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[en] This two-part paper investigates the potential of ORC (Organic Rankine Cycles) for the exploitation of low-medium enthalpy geothermal brines. Part A deals with thermodynamic analysis and optimization, while Part B focuses on economic optimization. In this part, an economic model was defined and implemented in the Matlab® code previously developed. A routine was also implemented to estimate the design of the turbine (number of stages, rotational speed, mean diameter), allowing to estimate turbine efficiency and cost. The tool developed allowed performing an extensive techno-economic analysis of many cycles exploiting geothermal brines with temperatures between 120 °C and 180 °C. By means of an optimization routine, the cycles and the fluids leading to the minimum cost of the electricity are found for each geothermal source considered. Cycle parameters found from the techno-economic optimization are compared with those assumed and found from the thermodynamic optimization. Quite relevant differences show the necessity to perform optimization on the basis of specific plant cost. As a general trend, it is however confirmed that configurations based on supercritical cycles, employing fluids with a critical temperature slightly lower than the temperature of the geothermal source, lead to the lowest electricity cost for most of the investigated cases. - Highlights: • We investigate 6 different cycle configurations adopting 54 working fluids. • We define components cost correlations and a turbine efficiency estimation method. • Techno-economic optimization is performed for various geothermal brine temperatures. • We set general rules for working fluid and cycle configuration selection
[en] The development of Enhanced Geothermal Systems (EGS) for the cogeneration of electricity and district heating is expected to be important in the future. The criteria to be accounted for in the energy conversion system design are the economic profitability, the thermodynamic efficiency in the usage of the resource, and the generated life-cycle environmental impacts, which are as well a key point for the public acceptance of geothermal energy. This paper presents a systematic methodology for the optimal design and configuration of geothermal systems considering environomic criteria. Process design and process integration techniques are used in combination with Life Cycle Assessment (LCA) and multi-objective optimization techniques, using a multi-period strategy to account for the seasonal variations in the district heating demand. It is illustrated by an application to the future EGS construction for cogeneration in the context of Switzerland. Different conversion cycles are considered: single and double-flash systems, organic Rankine cycles (ORC), and Kalina cycles. The optimal configuration is determined at each construction depth for the EGS from 3000 down to 10,000 m and at each district heating network installed capacity from 0 to 60 MWth. Results show that in the shallowest range of depths (3500–6000 m), the optimal configurations for all considered performance indicators are EGS between 5500 and 6000 m with a Kalina cycle for cogeneration, and a district heating network with an installed capacity between 20 and 35 MWth. In the deepest range (7500–9500 m), when compared with the single electricity production, the cogeneration of district heating is less favorable from an economic and exergetic perspective (11% and 17% of relative penalty, respectively, for a district heating network with an installed capacity of 60 MWth) but more favorable in terms of environmental performance (37% of relative improvement for avoided CO2 emissions). -- Highlights: ► Systematic methodology for the environomic design of Enhanced Geothermal Systems for Combined Heat and Power. ► Combination of process integration, thermoeconomic analysis, Life Cycle Assessment and multiobjective optimization. ► Optimal configurations of future EGS construction in Switzerland at different depths and district heating sizes. ► In shallowest depths, all criteria favor EGS between 5500 and 6000 m with a Kalina cycle, district heating between 20 and 35 MW. ► Between 7500 and 10,000 m, thermo-economic criteria favor single electricity production, environmental ones large CHP systems.
[en] Potential geothermal areas are identified through investigation of spatial relations between geothermal occurrences and their surrounding geological phenomena in western Anatolia, Turkey. The identification is based on only publicly available data. It is expected that the study will guide further preliminary investigations performed for large areas having limited information. Magnetic anomaly, Bouger gravity anomaly, earthquake epicenter and lineament datasets are used for the analysis. The first is used without any modification whereas the rest are utilized to extract three evidence maps; distance to major grabens, Gutenberg-Richter b-value and distance to lineaments, respectively. Predictor maps are produced from these evidence maps as well as from the unprocessed magnetic anomaly map by applying two different binarization procedures. From each binarization procedure a favorability map is produced separately using Index Overlay (IO) and Weights of Evidence (WofE) methods. The findings reveal that weighting predictor maps according to spatial association between evidence maps and training points lead to more accurate prediction in both WofE and IO methods. The potential areas in the final maps are Aydin, Denizli, Manisa, Balikesir and Kutahya of which first two have been explored and exploited, and thus found to be favorable, while the rest are nearly unexplored.
[en] A deterministic approach is devised to compare the safety features of various energy sources. The approach is based on multiattribute utility theory. The method is used in evaluating the safety aspects of alternative energy sources used for the production of electrical energy. Four alternative energy sources are chosen which could be considered for the production of electricity to meet the national energy demand. These are nuclear, coal, solar, and geothermal energy. For simplicity, a total electrical system is considered in each case. A computer code is developed to evaluate the overall utility function for each alternative from the utility patterns corresponding to 23 energy attributes, mostly related to safety. The model can accommodate other attributes assuming that these are independent. The technique is kept flexible so that virtually any decision problem with various attributes can be attacked and optimal decisions can be reached. The selected data resulted in preference of geothermal and nuclear energy over other sources, and the method is found viable in making decisions on energy uses based on quantified and subjective attributes. (author)
[en] The DX GSHP (direct-expansion ground source heat pump), which uses a buried copper piping network through which refrigerant is circulated, is one type of GSHP (ground source heat pump). This study investigates the performance characteristics of a vertical U-bend direct-expansion ground source (geothermal) heat pump system (DX GSHPS) for both heating and cooling. Compared with the conventional GCHP (ground coupled heat pump) system, the DX GSHP system is more efficient, with lower thermal resistance in the GHE (ground heat exchanger) and a lower (higher) condensing (evaporating) temperature in the cooling (heating) mode. In addition, the system performance of the whole DX GSHP system is also higher than that of the conventional GCHP system. A DX GSHP system in Xiangtan, China with a U-bend ground heat exchanger 42 m deep with a nominal outside diameter of 12.7 mm buried in a water well was tested and analysed. The results showed that the performance of this system is very high. The maximum (average) COPs of the system were found to be 6.08 (4.73) and 6.32 (5.03) in the heating and cooling modes, respectively. - Highlights: • The reasons for the higher performance of the DX GSHP (direct-expansion ground source heat pump) are analysed theoretically compared with the conventional GCHP (ground coupled heat pump). • The experimental performance of a DX GSHP system is investigated, which makes a valuable contribution to the literature. • The study is helpful in demonstrating the energy efficiency of the DX GSHP system
[en] As a result of decreasing fossil fuel resources and their adverse impacts on the environment, interest in renewable energy resources, particularly geothermal energy, has been revived. Finding approaches that are more accurate and systematic to the energy system development is of great importance for the exploitation of geothermal energy. The aim of this study was to carry out both conventional and advanced exergy analyses of an existing geothermal binary power system. In this way, in-depth information was collected about the exergy destroyed in the system and its parts. Through advanced analysis, it became possible to investigate the interactions between the system components and the actual performance of the reasonable improvements. The results show that the order of the primary improved components is CON 1, TURB 1 and VAP 2 for the conventional analysis and CON 1, CON 2 and PRE-HE 1 for the advanced analysis. The results of the advanced analysis were found to be more qualified than the results of the conventional one. The improvements made to the system, increased the modified exergy efficiency to 18.26%, while the total system efficiency was found to be 9.60% in the real conditions. - Highlights: • Evaluating thermodynamic performance of a GPP using advanced exergy analysis for the first time. • Investigating the interactions between system components and their improvement potential. • The conventional exergy efficiency is 9.60% while the modified exergy efficiency is 18.26% through improving. • Total avoidable exergy destruction indicates that the heat exchangers and the turbine all merit priority for modifications
[en] This two-part paper investigates the potential of ORC (organic Rankine cycles) for the exploitation of low-medium enthalpy geothermal brines. Part A deals with thermodynamic analysis and optimization, while Part B focuses on economic optimization. In ORC field the wide range of available working fluids and cycle configuration entails a non-univocal selection of fluid and cycle parameters for the exploitation of a given heat source. A Matlab® code was created in order to define the optimal combination of fluid, cycle configuration and cycle parameters. Thermodynamic properties of fluids are taken from Refprop® database. An extensive thermodynamic analysis is performed considering geothermal sources in the temperature range of 120–180 °C. All the assumptions for calculating the plant components performance are set on the basis of data from literature and real power plants data sheets. Thermodynamic optimization results, shown in terms of reduced variables, allow defining some general rules for the selection of the optimal combination of working fluid and cycle configuration. In particular, it is found that configurations based on supercritical cycles, employing fluids with a critical temperature slightly lower than the temperature of the geothermal source, lead to the highest efficiencies for most of the investigated cases. - Highlights: • We investigated 6 different cycle configurations adopting 54 working fluids. • We carried out multi-variable plant optimization and second law analysis. • We performed a sensitivity analysis on ambient and geothermal brine condition. • We set general rules for selecting working fluid and cycle configuration
[en] The primary objective of this study was to apply the ANN (artificial neural network) model with the ABC (artificial bee colony) algorithm to estimate annual hydraulic energy production of Turkey. GEED (gross electricity energy demand), population, AYT (average yearly temperature), and energy consumption were selected as independent variables in the model. The first part of the study compared ANN-ABC model performance with results of classical ANN models trained with the BP (back propagation) algorithm. Mean square and relative error were applied to evaluate model accuracy. The test set errors emphasized positive differences between the ANN-ABC and classical ANN models. After determining optimal configurations, three different scenarios were developed to predict future hydropower generation values for Turkey. Results showed the ANN-ABC method predicted hydroelectric generation better than the classical ANN trained with the BP algorithm. Furthermore, results indicated future hydroelectric generation in Turkey will range from 69.1 to 76.5 TWh in 2021, and the total annual electricity demand represented by hydropower supply rates will range from 14.8% to 18.0%. However, according to Vision 2023 agenda goals, the country plans to produce 30% of its electricity demand from renewable energy sources by 2023, and use 20% less energy than in 2010. This percentage renewable energy provision cannot be accomplished unless changes in energy policy and investments are not addressed and implemented. In order to achieve this goal, the Turkish government must reconsider and raise its own investments in hydropower, wind, solar, and geothermal energy, particularly hydropower. - Highlights: • This study is associated with predicting hydropower generation in Turkey. • Sensitivity analysis was performed to determine predictor variables. • GEED, population, energy consumption and AYT were used as predictor variables. • ANN-ABC predicted the hydropower generation more accurately than classical ANN. • Using the ANN-ABC model, the hydropower generation was forecasted until 2021
[en] Thermodynamic energy and exergy analysis of a PEM water electrolyzer driven by geothermal power for hydrogen production is performed. For this purpose, work is produced from a geothermal resource by means of the organic Rankine cycle; the resulting work is used as a work input for an electrolysis process; and electrolysis water is preheated by the waste geothermal water. The first and second-law based performance parameters are identified for the considered system and the system performance is evaluated. The effects of geothermal water and electrolysis temperatures on the amount of hydrogen production are studied and these parameters are found to be proportional to each other. We consider a geothermal resource at 160 °C available at a rate of 100 kg/s. Under realistic operating conditions, 3810 kW power can be produced in a binary geothermal power plant. The produced power is used for the electrolysis process. The electrolysis water can be preheated to 80 °C by the geothermal water leaving the power plant and hydrogen can be produced at a rate of 0.0340 kg/s. The energy and exergy efficiencies of the binary geothermal power plant are 11.4% and 45.1%, respectively. The corresponding efficiencies for the electrolysis system are 64.0% and 61.6%, respectively, and those for the overall system are 6.7% and 23.8%, respectively. - Highlights: • Thermodynamic analysis of hydrogen production by PEM electrolysis powered by geothermal energy. • Power is used for electrolyser; used geothermal water is for preheating electrolysis water. • Effect of geothermal water and electrolysis temperatures on the amount of hydrogen production. • Hydrogen can be produced at a rate of 0.0340 kg/s for a resource at 160 °C available at 100 kg/s. • Energy and exergy efficiencies of the overall system are 6.7% and 23.8%, respectively
[en] In this paper, energy and exergy analyses of the geothermal-based hydrogen production via thermochemical water decomposition using a new, four-step copper-chlorine (Cu-Cl) cycle are conducted, and the respective cycle energy and exergy efficiencies are examined. Also, a parametric study is performed to investigate how each step of the cycle and its overall cycle performance are affected by reference environment temperatures, reaction temperatures, as well as energy efficiency of the geothermal power plant itself. As a result, overall energy and exergy efficiencies of the cycle are found to be 21.67% and 19.35%, respectively, for a reference case.