Wellbore temperature and pressure calculation model for supercritical carbon dioxide jet fracturing

A new numerical calculation model for wellbore temperature and pressure for SC-CO₂ jet fracturing was proposed in this research. In our model, the impact of tubing, casing, and cement on heat transfer, and the heat generated by fluid friction losses are all taken into consideration. The CO₂ physical properties are calculated by the Span–Wagner and Vesovic models. Based on our calculation model, the factors that may affect the wellbore temperature and pressure are discussed. The results indicated that ignoring the influence of the cement sheath thermal resistance on heat transfer would lead to a wellbore temperature higher than the actual value. The wellbore CO₂ pressure is always higher than its critical value, but the CO₂ temperature at the jet point in some cases is lower than its critical value. The wellbore CO₂ temperature is increased with the increase in injection temperature and cement sheath thermal conductivity and the decrease in annulus injection rate and coiled tubing injection rate. However, the decrease in the coiled tubing injection rate and increase in the cement sheath thermal conductivity are the only effective ways to ensure that the CO₂ temperature at the jet point exceeds its critical value.     

Carbon Dioxide Emissions and Carbonation Sensors

Abstract

The gases with higher heat capacities than those of O₂ and N₂ cause greenhouse effects. Carbon dioxide (CO₂) is the main greenhouse gas associated with global climate change. At the present time, coal is responsible for 30–40% of world CO₂ emissions from fossil fuels. There was a higher correlation between the amount of carbon dioxide emission and percentage of carbon in the fuel for all equations. The squares of correlation coefficients were 0.9999, 0.9978, and 0.9995. The gas sensing characteristics of MgO and CaO as the CO₂ gas sensors and CO₂ emission capacities selected carbonaceous fuels have been investigated. It was found that increasing the percentage of carbon in carbonaceous fuel caused CO₂ emission increase. Carbonation is a stabilization of CO₂ by solidification process. The availability of a CO₂ fixation technology would serve as insurance in case global warming causes severe restrictions on CO₂ emissions. In order to prevent rapid climate change, it will be necessary to stabilize CO₂ as carbonate by the carbonation process. The carbonation was carried out using MgO and CaO as CO₂ sensors. The yield of carbonation increased with increasing temperature. The rate of carbonation conversion sharply increased in the initial 20 min and then reduced and reached a plateau value after about 40 min. The carbonation conversion with MgO is higher than that of CaO.     

Fixation of CO2 by carbonating calcium derived from blast furnace slag

Industrial waste materials, such as steelmaking slags, appear to be potential raw materials for reducing CO₂ emissions by carbonation. The suitability of applying a carbonation route based on acetic acid leaching to produce carbonates from blast furnace slag is presented in this study. The effect of solution pH, temperature, and CO₂ pressure on the precipitation of carbonates was experimentally studied. A simple thermodynamic model was used to verify our results. The feasibility of the process was also discussed, addressing energy input requirements and the consumption of chemicals.     

Modeling of carbonation reaction for CaO-based limestone with CO2 in multitudinous calcination-carbonation cycles

In the cyclic carbonation-calcination reaction processes, CaO-based solid sorbents have been substantiated to be the effective sorbents for CO₂ capture at high temperature. The carbonation reaction has been depicted the carbonation reaction by several kinetic models. Some kinetic models are capable to calculate the intrinsic carbonation rate in the cyclic carbonation-calcination reaction, but the mathematic equation of those models is basically complicated. In this work, a modified model was proposed to delineate the carbonation reaction in multitudinous carbonation-calcination cycles, and was qualified to characterize the whole progression of carbonation reaction in highly cycled particles. The sharp corner is inexistent simultaneously. Additionally, the mathematic equation of this model is apparent simplified. The disconnected pore size distribution is expressed by the log-normal function, and the time evolution of pore structure was also discussed.     

CO2 capture using carbide slag modified by propionic acid in calcium looping process for hydrogen production

Lime enhanced gasification (LEGS) process based on calcium looping in which CaO is employed as CO₂ sorbent is an emerging technology for hydrogen production and CO₂ capture. In this work, carbide slag which was an industrial solid waste was utilized as CO₂ sorbent in hydrogen production process. Modification of carbide slag by propionic acid was proposed to improve its reactivity. The CO₂ capture behavior of raw and modified carbide slags was investigated in a dual fixed-bed reactor (DFR) and a thermo-gravimetric analyzer (TGA). The results show that modification of carbide slag by propionic acid enhances its CO₂ capture capacity in the multiple calcination/carbonation cycles. The favorable carbonation temperature and calcination temperature for modified carbide slag are 680–700 °C and 850–950 °C, respectively. Prolonged carbonation treatment is beneficial to CO₂ capture of raw and modified carbide slags. The prolonged carbonation for 9 h in the 21st cycle increases the conversions of raw and modified carbide slags in this cycle. And then the carbonation conversions of the two sorbents were also improved in the subsequent cycles. Calcined modified carbide slag shows more porous microstructure compared with calcined raw one for the same number of cycles. Modification of carbide slag by propionic acid increases the surface area, pore volume and pore area. In addition, the volume and area of the pores in 20–100 nm in diameter were improved, which had been proved to be more effective to capture CO₂. The microstructure of calcined modified carbide slag favors its higher CO₂ capture capacity in the multiple calcination/carbonation cycles.     

Assessment of sugarcane bagasse gasification in supercritical water for hydrogen production

Sugarcane bagasse is one of the major resources of agricultural biomass waste in the world. In this work, supercritical water gasification characteristics of sugarcane bagasse were investigated. The effect of temperature (600–750 °C), concentration (3–12 wt%), residence time (5–20 min) and catalysts (Raney-Ni, K₂CO₃ and Na₂CO₃) on bagasse gasification were studied. A kinetic study on the non-catalytic and Na₂CO₃ catalytic bagasse gasification was conducted to describe the kinetic information of the bagasse gasification reaction. The results showed that a higher reaction temperature, a lower bagasse concentration and a longer residence time could favor the gasification of bagasse, leading to a higher hydrogen yield. Bagasse was nearly completely gasified at 750 °C without using any catalyst and the carbon gasification efficiency could reach up to 96.28%. The addition of employed catalysts remarkably promoted the bagasse gasification reactivity. The maximum hydrogen yield (35.3 mol/kg) was achieved at 650 °C with the Na₂CO₃ loading of 20 wt%. The experimental data fitted well with a homogeneous model based on a Pseudo-first-order reaction hypothesis. The kinetic study showed that Na₂CO₃ catalyst could lower the activation energy E_a of bagasse gasification from 117.88 kJ/mol to 78.25 kJ/mol.     

Development of porous solid reactant for thermal-energy storage and temperature upgrade using carbonation/decarbonation reaction

Cyclic reaction performances of solid reactants for a CaO–CO₂ chemical heat-pump designed for upgrading and storing high-temperature thermal energy were studied. Solid reactants composed of CaO as the reactant and CaTiO₃ as the inert framework were prepared using the conventional powder method or the metal alkoxide method. Upon experiments of cyclic operation between CaO carbonation and CaCO₃ decarbonation at 1023K, the reaction reversibility of the solid reactants with the inert CaTiO₃ framework was steady, whereas that of the solid reactant without the inert framework decreased with sintering of the solid particles during cyclic operation. Reaction rates for the first carbonation and the decarbonation of solid reactant prepared using the alkoxide method were about 1.8 and 2.4 times faster, respectively, than for those prepared by the powder method due to the smaller average diameter of reactant particles derived from the alkoxide method.     

Kinetic modeling and reaction pathways for thermo-catalytic conversion of carbon dioxide and methane to hydrogen-rich syngas over alpha-alumina supported cobalt catalyst

This study investigates the kinetic modeling and reaction pathway for the thermo-catalytic conversion of methane (CH₄) and Carbon dioxide (CO₂) over alpha-alumina supported cobalt catalyst. Rate data was obtained from the thermo-catalytic reaction at a temperature range of 923–1023 K and varying CH₄ and CO₂ partial pressure (5–50 kPa). The rate data was significantly influenced by the changes in the reaction temperature as well as the CH₄ and CO₂ partial pressure. To estimate the kinetic parameters, the rate data were fitted with five Langmuir-Hinshelwood kinetic models. The discrimination of the kinetic models using different parameters revealed that the Langmuir-Hinshelwood kinetic model with the assumption of CH₄ being associatively adsorbed on a single and CO₂ being dissociative adsorbed with bimolecular surface reaction best described the rate data. The analysis of the kinetic model using a non-linear regression solver results in activation energies of 15.88 kJ/mol, 36.78 kJ/mol, 65.51 kJ/mol, and 41.08 kJ/mol for CH₄ consumption, CO₂ consumption, H₂ production, and CO production, respectively. The thermo-catalytic reaction was influenced by carbon as indicated by the rate of carbon deposition which was mainly caused by methane cracking. The reaction pathway for the thermo-catalytic conversion of the CH₄ and CO₂ over the alpha-alumina supported cobalt catalyst can best be described as by CH₄ associative adsorption on the alpha-alumina supported cobalt catalyst single site and CO₂ dissociative adsorption with bimolecular surface reaction.     

Steam methane reforming on LaNiO3 perovskite-type oxide for syngas production,activity tests,and kinetic modeling

The kinetic experiments at various working conditions (ie, temperature: 500°C-900°C, pressure: 1-15 bar, H₂O/CH₄ ratio [S/C ratio] of 1-2.5, and gas hourly space velocity of 900-1700 1/h) in the presence of LaNiO₃ perovskite-type oxide were done to consider and assess the outcome of steam methane reforming (SMR) and to build up its kinetic models depending on Langmuir-Hinshelwood method in a fixed bed reactor. The outcomes demonstrate, the methane conversion, H₂ and CO yields and formed CO₂ are affected by the working parameters. Elevated temperature is profitable for more methane conversion, H₂ and CO yield. While high temperature has a negative effect on mol% of CO₂ in outlet products. The high working pressure will not profit SMR respect to CH₄ conversion and products distribution. The efficacy of S/C ratio on the CH₄ conversion and CO yield depended on temperature range. H₂ yield considerably diminishes with an increment in S/C ratio, while the trend was reverse for CO₂ value in outlet gas. The accuracy of suggested kinetic model was evaluated by correlation and statistical tests. Outcomes exhibited that the obtained data were well anticipated through the suggested model, owning to presumption of nonideal gas phase and by utilizing reasonable equation of state of PPR78.     

CO2 capture performance of calcium-based sorbent doped with manganese salts during calcium looping cycle

The effects of manganese salts including Mn(NO₃)₂ and MnCO₃ on CO₂ capture performance of calcium-based sorbent during cyclic calcination/carbonation reactions were investigated. Mn(NO₃)₂ and MnCO₃ were added by wet impregnation method. The cyclic CO₂ capture capacities of Mn(NO₃)₂-doped CaCO₃, MnCO₃-doped CaCO₃ and original CaCO₃ were studied in a twin fixed-bed reactor and a thermo-gravimetric analyzer (TGA), respectively. The results show that the addition of manganese salts improves the cyclic carbonation conversions of CaCO₃ except the previous cycles. When the Mn/Ca molar ratios are 1/100 for Mn(NO₃)₂-doped CaCO₃ and 1.5/100 for MnCO₃-doped CaCO₃, the highest carbonation conversions are achieved respectively. The carbonation temperature of 700-720 °C is beneficial to CO₂ capture of Mn-doped CaCO₃. The residual carbonation conversions of Mn(NO₃)₂-doped and MnCO₃-doped CaCO₃ are 0.27 and 0.24 respectively after 100 cycles, compared with the conversion of 0.16 for original one after the same number of cycles. Compared with calcined original CaCO₃, better pore structure is kept for calcined Mn-doped CaCO₃ during calcium looping cycle. The pore volume of calcined MnCO₃-doped CaCO₃ is 2.4 times as high as that of calcined original CaCO₃ after 20 cycles. The pores of calcined MnCO₃-doped CaCO₃ in the pore size range of 27-142 nm are more abundant relative to clacined original one. That is why modification by manganese salts can improve cyclic CO₂ capture capacity of CaCO₃.     

A novel hybrid iron-calcium catalyst/absorbent for enhanced hydrogen production via catalytic tar reforming with in-situ CO2 capture

An iron-calcium hybrid catalyst/absorbent (Ca–Al–Fe) is developed by a two-step sol-gel method to enhance tar conversion, cyclic CO₂ capture and mechanical strength of absorbent for hydrogen production in calcium looping gasification. The developed catalyst/absorbent consists of CaO and brownmillerite (Ca₂Fe₂O₅) with mayenite (Ca₁₂Al₁₄O₃₃) as inert support. Comparing with three candidate absorbents without Ca₂Fe₂O₅ or Ca₁₂Al₁₄O₃₃, cyclic carbonation reactivity and mechanical strength of Ca–Al–Fe are largely promoted. Meanwhile, Ca–Al–Fe approaches the maximum conversion rate of 1-methyl naphthalene (1-MN) with enhanced hydrogen yield around 0.15 mol/(h·g) under reforming conditions of present study. Ca–Al–Fe also shows the largest CO₂ absorption and lowest coke deposition. Influences of operation variables on 1-MN reforming are evaluated and recommended conditions can be iron to CaO mass ratio of 10%, reaction temperature of 800 °C and steam to carbon in 1-MN mole ratio of 2.0. Ca–Al–Fe hybrid catalyst/absorbent presents good potential to be applied in future.     

Chemical aspects of the water-splitting thermochemical cycle based on sodium manganese ferrite

Water thermolysis by means of the sodium manganese ferrite cycle for sustainable hydrogen production is reviewed, with particular focus on known elementary chemical processes taking place on solid substrates in the 600–800 °C temperature range. For the purpose, in-situ high temperature x-ray diffraction technique has been utilized to observe structural transformations produced by both temperature and reactive environment. The water-splitting reaction and the regeneration of initial reactants are described as multi-step reactions, in which the role of carbon dioxide, through carbonation and de-carbonation reactions is highlighted. A thermodynamic phase stability diagram is reported for the system MnFe₂O₄/Na₂CO₃/CO₂.     

Exergy analysis and CO2 emission evaluation for steam methane reforming

This paper investigates the industrial production of hydrogen through steam methane reforming (SMR) from both exergy efficiency and CO₂ emission aspects. An SMR model is constructed based on a practical flow diagram including desulfurizer, furnace, separation unit and heat exchangers. The influence of reformer temperature (Tr) and steam to carbon (S/C) ratio is analyzed to optimize exergy efficiency and CO₂ emission. A clear correlation is obtained between exergy efficiency and CO₂ emission. Results also show optimal S/C ratio decreases with Tr. An exergy load distribution analysis which evaluates interactions between the system and its subsystems with parameter variations is employed to find promising directions for efficiency improvement. Results show that the greatest improvement lies in increasing efficiency of furnace without increasing its relative exergy load. Integration of oxygen-enriched combustion (OEC) with SMR is also evaluated. The integration of OEC can increase the system efficiency greatly when the reformer operates above critical point, while in other cases the system efficiency may decrease.     

Syngas production from methane dry reforming over SmCoO3 perovskite catalyst: Kinetics and mechanistic studies

The kinetics of the methane dry (CO₂) reforming over the SmCoO₃ was investigated in the temperature ranged 973–1073 K by varying the CH₄ and CO₂ partial pressures. Based on detailed study of the reaction mechanism, a mechanistic model is proposed from which a kinetic model is derived. The mechanistic pattern assumes adsorption of CH₄ on reduced Co, followed by methane cracking and carbon deposition. CO₂ reacts with Sm₂O₃ to form Sm₂O₂CO₃ and the oxycarbonates react with carbon to produce CO. The power law and Langmuir–Hinshelwood kinetic model which is established on this mechanism were able to forecast the kinetic results.     

Correlations of minimum miscibility pressure for pure and impure CO2 in low permeability oil reservoir

Minimum miscible pressure (MMP) is an important indicator to evaluate the miscibility of CO₂ with oil, and it is of paramount importance to the implementation of CO₂ flooding. In this study, the sensitivities of MMP to its influencing factors were analyzed quantitatively. And the MMP correlations applying for pure and impure CO₂–oil in low permeability reservoir were presented. These correlations are conducive to predicting MMP quickly and precisely when limited experimental data are available. In low permeability reservoirs, the main sensitive factors of MMP are reservoir temperature, oil components (C₅₊ molecular weight, volatiles and intermediates) and the components of injected gas (characterized with pseudo-critical temperature). MMP increases with the volatile/intermediate ratio, especially in the neighborhood of unity and decreases with the pseudo-critical temperature of impure CO₂. MMP shows strong sensibility to the pseudo-critical temperature of impure CO₂ when the critical temperature is less than that of pure CO₂.     

CO2 capture efficiency and energy requirement analysis of power plant using modified calcium-based sorbent looping cycle

This paper examines the average carbonation conversion, CO₂ capture efficiency and energy requirement for post-combustion CO₂ capture system during the modified calcium-based sorbent looping cycle. The limestone modified with acetic acid solution, i.e. calcium acetate is taken as an example of the modified calcium-based sorbents. The modified limestone exhibits much higher average carbonation conversion than the natural sorbent under the same condition. The CO₂ capture efficiency increases with the sorbent flow ratios. Compared with the natural limestone, much less makeup mass flow of the recycled and the fresh sorbent is needed for the system when using the modified limestone at the same CO₂ capture efficiency. Achieving 0.95 of CO₂ capture efficiency without sulfation, 272 kJ/mol CO₂ is required in the calciner for the natural limestone, whereas only 223 kJ/mol CO₂ for the modified sorbent. The modified limestone possesses greater advantages in CO₂ capture efficiency and energy consumption than the natural sorbent. When the sulfation and carbonation of the sorbents take place simultaneously, more energy is required. It is significantly necessary to remove SO₂ from the flue gas before it enters the carbonator in order to reduce energy consumption in the calciner.     

Effect of operating conditions and effectiveness factor on hydrogenation of CO2 to hydrocarbons

The development of an efficient reactor for hydrocarbons (C₂–C₄) production through hydrogenation of CO₂, requires a deep understanding of the operating conditions effects. Subsequently, a model is proposed to analyze the reaction rates and investigate the sensitivity of hydrocarbons yield and products distribution to the variations of temperature, pressure and space velocity (SV). Besides, Thiele modulus and effectiveness factor are calculated for all of the reactions considered in the model. Results reveal that simultaneous occurrence of both endothermic reverse water gas shift (RWGS) and exothermic Fischer-Tropsch (FT) reactions, may be the main reason of temperature and rate fluctuations at the fixed-bed reactor inlet. In addition, increasing temperature and pressure, and decreasing SV can shift the process to produce more light olefins. Finally, sensitivity analysis demonstrates that reactor behavior is independent of the changes in pressure and SV at high temperature, which is an indication of high temperature dependency of this process. These findings can be effectively employed to achieve a better insight about appropriate operating conditions of hydrocarbons production via hydrogenation of CO₂.     

An experimental and modeling study of methyl propanoate pyrolysis at low pressure

Methyl propanoate (MP) pyrolysis in a laminar flow reactor was studied at low pressure (30 Torr) within the temperature range from 1000 to 1500 K. About 30 products were detected and identified in the pyrolysis process using the photoionization mass spectrometry, including H₂, CO, CO₂, CH₃OH, CH₂O, CH₂CO, C1 to C4 hydrocarbons and radicals (such as CH₃, C₂H₅ and C₃H₃). Their mole fraction profiles versus temperature were also measured. For the unimolecular dissociation reactions, the rate constants were calculated by high precision theoretical calculations. Based on the theoretical calculations and measured mole fraction profiles of pyrolysis species, a kinetic model of MP pyrolysis containing 98 species and 493 reactions was developed. The model simulates the primary decomposition process well with the calculated rate constants. According to the rate of production analysis, the decomposition pathways of MP and the formation channels of both oxygenated and hydrocarbon products were discussed. It is concluded that the main decomposition pathway is MP → CH₂COOCH₃ → CH₃CO + CH₂O → CO.     

The intrinsic kinetics of methane steam reforming over a nickel-based catalyst in a micro fluidized bed reaction system

Methane steam reforming (MSR) is studied experimentally and numerically. The intrinsic kinetics of the reaction are determined using a micro fluidized bed with a catalyst containing more than 50 wt % NiO/α-Al₂O₃. Intrinsic kinetic models are developed for parallel and serial reaction mechanisms, but the parallel mechanism is found to better match the experimental data. The activation energies for CO and CO₂ formation are 81.69 kJ/mol and 59.38 kJ/mol, respectively, and the pre-exponential factors are 316.6 mol/(g h kPa^0.85) and 0.00263 mol/(g h kPa^3.1), respectively. As the reaction temperature increases, the rate of CO formation increases and that of CO₂ decreases. At 800 °C, almost all the CH₄ is converted to CO and H₂, and the methane conversion rate (X_CH4), the hydrogen production rate (Y_H2), and the CO selectivity (S_CO) are 92.28%, 3.34, and 0.99, respectively. The effects of the steam-to-carbon ratio (S/C), inlet velocity, and preheating temperature at different reaction temperatures are simulated using the FLUENT software package. As S/C increases, X_CH4 and Y_H2 increase, but S_CO decreases. The higher the reaction temperature, the less S/C promotes X_CH4 and Y_H2. When the reaction temperature is 700 °C and the inlet velocity is 0.2 m/s (residence time is 0.5 s), X_CH4 is above 95%, and changes in the inlet velocity strongly influence the formation of CO. With increasing preheating temperature, X_CH4, Y_H2, and S_CO all increase gradually.     

Ga doped Ni3S2 ultrathin nanosheet arrays supported on Ti3C2-MXene/Ni foam: An efficient and stable 3D electrocatalyst for oxygen evolution reaction

Exploring cost-efficient electrocatalysts for oxygen evolution reaction (OER) is still a huge challenge in the electrochemical energy conversion technology. In this work, Gallium (Ga)-doped Ni₃S₂ nanosheet arrays grown on Ti₃C₂-MXene/nickel foam (Ga–Ni₃S₂/Ti₃C₂/NF) have been synthesized by a successive hydrothermal and sulfidization process. The Ga doping modulates the electronic structure of Ni₃S₂, so tuning the adsorption energies of oxygen intermediate (1OOH). The Ga–Ni₃S₂/Ti₃C₂/NF delivers outstanding catalytic activities toward OER with an overpotential of 340 mV at 100 mA cm^?2, and exhibits superior electrochemical durability. The excellent OER performance of Ga–Ni₃S₂/Ti₃C₂/NF can be ascribed to the 3D sheet arrays morphology and optimized electronic structure. Density functional theory (DFT) calculations also demonstrate that electronic disturbance attributed to Ga doping effectively improves the activity of Ni sites, leading to stronger binding strength of 1OOH intermediate at Ni sites nearby Ga. This study provides insights into the fabrication of advanced electrocatalysts for application.