Search Results (65)

Hydrogen and some of its derivatives (such as e-methanol, e-methane, and e-ammonia) are promising energy carriers that have the potential to replace conventional fuels, thereby eliminating their harmful environmental impacts. An innovative use of hydrogen as a zero-emission fuel is forming weakly ionized plasma by seeding the combustion products of hydrogen with a small amount of an alkali metal vapor (cesium or potassium). This formed plasma can be used as a working fluid in supersonic open-cycle magnetohydrodynamic (OCMHD) power generators. In these OCMHD generators, direct-current (DC) electricity is generated straightforwardly without rotary turbogenerators. In the current study, we quantitatively and qualitatively explore the levels of electric conductivity and the resultant volumetric electric output power density in a typical OCMHD supersonic channel, where thermal equilibrium plasma is accelerated at a Mach number of two (Mach 2) while being subject to a strong applied magnetic field (applied magnetic-field flux density) of five teslas (5 T), and a temperature of 2300 K (2026.85 °C). We varied the total pressure of the pre-ionization seeded gas mixture between 1/16 atm and 16 atm. We also varied the seed level between 0.0625% and 16% (pre-ionization mole fraction). We also varied the seed type between cesium and potassium. We also varied the oxidizer type between air (oxygen–nitrogen mixture, 21–79% by mole) and pure oxygen. Our results suggest that the ideal power density can reach exceptional levels beyond 1000 MW/m³ (or 1 kW/cm³) provided that the total absolute pressure can be reduced to about 0.1 atm only and cesium is used for seeding rather than potassium. Under atmospheric air–hydrogen combustion (1 atm total absolute pressure) and 1% mole fraction of seed alkali metal vapor, the theoretical volumetric power density is 410.828 MW/m³ in the case of cesium and 104.486 MW/m³ in the case of potassium. The power density can be enhanced using any of the following techniques: (1) reducing the total pressure, (2) using cesium instead of potassium for seeding, and (3) using air instead of oxygen as an oxidizer (if the temperature is unchanged). A seed level between 1% and 4% (pre-ionization mole fraction) is recommended. Much lower or much higher seed levels may harm the OCMHD performance. The seed level that maximizes the electric power is not necessarily the same seed level that maximizes the electric conductivity, and this is due to additional thermochemical changes caused by the additive seed. For example, in the case of potassium seeding and air combustion, the electric conductivity is maximized with about 6% seed mole fraction, while the output power is maximized at a lower potassium level of about 5%. We also present a comprehensive set of computed thermochemical properties of the seeded combustion gases, such as the molecular weight and the speed of sound. Full article

This work results from a numerical investigation of the thermochemical non-equilibrium effects on the surface properties of a hypersonic body. Non-equilibrium within an air mixture composed of 11 chemical species was considered when solving the Navier–Stokes–Fourier equations using a density-based algorithm in OpenFOAM. The influence of thermal and chemical non-equilibrium on the surface properties of a hypersonic double-cone test body was studied by considering two types of surfaces. It was found that the heat flux and pressure distribution along the surface are higher under non-equilibrium free-stream conditions. Unlike what was observed at the impingement point, where the vibrational non-equilibrium effects on the surface properties are almost independent of the surface type, at the stagnation point, these effects are highly dependent on the catalytic activity of the surface. At the stagnation point, the vibrational non-equilibrium effects are more pronounced on a fully catalytic surface than on a non-catalytic surface. Under the studied conditions, the vibrational non-equilibrium reduces the heat flux by 18% for a non-catalytic surface, while for a fully catalytic surface, it reduces the heat flux by 38%. Additionally, the presence of vibrational non-equilibrium in the free-stream reduces the pressure by 24% for a non-catalytic surface, while for a fully catalytic surface, it is reduced by 42%. Full article

In this work we propose a method of geochemical feed zone (FZ) analysis based on the assumption of thermochemical equilibrium between geothermal fluids and hydrothermal minerals, for each FZ contributing to well discharge. Using our method, it is possible to calculate the mass fraction and the chemistry of each FZ fluid, namely (1) the pH and the concentrations of SiO₂, CO₂, Na, K, Ca, Mg, HCO₃, SO₄, F, and Cl of FZ liquids, and (2) the concentrations of SiO₂ and CO₂ of FZ vapors. The method can be applied to wells with two single-phase FZs and to wells with either three single-phase FZs or two FZs, one single-phase and the other two-phase, with different temperature and fluid chemistry. Full article

Entropies for alkane isomers longer than C₁₀ are computed using our recently developed linear regression model for thermochemical properties which is based on second-order group contributions. The computed entropies show excellent agreement with experimental data and data from Scott’s tables which are obtained from a statistical mechanics-based correlation. Entropy production and heat input are calculated for the hydroisomerization of C₇ isomers in various zeolites (FAU-, ITQ-29-, BEA-, MEL-, MFI-, MTW-, and MRE-types) at 500 K at chemical equilibrium. Small variations in these properties are observed because of the differences in reaction equilibrium distributions for these zeolites. The effect of chain length on heat input and entropy production is also studied for the hydroisomerization of C₇, C₈, C₁₀, and C₁₄ isomers in MTW-type zeolite at 500 K. For longer chains, both heat input and entropy production increase. Enthalpies and absolute entropies of C₇ hydroisomerization reaction products in MTW-type zeolite increase with higher temperatures. These findings highlight the accuracy of our linear regression model in computing entropies for alkanes and provide insight for designing and optimizing zeolite-catalyzed hydroisomerization processes. Full article

Fired heaters upstream of distillation towers, despite their optimal thermal efficiency, often suffer from performance decline due to fluctuations in fuel composition and unpredictable operational parameters. These heaters have high energy consumption, as fuel properties vary depending on the source of the crude oil. This study aims to optimize the combustion process of a three-gas mixture, mainly refinery gas, by incorporating more stable fuels such as natural gas and liquefied petroleum gas (LPG) to improve energy efficiency and reduce LPG consumption. Using real-time gas chromatography-mass spectrometry (GC-MS) data, we accurately calculate the mass fractions of individual compounds, allowing for more precise burner flow rate determinations. Thermochemical data are used to calculate equilibrium constants as a function of temperature, with the least squares method, while the Newton–Raphson method solves the resulting nonlinear equations. Four key variables ($X_4,X_6,X_8,$ and $X_{11}$), representing $H_2,CO,O_2,$ and $N_2$, respectively, are defined, and a Jacobian matrix is constructed to ensure convergence within a tolerance of 1 ×${10}^{-6}$ over a maximum of 200 iterations, implemented via Python 3.10.4 and the scipy.optimize library. The optimization resulted in a reduction in LPG consumption by over 50%. By tailoring the fuel supply to the specific thermal needs of each processing unit, we achieved substantial energy savings. For instance, furnaces in the hydrocracking unit, which handle cleaner subproducts and benefit from hydrogen’s adiabatic reactions, require much less energy than those in the primary distillation unit, where high-impurity crude oil is processed. Full article

In the past two decades, advancements in thermochemical technologies have improved biomass gasification for distributed power generation, enhancing efficiency, scalability, and emission control. This study aims to optimize syngas production from biomass gasification by comparing two computational models: a quasi-equilibrium thermodynamic model implemented in Aspen Plus and an artificial neural network (ANN) model. Operating at 850 °C with varying steam-to-biomass (S/B) ratios, both models were validated against experimental data. Results show that hydrogen concentration in syngas increased from 19.96% to 43.28% as the S/B ratio rose from 0.25 to 0.5, while carbon monoxide concentration decreased from 24.6% to 19.1%, consistent with the water–gas shift reaction. The ANN model provided rapid predictions, showing a mean absolute error of 3% for hydrogen and 2% for carbon monoxide compared to experimental data, though it lacks thermodynamic constraints. Conversely, the Aspen Plus model ensures mass and energy balance compliance, achieving a cold gas efficiency of 95% at an S/B ratio of 0.5. A Multivariate Statistical Analysis (MVA) further clarified correlations between input and output variables, validating model reliability. This combined modelling approach reduces experimental costs, enhances gasification process control and offers practical insights for improving syngas yield and composition. Full article

The pairs of Cu₂O/CuO and CoO/Co₃O₄ as the carriers of transferring oxygen and storing heat are essential for the recently emerged high-temperature thermochemical energy storage (TCES) system. Reported research results of Cu₂O and CoO oxidation kinetics show that the reaction rate near equilibrium decreases with the temperature, which leads to the negative activation energy obtained using the Arrhenius equation and apparent kinetics models. This study develops a first-principle-based theoretical model to analyze the Cu₂O and CoO oxidation kinetics. In this model, the density functional theory (DFT) is adopted to determine the reaction pathways and to obtain the energy barriers of elementary reactions; then, the DFT results are introduced into the transition state theory (TST) to calculate the reaction rate constants; finally, a rate equation is developed to describe both the surface elemental reactions and the lattice oxygen concentration in a grain. The reaction mechanism obtained from DFT and kinetic rate constants obtained from TST are directly implemented into the rate equation to predict the oxidation kinetics of Cu₂O without fitting experimental data. The accuracy of the developed theory is validated by experimental data obtained from the thermogravimetric analyzer (TGA). Comparing the developed theory with the traditional apparent models, the reasons why the latter cannot appropriately predict the true oxidation characteristics are explained. The reaction rate is jointly controlled by thermodynamics (reaction driving force) and kinetics (reaction rate constant). Without considering the effect of the reaction driving force, the negative apparent activation energy of Cu₂O oxidation is obtained. However, for CoO oxidation, the negative apparent activation energy is still obtained although the effect of the reaction driving force is considered. According to the DFT results, the activation energy of the overall CoO oxidation reaction is negative, but the energy barriers of the elementary reactions are positive. Moreover, according to the first-principle-based rate equation theory, the pre-exponential factor in the kinetic model is dependent on the partition function ratio and decreases with the temperature for the Cu₂O and CoO oxidation near equilibrium, which results in the apparent activation energy being slightly lower than the actual value. Full article

Avoiding global dependence on fossil oils and improving the environmental impact of energy production are factors that drive research into renewable energies. Considering lignocellulosic biomass residues as a raw material for gasification, a thermochemical process that converts lignocellulosic resources into synthesis gas (H₂, CO, CH₄, and CO₂) is an alternative under study due to its low costs, high efficiency, and wide variety of applications. Fortunately, there are still areas for its improvement and technological development. For example, this can be achieved by gasification. Distinct types of lignocellulosic biomass, such as sugarcane bagasse, wheat straw, pine sawdust, or corn cob, differ in their physical, chemical, and morphological properties, which can affect the characteristics of the gasification process. This work uses the generalized stoichiometry and mass and atomic balances in the gasification reactor to predict the composition of syngas produced via the gasification of both individual substrates and mixtures. The results provide useful information for the design and operation of gasification reactors with an operating region between 2.0 bar and 4.5 bar and between 1023.15 K and 1223.15 K, particularly with regard to understanding the effects of distinct types of biomasses in terms of their humidity and molecular weight on the operation and performance of the process. One important conclusion reached after simulating the addition of more vapor is that the (H₂/CO) ratio cannot be increased indefinitely: it is limited by the thermodynamic equilibrium reached by the system. Full article

The valorization of slag from the production of high-carbon ferrochrome is a challenge for ferrochrome producers. The recycling of high-carbon ferrochrome slag was explored through the smelting route to recover Fe–Si–Al–Cr alloys and reengineer the residual slag for alumina-enriched refractory material. In this research, the focus was to reduce the SiO₂% and enrichment of Al₂O₃% in the final slag and recover the metallic value in the form of a complex alloy containing Fe, Si, Cr and Al. The manuscript consists of a thermochemical simulation of the smelting of FeCr slag followed by smelting experiments to optimize the process parameters such as temperature and the addition of coke, cast iron and alumina. An experimental investigation revealed that the maximum recovery of Si (57.4% recovery), Al in the alloy (20.56% recovery) and Al₂O₃ (85.78% recovery) in the slag was achieved at a charge mix consisting of 1000 g of FeCr slag, 300 g of alumina, 200 g of cast iron and 300 g of coke. The present study also demonstrated the usefulness of prior thermochemical calculations for smelting metallurgical wastes such as slag from high-carbon ferrochrome production for value creation and reutilization purposes. Full article

A complex thermochemical process during biomass gasification includes many chemical reactions. Therefore, a stoichiometric model can be applied to predict the composition of the producer gas during gasification. However, the prediction of methane and hydrogen gas is still limited by a significant margin using the present stoichiometric models. The purpose of this research was to develop novel stoichiometric models that account for the reaction equilibrium constant with correction factors. The new models would enable forecasting of the composition of CO, CO₂, CH₄, H₂, N₂, tar, lower heating value (LHV), and cold gasification efficiency (CGE). Model development consisted of two stages, whereas the development of the models and their validation adopted an artificial neural network (ANN) approach. The first stage was calculating new correction factors and defining the new equilibrium constants. The results were six stoichiometric models (M1–M6) with four sets of correction factors (A–D) that built up the new equilibrium constants. The second stage was validating the models and evaluating their accuracy. Validation was performed by the Root Mean Square Error (RMSE), whereas accuracy was evaluated using a paired t-test. The developed models predicted the composition of the producer gas with an RMSE of less than 3.5% and ΔH-value of less than 0. The models did not only predict the composition of the producer gas, but they also predicted the tar concentration. The maximum tar concentration was predicted by M2C with 98.733 g/Nm³ at O/C 0.644, H/C 1.446, ER 0.331, and T 923 K. The composition of producer gases (CO, CO₂, H₂, and N₂) was accurately predicted by models M1D, M2C, and M3C. This research introduces new models with variables N/C, O/C, H/C, ER, and T to simulate the composition of CO, CO₂, CH₄, H₂, N₂, and LHV-gas, with R² > 0.9354, tar (C₆H₆)-R² of 0.8638, and CGE-R² of 0.8423. This research also introduces correction factors and a new empirical correlation for the reaction equilibrium constants in new stoichiometric models using steam reforming. Full article

The submerged arc welding (SAW) process is operated at high temperatures, up to 2500 °C, in the arc cavity formed by molten oxy-fluoride flux (slag). These high arc cavity temperatures and the complex interaction of gas–slag–metal reactions in a small space below the arc render the study of specific chemical interactions difficult. The importance of gas phase reactions in the arc cavity of the SAW process is well established. A low-temperature (1350 °C) experimental method was applied to simulate and study the vaporisation and re-condensation behaviour of the gas species emanating from oxy-fluoride flux. Energy dispersive X-ray spectroscopy (EDX) analyses and reaction thermochemistry calculations were combined to explain the role of Al as a de-oxidiser element in gas phase chemistry and, consequently, in nano-strand formation reactions. EDX element maps showed that the nano-strands contain elemental Ti only, and the nano-strand end-caps contain Co-Mn-Fe fluoride. This indicates a sequence of condensation reactions, as Ti in the gas phase is re-condensed first to form the nano-strands and the end-caps formed from subsequent re-condensation of Co-Mn-Fe fluorides. The nano-strand diameters are approximately 120 nm to 360 nm. The end-cap diameter typically matches the nano-strand diameter. Thermochemical calculations in terms of simple reactions confirm the likely formation of the nanofeatures from the gas phase species due to the Al displacement of metals from their metal fluoride gas species according to the reaction: yAl + xMF_y ↔ xM + yAlF_x. The gas–slag–metal equilibrium model shows that TiO₂ in the flux is transformed into TiF₃ gas. Formation of Ti nano-strands is possible via displacement of Ti from TiF₃ by Al to form Al-fluoride gas. Full article

General interest in the deployment of molten salt reactors (MSRs) is growing, while the available data on uranium-containing fuel salt candidates remains scarce. Thermophysical data are one of the key parameters for reactor design and understanding reactor operability. Hence, filling in the gap of the missing data is crucial to allow for the advancement of MSRs. This study provides novel data for two eutectic compositions within the NaF-KF-UF₄ ternary system which serve as potential fuel candidates for MSRs. Experimental measurements include their melting point, density, fusion enthalpy, and vapor pressure. Additionally, their boiling point was extrapolated from the vapor pressure data, which were, at the same time, used to determine the enthalpy of vaporization. The obtained thermodynamic values were compared with available data from the literature but also with results from thermochemical equilibrium calculations using the JRCMSD database, finding a good correlation, which thus contributed to database validation. Preliminary thoughts on fluoride salt reactor operability based on the obtained results are discussed in this study. Full article

The screening of all non-radioactive metals without lanthanides for thermochemical hydrogen storage was performed based on physical chemistry calculations. The thermodynamic data were collected from the NIST (National Institute of Standards and Technology) public data repository, which was followed by calculations regarding the change in enthalpy, entropy, Gibbs free energy and equilibrium reaction temperature. The results were critically evaluated based on thermodynamic parameters, viable metals were identified, and their hydrogen storage densities and energy–enthalpy ratios were evaluated. The elements viable for controlled thermochemical hydrogen storage via the reversible reduction and oxidation of metal oxides and metals are manganese (Mn), iron (Fe), molybdenum (Mo) and tungsten (W). Manganese has the largest theoretical potential for hydrogen storage with reversible reduction and oxidation of metal oxides and metals. The second candidate is iron, while the other two (Mo and W) have much lower potential. More research efforts should be dedicated to experimental testing of the identified metals (Mn, Fe, Mo and W) and their different oxides for thermochemical hydrogen storage capabilities both on laboratory and pilot scales. Ferromanganese alloy(s) might also prove itself as an efficient and affordable thermochemical hydrogen storage material. Our theoretical investigation expanded the knowledge on thermochemical hydrogen storage and is accompanied with a brief literature review revealing the lack of experimental studies, especially on oxidation of metals with water vapor occurring during the hydrogen release phase of the cycle. Consequently, accurate modelling of transport, kinetics and other phenomena during hydrogen storage and release is scarce. Full article

Fixed nitrogen species generated by the early Earth’s atmosphere are thought to be critical to the emergence of life and the sustenance of early metabolisms. A previous study estimated nitrogen fixation in the Hadean Earth’s N₂/CO₂-dominated atmosphere; however, that previous study only considered a limited chemical network that produces NO_x species (i.e., no HCN formation) via the thermochemical dissociation of N₂ and CO₂ in lightning flashes, followed by photochemistry. Here, we present an updated model of nitrogen fixation on Hadean Earth. We use the Chemical Equilibrium with Applications (CEA) thermochemical model to estimate lightning-induced NO and HCN formation and an updated version of KINETICS, the 1-D Caltech/JPL photochemical model, to assess the photochemical production of fixed nitrogen species that rain out into the Earth’s early ocean. Our updated photochemical model contains hydrocarbon and nitrile chemistry, and we use a Geant4 simulation platform to consider nitrogen fixation stimulated by solar energetic particle deposition throughout the atmosphere. We study the impact of a novel reaction pathway for generating HCN via HCN₂, inspired by the experimental results which suggest that reactions with CH radicals (from CH₄ photolysis) may facilitate the incorporation of N into the molecular structure of aerosols. When the HCN₂ reactions are added, we find that the HCN rainout rate rises by a factor of five in our 1-bar case and is about the same in our 2- and 12-bar cases. Finally, we estimate the equilibrium concentration of fixed nitrogen species under a kinetic steady state in the Hadean ocean, considering loss by hydrothermal vent circulation, photoreduction, and hydrolysis. These results inform our understanding of environments that may have been relevant to the formation of life on Earth, as well as processes that could lead to the emergence of life elsewhere in the universe. Full article

Hydrogen is attracting attention as a low-carbon fuel. In particular, economical hydrogen production technologies without carbon emissions are gaining increasing attention. Recently, alkaline thermal treatment (ATT) has been proposed to reduce carbon emissions by capturing carbon in its solid phase during hydrogen production. By adding an alkali catalyst to the conventional thermochemical hydrogen production reaction, ATT enables carbon capture through the reaction of an alkali catalyst and carbon. In this study, a thermodynamic feasibility evaluation was carried out, and the effects of the process conditions for ATT with wheat straw grass (WSG) as biomass were investigated using Aspen Plus software V12.1. First, an ATT process model was developed, and basic thermodynamic equilibrium compositions were obtained in various conditions. Then, the effects of the process parameters of the reactor temperature and the mass ratio of NaOH/WSG (alkali/biomass, A/B value) were analyzed. Finally, the product gas compositions, process efficiency, and amount of carbon capture were evaluated. The results showed that the ATT process could be an efficient hydrogen production process with carbon capture, and the optimal process conditions were a reactor temperature of 800 °C, an A/B value of three, and a flow rate of steam of 6.9 × 10⁻⁵ L/min. Under these conditions, the maximum efficiency and the amount of carbon dioxide captured were 56.9% and 28.41 mmol/g WSG, respectively. Full article