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Structural modifications play a crucial role in enhancing the sustainability of natural gas power plants owing to their significant contribution to greenhouse gas emissions and irreversibility factors. One primary solution is using waste heat recovery systems integrated with these power plants, producing different products. Furthermore, integrating renewable energy resources into the entire system within a co-feed framework may be a viable method for further enhancements. The current study focuses on a novel heat integration process combined with a natural gas power plant, which uses geothermal energy as an auxiliary energy source. The newly designed system encompasses a gas turbine cycle, two modified geothermal power plants, a water electrolyzer unit, and a methanol synthesis unit. The process is simulated utilizing the Aspen HYSYS software, and to evaluate its viability, analyses are performed pertaining to energy, exergy, environment, and economics. Furthermore, a comprehensive parametric analysis is conducted on the primary performance indicators. The simulation results show that the process's energy, exergy, and electrical efficiencies equal 53.85%, 47.30%, and 40.26%, respectively. The environmental evaluation demonstrates that the specific carbon dioxide emissions associated with the total energy produced and the sum of power and heating are 0.27 kg/kWh and 0.294 kg/kWh, respectively. From the economic aspect, the total unit cost of the products and the cost of energy of the system are 20.69 $/GJ and 0.086 $/kWh, respectively. Also, total annual cost, investment cost, and net present value of 222.81 M$, 1010.64 M$, and 1220.57 M$, respectively. • Proposal of a novel polygeneration system using natural gas and geothermal energy. • Producing electricity, hot water, fresh water, and methanol simultaneously. • Use of Aspen HYSYS for simulation and multi-aspect study from 4E perspective. • Total exergy efficiency and total unit cost of the product are 47.3% and 20.69 /GJ. • The CO 2 emission based on the total energy produced equals 0.27 kg CO 2 / kWh. [ABSTRACT FROM AUTHOR]

The fuzzy proposed system is a multigeneration system capable of producing different multi-products including power, cooling, heating, and fresh water. The energy required for the operation of the system is geothermal renewable energy, which is a very serious issue in the green transient. To analyze the function of the suggested subsystems, such thermodynamic rules have been considered as an important tool. Another important parameter that is evaluated is the entransy parameter that evaluates the function of thermodynamic cycles. In this study, the rate of G ˙ l o s s is achieved at 699699 KW.K. The results of the suggested system demonstrate the rate of electrical power is 226.1 KW, the rate of cooling load is 24.5 KW, freshwater production is 0.235 kg/s, and the heating load is 418.5 KW of the system output products. In addition, energy efficiency and exergy are calculated as 59.51% and 51.5%, respectively. To provide an optimal performance state of the system, a multi-objective optimization method with a genetic algorithm method is used to optimize the objective functions ( G ˙ l o s s and η I I ) of Matlab software. In this research, it has been attempted to reduce entransy and increase exergy efficiency using algorithm genetic (GA). [ABSTRACT FROM AUTHOR]

Performance data from a geothermal power plant that uses a dry-type working fluid (n-Pentane) was evaluated. The experimental working conditions of the geothermal power plant were recorded. By using these recorded data the structural and parametrical optimisation of the plant was applied. As a structural modification, the probable performance of the plant was scrutinised by considering the integration of a superheater into the plant. For both present and structurally optimised cases, parametric optimisations were made as an operational modification. During the analyses, the high and low pressure Organic Rankine Cycles (ORCs) of the energy converter plant were optimised for varying turbine inlet temperatures and pressures. After comprehensive analyses, it was concluded that superheating the working fluid by structural modification (superheater integration) had a negative effect on the system performance. On the other hand, together with parametric analyses, a considerable improvement in system performance was obtained. For all cases and parametric values, the system was also evaluated in terms of environmental effect. [ABSTRACT FROM AUTHOR]

Different studies highlighted the environmental impacts of geothermal power plants (GPPs), especially in the operational phase. Primary data are essential for reliable environmental assessments, but these are not available when considering alternative configurations. Rigorous simulation can offer such a degree of information, representing also a tool for a digital twin technology transition. Considering a GPP in Tuscany, Italy, four alternatives configurations are simulated in UniSim Design®, performing accurate refinements to the thermodynamic model to properly estimate the behavior of different pollutants (Hg, H 2 S, NH 3 , and SO 2) among the various unit operations. The configurations alternate direct-contact and surface condensers as well as wet and dry towers as cooling systems, while a fifth one adopts an organic Rankine cycle. The actual plant model has been reconciliated with data collected during two different monitoring campaigns. Performance analysis shows a trade-off: the lowest pollutant emissions are obtained using the dry tower generating less net energy (20.17 MWe and 20.83 MWe), instead, adopting surface condenser and wet tower, 22.26 MWe are produced with NH 3 emissions almost 3 times the measured ones. The CO 2 and CH 4 amount in the well fluid is not abated in any configurations and therefore their emissions are the same among them. • Operational environmental assessments of geothermal power plants need primary data. • Modeling a geothermal power plant with UniSim Design® and custom thermodynamic package. • Data reconciliation with a power plant in Italy under different seasonal conditions. • Use of direct-contact or surface condensers and wet or dry towers for cooling or ORC. • Net power production and pollutants emissions compared for the various plant set-ups. [ABSTRACT FROM AUTHOR]

• Power flow diagram and actual operating data of a geothermal plant were used to simulate. • System's thermal analyses were performed using performance outputs obtained from simulation. • Thermal behaviour of system by examining the effects of turbine inlet parameters was analysed. • Results' variation trend when nearing/withdrawing from optimum parameters was scrutinized. • Lower/upper range of system's working parameters for safe operation was presented to manufacturers and users. In geothermal power plants with dual pressure cycle technology, the optimisation of turbine inlet parameters depending on the pressure and temperature of the geothermal fluid is a very important parameter affecting the production capacity of such plants. In combined systems, where the second stage (low pressure) is fed by the first stage (high pressure), failure to determine the appropriate operating conditions leads to the problem of not achieving optimum performance. In this context, the study aims to develop a methodology for predicting the performance of the system, based on the geothermal water temperatures entering and leaving the heat exchangers, in order to clearly see the effect of the operations carried out within the scope of optimising the turbine inlet parameters on the system behaviour. In this study, EBSILON® Professional software developed by Steag GbmH was utilised to simulate the determined correlations. The effect of the heat exchangers (preheater, evaporator and superheater) in both stage-1 and stage-2 on the temperature profiles and heat gains were determined at 10–17 bar, 126.5–165 °C for Turbine-1 and 4–8 bar, 84–135 °C for Turbine-2. Optimum turbine inlet temperature and pressure have been determined for maximum heat input and exergy efficiency. In this context, each cycle in the Energy Converter System (ECS) was first simulated by changing the turbine input parameters and then thermal analyses of the system were performed using the performance outputs obtained from the simulation software. For turbine-1, it is observed that heat transfer decreases in stage-1 with increasing pressure and temperature, while heat transfer increases in stage-2 fed from stage-1. After 12 bar and 136 °C, the heat transfer of the ECS started to increase and the maximum heat transfer amount was reached at 17 bar and 155 °C. However, it was determined that the exergy efficiency of the ECS started to decrease after 15 bar and 147.6 °C. For turbine-2, it was found that the increase in pressure and temperature decreases the ECS heat transfer but increases the exergy efficiency. As a result of numerous iterations with EBSILON® Professional software, a maximum exergy efficiency of 50.53% was achieved in turbine-1 (15 bar, 147.6 °C) and turbine-2 (8 bar, 114 °C). [ABSTRACT FROM AUTHOR]

This paper introduces an innovative integration of geothermal and solar energies to assess the production of power, cooling, and freshwater. These products are achieved through a modified absorption refrigeration cycle, a modified organic Rankine cycle, and humidification-dehumidification subsystems driven by a flash-binary configuration. The performance of the setup is evaluated using both thermodynamic and economic approaches. Additionally, three multi-objective optimizations are applied to determine a suitable optimal state. The approaches reveal net power, cooling, and freshwater production rates of 807.3 kW, 1345 kW, and 7.96 kg/s, respectively. The designed setup requires a total capital investment cost of $2,490,310 and has a payback period of 5.76 years in the base mode. The study highlights that the temperature difference of superheating significantly impacts the total capital investment cost and exergy efficiency, while the cooling production is mainly influenced by the evaporator temperature. The final optimal state achieved an exergy efficiency of 15.98 % and a net present value of $1,999,864. Overall, this innovative hybrid geothermal-solar setup demonstrates a viable solution for sustainable energy production, combining power generation, cooling, and freshwater production in a single integrated system. The findings support the system's potential for real-world applications, particularly in regions with suitable geothermal and solar resources. • Designing a novel multi-generation driven by solar and geothermal energies. • Considering the energy, exergy, and economic analyses for the performance evaluation. • Producing 807.7 kW net power, 1592 kW cooling, and 8.8 kg/s freshwater. • Achieving 15.98 % of exergy efficiency with a payback period of 5.36 years. [ABSTRACT FROM AUTHOR]

• CO 2 is the dominant gas in the gas phase of geothermal fluids. However, after a geothermal power plant is commissioned, reservoir pressure and CO 2 gas concentration tend to decrease. • In most geothermal power plants, hydrogen sulfide gas is more remarkable than carbon dioxide gas because of its impact on human and environmental health. • Although there is a high amount of CO 2 (99.8–9 %) in Kızıldere geothermal system, the amount of H 2 S (0.02–0.04 %) is relatively lower than other geothermal power plants in Türkiye. • The main focal points of this study are the reduction of H 2 S and CO 2 gasses. • A test study is conducted to reduce the amount of H 2 S in the non-condensable gas in the geothermal fluid using chemical washing methods. Geothermal power plants are among the most important renewable energy power plants owing to their high-capacity factors and integrated utilization possibilities. Currently, these power plants utilize geothermal fluid to generate electricity. Although their emissions are lower than those of conventional power plants, gasses such as CO 2 and H 2 S are released into the air from the cooling towers, particularly in flash-type geothermal power plants To reduce the emission of CO 2 gas released from geothermal power plants, reinjection studies have mainly been carried out around the world. These types of studies require extensive analysis of underground fracture systems, detailed geosciences, and the reservoir studies. However, these studies are considered risky and expensive for most plant operators because possible changes in underground fracture systems may affect the productivity of geothermal production zones. In terms of the environmental impact, hydrogen sulfide is a more harmful gas than CO 2. Effective H 2 S removal methods cannot be widely used, except in areas with extremely high concentrations, because they commonly incur significant costs for plant operators. Effective H 2 S removal methods are not widely available except for geothermal sites with high concentrations. The fact that local limit values can be exceeded in geothermal power plants with relatively low H 2 S concentrations, such as geothermal power plants in Türkiye, pushes plant operators to find new low-cost solutions due to high operation costs. For this reason, a treatment method that can be applied at every site and whose cost is not too high has not yet been put forward. However, NaOH is used for this purpose in geothermal fields such as steam-dominated Geyser field to increase the pH values in geothermal wells, which has been producing for a long time. In this study, field tests were carried out with five different chemicals and pure water to examine the reduction of non-condensable gasses in a geothermal power plant located in the Kızıldere (Denizli, Türkiye) geothermal field, one of the most important geothermal fields in the world. According to this, the capture of these gasses is technically possible using chemical methods, with a performance of up to 70 % observed in CO 2 gas capture. However, although it is possible to capture 70 % of non-condensable gasses with such chemical methods, the consumable cost of the operation is quite high. [ABSTRACT FROM AUTHOR]

Binary geothermal power plants (GPP) always attract researchers' attention as they are renewable-energy operated, low-temperature, high-performance, environmentally-friendly, and baseload power plants. In addition, they need to be monitored, controlled and optimized due to their complex structure and functioning. This article presents the application of the Simulated Annealing (SA) algorithm for the thermodynamic performance optimization on the verified thermodynamic model of the SINEM GPP operating in Aydın, Turkey. This algorithm is also compared to the Gravitational Search Algorithm (GSA). By using these methods, 17 optimization parameters in the plant model are simultaneously optimized for maximum exergy efficiency. Study results show that the exergy analysis, gravitational search algorithm and simulated annealing algorithm respectively determined the exergy efficiency of the plant as 14.48%, 30.62%, and 38.49%. The SA algorithm has a better performance compared to the other two methods. System components such as condensers, vaporizers, and pumps are made more efficient using the SA algorithm. In addition, the most effective parameters of the plant are evaporator pressure differences and the mass flow of ORC's working fluid. By using GSA and SA algorithm, the gross electricity generation in the power plant can be increased by 2.11 MW and 3.15 MW, respectively. While GSA uses the procedure of reducing the amount of component exergy destruction, the SA algorithm uses the procedure of reducing the amount of electricity spent in the operation of the plant equipment. The rate of non-condensing gas (NCG) outlet, which is harmful to the environment, can be reduced by using SA algorithm. In this way, a power plant can be operated more economically and in a more environmentally friendly manner. • It is used a simulated annealing (SA) algorithm for maximizing performance of a real GPP. • A comprehensive research and real-world constraints are conducted for design and off-design. • Simulation programs (SA and GSA) are compared with each other for a parametric study. • The gross electricity generation in GPP is increased by 2.11 MW and 3.15 MW with GSA and SA. • The release of non-condensing gas (NCG) can be reduced by using SA algorithm. [ABSTRACT FROM AUTHOR]

The Afyon Geothermal Power Plant is modeled using the Multi-Layer Feed-Forward Artificial Neural Network. The 100 × 8 data set obtained from the real Binary Geothermal Power Plant is divided into two parts: 80 × 8 training data and 20 × 8 test data. Geothermal Power Plant system modeling has been performed numerically on Matlab with three inputs and five outputs. There are ten neurons in the hidden layer in the Artificial Neural Network-based system, and the logarithmic sigmoid transfer function is used as the transfer function in each neuron. The neurons in the output layer have the purelin transfer function. As a result of the training process, the 3.06 × 10E-2 mean square error value was obtained from the ANN-based Binary Geothermal Power Plant system. The main point of the study is the optimization of the binary geothermal power plant. The genetic algorithm method with Artificial Neural Network-based is used for this purpose. The results obtained from the outputs of the Artificial Neural Network-based Binary Geothermal Power Plant system are presented. The plant's geothermal water temperature and mass flow rates are 110 °C and 150 kg/s. Energy and exergy efficiencies of the plant are calculated as 10.4% and 29.7%. The optimized simple payback period and exergy cost of the electricity generated in the plant is calculated as 2.87 years and 0.0176 $/kWh, respectively. Schematic configuration of Afyon Geothermal Power Plant. Image 1 • Modelling of Afyon Geothermal Power Plant is performed numerically based on ANN. • Geothermal temperature and mass flow rate of the plant are 110 °C, and 150 kg/s. • Energy and exergy efficiencies of the plant are calculated as 10.4%, and 29.7%. • The exergetic cost of the electricity from the plant is calculated as 0.0176 $/kWh. [ABSTRACT FROM AUTHOR]

• A new geothermal-thermoelectric hybrid system is controlled using intelligent models. • Intelligent models predict real-time power generation under electrical load. • Intelligent models are used to model energy production from waste geothermal fluid. • The outputs of intelligent models are important for sustainable energy management. This study focuses on the most effective use of energy resources, which is the main goal of sustainable energy systems. The first contribution of the research is to ensure that the waste and geothermal fluids generated during the geothermal energy production process are evaluated in the most efficient way and reused for energy production. For this purpose, a geothermal-thermoelectric hybrid experimental system has been designed to produce electrical energy through heat exchange and how waste thermal energy could be reused in this process has been examined. Experimental tests have been performed under electrical load and in the presence of real-time uncertainties such as temperature changes, thermal conductivity, electrical noise, heat losses and random variations in thermal interaction. The second main contribution of the study is to predict and evaluate different power generation performances in the Thermoelectric Generator (TEG) system, which is affected by the mentioned experimental limitations based on artificial intelligence models. In addition, the optimal prediction performance of artificial intelligence models using hyper-parameter optimization has also been compared. Experimental results have shown that intelligent models are a successful tool for energy prediction in geothermal power generation. As a result of the hyper-parameter optimization, each model is improved by ∼5 % to ∼30 % in various error metrics. However, it was observed that the decision tree-based learning techniques resulted in ∼46 % to ∼96 % less inaccurate predictions on various error metrics compared to other methods. Power production predictions obtained using intelligent models have been obtained with 98.7 % accuracy with LightGBM learning algorithms. Most of the models used to classify different hot and cold water levels exhibit very high classification performance. The results show the successful integration of artificial intelligence models in effectively utilizing waste thermal energy and adopting a sustainable approach to energy production. [ABSTRACT FROM AUTHOR]

• It is focused on exergoenvironmental (ExEn) analysis for a GPP and its equipment. • EIs of equipment, exergy destruction (ExD) and pollution formation (PF) are assessed. • The relative difference, ExEn factor and total EI are found as 122%, 2.5% and 2285 Pts/h. • 98% of total EI is cause of ExD related-EI and the rest is for PF related-EI. • EI of electricity equals to 0.108 Pts/kWh, higher than that of Europe, due to NCG. In this study, a geothermal power plant endowed with actual operational conditions and its equipment are evaluated using exergoenvironmental analysis from the perspective of environmental impact. Environmental impacts related to equipment (including construction, operation/maintenance and disposal), exergy destruction and pollution formation are taken into consideration. Moreover, effects of ambient temperature and brine input temperature with respect to environmental impact factors of the system are also discussed. Though this analysis, relative difference of specific environmental impacts, exergoenvironmental factor and total environmental impact are determined as 122% and 2.5% and 2285 Pts/h, respectively. The results of the study show that 98% of total environmental impact for the geothermal power plant is the cause of exergy destruction of the equipment involved. For this reason, improvement of exergetic efficiency for equipment should be considered rather than construction, operation/maintenance and disposal changes of system equipment. Hence, it is probably possible to have a higher capacity plant by getting a better condenser performance, as well as strengthening the vaporizers and the pumps. Besides, approximately 44 Pts/h of non-condensable gas-NCG (CO 2 mostly) released from vaporizer to atmosphere caused environmental impact of the system to be measured as high environmental impact value of electricity equal to 0.108 Pts/kWh. In conclusion, conditions during which the ambient temperature decreases and brine input temperature increases, the system's environmental impacts concurrently decrease. This study is expected to serve as a guidework for researchers involved in environmental impacts of geothermal power plants and improvement of the plants in terms of environmental impact. [ABSTRACT FROM AUTHOR]

Geothermal energy has significant potential to reduce fossil fuel consumptions and environmental impacts. To improve energy conversion efficiency of geothermal energy systems, numerous systems designs have been proposed and their optimization sought. At this point, it is worth reviewing current developed geothermal energy systems because understanding configurations and principles of basic and state-of-the-art technologies is important for developing advanced energy systems. A comprehensive review of the geothermal energy systems is carried out from the perspective of systems analysis, design, and optimization. Results illustrate that limited sets of parameters have been considered in most studies on design and optimization, though these studies provide great insight into specific designs. However, all influential factors have to be fully considered for practical applications. This study identifies and organizes influential factors for geothermal energy systems. In addition, critical analyses of studies on systems design and optimization are performed to determine limitations of current studies. As polygeneration systems produce various energy products (electricity, heat, and/or cooling), it might play key roles to maximize utilization of geothermal energy. Especially, polygeneration systems with binary technology, which can effectively produce electricity from moderate temperature geothermal resources, have significant potentials to enhance the overall performance. In this regard, the energy production strategy and technology selection are of significant importance to meet electric, heating, and cooling loads efficiently. To fill the knowledge gaps and to maximize geothermal energy utilization, this review proposes state-of-the-art multi-scale modeling and optimization framework. • Polygeneration systems are key for maximizing geothermal energy utilization. • Binary systems have great potentials to improve overall efficiency of polygeneration. • Multi-scale framework can play vital roles to find feasible and sustainable solutions. [ABSTRACT FROM AUTHOR]

• Energy and exergy efficiencies of the plant are 12.88% and 48.20%, respectively. • Efficiencies are higher than other plants with similar specific geofluid exergies. • Improvement potential analysis for each component in the cycle is evaluated. • Turbine-I has the highest exergy destruction ratio of 201,776 $/yr. • SUCP of the plant increases over 40% as the ambient temperature varies 30 °C. The thermodynamic and thermoeconomic performances of a 21 MW geothermal power plant with air-cooled two level binary type organic Rankine cycle was numerically investigated based on its design and operating data. The investigated plant is the Sinem Geothermal Power Plant in Germencik, Aydin, Turkey. The paper provides a detailed comparison of the exergetic performance of this plant with other eight similar type of plant units, which make use of geothermal resources with similar specific exergies. Results indicate that the exergetic efficiency of the Sinem Geothermal Power Plant is the highest with 48.2% and the others vary between 9.6% and 42.7%. This result is mainly related to the exergy losses due to suppression of heat transfer in this plant, via low temperature brine reinjection, small temperature difference in the heat exchangers and high efficiencies of the individual components. First and second law efficiencies, as well as the exergy losses and improvement potentials of each component in the plant are also calculated. In air-cooled geothermal power plants, since ambient temperature is a critical parameter for the plant performance, both thermal and economic analysis of the plant is performed based on variation in ambient air temperature. Specifically, thermoeconomic analysis of the plant is evaluated to determine the exergoeconomic factor, the relative cost difference and the sum unit cost of the product (SUCP) of the plant. The effect of ambient temperature on the SUCP of the power plant, power generation, energy and exergy efficiencies are also examined in the present study. The results showed that; when the ambient temperature increases from 5 °C to 35 °C the reduction in power generation is 6.8 MW, energy efficiency decreases from 13.7% to 9.2% while exergy efficiency decreases from 54.9% to 36.7 and SUCP of the plant increases from nearly 230 $/GJ to 330 $/GJ. [ABSTRACT FROM AUTHOR]

Highlights • It is focused on improving thermodynamic performance for a binary geothermal power plant. • An accurate modelled system simulating a real operating system is developed. • It is used the gravitational search algorithm to maximize its exergy efficiency. • System exergy efficiency can be maximized from 14% to 31% using gravitational search algorithm. • Thus, a more compatible operating strategy between system components is ensured. Abstract The limited energy resources globally, low efficiency of renewable energies, complicated and costly energy conversion systems and environmental pollution have significantly increased scholar's interest in innovative and efficient systems and their improvement studies. Therefore, it is necessary to increase the efficiency of power generation systems used in geothermal sources of medium or low enthalpy. This study aims to improve the thermodynamic performance of an existing binary geothermal system with organic Rankine cycle and its system components while trying to comprehend the physical events/changes during these improvement processes. A model has been developed that simulates the system completely and accurately. Seventeen system parameters which were considered as crucial to maximize the exergy efficiency of the system like turbine inlet, condenser temperature and so on, are optimized using a gravitational search algorithm. The results of the study show that the exergy efficiency of the system is 14% and thus it can be maximized to 31% with optimization. During the optimization process, the pressure of work fluid on the evaporator line is increased and thus 2.1 MW more power is produced compared to normal power production. The condenser, with the highest exergy destruction in the system, has performance improvements of 75%. As a result, with the optimization process, a more compatible operating strategy between system components is ensured. This will allow the system and its components to run for longer and without failures. [ABSTRACT FROM AUTHOR]

Finding an appropriate solution to find stable and continuous green energy is one of the significant problems of scientists in the field of renewable energy. In this study, a mixed type of system implementing two geothermal gas turbine energy combined using an innovative method, the suggested system continuously merits productivity of different production. Also, it implements renewable energies to provide the required power to generate conducts which is considered important in the green transient of governments. In addition, thermodynamic rules were used to analyze the suggested system. The results obtained from analysis and equations in the EES software show that power production and thermal load and cooling equal 1432.3kw, 937.9kw and 128.8kw, respectively. the total energy and exergy efficiency is calculated at 58.31 % and 42.17 %. The system's return on investment is calculated in twenty years, with the electricity price of 0.15$/GJ, 6.02 years and with the fuel price of C fuel = 21$/GJ, 7.15 years, and the system reaches profitability. to improve system function, the multiple optimized genetic algorithm is used. The objective function in optimizing the system is exergy efficiency and total cost, which is considered optimization MATLAB software, which means a decrease of total cost and an increase of exergy efficiency. [ABSTRACT FROM AUTHOR]

Abstract Optimizing a complex system/problem under real working conditions with optimization methods means ensuring that they operate more efficiently, economical, and eco-friendly. For this purpose, in order to maximize the exergy efficiency of a thermodynamic model of a real operated geothermal power plant (GPP), two optimization methods, namely Gravitational Search Algorithm (GSA) and Artificial Bee Colony (ABC), have been comparatively evaluated in this study. The selected thermodynamic model is a problem that is highly complex, non-linear and unsolvable through mathematical methods. In order to solve the problem, 17 optimization parameters have been selected on the model. In addition, the selected parameters have been divided into 11 groups according to the system equipment specifications to reduce time loss. The results of the study reported that GSA and ABC maximized the exergy efficiency of the real system from 14.52% to 26.31% and 23.92% respectively. The effects of the optimized parameters on the model are observed, and it has been verified by GPP operators, engineers and researchers that no contrariety to logic and engineering discipline existed. Hence, the results of GSA method for the engineering problem addressed in this study are better than those of ABC method and they responded in a much shorter time. The most effective group in both methods is the G3 group related to the turbines. Besides, the most effective optimization parameters on the system performance are the pressure differences in evaporators and mass flow of the geothermal fluid. Highlights • It is focused on comparative evaluation of two optimization methods, GSA and ABC. • Thermodynamic model of a geothermal power plant (REAL) is chosen as a complex and non-linear engineering problem. • To solve the problem, 17 optimization parameters in 11 groups have been selected on the model. • Maximum exergy efficiency is found as 26.31% and 23.92% for the GSA and ABC, respectively. • Results of GSA are better than those of ABC and most effective group is one related to turbines. [ABSTRACT FROM AUTHOR]

The present study highlights the attempt of incorporating geothermal power plant (GTPP), dish-Stirling solar thermal system (DSTS) and high voltage direct current transmission (HVDC) link, with the conventional thermal system, in automatic generation control of an interconnected power system under deregulated environment. Appropriate generation rate constraints are provided in thermal systems. A new fractional order (FO) cascade controller named as FO proportional-integral-FO proportional-integral-derivative (FOPI-FOPID) is proposed as secondary controller and its performance is compared with the commonly used classical controllers. A stochastic algorithm, Sine Cosine Algorithm (SCA) is used to optimize the controller gains and other parameters. Analyses of the dynamic responses reveal the superiority of FOPI-FOPID over the others in terms of settling time, peak deviation and magnitude of oscillation. Performance index comparison is carried out and integral squared error is selected. The effect of GTPP, DSTS and HVDC link have been examined separately and the responses disclose that integration of HVDC link to the combined system having both GTPP and DSTS along with thermal leads to better dynamics. Sensitivity analysis of SCA optimized FOPI-FOPID controller parameters obtained at nominal Disco Participation Matrix (DPM) validate that they are healthy enough and need not be optimized for change in DPMs. [ABSTRACT FROM AUTHOR]

This contribution presents the optimization of parallel distribution between electricity and heat production for a geothermal plant. The geothermal fluid is split into two streams, one used for an Organic Rankine Cycle (ORC) system, and the other for a District Heating Network (DHN). The superstructure to be used for the optimization problem includes the ORC components, one of which is an optional internal heat exchanger which allows exchange between the outlet streams of the turbine and the pump. Each of the components' characteristic dimensions (used in the installation cost) is an optimization variable. The operating cost of the ORC is proportional to the installation cost. The superstructure also includes the DHN topology constituted by a definite consumer and optional consumers. A Mixed Integer Non-Linear Programming (MINLP) optimization problem is formulated and solved using the GAMS software. The strategy used to overcome the critical point of the initialization of the MINLP problem is presented. It consists in dividing the general problem into sub-problems which are solved successively. Three different academic study cases are compared to a reference case. The results validate the stability and the robustness of this optimization tool. A sensitivity analysis is performed in geothermal source conditions. All these results highlight the relevance of the simultaneous approach. [ABSTRACT FROM AUTHOR]

A technical, financial, economic and environmental analysis of geothermal power plant developments in the Ecuadorian context was analysed by RETScreen-International Geothermal Project Model. Three different scenarios were considered. Scenario I and II considered incentives of 132.1 USD/MWh for electricity generation and grants of 3 million USD. Scenario III considered the geothermal project with an electricity export price of 49.3 USD/MWh. Scenario III was further divided into IIIA and IIIB case studies. Scenario IIIA considered a 3 million USD grant while Scenario IIIB considered an income of 8.9 USD/MWh for selling heat in direct applications. Modelling results showed that binary power cycle was the most suitable geothermal technology to produce electricity along with aquaculture and greenhouse heating for direct use applications in all scenarios. Financial analyses showed that the debt payment would be 5.36 million USD/year under in Scenario I and III. The corresponding values for Scenario II was 7.06 million USD/year. Net Present Value was positive for all studied scenarios except for Scenario IIIA. The equity paybacks were 3.2, 3.7, 16 and 5.6 years for Scenario I, Scenario II, Scenario IIIA and Scenario IIIB, respectively. Overall, Scenario II was identified as the most feasible project due to positive NPV with short payback period. Interestingly, Scenario IIIB could become financially attractive by selling heat for direct applications. Direct applications, public incentives and clean funding mechanisms are essential for the success of geothermal energy projects in the Ecuadorian context. The total initial investment for a 22 MW geothermal power plant was 114.3 million USD (at 2017 costs). Economic analysis showed an annual savings of 24.3 million USD by avoiding fossil fuel electricity generation. More than 184,000 tCO 2 eq. could be avoided annually. Thus, greenhouse emissions avoided by using geothermal energy would bring out environmental benefits and improve the socio-economic benefits in communities. [ABSTRACT FROM AUTHOR]

In this study, the thermodynamic performance of a binary geothermal power plant (GPP) is comparatively evaluated using the exergy analysis and optimization method. Thus, in addition to routes to improve the thermodynamic performance of the system, the thermodynamic relationships between the system components and improvement performances of the components are determined. With this aim, the Sinem GPP located in Aydın province in Turkey as a real system is selected. All data from the system are collected and a numerical model simulating the real system is developed. On the developed model, the conventional and advanced exergy analyses for exergy analysis and the artificial bee colony (ABC) method for optimization process are performed. The results of the study show that total exergy efficiencies of the conventional exergy analysis, advanced exergy analysis and artificial bee colony are determined as 39.1%, 43.1% and 42.8%, respectively. The exergy efficiency obtained from advanced exergy analysis is higher compared to the other two methods. This is due to the fact that theoretical and unavoidable operation assumptions in advanced exergy analysis are arbitrary as a single value depending on the decision maker. However, decision variables in the ABC method are within certain constraints chosen by the decision maker. It is better to select constraint limits instead of an arbitrary single value selection. Therefore, its arbitrary values should be confirmed with any optimization method. Additionally, the highest exergy destruction identified in the three methods is occurred in heat exchangers as the condenser and vaporizer. [ABSTRACT FROM AUTHOR]

This study aims at proposing a possible alternative solution to reactivate and maximize the energy potential of the Aluto Langano power plant in Ethiopia by performing thermodynamic analysis of the system for different working conditions and parameters. Detailed data from the plant has been collected. Modeling of the plant has been performed by using Matlab. A detailed sensitivity analysis has been performed by using different operating parameters (i.e. condenser pressure and working fluids), and a new production well has been also been introduced to upgrade the performance of the plant. The original plant used isopentane as a working fluid, and had a gross output of 4.648 MW under the current condition of the production wells. The simulation results indicate that the power outputs will increase for both n -butane and isobutane by 4.782 MW and 4.889 MW respectively. Therefore using butane as a working fluid would make the power plant more efficient and economical. [ABSTRACT FROM AUTHOR]

Geothermal power plants emit high amount of hydrogen sulfide (H 2 S). The presence of H 2 S in the air, water, soils and vegetation is one of the main environmental concerns for geothermal fields. There is an increasing interest in developing suitable methods and technologies to produce hydrogen from H 2 S as promising alternative solution for energy requirements. In the present study, the AMIS technology is the invention of a proprietary technology (AMIS ® - acronym for “Abatement of Mercury and Hydrogen Sulfide” in Italian language) for the abatement of hydrogen sulphide and mercury emission, is primarily employed to produce hydrogen from H 2 S. A proton exchange membrane (PEM) electrolyzer operates at 150 °C with gaseous H 2 S sulfur dimer in the anode compartment and hydrogen gas in the cathode compartment. Thermodynamic calculations of electrolysis process are made and parametric studies are undertaken by changing several parameters of the process. Also, energy and exergy efficiencies of the process are calculated as % 27.8 and % 57.1 at 150 °C inlet temperature of H 2 S, respectively. [ABSTRACT FROM AUTHOR]

This study investigated the utilization of available excess steam by the Kamojang geothermal power plant, which, owing to the vapor-domination of the steam, utilizes a dry steam cycle. A model of the system was validated against actual Kamojang Unit-2 data and found to produce accurate results within a low discrepancy level (<5% error). The modeled performance of the proposed system was obtained through optimization of the non-condensable gases (NCGs) gas removal system (GRS) based on heat balance calculations and assuming content of NCGs in the working fluid based on real operational data. To optimize the model, five GRS configurations were investigated: one-stage steam ejector, two-stage steam ejector, one-stage liquid ring vacuum pump (LRVP), two-stage LRVP, and hybrid system (ejector plus LRVP). To set constraints on the optimization, the allowable condenser pressure was defined based on the cooling water temperature and the maximum temperature difference. Under the best design configuration (a one-stage LRVP), the proposed plant generated a gross electric power of 15.9 MW with a parasitic power consumption of 755.2 kW. The proposed system to convert unused discharge steam into electricity suggests that its installation will result in an increase of the Kamojang geothermal power plant capacity. [ABSTRACT FROM AUTHOR]

In geothermal power generation, ammonia-water (NH 3 H 2 O) mixtures are considered as working fluids in order to improve efficiency from low enthalpy heat sources. During the evaporation process, the NH 3 H 2 O working pair as zeotropic working fluid has the advantage to evaporate not isothermal temperature but over a temperature glide to adapt better to the heat source temperature profile. By today, there is a lack of performance data from operational generation units available in literature that can be used for scientific works based on computational calculations to compare with. In this paper the data logs from the evaporation process of the geothermal power plant are analyzed in order to review the evaporator's performance. Data had been gathered for a period of 5 years and three key performance parameters were defined: pressure drop, vapor fraction and heat transmission capacity. The main parameters that influence the performance are the temperatures, pressures and flow rates. It turned out, that the NH 3 mass fraction plays only a minor role within the evaporation process. [ABSTRACT FROM AUTHOR]

We present the study of electricity generation by utilization of the Kalina cycle system (KCS) as a bottoming cycle in the Wayang Windu geothermal power plant. The KCS converts the thermal energy from the waste brine discharged to the earth crust as a heat source. Based on the brine temperature condition, KCS 11 is the most suitable system among others owing to excellent performance at low to mid-regime temperatures. The constraints of the investigation are focused on the consideration of minimum silica saturation index (SSI) standard of the brine, owing to high SiO 2 content. The system is optimized based on the most optimum ammonia-water mass ratio of the working fluid. The system can generate 1660.30 kW of electricity from 48 kg/s of unused brine with 13.20% thermal efficiency while maintaining the proper SSI standard. Owing to the nearly zero cost of heat production from the brine, this system can support the electrification of Wayang Windu geothermal power plant. [ABSTRACT FROM AUTHOR]

The exergy analysis method constitutes an alternative but very important technique for the evaluation of the utilization level of thermal plants as well for the comparison of different conversion processes. The loss of exergy provides a figure of merit for the inefficiencies of a process and a measure of the quality of the different forms of energy in relation to given environmental conditions. In this paper, data from an experimental geothermal drill in the Greek Island of Nisyros, located in the south of the Aegean Sea, have been used in order to estimate the maximum available work and the efficiency of a potential power plant. Different methods for estimating the exergy term are used and several types of conversion efficiencies have been calculated in order to obtain a more complemented view of the analysis. Overall, a system exergetic efficiency of 41% and a thermal one of 12.8% have been resulted supporting technical feasibility of the proposed geothermal plant. [ABSTRACT FROM AUTHOR]

A multi-generation geothermal-based energy system is proposed to convert geothermal renewable power into fuel gas and other valuable products such as electricity, cooling, and freshwater. The system is analyzed and optimized from a thermo-economic perspective. This system is constituted of a flash-binary geothermal power plant integrated into an Organic Rankine Cycle, a double-effect Li/Br absorption refrigeration cycle, a multi-stage flash desalination plant (MSF), and a solid oxide electrolyzer cell (SOEC) combined with a Sabatier methanation reactor. The steam leaving the steam turbine are utilized by the SOEC to generate hydrogen, which is used in the Sabatier reactor to hydrogenate CO 2 to produce methane. Cooling and Freshwater are respectively produced by the refrigeration cycle and MSF plant that are driven by the steam extracted from the intermediate stages of the steam turbine. The system can produce 22.9 g/s gas fuel with a lower heating value (LHV) of 28453 kJ/kg, of which 53% is methane, 554.4 kW net power, 3715 kW cooling, and 41.35 kg/s freshwater. The SOEC produces hydrogen with a rate of 6.52 g/s; the power demanded to generate this amount of hydrogen is 884.47 kW. The system's payback period is 7.3 years (regarding the tax). According to the optimization results, compared to baseline design conditions, the payback period and LHV of the generated fuel respectively decline by 18.7% and 35%, and the net output power enhances by 88% at optimum mode when power and payback period are objective functions. • Environmental conservation by geothermal PtG technique for CO 2 methanation. • Double-effect Li/Br absorption refrigeration cycle was used for cooling production. • Solid Oxide Electrolyzer Cell (SOEC) applied for hydrogen generation. • Applying Dusty Gas Model to simulate mass transfer inside the SOEC electrodes. • Thermo-economic optimization via non-dominated sorting genetic algorithm II. [ABSTRACT FROM AUTHOR]

A novel carbon capture and storage system integrated with geothermal energy was proposed to reduce energy consumption in the post-combustion CO 2 capture (PCC) process. Geothermal energy at medium temperature was used to provide the heat required for solvent regeneration. A technical and economic assessment was conducted based on a 300 MWe coal-fired power plant. Additionally, the integrated system was also compared with a stand-alone geothermal power (GP) plant to evaluate individual advantages. Both an enhanced geothermal system (EGS) and a hot sedimentary aquifer (HSA) reservoir were selected to identify the effect of geological properties and heat characteristics on system performance. The results indicated that the geothermal-assisted post-combustion CO 2 capture (GPCC) plant exhibited better performance than the PCC plant. The net plant average efficiency increased 5.56% and 4.42% in the EGS scenario and HSA scenario, respectively. Furthermore, the net incremental geothermal efficiency obtained corresponded to 21.34% and 20.35% in the EGS scenario and HSA scenario, respectively. The economic assessment indicated that the GPCC systems in both the EGS scenario and HSA scenario had lower marginal cost of electricity (70.84 $/MWh and 101.06 $/MWh) when compared with that of the stand-alone GP systems (151.09 $/MWh and 101.95 $/MWh). [ABSTRACT FROM AUTHOR]

The tendencies of the development of geothermal energy technologies on the base of utilizing geothermal fluid of different temperature are studied. It is shown that in recent years there are an increasing number of countries where the growth of installed capacity of geothermal power plants is mainly due to the construction of power units with a binary cycle. It allows to expand the resource base of geothermal energy through the development of low-temperature geothermal sources, the total capacity of which exceeds the one of high-temperature resources. It is noted that the low-temperature geothermal sources are widely available and in fact can be utilized almost anywhere in the world. The analysis of the scale and geography of the application binary energy technologies for the development of geothermal resources are shown. The features of the use of organic working fluids in binary power plants are described. The basic principles of the optimal working fluid selection for binary plant are explained. The results of numerical modeling of the working fluid selection on the performance of binary power plants are presented. It is shown, that use of the hydrogen-oxygen steam generator in combined power plants can increase the effectiveness of geothermal utilization. [ABSTRACT FROM AUTHOR]

In this paper, the design of an Organic Rankine Cycle (ORC) is optimized by means of numerical simulations. The systems of interest are the subcritical and transcritical thermodynamic cycles. Optimizations are performed with the objective of determining the design that maximizes the specific power output. The design variables include the operating parameters (pressures, mass flow rates), and the best working fluid is determined by comparing the performance of 36 refrigerants. Optimization runs are performed for a wide range of geofluid temperatures (from 80 to 180 °C), and for a wide range of condenser temperature (from 0.1 to 50 °C). The results are summarized in charts that may be used as efficient tools for designing optimal geothermal power plants. Finally, an approximate analysis allowed to develop a new correlation for predicting the maximal specific power output of an ORC. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to quantitatively evaluate thermodynamic performance of a geothermal power plant (GPP) from potential for improvement point of view. Thus, sources of inefficiency and irreversibilities can be determined through exergy analysis. The advanced exergy analysis is more appropriate to determine real potential for thermodynamic improvements of the system by splitting exergy destruction into unavoidable and avoidable portions. The performance critical components and the potential for exergy efficiency improvement of a GPP were determined by means of the advanced exergy analysis. This plant is the Bereket GPP in Denizli/Turkey as a current operating system. The results show that the avoidable portion of exergy destruction in all components except for the turbines is higher than the unavoidable value. Therefore, much can be made to lessen the irreversibilities for components of the Bereket GPP. The total exergy efficiency of the system is found to be 9.60%. Its efficiency can be increased up to 15.40% by making improvements in the overall components. Although the heat exchangers had lower exergy and modified exergy efficiencies, their exergy improvement potentials were high. Finally, in the plant, the old technology is believed to be one of the main reasons for low efficiencies. [ABSTRACT FROM AUTHOR]

Pakistan is among the naturally gifted countries that are rich in conventional and renewable energy resources. Despite the massive potential of energy resources, Pakistan is still an energy deficient country and have to import petroleum products to barely accomplish its energy demand. Geothermal energy is still one of the unexplored energy resources for electric power generation in Pakistan. Pakistan can overcome the energy shortage to a significant level by harnessing renewable energy resources, such as, geothermal energy. Majority of the geothermal hot springs and mud volcanoes exists within the seismic belt of Pakistan. Therefore, the country has viable geothermal energy manifestations. Several hot springs in Gilgit and Hunza region are originated due to the collision of Indian Plate with Eurasian Plate. Similarly, various geothermal reservoirs exist in Northeast to Southeast narrow belt along Indus basin margin. The survey discusses the current energy crisis in Pakistan and addresses the role of geothermal energy for the economic development of Pakistan. We served the manifestation and geographies of geologically active zones of Pakistan, like fault lines, plate tectonics, belt, and tectonic thrust, cleanest, base load, reliable, renewable, and sustainable geothermal energy resources. In our work, the hot springs and mud volcanoes of geologically active areas in maps are enlisted in Tables with potential features. The schemes used for extraction of geothermal energy for electric power generation are also investigated. The global electric power production from geothermal energy is visualized and discussed. Moreover, the suitable moderate temperature Binary Cycle Geothermal Power Plant for electric power generation in Pakistan is also described in detail. Furthermore, geothermal plants are experimentally summarized in different case studies. Finally the performance of geothermal and conventional thermal plants is critically analysed. [ABSTRACT FROM AUTHOR]

Geothermal power plants use geothermal fluids as a resource and create waste residuals as part of the power generation process. Both the geofluid resource and waste stream are considered produced fluids. The chemical and physical nature of produced fluids can have a major impact on the geothermal power industry and influence the feasibility of power development, exploration approaches, plant design, operating practices, and reuse/disposal of residuals. In general, produced fluids include anything that comes out of a geothermal field and must subsequently be managed on the surface. These fluids vary greatly, depending on the reservoir being harnessed, plant design, and life cycle stage in which the fluid exists, but generally include water and fluids used to drill wells, fluids used to stimulate wells in enhanced geothermal systems, and makeup and/or cooling water used during operation of a power plant. Additional geothermal-related produced fluids include many substances that are similar to waste streams from the oil and gas industry, such as scale, flash tank solids, precipitated solids from brine treatment, hydrogen sulfide, and cooling-tower-related waste. This review paper aims to provide baseline knowledge on specific technologies and technology areas associated with geothermal power production. Specifically, this research focused on management techniques related to fluids produced and used during the operational stage of a power plant, the vast majority of which are employed in the generation of electricity. The general characteristics of produced fluids are discussed. Constituents of interest that tend to drive the selection of treatment technologies are described, including total dissolved solids, noncondensable gases, scale, corrosion, silicon dioxide, metal sulfides, calcium carbonate, metals, and naturally occurring radioactive material. Management options for produced fluids that require additional treatment for these constituents are also discussed, including surface disposal; reuse/recycle; agricultural, industrial, and domestic uses; mineral extraction and recovery; and solid waste handling. [ABSTRACT FROM AUTHOR]

These days, many countries are involved in evaluation and development of geothermal projects, and this includes the installation and maintenance of geothermal steam turbine. High reliability and maintainability are required as a basic condition for the geothermal turbines and energetic components in order to provide a stable power supply. For increasing the reliability of geothermal steam turbines the lifespan assessment of materials under geothermal environment conditions is important. A leading cause of reduced availability in geothermal power plant, non-conventional energetic systems’ components is corrosion damages in turbines, especially blades and rotors corrosion. Improved turbine mechanical integrity and increased rotor steam-turbine life cycle demand optimization is achieved thermal spray depositing using multi composite systems. This specific paper objective is design and synthesis of new complex powder mixtures NiCr/NiCoCr with different addition of ZrO 2 stabilized with Y 2 O 3 that can be used to obtain protective layers with improved wear, thermal shock and abrasion resistance. These coating will be studied also in “in situ” conditions, in Hellisheiði geothermal system, to investigate the actual effects of geothermal steam on the surface coated with multi-composite structures. The results will be reported in a future paper for comparing laboratory and “in situ” conditions tests results. [ABSTRACT FROM AUTHOR]

• Estimation of the CO 2 eq per kWh el for a geothermal power station in Mexico. • Creation of a detailed life cycle inventory. • Identification of the CO 2 eq hotspots within the generation process. • Mitigation options to reduce the power station CO 2 footprint. • CO 2 emissions due to exploitation is 10 times higher than the natural CO 2 release in the area covered by the power station. This work presents the estimation of the CO 2 eq emissions of the geothermal power station in Los Humeros, Mexico. The calculation takes the emissions of the CO 2 contained on the extracted geothermal brine plus the CO 2 footprint by the power station construction. The carbon footprint estimation is based on technical reports generated by the owner company. It considers all the commissioning activities and also the operational phase of the power plant, which is assumed to span a lifetime of 30 years. The results indicate a total emission from 442 to 568 g C O 2 eq / kW h el. Of these emissions 9 to 12% are contributed indirectly by the power station construction whereas 88 to 91% are released directly during operations due to the natural content of CO 2 in the steam. When comparing the results with the natural discharge of CO 2 in the production area, the emissions of CO 2 eq is 10 times faster. Solutions are proposed to reduce the footprint of CO 2 eq per kWh el. In the short term the use of all the installed capacity in the field reduces the footprint by 25%. Another option is to use closed cycle technology with a binary power station instead of the single-flash power plants. This showed 82% reduction of CO 2 eq emissions; accompanied by a reduction of electricity production by 16% due to the lower conversion efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

For two-phase geothermal sources, Organic Rankine Cycle (ORC) based binary plant is often applied for power production. In this work, a network topology is designed with the open-source Thermal Engineering Systems in Python (TESPy) software to simulate the stationary operation of the ORC plant. With this topology, the performance of six different working fluids are compared. From the thermodynamic perspective, the gross and net power output are optimized respectively. Results show that R600 has the highest gross power output of 17.55 MW, while R245fa has the highest net power output of 12.93 MW. However, the turbine inlet temperatures for these two working fluids need to be designed at the upper theoretical limit. R245ca and R601a require the heat exchange rates of internal heat exchanger to be larger than 1.51 MW and 0.99 MW to satisfy the re-injection temperature limit, which are smaller than the R600 (6.7 MW) and R245fa (6.0 MW) cases. Besides, the working fluid with lower critical state is preferred for a geothermal source with smaller steam fraction to establish a stable ORC plant. The workflow for the ORC design and optimization in this work is generic, and can be further applied to thermo-economic investigation. • An ORC power plant is designed based on a two-phase geothermal source. • Six potential working fluids are selected and their performance is compared. • A general workflow for gross and net power output optimization is established. • Internal heat exchanger size is constrained by the re-injection temperature. • Higher geo-steam fraction, working fluid with higher critical state is preferred. [ABSTRACT FROM AUTHOR]

Highlights: [•] We analyze the exergy simulation of the geothermal power plant in Dieng, Indonesia. [•] We also optimize the power plant to consider the improvement of power output. [•] The total available exergy of the geothermal fluid is estimated to be 59.52MW. [•] It is found that the second law efficiency of the power plant is 36.48%. [•] With optimization, the power output increases by lowering the separator pressure. [Copyright &y& Elsevier]

Highlights: [•] We conduct the thermodynamic and economic analysis of various geothermal power cycles. [•] The optimization process was performed to minimize the exergy losses. [•] Kalina cycle is a new technology compared to flash and binary cycles. [•] It is shown that Kalina cycle presents a viable choice for both thermodynamically and economically. [Copyright &y& Elsevier]

Highlights: [•] Genetic algorithm compared to particle swarm for optimization of a geothermal power plant. [•] PSO achieves better specific work output across a range of algorithm control parameters. [•] PSO converges to optimum solution with lower computation cost. [ABSTRACT FROM AUTHOR]

Highlights: [•] A double-flash geothermal power plant employing a reheater is presented. [•] The plant is 3–5% more efficient than a double-flash plant. [•] The problems of silica precipitation and reservoir dry-out were analyzed. [•] For a 250°C reservoir the plant converts 46.5% of geofluid exergy into power. [•] The cost of the reheat system should be rapidly repaid due to extra generation. [ABSTRACT FROM AUTHOR]

Abstract: An exergy analysis of the Dora II geothermal power plant (DGPP) with 9.5 MW net power output is carried out by using actual plant data to evaluate plant performance and pinpoint the locations of exergy destructions/losses. It aims to determine exergy efficiencies, and exergy destructions in each component of the plant. Exergy destructions in each of the components of the whole plant are determined and illustrated based on the actual data. The exergy destructions/losses take place through losses in the vaporizer, preheater, turbines, pumps and cooling tower, and the re-injection of the geothermal fluid. The exergy destruction ratios for these units and processes accounts for 7.97%, 1.25%, 11.93%, 1.3%, 14.92% and 32.18% of the total exergy input to the plant, respectively. Among the observed components in the plant, the most efficient equipment is found to be the preheater with an exergy efficiency value of 98%. The overall energetic and exergetic efficiencies of the plant are calculated to be 10.7% and 29.6%, respectively. The results show that geothermal energy can make a significant contribution toward reducing the emissions of greenhouse gases. [Copyright &y& Elsevier]

Abstract: In the Republic of Croatia, there are several sources of medium-temperature geothermal water in the range of 90–140°C, with which it is possible to produce electricity in binary plants, either with the Organic Rankine Cycle (ORC) or with the Kalina cycle. In the literature, the Kalina cycle is viewed as more thermodynamically favourable than the ORC; i.e., the Kalina cycle has a higher thermal efficiency and produces more power. However, the Croatian experience with a medium-temperature geothermal source with the relatively high temperature of geothermal water (Velika Ciglena, 175°C) is that the ORC is thermodynamically better than the Kalina cycle. In this paper, a comparison between the ORC and the Kalina cycle is performed based on energy analysis results for a medium-temperature geothermal source with a relatively lower temperature (Lunjkovec–Kutnjak, 140°C). Additionally, in this case the ORC has better thermal efficiency (First Law efficiency) – 13.5% vs. 12.8% – and accordingly higher net power – 2225.5kW vs. 2101.4kW. This difference is explained by the relatively high average annual temperature of the cooling air in the condenser (15°C), which has a more unfavourable influence on the condensing pressure in the Kalina cycle than in the ORC (6.35bar vs. 0.68bar). [Copyright &y& Elsevier]

Abstract: The current world status of geothermal electricity production, including installed capacities, number of units and energy produced by exploitation technology, is presented in this paper. Four geothermal model plants based on different modes of high enthalpy technologies are analyzed from energy, environmental and economic points of view for specific reservoir characteristics. Once process parameters are optimized for the best plant operation, a cost and financial analysis is performed within a given economic frame. This analysis shows that Dry Steam power plants are the most efficient. Flash steam power plants increase their exergy efficiency with increasing reservoir temperature. Double Flash technology raises the energy produced with respect to Single Flash between 17 and 25%, and economic parameters become better. An additional third flash process increases power production by 10%, but economic parameters are not improved unless a reservoir of very high temperatures is considered. The energy and economic study conclude that the choice of the best flash technology depends on the resource characteristics, the financial frame and the technology costs. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Based on available surveys, it has been shown that Iran has substantial geothermal potential in the north and north-western provinces, where in some places the temperature reaches 240°C. In order to better exploit these renewable resources, it is necessary to study this area. Thus, the aim of this paper is a comparative study of the different geothermal power plant concepts, based on the exergy analysis for high-temperature geothermal resources. The considered cycles for this study are a binary geothermal power plant using a simple organic Rankine cycle (ORC), a binary geothermal power plant using an ORC with an internal heat exchanger (IHE), a binary cycle with a regenerative ORC, a binary cycle with a regenerative ORC with an IHE, a single-flash geothermal power plant, a double-flash geothermal power plant and a combined flash-binary power plant. With respect to each cycle, a thermodynamic model had to be developed. Model validation was undertaken using available data from the literature. Based on the exergy analysis, a comparative study was done to clarify the best cycle configuration. The performance of each cycle has been discussed in terms of the second-law efficiency, exergy destruction rate, and first-law efficiency. Comparisons between the different geothermal power plant concepts as well as many approaches to define efficiencies have been presented. The maximum first-law efficiency was found to be related to the ORC with an IHE with R123 as the working fluid and was calculated to be 7.65%. In contrast, the first-law efficiency based on the energy input into the ORC revealed that the binary cycle with the regenerative ORC with an IHE and R123 as the working fluid has the highest efficiency (15.35%). Also, the maximum first-law efficiency was shown to be given by the flash-binary with R123 as the working fluid and was calculated to be 11.81%. [Copyright &y& Elsevier]

Abstract: Exergy analysis of a binary geothermal power plant is performed using actual plant data to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy diagram, and compared to the energy diagram. The sites with greater exergy destructions include brine reinjection, heat exchanger and condenser losses. Exergetic efficiencies of major plant components are determined in an attempt to assess their individual performances. The energy and exergy efficiencies of the plant are 4.5% and 21.7%, respectively, based on the energy and exergy of geothermal water at the heat exchanger inlet. The energy and exergy efficiencies are 10.2% and 33.5%, respectively, based on the heat input and exergy input to the binary Rankine cycle. The effects of turbine inlet pressure and temperature and the condenser pressure on the exergy and energy efficiencies, the net power output and the brine reinjection temperature are investigated and the trends are explained. [Copyright &y& Elsevier]

Abstract: A thermodynamic screening of 31 pure component working fluids for organic Rankine cycles (ORC) is given using BACKONE equation of state. The fluids are alkanes, fluorinated alkanes, ethers and fluorinated ethers. The ORC cycles operate between 100 and 30°C typical for geothermal power plants at pressures mostly limited to 20bar, but in some cases supercritical pressures are also considered. Thermal efficiencies η th are presented for cycles of different types. In case of subcritical pressure processes one has to distinguish (1) whether the shape of the saturated vapour line in the T,s-diagram is bell-shaped or overhanging, and (2) whether the vapour entering the turbine is saturated or superheated. Moreover, in case that the vapour leaving the turbine is superheated, an internal heat exchanger (IHE) may be used. The highest η th-values are obtained for the high boiling substances with overhanging saturated vapour line in subcritical processes with an IHE, e.g., for n-butane η th=0.130. On the other hand, a pinch analysis for the heat transfer from the heat carrier with maximum temperature of 120°C to the working fluid shows that the largest amount of heat can be transferred to a supercritical fluid and the least to a high-boiling subcritical fluid. [Copyright &y& Elsevier]

Abstract: The Carnot cycle is reviewed as to its appropriateness to serve as the ideal model for geothermal binary power plants. It is shown that the Carnot cycle sets an unrealistically high upper limit on the thermal efficiency of these plants. A more useful model is the triangular (or trilateral) cycle because binary plants operating on geothermal hot water use a non-isothermal heat source. The triangular cycle imposes a lower upper bound on the thermal efficiency and serves as a more meaningful ideal cycle against which to measure the performance of real binary cycles. Carnot and triangular cycle efficiencies are contrasted and the thermal efficiencies of several actual binary cycles are weighed against those of the ideal triangular cycle to determine their relative efficiencies. It is found that actual binary plants can achieve relative efficiencies as high as 85%. The paper briefly discusses cycles using two-phase expanders that in principle come close to the ideal triangular cycle. [Copyright &y& Elsevier]

Abstract: Geothermal energy and the other renewable energy sources are becoming attractive solutions for clean and sustainable energy needs of Turkey. Geothermal energy is being used for electricity production and it has direct usage in Turkey, which is among the first five countries in the world for the geothermal direct usage applications. Although, Turkey is the second country to have the highest geothermal energy potential in Europe, the electricity production from geothermal energy is quite low. The main purpose of this study is to investigate the status of the geothermal energy for the electricity generation in Turkey. Currently, there is one geothermal power plant with an installed capacity of 20.4MWe already operating in the Denizli–Kizildere geothermal field and another is under the construction in the Aydin–Germencik field. This study examines the potential and utilization of the existing geothermal energy resources in Kutahya–Simav region. The temperature of the geothermal fluid in the Simav–Eynal field is too high for the district heating system. Therefore, the possibility of electrical energy generation by a binary-cycle has been researched and the preliminary feasibility studies have been conducted in the field. For the environmental reasons, the working fluid used in this binary power plant has been chosen as HCFC-124. It has been concluded that the Kutahya–Simav geothermal power plant has the potential to produce an installed capacity of 2.9MWe energy, and a minimum of 17,020MWh/year electrical energy can be produced from this plant. As a conclusion, the pre-feasibility study indicates that the project is economically feasible and applicable. [Copyright &y& Elsevier]

Abstract: HDRec (Hot Dry Rock economic) is a cost-benefit analysis program for geothermal projects that combines economic aspects with the technical characteristics of the surface installations and the hydrogeological and thermal properties of the subsurface. Investment and operation costs are evaluated and related to the revenues gained from electricity sales. The program also accounts for discounted cash flows when determining the characteristic financial parameters, as well as the time dependency of operation costs, and the reduction in income ensuing from decreasing reservoir temperatures. It is also possible to factor in the expense incurred for maintenance or refurbishment during production, as well as the cost of dismantling the system when exploitation ends. A simple tax model is also incorporated in the economic calculations. The characteristic financial parameters can be referenced to the start of exploration, or to the beginning and end of commercial energy production. A description is given of the workflow of the HDRec program, followed by an example of its application to a dataset representing conditions in the Upper Rhine Valley of France and Germany. The paper also provides a sensitivity analysis of the influence of the parasitic power demand of pumps and of different subsurface heat exchange areas between boreholes. Finally, a scenario is proposed for optimizing the economic performance of the system using the latest information on the characteristics of the Soultz-sous-Forêts reservoir. [Copyright &y& Elsevier]