 745.5 cm-1 for wood soot and printer ink which correspond to C-H of aromatic group, 1703.4 cm-1, 1699.7 cm-1. The XRF analysis reveals high concentration of Chromium and other toxic metals. The mineralogical components of the soot and printer ink samples revealed the presence of associated minerals. Generally, levels of toxic metal exceed the permissible legislative limit for air samples.

On the Deposition Equilibrium of Carbon Nanotubes or Graphite in the Reforming Processes of Lower Hydrocarbon Fuels

The modeling of carbon deposition from C-H-O reformates has usually employed thermodynamic data for graphite, but has rarely employed such data for impure filamentous carbon. Therefore, electrochemical data for the literature on the chemical potential of two types of purified carbon nanotubes (CNTs) are included in the study. Parameter values determining the thermodynamic equilibrium of the deposition of either graphite or CNTs are computed for dry and wet reformates from natural gas and liquefied petroleum gas. The calculation results are presented as the atomic oxygen-to-carbon ratio (O/C) against temperature (200 to 100 °C) for various pressures (1 to 30 bar). Areas of O/C for either carbon deposition or deposition-free are computed, and indicate the critical O/C values below which the deposition can occur. Only three types of deposited carbon were found in the studied equilibrium conditions: Graphite, multi-walled CNTs, and single-walled CNTs in bundles. The temperature regions of the appearance of the thermodynamically stable forms of solid carbon are numerically determined as being independent of pressure and the analyzed reactants. The modeling indicates a significant increase in the critical O/C for the deposition of CNTs against that for graphite. The highest rise in the critical O/C, of up to 290% at 30 bar, was found for the wet reforming process.

Reactivity of supercritical sulfur dioxide and carbon dioxide in a carbonate reservoir: An experimental investigation of supercritical fluid-brine-rock interactions relevant to the Madison Limestone of Southwest Wyoming

Managing impure carbon dioxide produced by fossil fuel-based generation of electricity is required for successful implementation of carbon capture, utilization, and storage. Impurities in carbon dioxide, particularly [Formula: see text] and [Formula: see text], are geochemically more reactive than the carbon dioxide and may adversely impact a carbon dioxide storage reservoir by generating additional acidity. Hydrothermal experiments are performed to evaluate geochemical and mineralogic effects of injecting [Formula: see text]-[Formula: see text] fluid into a carbonate reservoir. The experimental design is based on a natural carbon dioxide reservoir, the Madison Limestone on the Moxa Arch of Southwest Wyoming, which serves as a natural analog for geologic cosequestration of sulfur dioxide and carbon dioxide. Idealized Madison Limestone ([Formula: see text]) and [Formula: see text] brine ([Formula: see text], initial [Formula: see text]) reacted at reservoir conditions (110°C and 25 MPa) for approximately 165 days (3960 h). Carbon dioxide fluid containing 500 ppmv sulfur dioxide was injected and the experiment continued for approximately 55 days (1326 h). Sulfur dioxide partitions out of the supercritical carbon dioxide phase and dissolves into coexisting brine on the time scale of the experiments (55 days). Injecting supercritical [Formula: see text]-[Formula: see text] or pure supercritical carbon dioxide into a brine-limestone system produces the same in situ pH (4.6) and ex situ pH (6.4–6.5), as measured 28 h after injection because dissolution of calcite buffers in situ pH. Precipitation of anhydrite sequesters injected sulfur and, coupled with dissolution of calcite, effectively buffers the amount of dissolved calcium to the same concentrations measured in limestone-brine experiments injected with pure carbon dioxide. Supercritical [Formula: see text]-[Formula: see text] does not enhance the sequestration potential of a carbonate reservoir relative to pure supercritical carbon dioxide. Our results substantiate predictions from natural analog studies of the Madison Limestone that anhydrite traps sulfur and carbonate minerals ultimately reprecipitate and mineralize carbon in carbonate reservoirs.

Prospect for storage of impure carbon dioxide streams in deep saline aquifers—A convective dissolution perspective

Secure and permanent storage of CO2 in deep saline aquifers by solubility trapping depends highly on the rate at which it dissolves in formation brine by convective dissolution. A commonly-held belief is that injection of impurities along with CO2 retards the evolution of convective dissolution, thereby, negatively impacting solubility trapping of CO2. Injection of impurities along with CO2 provides an exceptional prospect for low-cost Carbon Capture and Storage (CCS) technologies and can potentially accelerate large scale implementation of geological storage of CO2. In this study, convective dissolution of CO2 streams with different portion of H2S impurities, which leads to solubility trapping of CO2 in deep saline aquifers, is studied using non-linear numerical simulations. We have shown that the rate of dissolution of an impure CO2 stream with H2S impurities less than 30mol% is nearly similar to that of a pure CO2 stream. It was also shown that an impure CO2 stream may lead to different convective mixing dynamics at early and late periods of dissolution process. These findings suggest that an impure CO2 stream can be engineered to improve the rate of dissolution and thus solubility trapping of CO2 leading to higher storage security and efficiency.

Effect of dissolved H2SO4 on the interaction between CO2-rich brine solutions and limestone, sandstone and marl

The effect of pure and impure carbon dioxide (CO2) on geological storage is uncertain. Oxidation of impurities such as sulfur dioxide (SO2) and hydrogen sulfide (H2S), which may be catalyzed by co-injected oxygen or nitrogen oxides, leads to the formation of sulfuric acid (H2SO4) and a decrease in pH of the formation water. We investigated the effect of 0.005molL−1 H2SO4 (corresponding to a worst case of 0.4% SO2 in the flue gas, anticipating total conversion of SO2 into H2SO4) on the reactivity of the reservoir (limestone and sandstone) and cap (marl) rocks of Hontomin (Spain) at P=pCO2=10bar and 60°C during 24days using flow-through column experiments. Aqueous element concentrations were measured from fluid extracts obtained periodically throughout the experiments to infer fluid-rock reactions over time. Results were modeled with the CrunchFlow reactive transport code.The added H2SO4 lowered the pH of the injected brine by ~1.5pH units with respect to the pH of ~3.6 of the H2SO4-free brine. In both H2SO4-free and H2SO4-rich brine, calcite dissolution fostered gypsum precipitation. A comparison between the reactivity of the rocks reacted in H2SO4-free and H2SO4-rich brine showed that calcite dissolution and gypsum precipitation rates were increased by 27–48% and 25–75%, respectively, in H2SO4-rich brine. Overall rock porosity increments in H2SO4-rich brine were 2.9–3.6%, 3.7–4.8%, and 2.1–2.7% for sandstone, limestone and marl, respectively. Porosities in H2SO4-rich brine were 6%, 23% and 250%, higher, respectively, than under pure CO2. Modeled porosity increments in the acid inlet zone in H2SO4-rich brine for sandstone, limestone and marl were 28–29%, 44–45% and 24–28%, respectively, corresponding to an increase of 1%, 250% and 25%, respectively, relative to H2SO4-free brine. Gypsum precipitation was consistently higher in marl than in limestone and sandstone, indicating kinetically favorable conditions for gypsum precipitation within the cap rock. Our results provide relevant data for long-term storage simulations of impure CO2 injection.