Increasing CO2 Partial Pressure Research Articles

Study on corrosion of Cr-containing steel under different CO2 partial pressures at high temperatures

To achieve the goal of "carbon peak " and "carbon neutral", CO2 injection in oilfields has become a major trend, but it also comes with the risk of CO2 corrosion on the pipe strings, particularly under high temperature and pressure (HTHP). This study utilizes a laboratory-made HTHP reactor to conduct corrosion tests on three commonly used chromium-containing steels (13Cr, S13Cr, and 25Cr) in oil fields under conditions of 200 °C and a total pressure of 70 MPa, with CO2 partial pressures of 10 MPa, 25 MPa, and 45 MPa respectively. The corrosion components, phase structure and three-dimensional morphology of the specimens are analyzed by SEM/EDS and other microscopic characterization means. Additionally, the critical safety factor after the casing pitting corrosion is calculated. The results indicates that under experimental conditions, the uniform corrosion rate of 13Cr decreases with the increase of CO2 partial pressure, while the uniform corrosion rate of S13Cr and 25Cr initially decreases and then increases with the rise of CO2 partial pressure. Moreover, with the increase of CO2 partial pressure, the pitting corrosion rate of specimens decreases. Under the action of Cl− in the medium solution, the passivation film on the surface of Cr-containing steel is damaged. The severity of pitting corrosion among the materials follows the order: 25Cr > 13Cr > S13Cr. The main elements responsible for severe corrosion are oxygen (O) and sulfur (S). When the depth of the corrosion pit reaches 2.06 mm, the critical internal pressure safety factor of the casing is reached.

Kinetic modeling of the oxidative dehydrogenation of propane with CO2 over a CrOx/SiO2 catalyst and assessment of CO2 utilization

Oxidative dehydrogenation of propane with carbon dioxide (ODPC) has gained attention as a sustainable process capable of simultaneously producing propylene and reducing carbon dioxide (CO2) emissions. In this study, we developed a kinetic model of the ODPC over a silica-supported chromium oxide catalyst based on the Mars–van Krevelen (MvK) mechanism using the experimental data obtained under controlled conditions. The constructed model estimated both reactant conversions and propylene yield within an absolute error of 3% of the experimental data, confirming the integrity of the kinetic model. The kinetic analysis provides insight into the activation of propane and CO2 via several reactions occurring under ODPC conditions, emphasizing that the ODPC cycle is limited by the high energy barrier for CO2 activation. In addition, it allows comparison of the contributions of non-oxidative and oxidative dehydrogenation reactions, the two main reactions producing propylene under ODPC conditions. The estimation results show a significant increase in the reaction rate of ODPC with increasing CO2 partial pressure, in contrast to a nearly constant reaction rate of non-oxidative dehydrogenation, highlighting the promoting effect of CO2 in enhancing the ODPC reaction. Furthermore, the potential of the ODPC process is assessed by considering propylene productivity, net CO2 emissions, including the energy consumption for the separation process, and the global warming index of the energy grid. A comprehensive investigation of the ODPC process through controlled experiments, kinetic modeling and evaluation of net CO2 utilization provides insight into future strategies for using the ODPC as an efficient and eco-friendly process.

One-step thermal oxidation synthesis of carbon-doped TiO2 with enhanced photocatalytic activity using CO2 as the carbon source

The study proposed a simplified carbon doping synthesis strategy to enhance the photocatalytic activity of titanium dioxide (TiO2). Utilizing CO2 gas as the carbon source, the material was directly synthesized onto a titanium substrate through a one-step thermal oxidation method. Raman and XPS analyses indicated that with the increase in CO2 partial pressure, the influence of the carbon source was amplified, resulting in carbon doping in a graphite-like structure and the induction of oxygen vacancies. Electrochemical impedance spectroscopy and UV–vis spectra demonstrated that the introduced carbon species acted as a photosensitizer, augmenting the transfer of photogenerated carriers. Photoluminescence spectra suggested that oxygen vacancies could enhance the non-radiative scattering of photogenerated carriers. These two effects synergistically improved the photocatalytic activity of TiO2 significantly, although the degree of enhancement was dependent on the optimized ratio of carbon content to oxygen vacancy content. Only with optimal carbon content and oxygen vacancy levels could the undesired radiative recombination of photogenerated carriers be prevented, ensuring that the energy derived from visible light was effectively utilized to drive chemical reactions. Under these optimal conditions, the TC-O5 and TC-O10 samples exhibited excellent photocatalytic degradation performance of methyl orange under visible light, with degradation rates of 86.27% and 82.54%, respectively, and displayed outstanding cycling stability, with the degradation rate remaining above 90% for three cycles. This method proved to be simple, efficient, and easily operable, offering significant advantages for industrial-scale preparation.

Corrosion reason analysis and countermeasures of buried oil unloading pipeline in an oilfield

The material, corrosion morphology and characteristics, as well as the compositions of corrosion products of a 20# steel unloading pipeline were studied using on-site C-scan detection, laboratory corrosion morphology analysis, material metallographic analysis, chemical composition analysis and tensile testing. The uniform corrosion and pitting behavior of 20# steel were studied using a high temperature and high pressure autoclave under conditions of 50 °C and CO2 partial pressure of 0.05 MPa, 0.1 MPa, and 0.2 MPa, respectively. The microstructure and composition of the surface and cross-section corrosion product film were analyzed by SEM. The results show that the uniform corrosion rate of 20# steel increases with the increase of CO2 partial pressure. When the CO2 partial pressure reaches 0.2 MPa, there are a large number of corrosion pits on the surface of the sample, and the maximum local corrosion rate reaches 1.8719 mm/a. The corrosion product film has a multi-layer structure, with a surface layer of FeCO3 corrosion product films and an inner layer of (Ca, Mg)CO3 deposition layer. There are obvious corrosion pits at the interface between the corrosion product film and the substrate locally. The severe thinning of the on-site pipeline wall is mainly caused by CO2 corrosion. The defects of the corrosion product film and the deposition of scale layer accelerate local corrosion.

MgO‐based binders

AbstractTo limit global temperature rise to below 2°C, we need to radically and rapidly change the way we build and use materials, since construction is responsible for 20‐40% of industrial CO2 emissions. Magnesium carbonate‐based cements have the potential to become a major carbon sink in construction industry, as CO2 will not be emitted during their production, but CO2 will rather be bound during hardening. Two different reaction mechanisms lead to setting and hardening of such HMC cements: i) hydration of MgO‐Mg‐carbonate, also in blends with silica and other mineral additions, in the presence of water or salt solutions (such as sodium bicarbonate solution) at ambient conditions or ii) carbonation hardening of MgO‐based systems at increased CO2 partial pressure and/or at increased temperatures.However, the utilization of hydrated magnesium carbonate and magnesium silicate cements is currently hampered by the lack of systematic experiments and of fundamental understanding of the factors affecting the hardening process, mechanical properties, long‐term behavior and durability. In particular, the role of temperature, relative humidity and addition of supplementary cementitious materials and/or industrial by‐products has not been systematically investigated. We need knowledge both on the practical side through systematic experiments with pastes, mortars and concretes as well as on a fundamental level through solubility and sorption experiments and thermodynamic modelling. In addition, reaction kinetics need to be optimized as well as the early formation of the preferred phases (stability enhancement) to develop efficient HMC cements for construction. Due to the socio‐economic relevance of cement and concrete, the impact of such “carbon”‐negative cements may go beyond a purely scientific one and lead to technological breakthroughs to the benefit of environment and society.

CO2-Induced Gate-Opening Adsorption on a Chabazite/Phillipsite Composite Zeolite Transformed from a Faujasite Zeolite Using Organic Structure-Directing Agent-Free Steam-Assisted Conversion.

Organic structure-directing agent-free steam-assisted conversion and Cs+ ion exchange were used to transform the faujasite (FAU)-type zeolite to the Cs+-type chabazite/phillipsite (CHA/PHI) composite zeolite. Compared with the pure PHI-type zeolite, the Cs+-type CHA/PHI zeolite showed gate-opening CO2 adsorption behavior and good thermal stability. In situ powder X-ray diffraction (PXRD) of the CO2 adsorption was measured to elucidate the mechanism for the gate-opening adsorption on the CHA/PHI zeolite. The Na+-type CHA/PHI zeolite did not show such adsorption behavior, and the PXRD pattern of the Na+-type CHA/PHI zeolite did not change with increasing CO2 partial pressure, which suggests that this unique adsorption behavior was caused by the PHI framework transition or Cs+ ions moving in both the CHA and PHI frameworks. Furthermore, in situ Fourier-transform infrared spectra of CO2 adsorption and CO2 breakthrough measurement on the Cs+-type CHA/PHI zeolite suggest that the CHA and PHI frameworks in the CHA/PHI zeolite shared eight-membered-ring windows and that CO2 molecules could easily diffuse from a CHA cage to a PHI framework. The ideal adsorbed solution theory was used to calculate the CO2/N2 separation selectivity for the Cs+-type CHA/PHI zeolite. At 298 and 318 K, the Cs+-type CHA/PHI composite zeolite showed a high CO2/N2 separation coefficient of >10,000 compared with other zeolites with high CO2 adsorption capacity. Furthermore, the CO2 working capacity was calculated for the Cs+-type CHA/PHI zeolite in both the pressure- and temperature-swing processes, and the results showed that the CHA/PHI composite zeolite could selectively separate CO2 from the CO2/N2 gas mixtures released from power generation plants operating using these processes.

Influence of CO2 partial pressure and flow rate on the corrosion behavior of N80 steel in 3.5% NaCl

In this paper, weight loss and in situ electrochemical measurements were carried out to investigate the influence of CO2 partial pressure and flow rate of corrosive media on the corrosion of N80 steel in 3.5% NaCl at 120 ℃. The corrosion product films obtained at different conditions were also analyzed by SEM and EDS. The results showed that with the increase of CO2 partial pressure, the corrosion rate decreases significantly. EIS results showed that the total resistance and charge transfer resistance of the film under all soaking times increased gradually with the increase of CO2 partial pressure, which indicates that the product film formed at high CO2 partial pressure was denser and had better protection to the matrix. Flow rate has limited influence on corrosion rate of N80 steel at tested conditions. EIS revealed that at different flow rates, the protection of corrosion product films increased with the soaking time. High flow rate is not favoarable to the formation of corrosion product film, or it is easy to break corrosion product film. And wall shear stress (WSS) is generally considered to be the main cause of failure, thus resulting in high corrosion rate of N80 steel.

Impact of sodium chloride and carbon dioxide on conidial germination and radial growth of Penicillium camemberti

Penicillium camemberti is a domesticated species adapted to the dairy environment, which is used as adjunct cultures to ripen soft cheeses. A recent population genomics analysis on P. camemberti revealed that P. camemberti is a clonal lineage with two varieties almost identical genetically but with contrasting phenotypes in terms of growth, color, mycotoxin production and inhibition of contaminants. P. camemberti variety camemberti is found on Camembert and Brie cheeses, and P. camemberti variety caseifulvum is mainly found on other cheeses like Saint-Marcellin and Rigotte de Condrieu. This study aimed to evaluate the impact of water activity (aw) reduced by sodium chloride (NaCl) and the increase of carbon dioxide (CO2) partial pressure, on conidial germination and growth of two varieties of P. camemberti: var. Camemberti and var. Caseifulvum. Mathematical models were used to describe the responses of P. camemberti strains to both abiotic factors. The results showed that these genetically distant strains had similar responses to increase in NaCl and CO2 partial pressure. The estimated cardinal values were very close between the strains although all estimated cardinal values were significantly different (Likelihood ratio tests, pvalue = 0.05%). These results suggest that intraspecific variability could be more exacerbated during fungal growth compared with conidial germination, especially in terms of macroscopic morphology. Indeed, var. Caseifulvum seemed to be more sensitive to an increase of CO2 partial pressure, as shown by the fungal morphology, with the occurrence of irregular outgrowths, while the morphology of var. Camemberti remains circular. These data could make it possible to improve the control of fungal development as a function of salt and carbon dioxide partial pressure. These abiotic factors could serve as technological barriers to prevent spoilage and increase the shelf life of cheeses. The present data will allow more precise predictions of fungal proliferation as a function of salt and carbon dioxide partial pressure, which are significant technological hurdles in cheese production.

Kinetics and Thermodynamics of CO2 Absorption in Aqueous 3-Dimethylaminopropylamine and Its Blend with Poly(ethylene glycol) Dimethyl Ether Using a Wetted Wall Column Reactor

Biphasic solvent 3-dimethylaminopropylamine (DMAPA)/poly(ethylene glycol) dimethyl ether (NHD)/H2O solution is a promising absorbent for CO2 capture. The kinetics of CO2 absorption in both DMAPA/NHD/H2O system and DMAPA/H2O systems was investigated and compared in a wetted wall column reactor with different CO2 loadings at different CO2 partial pressures from 30 to 70 °C. The equilibrium CO2 loadings were also determined. Meanwhile, the density and viscosity for both systems were measured. In both systems, the mass transfer flux of CO2 increases linearly with the increase of CO2 partial pressure. The kinetic data were interpreted by the zwitterion mechanism. The overall mass transfer constant was determined according to the absorption rate experiments performed in the pseudo-first-order regime. The overall mass transfer resistances increase with the increase of CO2 loading and decrease with the increase of temperature. The addition of NHD decreases the equilibrium CO2 loadings at the same CO2 partial pressure and temperature. However, it increases the enhancement factor significantly and can promote both the absorption and the desorption process. It provides basic information not only for the further utilization of DMAPA/NHD/H2O solution, which is helpful for the design of absorption reactor, but also for developing new phase-change absorbents for CO2 capture.

Investigation on the Effect of Temperature and CO<sub>2</sub> Partial Pressure on Corrosion of N80 Tubing Steel in Formation Water Environment

In the process of oil and gas extraction, N80 steel is used as a common tubing material. CO2 corrosion has become one of the most dangerous problems in its entire life cycle. In this paper, the conditions of different temperatures (90-220 °C) and CO2 partial pressure (0.2-3 MPa) were selected, and the dynamic rotating high-temperature autoclave was used to simulate N80 steel corrosion in formation water environments. The results showed that the corrosion rate of N80 steel gradually decreased with the increase of temperature, and the corrosion rate was the lowest at 150 °C. In addition to this, with the increase of CO2 partial pressure, the corrosion rate first increased and then decreased. The corrosion rate was the highest when the CO2 partial pressure was 0.8 MPa. Through surface analysis techniques (SEM and XRD) and electrochemical tests, it was found that the corrosion resistance of N80 under high temperature and high pressure is closely related to the corrosion product film (FeCO3). The compactness of FeCO3 product film determines the corrosion characteristics of the matrix.

A green approach to prepare polymorph CaCO3 for clean utilization of salt gypsum residue and CO2 mineralization

Salt gypsum residue, an industrial solid waste, is the by-product of vacuum evaporation in the salt-making industry. This study aimed to recover salt gypsum and prepare CaCO3 via NaOH leaching and pressure strengthening with CO2; meanwhile, CO2 mineralization was realized. The method can not only produce CaCO3 with controllable morphology, but also efficient realize CO2 solidification using metal cations in the salt gypsum residue and utilization of the industrial solid waste, so as to zero discharge of waste residue in the salt-making industry. The thermodynamic calculation results showed that the method is feasible. The experimental results showed that the phase transformation efficiency of salt gypsum residue was 99.94 % under the optimal experimental conditions at NaOH concentration of 3 mol/L, liquid–solid ratio of 8 mL/g, time of 10 min, temperature of 50 ℃, stirring at 300 rpm, and CO2 flow rate of 1.0 L/min. The diffusion of CO2 is the rate-limiting step of carbonation; it was disrupted by CO2 pressure strengthening, and the conversion efficiency of salt gypsum improved. Moreover, the migration of CaCO3 molecules to the crystal kink, nucleation, and growth rate of CaCO3 crystals were improved via increasing CO2 partial pressure, affecting the morphology of CaCO3 crystals. Therefore, Calcite and aragonite CaCO3 crystals were obtained when the CO2 pressure was 0.0 MPa and 0.2 MPa, respectively. Moreover, the CO2 mineralization efficiency and CaCO3 yield were 635.3 kg CO2/1000 kg salt gypsum residue and 975.0 kg CaCO3/1000 kg salt gypsum residue under optimal experimental conditions. These new observations are expected to provide further understanding and guidance for the clean utilization of salt gypsum residue and CO2 mineralization in the salt-making industry.

Corrosion Behavior of J55 and N80 Carbon Steels in Simulated Formation Water under Different CO2 Partial Pressures

The purpose of this paper is to reveal the corrosion behavior of J55 and N80 carbon steels in formation water under oil wells at different partial pressures, explore the formation process of corrosion product films under supercritical CO2 conditions, and analyze the reasons why the microstructure of carbon steel affects the corrosion behavior. The results show that the corrosion rate gradually increases with the increase in CO2 partial pressure. When the pressure exceeds 10 MPa, the corrosion rate of J55 increases slightly, and that of N80 decreases slightly. Under different partial pressures, the surface composition of the corrosion product film of J55 steel is FeCO3, and that of N80 steel is FeCO3 with a small amount of Fe3C. The analysis shows that the corrosion product films of two kinds of carbon steels can be divided into three layers under the condition of supercritical CO2. There are holes in the middle layer, which are formed first, and then the inner layer and the outer layer are formed at the same time. It is believed that the difference in the morphology and distribution of Fe3C is the reason why the corrosion rate of J55 steel is lower than that of N80 steel. Fe3C in J55 steel is lamellar, which can anchor FeCO3, promote the formation of corrosion product films, and improve the compactness of corrosion product films. However, the Fe3C in N80 is granular and dispersed in the ferrite matrix, which makes it easy to fall off the surface, form pits, and destroy the integrity of the corrosion product film.

Enhanced abundance and activity of the chloroplast ATP synthase in rice through the overexpression of the AtpD subunit

ATP, produced by the light reactions of photosynthesis, acts as the universal cellular energy cofactor fuelling all life processes. Chloroplast ATP synthase produces ATP using the proton motive force created by solar energy-driven thylakoid electron transport reactions. Here we investigate how increasing abundance of ATP synthase affects leaf photosynthesis and growth of rice, Oryza sativa variety Kitaake. We show that overexpression of AtpD, the nuclear-encoded subunit of the chloroplast ATP synthase, stimulates both abundance of the complex, confirmed by immunodetection of thylakoid complexes separated by Blue Native-PAGE, and ATP synthase activity, detected as higher proton conductivity of the thylakoid membrane. Plants with increased AtpD content had higher CO2 assimilation rates when a stepwise increase in CO2 partial pressure was imposed on leaves at high irradiance. Fitting of the CO2 response curves of assimilation revealed that plants overexpressing AtpD had a higher electron transport rate (J) at high CO2, despite having wild-type-like abundance of the cytochrome b6f complex. A higher maximum carboxylation rate (Vcmax) and lower cyclic electron flow detected in transgenic plants both pointed to an increased ATP production compared with wild-type plants. Our results present evidence that the activity of ATP synthase modulates the rate of electron transport at high CO2 and high irradiance.

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO 2 /Epoxide Copolymer

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO ₂ /Epoxide Copolymer

Corrosion Behavior Studies of Al and Zn Based Alloys for Internal Corrosion Protection in Natural Gas Transmission Pipelines

Internal coatings and liners can be used to minimize CO2 corrosion inside steel pipelines transporting natural gas. Many factors such as climate, gas velocity and properties of the gas traveling through the pipeline contribute to the complexity of designing an efficient metallic coating to mitigate internal corrosion. The objective of this study was to investigate the corrosion behavior of aluminum and zinc-based alloys as sacrificial coating candidates for protection of pipeline steel in a CO2-saturated aqueous electrolyte under natural gas conditions.To determine the corrosion resistance of the Al and Zn alloys, electrochemical studies using potentiodynamic polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) were performed in simulated natural gas environments. These environments included variable CO2 pressures simulating the partial pressures that are found in gas transmission over a solution of 3 ½ wt.% NaCl heated to 40 ºC. The effect of electrolyte flow and CO2 partial pressure on corrosion rate of Al and Zn were determined from weight loss data and electrochemical measurements. Also, the corrosion behavior of API 5L X65 pipeline steel coupled to Zn and Al immersed in CO2-statured 3.5 wt.% NaCl under flow and stagnant conditions was evaluated. Post-corrosion surface characterization was performed by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS).The results show that the corrosion rates for Al or Zn alloys increase with increasing CO2 partial pressure due to the increase of the cathodic reaction kinetics. Aluminum oxide and zinc carbonate-containing compounds as corrosion product layers were formed on API 5L X65 steel coupled to aluminum and zinc, respectively. The obtained data show that an Al and Zn based alloy can be used as sacrificial anodic materials to protect the interior of the steel pipeline against CO2 corrosion in a natural gas transmission environment.Keywords : CO2 corrosion, natural gas pipelines, aluminum alloy, zinc alloy, sacrificial coatings, electrochemical reaction autoclave

Modeling and Durability Behavior of Erosion-Corrosion of Sand Control Screens in Deepwater Gas Wells.

Deepwater gas wells usually have high production rates, which result in high-speed sand movement along with the gas flow and acid components such as CO2 in the gas flow. The erosion and corrosion effect intensifies the damage to sand screens and can further lead to sand control failures, which endanger the safety of production operations. In this paper, using a differential rotation device to simulate erosion, corrosion, and erosion–corrosion, experiments observing the impacts of several factors on sand screens were carried out. The factors include CO2 partial pressure, temperature, flow velocity, sand content, and sand particle size. Their impacts on erosion, corrosion, and erosion–corrosion rate are inspected independently, and the sensitivity of factors to the erosion–corrosion rate of a sand screen was determined using the range method. Traditional erosion models involving flow rate, sand content, and sand grain size and traditional corrosion models involving CO2 partial pressure and temperature are taken as references, and an erosion–corrosion coupled model of sand screens is established based on the experimental results using the multivariate regression analysis. With critical damage thickness taken as the failure criterion of a sand screen, a prediction method for sand screen failure is formed and is applied to the case study of the S deepwater gas field. The results show that under the experimental conditions, the screen loss rate due to erosion–corrosion is significantly higher than that of erosion only or corrosion only and is even higher than the sum of both. The erosion–corrosion rate increases with the increase of CO2 partial pressure, temperature, flow velocity, sand content, and sand particle size. It has an exponential relationship with the negative reciprocal of temperature, a linear relationship with the partial pressure of CO2, and power fitting relationships with flow velocity, sand content, and sand particle size. The ranking of sensitivities to the erosion–corrosion rate of high-quality screens is as follows: sand content > flow velocity > temperature > sand particle size > CO2 partial pressure. The error between the predicted results by the proposed model and the experimental results is in the range of 0.44–9.47%. The erosion–corrosion rate of sand screens in each production well of the S gas field is in the range of 0.0111–0.0521 mm/a, while the durability of the screens is 14–68 years. The erosion–corrosion rate model of a sand screen and the prediction method for sand screen failure proposed in this paper provide theoretical support to the durability evaluation of sand screen in deepwater gas wells, which is of great significance for ensuring the safe and efficient development of offshore oil and gas resources.

Alkali Metal Nitrates Promoted MgO Composites with High CO2 Uptake for Thermochemical Energy Storage

Thermochemical energy storage (TCES) by means of reversible chemical reactions represents a promising strategy for harnessing renewable energy and recovering industrial waste heat. In this work, alkali metal nitrate promoted MgO composites were synthesized, and the MgO–CO2 working pair was suggested as an alternative candidate for harvesting intermediate-temperature industrial waste heat. However, it remains unclear how operating parameters would affect the heat storage density, and the long-term cycling stability of the alkali metal nitrate promoted MgO composites under harsh conditions close to practical application scenarios needs to be clarified. The objectives of this work are to expound the effects of operating parameters on TCES performance and to evaluate the long-term cycling stability of the alkali metal nitrate promoted MgO composites. With increasing NaNO3 content, the heat storage density of NaNO3–MgO increases dramatically first and then exhibits no significant change. With rising carbonation temperature, the heat storage density of the 10NaNO3–MgO composite increases first and then declines marginally, while it increases with the increasing CO2 partial pressure. Doping alkali metal nitrate eutectic mixtures adversely affects the heat storage density. 10NaNO3–MgO exhibits a high heat storage density of 2291 kJ/kg at 340 °C in 100% CO2. The 10NaNO3–MgO and 10(K–Na)NO3–MgO composites suffer a significant decline in heat storage density within 10 consecutive cycles, while 10(Li–Na)NO3–MgO retains good stability with a slight decrease of heat storage density from 1073 to 770 kJ/kg in 50% CO2. The desired 10(Li–Na)NO3–MgO is suggested as a promising material for TCES application.

Gasification Kinetics of Victorian Brown Coal-Derived Char in Fluidized Bed Reactor

Abstract In a chemical looping combustion (CLC) system, gasification kinetics of char holds immense importance being the rate-limiting reaction in the fuel reactor. This paper studied the gasification kinetics of char derived from Victorian brown coal (VBC) in a fluidized bed reactor which mimics the fuel reactor conditions of a chemical looping combustion process. Mass of char, char particle size, and gas flow conditions were optimized to ensure the gasification reaction free from mass transfer limitations. Effect of oxygen carrier (OC), hematite, being the bed material was also studied. The experiments were conducted in the temperature range of 800 °C–950 °C, which is a typical range for fuel reactor. The experimental results were modeled with the help of grain model (GM) and random pore model (RPM) to analyze the kinetic parameters. Activation energy was found to be around 177 kJ/mol in sand bed and 175.5 kJ/mol in the hematite bed. Reaction in hematite bed was found to be 42% faster on average compared with the reaction in a sand bed. Fastest total conversion of char took as low as 4.1 min in hematite bed at 950 °C. While catalytic effect of hematite was ruled out due to insignificant change in activation energy, it was concluded that increase in CO2 partial pressure at the vicinity of char particle enhanced the reaction rate in the case of hematite bed. This study has generated relevant information for the CLC of Victorian brown coal with hematite as the oxygen carrier.

Two-step thermochemical cycles using fibrous ceria pellets for H2 production and CO2 reduction in packed-bed solar reactors

The thermochemical redox activity and performance of commercial-grade fibrous ceria pellets were determined including fuel production rates and yields from H2O and CO2 dissociation. Two solar reactors integrating the ceria pellets undergoing two-step thermochemical cycling (with temperature-swing between alternating redox steps) were experimentally tested. They consisted of packed-bed tubular and cavity-type solar reactors with direct or indirect heating of the reacting materials. The obtained fuel production rates compared favorably with the performance of other previously considered microstructured ceria materials such as templated foams, sintered felts, bioinspired or ordered macroporous morphologies. H2 production rates reached 2.3 mL.g−1.min−1 (with H2/O2 ratios approaching 2) in the indirectly-heated tubular reactor after reduction at 1400 °C and oxidation upon free cooling below 950 °C in steam atmosphere (57% molar content). The highest fuel production rate (~9.5 mL.g−1.min−1) and peak solar-to-fuel energy efficiency (~9.4%) were reached in the directly-irradiated cavity-type reactor (with a reduction step at 1400 °C under reduced pressure, and an oxidation step in pure CO2 below 950 °C). The reduction extent was favored at low pO2 (δ up to 0.056) and the fuel yields were thus improved notably (up to 315 μmol/g) by decreasing the total pressure below 0.1 bar during the reduction step. The fuel production rate increased when the oxidation temperature decreased (because the reaction was thermodynamically more favorable). An increase in CO2 partial pressure further promoted the oxidation kinetics (and decreased the pCO/pCO2 ratio, thus shifting the thermodynamic equilibrium toward CO product). The fibrous ceria structures exhibited stable morphologies with high fuel production performance similar to less scalable porous structures, thus offering the potential for versatile applications in packed-bed solar reactors.

Effects of CO2 gassy-supercritical phase transition on corrosion behaviors of carbon steels in saturated vapor environment

Corrosion behaviors of P110 and N80 tubular steels in CO2 gas phase and supercritical (S-CO2) phase in a saturated water vapor environment were explored in corrosion weight loss experiments by SEM, EDS, XRD, XPS and cross-section analysis techniques. With the increase in CO2 partial pressure, the average corrosion rate increased first and then decreased. The average corrosion rate reached the maximum value under the near-critical pressure. When CO2 partial pressure further increased to be above the critical pressure, the average corrosion rate gradually decreased and local aggregation of molecules was weakened.