Cost Rate Of System Research Articles

Risk and 4E analyses and optimization of a novel solar-natural gas-driven polygeneration system based on Integration of Gas Turbine–SCO2–ORC-solar PV-PEM electrolyzer

Harnessing combustion gases is paramount to reducing the environmental impacts caused by burning fossil fuels. In this study, an innovative solar-natural gas-driven polygeneration system is proposed for the simultaneous production of power, oxygen, and hydrogen to reduce the environmental impacts of the gas turbine flue gas. The system is composed of a Brayton cycle, supercritical carbon dioxide (SCO2) cycle, organic Rankine cycle (ORC), and a polymer electrolyte membrane (PEM) electrolyzer. An integrated Brayton cycle system is placed on top of this system. In order to recover heat from the exhaust gas of the Brayton cycle, the supercritical carbon dioxide (SCO2) cycle and the organic Rankine cycle (ORC) were used to integrate with this heat source. Also, a polymer electrolyte membrane (PEM) electrolyzer has been used to produce hydrogen and oxygen to increase the ability to produce different materials from this system. In the proposed system, part of the PEM electrolyzer power is provided by solar photovoltaic (PV) collectors to further increase the system's environmental performance. Comprehensive energy, exergy, exergoeconomic, and exergoenvironmental (4 E)-analyses are performed to identify the most significant system performance parameters in terms of thermodynamics, economics, and environment. The proposed system is also examined regarding hazard and risk by two different algorithms. Investigating the probability of occurrence of a hazardous event is done with the method of numerical risk analysis, considering the probability of occurrence of three hazardous incidents with the help of thermodynamic analysis results. Moreover, the integrated polygeneration system is optimized via a multi-objective approach combining genetic algorithm and particle swarm algorithm. The results show that the overall thermal and exergy efficiencies and the total system cost rate are 40.95%, 39.49%, and 7174.36 US$/h, respectively. They also indicated that the total system environmental impact rate is 233.01 Pt/h, while the hydrogen production is equal to 114.83 kg/h. The levelized cost of electricity generation is estimated at 0.056 US$/kWh, and the payback period at 1.4 years. Finally, the performance of six different organic fluids were evaluated and the best one was selected according to the 4 E-analysis of the integrated system. The results of 4 E-analysis reveal that R11 fluid presents the best performance compared to other working fluids. The risk analysis performed with fire and explosion indices shows that the system has a low risk. Numerical risk and risk per exergy unit for the integrated system are estimated at 1.92 × 10−5 injured/year and 5.97 × 10−8 injured/year.kW, respectively.

Utilizing the multi-objective particle swarm optimization for designing a renewable multiple energy system on the basis of the parabolic trough solar collector

Today, to preserve fossil resources, mankind has to search for new ways to respond to its ever-increasing energy needs. In this study, a hybrid system of energy and the use of a parabolic trough solar collector to attract solar radiation was investigated to produce clean electricity, cooling, and hydrogen from thermodynamic and economic aspects. The designed system consisted of a parabolic trough solar collector, organic Rankine cycle, lithium-bromide absorption refrigeration cycle, and proton exchange membrane electrolysis system. The evaporator input temperature, turbine inlet temperature, solar radiation intensity, mass flow rate of collector and parabolic trough collector surface area were set as decision variables and the effect of these parameters on system performance and system exergy loss were investigated. The objective functions of this research were exergy efficiency and cost rate. In order to optimize this system, multi-objective particle swarm optimization algorithm was employed. Optimization results with particle swarm optimization indicated that the best rate of exergy efficiency is 3.12% and the system cost rate is 16.367 US$ per hour, at the same time. The system is capable of producing 15.385 kW power, 0.189 kg/day hydrogen and 56.145 kW cooling in its optimum condition. The results of sensitivity analysis showed that increasing mass flow rate at the collector, temperature at the evaporator inlet, and temperature at the turbine inlet have positive effect on the performance of the proposed system.

Energy and exergy examinations of a PVT based hybrid system for power, heating and potable water production: Transient modeling

The current study deals with thermal and economic analyses of a photovoltaic-thermal (PVT) combined system to provide power, heating, and drinking water. To this end, an intellegent energy system, including a PVT, and a reverse osmosis (RO) unit, is designed. The suggested system is examined using real data form three locations, namely Doha, Stockholm, and Tehran. The Engineering Equation Solver (EES) and TRNSYS as leading simulation software are employed to model the behavior of the developed system. The obtained results indicate that the total annual net power for systems in Tehran, Doha, and Stockholm cities were 588.09, 12556.35, and −2656.83 kWhat the mass flow rate of 40 kg/h, respectively. In addition, the cost analysis indicated that the produced fresh water cost is 0.16, 0.88, and 0.24 Euro/m3 according to the Doha, Stockholm, and Tehran weather data conditions. Calculations represent that the system cost rate for the Doha location is 19.85 Euro/h as the lowest value among considered cities. The exergy analysis results represented that the PVT modules in three areas have the highest exergy destruction rate in comparison with heat storage thanks.

Exergoeconomic assessment of the ejector-based battery thermal management system for electric and hybrid-electric vehicles

The battery is a critical component for operating electric and hybrid electric vehicles where temperature control is vital for safe and efficient operation. In this paper, the ejector-based battery thermal management system (BTMS) performance is compared to the basic BTMS from thermal and exergoeconomic perspectives. The ejector is added to mix the refrigerant streams from the cabin evaporator and battery chiller, thus delivering the mixture to the compressor with higher pressure to reduce compression power and improve system performance. The exergoeconomic study is carried out for different evaporator, chiller, and condenser temperatures and different battery thermal loads to illustrate the ejector-based system's technical and economic feasibility. Results show an optimal (minimal) total system cost rate of 0.9092 US$/h for the ejector-based system, compared to 1.0222 US$/h for the basic system (11.1% reduction). Based on the applied conditions, the total exergy destruction is found to be 1.596 kW for the ejector-based BTMS and 2.243 kW for the basic BTMS, representing a 28.8% reduction compared to the basic system.

Multi-Objective Optimization of a Geothermal Steam Turbine Combined With Reverse Osmosis and Multi-Effect Desalination for Sustainable Freshwater Production

Abstract A novel geothermal desalination system is proposed and optimized in terms of maximizing the exergy efficiency and minimizing the total cost rate of the system. The system includes a geothermal steam turbine with a flash chamber, a reverse osmosis unit, and a multi-effect distillation system. First, exergy and economic analyses of the system are performed using Engineering Equation software. Then, an artificial neural network is used to develop a mathematical function linking input design variables and objective functions for this system. Finally, a multi-objective optimization is carried out using a genetic algorithm to determine the optimum solutions. The Utopian method is used to select the favorable solution from the optimal solutions in the Pareto frontier. Also, the distributions of the values of design variables within their allowable ranges are investigated. It is found that the optimum exergy efficiency and total cost rate of the geothermal desalination system are 29.6% and 3410 $/h, respectively. Increasing the seawater salinity and decreasing the intake geothermal water temperature result in an improvement in both exergy efficiency and total cost rate of the system, while variations in the flash pressure and turbine outlet pressure lead to a conflict between the exergy efficiency and the total cost rate of the geothermal desalination system over the range of their variations.

A maintenance strategy based on system reliability considering imperfect corrective maintenance and shocks

In this study, an innovative maintenance strategy is proposed for systems subject to normal degradation and shock process. The shock process is a non-homogeneous Poisson process, and a changing factor is considered for the dependence between the normal degradation and the occurrence intensity of shocks. The system reliability is divided into three stages, based on which maintenance activities are implemented. In Stage 1 and Stage 2, when a fatal shock occurs, corrective maintenance is performed if the number of completed corrective maintenance activities does not reach the allowed limit; Otherwise, the system is replaced. Replacement is always performed once the system reliability decreases to Stage 3. Corrective maintenance is imperfect, with a perfect or minimal effect at certain probabilities. Two control variables, the allowed numbers of corrective maintenance in Stage 1 and Stage 2, are determined to minimize the expected system cost rate, by using Particle Swarm Optimization algorithm. The proposed model and method are illustrated by an example of one sliding spool. The optimal result is verified by checking the results of feasible variables. Furthermore, the proposed maintenance policy is compared with two contrastive maintenance policies. The comparison results show the necessity and effectiveness of the proposed method.

Advanced Exergy, Exergoeconomic, and Exergoenvironmental Analyses of Integrated Solar-Assisted Gasification Cycle for Producing Power and Steam from Heavy Refinery Fuels

Integrated solar-assisted gasification cycles (ISGC) have emerged as a more flexible and environmentally friendly solution for producing power, steam, and other high-valued by-products from low-cost opportunity fuels. In this light, this paper investigates a new ISGC system for converting heavy refineries fuels into power and steam utilities while enhancing energy efficiency and economic and environmental performance indicators. In this approach, a solar energy field and a two-pressure heat recovery steam generator were integrated into the ISGC system to improve overall economic and environmental plant viability. The ISGC system was modelled in MATLAB software, and the results were validated using Thermoflex software. Conventional and advanced energy, exergy, exergoeconomic, and exergoenvironmental (4E) analyses were implemented to assess the main performance parameters and identify potential system improvements. The ISGC system produced 319.92 MW of power by feeding on 15.5 kg/s of heavy refinery fuel, with a thermal efficiency of 50% and exergy efficiency of 54%. The results also revealed an investment cost of $466 million, evaluated at a system cost rate of 446 $/min and an environmental impact rate of 72,796 pts/min. The conventional and advanced 4E analyses unveiled the process economic and environmental feasibilities, particularly for oil-rich countries with high availability of solar resources.

Proposal of a new low-temperature thermodynamic cycle: 3E analysis and optimization of a solar pond integrated with fuel cell and thermoelectric generator

The present research deals with a novel hybrid system that comprises of a salinity gradient solar pond (SGSP) integrated with a proton exchange membrane fuel cell (PEMFC) and a thermoelectric generator (TEG). The key novelty of this research is the use of PEMFC waste heat to increase the performance of the low-temperature heat source (solar pond). Also, a thermoelectric generator is employed in the proposed setup for complete waste energy recovery. In this paper, the proposed system's energy, exergy, and economic (3E) performance are investigated, as well as compared with two additional systems that were modelled by excluding TEG and PEMFC to showcase the benefits of the sub-systems in the final configuration. A parametric study is also conducted to investigate the effect of significant parameters on the overall system performance. The simulation results indicated that the integrated system's net output power is 2288.8 kW at a base case operating condition, with energy and exergy efficiency of 11.26% and 13.17%, respectively, and a system cost rate of 394 $/h. In comparison to other components in the integrated system, SGSP alone accounts for 75% of total exergy degradation and has the highest investment cost rate of 66.70 $/h. Further, to achieve the best system performance, a multi-criteria optimization is performed for the suggested system with net output power, energy efficiency, exergy efficiency, and system cost rate as objective functions. Besides, the multi-criteria decision analysis (MCDA) is also carried out on the obtained Pareto front using TOPSIS decision-maker to select the best operating condition that improves the output power, energy, and exergy efficiency by 52.6%, 49.6%, and 61.8%, respectively, at the expense of 5.2% increase in the system cost rate. The current investigation demonstrates how an appropriate optimized design of an integrated energy system using SGSP, PEMFC, and TEG can improve the overall performance with reasonable cost increment.

A Comprehensive Thermoeconomic Evaluation and Multi-Criteria Optimization of a Combined MCFC/TEG System

In this study, an integrated molten carbonate fuel cell (MCFC), thermoelectric generator (TEG), and regenerator energy system has been introduced and evaluated. MCFC generates power and heating load. The exit fuel gases of the MCFC is separated into three sections: the first section is transferred to the TEG to generate more electricity, the next chunk is conducted to a regenerator to boost the productivity of the suggested plant and compensate for the regenerative destructions, and the last section enters the surrounding. Computational simulation and thermodynamic evaluation of the hybrid plant are carried out utilizing MATLAB and HYSYS software, respectively. Furthermore, a thermoeconomic analysis is performed to estimate the total cost of the product and the system cost rate. The offered system is also optimized using multi-criteria genetic algorithm optimization to enhance the exergetic efficiency while reducing the total cost of the product. The power generated by MCFC and TEG is 1247.3 W and 8.37 W, respectively. The result explicates that the provided electricity and provided efficiency of the suggested plant is 1255.67 W and 38%, respectively. Exergy inquiry outcomes betokened that, exergy destruction of the MCFC and TEG is 13,945.9 kW and 262.75 kW, respectively. Furthermore, their exergy efficiency is 68.22% and 97.31%, respectively. The impacts of other parameters like working temperature and pressure, thermal conductance, the configuration of the advantage of the materials, etc., on the thermal and exergetic performance of the suggested system are also evaluated. The optimization outcomes reveal that in the final optimum solution point, the exergetic efficiency and total cost of the product s determined at 70% and 30 USD/GJ.

Green hydrogen & electricity production via geothermal-driven multi-generation system: Thermodynamic modeling and optimization

Concerning limited sources of fossil fuels, humankind should ensue new avenues to meet its energy demands. Towards this, geothermal energy is acknowledged as a promising, reliable, safe, and clean means for this aim. In the present study, a multi-generation system driven by geothermal energy, which produces electrical power, hydrogen, oxygen, and cooling, is proposed, appraised from thermodynamic and economic standpoints. Due to today's importance of hydrogen production, pure hydrogen production is one of the primary purposes of the system here described and analyzed. The subsystems include an organic Rankine cycle (ORC), a polymer electrolyte membrane (PEM) electrolyzer, and a lithium/bromide absorption refrigeration cycle. The model is implemented in the Engineering Equation Solver software and a multi-objective optimization is performed with NSGA-II.The results indicate that the parameters mostly affecting system performance include geothermal fluid mass flow rate, geothermal fluid temperature, ORC turbines inlet temperature, and evaporator pinch-point. The highest exergy destruction is pertinent to evaporators and the PEM electrolyzer, respectively. Moreover, the results reveal that the higher the geothermal well temperature, the higher the output parameters of the system. Also, a case study was carried out to implement the proposed system in Sabalan geothermal wells; the results indicate that the system can support the energy need of 160 families during one year by producing 4,696 MWh of electrical power. Lastly, the multi-objective optimization lead to a optimal scenario with 37.85 % exergy efficiency and 15.09 USD/h system cost rate.

Exergoeconomic investigation and multi-objective optimization of different ORC configurations for waste heat recovery: A comparative study

This paper compares four different architectures of organic Rankine cycle (ORC) namely the Basic ORC, Recuperative ORC, Regenerative ORC, and Recuperative-Regenerative ORC (RR-ORC) from the exergoeconomy viewpoint. First, a parametric analysis is performed to understand the effect of evaporator temperature, condenser temperature, and pinch point temperature difference on the performance of each system configuration. Next, a multi-objective optimization is performed to optimize the performance of the four configurations using Pareto Envelope-based Selection Algorithm-II (PESA-II) with exergy efficiency and the system cost rate as the objective functions. Pareto fronts, representing the set of optimal solutions, are obtained for each configuration, and multi-criteria decision analysis is done using the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) to select the best optimal solution. Next, the exergetic and exergoeconomic performance of the four ORC configurations is evaluated at their corresponding optimal conditions in order to provide a comparative assessment. It was found that, under optimal conditions, the RR-ORC performs superiorly to the other three configurations. Compared to the Basic ORC, the net power and exergy efficiency of the RR-ORC are 16.19% and 15.33% higher, while the system cost rate is 1.68 % low. After, the RR-ORC, the Regenerative, and the Recuperative ORCs are the second and the third-best configurations. It was also found that in all four configurations, the cost rate of exergy loss accounts for approximately 60 % of the total system cost rate.

Multiobjective Optimization of a Novel Solar Tower-Based Gas Turbine-Driven Multi-Generation Plant With Energy, Exergy, Economic, and Environmental Impact Analysis

AbstractIn this study, a novel solar tower-based gas turbine-driven multi-generation plant is proposed and analyzed in detail with energy, exergy, economic, and environmental impact analysis. A multiobjective optimization is performed by incorporating all performance indicators simultaneously. The proposed plant consists of an intercooling-regenerative-reheat solarized gas turbine cycle as the primary power cycle of a multi-generation plant for the first time. Two organic Rankine cycles are used to utilize waste heat of intercooling section and exhaust of gas turbine. To produce the multi-generation products of power, cooling, industrial process heating, fresh water, floor heating, green hydrogen, domestic hot water, hot air for food drying, and greenhouse heating, power cycles are integrated with a multi-effect desalination, a double-effect absorption refrigeration cycle, an electrolyzer, a drying hot air unit, a greenhouse heater, and an industrial process heater. A rigorous parametric analysis is performed to reveal the effects of variations of decision variables on the plant performance. At the optimum conditions, energy efficiency, exergy efficiency, average unit product exergy cost, and emission savings values are determined as 57.23%, 40.7%, 0.08315 $/kWh, and 948.7 kg CO2/h, respectively. Moreover, proposed plant can produce 1962 kW power and 3.353 kg/h hydrogen in addition to other utilities with a system cost rate of 0.05134 $/s and 3226 kW exergy destruction rate.

Performance comparison of multi-objective evolutionary algorithms for exergetic and exergoenvironomic optimization of a benchmark combined heat and power system

This paper compares the Non-dominated sorting genetic algorithm-II, Pareto envelope-based selection algorithm-II, and Strength Pareto evolutionary algorithm-II, while optimizing a benchmark combined heat and power system with two conflicting objectives. The most effective algorithm is determined based on the statistical parameters evaluated from 30 runs of execution, considering the hypervolume indicator and the average computational time as the performance criteria. A comparative assessment shows that the Pareto envelope-based selection algorithm-II is superior to the other two algorithms. Further, in this study, a multi-criteria decision analysis is performed on the Pareto set obtained from the Pareto envelope-based selection algorithm-II, using the technique for order preference by similarity to an ideal solution, combined with the Entropy method. To show the advantages of multi-objective optimization, the optimal solutions are also compared with the base case, and previously published results of the benchmark problem corresponding to single-objective optimization. From the Pareto envelope-based selection algorithm-II derived optimal solutions, 15.82% increase in the exergy efficiency and 12.22% reduction in the system cost rate are achieved over the base case results. The present optimal exergy efficiency is 11.89% higher and the system cost rate is 1.9% lower than the single-objective based optimal results.

Thermoeconomic assessment of a geothermal based combined cooling, heating, and power system, integrated with a humidification-dehumidification desalination unit and an absorption heat transformer

Population growth, economic challenges, and the environmental crisis force scientists and designers to pay more attention to clean, sustainable, and renewable-based energy systems. In this regard, due to the unlimited geothermal potential in many countries, the geothermal energy resource can be an economical alternative. Therefore, in the present work, a novel multi-generation system, based on a 100% geothermal resource, for power, cooling, heating, and desalination has been designed and analyzed, thoroughly. The system is evaluated from the energy, exergy, and thermo-economic viewpoints, and providing high heating/cooling potentials while reducing the thermoeconomic indexes is the major achievement of this study. The results demonstrate that the system's net power output, freshwater production rate, heating, and cooling capacities are 78.47 kW, 92.1 m3/day, 6251 kW, and 4991 kW, respectively. Moreover, the highest amount of exergy destruction occurs in the absorption heat transformer (42%) and the absorption chiller (35%), respectively. In addition, the chiller’s absorber has the highest cost rate of exergy destruction, and the turbine and the evaporator of the organic Rankine cycle have the highest investment costs. It is found that energy and exergy efficiencies are 60.55% and 17.05%, respectively for summer, and 70.58% and 43.59%, respectively for winter, and the system's total cost rate is 44.12 $/h with the payback period of 5.63 years. Furthermore, the parametric study shows that increasing the ambient temperature and decreasing the terminal temperature difference of the heat transformer’s evaporator lead to higher exergy efficiency and lower total system cost rate.

Advanced exergoeconomic analysis with using modified productive structure analysis: An application for a real gas turbine cycle

In this study, advanced exergoeconomic analysis is performed for a gas turbine cycle located in Inchon/South Korea. In addition, an approach combining advanced exergy analysis with modified productive structure analysis is applied to the system and the results are compared. Both methods showed that higher part of exergy destruction cost rate for overall system was unavoidable. The investment cost rate of system equipment was also unavoidable. Avoidable exergy destruction cost rate was higher than unavoidable part only for gas turbine. The exergy destruction cost rates obtained with approach are considerably lower than the results obtained with the advanced exergoeconomic analysis. This situation affected the strategies developed to obtain a cost-effective system for gas turbine. Advanced exergoeconomic analysis proposed reducing the exergy destruction cost rate for gas turbine. However, for gas turbine, the approach proposed reducing the investment cost rate. The sum of exergy destruction cost rate of system equipment was higher than that of overall system in advanced exergoeconomic analysis. However, the exergy destruction cost rate of overall system was equal to the sum of exergy destruction cost rate of system equipment in the approach. Finally, it can be concluded that the results obtained with the approach were more compatible.

A Comparative Study of Metaheuristic Techniques for the Thermoenvironomic Optimization of a Gas Turbine-Based Benchmark Combined Heat and Power System

Abstract This paper presents a comparative study of four metaheuristic techniques, namely, the particle swarm optimization (PSO), genetic algorithm (GA), simulated annealing (SA), and the harmony search (HS), used in thermoenvironomic optimization of a benchmark gas turbine-based combined heat and power system known as CGAM problem. The performance comparison of the metaheuristic techniques is conducted by executing each algorithm for 30 runs to evaluate the reproducibility and stability of the optimal solutions. The study takes the exergetic, economic, and environmental factors into consideration in defining the thermoenvironomic objective function in terms of system cost rate. The thermodynamic and the economic model vis-à-vis optimization is validated by comparing the present results with previously published ones. From the optimal results, the PSO was found to be the most effective technique for thermoenvironomic optimization of the CGAM problem. Further, to highlight the benefits of optimization, the results obtained from the best method (PSO) are compared with those obtained by using the base case design variables recommended previously for the classical CGAM problem. The comparative results reveal that the system cost rate and the exergoeconomic factor of the CGAM system are reduced by 10.25% and 5.58%, respectively. Besides, the CO2 emission also reduces from 16.34 tons/h to 15.17 tons/h.

Thermoeconomic analysis and optimization of a solar micro CCHP by using TLBO algorithm for domestic application

ABSTRACTIn the present study, a micro solar Combined Cooling, Heating and Power (CCHP) system based on Organic Rankine Cycle (ORC) is thermodynamically and exergoeconomically investigated. Adding a storage tank will lead to the sustainable supply of energy for summer and winter seasons. The model of conservation of energy, conservation of mass, and conservation of linear momentum are applied in order to energy analysis, while a model based on the first and the second laws of thermodynamics are used to exergy analysis. Determining the effective parameters of the system efficiency, including turbine input pressure, turbine inlet temperature, turbine output pressure, and evaporator temperature leads to improve and optimize the system performance. The Teaching–Learning-Based Optimization (TLBO), for the first time in this paper, is employed for both single-objective and multi-objective optimizations of the system for three working fluids (R123, R134a, and R245fa). The accuracy of the proposed model is validated by data presented in three different papers. For the summer season, the values of the energy efficiency, exergy efficiency, and cost rate for R123 working fluid are calculated as 24.81%, 9.94%, and 5383$/year, respectively. The implementation of the multi-objective optimization using TLBO for R123 working fluid improves 27.85% thermal efficiency, 27.66% exergy efficiency and reduces 9.90% of the system cost rate.

Evaluation of thermal pretreatment and digestion temperature rise in a biogas fueled combined cooling, heat, and power system using exergo-economic analysis

In a municipal wastewater treatment plant, the anaerobic digesters are able to support the whole or a portion of the required fuel to offset the energy demand. Also, by implementing some techniques on municipal sewage sludge, leading to biomethane productivity enhancement, it is possible to generate surplus power. In this work, using batch biomethane potential assays, thermal pretreatment at 70 °C & 90 °C for the durations of 0.5 h, 1 h, 2 h, 3 h, and 4 h, and digestion temperature rise from the mesophilic to the thermophilic conditions have been studied to boost the biomethane productivity of the sewage sludge. Also a combined cooling, heat, and power generating plant was suggested to evaluate the techniques thermo-economically. It was shown that, compared to the non-treated mesophilic digestion of the sewage sludge, thermal pretreatment at 70 °C and 90 °C for 0.5 h, and thermophilic digestion were able to raise the biomethane productivity by 13.63%, 59.82%, and 160.8%, respectively. In this regard, the thermodynamic and the thermo- economic model of the plant was developed. The energy analysis of the system revealed that not only the studied methods, but also the mesophilic digestion of the non-treated sewage sludge result in a positive energy recovery balance in the plant. The exergo-economic analysis indicated that the major origin of cost in the system is the anaerobic digester. Implementing thermal pretreatment at 90 °C for 30 min and digestion temperature rise led to decrease in the required volume of the digester, and subsequently, in the total system cost rate. Additionally, all the applied techniques provided more fuel compared to the non-treated mesophilic case, and consequently they could reduce the levelized cost of energy in the plant. Among the studied techniques, the most effective one was digestion temperature rise which decreased the total cost rate and the levelized cost of energy by 30.31% and 41.29%, respectively.

4-E based optimal management of a SOFC-CCHP system model for residential applications

Enhancing efficiency, meeting environmental standards, and preserving fuel resources are highly important objectives in power generation systems, at a time where world is endangered by several energetic, environmental, and health crises. Thus, better designs are constantly sought to increase the performance of such systems. In this study, an environment friendly trigeneration system based on solid oxide fuel cell (SOFC) is selected and designed for domestic applications. Negligible emissions are thus recorded as the SOFC is fueled solely by hydrogen. The system is modeled following three steps: the energy simulation of residential building to determine its demands, the system’s prime mover–SOFC, and the trigeneration recovery system ensuring the maximum coverage of heating, cooling, and domestic hot water loads respectively. The system is then evaluated under the 4-E assessment criteria: energy, exergy, economy, and environment. Depending on these criteria, the system is multi-objectively optimized. Two operation strategies are adopted: off-grid following electrical load and on-grid base load operations. Optimization results show that the trigeneration system is energetically and economically superior and performs well under both strategies. The maximum energy and exergy efficiencies (65.2% and 45.77%) and minimum system cost rate (22.2cents/kWh) are obtained under on-grid base load operation.

Exergoeconomic and environmental analyses of CO2/NH3 cascade refrigeration systems equipped with different types of flash tank intercoolers

Exergoeconomic and environmental analyses are presented for two CO2/NH3 cascade refrigeration systems equipped with (1) two flash tanks and (2) a flash tank along with a flash intercooler with indirect subcooler. A comparative study is performed for the proposed systems, and optimal values of operating parameters of the system are determined that maximize the coefficient of performance (COP) and exergy efficiency and minimize the total annual cost. The operating parameters considered include condensing temperatures of NH3 in the condenser and CO2 in the cascade heat exchanger, the evaporating temperature of CO2 in the evaporator, the temperature difference in the cascade heat exchanger, the intermediate pressure of the flash tank in the CO2 low-temperature circuit, the mass flow rate ratio in the flash intercooler and the degree of superheating of the CO2 at the evaporator outlet. The total annual cost includes the capital, operating and maintenance costs and the penalty cost of GHG emission. The results show that, the total annual cost rate for system 1 is 11.2% and 11.9% lower than that for system 2 referring to thermodynamic and economic optimizations, respectively. For thermodynamic and cost optimal design condition the COP and exergy efficiency of both systems are almost the same. Finally, in order to obtain the best balance between exergy destruction cost and capital cost, the exergoeconomic factor is defined for each component of proposed systems, for cases in which the system operates at the best performance conditions.