System Exergy Research Articles

Exergy analysis of alternative configurations of biomass gasification-mixed alcohol production system via catalytic synthesis and fermentation

In-depth exergy analysis of three conceptual biomass-mixed alcohol systems using syngas platform has been studied, according to the distribution strategy of synthesis tail gas and syngas. The system configurations are base case, cascade case and parallel case. The results show that higher alcohol yield (C2+OH) is highest in base case, which is a catalytic synthesis process with synthesis tail gas recycling. Yet its exergy efficiency is lower than that of 43.8% in the hybrid conversion configuration of cascade case, of which synthesis tail gas is recycled to an additional subsystem for gas fermentation. And it has increased bioconversion of COX components (CO and CO2) in tail gas for ethanol production under moderate bioreaction condition and biomass carbon utilization ratio of 38.8% is obtained in cascade case. With the detailed exergy analysis at the levels of system, subsystem, and operation component, it highlights that the subsystems of gasification and steam & power generation contribute above 70% of total system exergy destruction, mainly from gasifier and combustor. The results of this study provide a further understanding towards bio-mixed alcohol production configuration to improve its thermodynamic performance as exergy efficiency via the hybrid conversion processes of catalytic synthesis and metabolic fermentation pathway.

Investigation of energy, exergy, and economy of co-generation system of solar electricity and cooling using linear parabolic collector for a data center

At present, data centers serve as primary providers of information technology infrastructure, thereby consuming a significant quantity of electrical energy. Considering the growing trend of heightened electricity consumption and heat generation within data centers, leading to increased expenses, coupled with mounting attention to energy preservation and ecological preservation, the deployment of electricity generation systems and solar cooling technologies presents an alluring solution. The present study introduces an integrated system powered by a parabolic collector, an organic Rankine cycle, and a two-effect absorption chiller. A solar parabolic collector system was evaluated as a potential means of providing thermal energy to the power generation and cooling systems. The methodology employed in this study involved the utilization of an Organic Rankine Cycle (ORC) to produce electricity while the cooling generation process was carried out using an absorption cycle. The optimization of both the absorption system and the ORC was performed utilizing the temperature data derived from the parabolic collector. Ultimately, a contrastive analysis was conducted to explore the correlation between cooling storage and electrical power depending on the degree of the parabolic collector. The collective expenditure for electricity and cooling system maintenance within the data center amounts to 1202392 USD. Based on an analysis of the associated expenses for electricity and cooling, the Payback Period (PBP) is determined to be 3.407 years, whereas the Levelized Cost of Energy (LCOE) stands at 0.05815 $ per kilowatt hour. The proposed system underwent an annual assessment encompassing analysis of performance, as well as considerations of the pertinent factors of energy, economics, and the environment. The findings indicate that the utilization of this system can mitigate the release of 1421 metric tons of carbon dioxide annually. The suggested amalgamated framework that couples solar power generation and cooling system holds immense promise in the realm of sustainable development. This optimism stems from the notable advantages of energy conservation, prospective economic benefits, and eco-friendliness that the system embodies.

Exergy and environmental analysis of oscillating wave energy converter hybrid with other renewable energy resources: A case study

ABSTRACT In order to evaluate the hybrid renewable configurations in diverse applications, this inquiry tries to propose a novel decision-making procedure. The open-source WEC dynamics simulator, exergetic assessment, and Hybrid Optimization Model for Electric Renewables Pro software are integrated. In this innovative method, the exergy of the component is calculated using MATLAB software. Technical analysis for the goal of rural electrification is examined in this work. Thus, several integrated energy systems are technically researched. This study deals with the exergy, environmental, and exergoenvironmental analyses of the hybrid renewable energy system, to assess its performance and environmental impact when operating on Siri Island. In the photovoltaic solar panels, wind turbines, wave energy converters, diesel generators, and batteries set up, the total exergy efficiency and exergy destruction rate were 18.4% and 7.24 106 kWh/year, respectively. Additionally, it was discovered that the wave energy converter was responsible for 5% of the total energy wasted. Photovoltaic solar panels, wind turbines, and wave energy converters all have mean annual exergy efficiencies calculated to be 11.7%, 13.1%, and 20.8%, respectively. Environmental and exergoenvironmental analyses illustrate that the off-grid scenario decreases CO2 emission by 95% compared to the on-grid scenario and utilizing diesel generators increases the exergy stability factor of the energy system. The suggested decision-making procedure can be a potent and reliable instrument for analyzing any hybrid renewable arrangement from a technological standpoint.

Biomass co-fired combined cycle with hydrogen production via proton exchange membrane electrolysis and waste heat recovery: Thermodynamic assessment

The application of renewable energy sources such as biomass for power generation is becoming increasingly important, as is hydrogen production for use as a fuel or for other purposes. A novel combined cycle based on a gas turbine is proposed for a fixed power output of 10 MW using biomass as a co-fuel with natural gas, and integrated with hydrogen production via a proton-exchange membrane (PEM) electrolyzer. This combined cycle consists of two bottoming cycles: organic Rankine and steam Rankine. These allocate the generated power to the electrolyzer for hydrogen production. Energy and exergy analyses of the proposed cycle are performed to better understand it and its behavior. The produced hydrogen can be either sold in the marketplace for a variety of uses or injected into the combustion chamber. These two possibilities are considered two layouts of the system, for purposes of comparison. Hydrogen injection reduces natural gas consumption by around 33% and lowers CO2 emissions by around 11%, in addition to other environmental benefits, while hydrogen injection lowers the system exergy destruction and loss rates by around 2% and 19%, respectively. System energy and exergy efficiencies of around 58% and 52% respectively are determined for the hydrogen production layout and of 51% and 45% respectively are determined for the hydrogen injection layout.

Experimental investigation on RORC system performance for recovering LNG cold energy under heating and cooling capacities variations

A large amount of available cold energy exists in Liquid Natural Gas (LNG). While it is not efficiently utilized and is released into the ocean. To efficiently utilize LNG cold energy, a power generation test bench based on the organic Rankine cycle has been established with R290 as the working fluid, a scroll expander as the thermal conversion device, and a multi-stream heat exchanger as the high-efficiency heat exchange device. The low-grade heat source and LNG are simulated by electrically heated hot water and −198 °C liquid nitrogen. The following are the main conclusions: (1) Heating and cooling capacities have different degrees of influence on system performance, and there is a matching relationship between the two capacities; (2) system maximum thermal efficiency and cold energy utilization rate are 6.13% and 12.04%, respectively. The comprehensive performance reaches the highest when the ratio of heating-to-cooling capacity is 1.96; (3) among the main components in the system, the increasing proportion of expander exergy destruction plays a positive role in improving the total system exergy efficiency. While the increasing proportion of heat exchangers exergy destruction has a negative influence in system exergy efficiency.

Conventional and advanced exergy and exergoeconomic analysis of a novel multi-fueled cogeneration system with desalination

This work presents the economic, advanced thermodynamic, and exergoeconomic studies of a system for producing power and freshwater. The proposed system comprises a multi-effect desalination system, an organic Rankine cycle, a centrifuge, and process heaters by utilizing a mix of bagasse and municipal solid waste as primary fuels. The amounts of avoidable, unavoidable, endogenous, and exogenous shares of exergy destruction for the cycle’s components have been calculated by an advanced exergy method. For the integrated cycle, the electricity generation and freshwater productions are 36.6 MW and 7000 m3 per day, respectively. The costs of electricity production and water desalination are 2.6 US$/GJ and 4.6 US$/m3. To present an improved understanding of the system operation, an advanced exergy study is conducted on each involved component of the system at their operating conditions to identify the share of the avoidable irreversibilities. For the integrated system, 85% of the total exergy destruction is calculated to be unavoidable and just 15% of the estimated amount is avoidable. In this case, the opportunity to enhance the system’s operation is roughly limited. Additionally, 76% of the exergy destruction is endogenous, and the remaining belongs to exogenous exergy destruction.

Qualitative, energy and economic analysis of forced convective solar drying of tomatoes slices

Solar drying is a thermodynamic method of controlling moisture content that uses a non-depletable free renewable energy source. This work discussed a qualitative and economic analysis of a forced convection drying system for tomato slices in an agricultural greenhouse under Tunisian climatic conditions. Then an exergy and energy balances of the drying system were presented. The tomato’s thin layer was dried in a mixed convection solar drier for 79 h and 127 h in a conventional sun drying process from an initial moisture content of 20.27 to 0.36 kg H2O per kg of dry matter. Energy and exergy analyses of the tomato’s drying process were investigated. It was also discovered that the exergy efficiency of the drying chamber ranged from 16.44 percent to 70.47 percent. The overall efficiency of the greenhouse and the solar air collector were calculated to be 42 percent and 62 percent, respectively. To determine the quality of fresh and dried tomatoes, color analysis was performed. A cost-benefit analysis was performed, and the payback period for the system was estimated to be 1.82 years.

Performance enhancement of Photovoltaic-thermal system using hybrid tubes: An assessment of thermodynamic and thermohydraulic efficiencies

In this study, a novel hybrid tube configuration is proposed to develop an efficient photovoltaic thermal system. Subsequently, the impact of different working fluids is investigated, including ternary nanofluids and phase-change material slurries. The performance of the system is optimized by varying the geometrical parameters and working fluids. The combined impact of the hybrid tube and the working fluid is numerically investigated. Thermal, exergy, electrical, and hydraulic efficiencies of the PVT system are analyzed to ascertain the feasibility of the proposed configuration and working fluid. Compared to straight and wavy tubes, the proposed hybrid tube configuration achieves a more uniform and reduced temperature distribution. The optimised hybrid tube configuration performs significantly better than the straight tube configuration, with an improvement of 8.01%, 5.5%, and 32% in primary, exergy, and thermohydraulic efficiencies, respectively. However, compared to wavy tubes, marginally better performance is achieved coupled with a 30% reduction in pressure drop. Moreover, compared to water, the primary, exergy, and thermohydraulic efficiencies are improved by 6.3%, 1.1%, and 20%, respectively, when the optimized hybrid tube is used in conjunction with the proposed slurry. Thus, the hybrid tube design and novel slurry demonstrate high potential for photovoltaic thermal system applications.

Decarbonization performances of a transcritical CO2 heat pump for building heating: A case study

An experimental transcritical CO2 heat pump system was implemented in the severely cold region, Harbin (China), and the energy and exergy performances as affected by the expansion valve opening were compared and the environmental and economic performances of CB (Coal-fired Boiler), GB (Gas-fired Boiler), EB (Electric Boiler), and HP (Heat Pump) were analyzed. The results showed that the system COP decreased by around 0.2 when the expansion valve opening was increased from 60% to 80% with the highest system COP of 2.40. The system exergy destruction and exergy efficiency increased from 5.12 and 33% to 5.61 kW and 37% when an increase in the expansion valve opening from 60% to 80%, respectively. The CO2 and pollutants emissions of HP were 52% ∼ 92% lower than CB and EB. The life-cycle cost of HP for a 15-year working period was the lowest (36.57 × 104 CNY) and it was 84%, 77%, and 39% of CB, GB, and EB, respectively. The results revealed that the transcritical CO2 heat pump system has better environmental and economic performances than CB, GB, and EB, its emissions were 52% lower than CB and EB and its life-cycle cost was only 39% of EB.

Design of a multigenerational energy system with hydrogen production for clean cement plants

The article aims to provide the design and analysis of a new and unique multigeneration system. This multigeneration system primarily produces methane/natural gas by extracting carbon dioxide from the cement production processes through calcium looping. The hydrogen gas generated in the system was synthesized through polymer electrolyte membrane electrolysis, supported by hydroelectric power. After this, a portion of the hydrogen produced from the system is reacted with carbon dioxide to produce methane. The other useful outputs of the system include electricity, space heating, and domestic hot water. The implemented system design also harnesses other renewable resources, such as solar energy, to enhance other aspects of the design. The system achieved hydrogen and methane production rates of 0.01028 kgs-1 and 0.02045 kgs-1, respectively. Additionally, the system's exergy and energy efficiencies are obtained to be 44.5% and 77.5%, respectively. Furthermore, the energy and exergy heating coefficient of performance values are found to be 1 and 0.5624, respectively.

Study on fuel cold energy utilization of large ammonia powered ship

Taking large ammonia powered container ship as the research object, a set of liquid ammonia cold energy cascade comprehensive utilization system is designed. The system mainly includes low temperature cargo hold system, high temperature cargo hold system and marine air conditioning system. Aspen HYSYS software is used to simulate the system scheme. Based on the utilization rate of cold energy in the low temperature cargo hold system, the maximum of liquid ammonia flow fraction under different operating conditions was determined, and the cold energy utilization system exergy efficiency was calculated. In the 75% working condition of the ship, when the flow fraction was 40%, the whole cold energy utilization system exergy efficiency was 34.42%, in this way, the effective utilization of liquid ammonia cold energy is realized.

Exergy, economic, and climate performance evaluation of an efficient clean cogeneration system driven by low-temperature waste-heat

Currently, waste-heat emissions from industrial processes contribute significantly to climate change. Effective recovery of waste-heat is crucial for saving energy and mitigating global warming. In this study, we proposed a clean, low energy consuming cooling and power generation system driven by waste-heat at 130 °C, and compared it to the existing system. For comparing the two systems, R1234yf was used as the refrigerant, which was the best-performing refrigerant among the seven HFOs evaluated. The performance, economic efficiency, and environmental impact of the two systems were comprehensively compared based on exergy, economic, and climate performance assessments. The results showed that exergy efficiency of the proposed system was 85.46%, which was 10.08% higher than that of the original system. The equipment investment cost by the proposed system decreased by 21.17% (from $3.36 × 105 to $2.65 × 105), as compared to the original system. Moreover, the annual operating and total costs were reduced by 24.59% and 21.28%, respectively, compared to the original system. In terms of climate performance assessment, the proposed system reduced emissions by 1.18 × 107 kg CO2eq. Additionally, the proposed system reduced 1.33 × 107 kg CO2eq compared to the original system that produced 1.50 × 106 kg CO2eq. Taken together, the proposed system achieved higher exergy efficiency while reducing costs and environmental impact. This was due to the heat integration technology used to achieve energy cascading, low-energy ejectors instead of energy-intensive compressors, and the use of environmentally friendly HFO as refrigerant. In future, the proposed system could provide a reference for efficient recovery of low-temperature industrial waste-heat and development of energy systems adapted to current trends in clean industrial production.

Thermal analysis of the hybrid HVAC unit using interpolant function

This study aims to cover the thermodynamic aspect of a geothermal site using the Hermite interpolant. The energy distribution, determination of the system exergy and the energy ratio are some of the factors investigated thoroughly. The steady flow energy equation was used to determine the design parameters related to the hybrid heating, ventilation, and air condition (HVAC) system. For the underground heat exchanger, it was assumed that the heat capacity ratio, R, was small in magnitude. The energy ratio estimated in the corridor of the lecture hall increased by 17% as compared to the hall area. The exergy destruction of the system was estimated to be 25%, whereas the maximum exergy gain computed at the secondary side of the geothermal unit, followed by the second fan coil, the first fan coil, and the radiator. The calculated heating rate was found to be 25.273% lower than the required sensible heat gain. The installed unit could attain the maximum energy ratio of 4.031 if the convective losses across the building material are minimised.

Energy, Exergy, and Economic (3E) Analysis of Boil-Off Gas Re-Liquefaction Systems Using LNG Cold Energy for LNG-Fueled Ships

Liquefied natural gas (LNG)-fueled ships have the effect of reducing most pollutants, which is advantageous for responding to strict regulations. Because boil-off gas (BOG) is generated in the LNG storage tank of an LNG-fueled ship, a BOG re-liquefaction system is required. The representative systems for LNG-fueled ships were proposed by Kwak and Shen, but their exergy efficiencies were only 19.6% and 24.9%, respectively. To improve the system, this paper proposes novel BOG re-liquefaction systems combined with the fuel gas supply system. The systems utilize LNG cold energy in the BOG stream and N2 reverse Brayton cycle, respectively. The proposed systems were simulated using a commercial program and were optimized using a genetic algorithm. The results of energy, exergy, and economic (3E) analyses performed for comprehensive evaluation of the proposed system show that the system in which LNG cold energy is applied to the BOG stream has the best performance. Specific energy consumption, exergy efficiency, and total annual costs of this system were improved by up to 78.6%, 69.2%, and 68.2%, respectively, compared to those of the existing systems. The overwhelmingly superior system is expected to greatly contribute to the improvement of the BOG re-liquefaction system for LNG-fueled ships.

Multi-Objective Optimization of Graded Thermal Storage System for Direct Steam Generation with Dish Concentrators

A single sensible thermal storage system has the disadvantage of poor system efficiency, and a sensible-latent graded thermal storage system can effectively solve this problem. Moreover, the graded thermal storage system has the virtue of being adjustable, which can be adapted to many power generation systems. Therefore, this paper first analyzes the influence factors of the graded thermal storage system’s exergy and thermal efficiency. Subsequently, each factor’s significance was analyzed using the response surface method, and the prediction model for system exergy efficiency and cost was established using the support vector machine method. Finally, the second-generation nondominated sorting genetic algorithm (NSGA-II) was used to globally optimize the graded thermal storage system’s exergy efficiency and cost by Matlab software. As a result, the exergy efficiency was increased by 11.01%, and the cost was reduced by RMB 5.85 million. In general, the effect of multi-objective optimization is obvious.

Energy, exergy, economic and environmental analysis of a regasification system integrating simple ORC and LNG open power cycle in floating storage regasification units

A thermodynamic, economic and environmental analysis of a regasification system including a simple Organic Rankine Cycle (ORC) and an Open Organic Rankine Cycle (OC) to utilise the liquefied natural gas (LNG) cold energy is carried out in the present paper. The proposed system, called ORC-OC, uses ambient seawater as heat source (open loop) and is implemented on board a Floating Storage Regasification Unit (FSRU) in order to reduce the greenhouse gas (GHG) emissions associated with the electricity generation plant, i.e., dual fuel (DF) engines. Regarding the ORC working fluids analysed, an ethane/propane zeotropic mixture is applied. The ORC-OC is compared with the simple ORC architecture, giving the first one better energy (lower specific energy consumption), exergy (higher exergy efficiency) and environmental (lower CO2e emissions) results. When compared to the regasification systems installed on board, the ORC-OC system reduces the specific energy consumption by 86.99 % and increases the exergy efficiency by 17.82 % with respect to the most efficient conventional system installed on FSRUs (direct seawater regasification system), leading to a reduction of CO2e emissions of more than 80 %. In addition, the ORC-OC system is more cost-effective than conventional regasification systems when the LNG price is above 6,508 USD/MMBtu.

Thermodynamic Analysis and Optimization of the Micro-CCHP System with a Biomass Heat Source

In this article, new multiple-production systems based on the micro-combined cooling, heating and power (CCHP) cycle with biomass heat sources are presented. In this proposed system, absorption refrigeration cycle subsystems and a water softener system have been used to increase the efficiency of the basic cycle and reduce waste. Comprehensive thermodynamic modeling was carried out on the proposed system. The validation of subsystems and the optimization of the system via the genetic algorithm method was carried out using Engineering Equation Solver (EES) software. The results show that among the components of the system, the dehumidifier has the highest exergy destruction. The effect of the parameters of evaporator temperature 1, ammonia concentration, absorber temperature, heater temperature difference, generator 1 pressure and heat source temperature on the performance of the system was determined. Based on the parametric study, as the temperature of evaporator 1 increases, the energy efficiency of the system increases. The maximum values of the energy efficiency and exergy of the whole system in the range of heat source temperatures between 740 and 750 K are equal to 74.2% and 47.7%. The energy and exergy efficiencies of the system in the basic mode are equal to 70.68% and 44.32%, respectively, and in the optimization mode with the MOOD mode, they are 87.91 and 49.3, respectively.

Performance evaluation of a hybrid thermoelectric generator and flat plate solar collector system in a semi-arid climate

This study investigates the performance of a hybrid system that combined thermoelectric generators (TEG) with a solar flat plate collector system (SFPC) to turn more renewable energy into useable energy under normal operating and environmental conditions. A multi-month case study was first time conducted to explore the performance of SFPC with and without TEGs under the cold climatic conditions of Abha, Saudi Arabia. The result demonstrates that the heat losses from the rear surface of the SFPC's absorber plate were effectively utilized by TEGs, thereby decreasing overall heat losses and increasing the SFPC's overall thermal efficiency. Further, it was found that adding TEGs at the rear surface of SFPC's absorber plate improves thermal efficiency and exergy efficiency by 8.4% and 1.3%, respectively. The hybrid TEG-SPFC system can turn waste heat into useable electricity, with a peak power output of 2.2 W at midday. Maximum power was generated around midday, when the temperature differential between the upper and lower layers of TEGs was greatest. In addition, it was noticed that the thermal efficiency of the SFPC diminishes when the inlet water temperature rises. A hybrid TEG-SFPC system's exergy efficiency depends on ambient temperature variation and solar irradiance.

Environmental analysis and optimization of fuel cells integrated with organic rankine cycle using zeotropic mixture

The use of fuel cell (FC) is considered one of the methods of producing electricity with relatively high efficiency. So, it has attracted many researchers' attention to develop and improve its performance. The present study deals with the technical-economic optimal design of a hybrid power generation system based on a Proton Exchange Membrane (PEM) FC combined with an Organic Rankine Cycle (ORC). ORC is used to recover the generated heat in PEM FC. The decision variables of this study include FC operating pressure and temperature, current density, FC area, the quantity of FC, and operating parameters of the ORC system, including HRVG PPTD, condenser PPTD, and refrigerant mass fraction in zeotropic mixture. In this study, three zeotropic mixtures, including R11-R245fa, R11-R123, and R123-R245fa, are studied as the working fluid of the ORC system. The objective functions considered to be optimized are the system's exergy efficiency and total cost rate (TCR). Finally, it is observed that the highest exergy efficiency is obtained using the zeotropic mixture R11-R245fa with a value of 54.15%, and the lowest TCR is obtained with the mixture R11-R123 with a value of 0.65 $/s. Zeotropic mixture R11-R123 has the exergoenvironmental index, environmental damage effectiveness index, and exergy stability factor of 0.5506, 1.277, and 0.4750, respectively.

Thermodynamic analysis of SOFC–CCHP system based on municipal sludge plasma gasification with carbon capture

To solve the environmental problems associated with municipal sludge incineration and landfilling, a combined cooling, heating, and power (CCHP) system integrating plasma gasification, solid oxide fuel cell (SOFC), gas turbine, supercritical carbon dioxide (S-CO2) cycle, and double-effect absorption refrigeration cycle (ARC) is proposed. Additionally, the CO2 generated in the system is captured to reduce the environmental impact. Energy, exergy, and sensitivity analyses of the developed system are conducted. Key parameters such as the SOFC temperature, SOFC pressure, and fuel utilization rate affecting the system performance are studied. The results show that net electrical efficiencies of the SOFC and the system are 41.96 % and 50.00 %, respectively. The exergy efficiency and comprehensive energy utilization rate of the system are 47.04 % and 87.59 %, respectively. The system can generate a power of 175.03 kW, cooling of 45.70 kW, and heating of 85.82 kW under the design conditions, accounting for 67.46 %, 21.23 %, and 11.31 % total energy output of system, respectively. The three main sources of exergy destruction of the system are the plasma gasification, SOFC, and supercritical CO2 cycle subsystems, accounting for 36.8 %, 12.2 %, and 10.7 % exergy destruction, respectively. The system performs the best when the SOFC temperature is 910 °C and the fuel utilization rate is between 0.85 and 0.90. The SOFC pressure has little effect on the system performance. In addition, the carbon capture rate of the system can reach 97.50 %. The CCHP system has high thermodynamic efficiency and hence can convert municipal sludge efficiently into clean energy; therefore, this study provides a new concept for resource treatment of urban sludge.