Advanced Exergetic Analysis Research Articles

Advanced Exergo-Environmental Assessments of an Organic Rankine Cycle as Waste Heat Recovery System from a Natural Gas Engine

This paper aims to present the real improvement opportunities of a simple organic Rankine cycle (ORC) as waste heat recovery system (WHRS) from the exhaust gases of a natural gas engine using toluene as the working fluid, based on the exergy and environmental point of view. From the energy and exergy balances, the advanced exergetic analysis was developed to determine the irreversibilities and opportunities for improvement. Since the traditional exergo-environmental analysis, it was found that the component with the greatest potential environmental impact associated with exergy (bF = 0.067 mPts/MJ) and per unit of exergy (ḂD = 8.729 mPts/h) was the condenser, while the exergy-environmental fraction was presented in the turbine (52.51%) and pump-2 (21.12%). The advanced exergo-environmental analysis showed that the environmental impact is more associated with the operational behavior of the components, with 75.33% of the environmental impacts being of endogenous nature, showing that the environmental impacts are generated to a reduced magnitude through the interactions between components. However, it was identified that much of the environmental impacts in ITC 1 could be reduced, with 81.3% of these impacts being avoidable. Finally, the sensitivity analysis results revealed that steel is the material of the components with the least environmental impact.

Exergetic sustainability comparison of turquoise hydrogen conversion to low-carbon fuels

Turquoise hydrogen is produced from methane cracking, a cleaner alternative to steam methane reforming. This study evaluates two proposed systems based on solar methane cracking for low-carbon fuel production. The systems employ different pathways to convert the turquoise hydrogen into a suitable form for transportation and utilize the carbon solid by-product. A direct carbon fuel cell is integrated to utilize the carbon and capture the CO2 emissions. The generated CO2 is utilized for fuel production using CO2 hydrogenation or co-electrolysis. An advanced exergetic analysis is conducted on these systems using Aspen plus simulations of the process. The exergetic efficiency, waste exergy ratio, exergy destruction ratio, exergy recoverability ratio, environmental effect factor and the exergetic sustainability index were determined for each system and the subsystems. Solar methane cracking was found to have an environmental effect factor of 0.08 and an exergetic sustainability index of 12.27.

Exploring the improvement potentials in an existing industrial olefin plant through advanced exergy-based analyses

The production of light olefins via the thermal cracking of hydrocarbons is the most energy-demanding process in the petrochemical industry, and an important producer of greenhouse gasses worldwide. But, which sections or components of this process are major contributors to its energy-intensiveness, and high environmental impacts? And, how these problems can be avoided and to what extent?Presently, conventional and advanced exergetic, exergoeconomic, and exergoenvironmental analyses are introduced as the most promising methods which could answer these questions, therefore, in this work, are used to identify the real priorities of improvement in an olefin plant in the south of Iran (Assaluyeh), by first simulating the plant in ASPEN HYSYS simulator. The environmental impacts of components and input streams of plant were calculated using Eco-Indicator 99 method of Life Cycle Assessment (LCA). Results of the study indicated that although the cracking furnace causes 55.3% of total exergy destruction of the plant, only 15.36% of it is avoidable endogenous. Furthermore, the considerable share of steam system in the total exergy destruction of plant (as the second exergy destructive section with a share of 14%) showed that ignoring this zone of an olefin plant in the exergy-based analyses leads to major mistakes to diagnose the priorities of improvements. The results showed that considering prespecified costs and environmental impacts for internal material or energy streams produced within the process introduces a significant error to identify the improvement priorities regarding the economic and environmental aspects.

Advanced exergy and exergoeconomic analyses to evaluate the economy of LNG oxy-fuel combined cycle power plant

Oxy-fuel combustion has attracted wide attention since it is thought to be an advanced technology for CO2 capture from the power generation plant on a large scale. An oxy-fuel combustion system is proposed to raise system energy efficiency utilizing cold energy from liquefied natural gas (LNG). The quantitative research on the exergy consumption, economic feasibility, and optimization strategies of the LNG oxy-fuel combustion system is conducted by advanced exergetic and exergoeconomic analyses. The results show the oxy-fuel system has an exergy efficiency of 46.83 %. The exergy destruction of the oxy-fuel system is 445.51 MW, of which the avoidable part accounts for 81.68 %. In terms of economic feasibility, the oxy-fuel system costs approximately 4.44 × 106$/h, which is considerably higher than the value of 1.99 × 106$/h in the air system. Moreover, more than 78.21 % of the cost in the oxy-fuel system is avoidable, 36.05 % higher than that of the air system. The work discovers that in the combustor of the oxy-fuel system, the improvement of the flue gas treatment unit (FGU) has a significant impact on promoting its net efficiency, and increasing its investment cost rate is not an economic limitation to save the system economy. The study is crucial for the application of oxy-fuel combustion electricity generation technologies.

Optimal design and analysis of a combined freshwater-power generation system based on integrated solid oxide fuel cell-gas turbine-organic Rankine cycle-multi effect distillation system

Gas turbine output has a very good capability for heat recovery and increases production capacity by heat recovery steam generator and heat recovery vapor generator. Also, gas turbines have good potential for coupling with a solid oxide fuel cell to increase power generation. The present research proposes and evaluates a novel combination of a solid oxide fuel cell and gas turbine system with an organic Rankine cycle and a multi-effect thermal desalination system. Conventional and advanced exergetic, exergoenvironmental and exergoeconomic analyses are performed to better understand the proposed system in view of performance, economic, and environmental impacts. To find the optimal design values, minimize the total exergetic environmental impacts and total exergetic cost rate, and maximize exergetic efficiency, as objective functions, multi-target optimization using the multi-target water cycle algorithm and the multi-target genetic algorithm is used. The analyses are conducted using MATLAB software. Results determine the optimal hybrid system could produce 5000 m3/day of freshwater, with five effects on the MED-TVC. The energy and exergy efficiencies of the suggested hybrid system reached 47.85% and 41.94%, respectively, an increase of 11.6% and 3.6% compared to the coupled gas turbine system and solid oxide fuel cell. Furthermore, by applying the Multi-objective Genetic Algorithm and Multi-objective Water Cycle Algorithm optimization, the overall efficiency of cogeneration is increased by 28% and 27.5%. The total exergetic cost is reduced by 23.12% and 22.46%, and the total exergetic environmental impact is reduced by 20.15% and 19.65%, respectively.

Simulation and Exergy Analysis of a Refrigeration System Using an Open-Source Web-Based Interactive Tool—Comparison of the Conventional Approach and a Novel One for Avoidable Exergy Destruction Estimation

Avoidable endogenous/exogenous parts of the exergy destruction in the components of an energy conversion system can be computed by applying advanced exergy analysis. Their calculation is crucial for the correct assessment of the real thermodynamic enhancement achievable by the investigated energy conversion system. This work proposes a new approach to estimate the avoidable exergy destruction rates of system components, being more rigorous compared to the conventional method due to the elimination of the need for the implementation of theoretical assumptions associated with the idealization of processes. An open-source web-based interactive tool was implemented to contrast the results of the conventional advanced exergy analysis to those involving the new approach for avoidable exergy destruction estimation. The comparison was based on the same case study, i.e., a refrigeration system selected from the literature. It was observed that the developed tool can be properly employed for comparing the two approaches within exergy analyses, and the results obtained presented some differences for the compressor and the condenser. Compared to the new approach, the existing methodology of advanced exergy analysis suggests lower values of the avoidable part of exergy destruction, which can be reduced by improving the efficiency of the compressor and the condenser. Moreover, the avoidable parts of exergy destruction, which could be removed within these components by improving the efficiencies of the remaining components, were higher in the case of the application of the existing advanced exergetic analysis as compared with the findings obtained by the proposed approach. These differences were due to the impossibility of the existing advanced exergy analysis to implement complete thermodynamic “idealization” for the condenser and evaporator.

Thermodynamic Evaluation of a Direct Expansion Ground-Sourced Heat Pump with Horizontal Ground Heat Exchangers Using Advanced Exergy Analysis

This paper deals with the advanced exergetic analysis of a horizontal direct-expansion ground sourced CO2 heat pump operating in a transcritical cycle. The cycle is thermodynamically modeled in Engineering Equation Solver (EES) considering the pressure drops in both high and low temperature heat exchangers, and the system is to provide a fixed heating load. Conventional exergy analysis orderly suggests a compressor, expansion valve, gas cooler and ground heat exchanger to be considered for system improvement, while tracing exergy destruction of all components in detail demonstrates true improvement potential of each and all components and the system as a whole and offers a different order. Advanced exergy analysis points out that the compressor is directly and indirectly responsible for 56% of the overall exergy destruction generated in the cycle, confirming the detrimental role of this component in the system. The second influential component is recognized to be a ground heat exchanger accounting for 20% exergy destruction of the compressor as well as submitting 89% avoidability in its own exergy destruction, and expansion valve proves to be the last option for system improvement according to this analysis.

Advanced Exergy and Exergoeconomic Analysis of a Gas Power System with Steam Injection and Air Cooling with a Compression Refrigeration Machine

Gas turbine power plants have been widely studied, and as a result the negative effects on their output power and thermal efficiency have been known when operating in atmospheric conditions exceeding ISO conditions. For this reason, different technologies and methodologies have been implemented, aiming to increase the output power and improve the thermal efficiency. Unfortunately, the lack of operational parameters for this system limited its characterization and implementation of strategies to improve its performance. Advanced exergetic and exergoeconomic analyses have been applied to improve energy and economic performance in steam injection gas turbine (STIG) cycle power plants with air cooling with a compression refrigeration machine. Results shows that the main sources of irreversibilities and higher costs are in the Combustion Chamber (CC), Heat Recovery Steam Generator (HRSG) and Gas Turbine (GT). From these components, the components of the HRSG and GT have the greatest potential for improvement, and this can be achieved by improving the overall configuration of the system, due to the fact that the destruction of exogenous exergy is in more significant measure avoidable. While the higher costs of investment can be reduced in the Combustion Chamber and Gas Turbine.

Dynamic Advanced Exergetic, Exergoeconomic, and Environmental Analyses of a Hybrid Solar City Gate Station

Abstract The use of solar energy to preheat natural gas before a city gate station (CGS) for reducing fuel consumption and environmental emissions is investigated in a real CGS. All analyses are conducted with a 1-h time-step throughout the entire year so that seasonal climate changes are accounted for precisely. A thermodynamic analysis of the hybrid system is performed with TRNSYS and verified with THERMOFLEX so as to ensure reliability. In addition, dynamic exergetic, exergoeconomic, and exergoenvironmental analyses for the proposed system are carried out. A life cycle assessment (LCA) based on Eco-indicator 99 is performed using SIMA PRO to compute the environmental impacts for each component of the system. The exergetic, exergoeconomic, and environmental analyses are performed in Engineering Equation Solver (EES) software. To perform the transient exergetic, exergoeconomic, and environmental analyses, the results of the thermodynamic analysis from TRNSYS are automatically imported into the EES code. The advanced exergetic, exergoeconomic, and exergoenvironmental analyses are performed to better determine components that have high potentials for improving the system; potentials are considered based on the exergy destruction, exergetic cost of destruction, and environmental impacts associated with exergy destruction.

Advanced Exergy, Exergoeconomic, Exergoenvironmental Evaluation of a Solar Hybrid Trigeneration System Based on Solar Gas Turbine for an Office Building

Abstract In this article, optimal design and advanced exergetic, exergoeconomic, and exergoenvironmental analyses of a trigeneration system for an office building based on integration flat plate solar collector and gas turbine have been performed. The proposed system includes a heat recovery steam generator, a steam turbine, a solar plate collector, and an absorption chiller. The transient simulation for solar calculation has been done using transys software. In addition, a computer code was built to compute conventional and advanced exergy, exergoeconomic, and exergoenvironmental evaluation dynamically. Furthermore, multiobjective optimization by NSGA-II and cuckoo Search algorithm with maximum exergetic efficiency, minimum total exergetic cost, and minimum exergetic environmental impacts has been carried out simultaneously. The results demonstrate that the three objective parameters have been enhanced. Also, the endogenous, exogenous, available, and unavailable parts of exergy destruction have been determined.

Regenerative Organic Rankine Cycle as Bottoming Cycle of an Industrial Gas Engine: Traditional and Advanced Exergetic Analysis

This investigation shows a traditional and advanced exergetic assessment of a waste heat recovery system based on recuperative ORC (organic Rankine cycle) as bottoming cycle of a 2 MW natural gas internal combustion engine. The advanced exergetic evaluation divides the study into two groups, the avoidable and unavoidable group and the endogenous and exogenous group. The first group provides information on the efficiency improvement potential of the components, and the second group determines the interaction between the components. A sensitivity analysis was achieved to assess the effect of condensing temperature, evaporator pinch, and pressure ratio with net power, thermal efficiencies, and exergetic efficiency for pentane, hexane, and octane as organic working fluids, where pentane obtained better energy and exergetic results. Furthermore, an advanced exergetic analysis showed that the components that had possibilities of improvement were the evaporator (19.14 kW) and the turbine (8.35 kW). Therefore, through the application of advanced exergetic analysis, strategies and opportunities for growth in the thermodynamic performance of the system can be identified through the avoidable percentage of destruction of exergy in components.

Economic and Exergo-Advance Analysis of a Waste Heat Recovery System Based on Regenerative Organic Rankine Cycle under Organic Fluids with Low Global Warming Potential

The waste heat recovery system (WHRS) is a good alternative to provide a solution to the waste energy emanated in the exhaust gases of the internal combustion engine (ICE). Therefore, it is useful to carry out research to improve the thermal efficiency of the ICE through a WHRS based on the organic Rankine cycle (ORC), since this type of system takes advantage of the heat of the exhaust gases to generate electrical energy. The organic working fluid selection was developed according to environmental criteria, operational parameters, thermodynamic conditions of the gas engine, and investment costs. An economic analysis is presented for the systems operating with three selected working fluids: toluene, acetone, and heptane, considering the main costs involved in the design and operation of the thermal system. Furthermore, an exergo-advanced study is presented on the WHRS based on ORC integrated to the ICE, which is a Jenbacher JMS 612 GS-N of 2 MW power fueled with natural gas. This advanced exergetic analysis allowed us to know the opportunities for improvement of the equipment and the increase in the thermodynamic performance of the ICE. The results show that when using acetone as the organic working fluid, there is a greater tendency of improvement of endogenous character in Pump 2 of around 80%. When using heptane it was manifested that for the turbine there are near to 77% opportunities for improvement, and the use of toluene in the turbine gave a rate of improvement of 70%. Finally, some case studies are presented to study the effect of condensation temperature, the pinch point temperature in the evaporator, and the pressure ratio on the direct, indirect, and fixed investment costs, where the higher investment costs were presented with the acetone, and lower costs when using the toluene as working fluid.

Comparative Performance Metric Assessment of A Military Turbojet Engine Utilizing Hydrogen And Kerosene Fuels Through Advanced Exergy Analysis Method

This study dealt with evaluating the (J85-GE-5H) military turbojet engine (TJE) in terms of exergetic and advanced exergetic analyses at Military (MIL) and Afterburner (AB) process modes by utilizing kerosene (JP-8) and hydrogen (H2) fuels. First, exergy and advanced exergy analyses of the engine were performed using JP-8 fuel as per actual engine operating conditions. These analyses of the turbojet engine using hydrogen fuel were also examined parametrically. The performance evaluation of the engine was lastly executed by comparing the obtained results for both fuels. Based on the parametric studies undertaken, the entire engine’s exergetic efficiency with JP-8 was reckoned 30.85% at the MIL process mode while it was calculated as 16.98% at the AB process mode. With the usage of H2, the efficiencies of the engine decreased to 28.62% and 15.33% for the above mentioned two modes, respectively. As the supreme exergy destructions occurred in the combustion chamber (CC) and afterburner exhaust duct (ABED) segments, the new technological developments should be considered to design more efficient engines. As a result, the engine worked less efficiently with hydrogen fuel due to the enhancement in exergy destructions. Conversely, the greenhouse gas (GHG) emission parameters lessened with the utilization of H2 fuel.

Exergy-based Investigation of Various Heat Pumps for Enhancement of Their Thermodynamic Efficiency

The work demonstrates the results of application of the detailed advanced exergetic analysis to air-source, watersource and wastewater-source heat pumps providing space heating in the built environment. Cumulative values based on seasonal exergy destruction are used for deriving conclusions. It is shown that in the specified conditions of the investigated systems priorities for improving should be given to heat exchangers.

Advanced Exergy Analysis of a Compression–Absorption Cascade Refrigeration System

This work presents a theoretical thermodynamic study of a compression–absorption cascade refrigeration system using R134a and a lithium bromide–water solution as working fluids. First and second law of thermodynamics analyses were carried out in order to develop an advanced exergetic analysis, by splitting the total irreversibility and that of every component. The potential for improvement of the system is quantified, in the illustrated base-case 55.4% of the irreversibility is of avoidable nature and it could be reduced. The evaporator is the component that shows a significant potential for improvement, followed by the cascade heat exchanger, the compressor, and finally, the generator. The results of the advanced exergetic analysis can be very useful for future design and experimentation of these kinds of systems.

Conventional and Advanced Exergetic and Exergoeconomic Analysis Applied to an Air Preheater System for Fired Heater (Case Study: Tehran Oil Refinery Company)

TThe present paper evaluates the plan of combustion air pre-heater installation on the fired heater from thermodynamics and thermos-economics point of view. As a real case study, one of the fired heaters (H_101) of Distillation unit in Tehran Oil Refinery, Iran, is intended. With applying an air pre-heater in this study, flue gases temperature falls down from 430 oC to 200oCand combustion air temperature grows up from 25oCto 350 oC. By examining the energy and exergy analyses before and after the installation of air pre-heater, the increase in thermal efficiency by 20% and exergy efficiency by 37% and accordingly decreasing fuel consumption by 20% is observed. It is also indicated that the most exergy destruction is accrued in the fired heater (57.24%). In this study for the first time, based on advanced exergy analyses and concepts of endogenous/exogenous and avoidable/unavoidable parts, exergy destruction, exergy destruction cost rates and capital investment of combustion air preheater system are found which results show the endogenous and unavoidable parts in overall system are dominant. Also, the effect of flue gases temperature (T5) on the system performance is investigated through sensitivity analyses. It is seen that with rising T5, thermal efficiency and exergy efficiency in real, theory and unavoidable conditions decrease. The results demonstrate the majority parts of exergy destruction in fired heater and air preheater is endogenous, unavoidable and unavoidable endogenous. Considering the cost of air preheater and related equipment and operating and maintenance costs annually, the payback period is estimated to be less than 2 years. In this research, the EES and Excel were applied to calculate the amount.

Advanced Exergetic Analysis of a Heat Pump With Wastewater Heat Exchanger

In contrast to conventional exergy-based methods, advanced exergetic analyses can evaluate exergy destructions due to interactions among components of the energy-conversion system and the real potential for improving system components. Application of the advanced exergetic analysis to a wastewater source heat pump with wastewater heat exchanger providing space heating in variable operation modes is proposed in the work. In order to determine thermodynamic parameters of the refrigeration vapor compresion cycle a special simulation model was used. The so-called thermodynamic-cycle-based approach was applied to split the exergy destruction within each component of a heat pump into unavoidable, avoidable, endogenous and exogenous parts. It is shown that in the investigated system only about 53 % of the total seasonal destruction in the heat pump can be avoided. About 48 % of this avoidable thermodynamic inefficiency is caused by interactions among components. It is shown that in the investigated conditions, the biggest part of exergy destruction in the throttling valve and compressor can be avoided by reducing irreversibilities in the remaining components of the system. Exergy destruction, which can be avoided in the condenser, evaporator and the wastewater heat exchanger, is mainly caused by irreversibilities within these components.

Advanced Analysis of Dew Point Control Unit of Hybrid Refrigeration Systems in Gas Refineries

In this paper, an advanced analysis of a novel hybrid compression-absorption refrigeration system (HCARS) for natural gas dew point control unit in a gas refinery is presented. This unit separates the heavy hydrocarbon molecules in the natural gas, which is traditionally carried out by natural gas cooling in a compression refrigeration cycle (CRS). The power input required for the refrigeration cycle compressors is usually provided by gas turbines. The low efficiency of gas turbines and the excessive power required for running the CRS compressors have made it crucial to investigate different means to decrease the energy consumption of this cooling system. The waste heat of gas turbines flue gas can be recovered and utilized as the heating source for running an absorption refrigeration system (ARS) to provide part of the needed cooling load; hence, a hybrid compression absorption refrigeration system (HCARS) is launched. In this work, the application of HCARS is extended to the Fajr-e-Jam gas refinery currently operating with a CRS, and an advanced exergetic analysis of the proposed ARS is performed to further improve the proposed system. The effect of different variables on the performance of the proposed HCARS is also inspected. The proposed system and these analyses are novel for the gas refinery dew point control unit. Real CRS operational data are utilized in all the investigations, and proper means are presented for the validation of the simulation results. The proposed system resulted in 63% additional cooling capacity of the HCARS (12550 KW) in comparison to the current CRS (7670 kW) for the equal natural gas consumption, which overall saves about 50000 SCMD of natural gas. Based on the exergy analysis of all the equipment, the exergy efficiency of the proposed ARS is 0.155. In addition, the parametric study of the effects of the gas turbine flue gas exit temperature and flow rate, ambient temperature, partial load operation of CRS, absorption solution flow rate, and concentration on the HCARS performance is carried out. These studies should provide the information needed for operating the proposed system in different situations.

Analyzing thermodynamic improvement potential of a selected cement manufacturing process: Advanced exergy analysis

Cement industry uses very energy-intensive operations resulting in a suboptimal sustainable performance. The objective of this research is to provide insight into the value of exergy analysis in sustainability assessment of cement industry. For that purpose, a detailed exergy evaluation of a complete cement plant located in Morocco was performed using both conventional and advanced exergetic analysis. The major internal exergy losses were identified during the calcination process and the two raw mill departments, which amounts to about 78.66%, 70.86%, and 72.12% respectively. Those irreversibilities are split into avoidable/unavoidable exergy destruction in the advanced exergy analysis. Findings show that 15%, 29.21% and 31.54% of the total exergy destruction in the calciner and the raw mills 1 and 2 respectively are avoidable. However, there is a need for optimization of comminution and combustion operating parameters in the cement production process currently in use.

Advanced exergy analysis and environmental assesment of the steam cycle of an incineration system of municipal solid waste with energy recovery

This work presents an advanced exergy and environmental analysis of a steam cycle of a municipal solid waste incineration plant, with energy recovery for electricity generation; employing MSW of the city of Santo André in São Paulo State, Brazil. Initially, a plant energy analysis is accomplished to determine some thermodynamic performance indicators, as well a conventional exergetic analysis is performed, to determine the magnitude of exergy destruction in each one of plant main components. To identify the potential for improvement in the incineration steam cycle, an advanced exergetic analysis was done, with exergy destruction divided into four categories: endogenous, exogenous, avoidable and unavoidable. With all this it was calculated that total plant exergy destruction can be reduced by 8.4%, through increments in efficiency in plant components taking into account best existing technologies and operating parameters that represent an avoidable total cost of $2′830,624 per year.Finally, a Life Cycle Analysis using the IMPACT Method 2002 + was carried out to determine environmental impacts of plant operation considering two cases: Reference Case (Case A) and the Improved One (Case B). Case B was divided in three comparative scenarios (B1, B2 and B3) which were considered to evaluate the environmental impact of plant operation and dislocation of primary energy. The results shows that reduction of avoidable exergy destruction in a steam generating cycle leads to an emission index reduction from 531 to −224 kg CO2eq/MWh, while a primary energy displacement about 3.69 kWh per unit of electric energy available was reached, using MSW as fuel in steam cycle.