Modified exergoeconomic modeling of geothermal power plants

In this study, a modified exergoeconomic model is proposed for geothermal power plants using exergy and cost accounting analyses, and a case study is in this regard presented for the Tuzla geothermal power plant system (Tuzla GPPS) in Turkey to illustrate an application of the currently modified exergoeconomic model. Tuzla GPPS has a total installed capacity of 7.5 MW and was recently put into operation. Electricity is generated using a binary cycle. In the analysis, the actual system data are used to assess the power plant system performance through both energy and exergy efficiencies, exergy losses and loss cost rates. Exergy efficiency values vary between 35% and 49% with an average exergy efficiency of 45.2%. The relations between the capital costs and the exergetic loss/destruction for the system components are studied. Six new exergetic cost parameters, e.g., the component annualized cost rate, exergy balance cost, overall unavoidable system exergy destruction/loss cost rate, overall unavoidable system exergy destruction/loss cost rate, overall unavoidable system exergy production cost rate and the overall unavoidable system exergy production cost rate are studied to provide a more comprehensive evaluation of the system.     

Performance improvement of combined cycle power plant based on the optimization of the bottom cycle and heat recuperation

Many F class gas turbine combined cycle(GTCC)power plants are built in China at present because of less emis-sion and high efficiency.It is of great interest to investigate the efficiency improvement of GTCC plant.A com-bined cycle with three-pressure reheat heat recovery steam generator(HRSG)is selected for study in this paper.In order to maximize the GTCC efficiency,the optimization of the HRSG operating parameters is performed.Theoperating parameters are determined by means of a thermodynamic analysis,i.e.the minimization of exergylosses.The influence of HRSG inlet gas temperature on the steam bottoming cycle efficiency is discussed.Theresult shows that increasing the HRSG inlet temperature has less improvement to steam cycle efficiency when itis over 590℃.Partial gas to gas recuperation in the topping cycle is studied.Joining HRSG optimization with theuse of gas to gas heat recuperation,the combined plant efficiency can rise up to 59.05% at base load.In addition,the part load performance of the GTCC power plant gets much better.The efficiency is increased by 2.11% at75% load and by 4.17% at 50% load.     

Parametric analysis and optimization for a combined power and refrigeration cycle

A combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the absorption refrigeration cycle. This combined cycle uses a binary ammonia–water mixture as the working fluid and produces both power output and refrigeration output simultaneously with only one heat source. A parametric analysis is conducted to evaluate the effects of thermodynamic parameters on the performance of the combined cycle. It is shown that heat source temperature, environment temperature, refrigeration temperature, turbine inlet pressure, turbine inlet temperature, and basic solution ammonia concentration have significant effects on the net power output, refrigeration output and exergy efficiency of the combined cycle. A parameter optimization is achieved by means of genetic algorithm to reach the maximum exergy efficiency. The optimized exergy efficiency is 43.06% under the given condition.     

Exergoeconomic analysis and optimization of combined heat and power production: A review

Exergoeconomics is also called thermoeconomics, and thermoeconomic analysis methodologies combine economic and thermodynamic analysis by applying the cost concept to exergy which accounts for the quality of energy. The main concept of thermoeconomics is the exergetic cost and it deals with cost accounting methods. This paper is a review on the exergoeconomic analysis and optimization of combined heat and power production (CHPP). A brief historical overview on the exergoeconomics analysis and optimization is given. The concept of exergetic cost and cost accounting methods are discussed. An application of relevant formulation is given using a diesel engine powered cogeneration system as an example. Main thermoeconomic methodologies available in literature are described and their advantages and disadvantages with respect to one another are compared and discussed through a well-known problem, namely CGAM. Important studies on thermoeconomic analysis and optimization of combined heat and power production are listed based on the methodology used and the type of system considered.     

Comprehensive exergetic and economic comparison of PWR and hybrid fossil fuel-PWR power plants

A typical 1000 MW Pressurized Water Reactor (PWR) nuclear power plant and two similar hybrid 1000 MW PWR plants operate with natural gas and coal fired fossil fuel superheater-economizers (Hybrid PWR-Fossil fuel plants) are compared exergetically and economically. Comparison is performed based on energetic and economic features of three systems. In order to compare system at their optimum operating point, three workable base case systems including the conventional PWR, and gas and coal fired hybrid PWR-Fossil fuel power plants considered and optimized in exergetic and exergoeconomic optimization scenarios, separately. The thermodynamic modeling of three systems is performed based on energy and exergy analyses, while an economic model is developed according to the exergoeconomic analysis and Total Revenue Requirement (TRR) method. The objective functions based on exergetic and exergoeconomic analyses are developed. The exergetic and exergoeconomic optimizations are performed using the Genetic Algorithm (GA). Energetic and economic features of exergetic and exergoeconomic optimized conventional PWR and gas and coal fired Hybrid PWR-Fossil fuel power plants are compared and discussed comprehensively.     

Exergetic and exergoeconomic optimization of a cogeneration pulp and paper mill plant including the use of a heat transformer

Energy conservation is a central concern of the current industrial world, where increasing efficient energy usage is the only way of reducing a high energy demand. In the present study the optimization of a pulp and paper mill with a cogeneration plant has been carried out. The optimization was realized with a methodology which includes exergy, exergoeconomics, thermoeconomics and pinch analysis. The proposed methodology was useful in determining not only the best plant operating conditions but also establishing the components or subsystems with the highest irreversibilities. As a result of the study, operation changes in the recovery boiler, the turbogenerator, the thermal treatment and the deaerator were realized. Due to the higher irreversibility in the actual evaporator line, a new line of evaporators was proposed. Also, an innovative heat recycling technology as to the use of heat transformers was proposed in order to reduce waste heat discharged to the atmosphere. The results obtained with the proposed methodology, which integrates the different optimization methods, allowed reaching higher efficiencies and lower operational costs than those obtained with the optimization methods working separately.     

Exergoeconomic and environmental impact analyses of a renewable energy based hydrogen production system

In this study, exergoeconomic and environmental impact analyses, through energy, exergy, and sustainability assessment methods, are performed to investigate a hybrid version renewable energy (including wind and solar) based hydrogen and electricity production system. The dead state temperatures considered here are 10 °C, 20 °C and 30 °C to undertake a parametric study. An electrolyzer and a metal hydride tank are used for hydrogen production and hydrogen storage, respectively. Also, the Proton Exchange Membrane Fuel Cell (PEMFC) and battery options are utilized for electricity generation and storage, respectively. As a result, the energy and exergy efficiencies and the sustainability index for the wind turbine are found to be higher than the ones for solar photovoltaic (PV) system. Also, the overall exergy efficiency of the system is found to be higher than the corresponding overall energy efficiency. Furthermore, for this system, it can be concluded that wind turbine with 60 gCO₂/month is more environmentally-benign than the solar PV system with 75 gCO₂/month. Finally, the total exergoeconomic parameter is found to be 0.26 W/$, when the energy loss is considered, while it is 0.41 W/$, when the total of exergy loss and destruction rates are taken into account.     

Exergy analyses and parametric optimizations for different cogeneration power plants in cement industry

The cement production is an energy intensive industry with energy typically accounting for 50–60% of the production costs. In order to recover waste heat from the preheater exhaust and clinker cooler exhaust gases in cement plant, single flash steam cycle, dual-pressure steam cycle, organic Rankine cycle (ORC) and the Kalina cycle are used for cogeneration in cement plant. The exergy analysis for each cogeneration system is examined, and a parameter optimization for each cogeneration system is achieved by means of genetic algorithm (GA) to reach the maximum exergy efficiency. The optimum performances for different cogeneration systems are compared under the same condition. The results show that the exergy losses in turbine, condenser, and heat recovery vapor generator are relatively large, and reducing the exergy losses of these components could improve the performance of the cogeneration system. Compared with other systems, the Kalina cycle could achieve the best performance in cement plant.     

A grid based multi-objective evolutionary algorithm for the optimization of power plants

There is an increasing need for optimization of energy conversion systems, in particular concerning energy consumption and efficiency to reduce their environmental impact. Usually, optimization is based on designers’ backgrounds, which are able to analyze system performances and modify appropriate operating parameters. However, if these changes aim to optimize simultaneously multiple conflicting objectives, the task becomes quite complex and the use of sophisticated tools is mandatory. This paper presents a multi-objective optimization method that permits solutions that simultaneously satisfy multiple conflicting objectives to be determined. The optimization process is carried out by using an evolutionary algorithm developed around an innovative technique that consists of partitioning the solution search space (i.e., a population of solutions) into parallel corridors. Within these corridors, “header” solutions are trapped to be then involved in a reproduction process of new populations by using genetic operators. The proposed methodology is coupled to specific power plant models that are used to optimize two different power plants: (i) a cogeneration thermal plant and (ii) an advanced steam power station. In both cases the proposed technique has shown to be very powerful, robust and reliable. Further, this methodology can be used as an effective tool to find the set of best solutions and thus providing a realistic support to the decision-making.     

Implementing of the multi-objective particle swarm optimizer and fuzzy decision-maker in exergetic, exergoeconomic and environmental optimization of a benchmark cogeneration system

Multi-objective optimization for design of a benchmark cogeneration system namely as the CGAM cogeneration system is performed. In optimization approach, Exergetic, Exergoeconomic and Environmental objectives are considered, simultaneously. In this regard, the set of Pareto optimal solutions known as the Pareto frontier is obtained using the MOPSO (multi-objective particle swarm optimizer). The exergetic efficiency as an exergetic objective is maximized while the unit cost of the system product and the cost of the environmental impact respectively as exergoeconomic and environmental objectives are minimized. Economic model which is utilized in the exergoeconomic analysis is built based on both simple model (used in original researches of the CGAM system) and the comprehensive modeling namely as TTR (total revenue requirement) method (used in sophisticated exergoeconomic analysis). Finally, a final optimal solution from optimal set of the Pareto frontier is selected using a fuzzy decision-making process based on the Bellman-Zadeh approach and results are compared with corresponding results obtained in a traditional decision-making process. Further, results are compared with the corresponding performance of the base case CGAM system and optimal designs of previous works and discussed.     

Sensitivity analysis of steam power plant-binary cycle

This paper analyses a steam power – two-stage binary cycle plant (SPP–2BCP), in which low temperature waste heat from a conventional steam power plant can be efficiently utilized to generate electricity by installing a bottoming binary cycle. The result from a previous calculation on the installation of binary cycle technology on a Steam Power Plant (SPP) with n-Pentane working fluid indicates an increase in plant efficiency of about 9%. The purpose of this study is to analyze the sensitivity of performance of the binary cycle system against variations in the SPP operational load and the condenser’s cooling water temperature. The calculation is conducted on SPP load variations of 25%, 50%, 75% and 100%, inlet turbine pressure variations of 5 bar–30 bar, and inlet turbine temperature variations of 125 °C up to 235 °C. Each of these is also analyzed with ambient cooling water temperatures of 30 °C–37 °C. The results of the analysis indicate that the performance of this binary cycle SPP degrades slightly with SPP load, turbine inlet temperature, and turbine inlet pressure variations and with cooling water variations.     

A preliminary study of the kalina power cycle in connection with a combined cycle system

Combined cycle systems have been recognized as efficient power systems in which exhaust gas from the topping cycle provides the available energy to the bottoming cycle. Since most heat sources available to the bottoming cycle are sensible-heat sources, there may be a better thermal match, and an increase thermodynamic efficiency, on reducing the entropy generation of the simple combined cycle. To increase the efficiency of the Rankine cycle working with sensible heat, two conventional methods have been proposed: one is to incorporate a multipressure boiler; the other is to implement a supercritical cycle. An alternative method is to use a multicomponent working fluid boiling at a variable temperature with a change in the liquid composition of the components, and yielding a better thermal match with the sensible-heat source than the constant temperature boiling process. The Kalina cycle is an implementation of this concept, where ammonia/water mixtures are used as the working fluid. The purpose of this study is to conduct a preliminary study of the Kalina power cycle system in connection with a combined cycle system, comparing the Kalina cycle and the Rankine cycle. This study is performed using new thermodynamic properties of ammonia/water mixtures developed by the authors.     

Exergy-based method for analyzing the composition of the electricity cost generated in gas-fired combined cycle plants

The proposed method to analyze the composition of the cost of electricity is based on the energy conversion processes and the destruction of the exergy through the several thermodynamic processes that comprise a combined cycle power plant. The method uses thermoeconomics to evaluate and allocate the cost of exergy throughout the processes, considering costs related to inputs and investment in equipment. Although the concept may be applied to any combined cycle or cogeneration plant, this work develops only the mathematical modeling for three-pressure heat recovery steam generator (HRSG) configurations and total condensation of the produced steam. It is possible to study any n×1 plant configuration (n sets of gas turbine and HRSGs associated to one steam turbine generator and condenser) with the developed model, assuming that every train operates identically and in steady state. The presented model was conceived from a complex configuration of a real power plant, over which variations may be applied in order to adapt it to a defined configuration under study [Borelli SJS. Method for the analysis of the composition of electricity costs in combined cycle thermoelectric power plants. Master in Energy Dissertation, Interdisciplinary Program of Energy, Institute of Eletro-technical and Energy, University of São Paulo, São Paulo, Brazil, 2005 (in Portuguese)]. The variations and adaptations include, for instance, use of reheat, supplementary firing and partial load operation. It is also possible to undertake sensitivity analysis on geometrical equipment parameters.     

Exergy analysis and optimization of a biomass gasification, solid oxide fuel cell and micro gas turbine hybrid system

A hybrid plant producing combined heat and power (CHP) from biomass by use of a two-stage gasification concept, solid oxide fuel cells (SOFC) and a micro gas turbine was considered for optimization. The hybrid plant represents a sustainable and efficient alternative to conventional decentralized CHP plants. A clean product gas was produced by the demonstrated two-stage gasifier, thus only simple gas conditioning was necessary prior to the SOFC stack. The plant was investigated by thermodynamic modeling combining zero-dimensional component models into complete system-level models. Energy and exergy analyses were applied. Focus in this optimization study was heat management, and the optimization efforts resulted in a substantial gain of approximately 6% in the electrical efficiency of the plant. The optimized hybrid plant produced approximately 290 kW_e at an electrical efficiency of 58.2% based on lower heating value (LHV).     

Thermodynamic analyses and optimization of a recompression N2O Brayton power cycle

Thermodynamic analyses and simultaneous optimizations of cycle pressure ratio and flow split fraction to get maximum efficiency of N₂O recompression Brayton cycle have been performed to study the effects of various operating conditions and component performances. The energetic as well as exergetic performance comparison with its counterpart recompression CO₂ cycle is presented as well. Optimization shows that the optimum minimum cycle pressure is close to pseudo-critical pressure for supercritical cycle, whereas saturation pressure corresponding to minimum cycle temperature for condensation cycle. Results show that the maximum thermal efficiency increases with decrease in minimum cycle temperature and increase in both maximum cycle pressure and temperature. Influence of turbine performance on cycle efficiency is more compared to that of compressors, HTR (high temperature recuperator) and LTR (low temperature recuperator). Comparison shows that N₂O gives better thermal efficiency (maximum deviation of 1.2%) as well as second law efficiency compared to CO₂ for studied operating conditions. Component wise irreversibility distribution shows the similar trends for both working fluids. Present study reveals that N₂O is a potential option for the recompression power cycle.     

Energy and exergy analyses of magnesium-chlorine (Mg-Cl) thermochemical cycle

In this paper, we conduct energy and exergy analyses of the magnesium-chlorine (Mg-Cl) thermochemical cycle for hydrogen production and examine the respective cycle energy and exergy efficiencies. We also undertake a parametric study to investigate how the overall cycle performance is affected by changing the reference environment temperature and operating conditions. The results show that Mg-Cl cycle offers a good potential due to its high energy and exergy efficiencies as 63.63% and 34.86%, respectively, based upon the conditions and parameters considered. In this regard, Mg-Cl cycle appears to be a promising low temperature thermochemical cycle. It may, therefore, compete with other low temperature thermochemical and hybrid cycles such as the copper–chlorine cycle.     

Exergy analysis and optimisation of waste heat recovery systems for cement plants

In the last decades, heat recovery systems have received much attention due to the increase in fuel cost and the increase in environmental issues. In this study, different heat recovery systems for a cement plant are compared in terms of electricity generation and exergy analysis. The heat sources are available in high temperature (HT) and low temperature (LT). For the HT section a dual pressure Rankine cycle, a simple dual pressure Organic Rankine Cycle (ORC) and a regenerative dual pressure ORC are compared. Also, for the LT section, a simple ORC is compared with transcritical carbon dioxide cycle. To find the best system, an optimisation algorithm is applied to all proposed cycles. The results show that for the HT section, regenerative ORC has the highest exergy efficiency and has the capability of producing nearly 7?MW electricity for a cement factory with the capacity of 3400 ton per day. The main reason for this is introducing the regenerative heat exchanger to the cycle. For the LT section, ORC showed a better performance than the CO₂ cycle. It is worth mentioning that the generated power in this section is far lower than that of the HT section and is equal to nearly 300?kW.     

A solar-driven combined cycle power plant

The main results of a feasibility study of a combined cycle electricity generation plant, driven by highly concentrated solar energy and high-temperature central receiver technology, are presented. New developments in solar tower optics, high-performance air receivers and solar-to-gas turbine interface, were incorporated into a new solar power plant concept. The new design features 100% solar operation at design point, and hybrid (solar and fuel) operation for maximum dispatchability. Software tools were developed to simulate the new system configuration, evaluate its performance and cost, and optimize its design. System evaluation and optimization were carried out for two power levels. The results show that the new system design has cost and performance advantages over other solar thermal concepts, and can be competitive against conventional fuel power plants in certain markets even without government subsidies.     

Exergy analysis of the woody biomass Stirling engine and PEM-FC combined system with exhaust heat reforming

The woody biomass Stirling engine (WB-SEG) is an external combustion engine that outputs high-temperature exhaust gases. It is necessary to improve the exergy efficiency of WB-SEG from the viewpoint of energy cascade utilization. So, a combined system that uses the exhaust heat of WB-SEG for the steam reforming of city gas and that supplies the produced reformed gas to a proton exchange membrane fuel cell (PEM-FC) is proposed. The energy flow and the exergy flow were analyzed for each WB-SEG, PEM-FC, and WB-SEG/PEM-FC combined system. Exhaust heat recovery to preheat fuel and combustion air was investigated in each system. As a result, (a) improvement of the heat exchange performance of the woody biomass combustion gas and engine is observed, (b) reduction in difference in the reaction temperature of each unit, and (c) removal of rapid temperature change of reformed gas are required in order to reduce exergy loss of the system. The exergy efficiency of the WB-SEG/PEM-FC combined system is superior to EM-FC.     

Energy and exergy analyses of hybrid photocatalytic hydrogen production reactor for CuCl cycle

The present paper concerns electrochemical, energy, exergy and exergoeconomic analyses of a hybrid photocatalytic-based hydrogen production reactor which is capable of replacing the electrolysis sub-system of the CuCl thermochemical cycle. Several operating parameters, such as current density, reactor temperature, ambient temperature and electrode distance, are varied to study their effects on the hydrogen production rate, the cost of hydrogen production and energy and exergy efficiencies. The present results show that the voltage drops across the anolyte solution (sol 1), catholyte solution (sol 2), an anode, cathode, and cation exchange membrane vary from 0.005 to 0.016 V, 0.004–0.013 V, 1.67–2.168 V, 0.18–0.22 V and 0.06–0.19 V, respectively with an increase in current density from 0.5 to 1.5 A/cm². The energy and exergy efficiencies of the hybrid photocatalytic hydrogen production reactor decrease from 5.74 to 4.54% and 5.11 to 4.04%, respectively with an increase in current density.