Free Energy Minimization Method Research Articles

Experiment and simulation assessment of supercritical underground coal gasification in deep coal seam

To explain the impact of geological and process factors on underground coal gasification in deep coal seam (>2200 m) and promote the efficient and clean extraction and conversion of coal, this study employs the orthogonal experimental design method to investigate the impact of CO2 coefficient (0–1), moisture content (30–80 wt%), calcite content (0–10 wt%), albite content (0–10 wt%), kaolinite content (0–20 wt%), reaction temperature (550–650 °C), and reaction pressure (23–27 MPa) on the characteristics of coal underground gasification under supercritical H2O/CO2 conditions. Furthermore, range analysis and variance analysis are utilized to determine the degree of influence of each factor and the interaction between factors. Finally, the Gibbs free energy minimization method is used to conduct a thermodynamic equilibrium analysis of coal supercritical H2O/CO2 gasification at high temperatures (750–1000 °C). The results indicate that the three most significant factors affecting the process of coal supercritical H2O/CO2 gasification are the CO2 coefficient, moisture content, and reaction temperature. The maximum carbon gasification efficiency at 650 °C in experimental cases and 1000 °C in simulation cases is 22.2% and 88.1%, respectively. Although the addition of CO2 at lower temperatures reduces the carbon gasification efficiency, at high temperatures (>900 °C), a higher initial CO2 concentration increases the carbon gasification efficiency. The addition of CO2 under conditions of low moisture content increases the mole fraction of H2, but reduces it under conditions of high moisture content (≥70 wt%). Among the three minerals, calcite has the most significant influence on the gasification process.

VALORIZATION OF WASTE FRUIT PEELS: A COMPUTATIONAL STUDY ON PREDICTION OF GASIFICATION PRODUCT COMPOSITION

In this work, a variety of discarded fruit peels are investigated using a computational technique in order to anticipate the products of their gasification when subjected to higher temperatures, namely 800°C and 900 °C. The proximate and ultimate analyses of eight different fruit peels were collected from a variety of published sources, and the composition of gasification was predicted by applying the Gibbs free energy minimization method to each fruit peel individually and to both temperatures using the Solver Tool feature of the Microsoft Excel Spreadsheet. As input for the simulation, the thermodynamic constants for each gaseous component and the elemental analysis of each fruit peel were needed. The predicted gaseous composition was compared with some of the data obtained in the literature, and it was determined to be in a close match based on the root mean square error for each number. This was done while taking into account the fact that the carbon conversion process during gasification was only partially successful. For citation: Khedkar R.S., Khonde R.D., Meshram P. Valorization of waste fruit peels: a computational study on prediction of gasification product composition. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 6. P. 127-134. DOI: 10.6060/ivkkt.20246706.6959. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chemical looping reforming of the micromolecular component from biomass pyrolysis via Fe2O3@SBA-16

AbstractTo solve the problems of low gasification efficiency and high tar content caused by solid–solid contact between biomass and oxygen carrier in traditional biomass chemical looping gasification process. The decoupling strategy was adopted to decouple the biomass gasification process, and the composite oxygen carrier was prepared by embedding Fe2O3 in molecular sieve SBA-16 for the chemical looping reforming process of pyrolysis micromolecular model compound methane, which was expected to realize the directional reforming of pyrolysis volatiles to prepare hydrogen-rich syngas. Thermodynamic analysis of the reaction system was carried out based on the Gibbs free energy minimization method, and the reforming performance was evaluated by a fixed bed reactor, and the kinetic parameters were solved based on the gas–solid reaction model. Thermodynamic analysis verified the feasibility of the reaction and provided theoretical guidance for experimental design. The experimental results showed that the reaction performance of Fe2O3@SBA-16 was compared with that of pure Fe2O3 and Fe2O3@SBA-15, and the syngas yield was increased by 55.3% and 20.7% respectively, and it had good cycle stability. Kinetic analysis showed that the kinetic model changed from three-dimensional diffusion to first-order reaction with the increase of temperature. The activation energy was 192.79 kJ/mol by fitting. This paper provides basic data for the directional preparation of hydrogen-rich syngas from biomass and the design of oxygen carriers for pyrolysis of all-component chemical looping reforming.

Equilibrium Study of Carbon Dioxide Reforming of Methane to Syngas

Fugacity coefficients for the components in the gas mixture are determined using the Soave–Redlich–Kwong (SRK) equation of state. The Gibbs free energy minimization method is employed to determine the equilibrium composition of the components for CO2 reforming of CH4 to syngas. To utilize CO2 efficiently and avoid carbon deposition, CO2 composition in the initial feed should not be greater than 1 (nCH4,0 = 1), and the reaction is preferably operated at atmospheric pressure. Setting nCH4,0:nCO2,0 to 1:1, and increasing nO2,0 in the feed from 0 to 1.0 to adjust the initial composition, results in a decrease in the syngas equilibrium yield, and a increase in both nCO2,e and nH2O,e. The temperature required for complete carbon deposition removal decreased. Considering the effective utilization of CO2 at nCH4,0:nCO2,0 1:1, it is recommended to set nO2,0 in the feed to less than 0.5.

ბუნებრივი რესურსის ბაზაზე მიღებული სორბენტებით CO2-ის ადსორბციისას შესაძლო პროცესთა თერმოდინამიკური ანალიზი

This research paper examines the potential mechanisms involved in the adsorption of carbon dioxide using sorbents derived from the natural resources found in Georgia (with a primary focus on zeolite-based materials). A succinct characterization of zeolites obtained from the Dzegvi deposit is provided, along with the presentation of the average chemical composition of the collected samples. The study identifies three distinct series of reactions for in-depth investigation. According to the referenced sources, the standard molar values of the thermodynamic properties of the substances involved in the reaction are sought. The Gibbs free energy minimization method is employed to ascertain both the magnitudes and directions of the free energy changes and equilibrium constants for the proposed reactions within the temperature range spanning 400 to 1200 Kelvin. Their temperature dependence is expressed graphically. Reactions are evaluated based on thermodynamic point of view.

Understanding thermodynamic stability and carbothermal reduction in SiOC

This study explores the phase evolution, carbothermal reduction, and energetics in SiOaCb derived from the pyrolysis of trimethylsilyl terminated polyhydromethylsiloxane (PHMS-TMS) from 1200 to 1600 °C. High-resolution X-ray photoelectron spectroscopy (XPS) shows notable differences in the constituent bond arrangement between the more Si-rich SiOC ceramics and the more C-rich SiOC ceramics, which subsequently affects the microstructure of the SiOC systems. Carbothermal reduction starts at lower temperatures than previously reported and indicates no phase separation of SiOC or formation of SiO2 nanodomains. The thermodynamic stability of the thus-obtained SiOC ceramics is evaluated using a Gibbs free energy minimization method. The results suggest that differences in silicon mixed bonding environments and their relative amounts (SiO2C2, SiOC3, or SiC4) lead to differences in thermodynamic stability.

Thermodynamic performance comparison of a SOFC system integrated with steam reforming and dry reforming by utilizing different fuels

This work investigates the thermodynamic analysis of syngas production from several fuels by steam reforming or dry reforming for SOFC-integrated systems. Four commonly used fuels are considered: methanol and glycerol (alcohols), methane, and diesel (hydrocarbons). The integrated system is modeled on Aspen Plus using the Gibbs free energy minimization method and a generic electrochemical model to assess the effect of critical parameters on system performance. The results indicate a carbon-free zone within the reformer, and alcohols provide better resistance to carbon deposition than hydrocarbon fuels. Elevating the reforming temperature and STCR/CTCR increases the hydrogen concentration of syngas while also avoiding carbon deposits in the external reformer. Increasing the temperature and fuel utilization factor of SOFCs has been found to enhance electrical efficiency but at the expense of diminished thermal and total efficiency. For given operating conditions, the electrical efficiencies of methanol, glycerol, methane, and diesel are observed to be 47%, 46%, 51%, and 49% for the SR-SOFC system, and 45%, 42%, 42%, and 33% for the DR-SOFC system, respectively. The methane-SR-SOFC and methanol-DR-SOFC systems have the highest electrical efficiency, while diesel is unsuitable for the DR-SOFC system. This work can advise engineers to select the appropriate fuel types and reform technologies for SOFC-integrated systems.

A study on the applicability of non-stoichiometric thermodynamic models for the prediction of carbon black yield and off-gas composition in oil furnace process

The effect of feed composition and temperature on the carbon black yield and off-gas amount and composition was studied for oil-furnace process reactor with benzene as a model feedstock. Because of the high furnace temperature (>1200 °C), the reactions were considered as very fast and thus the products close to chemical equilibrium. The equilibrium composition was calculated by a non-stoichiometric thermodynamic model using Gibbs free energy minimization method. The equilibrium and energy balance equations were solved simultaneously to obtain the product composition and reactor temperature under different reaction conditions. The equilibrium carbon black yield increases with gas/air and oil/air ratio whereas the reactor temperature exhibits the reverse trend which are consistent with practical data. Quantitative comparison with real data showed that the product may be kinetically controlled, and thus the thermodynamic model gives the lower limit of carbon black yield. The model can be easily applied to any feedstock including bio-oil without a need for the specific properties.

Influence of oxygen on solid carbon formation during arcing of eco-friendly SF6-alternative gases

During the arc breaking process of high-voltage circuit breakers, the eco-friendly SF6-alternative gases will inevitably decompose and generate various decomposition products. In some cases, this will contain solid by-products such as solid carbon, which will have a deterioration effect on the electrical insulation performance of the equipment. It has been found that adding a proper amount of O2 can effectively inhibit the formation of solid carbon. In this paper, based on the improved Gibbs free energy minimization method, a calculation model considering the solid decomposition products was established, and the arc plasma composition of CO2/O2 mixtures with the new eco-friendly gases, such as C4F7N, C5F10O, HFO-1234ze(E) and HFO-1336mzz(E), in local thermodynamic equilibrium state was calculated. The change of decomposition products with the initial O2 ratio is studied, and the criterion expression of inhibiting solid carbon formation is obtained. We also applied the method to the calculation of other SF6-alternative gases containing sulfur atoms such as NSF3 and CF3SO2F. Finally, we showed that solid carbon can be inhibited when a proper molecule formula is satisfied. This work may provide new ideas for further exploring the potential of SF6-alternative gases.

Modeling and Thermodynamic Studies of γ-Valerolactone Production from Bio-derived Methyl Levulinate.

The exploitation of biomass to reduce the dependency on fossil fuels represents a challenge that needs to be solved as soon as possible. Nowadays, one of the most fashionable processes is γ-valerolactone (GVL) production from bio-derived methyl levulinate (ML). Deep understanding of the thermodynamic aspects involved in this process is key for a successful outcome, but detailed studies are missing in the existing literature. A thermodynamic study of the reaction of γ-valerolactone (GVL) production from bio-derived methyl levulinate (ML) is performed by the Gibbs free energy minimization method. The effect of various reaction conditions (temperature, concentration, flow rate) and the implication of possible intermediates and byproducts are assessed. Conversion and selectivity are calculated from the simulation of the ML hydrogenation using isopropanol as the hydrogen donor under continuous flow conditions. Significant increases in GVL selectivity can be achieved under dry conditions, keeping the high conversion. Comparison between theoretical and experimental results from a previous article discloses the effect of using 5%RuTiO2 catalysts, which increases the selectivity from 3-40% to 41-98%. Enthalpy and Gibbs free energy of the reactions at issue are also calculated from models using Barin equations according to Aspen Physical Property System parameters.

Prediction of Pyrolysis Gas Composition Based on the Gibbs Equation and TGA Analysis

Conventional methods used to determine pyrolysis gas composition are based on chemical kinetics. The mechanism of those reactions is often unknown, which makes the calculations more difficult. Solving complex chemical reactions’ kinetics involving a nonlinear set of equations is CPU time demanding. An alternative approach is based on the Gibbs free energy minimization method. It requires only the initial composition and operation parameters as the input data, for example, temperature and pressure. In this paper, the method for calculating the pyrolytic gas composition from biogenic fuels has been presented, and the thermogravimetric experimental results have been adopted to determine the total gas yield. The studied problem has been reduced to the optimization method with the use of the Lagrange multipliers. This solution procedure is advantageous since it does not require knowledge of the reaction mechanism. The obtained results are in good agreement with experimental data, demonstrating the usefulness of the proposed method.

Assessment of the groundwater for household and drinking purposes in central Kazakhstan

Water resources, including potable water availability, are complicated issues in many Kazakhstan regions. Central Kazakhstan region is one such region, which requires the proper support in the water supply. Most of the Kazakhstan regions had been using mostly surface water, however, with the limitation of the surface water, the groundwater resources have been used more intensively during the last decades. At the same time, the groundwater chemical composition plays a decisive role for categorization as the potable water. Within this research work the chemical composition of groundwater formation features in the arid conditions of Kazakhstan are presented. The regional hydrogeochemical field works were carried out to establish the patterns of fresh and brackish groundwater formation. In the arid conditions of Kazakhstan, the two main factors influencing the chemical compositions were investigated, including: a) the water-rock interaction for mountain-folded areas, and b) water-soil-gas interaction and evaporative concentration (water evaporation and salts accumulation) for flat areas. The physical and chemical modeling by the Gibbs free energy minimization method, which is based on the thermodynamics laws, were provided to analyze processes of these two main factors influencing the chemical compositions. The results of these analyses, for the a) mountain-folded areas, we found that with the growth of gypsum (1.2%) in the rock, the content of sulfate compounds in water increases tenfold. In the fractured rocks of mountain-folded areas with free access to atmospheric air (open system), waters are enriched with oxygen and carbon dioxide. At the same time, the cationic composition of waters is determined by the lithological composition of the rocks. The sodium cations predominate in granite massifs. Calcium is predominant in enriched calcium minerals. Bicarbonate anions predominate in the anionic component with weak mineralization. For the b) flat areas, as mineralization increases due to the interaction of water-soil-gas and evaporative concentration, the chemical composition changes. The changes occur from sulfate to chloride in anions and from calcium to sodium in cations. These two main factors pattern a-b influencing the chemical compositions were also observed in the bigger regional hydrogeochemical studies, mountain-folded with connected flat areas. Waters are predominantly fresh bicarbonate calcium-sodium in the feeding zones of the mountain-folded areas originally. With water movement down to the flat areas, the mineralization increases. The water's mineralization increases and becomes more sulfate to chloride. The hydrogeochemical zonings are traced. This study is applicable for forecasting, searching the fresh and slightly brackish waters, which could be suitable for domestic water supply.

Study of the Thermodynamic Properties of Thermal Plasmas of Fluoroalkylamine-Air Mixtures

Knowledge of thermodynamic properties as well as parameters such as energy density and power flow isimportant for modeling thermal plasmas of fluoroalkylamine-air mixtures. In this paper, these thermodynamic properties of fluoroalkylamine-air mixture plasmas are calculated in a temperature range of 500 K to 20,000 K at atmospheric pressure and local thermodynamic equilibrium (LTE). The Gibbs free energy minimization method is used to determine the chemical equilibrium compositions of the plasmas that are needed to calculate the thermodynamic properties. These thermodynamic properties are then used to calculate the energy density and power flow of these plasmas. The variation of the energy density is related to the variations of the density and mass enthalpy. We notice that, this energy density increases with the percentage of air in the mixture for temperatures higher than 7000 K. The power flow, which depends also on density, enthalpy mass and sound speed, increases with the percentage of air in the same temperature range. Energy density and power flow results show that increasing air percentage in the mixture can be more interesting for damaging gaseous chemical species such as CF2, CO, HCN, and HF appearing at low temperatures with high concentrations.

Thermodynamic assessment of hydrothermal combustion assisted fossil fuel in-situ gasification in the context of sustainable development

Developing countries cannot get rid of the fate of relying on fossil energy development in the short term, so the low-carbon transformation must be carried out in the development process to achieve the goal of net zero emissions. This work proposed a novel hydrothermal combustion assisted fossil fuel in-situ gasification (HC-ISG) system combining renewable energy, supercritical hydrothermal combustion technology and supercritical water gasification technology. The system has the advantages of high thermal efficiency, high hydrogen yield, carbon dioxide utilization and storage, and landfill of hazardous waste. Firstly, based on the concept of energy grade, the effects of renewable energy and auxiliary fuel on the characteristics of energy grade change in HC-ISG system is studied. Then, the Gibbs free energy minimization method is conducted to discuss the effects of fossil fuels, oxidants, sub- and supercritical water on the key parameters of the system. The results indicated that for HC-ISG system, the energy grade and input amount of renewable energy have the optimal values. Compared with coke and methane, the system with methanol as an auxiliary fuel for hydrothermal combustion owned better the matching between energy quantity and energy grade. Moreover, increasing the reaction temperature could reduce the exergy destruction of the system and increase the energy grade change of the input energy. When the combustion coefficient was 0.2–0.3, the molar fraction of H2 reached the maximum value. When fossil fuel with high carbon content was used, the maximum H2 yield could reach 89.4 mol/kg, and the carbon emission was 3.9 kg CO2/kg H2, so the HC-ISG system could produce clean hydrogen. The system proposed in this study may provide a promising method for efficient and low-carbon in-situ conversion of fossil energy to hydrogen production.

Thermodynamic Study of One-step Production from Isobutene to Methyl Methacrylate

Methyl methacrylate (MMA) has emerged as an essential industrial monomer. However, the toxic by-production and shortage supply of MMA in the global market has gained great attention. Herein, a one-step synthesis to produce MMA from isobutene via a direct oxidative esterification process has been demonstrated to curb the aforementioned downsides. Thermodynamic analysis via Gibbs free energy minimization method proved the feasibility of this route via the equilibrium constant. Despite tert-butanol and isobutane showed higher equilibrium constant than isobutene, they should be avoided. Isobutane is highly flammable while the precursor of tert-butanol is exorbitant. Thus, isobutene was selected for the equilibrium compositions screening. Isobutene conversion was 90% and 15% MMA yield at 700 °C and IBN: O2: MeOH ratio with 1:7:1. This route is mainly limited by the generation of side reactions from the reaction of CH3OH and O2. By varying the feedstock ratio at 1:2:1, the MMA yield increased to ~25%. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Study on Thermal Plasma Combined Treatment for Medical Waste

A thermal plasma combined treatment of medical waste proposed here combines the advantages of pyrolysis and gasification technologies, which provides an option for the harmless, reduction and recycling treatment of medical waste. In addition, a simulation model based on the Gibbs free energy minimization method was developed to explore the characteristics of plasma pyrolysis, gasification, and combined treatment methods. Compared with the plasma pyrolysis method, the plasma combined treatment method can not only produce more syngas with high calorific value but also achieve higher process efficiency. Different from the plasma gasification method, the combined treatment method uses nonoxidizing gas as the working gas for plasma torches, which helps slow down the ablation of plasma torch cathode. Besides, three main components of medical waste were analyzed through the plasma combined treatment model. Simulation results show that materials with high carbon and hydrogen content, such as plastic and rubber, can not only help to increase syngas output and calorific value but also improve system efficiency to a certain extent.

Thermochemical recuperation by steam methane reforming as an efficient alternative to steam injection in the gas turbines

Improving the energy efficiency of gas turbines is an extremely important task of the world energy industry. This paper presents the results of thermodynamic analysis of a gas turbine unit with thermochemical exhaust heat recuperation by steam methane reforming (chemically recuperated gas turbine — CRGT). The thermochemical exhaust heat recuperation systems consist of a reformer, a steam–methane mixture preheater, and a steam generator. The main goal of this paper is comparing CRGT efficiency with the efficiency of a gas turbine unit with steam injection (STIG). To calculate the recuperated heat in a reformer, the thermodynamic analysis of steam methane reforming was performed via Gibbs free energy minimization method. Both thermodynamic cycle and reforming analysis were performed via Aspen HYSYS. The analysis was performed in the temperature range of working fluid at a turbine inlet (Tin) of 800–1300 °C and the steam-to-methane ratio of 1, 2, 3 (mol-to-mol). The results showed that thermochemical exhaust heat recuperation can be considered as an alternative to steam injection in gas turbines. The efficiency of CRGT is higher than the efficiency of STIG for the same steam-to-methane ratio. With increasing in Tin the efficiency of CRGT is increasing. The efficiency of STIG and CRGT at Tin=1300 °C for a steam-to-methane ratio of 3 is 37.4% and 47.3%, respectively.

Free energy calculation and ghost force correction for hot‐QC

A new efficient variant of hot-QC, the finite temperature version of the quasicontinuum (QC) method, is presented. In the original formulation of hot-QC, a dynamically evolving atomistic region is coupled with either a dynamic (hot-QC-dynamic) or a static (hot-QC-static) continuum region. In the current work, a free energy minimization method is employed in which atom positions in both the atomistic and continuum regions always occupy equilibrium positions. The effect of ghost forces at the interface of the atomistic and continuum regions is discussed for all three variants of hot-QC using two examples: a perfect cubic crystal and a Lomer dislocation dipole. Errors due to ghost forces and due to mesh entropy are considered and the efficacy of their correction terms are evaluated. It is shown that the proposed free energy minimization method has comparable accuracy to the other methods with significantly higher efficiency.

Liquid organic hydrogen carriers (LOHCs) in the thermochemical waste heat recuperation systems: The energy and mass balances

This paper is presented a concept of thermochemical recuperation of waste heat based on hydrogen extraction from liquid organic hydrogen carriers (LOHC), on the example of methylcyclohexane-toluene system. The advantages of this concept is described, for example, a possibility to use a moderate low temperature of waste heat for generation high-exergy “green” hydrogen fuel. To understand the effect of operating parameters on the energy and mass balance, the thermodynamic analysis was performed. The chemical system for hydrogen generation was analyzed via Gibbs free energy minimization method. The thermodynamic analysis was conducted under various operating conditions: temperature of 100–400 °C, pressure of 1–4 bar. Aspen HYSYS software was used for the energy and mass conservation analysis. Sankey diagram for the energy flows is depicted. The results showed that the maximum energy efficiency the thermochemical waste heat recuperation system have in the temperature range above 300–350 °C. In this temperature range, the effect of pressure on the energy balance is negligible and it is recommended for the thermochemical recuperation system to use LOHC with a pressure of 1.5–2 bar. Based on the analysis, it was concluded that the temperature potential of waste heat for about 300–350 °C is enough for the investigated concept. An analysis of a mass balance showed that the decreasing in condensation temperature leads to a significant increasing in the share of condensed toluene from toluene-hydrogen mixture after a reactor. If temperature of a hydrogen-toluene mixture of 20 °C at pressure above 2 bar about 96% of toluene can be condensed after the first condenser.

Efficiency of chemically recuperated gas turbine fired with methane: Effect of operating parameters

Previously, a set of optimistic studies have been published to show the efficiency of chemically recuperated gas turbines (CRGT) based on steam methane reforming. The thermodynamic efficiency of such turbines is depending not only on temperature and pressure in a cycle but also on temperature, pressure and steam-to-methane ratio in a recuperation system. In this paper, the effect of operational parameters (temperature, pressure, steam-to-methane ratio) on the efficiency of CRGT was determined. Exhaust heat recuperation in CRGT is taking place due to methane reforming, steam-methane mixture heating, and steam generation. A thermodynamic enthalpy of steam methane reforming process was determined via Gibbs free energy minimization method. The thermodynamic analysis of CRGT was performed in Aspen HYSYS. The efficiency of CRGT was determined for a wide range of operational parameters (gas turbine inlet temperature of 800–1500 °C, pressure of 5–25 bar, steam-to-methane ratio of 1...3). Based on the analysis it was confirmed that the efficiency of CRGT and thermochemical exhaust heat recuperation system is increasing with an increase in temperature. An increase in temperature and steam-to-methane ratio leads to an increase in a share of recuperated heat in a reformer. The heat recuperation rate is up to 0.63 for a high-temperature gas turbine and a steam-to-methane ratio of 3. The efficiency of CRGT is up to 49% for gas turbines with inlet gas temperature of 1500 °C which is an available level in modern gas turbines from Mitsubishi, Siemens, Alstom, etc. • Concept of chemically recuperated gas turbine (CRGT) based on steam methane reforming. • Effect of pressure, temperature and steam-to-methane ratio on CRGT efficiency is studied. • CRGT shows high efficiency due to complex exhaust heat recuperation. • CRGT efficiency increases with increasing in gas temperature at turbine inlet. • Efficiency of CRGT can reach up to 0.49 for inlet gas temperature of 1500 ℃.