Results 1 - 10 of 65
Results 1 - 10 of 65. Search took: 0.018 seconds
|Sort by: date | relevance|
[en] Highlights: • Hybrid solar and geothermal energy conversion system was modelled using subcritical and supercritical ORCs. • Solar thermal and geothermal energy can be effectively hybridised. • Greater thermodynamic advantages and economic benefits can be achieved using the supercritical hybrid plant. • Hybrid plants can produce up to 19% more annual electricity than the two stand-alone plants. • Solar-to-electricity cost in the supercritical hybrid plant is about 4–19% less than in the subcritical plant. - Abstract: A supercritical Organic Rankine Cycle (ORC) is renowned for higher conversion efficiency than the conventional ORC due to a better thermal match (i.e. reduced irreversibility) presented in the heat exchanger unit. This improved thermal match is a result of the obscured liquid-to-vapor boundary of the organic working fluid at supercritical states. Stand-alone solar thermal power generation and stand-alone geothermal power generation using a supercritical ORC have been widely investigated. However, the power generation capability of a single supercritical ORC using combined solar and geothermal energy has not been examined. This paper thus investigates the hybridisation of solar and geothermal energy in a supercritical ORC to explore the benefit from the potential synergies of such a hybrid platform. Its performances were also compared with those of a subcritical hybrid plant, stand-alone solar and geothermal plants. All simulations and modelling of the power cycles were carried out using process simulation package Aspen HYSYS. The performances of the hybrid plant were then assessed using technical analysis, economic analysis, and the figure of merit analysis. The results of the technical analysis show that thermodynamically, the hybrid plant using a supercritical ORC outperforms the hybrid plant using a subcritical ORC if at least 66% of its exergy input is met by solar energy (i.e. a solar exergy fraction of >66%), namely producing 4–17% more electricity using the same energy resources. Exergy analysis shows that with a solar exergy fraction of more than 66% the exergetic efficiency of the hybrid plant is about 27–34% for the supercritical hybrid plant and 23–32% for the subcritical hybrid plant. The figure of merit analysis indicates that the hybrid plant produces a maximum of 15% (using a subcritical ORC) and 19% (using a supercritical ORC) more annual electricity than the two stand-alone plants. Economically, the hybrid plant using the supercritical ORC has a solar-to-electricity cost of approximately 1.5–3.3% less than those of the subcritical scenario
[en] Two different methods to determine the effective thermal conductivity of six Mexican cementing systems used in geothermal well completion were compared in the temperature range from 28 to 200 deg. C. Measurements were taken using the classical line-source method and the Jaeger method. The experimental thermal conductivity uncertainties were 4% and 11.8% for the line source and Jaeger's methods, respectively
[en] Highlights: ► ANN has been modeled for predicting exergy efficiency a GDHS thought exergy analysis. ► The network yields a maximum correlation coefficient with minimum coefficient of variance and root mean square values. ► The ANN modeling can provide high accuracy and reliability for predicting the exergy efficiency of GDHSs. ► Thus, online monitoring system and the performance of GDHS can be implemented. - Abstract: This paper deals with an artificial neural network (ANN) modeling to predict the exergy efficiency of geothermal district heating system under a broad range of operating conditions. As a case study, the Afyonkarahisar geothermal district heating system (AGDHS) in Turkey is considered. The average daily actual thermal data acquired from the AGDHS in the 2009–2010 heating season are collected and employed for exergy analysis. An ANN modeling is developed based on backpropagation learning algorithm for predicting the exergy efficiency of the system according to parameters of the system, namely the ambient temperature, flow rate and well head temperature. Then, the recorded and calculated data conducted in the AGDHS at different dates are used for training the network. The results showed that the network yields a maximum correlation coefficient with minimum coefficient of variance and root mean square values. The results confirmed that the ANN modeling can be applied successfully and can provide high accuracy and reliability for predicting the exergy performance of geothermal district heating systems.
[en] Highlights: • We proposed and analyzed a geothermal power cycle for the generation of electricity. • The second law analysis of the cycle was perfor • med. • A parametric study was performed to test the proposed system under different reservoir conditions. • The proposed system was operated for the living data that belongs to a geothermal district of Ömerbeyli. - Abstract: In this study, a geothermal power cycle was analyzed for the generation of electricity at different reservoir conditions by using carbon-dioxide at super-critical condition. The second law analysis was performed and it was found that the buoyancy effect was sufficient to cycle the working fluid of carbon-dioxide. A parametric study was performed to test the proposed system under different reservoir conditions, i.e., reservoir depth, temperature, permeability, distance between the injection and production wells, and also the environmental conditions. Finally, the proposed system was operated for the data that belongs to a geothermal district of Ömerbeyli near the city of Aydın in Turkey
[en] Highlights: • We monitor the Gonen geothermal district heating system for a one-year period. • Six different operating cases are proved to exist in the system. • Energy and exergy analysis is carried out for each case. • Case-based analyses are used to show the annual system performance. - Abstract: In this paper, the effects of different operating conditions of the Gonen geothermal district heating system (GDHS) on its annual energy and exergy performance are investigated. The system parameters such as temperature, pressure and flow rate are monitored by using fixed and portable measuring instruments over a one-year period. Thus the main differences in the annual system operation are detected. The measurements show that the Gonen GDHS has six different operating cases depending on the outside temperature throughout the year. The energy and exergy analysis of the system is carried out for each case using the actual system parameters at the corresponding reference temperatures, which are 3.86, 7.1, 8.88, 11.83, 15.26 and 20.4 °C. The highest and lowest energy (57.32%, 35.64%) and exergy (55.76%, 41.42%) efficiencies of the overall system are calculated at the reference temperatures of 15.26 °C and 3.86 °C, respectively. Besides, taking the six case-based energy and exergy analyses into account, the annual average energy and exergy efficiencies are determined to be 45.24% and 47.33%, respectively
[en] Highlights: • We model hybrid solar thermal and geothermal energy conversion system in the Australian context. • Solar thermal and geothermal energy can be effectively hybridised. • Thermodynamic advantages and economic benefits are realised. • Hybrid system overcomes adverse effects of diurnal temperature change on power generation. • Cost of electricity of an Enhanced Geothermal System can drop by more than 20% if hybridised with solar energy. - Abstract: A major problem faced by many standalone geothermal power plants, particularly in hot and arid climates such as Australia, is the adverse effects of diurnal temperature change on the operation of air-cooled condensers which typically leads to fluctuation in the power output and degradation of thermal efficiency. This study is concerned with the assessment of hybrid solar–geothermal power plants as a means of boosting the power output and where possible moderating the impact of diurnal temperature change. The ultimate goal is to explore the potential benefits from the synergies between the solar and geothermal energy sources. For this purpose the performances of the hybrid systems in terms of power output and the cost of electricity were compared with that of stand-alone solar and geothermal plants. Moreover, the influence of various controlling parameters including the ambient temperature, solar irradiance, geographical location, resource quality, and the operating mode of the power cycle on the performance of the hybrid system were investigated under steady-state conditions. Unsteady-state case studies were also performed to examine the dynamic behaviour of hybrid systems. These case studies were carried out for three different Australian geographic locations using raw hourly meteorological data of a typical year. The process simulation package Aspen-HYSYS was used to simulate plant configurations of interest. Thermodynamic analyses carried out for a reservoir temperature of 120 °C and a fixed brine flow rate of 50 kg/s revealed that under Australian climatic conditions (with a typical ambient temperature of 31 °C in summer) a hybrid plant would outperform stand-alone geothermal and solar power plants if at least 68% of its energy input is met by solar energy (i.e. a solar energy fraction of ≈68%). This figure drops to about 19% for reservoir temperatures greater than 170 °C. Case studies also showed that, for a mid-range reservoir temperature of 150 °C, the cost of electricity production can be reduced by 20% when a hybrid plant is used instead of the stand-alone Enhanced Geothermal System (EGS)
[en] Highlights: • Economic evaluation of GDHS using advanced exergoeconomic analysis for the first time. • The results obtained for two different GDHSs are compared under same condition. • Each component of the Sarayköy GDHS is to operate more economically. • The usefulness of this analysis was clearly demonstrated comparing both the systems. - Abstract: This paper refers to an economic comparison and evaluation of two geothermal district heating systems (GDHSs) under same reference state condition and mechanic/economic parameters by using an advanced exergoeconomic analysis. In this analysis, costs of investment and exergy destruction of each component for the thermal systems such as the Afyon and Sarayköy GDHSs were split into endogenous/exogenous and unavoidable/avoidable parts, and were also compared with each other for the first time. The results obtained show that the advanced exergoeconomic analysis makes the information more accurate and useful, and supplies additional information that cannot be provided by the conversional analysis. Furthermore, the Afyon GDHS can be made more cost effectiveness, removing the system components’ irreversibilities, technical-economic limitations, and poorly chosen manufacturing methods, according to the Sarayköy GDHS. The majority of the components in the Sarayköy GDHS are to operate more economically than those in the Afyon GDHS. As a result, the usefulness of this method was clearly demonstrated comparing both the systems
[en] Highlights: • Geothermal energy assisted milk powder production line was studied thermodynamically. • The first study on exergy analysis of a milk powder production line. • The overall energy and exergy efficiencies were calculated as 85.4 and 57.45%, respectively. • The evaporator, has the highest exergy destruction rate with 333.6 kW, needs a detailed assessment. - Abstract: Milk has been consumed since time immemorial because of its unique nutritional properties and produced almost 816 million tonnes in the year of 2016. Due to its highly perishable characteristic, milk is processed into more stable milk products such as cheese, yoghurt, and butter and milk powder. Among them, milk powder is distinctive for its longer shelf life and can be stored at ambient temperature. The other advantages of milk powder are less volume requirement during its transportation and higher selling price. Therefore, it is widely used in many food products such as ice cream, bakery products, and sausages. According to a recent study on the statistics from Food and Agriculture Organization, world production of whole dried milk was 3,597,015 tonnes in 2014: Oceania 36.5%, Americas 36.1% and Europe 24.1% of the World production. Milk powder production is a process that requires high energy, especially for evaporation. Recently, reducing energy use has been gaining importance by increasing energy and exergy efficiency. Conventional energy analysis is performed based on the First Law of Thermodynamics. Unlike from the First Law, the Second Law or exergy analysis (defined as useful work) has appeared in the literature, while this analysis not only assesses quantity but also quality of energy. In this study, exergy analysis of a milk powder production system, mainly includes 3 processes (pasteurization, evaporation and spray drying) which will be presented. The aim of the study is to apply a thermodynamic analysis including comprehensive exergy analysis by using different performance parameters such as exergy efficiency, improvement potential rate, sustainability index, relative irreversibility and exergetic factor for the milk powder production system. As a result, exergetic efficiencies of the system components were found in the range of 9–83%. The overall energy and exergy efficiencies of the whole milk powder production system were calculated as 85.4 and 57.45%, respectively. Additionally, it was found that the evaporator and the heater have a higher impact in improvement actions.
[en] An ejector refrigeration system has been designed and constructed to operate with hot water. Such a refrigeration system, designed for low pressure refrigerants, can be operated using energy sources such as solar energy, geothermal energy and waste heat. In this study, the effects of the main operating parameters on system performance were experimentally investigated using R-11 as the working fluid and keeping constant the position of the primary nozzle end at the inlet plane of the mixing chamber section of the ejector. The experimental study was performed over a range of vapor generator temperatures from about 90 to 102 oC, evaporator temperatures from 0 to 16 oC and condenser pressures from 114 to 143 kPa, and a COP up to 0.25 was obtained. It was seen that if higher cooling capacity and also lower evaporator temperature are desired from the system, the vapor generator temperature should be increased considerably
[en] Highlights: • Using Failure Modes and Effects Analysis (FMEA) to find potential failures in geothermal power plants. • We considered 5 major parts of geothermal power plants for risk analysis. • Risk Priority Number (RPN) is calculated for all failure modes. • Corrective actions are recommended to eliminate or decrease the risk of failure modes. - Abstract: Renewable energy plays a key role in the transition toward a low carbon economy and the provision of a secure supply of energy. Geothermal energy is a versatile source as a form of renewable energy that meets popular demand. Since some Geothermal Power Plants (GPPs) face various failures, the requirement of a technique for team engineering to eliminate or decrease potential failures is considerable. Because no specific published record of considering an FMEA applied to GPPs with common failure modes have been found already, in this paper, the utilization of Failure Modes and Effects Analysis (FMEA) as a convenient technique for determining, classifying and analyzing common failures in typical GPPs is considered. As a result, an appropriate risk scoring of occurrence, detection and severity of failure modes and computing the Risk Priority Number (RPN) for detecting high potential failures is achieved. In order to expedite accuracy and ability to analyze the process, XFMEA software is utilized. Moreover, 5 major parts of a GPP is studied to propose a suitable approach for developing GPPs and increasing reliability by recommending corrective actions for each failure mode