High Temperature Supercritical Carbon Dioxide Research Articles

Mechanism of pore expansion and fracturing effect of high-temperature ScCO2 on shale

To elucidate the mechanisms underlying the alteration of shale pore fractures by high-temperature supercritical carbon dioxide (ScCO2), this study employed medium–low maturity shale samples from a specific region as research subjects. The samples were subjected to high-temperature ScCO2 reactions in a corrosion-resistant high-pressure reaction vessel at various temperatures. A suite of analytical techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ImageJ image processing software, N2 and CO2 adsorption experiments, thermal gravimetric-differential thermal analysis (TG-DTG) of CO2 pyrolyzed shale oil, and gas chromatography (GC) analysis, were utilized to investigate and analyze the microstructural changes in the shale samples before and after ScCO2 treatment.The results reveal a subtle increase in the content of clay minerals and quartz, accompanied by a decrease in the content of carbonates, potassium feldspar, and calcite. These mineral transformations, encompassing dissolution, precipitation, and swelling processes, exert a substantial impact on the shale surface microstructure and modify the internal pore structure. Consequently, a shift in the mechanical properties of the rock is observed, which bears significance for its fracturing behavior.The experimental results reveal a steady growth in fracture area following high-temperature ScCO2 treatment. Importantly, the extent of initial fracture development plays a crucial role in determining the efficacy of hydraulic fracturing, indicating a positive correlation. Moreover, the connection between fracture area and temperature exhibits a clear trend marked by an initial rise, a subsequent decline, and finally, a resurgence. In particular, the thermal fracturing threshold temperature for the shale samples was found to be around 400 °C.From the analysis, it can be inferred that ScCO2, when subjected to an elevated temperature range of 100-200℃, exhibits mutual interactions with the shale. This results in effective extraction of organic matter and dissolution of mineral constituents within the shale matrix. Consequently, this treatment process leads to a significant reduction in the number of micropores (pore sizes less than 2 nm), while the quantities of mesopores (pore sizes between 2 and 50 nm) and macropores (pore sizes greater than 50 nm) display a noticeable increase.Upon exposure to a temperature range of 200-300℃, a remarkable affinity of the shale for CO2 adsorption becomes evident. The adsorption process contributes to the expansion of the matrix material and deposition of minerals, effectively filling the pore spaces. As a result, the contraction of mesopores and macropores is mitigated, with the predominant change being an increase in the number of micropores.When temperatures reach 300-500℃, the intensified heat initiates thermal decomposition of the kerogen, culminating in the release of pore spaces. This phenomenon prompts an increase in the number of micropores and mesopores, thereby augmenting the pore volume and specific surface area of the shale.

Corrosion behavior of heat-resistant steel T91 in high-temperature supercritical carbon dioxide with impurity O2, SO2 or H2S

This study investigated corrosion of T91 in supercritical carbon dioxide (sCO2) with impurity of 100 ppm O2, SO2 or H2S at 550 ℃ and 15 MPa. O2 slightly increased mass gain of corroded T91, and the corrosion kinetics both in pure sCO2 and in sCO2 with O2 impurity followed parabolic law. Fe2O3 was formed in outer corrosion layer due to enhanced partial pressure of oxygen. SO2 or H2S remarkably exacerbated T91 corrosion. For test in sCO2 with SO2 impurity, outer corrosion product was magnetite, and the inner was composed of Fe-Cr spinel and FeS, different from that in pure sCO2. Addition of H2S caused an external FeS layer and internal Fe-Cr spinel. Introduction of all the three impurities reduced carburization in the underlying alloy substrate.

Corrosion behavior of T91 tubing in high temperature supercritical carbon dioxide environment

The effect of stress on the corrosion behavior and mechanical properties of T91 tube exposed to high-temperature supercritical carbon dioxide (S-CO2) was investigated. Both yield strength, ultimate tensile strength, and elongation of T91 tube was decreased after being exposed to S-CO2. Besides, a large number of carbide precipitates were observed in the Fe-Cr-rich corrosion layer of T91 tube, which was attributed to higher ion diffusion and carburizing rate under the action of stress. As a result, the corrosion rate of T91 tube was significantly faster than that of T91 coupon.

Measurements of binary diffusion coefficient for platinum(II) acetylacetonate in high temperature supercritical carbon dioxide by the chromatographic impulse response method

Infinite dilution binary diffusion coefficients D12 and retention factors k for platinum(II) acetylacetonate in high temperature supercritical carbon dioxide (scCO2), at temperatures from (323.3–454.2) K and pressures from (11.0–25.0) MPa, were measured by the chromatographic impulse response method. Although diffusion coefficients for various compounds up to 353 K in scCO2 reported in the literature were well represented by the hydrodynamic equation, the present data deviated more from the equation as the CO2 viscosity decreased. The deviating D12 data corresponded to the gas-like scCO2 region whose conditions were situated below the density fluctuation ridge line on the pressure (or density) − temperature phase diagram, as observed for Cr(acac)3 measured in the authors’ previous study. All the present D12 data and those previously measured below 343 K over the entire region from gas-like to liquid-like scCO2 were well represented by the Schmidt number correlation over the temperature range from 308.2 K to 454.2 K with an average relative deviation (ARD) of 6.5% for 109 measurement conditions. The retention factors measured in the present study were correlated with CO2 density, with temperature dependent constants having an ARD of 4.4% for 47 measurement conditions.

Measurements and correlation of infinite dilution binary diffusion coefficients for Cr(acac)3 in high temperature supercritical carbon dioxide

The infinite dilution binary diffusion coefficient (D12) for chromium (III) acetylacetonate (Cr(acac)3) in supercritical carbon dioxide (scCO2) was measured at temperatures from 343 K to 423 K and pressures from 10 MPa to 22 MPa by the chromatographic impulse response (CIR) method. We previously reported D12 data at relatively low temperatures below 343 K; the D12 data were accurately represented by the hydrodynamic equation where the D12/T vs. CO2 viscosity were expressed by a straight line on a logarithmic plot. However, the newly measured D12 values in the present study showed greater deviations at higher temperatures or lower viscosities (lower pressures/densities) from the correlation determined for low – temperature D12 data. The maximum deviation was 68% at the lowest measured CO2 viscosity of 22 μPa s; thus, the hydrodynamic equation could be no longer applied in this region. The D12 data that deviate from the hydrodynamic equation fully correspond to the gas-like scCO2 region, whereas those fitted by the equation correspond to the liquid –like scCO2 region. The gas–like and liquid–like regions can be separated on the basis of density fluctuations and a ridge line in a pressure vs. temperature diagram, claimed by Nishikawa and Morita [Chem. Phys. Lett., 316 (2000) 238]. Compared with the accuracy in predicting the D12 data by the original Schmidt number correlation, the accuracy was improved by the modified Schmidt number correlation, with an average relative deviation of 6.20 % for 136 conditions, including both gas–like and liquid–like scCO2 regions.

Compatibility of Different Commercial Alloys in High Temperature Supercritical Carbon Dioxide

Compatibility of Different Commercial Alloys in High Temperature Supercritical Carbon Dioxide

Corrosion Behavior of Si Diffusion Coating on an Austenitic Fe-Base Alloy in High Temperature Supercritical-Carbon Dioxide and Steam Environment

In order to enhance corrosion resistance of stainless steel (SS) 316LN at high temperature environments, surface modification was carried out by Si deposition and subsequent heat treatment at 900 °C for 1 h. This resulted in the formation of Fe5Ni3Si2 phase on the surface region. The surface-modified alloy was exposed to high temperature S-CO2 (650 °C, 20 MPa) and steam (650 °C, 0.1 MPa) for 500 h and evaluated for its corrosion behavior in comparison to the as-received alloy. In S-CO2 environment, the as-received SS 316LN showed severe oxide spallation and thick Fe-rich oxide formation, while the surface-modified alloy formed a continuous and adherent Si- and Cr-rich oxide layer. In steam, as-received SS 316LN formed very thick duplex Fe- and Cr-rich oxide layers. On the other hand, surface-modified SS 316LN formed notably thinner oxides, which could be attributed to the formation of Si-rich oxide under outer Fe-rich oxides on the surface-modified alloy. Thus, in view of the weight changes, oxide thickness, and morphologies of the two conditions, it was found that Si diffusion coating was effective in improving the corrosion resistance of SS 316LN in both S-CO2 and steam environments.

Development of aluminide diffusion coatings on ODS ferritic-martensitic steel for corrosion resistance in high temperature super critical-carbon dioxide environment

Aluminide diffusion coatings were applied on an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel as surface modification methods. Either thin layer of Al or NiAl was deposited on the ODS-FM steels, which were subjected to inter-diffusion heat treatment (IDHT) to produce Al-IDHTed or NiAl-IDHTed specimens, respectively. After corrosion test in high temperature super-critical carbon dioxide (S-CO2), both Al-IDHTed and NiAl-IDHTed specimens showed significantly improved corrosion resistance with lower weight gains and effectively supressed carburization in the matrix. The improvement in corrosion resistance was attributed to the presence of continuous alumina layer on top of surface layer. For Al-IDHTed specimen, extensive diffusion of Al from surface layer and inter-diffusion zone to substrate was observed after the S-CO2 corrosion test. However, for NiAl-IDHTed specimen, an Al-rich surface layer was well-maintained after S-CO2 corrosion as Ni acted as a diffusion barrier.

Effect of high-temperature supercritical carbon dioxide exposure on the microstructure and tensile properties of diffusion-bonded Alloy 690

Alloy 690 was diffusion-bonded and exposed to the high-temperature supercritical CO2 environment, and the effect of exposure on the microstructure and mechanical properties was investigated. In the as-bonded joint, some small carbides are discontinuously arranged along the bonding line. After exposure at 550 °C and 600 °C, the continuous carbides are developed and occupy all the grain boundaries and bonding line. The continuous carbides transform into the discrete large particles when the exposure temperature further increases to 650 °C. With the increase in exposure temperature, the tensile strength and microhardness of the joints decrease, while the elongation first slightly increases and then decreases at 650 °C. For the as-bonded joint and the joints exposed at 550 °C and 600 °C, the fracture occurs at the parent Alloy 690 and the main fracture mode is the ductile dimple fracture. However, for the joint exposed at 650 °C, the fracture occurs at the bond line with a manner of brittle fracture. The degradation of strengths and elongation after exposure to supercritical CO2 at 650 °C were associated with the growth of carbides along the bond line.

Comparative energy, exergy and exergo-economic analysis of solar driven supercritical carbon dioxide power and hydrogen generation cycle

Parabolic dish solar collector system has capability to gain higher efficiency by converting solar radiations to thermal heat due to its higher concentration ratio. This paper examines the exergo-economic analysis, net work and hydrogen production rate by integrating the parabolic dish solar collector with two high temperature supercritical carbon dioxide (s-CO2) recompression Brayton cycles. Pressurized water (H2O) is used as a working fluid in the solar collector loop. The various input parameters (direct normal irradiance, ambient temperature, inlet temperature, turbine inlet temperature and minimum cycle temperature) are varied to analyze the effect on net power output, hydrogen production rate, integrated system energetic and exergetic efficiencies. The simulations has been carried out using engineering equation solver (EES). The outputs demonstrate that the net power output of the integrated reheat recompression s-CO2 Brayton system is 3177 kW, whereas, without reheat integrated system has almost 1800 kW net work output. The overall energetic and exergetic efficiencies of former system is 30.37% and 32.7%, respectively and almost 11.6% higher than the later system. The hydrogen production rate of the solarized reheat and without reheat integrated systems is 0.0125 g/sec and 0.007 g/sec, accordingly and it increases with rise in direct normal irradiance and ambient temperature. The receiver has the highest exergy destruction rate (nearly 44%) among the system components. The levelized electricity cost (LEC) of 0.2831 $/kWh with payback period of 9.5 years has proved the economic feasibility of the system design. The increase in plant life from 10 to 32 years with 8% interest rate will decrease the LEC from (0.434-0.266) $/kWh. Recuperators have more potential for improvement and their cost rate of exergy is higher as compared to the other components.

Corrosion and Carburization Behavior of Heat-Resistant Steels in a High-Temperature Supercritical Carbon Dioxide Environment

The corrosion behavior of heat-resistant steels, including T91, VM12, Super 304H, and Sanicro 25, in high-temperature supercritical carbon dioxide at 650 °C and 15 MPa for 1000 h was investigated. X-ray diffraction, Raman spectroscopy, and glow-discharge optical emission spectrometry were employed to characterize the corrosion products. The results showed that the weight gain of the investigated steels is in the order of T91 > VM12 > Super 304H > Sanicro 25. Compared with the dual layers of Fe3O4 and FexCr3−xO4 on T91 and VM12, the chromia-rich oxide scales on Super 304H and Sanicro 25 enhanced their corrosion resistance. Internal carburization zones were found underneath the oxide scales, indicating the presence of oxidation and carburization reactions in the supercritical carbon dioxide. Moreover, the total carbon uptake into the T91 and VM12 steels approximately followed a parabolic law with experimental time but followed a linear law for the austenitic heat-resistant steel Sanicro 25. A corrosion mechanism that couples oxidation and carburization is summarized and quantified for oxidation and carburization to determine the dominant reaction.

Corrosion performance of heat-resisting steels and alloys in supercritical carbon dioxide at 650 °C and 15 MPa

Abstract The corrosion behavior of martensitic heat-resistant steel T91, austenitic heat-resistant steel TP347HFG and nickel-based alloy 617 in high-temperature supercritical carbon dioxide at 650 °C and 15 MPa was investigated. Raman spectrum, X-ray diffraction, and glow-discharge optical emission spectrometry were employed to characterize the corrosion products. Results show that weight gain of T91 in supercritical carbon dioxide at 650 °C was significantly higher than that of TP347HFG and 617. The corrosion kinetics of investigated materials follow a sub-parabolic corrosion law. The chromia-rich oxide scales formed on TP347HFG and 617 enhanced their corrosion resistance, which was mainly attributed to higher Cr content in TP347HFG and 617. The internal oxidation rate of 617 was much more serious than the rate of carburization. Oxidation products on T91 consisted of Fe3O4 and (Fe, Cr)3O4. Moreover, Cr-depletion and carburization zones were observed beneath the oxide scales. Based on the presence of Cr-depletion and carburization zones, it is proposed that corrosion resistance of heat-resistant steels and alloys in supercritical carbon dioxide can be evaluated by the corrosion degradation depth.

Oxidation behavior of high-strength FeCrAl alloys in a high-temperature supercritical carbon dioxide environment

The oxidation behavior of three high-strength FeCrAl alloys was investigated in supercritical carbon dioxide environment at 650 °C. After exposure for 500 h, the weight gains of the FeCrAl alloys gradually decreased with increasing Al content. The oxide scales are primarily composed of α-Al2O3 and spinel oxides. With increasing Al content, the amount of α-Al2O3 increases and the C content decreased in the oxide scale and sub-scale matrix. Moreover, larger (Nb,Mo)C carbides formed in the sub-scale matrix and their number decreased with the increase of Al content.

Design of a methanation reactor for producing high-temperature supercritical carbon dioxide in solar thermochemical energy storage

Methane reforming with CO2 has been intensively investigated for solar thermochemical energy storage, including endothermic reactor design, reaction kinetics study and endothermic reactor performance analysis. A considerable body of research has been amassed concerning the charging loop, i.e., solar CO2 reforming of methane. However, little research has been conducted on the discharging loop, i.e., the subsequent heat recovery in a methanation reactor at temperatures high enough for electricity generation. This paper explores the preliminary design of a methanation reactor for producing sCO2 at 700 °C in solar thermochemical energy storage. A two-dimensional, steady-state, pseudo-homogeneous model is proposed to simulate heating secondary working fluid, e.g., sCO2, with methanation reaction in a tubular packed bed reactor. The model is validated by comparing temperature profiles and methane conversions generated in this study with the established data from other publications. Parametric studies are performed to investigate the effects of reactor diameters and mass flow rates on the reactor capital cost and energy efficiency. The results show that the estimated catalyst cost is comparable to the reactor wall material cost although the unit price of the catalyst is much higher. Basically, enhancing heat transfer by decreasing reactor diameters can reduce the capital cost. But the energy efficiency decreases with reactor diameters decreasing due to a larger pumping power required. Similarly, enhancing heat transfer by increasing the mass flow rates, i.e., the gas mass flow rate and the sCO2 mass flow rate, also reduces the cost. Different from the effect of decreasing reactor diameters, increasing the sCO2 mass flow rate cannot only reduce the cost but improve the energy efficiency, while increasing the syngas mass flow rate leads to a lower energy efficiency.

Surface modification of austenitic stainless steel for corrosion resistance in high temperature supercritical-carbon dioxide environment

Surface-modification was applied to austenitic stainless steel 316LN in order to improve the corrosion resistance in high temperature supercritical-carbon dioxide (S-CO2) environment. The surface-modification methods consisted of deposition of either a single Al layer or a NiAl bi-layer on the surface, followed by inter-diffusion heat treatments. The former resulted in formation of a surface layer composed of a mixture of NiAl and ferrite phases, and the latter resulted in formation of a continuous NiAl surface layer. Surface-modified 316LN showed reduced weight gains than the as-received 316LN alloy after exposure to S-CO2 at 650 °C (20 MPa) for 500 h. Pre-oxidation in helium at 900 °C before S-CO2 exposure further improved corrosion resistance by forming inner α-Al2O3 layer. On the other hand, the extent of inter-diffusion zone was less for the specimen with a continuous NiAl surface layer before and after S-CO2 exposure.

Characterization of Alloy 600 joints exposed to a high-temperature supercritical-carbon dioxide environment

Two types of Alloy 600 joints, such as diffusion-bonded joint and Alloy 182 fusion-weld, were exposed to supercritical-CO2 environment at 550 and 650 °C (20 MPa) for 1000 h. The diffusion-bond region showed similar oxidation characteristics as parent Alloy 600, but the migration of diffusion bond line below oxide layer was observed due to the Cr-depletion induced recrystallization. For Alloy 182 fusion-weld, outer Mn-rich oxides (Mn3O4 and MnCr2O4) and a small amount of inner SiO2 mixed with chromia were formed due to high Mn and Si contents. The presence of SiO2 in chromia suppressed carburization at the oxide/matrix interface, which resulted in the formation of an amorphous C layer between the outer Mn-rich oxide and inner Cr-rich oxide. For Alloy 182 fusion-weld, tensile property changes after exposure to supercritical-CO2 environment were negligible.

Corrosion and Carburization Behaviour of Ni-xCr Binary Alloys in a High-Temperature Supercritical-Carbon Dioxide Environment

Pure Ni and Ni-xCr (x = 7, 14, 22 and 27 wt%) binary alloys were exposed to supercritical-carbon dioxide environment at 600 °C and 20 MPa for 200 h. For pure Ni, a thick NiO layer was formed on the surface. Meanwhile, for Ni-7Cr alloy, an inner oxide layer consisted of rather irregular chromia and NiO was formed below the outer NiO layer. When Cr content was greater than 14%, a continuous chromia layer was formed, resulting in much lower weight gain and oxide thickness. However, amorphous carbon layers had developed along the oxide–matrix interface when chromia was formed. The presence of the carbon layer was explained in view of the high C activity corresponding to the low equilibrium oxygen potential of chromia.

Recuperators investigation for high temperature supercritical carbon dioxide power generation cycles

Supercritical carbon dioxide (s-CO2) Brayton cycles are a promising technology for the next generation power conversion cycles, attaining equivalent or higher cycle efficiency compared to conventional power cycles at similar temperatures (550–750°C). The recompression cycle attracts the main research interest among the s-CO2 layouts. Recompressing a fraction of the flow without heat rejection, results to an increase in thermal efficiency, while the majority of heat transfer occurs in recuperators. In this study, a thermodynamic analysis of a 600MWth power cycle has been carried out using two different simulation tools to model the recompression system. The analysis focuses on the parameters that have the most significant impact on the components and cycle efficiency. A segmental analysis of the recuperators took place to assess the effect of flow characteristics on the heat transfer. Finally, a comparative analysis of the results of the two simulation tools versus the results of a reference cycle from literature is carried out, showing that the prediction of the overall heat transfer coefficient and recuperator effectiveness between the developed code and reference model has a maximum deviation of 4%, whereas the prediction deviation between the commercial software and reference model is about 2.8%.

Corrosion of Alloy Haynes 230 in High Temperature Supercritical Carbon Dioxide with Oxygen Impurity Additions

The corrosion of Ni-based alloy Haynes 230 in supercritical carbon dioxide at temperatures of 650 and 750 °C at a pressure of 20 MPa was investigated. In high-purity research grade CO2, the corrosion performance of the alloy was excellent with a thin, uniform, protective chromium-rich oxide layer forming on the surface. Introduction of 10 and 100 ppm O2 impurity in the CO2 environment noticeably enhanced oxidation with evidence of oxide spallation and nodule formation. In these oxygen impurity added tests, increased oxidation led to subsurface voids due to the more rapid outward diffusion of chromium as well as intergranular alumina and chromia. The oxygen concentration at the inlet and the outlet of the autoclave was measured and used to support the results of characterization of the surface oxide to develop a more holistic understanding of the role of oxygen impurity on the corrosion process. In all cases, there some carbon was observed, which manifested as slightly higher concentration of chromium–carbide phase at the grain boundaries compared to the unexposed alloy.

Experimental approach to estimate diffusivity of metal organics in supercritical CO2 at high temperatures

A new experimental method to measure the diffusivity of reactive metal organics in high-temperature (>150°C) supercritical carbon dioxide (scCO2) is reported. The technique used supercritical fluid deposition (SCFD) to deposit films on planar and high-aspect-ratio (high-AR) trench substrates. SCFD consists of carrying out chemical reactions in scCO2 and is a commonly used method to form inorganic films. Diffusivity can be estimated by fitting the profile using surface reaction kinetics measured on a planar substrate, as the film thickness profile within a trench is a consequence of the diffusion and surface reactions of the source precursor. The method was demonstrated for titanium-di(isopropoxide)bis(tetramethylhexanedionate) at 250–325°C and 10–20MPa. The obtained diffusivities were correlated by the Stokes–Einstein and Chapman–Enskog equations, derived for liquids and gases, respectively. The diffusivity was well fit by the modified Chapman–Enskog equation, incorporating a collision parameter to express the behavior of a supercritical fluid. This modeling indicated that the mass transfer was similar to that of gases, which was consistent with our experimental conditions that were close to gaseous.