Graphical Exergy Analysis Research Articles

Thermodynamic performance analysis of solid oxide fuel cell - combined cooling, heating and power system with integrated supercritical CO2 power cycle - organic Rankine cycle and absorption refrigeration cycle

A novel cascade energy utilization system with Solid Oxide Fuel Cell (SOFC) as the prime mover is designed and analyzed. The upper loop contains SOFC and Gas Turbine (GT), and the bottom loop includes Supercritical CO2 (SCO2) power cycle - Organic Rankine Cycle (ORC) combined cycle, single - effect Absorption Refrigeration Cycle (ARC), and heating subsystem. Based on simulation data and mathematical models of the system, energy analysis, conventional and graphical exergy analysis, and sensitivity analysis are conducted. The simulation result demonstrates that the net power efficiency, overall energy efficiency, exergy efficiency and SOFC electrical generation efficiency are 59.62%, 77.61%, 59.08% and 43.18%, respectively. The exergy analysis reveals that the system exergy losses obtained from conventional exergy and graphical exergy analysis are 383.29 kW and 372.46 kW, respectively, a relative error of 2.91%. However, the SOFC subsystem has the greatest exergy destruction, reaching 65.77% (graphical exergy analysis) or 65.06% (conventional exergy analysis) of the total system exergy loss. The system with favorable energy efficiency provides a reference direction for the future research and optimization of Solid Oxide Fuel Cell (SOFC) - Combined Cooling, Heating and Power (CCHP) system.

A thermodynamic analysis and economic evaluation of an integrated cold-end energy utilization system in a de-carbonization coal-fired power plant

Huge amount of cold-end energy discharged from the CO2 capture/compression process is not thermodynamically satisfactory for monoethanolamine (MEA)-based de-carbonization coal-fired power plants. In this study, an improved cold-end energy utilization concept for a MEA-based de-carbonization coal-fired power plant was innovatively proposed, which highly integrates the CO2 capture/compression, steam bleeding, and boiler air pre-heating processes to cascade utilize the system cold-end energies, and beneficially supplies the heat required for solvent regeneration and air preheating. To be specific, three paths have been adopted: (1) reboiler condensate recirculation: part of the reboiler condensate is recirculated to mix with the steam bleed to provide the heat for solvent regeneration; (2) absorption heat transformer (AHT): upgrading the reboiler condensate heat for solvent regeneration; and (3) multi-stage air heating: cascade utilization of the heat discharged from coolers within CO2 capture/compression process to preheat combustion air prior to the flue gas-air preheater, saving part of the flue gas heat to be used in a more cascade way. The mass and energy balance of the proposed system and the overall system performance were determined using the process simulation. The energy saving mechanism of the adopted three paths were investigated through adopting the graphical exergy analysis for the reboiler block and air preheating process. The cost of electricity (COE) and cost of CO2 avoided (COA) of the proposed system were also determined. Results showed that the energy efficiency of the proposed system could be 3.2 percentage points higher than that of the conventional de-carbonization plant without cold-end energy utilization. The COE and COA of the proposed system were reduced by 8.0% and 22.2%, respectively.

An improved supercritical coal-fired power generation system incorporating a supplementary supercritical CO2 cycle

Large superheat degree of the steam bleeds from regenerative heaters as well as the large heat transfer temperature difference during the air preheating process is not thermodynamically satisfactory in advanced supercritical power plants with the aim of high power generation efficiency. In this study, an improved supercritical coal-fired power generation system, which integrates a supercritical CO2 (S-CO2) power cycle to utilize the superheat of the steam bleeds as well as to heat the combustion air, was proposed. In the proposed system, the heat transfer temperature difference within the steam regenerative trains and air preheating process could be reduced, leading to less exergy destructions. Moreover, less required heat for flue gas air heaters makes it possible to adopt a low-temperature economizer (LTE) between the arranged two-stage flue gas air heaters, saving part of the steam bleeds, even if the exhaust flue gas temperature is kept constant. The detailed exergy distributions within the regenerative heaters and air pre-heating process were discussed using the graphical exergy analysis. The mass and energy balance of the proposed system and the overall system performance were determined using the process simulation. The economic viability and the implementation feasibility of the proposed system was also analyzed. Results showed that the exergy destruction of the regenerative heaters and air preheating process could be reduced by 4.47 MW and 11.95 MW, respectively. The gross electric power output from the proposed system was 1007.79 MW with a satisfactory energy efficiency at 46.0%, 0.4 percentage point higher than the reference power plant. The payback period of the proposed system is slightly longer than that of the reference plant at the current market condition and it will be more profitable as the S-CO2 cycle becomes more commercially mature.

Graphical exergy analysis for a scramjet thermodynamic performance evaluation

Graphical exergy analysis was applied to a scramjet at cruise conditions. A zero-dimensional scramjet model was developed to describe the thermodynamic process of a hypersonic propulsion system. Energy utilisation diagrams (EUDs) were drawn to present the relationship between energy and energy level at cruise conditions. Performance optimisation based on the exergy efficiency was completed ranging from Ma 5.35 to Ma 6.23. The results indicate that the exhausting process produces the most exergy destruction, then the combustion process, and the exergy loss in the expansion process is the smallest. There is a maximal exergy efficiency with the variation of fuel equivalence ratio for a certain entrance condition, and the maximum increases with the cruise Mach number and the altitude. The advantages of graphical exergy analysis, such as visual representation of the relationships among different components and the convenience of analysis, were also shown by the example in this paper.

Graphical exergy analysis of reactive distillation column for biodiesel production

This paper brings the novelty of the exergy analysis technique using Ex-N-A diagram to a packed reactive distillation (RD) column for biodiesel production. In this study, biodiesel is produced through the esterification of fatty acid with methanol. The simulation of the column was performed based on the non-equilibrium (NEQ) model of a three-phase packed RD system. The graphical Ex-N-A method was utilised to evaluate exergy features of the internal RD column. This technique rigorously demonstrated the value of exergy losses at each increment of the column, i.e., losses owing to the temperature change, phase change, mixing in liquid and vapour phases and chemical reaction. The effects of the molar ratio of the reactant and the height of the packed column on the conversion and exergy losses were examined and displayed in a simple figure.

A Novel Multifunctional Energy System for CO2 Removal by Solar Reforming of Natural Gas

In this paper, a novel multifunctional energy system (MES) fueled by natural gas and solar radiation is proposed. In this MES, hydrogen and electricity are cogenerated and approximately 92% of CO2 derived from natural gas is removed. The solar concentrated process provides high-temperature thermal energy to the methane/steam reforming reaction. The resulting syngas enters a pressure swing adsorption unit to separate approximately 80% of hydrogen. This process significantly increases the concentration of carbon dioxide in syngas from nearly 19% to 49%, which decreases energy consumption in CO2 removal. As a result, the overall power efficiency of the new system becomes about 39.2%. Compared to a conventional natural gas-based hydrogen plant with CO2 removal and a concentrated solar power tower plant, the overall power efficiency of the new system is increased by 7.9 percentage points. Based on the graphical exergy analysis, the integration of synthetic utilization of natural gas and solar radiation, combination of the hydrogen production plant and power plant, and integration of the energy utilization processes and CO2 separation were found to play significant roles to improve thermodynamic performance. The result obtained here provides a new approach for highly efficient use of solar radiation by hybrid natural gas.

Graphical exergy analysis of retrofitted distillation column

Thermodynamic analysis of a distillation column has important role for synthesising and developing energy-efficient distillation process. We have invented representation of this analysis to integrate characteristics of separation performance and exergy features of internal distillation column using Material-Utilisation Diagram (MUD). In this paper, we analyse separation performance and exergy loss phenomena for retrofitted distillation column, i.e., side heating?cooling and pump around in a distillation, on MUD. This MUD methodology displays Minimum Driving Force (MDF) for side heating-cooling and Close to Equilibrium Point (CEP) for pump-around system at a particular heat load.

Optimal design of distillation column using three dimensional exergy analysis curves

Abstract This paper presents two main contributions. Firstly, a new exergy graphical method is proposed for optimal design of distillation column with minimum exergy lost. The method is applicable to both grass-root and retrofit cases, respectively. The effect of design and operating parameters of a distillation column on the exergy lost is graphically visualized by three dimensional exergy analysis curves. The curve shows the correlations between exergy lost, design and operating parameters of a distillation column. This technique can be used as an effective method to reduce the simulation effort to search for the optimum design and operating parameters of a distillation column at minimum exergy lost. Besides, visualization also enhances the engineers’ understanding of the column performance. The other contribution is a four-level idealization concept, which is based on three dimensional graphical exergy analysis curves. The concept defines the effect of transport rate and configuration on exergy lost of distillation column. The effectiveness of the method has been demonstrated on a xylene column, which suggested that an implementation of feed pre-heater yields a significant reduction in exergy lost by up to 15.5%.

A Novel Multifunctional Energy System (MES) for CO2 Removal With Zero Energy Penalty

This paper proposes a novel, multifunctional energy system (MES), in which hydrogen and electricity are cogenerated and about 90% of CO2 is removed. By integrating the methane/steam reforming reaction and combustion of coal, the natural gas and coal are utilized synthetically, and coal is burned to provide high-temperature thermal energy to the methane/steam reforming reaction. Afterwards, the resulting syngas enters a pressure swing adsorption (PSA) unit to separate about 70% of hydrogen, thereby significantly increasing the concentration of carbon dioxide from nearly 20% to 43% in the PSA tail gas. As a result, the overall efficiency of the new system becomes 63.2%. Compared to a conventional natural gas-based hydrogen plant and a coal-firing steam power plant without CO2 removal (the overall efficiency of the two systems is 63.0%), the energy penalty for CO2 removal in the new system is almost totally avoided. Based on the graphical exergy analysis, we propose that the integration of synthetic utilization of fossil fuel (natural gas and coal) and the CO2 removal process plays a significant role in zero energy penalty for CO2 removal and its liquefaction in the MES. The result obtained here provides a new approach for CO2 removal with zero or low thermal efficiency reduction (energy penalty) within an energy system.

Proposal of a natural gas-based polygeneration system for power and methanol production

A new kind of natural gas-based polygeneration system for methanol and power production is proposed in this paper. With the sequential connection between chemical production and power generation, the new system adopts innovative integration of partial-reforming and partial-recycle scheme in methanol synthesis subsystem. To reveal the characteristics of the new system, exegetic comparisons between the new system and a reference polygeneration system with full-reforming and once through methanol synthesis scheme have been carried out. Results indicate that the new system can save energy about 6 percentages versus single product systems. By the aid of graphical exergy analysis methodology, the specific information on internal phenomena of key processes was illustrated. The analysis shows that it is the synergetic combination of partial-reforming and partial-recycle schemes that makes the significant contribution to the performance improvement, and plays the most important role in system integration.

Exergy analysis of coal-based polygeneration system for power and chemical production

To develop total energy systems and reveal characteristics of polygeneration systems, we have investigated one coal-based polygeneration system for power and methanol production, and compared it with its original individual processes. The results indicate that the polygeneration system will save 3.9–8.2% energy compared to the individual processes. By the aid of graphical exergy analysis and comparison of systems, we have indicated some specific information on internal phenomena. The result reveals that synthesis on the basis of thermal energy cascade utilization is the main contribution to the performance benefit of the polygeneration system. Moreover, the capacity ratio of chemical process to power system strongly affects matching between two sides, which is a key criterion in polygeneration system. Hence, synergetic integration of the power system and the chemical processes in polygeneration systems will provide promising performance in the future.

Cooling System Design

Cooling water systems and refrigeration systems are required to provide cold utility to chemical processes. Little attention has been placed on the structure and system interactions between cooling systems and processes. In this article, an integrated design and retrofit method for cooling systems is reviewed. For cooling water system design, a new design methodology has been developed for debottlenecking of cooling water systems. Reuse of cooling water between different cooling duties enables cooling water networks to be designed with series arrangements. This allows better cooling tower performance and increased cooling tower capacity. The interactions between the performance of the cooling tower and the design of cooling water networks are explored systematically. For refrigeration system design, a systematic design and retrofit method has been proposed for refrigeration systems using pure or mixed refrigerants. A graphical exergy analysis method, the z -H diagram, is introduced to help engineers obtain understanding and insights into complex refrigeration systems. The systematic synthesis method proposed in this article can greatly improve operating efficiency for refrigerant systems.

Exergy Evaluation of Two Current Advanced Power Plants: Supercritical Steam Turbine and Combined Cycle

Two operating advanced power plants, a supercritical steam plant and a gas-steam turbine combined cycle, have been analyzed using a methodology of graphical exergy analysis (EUDs). The comparison of two plants, which may provide the detailed information on internal phenomena, points out several inefficient segments in the combined cycle plant: higher exergy loss caused by mixing in the combustor, higher exergy waste from the heat recovery steam generator, and higher exergy loss by inefficiency in the power section, especially in the steam turbine. On the basis of these fundamental features of each plant, we recommend several schemes for improving the thermal efficiency of current advanced power plants.

Graphic exergy analysis of processes in distillation column by energy‐utilization diagrams

AbstractThe graphical construction called an energy‐utilization diagram (EUD) is adopted for analyses of energy transformation and exergy losses in a distillation column. The overall exergy loss on one plate of a column can be decomposed into six kinds of exergy losses and are represented graphically. Two of them are caused by mixing and cooling in the vapor phase, and the other two by mixing and heating in the liquid phase. To display the remaining two yielded by condensation and evaporation of each component, the concept of the individual energy level is applied. The relationship between the individual energy level and the xy diagram is presented as well as effects of the reflux ratio and the feed location on the EUD for the whole column. Separation of n‐hexane and n‐octane is used to illustrate the methodology.

Three-dimensional graphical exergy analysis of a distillation column.

This paper demonstrates a three-dimensional graphical representation of energy losses in a distillation column by applying an Energy-Utilization Diagram (EUD). The concepts of both premixing model and individual energy level are applied to classify the energy loss in a column into six kinds; losses due to heating, and mixing in liquid phase, losses due to cooling and mixing in vapor phase, and losses due to evaporation of light components and condensation of heavy components through phase changes. The diagram displays transformed energy, its energy level, and unit height of the column in three-dimensional space. This diagram is useful for qualifying and quantifying the energy loss in a distillation column, and the target to minimize the energy and exergy consumption can be identified. The characteristics of close-to-equilibrium points (CEP) are also demonstrated.

Graphical exergy analysis of a new type of advanced cycle with saturated air

A new type of advanced cycle with saturated air called a gas turbine cycle with saturation for air (GTSA) is analyzed by graphical exergy methodology based on energy-utilization diagrams (EUDs). By comparing it with an advanced steam-injected gas turbine cycle (STIG), key features of the GTSA system are clarified. The model system may achieve an efficiency as high as 56%. It is about 8% more efficient than the STIG. In addition, some suggestions are pointed out for further research.

Graphical exergy analysis of complex cycles

Advanced thermal power systems (i.e. the gas-steam combined cycle, the steam injected gas turbine cycle and the regenerative gas turbine cycle) are complex systems with a basic gas turbine cycle. They have been analyzed by using a graphical exergy analysis that generates energy-utilization diagrams (EUDs). Comparison of the EUDs shows that the recently advanced systems have potential for substantial improvements. Suggestions for future improvements are described.

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9-2.燃料電池発電システムのグラフィックエクセルギー解析(Session(9)燃料電池の実用化に向けて)

Application of energy-utilization diagram for graphic exergy analysis of multicomponent distillation columns.

A new method for graphic exergy analysis of multicomponent distillation and for visualization of rate characteristics of a distillation column is proposed by applying an energy-utilization diagram, EUD. By introducing the concept of a premixing model, the exergy losses in a distillation column can be decomposed into losses caused by premixing in liquid phase and those caused by premixing in vapor phase. Also, the energy exchange in a phase change such as condensation or evaporation of each component is displayed individually. By introducing the concept of partial molar quantities, those exergy losses in liquid phase and vapor phase can be categorized into losses caused by heating and mixing in liquid phase and losses caused by cooling and mixing in vapor phase. To use this method, the energy exchanged (ΔH ea ) and the energy levels (A ed and A ea ) are displayed systematically on EUD. As a case study, simulation of the separation of n-hexane, n-heptane and n-octane is conducted for a column with 11 plates. The effect of reflux ratio and side-cooling or side-heating is discussed by using EUDs

Performance of an internal direct-oxidation carbon fuel cell and its evaluation by graphic exergy analysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPerformance of an internal direct-oxidation carbon fuel cell and its evaluation by graphic exergy analysisNobuyoshi Nakagawa and Masaru IshidaCite this: Ind. Eng. Chem. Res. 1988, 27, 7, 1181–1185Publication Date (Print):July 1, 1988Publication History Published online1 May 2002Published inissue 1 July 1988https://doi.org/10.1021/ie00079a016RIGHTS & PERMISSIONSArticle Views482Altmetric-Citations112LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (550 KB) Get e-Alerts Get e-Alerts