Double-flash Geothermal Power Plant Research Articles

Evaluation of the energy and exergy of a trans‐critical CO2 cycle driven by a double flash geothermal power plant

AbstractFacing the dual challenges of environmental impact and the finite nature of fossil fuels, the shift toward sustainable energy sources is imperative. Geothermal energy, a renewable and underutilized resource, offers a promising alternative. This study ventures into a novel domain, exploring the integration of trans‐critical CO2 (tCO2) cycle with a double‐flash geothermal (DFG) cycle, an area not extensively covered in existing research. This study aims to develop a recovery system that utilizes a tCO2 cycle powered by a DFG cycle. A crucial part of this study involves conducting a sensitivity analysis to evaluate the system's energy and exergy performance. This analysis focuses on understanding the impact of changes in key system design parameters, such as energy efficiency, exergy efficiency, net power output, and total exergy destruction rate, to determine the optimal values for these parameters. The results indicate that the recovery system shows a significant improvement of 22% in energy efficiency over the basic cycle. However, there is a decrease in exergy efficiency in the recovery system, which represents a 5.26% decline. As a result, this study paves the way for innovative approaches in geothermal energy use, suggesting potential breakthroughs in renewable technologies.

A Pore-to-Process Digital Design Methodology to Evaluate Efficiency of Geothermal Power Plants

Summary The development and operation of geothermal plants play a crucial role in the transition to sustainable and low-carbon energy systems. In this paper, we have presented a seamless and flexible pore-to-process digital solution for the design and assessment of geothermal systems, encompassing the geothermal reservoir, gathering network, and geothermal power plant. Our primary focus in this study centers on the geothermal power plant with a detailed analysis of the functionality and performance of two commonly used configurations—a single-flash power plant and a double-flash geothermal power plant. Our work highlights that overall exergy efficiency of the studied geothermal power plants declines over time, primarily due to a decrease in the quality of the geothermal reservoir. Additionally, our analysis demonstrated that variations in the inlet separator pressure have a notable impact on the overall behavior of the power plant. Parametric studies also reveal that increasing the inlet separator pressure leads to decreased overall exergy efficiency and turbine power, resulting from less efficient conversion of available exergy into useful work. Our studies showed that a substantial portion of the available exergy in the geothermal fluid is being dissipated in the condenser. Consequently, optimizing the design and operation of the condenser emerges as a crucial factor in enhancing the overall efficiency of geothermal power plants.

Environmental Assessment of Hellisheidi Geothermal Power Plant based on Exergy Allocation Factors for Heat and Electricity Production

The Hellisheidi geothermal power plant, located in Iceland, is a combined heat and power double-flash geothermal plant with an installed capacity of 303.3 MW of electricity and 133 MW of hot water. This study aimed to elucidate the environmental impacts of the electricity and heat production from this double-flash geothermal power plant. In this vein, firstly, the most updated inventory of the plant was generated, and secondly, a life-cycle assessment approach based on the exergy allocation factor was carried out instead of applying the traditionally used allocations in terms of mass and energy. The functional unit was defined as the production of 1 kWh of electricity and 1 kWh of hot water for district heating. The life-cycle stages included the (i) construction, (ii) operation (including abatement operations and maintenance), and (iii) well closure of the geothermal plant. All of the life-cycle stages from construction to dismantling were considered. Finally, the results on the partitioning of the environmental impact to electricity and heat with exergy allocations showed that most of the impact should be charged to electricity, as expected. Furthermore, the distribution of the environmental impacts among the life-cycle stages determined that the construction stage was the most impactful for the electricity and heat production. This result was attributable to the large consumption of steel that was demanded during the construction of the geothermal power plant (geothermal wells, equipment, and buildings). Impacts due to the abatement stage demonstrated that this stage satisfactorily reduced the total impact attributed to the three life-cycle stages of the geothermal power plant.

A novel total-flow geothermal power generator using Turgo turbine: Design and field tests

This paper presents a unique design of a total-flow geothermal power generator that uses Turgo turbine and two-phase supersonic nozzles. The high-speed flashing jets are formed by high-pressure subcooled liquid from the well through the nozzles and impinge turbine blades obliquely to drive the Turgo turbine. This new generator converts geothermal power directly from the geothermal fluid without implementing any phase separator or heat exchanger, which results in a simple and easy-to-maintain system. A prototype of the total-flow geothermal power generator was built and field-tested in Yilan, Taiwan. Results show that compared to traditional Organic Rankine Cycle generators and double flash geothermal power plants, the new design has a competitive geothermal efficiency operating at moderate reservoir enthalpies.

Energy, exergy and exergy-economic analysis of a new multigeneration system based on double-flash geothermal power plant and solar power tower

In this research, a multigeneration system consisting of a double-flash geothermal power plant, solar power tower, organic Rankine cycle, alkaline electrolyzer and a single-stage absorption chiller is presented. In this research, the solar power tower has been used to improve the performance of the double-flash geothermal power plant. Combining such a Concentrated solar power system with a double-flash geothermal power plant was not previously addressed. Also, to increase the whole system's efficiency, the waste heat from the double-flash geothermal power plant and the solar power tower in the proposed system have been used. The proposed system is capable of producing power, hydrogen, heating, and cooling. The multigeneration system has been analyzed by EES software for energy, exergy, and exergy-economy. To study the impact of important parameters on system performance, it has been analyzed parametrically in different conditions. The proposed system is capable of generating 43,640 kW of electricity, 161,604 kgh of hydrogen, cooling of 1243 kW and hot water consumption of 8870 kW in full use of the geothermal source. In the present research, in order to improve the lifetime of the geothermal well, the flow rate of geothermal fluid entering the system is reduced to reach the production capacity of the reference geothermal power plant to achieve the same amount of electricity generation as the base system by the proposed multigeneration system. In this case, 21% less geothermal fluid is extracted from the geothermal source. Under these conditions, the multigeneration system has Energy and Exergy efficiency of 19% and 19.29%, respectively, and the cost of electricity and H2production is equal to 0.1477 $kWhand 7.626 $kg.

LCA and Exergo-Environmental Evaluation of a Combined Heat and Power Double-Flash Geothermal Power Plant

This study deals with the life cycle assessment (LCA) and an exergo-environmental analysis (EEvA) of the geothermal Power Plant of Hellisheiði (Iceland), a combined heat and power double flash plant, with an installed power of 303.3 MW for electricity and 133 MW for hot water. LCA approach is used to evaluate and analyse the environmental performance at the power plant global level. A more in-depth study is developed, at the power plant components level, through EEvA. The analysis employs existing published data with a realignment of the inventory to the latest data resource and compares the life cycle impacts of three methods (ILCD 2011 Midpoint, ReCiPe 2016 Midpoint-Endpoint, and CML-IA Baseline) for two different scenarios. In scenario 1, any emission abatement system is considered. In scenario 2, re-injection of CO2 and H2S is accounted for. The analysis identifies some major hot spots for the environmental power plant impacts, like acidification, particulate matter formation, ecosystem, and human toxicity, mainly caused by some specific sources. Finally, an exergo-environmental analysis allows indicating the wells as significant contributors of the environmental impact rate associated with the construction, Operation & Maintenance, and end of life stages and the HP condenser as the component with the highest environmental cost rate.

A Novel Total-Flow Geothermal Power Generator Using Turgo Turbine: Design and Field Tests

This paper presents a unique design of a total-flow geothermal power generator that uses Turgo turbine and two-phase supersonic nozzles. The high-speed flashing jets are formed by high-pressure subcooled liquid from the well through the nozzles and impinge turbine blades obliquely to drive the Turgo turbine. This new generator converts geothermal power directly from the geothermal fluid without implementing any phase separator or heat exchanger, which results in a simple and easy-to-maintain system. A prototype of the total-flow geothermal power generator was built and field-tested in Yilan, Taiwan. Results show that compared to traditional Organic Rankine Cycle generators and double flash geothermal power plants, the new design has a competitive geothermal efficiency operating at moderate reservoir enthalpies.

A new high-efficient cooling/power cogeneration system based on a double-flash geothermal power plant and a novel zeotropic bi-evaporator ejector refrigeration cycle

Abstract An innovative Bi-Evaporator Ejector Refrigeration Cycle (BE-ERC) working with different zeotropic mixtures is devised in this study. Next, the proposed BE-ERC system is used as binary cycle of a modified Double-Flash Geothermal Power Plant (DF-GPP) to simultaneously produce cooling and power from the same geothermal well. A comprehensive modeling of the proposed integrated system is carried out from thermodynamics laws viewpoints and the results are elaborated in detail. Based upon the results, the use of R142b/Pentane (0.6/0.4) is highly commendable due to achieving the maximum refrigeration load, Coefficient of Performance (COP), and total energy efficiency of 137.83 kW, 0.329, and 20.37%, respectively. Although net electricity and exergy efficiency were not maximum at this condition, their value was competitive. Accordingly, with the use of R142b/Pentane (0.6/0.4), the net electricity, exergy efficiency of the BE-ERC, and total exergy efficiency were calculated 18.61 kW, 2.16%, and 20.95%, respectively. Among all elements of the integral set-up, the first ejector (the main ejector in the BE-ERC) had the highest exergy destruction of 26.09 kW out of overall fuel exergy of 190.7 kW (13.68%), followed by the vapor generator with exergy destruction of 24.4 kW.

Exergoeconomic optimization of a new double-flash geothermal-based combined cooling and power (CCP) system at two different cooling temperatures assisted by boosters

A new cooling/power cogeneration system applicable to double-flash geothermal power plants is devised which provides cooling load at two different adjustable cooling temperatures. To further increase efficiency of the set-up, two boosters are employed to boost pressure of the secondary flow of each ejector due to the considerable drop of pressure of the geofluid through the steam turbines as well as the throttling valves. A comprehensive modeling of the proposed system is achieved from thermodynamics laws as well as economic perspectives and the results are elaborated with more details. In comparison with the previous integrated systems based on the flash geothermal power plants, the present system produces around 47.8% more cooling load and 38.9% more electricity. Also, the results of multi-objective optimization revealed that the net electrical power and exergetic efficiency can be increased approximately 20.59% and 68.11%, respectively. However, the unit cost of power and cooling (UCPC) is decreased around 36.3%. Meantime, the total exergy destruction rate is decreased after optimization. Among all elements, the highest exergy destruction occurred in the condenser by 2570 kW out of 7609 kW (in base mode) and 2333 kW out of 6836 kW (in optimum mode). Also, it is found that the energy efficiency of the proposed system can be increased by increasing turbines outlet pressure, boosters pressure ratio, and separator 1 pressure or decreasing separator 2 pressure.

A Combined Binary-Cycle Geothermal Power Plant with a Secondary Flash Steam Superheating System: Choice of Optimal Working Fluids

The article presents the results from numerically modeling the process circuit of a combined binary-cycle double-flash geothermal power plant (GeoPPs) with the use of secondary flash steam superheating by means of a hydrogen–oxygen steam generator. Geothermal heat carrier from substandard wells of the Mutnovsk geothermal field, as well as separated steam and waste brine from the Mutnovsk GeoPP, were taken as the primary heat source. Numerical investigation results have shown that the application of secondary flash steam superheating by means of a hydrogen–oxygen steam generator makes it possible to increase the steam turbine’s power output and its flow path efficiency owing to the steam wetness reduced by more than a factor of two. In addition, reduced steam wetness helps prevent erosion damage to the last-stage turbine rotor blades. Data on the effect that the use of different organic substances has on the efficiency and power output of the binary installation and of the GeoPP as a whole are given. Optimization investigations have shown that the highest power output and efficiency values of the binary installation used as part of a combined binary-cycle GeoPP at the lowest specific brine flowrate are achieved in using organic substances from the groups of nontoxic fire- and flame-proof (R-31-10 and RC-318) and low-toxic fire- and flame-proof ones (R-227ea, R-236fa, R1318, and R-134a) as working fluids. It has been established that the highest power output values of a combined binary-cycle double-flash GeoPP with secondary flash steam superheating by means of a hydrogen–oxygen steam generator are achieved in using the organic working fluids R-31-10, R‑227ea, and RC-318. In so doing, the optimum design pressure in the expander-separator at which the highest efficiency and power output of the studied GeoPP are obtained makes 0.47 MPa. In solving optimization problems on selecting the working fluids for binary combined-cycle GeoPP installations, it is proposed to use multiaxial composite diagrams of the relative values of geothermal power plant parameters and characteristics. An example of drawing a multiaxial composite diagram for the relative values of parameters and characteristics for a combined binary-cycle GeoPP for the R-290, R-31-10, R-32, and RC-318 working fluids is given. The numerical investigation results can be used in designing new and modernizing the operating GeoPPs that use steam geothermal sources.

Impacts of boundary conditions on reservoir numerical simulation and performance prediction of enhanced geothermal systems

Fractured reservoir boundary conditions are crucial to numerical study on reservoir simulation and performance prediction of an enhanced geothermal system (EGS) but have received little attention in previous studies. We established an integrated model involving fractured reservoir and Double-flash geothermal power plant to compare heat extraction and power generation of the EGS under “recharge” and “no-flow” boundary conditions based on geothermal characteristics of Gonghe Basin, China. The “recharge” boundary conditions allow fluxes of mass and heat to cross reservoir boundaries, whereas the “no-flow” disallow such fluxes. The results show that the heat extraction potential around the periphery of the reservoir is overlooked under “no-flow” boundary conditions. Moreover, the fluxes of mass and heat across the reservoir boundaries exert limited influence on heat extraction process in initial stage, but they affect the process significantly in later stage. Additionally, compared with the EGS under “no-flow” boundary conditions, that under the “recharge” has a longer lifespan of 20%, and produces 8% more electricity power. It is also found the EGS maintains high-level power generation performance in the initial period under both boundary conditions, while the electricity output and thermal efficiency decrease significantly in the following stage.

Multi-objective optimization of two double-flash geothermal power plants integrated with absorption heat transformation and water desalination

Abstract Two configurations of double-flash geothermal power plants, one is combined with water desalination and one integrated with absorption heat transformation and water desalination, are proposed and investigated from the viewpoint of exergoeconomics. The main purpose of investigated systems is the simultaneous generation of electrical power and distilled water. A three-objective optimization procedure is performed to determine the optimal design points, considering for all configurations the decision parameters to be the pressures of low and high-pressure flash chambers and the temperatures of the evaporator and generator. The optimization aims to minimize the product unit cost, while maximizing the electric power generated and the production rate of distilled water. The Pareto frontiers for each configuration are drawn as part of the procedure. It is shown that, at constant and equal pressures of the high-pressure flash chamber, the product unit cost for the system combined with the absorption heat transformer is the lower of the two systems considered. In addition, under the optimized conditions, the product unit costs are approximately equal for the two studied configurations. However, the value of generated power for the system with an absorption heat transformer is about 17% greater than for the alternate system. Moreover, the system integrated with an absorption heat transformer has higher thermal and exergy efficiencies, at about 20% and 3%, respectively.

Thermodynamic evaluation of solar-geothermal hybrid power plants in northern Chile

A thermodynamic model was developed using Engineering Equation Solver (EES) to evaluate the performance of single and double-flash geothermal power plants assisted by a parabolic trough solar concentrating collector field, considering four different geothermal reservoir conditions. The benefits of delivering solar thermal energy for either the superheating or evaporating processes were analyzed in order to achieve the maximum 2nd law efficiency for the hybrid schemes and reduce the geothermal resource consumption for a constant power production. The results of the hybrid single-flash demonstrate that the superheating process generates additional 0.23kWe/kWth, while supplying solar heat to evaporate the geothermal brine only delivers 0.16kWe/kWth. The double-flash hybrid plant simulation results allow obtaining 0.29kWe/kWth and 0.17kW/kWth by integrating solar energy at the superheater and evaporator, respectively. In this context, the hybrid single-flash power plant is able to produce at least 20% additional power output, depending on the characteristics of the geothermal resource. Moreover, all of the cases analyzed herein increased the exergy efficiency of the process by at least 3%. The developed model also allowed assessing the reduction on the consumption of the geothermal fluid from the reservoir when the plant power output stays constant, up to 16% for the hybrid single-flash, and 19% for the hybrid double-flash. Based on the results obtained in this study, the solar-geothermal hybrid scheme increases the power generation compared with geothermal-only power plants, being an attractive solution for improved management of the geothermal reservoir depletion rates. The study shows evidence of existing optimum configurations for the hybrid systems. A relative performance map was developed in order to determine the best operation approaches according to the reservoir conditions and solar field size.

Improvement of Double-Flash geothermal power plant design: A comparison of six interstage heating processes

In this paper, six different modifications of the Double-Flash power plants are proposed. These modifications are named “interstage heating” and consist of additional heat exchangers properly located in the system. The six interstage heating designs are analysed, optimized and then compared to an optimized Double-Flash reference power plant. The objective function is the power plant specific output (kJ/kg), and the design variables are the separator temperatures (°C) and the split fraction. Optimizations are performed for a wide range of reservoir temperatures (i.e., from 140°C to 240°C). Results show that interstage heating processes may increase the specific output of the plant by about 5%, decrease the liquid content in the low pressure turbine by about 50%, and decrease the required cooling capacity of the plant by about 10%. On the other hand, the analysis showed that the new designs proposed have negligible influence on the high pressure turbine liquid content or on the silica saturation coefficient.

Efficient synthesis and reaction kinetics of readily water soluble esters containing sulfonic groups.

A series of various readily water soluble esters were synthesized by a very efficient procedure. These compounds can be useful as thermosensitive tracers for studying the cooling progress in a low enthalpy georeservoir exploitable by double flash geothermal power plant systems. The kinetics of their hydrolysis was investigated. Acylation of primary alcohols or phenols was carried out by a method based on a single-phase solvent system consisting of ethyl acetate acting as an organic solvent and triethylamine acting as a catalyst. Products were characterized by 1H-NMR, and 13C-NMR.

Comparison of genetic algorithm to particle swarm for constrained simulation-based optimization of a geothermal power plant

The performance of a genetic algorithm is compared with that of particle swarm optimization for the constrained, non-linear, simulation-based optimization of a double flash geothermal power plant. Particle swarm optimization converges to better (higher) objective function values. The genetic algorithm is shown to converge more quickly and more tightly, resulting in a loss of solution diversity. Particle swarm optimization obtains solutions within 0.1% and 0.5% of the best known optimum in significantly fewer objective function evaluations than the genetic algorithm.

The constrained design space of double-flash geothermal power plants

This paper investigates the constrained double-flash geothermal power plant design space across a range of brine and condenser temperatures. Silica deposition and/or turbine exhaust quality constraints reduce specific work output at most brine temperatures. Some combinations of brine temperature and condenser temperature are also shown to be infeasible. Reducing condenser temperature is shown to improve specific work output up to 47% with diminishing effect as brine temperature increases. Relaxing the silica constraint is shown to yield up to an 8% increase in specific work output. These results are useful to a plant designer in determining the value of installing improved condensing or silica control equipment.

Geothermal double-flash plant with interstage reheating: An updated and expanded thermal and exergetic analysis and optimization

The concept of a double-flash geothermal power plant with an interstage reheater is updated and extended. The conceptual plant holds a thermodynamic performance advantage over a conventional double-flash plant over the range of reservoir temperatures studied from 220 to 320°C, with the advantage increasing as the temperature increases. An exergy assessment is performed on the whole plant with a detailed examination of the reheater. The effect on performance of the terminal temperature difference in the reheater is found to be small. The trend in performance of the new plant is determined as a function of rising wellhead quality in the event that the reservoir begins to “dry out” yielding higher steam fractions at the wellhead. The potential for silica scaling in the lower-temperature components is examined and found to be of concern. The exact optimized separator and flash temperatures are compared to the simple rule-of-thumb, the “equal-temperature-split” rule, which turns out to be quite accurate. A conventional double-flash plant using a turbine designed to remove moisture after each stage is also examined and found to be theoretically roughly equal to the conceptual plant in terms of power performance. The extra power that can be generated by a reheat plant is monetized to compare with the extra cost involved in the more complex plant relative to a conventional double-flash plant. The projected payback is relatively short indicating that the proposed plant should be both thermodynamically and economically worthwhile on condition that some means of controlling silica precipitation is adopted.

Exergetic analysis of various types of geothermal power plants

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%.

Performance Analysis and Optimization of Double-Flash Geothermal Power Plants

One of the most important cycles for electricity generation from geothermal energy is the double-flash cycle. Approximately 25% of the total geothermal based electricity generation all over the world comes from double-flash geothermal power plants. In this paper, performance analysis of a hypothetical double-flash geothermal power plant is performed and variations of fundamental characteristics of the plant are examined. In the performance analysis, initially, optimum flashing pressures are determined, and energy and exergy values of the base points of the plant are calculated. In addition, first and second law efficiencies of the power plant are calculated. Main exergy destruction locations are determined and these losses are illustrated in an exergy flow diagram. For these purposes, it is assumed that a hypothetical double-flash geothermal power plant is constructed in the conditions of western Turkey. The geothermal field where the power plant will be built produces geofluid at a temperature of 210°C and a mass flow rate of 200kg∕s. According to simulation results, it is possible to produce 11,488kWe electrical power output in this field. Optimum first and second flashing pressures are determined to be 530kPa and 95kPa, respectively. Based on the exergy of the geothermal fluid at reservoir, overall first and second law efficiencies of the power plant are also calculated to be 6.88% and 28.55%, respectively.