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Conceptual scheme of the multidisciplinary approach proposed, with the connections between the three areas involved.
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A multidisciplinary approach for the design of geothermal power plants for water dominant resources is here proposed. The importance of a strategic approach is underlined, considering all the connections between the analysis of the geothermal potential of the reservoir (geophysical exploration and geochemical analysis) with the design of the plant...
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Context 1
... source or from technical optimization of the plant variables. The oversizing of a power plant is a typical error in the design step. It can be a consequence of an incorrect evaluation of the energy storage and of the long-term behavior of the Reservoir-Plant system. Starting from the aforementioned basis, in this paper the authors remark the importance of a multidisciplinary approach based mainly on a complete geological characterization of the particular reservoir system considered; the method is based on the integration of three different areas of analysis: Thermodynamics and Energy aspects, directly related to the power plant design; Geochemical and Geophysical background and Reservoir Engineering that can strongly affect the operation of the power plants ( Fig. 1). Referring to Fig. 1 a de fi nition of “ geothermal system ” can be given: it comprehends the power plant but also the utilization facilities, the wells, the geothermal reservoir, the groundwater circulation system and all the possible connections between these parts and the environment. The connection among the various parts of the geothermal systems is particularly important mainly in the case of ORC plants. The utilization experience of geothermal fi elds in the past years showed that equilibrium between production and recharge of the resource is fundamental. Axelsson de fi nes in [14] the maximum energy production E 0 , as the level of exploitation which permits to maintain a constant production for long time. This value can be used to identify “ sustainable ” versus “ excessive ” production levels. Moreover a preliminary estimation of the power plant size is furthermore important because most of the low-temperature geothermal binary plants have quite high installation costs and presently need to be subsidized from the public purse and the question arises if the environmental bene fi t of geothermal energy supply exist for the particular reservoirs analyzed. Moving from the aforementioned consideration, in the paper a concise and global evaluation of the connections between geological-geophysical investigation and power plant design is discussed and a methodological approach for binary cycle power plant design in the perspective of the connection “ Reservoir-Plant ” system is proposed. Organic Rankine Cycle units (scheme in Fig. 2) are surely the best option to convert thermal energy from geothermal reservoirs at medium-low temperature [5]. In a binary cycle power plant the heat of the geothermal water is transferred to a secondary working fl uid, usually an organic fl uid that has a low boiling point and high vapour pressure when compared to water at a given temperature. The cooled geothermal water is then returned to the ground to recharge the reservoir [2]. These geothermal plants have no emissions to the atmosphere except for water vapour from the cooling towers (only in case of wet cooling) and no losses of working fl uid. Thus, environmental problems that may be associated with the exploitation of higher temperature geothermal resources, like the release of greenhouse gases (e.g. CO 2 and CH 4 ) and the discharge of toxic elements (e.g. Hg and As), are avoided. Another advantage of the binary technology is that the geothermal fl uids (or brines) do not contact the moving mechanical components of the plant (e.g. the turbine), assuring a longer life for the equipment. There is a huge literature about this technology, often based on speci fi c and local industrial application. Till now each installation is designed for the conditions at a given location and the various systems have been tailored to speci fi c geothermal fl uid characteristics. The major manufacturers in this fi eld, like Ormat, Ma fi Trench, Siemens and UTC Power have adopted this approach. At present the technology is not at a stage of development capable of providing “ standard machinery ” , but recently some manufacturers have proposed the use of standard systems (e.g. UTC Power proposed The PureCycle Ò Power System) and this approach could be the key element for a large diffusion of small size geothermal plants. This will be possible only if adequate provisional instruments will be developed. For a correct sizing of a plant, mainly of an ORC plant, two elements are of primary importance: the de fi nition of the geothermal potential assessment and of the reinjection strategy. The geothermal potential of a particular area means the de fi nition of temperature ( T geo ) and pressure ( p geo ) of the geothermal fl uid and also of the maximum mass fl ow rate ( M geo ) that can be extracted maintaining for a long time the thermal and chemical properties of the reservoir and of the fl uid. The task is assuring a sustainable withdrawn of geothermal fl uid and thermal energy allowing a correct operation and management of the power unit and of the reservoir. A brief list of the general results that an evaluation of the geothermal potential of an area should achieve is here proposed, taking into account the results of previous analysis (modi fi ed from [15]): energy available (stored, present at a certain time) in the reservoir; temperature, pressure and rate of the extracted fl uid; chemical composition of the fl uid and saltiness, that de fi ne the lowest reinjection temperature ( T rej ) to maintain an acceptable scaling deposition rate; number of wells and mutual distances; time interval to have a decrease in the rate and temperature of fl uid (or productivity) and number of wells for compensation; effects of reinjection on productivity; siting of the reinjection wells and reinjection strategy. The value of the difference between the temperature of the reservoir ( T geo ) and the reinjection temperature ( T rej ), together with the geo fl uid availability ( M geo ) de fi nes the exergy and energy potential of the geothermal fi eld. In particular, to de fi ne the exergetic availability of a geothermal resource, two ratios can be de fi ...
Context 2
... source or from technical optimization of the plant variables. The oversizing of a power plant is a typical error in the design step. It can be a consequence of an incorrect evaluation of the energy storage and of the long-term behavior of the Reservoir-Plant system. Starting from the aforementioned basis, in this paper the authors remark the importance of a multidisciplinary approach based mainly on a complete geological characterization of the particular reservoir system considered; the method is based on the integration of three different areas of analysis: Thermodynamics and Energy aspects, directly related to the power plant design; Geochemical and Geophysical background and Reservoir Engineering that can strongly affect the operation of the power plants ( Fig. 1). Referring to Fig. 1 a de fi nition of “ geothermal system ” can be given: it comprehends the power plant but also the utilization facilities, the wells, the geothermal reservoir, the groundwater circulation system and all the possible connections between these parts and the environment. The connection among the various parts of the geothermal systems is particularly important mainly in the case of ORC plants. The utilization experience of geothermal fi elds in the past years showed that equilibrium between production and recharge of the resource is fundamental. Axelsson de fi nes in [14] the maximum energy production E 0 , as the level of exploitation which permits to maintain a constant production for long time. This value can be used to identify “ sustainable ” versus “ excessive ” production levels. Moreover a preliminary estimation of the power plant size is furthermore important because most of the low-temperature geothermal binary plants have quite high installation costs and presently need to be subsidized from the public purse and the question arises if the environmental bene fi t of geothermal energy supply exist for the particular reservoirs analyzed. Moving from the aforementioned consideration, in the paper a concise and global evaluation of the connections between geological-geophysical investigation and power plant design is discussed and a methodological approach for binary cycle power plant design in the perspective of the connection “ Reservoir-Plant ” system is proposed. Organic Rankine Cycle units (scheme in Fig. 2) are surely the best option to convert thermal energy from geothermal reservoirs at medium-low temperature [5]. In a binary cycle power plant the heat of the geothermal water is transferred to a secondary working fl uid, usually an organic fl uid that has a low boiling point and high vapour pressure when compared to water at a given temperature. The cooled geothermal water is then returned to the ground to recharge the reservoir [2]. These geothermal plants have no emissions to the atmosphere except for water vapour from the cooling towers (only in case of wet cooling) and no losses of working fl uid. Thus, environmental problems that may be associated with the exploitation of higher temperature geothermal resources, like the release of greenhouse gases (e.g. CO 2 and CH 4 ) and the discharge of toxic elements (e.g. Hg and As), are avoided. Another advantage of the binary technology is that the geothermal fl uids (or brines) do not contact the moving mechanical components of the plant (e.g. the turbine), assuring a longer life for the equipment. There is a huge literature about this technology, often based on speci fi c and local industrial application. Till now each installation is designed for the conditions at a given location and the various systems have been tailored to speci fi c geothermal fl uid characteristics. The major manufacturers in this fi eld, like Ormat, Ma fi Trench, Siemens and UTC Power have adopted this approach. At present the technology is not at a stage of development capable of providing “ standard machinery ” , but recently some manufacturers have proposed the use of standard systems (e.g. UTC Power proposed The PureCycle Ò Power System) and this approach could be the key element for a large diffusion of small size geothermal plants. This will be possible only if adequate provisional instruments will be developed. For a correct sizing of a plant, mainly of an ORC plant, two elements are of primary importance: the de fi nition of the geothermal potential assessment and of the reinjection strategy. The geothermal potential of a particular area means the de fi nition of temperature ( T geo ) and pressure ( p geo ) of the geothermal fl uid and also of the maximum mass fl ow rate ( M geo ) that can be extracted maintaining for a long time the thermal and chemical properties of the reservoir and of the fl uid. The task is assuring a sustainable withdrawn of geothermal fl uid and thermal energy allowing a correct operation and management of the power unit and of the reservoir. A brief list of the general results that an evaluation of the geothermal potential of an area should achieve is here proposed, taking into account the results of previous analysis (modi fi ed from [15]): energy available (stored, present at a certain time) in the reservoir; temperature, pressure and rate of the extracted fl uid; chemical composition of the fl uid and saltiness, that de fi ne the lowest reinjection temperature ( T rej ) to maintain an acceptable scaling deposition rate; number of wells and mutual distances; time interval to have a decrease in the rate and temperature of fl uid (or productivity) and number of wells for compensation; effects of reinjection on productivity; siting of the reinjection wells and reinjection strategy. The value of the difference between the temperature of the reservoir ( T geo ) and the reinjection temperature ( T rej ), together with the geo fl uid availability ( M geo ) de fi nes the exergy and energy potential of the geothermal fi eld. In particular, to de fi ne the exergetic availability of a geothermal resource, two ratios can be de fi ...
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Citations
... Besides, the key benefit of geothermal energy is stability. However, the temperature of 70% geothermal energy is below 150 • C [5]. As a result, it is significant to utilize the low-middle temperature geothermal fluid through some technologies. ...
Owing to different temperature rages of power generation and refrigeration in the cogeneration system, for the sake of selecting the working fluids that are suitable for both power generation and refrigeration simultaneously, 17 commonly used working fluids are evaluated in this paper, based on an organic Rankine cycle coupled with a two-stage vapor compression cycle system in different geothermal fluid temperatures. The performances of working fluids under different working conditions, and the maximum power generation as well as cooling capacity are analyzed. Additionally, the main parameters are analyzed to optimize the system performance. The results indicate that net power output has a local maximum where it corresponds to the optimal evaporation temperature. Besides, the lower the critical temperature, the greater the thermal conductance, and the pressure ratio decreases with evaporation temperature. Hydrocarbons all have higher total heat source recovery efficiency. R1234yf, propane and R1234ze, R152a have excellent maximum net power output when the geothermal fluid temperature is low and high, respectively. R134a always has better maximum net power output and cooling capacity. The net power output is used for cooling, and the COP is closed, therefore, maximum net power output results in the maximum cooling capacity. In addition, that of propane and R1234yf are excellent until the geothermal fluid temperature are 140 °C and 120 °C separately. R1234ze and R152a are good when the geothermal fluid temperatures are 140 °C and 150 °C, respectively.
... Real-time energy convex optimization, via electrical storage, in buildings was performed by Georgiou et al. [111]. A multidisciplinary approach for sustainable exploitation of medium to low enthalpy sources was proposed by Franco and Vaccaro [112]. In the study by Astolfi et al. [113] a techno-economic optimization of different ORC configurations operating with a number of working fluids was performed, considering equipment cost correlations and a model to estimate the turbine design and efficiency. ...
Renewable energy resources are gaining popularity and they have proven their reliability to
achieve a sustainable future, their efficiency increases due to advancement in innovative
technologies, and that leads to less uncertainty and increased contribution to the energy mix of future society.
Geothermal energy carries its own uncertainty due to its nature, it requires high capital
investment owing to the very high cost of well drilling and the journey from exploration to
exploitation can be very stressful for investors and decision-makers. Since the nature of
geothermal resources dictates their method of utilization, it is important to categorize available resources. There is no consensus on the classification of geothermal resources. Most scientists, from geologists to engineers, agree on the term temperature. However, temperature or enthalpy alone cannot describe the nature of fluids. Other classification methods discussed in this paper are assessment confidence, Australian, Canadian, and GEA Codes, Geologic Setting,thermodynamic properties, resources potential, stored heat, and geothermal resources utilization including direct uses. Even within the framework of each classification, there are conflicting opinions between scientists. Well-organized and easily understandable frameworks for classifying geothermal resources are essential for the assessment, exploration, development, and reporting and this paper aims to illustrate a comprehensive analysis of existing methods to come up with a recommendation of the most appropriate method for classification of the geothermal resources.
... With heat sink temperature constraint from the reservoir engineering side in consideration, Sun et al. [16] investigated the effects of evaporator pinch point temperature difference on the thermo-economic performance of the ORC plant. Franco and Vaccaro [17] proposed an integrated model including both the reservoir and power plant behavior. They also considered the re-injection temperature into the plant control strategy. ...
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.
... Large variation in the ambient conditions is another issue to achieve profitable generation [64]. In low-temperature projects, energy extraction occurs from a small temperature difference, and the conversion unit generally employs air cooling (more sensitive to ambient conditions) to drop the temperature [151]. Sanyal and Butler [64] have found that power output could drop as low as 50% in summers which is not encouraging from a profit point of view. ...
Hydrocarbon fields around the world may possess suitable features for low-temperature geothermal energy extraction (below 190 °C). Few demonstration plants prove the technical feasibility of power generation from such fields. Case studies are reviewed and discussed to identify deciding parameters for an economical geothermal system. An insightful discussion outlining the unique characteristics of a power project in oil and gas fields is presented. A low-temperature geothermal system set up on unused wells in depleted reservoirs must justify the challenging economics to become an investment opportunity. Interlinked economic, technical and geological parameters influence a profitable development. The long-term behaviour of the resource is uncertain and sustainable resource management in such fields is rarely discussed. Reservoir and wellbore simulations are likely to allow an improved understanding of resource behaviour. It will facilitate the evaluation of the reservoir capability to sustain the estimated capacity for longer.
... The evaporator inlet temperature can be significantly increased in the regenerator using waste heat in the saturated liquid from the flash separator. The geothermal water reinjection temperature was assumed to be 70 ℃ to avoid silica oversaturation which can lead to scaling and fouling in the heat exchanger and mineral deposits in the pipes and valves [11,[51][52]. The working fluid temperatures at evaporator inlet and outlet must be limited by the pinch point temperature difference to maximize the geothermal heat utilization. ...
Organic Flash Cycles (OFCs) provide a good temperature match between the heat source fluid and the working fluid; however, the heat loss from the saturated liquid in the flash separator reduces the efficiency. Regeneration can recover much of the heat from the saturated liquid to preheat the working fluid to improve the thermo-dynamic performance. The interactions between the evaporation and the flash temperatures for an OFC with an internal heat exchanger (OFC + IHE), an OFC with a regenerator (ROFC), a ROFC with an IHE (ROFC + IHE), and a modified OFC (MOFC) are discussed in this study. The evaporation and flash temperatures are simultaneously optimized to obtain the maximum net power outputs for geothermal water temperatures from 120 • C to 180 • C with a reinjection temperature of 70 • C. The optimal flash temperatures for ROFC, ROFC + IHE and MOFC are lower than for the basic OFC (BOFC) due to the limits of the preheat load and the pinch point which result in higher vapor mass flow rates. The relative increases in the net power outputs and the decreases in the evaporator exergy losses by ROFC, ROFC + IHE and MOFC over those for BOFC decrease with increasing geothermal water inlet temperature. MOFC produces the maximum net power that is up to 66.2% higher than for BOFC for a geothermal water inlet temperature of 120 ℃. However, MOFC requires 51-78% more evaporator area but 13-42% less condenser area than BOFC to generate the same power.
... The calculation of a geothermal field capacity based on numerical modeling has been widely used. The method has been applied in several fields such as Wairakei (Mannington et al. 2004;OÕSullivan et al. 2009), Momotombo (Porras et al. 2007;Franco and Vaccaro 2012), Kamojang (Suryadarma et al. 2010), Larderello (Romagnoli et al. 2010), Hatchobaru (Yahara and Tokita 2010), Ahuachapan (Monterrosa and Montalvo Ló pez 2010), Sabalan (Noorollahi and Itoi 2011) and Karaha Talaga-Bodas . Numerical reservoir modeling is the most powerful tool available to investigate sustainable management of geothermal resources. ...
An integrated numerical modeling of reservoir and power plant thermodynamics is proposed to assess the Patuha geothermal field development strategy. Power plant technologies, namely as dry-steam cycle unit (DSCU) and integrated geothermal combined-cycle unit (IGCCU), were selected for field development strategy options.
TOUGH2 was used to simulate the effects of these technologies on reservoir production sustainability. The selection of power plant technology and field production strategy clearly affects the performance of the reservoir. The simulation results show that the IGCCU is less sustainable if hot fluid is produced only from the steam zone. However, the energy extraction from the brine zone is proven advantageous to maintain the steam zone pressure. In addition, higher injection rates into the brine zone from IGCCU power plant can yield to higher electrical power generation than DSCU.
... Reservoir simulation is an important step in geothermal exploration to accomplish more accurate conceptual models and define exploitation strategies (Franco and Vaccaro, 2012). In particular, it can be a powerful tool to test hypotheses made on the thermal regime of the system (Verma and Gómez-Arias, 2016;Guerrero-Martínez and Verma, 2013;Della-Vedova et al., 2008;Stimac et al., 2001) and also to gain insight on physical processes governing it (Ingebritsen et al., 2010). ...
Three-dimensional temperature simulations of the Acoculco caldera complex are undertaken to improve our understanding of its thermal regime. This volcanic caldera has been considered a Conduction-Dominated Crystalline-Rock geothermal play based on evidences of low permeability of the formations hosting the heat source. An estimated Curie isotherm at depth is obtained from the de-fractal method to establish the background heat flow in the area. Additionally, local thermal anomalies and radiogenic heat generation are considered. The description of the structures controlling the heat flow is based on limited borehole data along with field observations, it includes stratigraphic columns and fracture zones. The heat transfer equation is solved in steady state with a Finite Volume numerical method and a Conjugate Gradient algorithm. The resulting computational model constitutes a workable instrument to test assumptions on the thermal regime in the Acoculco caldera that can be gradually constrained, as more data become available. Numerical results show that shallow and localized thermal anomalies (750 °C) lead to geothermal gradients as high as those measured in the field. The thermal anomalies turn out between 3300 and 3800 m below ground surface as the mean depth, shallower than those assumed in previous 1D thermal models in this caldera complex.
... Assessment of geothermal resources involves determination of the size and geoscientific characteristics of each resource area to calculate the accessible resource base (residual and useful thermal energy stored in the reservoir) and the resource (recoverable thermal energy) (Franco, 2012). ...
The Awibengkok geothermal field, also known as Salak, is a liquid-dominated field. The commercial Awibengkok reservoir is a moderate-to-high temperature (240–312 ◦C) geothermal resource with high fracture permeability, moderate porosity, and moderate-to-low matrix permeability, and can generate electricity up to 377 MW. This field fracture-controlled reservoir has benign chemistry and low-to-moderate non-condensable gas content. The geothermal reservoir is associated with youngvolcanism and intrusions in a highland area in the west of Salak Mountain and east of the Cianten caldera, a collapsed andesitic stratocone. In this paper, numerical method for calculation is used for modelling and reservoir simulation. A simulator is used to build the model. The model was built until it reached the natural state. The method used for model calibration is through pressure and temperature matching of two wells P-T logging data. One of the well is located on the western region of Salak geothermal field, while the other is located on the eastern region. Salak geothermal field model would reach natural state with simulation time up to millions of years. The model state the field is a liquid-dominated field and has steam caps in western and eastern area. The material on those two areas are different, thus the initial conditions are different. The temperature is higher in the western area. The gas saturation vary between 0.127 to 0.5 and there is a caprock with permeability 9mD.
... The estimation of the reservoir potential (and the uncertainty associated with this value) connected to power plant sizing was frequently the object of studies and discussion [10][11][12], as clearly remarked by Steffansson in [13] and DiPippo in the classic textbook about geothermal power plants [14]. ...
... In some cases, the plants showed significant reductions in power output due to the depletion of the reservoirs [10][11][12]. Wrong sizing in this case was generated by an overestimation of the reservoir potential, driven by the desire of a fast recovery of the main economic investment. ...
... The definition of a sustainable size of a geothermal power plant was the object of analysis in some papers by the authors of the present paper [12,15]. The definition of a geothermal system is very useful for the purpose of this paper: it can be seen as made up of the power plant, the geothermal reservoir, the groundwater circulation system, and all the possible connections among the various parts of the plant and the environment. ...
The paper analyzes the problem of defining the potential of geothermal reservoirs and the definition of a sustainable size of a geothermal power plant in the preliminary design phase. While defining the size of a geothermal plant, the objective is to find a compromise between renewability, technical sustainability, and economic return-related issues. In the first part of the paper the simplified lumped parameter approach based on the First-Order methods and their further evolutions and limitations is proposed. Experimental data available for some geothermal reservoirs are used for critical analysis of the simplified approaches for estimating the renewability and sustainability of the production of geothermal plants. In the second part the authors analyze methods based on theoretical heat transfer analysis supported by experimental data acquired from the geothermal field (thermal properties of the rock, porosity of the reservoir, and natural heat flux) and finally consider the numerical simulation as a method to connect the two approaches discussed before. The sustainability of geothermal power production can be estimated taking into account the energy stored in the reservoir and the thermal and fluid dynamic analysis of the reservoir. From this perspective, the numerical simulation of the reservoir can be considered as an effective method for the estimation of a sustainable mass flow rate extraction. Some specific cases are analyzed and discussed.
... However, it would be desirable to adopt a more comprehensive approach, which includes also the subsurface part of the geothermal power plant. A first attempt in this direction is due to Frick et al (2010), and also Blocher et al. (2010); further contributes were given by Franco and Vaccaro (2012) which underline the importance of a sustainable exploitation. ...
Geothermal binary power plants are generally designed and optimized considering only the surface equipment of the plant. The optimization process consists of selecting the most suitable working fluid for the power cycle together with optimum operating parameters, namely the cycle pressures and temperatures. However, it would be desirable to adopt a more comprehensive approach, which includes also the subsurface part of the geothermal power plant: such an approach, though often invoked, is not commonly adopted. In this paper, an open-source software, aimed at the calculation of the performance of a geothermal doublet, is coupled to a commercial software, typically employed for power plant design. Particular attention is given to the combined subsurface/surface calculation, and plant performance will be optimized starting from the reservoir conditions. Ascertained that the reservoir temperature is the most important design parameter for the whole installation, the paper aims at investigating the effect of the other subsurface features on the design point of the surface installations, so as to attain a fully optimized power plant and the highest available conversion efficiency. The simulation model will feature a geothermal doublet coupled to an ORC plant for the power generation; several parametric calculations will be conducted, considering different reservoir conditions and a selection of appropriate working fluids for the ORC. Results of simulations will be discussed with the aid of Second Law analysis, with the scope of pointing out the key outcome of the integrated design procedure.
