Exergetic Efficiency: A Detailed Reaction Mechanism Analysis of Hydrogen Combustion With Singlet Oxygen

2015 ◽  
Author(s):  
DeVon A. Washington ◽  
Howard N. Shapiro
Keyword(s):  
Singlet Oxygen ◽  
Reaction Pathways ◽  
Combustion Mechanism ◽  
Mechanism Analysis ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Chemical Induction ◽  
Fuel Use ◽  
Detailed Reaction Mechanism ◽  
Thermal Induction

In previous work the authors have demonstrated that when hydrogen is combusted in stoichiometric proportions at 1 atm and 1200 K, and singlet oxygen comprises 0–20% of the oxidizer, an optimal range of exergetic efficiency exists. The maximum exergetic efficiency occurs at approximately 10%. Over this range, roughly 60% of the total exergy destruction occurs prior to ignition. This is a significant result because it suggests that the exergetic efficiency of combustion might be improved at a fundamental level by chemical means, thereby inherently increasing the efficiency of fuel use for a desired energy application. The objective of the study presented in this paper is to analyze the reaction mechanisms for combustion with varying percentages of singlet oxygen, to determine which reaction pathways most influence the observed trends in exergy destruction and exergetic efficiency. This was accomplished by performing both sensitivity and rate-of-production analyses of the hydrogen-oxygen combustion mechanism. The results of the analysis show that the presence of singlet oxygen governs the rate of production of hydroxyl and other key radicals. These key radicals directly affect the phenomenological processes associated with chemical induction and thermal induction during ignition. Therefore, the observed optimum exergetic efficiency correlates to the quantity of singlet oxygen in the inlet charge that minimizes exergy destruction by fostering chemical reactions due to radical formation to a greater extent than thermal heat release. The results of this analysis are noteworthy and provide new insight regarding how the exergetic efficiency of combustion may be optimized by introducing singlet oxygen, thereby altering the reaction pathways to enhance energy conversion in a fundamental way that could have important implications for improved fuel use.

Parametric Effects on Exergetic Efficiency During H2-O2 Combustion Including Singlet Oxygen

2014 ◽  
Author(s):  
DeVon A. Washington ◽  
Howard N. Shapiro
Keyword(s):  
Singlet Oxygen ◽  
Ignition Temperature ◽  
Equivalence Ratio ◽  
Flow Reactor ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Inlet Concentration ◽  
Optimal Range

Previous work conducted by the authors showed that for a stoichiometric inlet fuel-oxidizer ratio at 1 atm and 1200 K, an optimal range of exergetic efficiency exists for H2 combustion when singlet oxygen composes 0–20% of the oxidizer; with the maximum occurring at approximately 10%. Additionally, in the optimal range, 60% of the total exergy destruction occurs before ignition. These results provide encouraging evidence that it is possible to improve the exergetic efficiency of combustion inherently and thereby reduce fuel usage for a desired energy transfer. The focus of this study is to determine if the exergetic efficiency of combustion can be further optimized by varying other combustion parameters in addition to the inlet concentration of singlet oxygen. The chemical kinetics simulation was accomplished by developing an adiabatic plug flow reactor model in CHEMKIN-PRO® and employing the Moscow State University H2-O2 mechanism. The ranges of parameters considered were: equivalence ratio 0.7–1.3, inlet temperature 1100–1300 K, inlet concentration of singlet oxygen 0–20%, and diluent type (Ar, N2, no dilution). Pressure was held fixed at 1 atm. The calculated quantities were: exergetic efficiency, exergy destruction before ignition, molar conversion of H2, exit temperature, ignition temperature, and ignition distance. Results of the study show that over the optimum range the maximum exergetic efficiency occurs for an equivalence ratio of 1.3, with no dilution at 1300 K. Furthermore, the data show that for 20% inlet singlet oxygen there is significant variability in exergy destruction before ignition, ignition temperature, and ignition distance. Understanding how varying traditional combustion parameters impacts the enhancing effect that singlet oxygen has on the exergetic efficiency of H2 combustion provides a framework for directing future research efforts for hydrocarbon combustion under a broader range of operating conditions of practical engineering interest.

A Phenomenological Analysis of Exergy Destruction During Hydrogen Combustion With Electronically Excited Oxygen

2013 ◽  
Author(s):  
DeVon A. Washington ◽  
Howard N. Shapiro
Keyword(s):  
Singlet Oxygen ◽  
Flow Reactor ◽  
Hydrogen Oxidation ◽  
Combustion Process ◽  
Hydrogen Combustion ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Optimal Range ◽  
Electronically Excited ◽  
Excited Oxygen

This study investigates the effects of introducing electronically excited oxygen on trends in exergy destruction during hydrogen combustion. Electronically excited oxygen enhances many properties of combustion. By understanding how it alters the chemical kinetics, and hence the destruction of exergy, it may be possible to improve the overall exergetic efficiency of combustion thereby reducing fuel use to achieve desired energy conversion. A numerical model was developed of an adiabatic plug flow reactor using CHEMKIN-PRO; in conjunction with a hydrogen oxidation mechanism that includes explicit reaction pathways for various electronically excited species. Exergy destruction was calculated for cases where singlet oxygen composed 0%–100% of the oxidizer while maintaining a stoichiometric oxidizer-fuel ratio; all other inlet conditions were held fixed. Results show that an optimal range of exergetic combustion efficiency exists between 0%–20%, with the maximum occurring at approximately 10%. A detailed assessment of the total exergy destruction reveals that, for the optimal range of exergetic combustion efficiencies, as much as 60% of the total exergy destruction occurs prior to ignition. For inlet percentages of singlet oxygen greater than 20%, the majority of the total exergy destruction occurs after ignition. This paper examines the phenomenological events taking place in the reaction mechanism that give rise to the destruction of exergy during combustion. Understanding these mechanisms and the effects of introducing excited oxygen into the combustion process, sheds light on how we might use excited oxygen to increase the exergetic efficiency of combustion.

Advanced Energy, Exergy, and Environmental (3E) Analyses and Optimization of a Coal-Fired 400 MW Thermal Power Plant

2020 ◽  
Vol 143 (8) ◽  
Author(s):  
Siamak Hoseinzadeh ◽  
P. Stephan Heyns
Keyword(s):  
Energy Consumption ◽  
Power Plant ◽  
Environmental Analysis ◽  
Thermal Power Plant ◽  
Co2 Emission ◽  
Environmental Temperature ◽  
Thermal Power ◽  
Energy Losses ◽  
Exergy Destruction ◽  
Exergetic Efficiency

Abstract In this article, energy, exergy, and environmental (3E) analysis of a 400 MW thermal power plant is investigated. First, the components of the power plant are examined in terms of energy consumption, and subsequently the energy losses, exergy destruction, and exergetic efficiency are obtained. It is shown that the highest energy losses are in the closed feedwater heaters Nos. 1 and 5 and the boiler with amounts of 7.6 × 10 J/s and 6.5 × 107 J/s, respectively. The highest exergy destruction occurs in the boiler and amounts to 4.13 × 108 J/s. The highest exergetic efficiency is 0.98 and is associated with the closed feedwater heaters Nos. 4 and 8. It is observed that the exergetic efficiency and exergy destruction in the boiler are the primarily affected by changes in the environmental temperature. Furthermore, by increasing the main pressure in the turbine, the load on the power plant is increased, and increasing the condenser pressure reduces the load on the power plant. In an environmental analysis, the production of pollutants such as SO2 production and CO2 emission has been investigated.

Exergy Analysis of Part Flow Evaporative Gas Turbine Cycles: Part 2 — Results and Discussion

2002 ◽  
Author(s):  
Maria Jonsson ◽  
Jinyue Yan
Keyword(s):  
Gas Turbine ◽  
Heat Recovery ◽  
Exergy Analysis ◽  
Compressed Air ◽  
Cycle Performance ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Recovery System ◽  
Heat Recovery System ◽  
Flow Case

This paper is the second part of a two-part paper. The first part contains an introduction to the evaporative gas turbine (EvGT) cycle and the methods used in the study. The second part contains the results, discussion, and conclusions. In this study, exergy analysis of EvGT cycles with part flow humidification based on the industrial GTX100 and the aeroderivative Trent has been performed. In part flow EvGT cycles, only a fraction of the compressed air is passed through the humidification system. The paper presents and analyzes the exergetic efficiencies of the components of both gas turbine cycles. The highest cycle exergetic efficiencies were found for the full flow case for the GTX100 cycles and for the 20% part flow case for the Trent cycles. The largest exergy destruction occurs in the combustor, and the exergetic efficiency of this component has a large influence on the overall cycle performance. The exergy destruction of the heat recovery system is low.

scholarly journals Exergy Analysis of VCR Systemwith Air-Cooled Condenser Working with Refrigerants R-134a & Hydrocarbon

2019 ◽  
Vol 9 (2) ◽  
pp. 2834-2839
Keyword(s):  
Global Warming ◽  
Global Warming Potential ◽  
Exergy Analysis ◽  
Exergy Destruction ◽  
Refrigeration System ◽  
Exergetic Efficiency ◽  
Domestic Refrigerator ◽  
R 134A ◽  
Main Components ◽  
Vapour Compression

This paper gives a detailed exergy analysis of a Vapour Compression Refrigeration System with the refrigerants R-134a and HC (mixture of R-290/R-600a). The aim of this paper is to find out the Exergy Analysis, Exergetic efficiency, Exergy Product, Exergy Destruction Ratio (EDR), Co-efficient of performance and 2nd law efficiency for the main components of the system such as compressor, condenser, evaporator and expansion device (throttle valve). The objective of this work is to find out an exergy analysis of the Hydrocarbon refrigerant as an alternative for R-134a. The VCRS performance using R134a will be evaluated for the effect of evaporating temperature on COP, exergetic efficiency and EDR and then compared with Hydrocarbon refrigerant. Due to prevention of GWP (Global Warming Potential), Hydrocarbon and R-134a are used as refrigerants to give better result for domestic refrigerator operation[8] .

Exergy analysis of an atmospheric residue desulphurization hydrotreating process for a crude oil refinery

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Poland Jelihi ◽  
Edwin Zondervan
Keyword(s):  
Crude Oil ◽  
Energy Use ◽  
Oil Refinery ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Atmospheric Residue ◽  
Chemical Exergy ◽  
Exergetic Analysis ◽  
Renewable Hydrogen ◽  
Petroleum Reserves

Abstract The exhaustion of petroleum reserves and the declining supply of conventional feedstock have forced refineries to use heavier crude oil in their production. Removing the undesirable components containing sulphur and metals in the atmospheric residue (AR) fraction requires extensive catalytic hydrotreating (HT) atmospheric residue desulphurization (ARDS) process. In this work, we endeavour to collect and present a comprehensive dataset to develop and simulate the ARDS HT model. This model is then used for an exergetic analysis to evaluate the performance of the ARDS HT model regarding the exergy destruction, the location of losses and exergetic efficiency. The massive exergy destruction is caused by significant differences in chemical exergy of source and product streams during separations, fractionation and reactions. The exergy destruction in the equipment independent of chemical exergies such as heat exchangers, pumps and compressors is relatively low. This exergetic analysis revealed that the majority of the processing equipment in the ARDS HT process performed satisfactorily. However, the remaining equipment requires improvement for its performance in regards to exergetic efficiency or/and avoidable exergetic losses. To enhance the efficiency of the equipment that is intensive in terms of exergy and energy use, the use of clean and high purity renewable hydrogen and several process rectification is proposed.

Genetic Algorithm for Multi-Objective Exergetic and Economic Optimization of Parabolic Trough Collectors Integration Into Combined Cycle System (ISCCS)

2010 ◽  
Author(s):  
Ali Baghernejad ◽  
Mahmood Yaghoubi
Keyword(s):  
Decision Making ◽  
Pareto Frontier ◽  
Optimal Solution ◽  
Combined Cycle ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Economic Optimization ◽  
Cost Rate ◽  
Multi Objective ◽  
Cycle System

Thermoeconomic analyses of any thermal system design are always based on the economic objectives. However, knowledge of economic optimization may not be sufficient for decision making process, since solutions with higher thermodynamic efficiency, in spite of small increases in total costs, may result in much more interesting designs due to changes in the energy market prices or in the energy policies. In this paper a multi-objective optimization scheme is developed and applied for an Integrated Solar Combined Cycle System (ISCCS) that produces 400 MW of electricity to find solutions that simultaneously satisfy exergetic as well as economic objectives. This corresponds to search for a set of Pareto optimal solutions with respect to the two competing objectives. The optimization process is carried out by a particular class of search algorithms known as multi-objective evolutionary algorithms (MOEAs). For such MOEAs, an example of decision-making is presented and a final optimal solution has been introduced. The final optimal solution that is selected in this analysis belongs to the region of Pareto Frontier with significant sensitivity to the costing parameters. However, the region with lower sensitivity to the costing parameter is not reasonable for the final optimum solution due to a weak equilibrium of Pareto Frontier in which a small changes in exergetic efficiency of plant due to variation of operating parameters may lead to the danger of increasing the cost rate of product, drastically. The analysis shows that optimization process leads to 3.2% increasing in the exergetic efficiency and 3.82% decreasing of the rate of product cost. Also optimization leads to the 2.73% reduction on the fuel exergy, 5.71% reductions in the total exergy destruction and also 3.46% and 7.32% reductions in the fuel cost rate and cost rate relating to the exergy destruction, respectively.

scholarly journals Mechanism Analysis and Kinetic Modelling of Cu NPs Catalysed Glycerol Conversion into Lactic Acid

Catalysts ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 231 ◽  
Author(s):  
Sergey Zavrazhnov ◽  
Anton Esipovich ◽  
Sergey Zlobin ◽  
Artem Belousov ◽  
Andrey Vorotyntsev
Keyword(s):  
Experimental Data ◽  
Lactic Acid ◽  
Activation Barrier ◽  
Kinetic Modelling ◽  
Batch Reactor ◽  
Alkaline Media ◽  
Reaction Pathways ◽  
Model Parameters ◽  
Mechanism Analysis ◽  
Glycerol Conversion

Mechanism analysis and kinetic modeling of glycerol conversion into lactic acid in the alkaline media with and without heterogeneous catalyst Cu NPs are reported. The reaction pathways were determined in agreement with the experimental results and comprise several types of reactions, namely dehydrogenation, hydrogenolysis, dehydration and C–C cleavage. Experimental concentration-time profiles were obtained in a slurry batch reactor at different glycerol, NaOH and Cu NPs concentrations in a temperature range of 483–518 K. Power law, Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) models were chosen to fit the experimental data. The proposed reaction pathways and obtained kinetic model adequately describe the experimental data. The reaction over Cu NPs catalyst in the presence of NaOH proceeds with a significantly lower activation barrier (Ea = 81.4 kJ∙mol−1) compared with the only homogeneous catalytic conversion (Ea = 104.0 kJ∙mol−1). The activation energy for glycerol hydrogenolysis into 1,2-propanediol on the catalyst surface without adding hydrogen is estimated of 102.0 kJ∙mol−1. The model parameters obtained in this study would be used to scale an industrial unit in a reactor modeling.

scholarly journals Energetic and Exergetic Investigations of Hybrid Configurations in an Absorption Refrigeration Chiller by Aspen Plus

Processes ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 609 ◽  
Author(s):  
Xiao Zhang ◽  
Liang Cai ◽  
Tao Chen
Keyword(s):  
Heat Transfer ◽  
Waste Heat ◽  
Aspen Plus ◽  
Coefficient Of Performance ◽  
Heat Sources ◽  
Exergy Destruction ◽  
Absorption Refrigeration ◽  
Exergetic Efficiency ◽  
Complex Heat Transfer ◽  
Steady State Simulation

In the present study, a steady-state simulation model was built and validated by Aspen Plus to assess the performance of an absorption refrigeration chiller according to the open literature. Given the complex heat transfer happening in the absorbers and the generator, several assumptions were proposed to simplify the model, for which a new parameter ε l i q was introduced to describe the ratio of possible heat that could be recovered from the absorption and heat-transferring process in the solution cooling absorber. The energetic and the exergetic investigations of a basic cycle and hybrid cycles were conducted, in which the following parameters were analyzed: coefficient of performance (COP), exergetic efficiency, exergy destruction, and irreversibility. According to the results, the basic cycle exhibited major irreversibility in the absorbers and the generator. Subsequently, two proposed novel configurations were adopted to enhance its performance; the first (configuration 1) involved a compressor between a solution heat exchanger and a solution cooling absorber, and the second (configuration 2) involved a compressor between a rectifier and a condenser. The peak COP and the overall exergetic efficiency (η) of configuration 1 were found to be better, increasing by 15% and 5.5%, respectively, and those of configuration 2 were also upregulated by 5% and 4%, respectively. The rise in intermediate compressor ratio not only reduced the driving generator temperature of both configurations but also expanded the operating range of the system under configuration 1, thus proving their feasibility in waste heat sources and the superiority of configuration 1. Detailed information about the optimal state for hybrid cycles is also presented.

Exergy Analysis of a Micro-Gas Turbine Fueled with Syngas

2013 ◽  
Vol 465-466 ◽  
pp. 142-148
Author(s):  
Hussain Sadig ◽  
Shaharin Anwar Sulaiman ◽  
Ibrahim Idris
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Air Temperature ◽  
Heat Input ◽  
Ambient Air ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Micro Gas Turbine ◽  
Ambient Air Temperature ◽  
Excess Air

A theoretical exergetic analysis of a small-scale gas-turbine system fueled with two different syngas fuels is discussed in this paper. For carrying out the analysis, a micro-gas turbine system with a thermal heat input of 50 kW was simulated using ASPEN plus simulator. Quantitative exergy balance was applied for each component in the cycle. The effects of excess air, ambient air temperature, and heat input on the exergy destruction and exergetic efficiency for each component were evaluated and compared with those resulted from fueling the system with liquefied petroleum gas (LPG). For 50 kW heat input and 50% excess air, the total exergy destruction for LPG, Syngas1, and Syngas2 were found to be 17.3, 14.3, and 13.6 kW, respectively. It was found that increasing the excess air ratio to 100% increased the combustion chamber exergetic efficiency by 8%-10% but it reduced the exergetic efficiency of other components. The same trend was observed when tested ambient air temperature. The results also showed a reduction in the combustion chamber exergetic efficiency by 2%-4% when a 20% heat input increase was applied.

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