Chemical Exergy Research Articles

Biomass chemical exergy estimation using novel intelligent tool: application to biorefinery sustainability

ABSTRACT In response to the growing importance of sustainable energy and environmental considerations in biorefinery technologies, this study introduces a novel hybrid artificial intelligence approach for predicting biomass chemical exergy. The proposed least-squares support vector machine method based on an imperialist competitive algorithm (ICA-LSSVM) combines composition and energy analysis methods to model the chemical energy of biomass accurately. Extensive data were collected to train the model, resulting in a high-precision prediction with a coefficient of determination (R2) of 0.999 and a root mean square error (RMSE) of 30.3. The main point of this study is the development of this accurate model to determine the chemical energy, and also different forms of comparison are used to prove this issue. The sensitivity analysis highlights the direct impact of carbon (C%), hydrogen (H%), and oxygen (O%) percentages on biomass chemical exergy, while nitrogen (N%) and sulfur (S%) exhibit an inverse relationship. The model outperforms existing correlations in the literature, emphasizing its accuracy and practicality for biomass chemical exergy prediction, and contributing to both laboratory and industrial applications. The study emphasizes the model’s real-data reliance and suggests further exploration with an expanded dataset for enhanced industrial applicability.

Exergy Analysis in Highly Hydrogen-Enriched Methane Fueled Spark-Ignition Engine at Diverse Equivalence Ratios via Two-Zone Quasi-Dimensional Modeling

In the endeavor to accomplish a fully de-carbonized globe, sparkling interest is growing towards using natural gas (NG) having as vastly major component methane (CH4). This has the lowest carbon/hydrogen atom ratio compared to other conventional fossil fuels used in engines and power-plants hence mitigating carbon dioxide (CO2) emissions. Given that using neat hydrogen (H2) containing nil carbon still possesses several issues, blending CH4 with H2 constitutes a stepping-stone towards the ultimate goal of zero producing CO2. In this context, the current work investigates the exergy terms development in high-speed spark-ignition engine (SI) fueled with various hydrogen/methane blends from neat CH4 to 50% vol. fraction H2, at equivalence ratios (EQR) from stoichiometric into the lean region. Experimental data available for that engine were used for validation from the first-law (energy) perspective plus emissions and cycle-by-cycle variations (CCV), using in-house, comprehensive, two-zone (unburned and burned), quasi-dimensional turbulent combustion model tracking tightly the flame-front pathway, developed and reported recently by authors. The latter is expanded to comprise exergy terms accompanying the energy outcomes, affording extra valuable information on judicious energy usage. The development in each zone, over the engine cycle, of various exergy terms accounting too for the reactive and diffusion components making up the chemical exergy is calculated and assessed. The correct calculation of species and temperature histories inside the burned zone subsequent to entrainment of fresh mixture from the unburned zone contributes to more exact computation, especially considering the H2 percentage in the fuel blend modifying temperature-levels, which is key factor when the irreversibility is calculated from a balance comprising all rest exergy terms. Illustrative diagrams of the exergy terms in every zone and whole charge reveal the influence of H2 and EQR values on exergy terms, furnishing thorough information. Concerning the joint content of both zones normalized exergy values over the engine cycle, the heat loss transfer exergy curves acquire higher values the higher the H2 or EQR, the work transfer exergy curves acquire slightly higher values the higher the H2 and slightly higher values the lower the EQR, and the irreversibility curves acquire lower values the higher the H2 or EQR. This exergy approach can offer new reflection for the prospective research to advancing engines performance along judicious use of fully friendly ecological fuel as H2. This extended and in-depth exergy analysis on the use of hydrogen in engines has not appeared in the literature. It can lead to undertaking corrective actions for the irreversibility, exergy losses, and chemical exergy, eventually increasing the knowledge of the SI engines science and technology for building smarter control devices when fueling the IC engines with H2 fuel, which can prove to be game changer to attaining a clean energy environment transition.

Efficient Exergy Analysis of Chemical Processes through Process Engineering Software

In this work, authors present a simple methodology for computing physical, chemical and total exergies, and the exergy destruction and the exergetic efficiency of simple and complex processes by using the object linking and embedded (OLE) automation by connecting Aspen HYSYS to MS Excel VBA. For this purpose, a simple flowsheet was added to the main one with the same number of streams as that of the components. By introducing all these streams in a mixer and then consecutively conducted to a heater to condition the outlet stream, a separator and a mixer, the VBA application was able to compute the chemical exergy of the different streams of the main flowsheet. To demonstrate the procedure here described seven cases were considered: single streams, a CO2 mixer, a cooler, a distillation column, a reactor, a multiple recirculation process, and different configurations of separating components by distillation, which can be extended to very complex processes. The former was selected to validate the methodology here proposed whereas the rest of cases were used to demonstrate the potential of the tool here developed, which in turn could be used for discriminating among different process alternatives.

Two-stage hydrothermal liquefaction of Spirulina: Experimental observations, energy analysis and techno-economic assessment

The intensification of environmental pollution and significant consumption of fossil fuels has led to widespread attention on developing renewable resources. As a carbon-containing renewable energy source, Spirulina is characterized by its fast growth cycle and wide distribution. Currently, one of the research hotspots is the conversion of Spirulina into bio-oil through hydrothermal liquefaction. However, studies on the two-stage hydrothermal liquefaction of Spirulina predominantly concentrate on the product yield or composition. There is relatively little research on thermodynamic (energy) analysis and techno-economic assessment during the reaction process. The main bio-oil components from two-stage hydrothermal liquefaction of Spirulina are ketones and acids with 44.9 % and 34.1 %, respectively. Compared to no-catalysis, two-stage hydrothermal liquefaction of Spirulina over HZSM-5, alkili-modified HZSM-5, and Ni@alkali-modified HZSM-5 increase the relative content of hydrocarbons to 6.6 %, 32.9 % and 48.1 %, respectively. Energy analysis and techno-economic assessment are conducted with Aspen Plus simulation, revealing a exergy efficiency of 56.4 % for the catalytic two-stage hydrothermal liquefaction of Spirulina compared with 43.6 % over no-catalyst. The primary losses occur in the first stage of the reaction process (248.6 kW) and the cooling process (10.7 kW) for catalytic two-stage hydrothermal liquefaction of Spirulina. The hourly price of producing 1 kg bio-oil with a catalyst is $3.67, while without a catalyst, it is $4.54 kg−1; obtaining a unit of chemical exergy costs $0.14×10−3 kJ−1 through catalysis. Moreover, the fluctuations in the prices of sulfuric acid and catalysts are most sensitive to the cost price of bio-oil with or without catalysts in the two-stage hydrothermal liquefaction process, with the values being 10.06 % and 8.10 %. This study has important significance for efficient transformation and energy utilization of Spirulina.

Energy and exergy analysis of an innovative solar system for hydrothermal carbonization process using photovoltaic solar panels

Using renewable energy is a solution to combat environmental problems; in this context, hydrothermal carbonization is an excellent method for converting biomass into solid fuels. However, this process is energy-intensive. Systems utilizing parabolic trough solar collectors proposed in the literature present some limitations and challenges. Therefore, to overcome this issue, a novel conception combining photovoltaic solar panels and a batch reactor with a heating collar has been proposed. It was experimentally investigated and subjected to energy and exergy analyses. The experimental results showed that subcritical conditions (220 °C temperature and 40 bar pressure) were achieved. The chemical exergy of the biomass increased from 19.89 MJ/kg to 29.2 MJ/kg for the hydrochar. Due to dehydration and decarboxylation, the O/C and H/C atomic ratios decreased over time, and the hydrochar properties approximated lignite. The solar panel system achieved average energy and exergy efficiencies of 14 % and 15 %, respectively, with high thermal exergy destruction of 825.94 kWh under higher wind speeds and cell temperatures, resulting in a total entropy of 1.4 kW/K. The system's Improvement Potential ranged from 15 kW to 23 kW. The results demonstrate the feasibility of this innovative system to achieve the necessary conditions for HTC in an environmentally friendly manner.

Thermodynamic and life cycle assessment analysis of polymer-containing oily sludge supercritical water gasification system combined with Organic Rankine Cycle

With the development of polymer flooding technology, polymer-containing oily sludge (PCOS) has become a major pollutant on offshore oil platforms. Supercritical water gasification system is an efficient and pollution-free technology compared to conventional PCOS treatment. However, the system model for PCOS has not yet been established and the theoretical model for system optimization is insufficient. In this work, a novel auto-thermal system is established based on supercritical water gasification technology for the treatment of PCOS. Through the thermodynamic analysis, an optimization plan is concluded and used for the establishment of a modified system with Organic Rankine Cycle. Results show that the two-stage reactor reduces the gasification reaction temperature from 652 °C to 502 °C, and the Organic Rankine Cycle system using Isopropanol recover 9.1 % chemical exergy of feedstock with the optimal parameters (superheat, evaporation temperature and circulating pressure). The energy and exergy efficiency of the modified system has increased by 52.4 % and 42.4 % compared to the original system. Besides, a life cycle assessment is adopted for the environment analysis. The results show that the increasing gasification temperature and PCOS slurry concentration can reduce system unit exergy loss. Global Warming Potential reaching the minimum value of 26.1 at 65 wt%.

Thermodynamic and exhaust emission studies of CI engine powered by neem oil methyl ester blends doped with nickel oxide nano additives

AbstractAssessment of alternate fuel is categorized on thermophysical aspects and performance—emission derived due to its combustion. Data derived from such analysis is short as the energy expenditure to available chemical exergy of fuel is rarely studied. The study of energy derived from fuel energy gives a detailed picture of fuel efficiency and broadens the field of fuel search criteria. The current article aims to find the thermodynamic effects in terms of energy and exergy utilization of neem biodiesel blends and nickel oxide nano additive dosed neem biodiesel blends. Neem biodiesel was transesterified using standard procedures and analyzed using gas chromatography and mass spectroscopy. Later, neem biodiesel was blended with diesel in three volumetric proportions, that is, NB25, NB50, NB75, and pure Neem Oil Methyl ester was investigated as an engine fuel, and later synthesized nickel oxide nano additives of 25 mg/L was added to all the above fuels and further studied for energy, exergy utilization on a TV‐1 VCR engine test rig under varying engine CR. Nickel oxide additives were manufactured using homogenous addition method and were thoroughly studied for formation and presence of constituents using XRD, FE‐SEM, and EDS methods. The usage of nano additives does prove reduction in exergy destruction and entropy generation for NB25 base blend with 25 mg/L NiO leading to a reduction of 8.2% and 9.7% when compared to base blends. Also, the emission found for hydrocarbon, and carbon monoxide for all base fuel blends reduced by an average of 16.8% and 7.35%.

Energy optimization of hydrogen liquefaction process via process knowledge combined with multivariate Coggin's algorithm

Sustainable and cost-effective transportation of hydrogen is one of the major challenges to futuristic hydrogen value chain. Hydrogen, in its produced form, exhibits low energy density and large volume, rendering it highly unsuitable for transportation, particularly over extended distances. Liquefaction is one of the promising approaches to improve hydrogen's energy density and to make it more compact. However, liquefaction is an energy intensive process, raising the cost of transportation. In this study, the specific energy consumption of the hydrogen liquefaction process is aimed to reduce through knowledge-based optimization followed by optimization using the multivariate Coggin's algorithm to improve energy and economic profiles of the process. Design variables, composite curve, exergy, and economic analyses are performed to evaluate and compare the thermodynamic, economic, and environmental feasibility of the optimized process. The results depict a significant reduction (14.3%) in specific energy consumption to 9.40 kW/kgLH2 without increasing process complexity. Further key improvements include a massive drop in refrigerant flowrates (9.2%), annualized cost (m$ 0.15), and annual CO2 emissions (1008.45 tCO2/annum). The largest exergy destruction is observed in CHX-201, reflecting further room for improvement. These results underscore the potential for optimizing hydrogen liquefaction processes to enhance energy efficiency, process economics and environmental impact, providing valuable insights for researchers and industry professionals seeking to advance hydrogen liquefaction technologies. However, challenges remain in the comprehensive evaluation of chemical exergy for ortho- and para-hydrogen and in conducting advanced exergy analyses to further optimize hydrogen liquefaction processes without adding complexity.

Estimating the higher heating value and chemical exergy of solid, liquid, and natural gas fossil fuels

The escalating global population has spurred a significant surge in energy demand. While developed nations pivot towards renewable energy sources, many developing countries rely heavily on fossil fuels. Understanding these fuels' higher heating value and chemical exergy is crucial for energy analysis, second law analysis, optimal energy generation, and resource conservation.This study introduces an adaptable analytical method for calculating the higher heating value and chemical exergy of fossil fuels (coal, oil, natural gas). It demonstrates minimal error, with approximately a 3.5 % deviation for higher heating value and 8 % for chemical exergy compared to empirical relations.Novel relationships, developed through linear regression and computer programming, address research gaps and exhibit a maximum 2.6 % difference for higher heating value and 5.4 % for chemical exergy compared to existing empirical references. These contributions will greatly benefit energy professionals and engineers.This research addresses critical gaps in current methodologies for estimating higher heating value and exergy by offering a compact form for calculating various fossil fuels within a wide range of Carbon-to-Hydrogen ratios (3–105). Additionally, it provides specific equations applicable to both mole and mass fractions for natural gases, primarily composed of methane, with mole fractions ranging from 55 % to 99 %.

Thermodynamic and economic analysis of a new methanol synthesis system coupled with a biomass integrated gasification combined cycle

An innovative design has been developed to optimize the performance of the methanol synthesis (MS) by integration with a biomass integrated gasification combined cycle (BIGCC) system based on the principle of the cascade utilization of chemical and thermal exergy. In the integrated system, the efficient utilization of the chemical energy present in feedstocks is made possible by combining exothermic MS chemical processes and integrating different grades of thermal energy. The graded conversion of methanol facilitates the manifestation of both its chemical and fuel attributes. By such incorporation, the waste heat and purge gas in MS process are utilized in a more efficient way and the biomass consumption in BIGCC plant is significantly reduced. A thermodynamic analysis conducted on a 100 kt/yr methanol production plant and a 41.8 MW BIGCC power plant reveals an increase in energy efficiency of 3.46 % and an achievement of 61.9 % exergy efficiency. Moreover, this design yields a profit of 72.6 M$ more than that generated by individuals throughout its lifespan. Sensitivity analysis further indicates that the optimal conditions for the polygeneration system are approximately 250 °C and 60 bar, with a preference for a 0.90 MS recycle ratio.

Plant wide modelling and thermodynamic optimization of a petroleum refinery for improvement potentials

In this work, plant wide modelling of a petroleum refinery was conducted for the optimization. An Aspen HYSYS® model of a petroleum refinery was used for collection of the information to perform the thermodynamic (exergy) analysis. The plant wide model consisted of alkylation unit, reformer, naphtha hydrotreater, catalytic cracker, diesel hydrotreater, isomerization unit, hydrocracker, and kerosene hydrotreater. Seventeen (17) independent input streams and twenty-eight (28) output streams of the plant were considered for the analysis. The physical and chemical exergies of the streams were summed for assessing the overall exergy efficiency, exergy destruction, and improvement potentials of the plant. Exergy efficiency of the plant was 91.38 % with exergy destruction of 704054.64 kW and exergetic improvement potential of 60707.50 kW. The current study gives an insight into the plant-wide analysis ranging from physical exergies of the process streams and utilities to the chemical exergies of the fuels (product) produced in the refineries.

Thermodynamic analysis of power generation thermal management system for heat and cold exergy utilization from liquid hydrogen-fueled turbojet engine

Hydrogen propulsion is generally treated as the ultimate net zero-emission option for aviation, therein liquid hydrogen storage appears to provide the only feasible solution for aircraft with the constraints imposed by aircraft weight and volume. Hydrogen liquefaction consumes a great amount of energy, which significantly boosts the cost of hydrogen as an aviation fuel. Besides the H2 chemical exergy for combustion to provide thrust, the H2 physical exergy in the form of cold energy is also a kind of high-quality clean energy to produce power output, which offers great opportunities to achieve cost-effective use of hydrogen fuel. Thus, this paper presents a Rankine cycle and H2 direct expansion cycle (RC-DEC) combined power generation thermal management system for the simultaneous utilization of exhaust gas heat exergy and hydrogen fuel cold exergy from the liquid hydrogen-fueled turbojet engine. In the Rankine cycle, the transcritical mode is applied on the hot side while the liquid separation condensation concept is adopted on the cold side to achieve better thermal matchings with heat and cold sources. The hydrocarbon/inert gas binary mixture is proposed as the working fluid of the Rankine cycle. The effects of key thermodynamic parameters and the influence of Para-Ortho hydrogen conversion on system performance are discussed, then a comparison of the mixture working fluid is conducted. Results show that there exists an optimal separation temperature ratio and condensation pressure of RC to obtain maximum total net power output. As the DEC expander inlet pressure increases, the total net power output first increases and then levels off. The introduction of the Para-Ortho hydrogen conversion has a negligible impact on net power output but leads to a significant reduction in the exergy efficiency, which is attributed to the cold energy release nature of Para-Ortho hydrogen conversion. The results of the working fluid comparison indicate that the optimal inert gas retardant for CH4 is Kr, while those for C2H6 and C3H8 are Xe to achieve the maximum net power output and exergy efficiency of the proposed power generation system. Among them, C2H6/Xe(0.6/0.4) obtains the maximum net power output of 2717.9 kW and maximum exergy efficiency of 33.1%, which suggests an opportunity to provide megawatts of electrical power for the aircraft in place of the APU.

Efficiency of aqueous oleosome extraction from capsicum seeds compared to classical oil extraction

The extraction of oil from oilseeds in intact oleosomes is one of the suggested processes that could replace the extraction of oil by pressing and solvent extraction, being milder, environmentally less impactful and potentially more efficient in its use of resources. This study assesses the latter using an exergy assessment of oleosome extraction for food emulsions. The contribution of each part of the process to the overall impact was investigated. Based on current lab-scale data, oleosome extraction has nearly twice the exergy loss compared to the industrial process of oil extraction and industrial assembly of emulsions. The exergy losses of the lab-scale oleosome extraction are currently dominated by the chemical exergy associated with product loss during the separation of oleosomes from the rest of the biomass. This loss is expected to significantly decrease when upscaled to industrial scale. When substituted with industrial material efficiencies, the total exergy loss decreased to nearly a quarter of the original loss, representing oleosome extraction as a potentially more effective and environment-friendly option.

Minimum work associated with separating nitrogen from air: An exergy analysis

Background Nitrogen is essential for a variety of industries, including heat treatment, laser cutting, fire protection, and food packaging. Many companies in these industries obtain nitrogen via on-premises air separation processes. The three main processes for separating nitrogen from ambient air are cryogenic distillation, membrane separation, and pressure-swing adsorption (PSA). Improvements to these processes will likely focus on increasing efficiency, resulting in reduced environmental impact owing to less electrical power demand and opportunities for economic incentives. Regardless of the process utilized, a minimum theoretical amount of work input is required to obtain nitrogen gas at different pressures and concentrations compared to ambient conditions. Methods An equation was derived to evaluate the total exergy (including thermo-mechanical and chemical exergy) of product and exhaust mixtures resulting from air separation, indicating the minimum theoretical work input as a function of the product pressure, purity, and process recovery rate. This analysis considered an air separation system as a black box, with the input, output, and exhaust assumed to be ideal gas mixtures of nitrogen and oxygen at 15°C. The analysis applies to cryogenic distillation if the product and exhaust mixtures return to the gas phase. Results In general, the minimum required work input increases with product purity and recovery rate. Plots of minimum theoretical work versus product purity and recovery rate were made for two product pressures (atmospheric and 800 kPa) to show the behavior of the derived equation. Conclusions The analysis allows for direct efficiency (based on the second law of thermodynamics) comparisons between existing processes and future technological innovations in the field of air separation. Actual air separation systems have low efficiencies compared to ideal systems; actual PSA systems were estimated to have second law efficiencies of 5.5–11.2%. Therefore, there is great potential for improvements to current air separation systems.

Maximizing efficiency in solar ammonia–water absorption refrigeration cycles: Exergy analysis, concentration impact, and advanced optimization with GBRT machine learning and FHO optimizer

A detailed analysis of energy and exergy is conducted on a single-effect solar ammonia–water (NH3–H2O) absorption refrigeration cycle (ARC) using TRNSYS and EES software. Considering the physical and chemical exergies, the exergy destruction rate (ĖD) in each component of the system is calculated, highlighting its contribution to the overall ĖD. The study explores the effects of varying refrigerant mass flow rate (ṁᵣ) and ammonia concentration in strong and weak solutions (Xs and Xw) on key performance parameters, including coefficient of performance (COP), exergy efficiency (ĖD), and overall ĖD across a range of generator temperatures (Tg). In this study, a gradient boosting regression tree (GBRT) is employed as a supervised machine-learning technique for classification and regression problems, utilizing boosting to enhance conventional decision tree predictions. The Fire Hawk Optimizer (FHO) approach is also utilized to optimize performance parameters, maximizing COP and ηηEwhile minimizing Tg and ĖD. The GBRT models are developed using available experimental and simulation data, revealing relationships between variables (ṁᵣ, Xs, Xw, and Tg) and outcomes (COP, ĖD, and overall ĖD). The results revealed that the generator exhibits considerable ĖD regardless of operating conditions, underscoring its pivotal role in the ARC. It emerges as the primary ĖD contributor (50 %), followed by the evaporator (17 %) and the absorber (15 %). However, ĖD associated with the recooler, pump, and expansion valves is negligible in comparison. Optimization results reveal that, when minimizing Tg and ĖD, the highest COP and ĖD at Tg of 373.15 K reach 0.8081 and 0.46, respectively.

An efficient methanol pre-reforming gas turbine combined cycle with integration of mid-temperature energy upgradation and CO2 recovery: Thermodynamic and economic analysis

An innovative design has been developed to optimize the performance of the gas turbine combined cycle (GTCC) by integration with a decarbonized methanol steam reforming (MSR-deCO2) system based on the principle of the cascade utilization of chemical and thermal exergy. In the integrated system, the primary fuel is reformed with the steam extracted from GTCC and decarbonized before combustion. The reforming process leads to a significant reduction of exergy loss in the combustor. Introducing methanol as a viable turbine fuel presents an opportunity for recuperating mid-temperature heat as chemical energy through endothermic MSR and redeeming it as high-grade thermal energy in the combustor. By such incorporation, the power generation of the mid-temperature heat in the bottoming cycle is significantly enhanced, and most of the CO2 is removed as the liquid phase. Based on a 530 MW GTCC plant, thermodynamic analysis reveals a 4.6% energy efficiency increase, a 4.3% exergy efficiency boost, and an 82.2% CO2 recovery with a 0.354 MJ/kgCO2 energy penalty. The proposed design yields 454.4 M$ more profit than the reference power plant throughout its lifespan. Additionally, sensitivity analysis indicates optimal conditions for MSR at approximately 250 °C, a 1:1 water-to-methanol ratio, and a higher reaction pressure preference.

Energetic and exergetic performances of a multi‐effect desalination unit driven by a gas turbine

AbstractDesalination can provide additional water resources in water‐stressed zones and also in zones suffering from water pollution or insufficient/overexploited groundwater. This study carried out the energy and exergy assessments of a multi‐effect desalination unit driven by a gas turbine based on the specific exergy cost (SPECO) approach. The chemical exergies of brine and seawater are explicitly considered (most studies consider the same specific heat for input seawater and output brine). In addition, the enthalpy of each flow of the desalination unit is considered according to its salt concentration (results are then compared to the constant specific heat model). The highest exergy rates of fuel and product are obtained at the combustion chamber, and its exergy efficiency is 67.83%. The lowest exergy efficiencies were obtained at the condenser, followed by the first effect of the desalination unit, and the heat recovery steam generator. The overall exergy efficiency of the multi‐effect distillation unit is 21.49%. Regarding exergy destruction, as expected, the highest rate was obtained at the combustion chamber, which contributed with 41% to the overall exergy destruction, followed by the regenerator and heat recovery steam generator, with contributions of 16% and 11%, respectively, to overall exergy destruction.

Exergy analysis of thermodynamic performance of a gas turbine unit

BACKGROUND: Gas turbine units are the most widespread type of power plants used in almost all industries. Such a wide distribution in combination with a high level of energy characteristics, high specific power and flexibility determine the relevance of research in the field of assessing their operating parameters.
 AIM: Determining the exergy characteristics (exergy efficiency and exergy dissipation factor) of a gas turbine plant and evaluation the efficiency of energy use in a gas turbine plant, as well as analysis of the influence of ambient temperature on the selected parameters.
 METHODS: The paper presents the results of an exergy analysis of the gas turbine plant as part of the Jandar Thermal Power Plant, Syria. To evaluate the described parameters, the method of exergy analysis of the thermodynamic characteristics of a gas turbine plant based on the first and second laws of thermodynamics in conjunction with the laws of conservation of mass and energy was used. An important feature of the study, which also emphasizes its novelty, is taking into account the chemical exergy of combustion gases during the exergy analysis.
 RESULTS: Based on the results of the study, it was found that the maximum exergy efficiency was 92.8% and was typical for a turbine as part of a gas turbine, while the highest exergy dissipation was observed in the process of fuel combustion in the combustion chamber and was equal to 80% (117.3 MW). The lowest exergy values corresponded to the compressor — 6.0% (9 MW). For the gas turbine unit as a whole, the total exergy dissipation was 147.3 MW and the exergy efficiency was 53.3%. In this case, the main sources of irreversibility in the gas turbine unit are the combustion chamber and combustion gases.
 CONCLUSION: Exergy analysis is a convenient method for evaluating the thermodynamic perfection of gas turbine units. As a further line of the study, it is necessary to evaluate the effects of various conditions, such as air humidity or compressor pressure ratio, on the exergy characteristics of the gas turbine fuller.

Highly dispersed Ag2O-CuO nanospheres supported on γ-χ-Al2O3 for methanol dehydration to dimethyl ether

In this manuscript, the wet impregnation method was used to support Ag2O, CuO, and Ag2O-CuO nanoparticles on γ-χ-Al2O3 to assess their catalytic capabilities in the methanol dehydration (MD) reaction to produce dimethyl ether (DME); the operation conditions were 1 atm and temperature ranging between 200 and 240 °C. It was found that Ag2O-CuO/γ-χ-Al2O3 catalyst result in MD conversions up to 88 % and selectivities of 100 %, under 240 °C conditions. The catalytic activity of the Ag2O-CuO/γ-χ-Al2O3 catalyst is related to the high dispersion, homogeneity and larger size of the Ag2O-CuO nanoparticles (∼12.6 nm) compared to Ag2O and CuO nanoparticles, which have sizes of ∼ 9.52 and 10 nm, respectively. Additionally, the catalytic activity of the Ag2O-CuO/γ-χ-Al2O3 material is related to its total acidity (weak and moderate), 0.056 mmol/g, showing a difference of 25 %, 28.57 and 5.35 % with respect to the γ-χ-Al2O3, CuO/γ-χ-Al2O3 and Ag2O/γ-χ-Al2O3 materials, respectively. Finally, the catalytic stability measurements of the Ag2O-CuO/γ-χ-Al2O3 catalyst remained relatively constant over time, presenting a conversion value of 79 % after 2.6 h of reaction due to the low apparent activation energy, 112.6 kJ/mol. The results of the exergy analysis indicate that the chemical exergy of the system ranges between 1/6 and 1/3 of the physical exergy, and most of the energy available to produce work is in the form of heat.

Exergy analysis on the low flow rate of solution in the atomization-based liquid desiccant system

The purpose of this study is to analyse the proposed liquid desiccant absorber with low solution flow rate compared with the conventional packbed-type absorber. The total exergy destruction and exergy efficiency were estimated to assess the system performance. To determine the total exergy destruction and exergy efficiency, it was predicted that the specific thermal and chemical exergy in the inlet and outlet both air and solution side of the absorber. The results indicated that the average total thermal and chemical exergy destruction is 0.054 kW and 0.080 kW in the proposed system while it is 0.292 kW and 0.093 kW in the conventional absorber. The exergy efficiency is 0.573 and 0.114 on average in the proposed and conventional absorber, respectively.