Geothermal Power Systems Research Articles

Entropy generation due to micro-rotating Casson's nanofluid flow over a nonlinear stretching plate: numerical treatment

Objective: This article numerically investigates the entropy generation due to micro-rotating Casson's nanofluid along with an impact of an inclined magnetic field past a nonlinear stretching surface. Heat and mass transfer analysis is carried out in association with the heat source/sink and chemical reaction coefficient. Furthermore, heat dissipation is computed via viscous dissipation and joule heating phenomena. Attributes of nanofluid are disclosed by taking Brownian motion and thermophoresis phenomena. Results and conclusion: Numerical solutions of out-coming differential equations are obtained employing Runge–Kutta fourth-order with shooting technique. The behavior of multiple parameters has been displayed via graphs. Entropy profile is developed effectively for accelerating values of Hartmann and Brinkman number. Moreover, the temperature profile accelerates significantly with an enhancement in the heat transfer Biot number. Practice implications: The study of entropy generation due to micro-rotating Casson's nanofluid has numerous applications in engineering and heat-storing devices such as pumped heat electricity storage, phase change material, solar and geothermal power systems. The minimization of entropy plays a significant role in the design of the mechanical system that relies on heat transfer.

Technical Performance Optimization of a Novel Geothermal Hybrid Power Generation System

Geothermal Aided Power Generation (GAPG) technology is a geothermal hybrid power system that geothermal energy has been integrated into the fossil fired plant to preheat the feedwater, and displace the extraction steam of fossil fired plant. In such a power system, the heat exchange process between extraction steam and geo-fluid occurs in a heat exchange between. When the geo-fluid in the heat exchanger quench to lower temperature for heat transfer purpose, silica scaling would occur in the heat exchanger system. The performance of the GAPG plant would be influenced by the configuration of the heat exchanger and silica scaling in the heat exchanger. For a GAPG plant, it has two possible configurations for a heat exchanger system: series arrangement and parallel arrangement. The different configuration also impacts on the technical performance of the GAPG plant. The silica scaling in the heat exchanger system would harm the performance of the GAPG plant. In this study, a GAPG power system from a 300 MW power plant is used as a case study to understand the impact of displacement selections and heat exchanger arrangement on the performance of the GAPG plant. It was found that there is no silica scaling occurring in heat exchangers system if geo-fluid is used to displace to high-grade extraction steam only. Furthermore, the Parallel arrangement is better than the Series arrangement in terms of the additional power output. Moreover, the GAPG plant has protentional to reduce carbon dioxide emissions by 13%.

A Comparative Study of Cooling Sources in Organic Rankine Cycle for Low-Temperature Geothermal Heat Sources

Geothermal energy refers to ground heat sources exploited for many purposes (for example, generating electricity). A steam power plant, that uses water as a medium and operating on the Rankine cycle, is a prospective technology that can be used to generate electricity utilizing geothermal heat. However, due to the thermal properties of the applied working fluid, the steam power plant has the limitation that may not utilize cold source like liquefied dimethyl ether (DME) at the temperature of around -25 °C or the extreme one, like liquefied natural gas (LNG) at the temperature of around -160 °C. For this reason, it seems that RC using an organic working fluid (so-called ORC) is an appropriate technology to utilize heat sources of extremely low temperatures. Selected ORC working fluids are considered suitable to absorb the cold source. This paper reported the thermodynamic modelling analysis and a comparison of geothermal power systems exploiting air, water, LNG, and DME as the cooling medium of the ORC. The simple scheme of ORC is used for modelling, furthermore, the Trilateral Flash Cycle (TFC) is described as a comparative study. Thanks to the LNG technology, it is already mature enough, and the method of altering the phase into liquefied form is likely to store the energy (i.e., the power to liquid). In the liquefied form, natural gas can be easily distributed and transported at a certain distance. In this model system, the result shows that LNG and DME appear to be excellent options for increasing the operating range of ORC. The modelling result shows that combining propane (a working fluid inside the cycle) and LNG (a cooling source) has a wider operating range and is a good option to exploit low-temperature geothermal heat as a power generation system. Also, using DME for both cooling sources and the working fluid inside the geothermal power system employing ORC outperforms other ones. Taking advantage of using them as a cooling source is significantly boosting the potential deriving from low-temperature geothermal energy (i.e., below 90 °C) as promising sources in the future.

The feasibility of clean power generation from a novel dual-vertical-well enhanced geothermal system (EGS): A case study in the Gonghe Basin, China

Recently, the first demonstration enhanced geothermal system (EGS) is being constructed at the Gonghe Basin, northwestern China, where manifests a massive potential source of geothermal energy for clean power generation within the hot dry rock (HDR). Based on the available geological data, a conceptual EGS with a novel dual-vertical-well is proposed to investigate the potential of clean power generation from the target geothermal reservoir in the Gonghe Basin. Particularly, the multiple interacting continua approach is employed to accurately delineate the transport of heat and fluid within the high-temperature fractured geothermal reservoir. The feasibility of power generation at depths between 2900 m and 3300 m is reasonably forecasted over the 30 years with a production rate of 40 kg/s. The results demonstrate that the proposed EGS can obtain an ascending production in the first 10 years, and a slight temperature drop by 7.7% in the following 20 years. In addition, the electric power ranges within 2.86–3.23 MW, and the electric energy efficiency ranges within 13.88–18.47 over the 30 years, showing a promising production performance. The levelized cost of energy (LCOE) for the proposed geothermal power system is estimated at 0.035 $/kWh, and the reduction in total greenhouse gas emissions is expected at 0.29–1.01 million tons. Thus, the spread of this proposed geothermal power plant is very important for realizing carbon neutrality by 2060 in China. The sensitivity analysis indicates that the injection temperature and injection rate are two key parameters that have significant effects on the production performance. For the proposed geothermal system in the Gonghe Basin, the suitable injection temperature and injection rate are recommended as 60 °C and 40 kg/s, respectively. This work also provides a guideline for the exploitation, reservoir stimulation, and flow test of future EGS development in the Gonghe Basin and other sites under similar conditions.

Experimental study on horizontal tube spray falling film evaporator in a low temperature geothermal binary cycle power system

The horizontal tube spray falling film evaporator is an efficient evaporation equipment, which has the advantages of good heat exchange effect, small equipment volume and low cost. In this paper, R245fa is used as the working fluid to build a heat transfer test platform for the horizontal pipe spray falling film evaporator of the Organic Rankine Cycle(ORC) power generation system. The effect of factors such as the spray density of the organic working fluid, the initial temperature of the geothermal water and the flow on the heat transfer coefficient outside the tube is studied. The experimental results show that with the increase of the spray density of the organic working fluid, the initial temperature of the geothermal water, and the flow of the geothermal water, the heat transfer coefficient first increases and then decreases.

Optimal solar thermal retrofit for geothermal power systems considering the lifetime brine degradation

Geothermal power plants usually suffer from performance deterioration during the operation due to the geothermal resource's degradation. Combining solar thermal energy to retrofit the system is considered an effective way to alleviate this problem. This study explores the off-design performance of organic Rankine cycle-based hybrid system throughout a 30-year life span, rather than a typical single year as the previous research. Then several interesting questions are consequently discussed: (1) Which year is most suitable for system retrofit? (2) How many times should the system be retrofitted? (3) How much is the difference between the 30-year-based results and the conventional single-year-based analysis? Results indicate that the single-year-based approach could greatly underestimate the Levelized cost of electricity (LCOE) by up to 18% and also significantly overestimate the increment in electricity generation (Etot). Thus a life-span-based approach is highly recommended for geothermal-based hybrid plants. Besides, the retrofit year has huge impacts on both thermodynamic and economic performance, and the optimal retrofit should be carried out in 6th year. Moreover, this study reveals that multiple retrofits can indeed further increase the Etot but are not cost-effective. Therefore, a single solar thermal retrofit is recommended for existing geothermal power systems rather than multiple retrofits.

Thermo-economic simulation of four power generations based on genetic algorithm

The thermodynamic and economic suitability of four geothermal power systems is analyzed. When the heat source temperature ranges from 100-150?C, the performance indicators of power capacity per unit geo-fluid, exergy efficiency, payback period, net present value and internal rate of return for four types of the power system are calculated. The results show that when the heat source temperature increases from 100-150?C, the power capacity per unit geo-fluid for single flash, organic rankine cycle (ORC), double flash, and flash-ORC system increases from 2.26-7.72 kWh/t, 2.05-8.37 kWh/t, 2.96-9.96 kWh/t, and 2.76-9.82 kWh/t, respectively, and the performance indicators of two-stage energy conversion systems are better than single systems. R245fa is selected as the working fluid based on anti-scaling and better performance. When the heat source temperature is 130?C, the payback period, net present value and internal rate of return of flash-binary power system are six years, 2508000 US$ and 16.09%, respectively. The research shows that, unlike the single objective optimization of the two power systems, the multi-objective feasibility analysis is a technical integration innovation of the existing research. The research can provide technical support for power construction and realize the sustainable development of clean energy in China.

The exergoeconomic optimisation and economic sensitive analysis for flash-binary and double flash geothermal power systems

The exergoeconomic optimisation and economic sensitive analysis for flash-binary and double flash geothermal power systems

The exergoeconomic optimisation and economic sensitive analysis for flash-binary and double flash geothermal power systems

The exergoeconomic optimisation and economic sensitive analysis for flash-binary and double flash geothermal power systems

Thermodynamic analysis and economic assessment of an improved geothermal power system integrated with a biomass-fired cogeneration plant

A novel geothermal power system integrated with a biomass-fired cogeneration plant has been developed, which feeds the obtained geothermal energy into the steam cycle of the biomass plant. Under the cogeneration scenario, the geothermal water provides heat to the supply-water for district heating together with the extraction steam of the turbine, while in the power generation scenario, the geothermal water is employed to warm the feedwater of the biomass plant. Consequently, much extraction steam of the turbine can be saved to produce additional electricity that can be regarded as geothermal energy-based electricity. Based on a 35 MW biomass cogeneration plant, the thermodynamic and economic performance of the proposed system was evaluated, and the effects of the main parameters were investigated as well. The results indicated that the geothermal power generation efficiency can reach 25.47% or 5.62% under the cogeneration mode or power generation mode. In a whole year, 16935.48 MWh electricity can be yielded from geothermal energy with an annual geothermal power generation efficiency of 17.08%. The levelized cost of geothermal energy-based electricity is only 0.0329 $/kWh when adopting the new design. Generally, the novel concept is quite advantageous from both the thermodynamic and economic perspectives.

Thermodynamic evaluation and comparison of direct geothermal power systems and their expanders

Direct geothermal power system is an effective method to utilize medium-high temperature geothermal resources employing geothermal steam as working fluid. The most widely applied technology are single flash and double flash system. Recently, full flow system has been introduced into geothermal fields and developed to work with two-phase expansion in several geothermal fields in China. To theoretically understand the thermodynamic characteristics of these three direct geothermal power systems and their expanders, a comparative study and thermodynamic evaluation were performed in this paper. A thermodynamic model, taking into account the power consumption of cooling water pump and fan, was developed to simulate the performance of direct geothermal power systems and their expansion equipment. The effects of operating parameters were discussed and analyzed, including inlet dryness, inlet temperature and outlet temperature. Results showed that full flow system has larger output power and thermal efficiency than flashing systems, especially at lower inlet dryness. When inlet dryness is 0.1, the thermal efficiency of full flow system is 38% higher than that of single flash system. Moreover, the output power increases with inlet dryness under constant mass flowrate, but shows opposite variation trend under constant volume flowrate. Higher inlet temperature and lower outlet temperature lead to higher output power and thermal efficiency, however it is limited by the expansion ratio and volume flowrate of expanders. The full flow system is more competitive than flash systems when the isentropic efficiency of full flow expander can reach 50%–70%.

Comparative exergy, multi-objective optimization, and extended environmental assessment of geothermal combined power and refrigeration systems

In the present work a comparative exergy analysis, multi-objective optimization, as well as extended environmental analysis of a geothermal-based power and refrigeration system, is carried out. Different arrangements with the ammonia-water refrigeration cycle, organic Rankine cycle (ORC), and thermoelectric generator (TEG) are investigated. The current work novelties are the presentation of a novel power-refrigeration system driven by a geothermal source and the employment of TEG units to recover geothermal energy, besides extended environmental assessment. The results of sensitivity analysis indicate that the highest net output work capacity is for the suggested system (configuration 3). Exergy analysis exhibits that in all cases, the absorber has the highest exergy destruction rate and one of the lowest exergy efficiency because it is the first component, which gains the heat from the geothermal source. The suggested system produces 495.2 kW net output power and the highest energy efficiency of 19.42%, which are 131.7 kW, and 3.84% higher than configuration 1(base system). Optimization results represent that in the optimum point, Ẇnet shows about 33.3% improvement compared with the un-optimized condition. It is found that configuration 3 which consists of cogeneration with two loops of ammonia-water power cycle with refrigeration system along with an additional thermoelectric generator for enhanced waste heat recovery has the highest environmental footprints because of multiple components installed that would occupy more space, electricity, materials, and other resources for its construction, operation, maintenance, and end-of-life.

Prospects of power generation from the deep fractured geothermal reservoir using a novel vertical well system in the Yangbajing geothermal field, China

Deep geological exploration via well ZK4001 indicated that there exist high-temperature fractured geothermal reservoirs at the depth of 950–1350 m in the Yangbajing geothermal field. The detected reservoir temperature reached approximately 248 °C, showing a huge production potential. In this work, a novel geothermal production system using vertical wells was designed to investigate the power generation potential from the deep fractured geothermal reservoir at this site. A large well field with multiple wells arranged in a five-spot configuration was proposed to maximize the commercial scale electricity generation. The optimal mass flow rate was 17 kg/s for the single geothermal production unit. And a total of 24 single units could be reached using 8 production wells and 8 injection wells. The results showed the production temperature within the range of 240–248 °C, only reduced by 3.3% in 30 years lifetime. The total installed capacity of the proposed geothermal power system reached 66.0 MW. The levelized cost of electricity (LCOE) was estimated at 15 $/MWh, which was significantly cheaper than the electricity price of Tibet in 2019. Furthermore, the operation of this power system could reduce greenhouse gas (GHG) emissions with the maximum value of 20.3 Mt by replacing the same installed capacity of fossil fuel plant over a 30-year production period. This work provides important references for the sustainable power generation and future capacity expansion in the Yangbajing geothermal field.

Crustal Fault Zones (CFZ) as Geothermal Power Systems: A Preliminary 3D THM Model Constrained by a Multidisciplinary Approach

The Pontgibaud crustal fault zone (CFZ) in the French Massif Central provides an opportunity to evaluate the high-temperature geothermal potential of these naturally permeable zones. Previous 2D modeling of heat and mass transfer in a fault zone highlighted that a subvertical CFZ concentrates the highest temperature anomalies at shallow depths. By comparing the results of these large-scale 2D numerical models with field data, the depth of the 150°C isotherm was estimated to be at a depth of 2.5 km. However, these results did not consider 3D effects and interactions between fluids, deformation, and temperature. Here, field measurements are used to control the 3D geometry of the geological structures. New 2D (thin-section) and 3D (X-ray microtomography) observations point to a well-defined spatial propagation of fractures and voids, exhibiting the same fracture architecture at different scales (2.5 μm to 2 mm). Moreover, new measurements on porosity and permeability confirm that the highly fractured and altered samples are characterized by large permeability values, one of them reaching 10-12 m2. Based on a thermoporoelastic hypothesis, a preliminary 3D THM numerical model is presented. A first parametric study highlights the role of permeability, stress direction, and intensity on fluid flow. In particular, three different convective patterns have been identified (finger-like, blob-like, and double-like convective patterns). The results suggest that vertical deformation zones oriented at 30 and 70° with respect to the maximum horizontal stress direction would correspond to the potential target for high-temperature anomalies. Finally, a large-scale 3D numerical model of the Pontgibaud CFZ, based on THM coupling and the comparison with field data (temperature, heat flux, and electrical resistivity), allows us to explore the spatial geometry of the 150°C isotherm. Although simplified hypotheses have been used, 3D field data have been reproduced.

Design of a scaling reduction system for geothermal applications

The aim of the EU 2020 GeoSmart project relies on the demonstration of innovative solutions to improve the flexibility and the efficiency of geothermal heat and power systems. This specific study focuses on issues related to silica scaling and its deposition on the reinjection wells. A limiting constraint for geothermal plants to fully utilize the thermal energy form well fluids is in fact the need to reinject geothermal brine at a high enough temperature to prevent thermodynamic fouling by silica scale deposition. GeoSmart aims to develop a solution based on retention system technology to control and reduce the silica scale formation before re-injection. Lowering reinjection temperature would strongly increase plant efficiency by providing extra useful heat. Based on silica scaling numerical simulation, the effects of parameters like pH, temperature and brine composition on silica polymerization and scaling deposition rates, the design and optimization of the retention system has been developed. The design aims to promote polymerization phenomena inside the tank so that scaling is consequently inhibited in the reinjection well pipes. Chemical additives and specific coatings have also been evaluated to guarantee the optimal required conditions. The case study is based on real-data referred to operational conditions and brine composition of the Zorlu Kizildere plant in Turkey. The economic and environmental impact of the retention system has been evaluated with positive outcomes. The in-site test and validation at industrial level of the above mentioned technology will be provided during the next activities of the GeoSmart project

Prospects of Power Generation from the Deep Fractured Geothermal Reservoir Using a Novel Vertical Well System in the Yangbajing Geothermal Field, China

Deep geological exploration via well ZK4001 indicated that there exist high-temperature fractured geothermal reservoirs at the depth of 950–1350 m in the Yangbajing geothermal field. The detected reservoir temperature reached approximately 248 ℃, showing a huge production potential. In this work, a novel geothermal production system using vertical wells was designed to investigate the power generation potential from the deep fractured geothermal reservoir at this site. A large well field with multiple wells arranged in a five-spot configuration was proposed to maximize the commercial scale electricity generation. The optimal mass flow rate was 17 kg/s for the single geothermal production unit. And a total of 24 single units could be reached using 8 production wells and 8 injection wells. The results showed the production temperature within the range of 240–248 ℃, only reduced by 3.3% in 30 years lifetime. The total installed capacity of the proposed geothermal power system reached 66.0 MW. The LCOE (levelized cost of electricity) was estimated at 15 $/MWh, which was significantly cheaper than the electricity price of Tibet in 2019. Furthermore, the operation of this power system could reduce greenhouse gas (GHG) emissions with the maximum value of 20.3 Mt by replacing the same installed capacity of fossil fuel plant over a 30-year production period. This work provides important references for the sustainable power generation and future capacity expanding in the Yangbajing geothermal field.

Physical and Thermodynamic Analysis of the Geothermal Power Systems

Physical and Thermodynamic Analysis of the Geothermal Power Systems

A critical review on environmental impacts of renewable energy systems and mitigation strategies: Wind, hydro, biomass and geothermal

The annual growth of global energy demand and the associated environmental impacts (EIs) has an important role in the large sustainable and green global energy transition. Renewable energy systems have been attracting substantial economic, environmental, and technical attention throughout the last decade, while some have been in the market for almost a century. However, even renewable energy may negatively affect the environment, which is widely considered much less harsh than fossil energy resources. This, in return, requires more consideration and appropriate precautions to be taken. This work discusses the environmental impacts (EIs) of small and medium-sized wind, hydro, biomass, and geothermal power systems. The approach goes through all stages from planning and conception to construction and installation and throughout service life and decommissioning. For various circumstances and technically and ecologically viable guidelines for their effect on natural resources and wildlife, clear and comprehensive solutions have been given.

Combining brine or CO2 geothermal preheating with low-temperature waste heat: A higher-efficiency hybrid geothermal power system

Abstract Hybrid geothermal power plants operate by using geothermal fluid to preheat the working fluid of a higher-temperature power cycle for electricity generation. This has been shown to yield higher electricity generation than the combination of a stand-alone geothermal power plant and the higher-temperature power cycle. Here, we test both a direct CO2 hybrid geothermal system and an indirect brine hybrid geothermal system. The direct CO2 hybrid geothermal system is a CO2 Plume Geothermal (CPG) system, which uses CO2 as the subsurface working fluid, but with auxiliary heat addition to the geologically produced CO2 at the surface. The indirect brine geothermal system uses the hot geologically produced brine to preheat the secondary working fluid (CO2) within a secondary power cycle. We find that the direct CPG-hybrid system and the indirect brine-hybrid system both can generate 20 % more electric power than the summed power of individual geothermal and auxiliary systems in some cases. Each hybrid system has an optimum turbine inlet temperature which maximizes the electric power generated, and is typically between 100 °C and 200 °C in the systems examined. The optimum turbine inlet temperature tends to occur where the geothermal heat contribution is between 50 % and 70 % of the total heat addition to the hybrid system. Lastly, the CO2 direct system has lower wellhead temperatures than indirect brine and therefore can utilize lower temperature resources.

Modeling of geothermal power system equipped with absorption refrigeration and solar energy using multilayer perceptron neural network optimized with imperialist competitive algorithm

For geothermal energy system, the low geothermal well operating lifetime and temperature is one of the main obstacles. Also, finding the optimum design parameters and operating conditions requires many experimental tests and intricate mathematical models. Besides, improving the energy efficiency and lacking technical feasibility of the combined geothermal systems are other challenges concerning geothermal systems. To cover the mentioned challenges, in the current study, a hybrid geothermal/absorption refrigeration system (ARS) incorporated with solar thermal collector, desalination unit and hydrogen storage system is designed and assessed. The proposed system is investigated by developing two methods of artificial intelligence (AI) as well as thermodynamic model. The intelligent methods are multilayer perceptron (MLP) neural network optimized with imperialist competitive algorithm (ICA), MLP-ICA, and MLP optimized with genetic algorithm (GA), MLP-GA. These methods are manufactured based on the solar irradiance, cooling water temperature difference, ambient temperature, pinch-point temperature, evaporating and condensing temperatures as independent parameters. These parameters are utilized to obtain the power generation, coefficient of performance of the ARS (COPchiller), heat exchanger area of the ARS, and cycle thermal efficiency.The obtained results show that simulation of the system by MLP-ICA was successfully carried out and this model operates substantially better than the MLP-GA for simulating the behavior of the system. Also, the payback time for the proposed system (with the interest rate of 3%) was obtained around 8 years.