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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]

Geothermal energy is the energy that is stored inside the earth and which may be used by man either directly (with no transformation) or to generate electricity by means of a geothermal power plant. This article estimates the participation of geothermal energy in Colombia's electricity market by the year 2025, based on a review of current installed capacity in the country; potential sources of geothermal energy for electric power generation; the existing regulatory framework for projects involving renewable sources, and the geothermal projects currently under development in the national territory. Demand for electricity in Colombia will continue to increase, which implies that new electric power generation projects must be undertaken in order to meet the country's demand. The conclusion is that geothermal energy is a good alternative to help achieve this objective. By 2025, geothermal sources are expected to generate at least 1400 GWh of electric power per year, equivalent to 1.65% of total electricity estimate demand in Colombia. If the full potential that has been assessed were exploited, generation capacity could reach up to 17,400 GWh/year (equivalent to close to 20% of the country's demand) by 2025. [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]

Geothermal energy is a renewable form of energy, however due to misuse, processing and management issues, it is necessary to use the resource more efficiently. To increase energy efficiency, energy systems engineers carry out careful energy control studies and offer alternative solutions. With this aim, this study was conducted to improve the performance of a real operating air-cooled organic Rankine cycle binary geothermal power plant (GPP) and its components in the aspects of thermodynamic modeling, exergy analysis and optimization processes. In-depth information is obtained about the exergy (maximum work a system can make), exergy losses and destruction at the power plant and its components. Thus the performance of the power plant may be predicted with reasonable accuracy and better understanding is gained for the physical process to be used in improving the performance of the power plant. The results of the exergy analysis show that total exergy production rate and exergy efficiency of the GPP are 21MWand 14.52%, respectively, after removing parasitic loads. The highest amount of exergy destruction occurs, respectively, in condenser 2, vaporizer HH2, condenser 1, pumps 1 and 2 as components requiring priority performance improvement. To maximize the system exergy efficiency, the artificial bee colony (ABC) is applied to the model that simulates the actual GPP. Under all the optimization conditions, the maximum exergy efficiency for the GPP and its components is obtained. Two of these conditions such as Case 4 related to the turbine and Case 12 related to the condenser have the best performance. As a result, the ABC optimization method provides better quality information than exergy analysis. Based on the guidance of this study, the performance of power plants based on geothermal energy and other energy resources may be improved. [ABSTRACT FROM AUTHOR]

Excellence in skilled operation is vital for the efficiency of geothermal power plants. Mount Salak geothermal power plant unit 1-2-3 has consistently produced no less than 180 MWe to the Java-Bali grid since its first commercial operation in 1994, with an equivalent availability factor (EAF) average of 96%. Owing to this long operation period, power plant efficiency must be improved for the sustainable production of electricity. In this study, energy and exergy analysis has been undertaken to ascertain the amount of energy that is used in the power plant's current condition, and to determine the plant's overall system losses. Research was carried out by collecting data relating to temperature, pressure, and mass flow rate. Data were analyzed using the control volume to assess the thermal and mass balance and ascertain the value of exergy. Analysis was conducted theoretically and compared with results calculated by Engineering Equation Solver (EES) software. The results showed that from 1069,90 MWe in steam energy entering the system, the total amount of exergy was 302.42 MWe. Mount Salak geothermal power plant unit 1-2-3 had an overall first law efficiency of 16.75% and an overall second law efficiency of 59.27%. The greatest losses - 27.84% of the total exergy - were in the condensers. This was caused by the quality of cooling water entering condensers, which was in turn a result of cooling tower performance. Results suggest that turbine unit 1 should be investigated further to determine causes of decreased capacity. [ABSTRACT FROM AUTHOR]

The first part of the review presents information on the scale and specific features of geothermal energy development in various countries. The classification of geothermal power plant (GeoPP) process flow diagrams by a phase state of the primary heat source (a geothermal fluid), thermodynamic cycle, and applicable turbines is proposed. Features of geothermal plants using methods of flashing and steam separation in the process loop and a flowsheet and thermodynamic process of a geothermal fluid heat-to-power conversion in a GeoPP of the most widespread type using a double-flash separation are considered. It is shown that, for combined cycle power units, the specific power-to-consumption geothermal fluid ratio is 20-25% higher than that for traditional single-loop GeoPP. Information about basic chemical components and their concentration range for geothermal fluids of various formations around the world is presented. Three historic stages of improving geothermal energy technologies are determined, such as development of high-temperature geothermal resources (dry, superheated steam) and application of a two-phase wet-steam geothermal fluid in GeoPP power units with one or two expansion pressures and development of binary cycle GeoPPs. A current trend of more active use of binary power plants in GeoPP technological processes is noted. Design features of GeoPP's steam turbines and steam separating devices, determined by the use of low-potential geothermal saturated steam as a working medium, which is characterized by corrosion aggressiveness and a tendency to form deposits, are considered. Most promising Russian geothermal energy projects are determined. A list of today's most advanced geothermal turbine performance technologies is presented. By an example of a 25 MW steam turbine design, made by JSC Kaluga Turbine Works, advantages of the internal moisture separation with a special turbine-separator stage are shown. [ABSTRACT FROM AUTHOR]

This article is intended to raise awareness of the public, with the aim that anyone can judge reality and accuracyof records that appear in the media on the exploitation of geothermal energy. It provides a comprehensive overviewof geothermal systems, potential of hydrothermal and enhanced geothermal systems, of mechanisms and characteristicsof middle and high enthalpy geothermal resources. It also deals with a mode of their conversion into electricity.Featured are the main factors affecting the decision on effectiveness of conversion of geothermal energy intoelectricity. Given are the review of the research necessary to establish the geothermal potential and assessment oftechnological and economic possibilities of installing geothermal power plants in Slovenia. The paper also describesthe state of knowledge of middle- and high temperature geothermal resources in Slovenia with initial conditions forconstructing geothermal power plants. In addition, we present theoretical calculations of the conversion efficiencyof geothermal energy into electricity with conventional turbines and present some problems for the exploitationof geothermal energy, which are associated with additional costs and further reduce the efficiency of investment.Described are the characteristics and performance of binary geothermal power plants and foreign experience inobtaining electricity from the EGS (Enhanced Geothermal System). We also address the overlapping of the oil andgas industry with the operation of the EGS and the possibility of exploiting oil and gas wells for producing thegeothermal electricity.

General guidelines are proposed to select the optimal subcritical organic Rankine cycle configuration considering reinjection temperature limits for a low-temperature geothermal brine power plant. Saturated/superheated, non-regenerative/regenerative cycles are investigated. Evaporating temperature and overheating degree at the turbine inlet are selected as design variables, and highest plant exergy efficiency is pursued for current optimizations. Through theoretical analysis of mathematical modelling and typical case studies, a simple optimization approach is presented. The new approach consists of up to three judgements on reinjection temperature and evaporating temperature in comparison two optimization calculations along the saturated line and along the given reinjection temperature line. The potential optimal cycle configurations are saturated non-regenerative cycle, saturated regenerative cycle and superheated regenerative cycle. Then, this new optimization approach is applied to obtain optimal cycle configuration and relevant working condition. The working fluids investigated are R245fa, R1234ze(Z), isopentane, and isobutane. The saturated non-regenerative cycle is the optimal cycle when the reinjection temperature limit is equal or less than the optimal reinjection temperature with no reinjection constraint. Otherwise, the reinjection temperature limit influences not only the optimal cycle configuration but also the optimal working condition. Working fluid isobutane always achieves highest plant exergy efficiency for optimal cycles with either reinjection temperature limit.

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]

The Hungarian petroleum industry has always participated in the utilization of favourable geothermal conditions in the country. Most of the Hungarian geothermal wells were drilled by the MOL Ltd. as CH prospect holes. Accordingly, the field of geothermics belonged to the petroleum engineering, although marginally. It was therefore a surprise to hear of the decision of MOL Ltd. to build a geothermal power plant of about 2-5 MW. The tender was published in 2004.The site selected for the geothermal project is near the western border of an Hungarian oilfield, close to the Slovenian border. The location of the planned geothermal power plant was chosen after an analysis of suitable wells owned by the MOL Rt. The decision was made on the bases of different reservoir data. The existence of a reservoir of the necessary size, temperature, permeability, productivity and the water chemistry data was proved. The wells provide an enough information to understand the character of the reservoir and will be the production wells used by the planned power plant.The depth of the wells is about 2930 - 3200 m. The Triassic formation is reached at around 2851 m. The production and the reinjection wells are planned. The primary objective of the evaluation is to further learn the nature of the geothermal system. First a one-day discharge test is carried out. If this short-term test is successful, a six-months long-term discharge test will follow. The first period of the test is a transient phenomenon. Within the well test, the wellhead pressure, the flow rate, the outflowing water temperature, the dynamic fluid level, and the chemical components will be measured. The heat transfer around the bore-hole is influenced by the flow rate and the time. For the right appreciation of the measured data, it is very important to analyse the heat transfer processes around the bore-hole. The obtained data from the experiments must be also fitted into the framework of a mathematical model in order to form a coherent system.Before the drilling operations and the discharge tests, the temperature of the outflowing water can be prognosticated. This is made possible by applying recently elaborated simulation methods (Bobok, Tóth 2003; Tóth, 2004).

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]

In this study, geothermal resources in Kutahya-Simav region having geothermal water at a temperature suitable for power generation is considered. The study is aimed to yield the method of the most effective use of the geothermal resource and a rational thermodynamic comparison of various cycles for a given resource. Maximum first law efficiencies vary between 6.9 to 10.6% while the second law efficiencies vary between 38.5 to 59.3% depending on the cycle considered. The maximum power output, the first law, and the second law efficiencies are obtained for Kalina cycle followed by combined cycle and binary cycle. [ABSTRACT FROM PUBLISHER]

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]

It is obvious that Geothermal Power Plant is the kind of projects, which may be very attractive in certain regions but may seems difficult and risky on the first look and if not properly developed. Specially in the regions and countries where are missing references for such kind of projects this project may be "pioneer" type and from the beginning will for sure request lot of ambitions and patience from site of developer and project owners and lot of confidence from administration and official governmental bodies and or banks and investors. It is therefore necessary to have a precise formation in the early beginnings in the individual feasibility studies. On this particular example can be seen as specifically described below in respect of this project geothermal energy. The case study compares three possible alternatives, not only technically but also economically. Also, comparing the results through dynamic economic indicators, which taking into account in particular the aspect of time, thus are leading to significantly greater objectivity and project implementation. [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]

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]

SUMMARY Higher demand for energy consumption and importance of environmental issues has encouraged researchers and policy makers to consider renewable energies more seriously. Geothermal resources are a green energy source that can make a considerable contribution in some countries. Japan has the third ranking geothermal energy potential, and its geothermal electricity production is currently eighth in the world. Since the nature of geothermal resources dictates its method of utilization, it is important to categorize available resources. There is no consensus on classification of geothermal resources. Most scientists, from geologist to engineers, agree on the term temperature. However, temperature or enthalpy alone cannot describe the nature of fluids; they can have same temperature with different phases, such as saturated water or saturated steam. Using exergy for resource classification benefits their comparison, according to their ability to do work. In this paper, exergetic classification of geothermal resources was applied to 18 under-operating geothermal power plants in Japan. Six geothermal fields have high exergy resources according to their SExI values in excess of 0.5. The remaining geothermal fields in Japan are classified in the medium resources zone. Classification results can be used by decision makers as a reference for future geothermal development. Copyright © 2012 John Wiley & Sons, Ltd. [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]

An effective method of low-enthalpy energy acquiring from waters pumped out from mines in a low-temperature geothermal power plant with the capacity of 5 MWt has been presented. The geothermal power plant will allow to achieve favorable energy and ecological effects. It can be built in all underground mines in the Upper Silesian Coal Basin (USCB) that ensure access to the water stream in a suitably long period of time, minimum a dozen or so years. Cooled waters can be injected back into mine workings - however, this depends on local geological and mining conditionings. With the aim of quick selection of installation capacity a nomogram was constructed to determine the parameters of the geothermal power plant installations. [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]