Geothermal Fluid Temperature Research Articles

Thermodynamic and exergo-economic assessments of a new geothermally driven multigeneration plant

In this paper, a new geothermal-based multigeneration system is designed and investigated in both thermodynamic and economic analyses. The reason to select the geothermal source is that geothermal power is a renewable and sustainable power resource, and also it is not weather dependent. The proposed geothermal-based multigeneration plant is able to produce power, heating, cooling, swimming pool heating, and hydrogen. The main idea in this renewable-based multigeneration system is to create valuable products by using waste heat of subsystems. Then, by applying thermodynamic analyses, the energy and exergy performances of proposed multigeneration system are computed. Also, parametric work has been performed in order to see the impacts of the reference temperature, geothermal fluid temperature, and geothermal water mass flow rate. Finally, exergo-economic analysis based on exergy destruction or thermodynamic losses is done to gain more information about the system and to evaluate it better. According to the calculations, the overall plant's energy and exergy performances are 32.28% and 25.39%. Economic analysis indicates that hydrogen production cost can be dropped down to 1.06 $/kg H2.

The Coupled Effects of Dryness and Non‐condensable Gas Content of Geothermal Fluid on the Power Generation Potential of an Enhanced Geothermal System

AbstractThe Enhanced Geothermal System (EGS) is a recognized geothermal exploitation system for hot dry rock (HDR), which is a rich resource in China. In this study, a numerical simulation method is used to study the effects of geothermal fluid dryness and non‐condensable gas content on the specific enthalpy of geothermal fluid. Combined with the organic Rankine cycle (ORC), a numerical model is established to ascertain the difference in power generation caused by geothermal fluid dryness and non‐condensable gas content. The results show that the specific enthalpy of geothermal fluid increases with the increase of geothermal fluid temperature and geothermal fluid dryness. If the dryness of geothermal fluid is ignored, the estimation error will be large for geothermal fluid enthalpy. Ignoring non condensable gas will increase the estimation of geothermal fluid enthalpy, so the existence of the non‐condensable gas tends to reduce the installed capacity of a geothermal power plant. Additionally, both mass flow of the working medium and net power output of the ORC power generation system are increased with increasing dryness of geothermal fluid, however there is some impact of geothermal fluid dryness on thermal efficiency.

Exergoeconomic Optimization of Polymeric Heat Exchangers for Geothermal Direct Applications

The highest economic costs of a geothermal plant are basically related to well drilling and heat exchanger maintenance cost due to the chemical aggressiveness of geothermal fluid. The possibility to reduce these costs represents an opportunity to push toward geothermal plants development. Such challenges are even more important in the sites with a low-medium temperature geothermal fluids (90–120 °C) availability, where the use of these fluids for direct thermal uses can be very advantageous. For this reason, in this study, a direct geothermal heating system for a building will be investigated by considering a plastic plate heat exchanger. The choice of a polymeric heat exchanger for this application is upheld by its lower purchase cost and its higher fouling resistance than the common metal heat exchangers, overcoming the economic issues related to conventional geothermal plant. Thus, the plastic plate heat exchanger was, firstly, geometrical and thermodynamical modeled and, after, exergoeconomic optimized. In particular, an exergoeconomic analysis was assessed on the heat exchanger system by using a MATLAB and REFPROP environment, that allows for determination of the exergoeconomic costs of the geothermal fluid extraction, the heat exchanger, and the heating production. A sensitivity analysis was performed to evaluate the effect of main design variable (number of plates/channels) and thermodynamic variable (inlet temperature of geothermal fluid) on yearly exergoeconomic product cost. Then, the proposed methodology was applied to a case study in South of Italy, where a low-medium enthalpy geothermal potential exists. The plate-heat exchanger was used to meet the space heating requests of a single building by the exploitation of low-medium temperature geothermal fluids availability in the selected area. The results show that the inlet temperature of geothermal fluid influences the exergoeconomic cost more than the geometrical parameter. The variation of the exergoeconomic cost of heat exchanger with the inlet geothermal fluid temperature is higher than the change of the exergoeconomic costs associated to wells drilling and pumping with respect to the same variable. This is due the fact that, in the selected zone of South of Italy, it is possible to find geothermal fluid in the temperature range of 90–120 °C, at shallow depth. The product exergoeconomic cost is the lowest when the temperature is higher than 105 °C; thus, the smallest heat exchange area is required. The exergoeconomic optimization determines an optimum solution with a total product cost of 922 €/y for a temperature of geothermal fluid equal to 117 °C and with a number of plates equal to 15.

Different Geothermal Power Cycle Configurations Cost Estimation Models

An economic assessment of different geothermal power cycle configurations to generate cost models is conducted in this study. The thermodynamic and exergoeconomic modeling of the cycles is performed in MATLAB coupled to Refprop. The models were derived based on robust multivariable regression to minimize the residuals by using the genetic algorithm. The cross-validation approach is applied to determine a dataset to examine the model in the training phase for validation and reduce the overfitting problem. The generated cost models are the total cost rate, the plant’s total cost, and power generation cost. The cost models and the relevant coefficients are generated based on the most compatibilities and lower error. The results showed that one of the most influential factors on the ORC cycle is the working fluid type, which significantly affects the final economic results. Other parameters that considerably impact economic models results, of all configurations, are geothermal fluid pressure and temperature and inlet pressure of turbine. Rising the geothermal fluid mass flow rate has a remarkable impact on cost models as the capacity and size of equipment increases. The generated cost models in this study can estimate the mentioned cost parameters with an acceptable deviation and provide a fast way to predict the total cost of the power plants.

Green hydrogen & electricity production via geothermal-driven multi-generation system: Thermodynamic modeling and optimization

Concerning limited sources of fossil fuels, humankind should ensue new avenues to meet its energy demands. Towards this, geothermal energy is acknowledged as a promising, reliable, safe, and clean means for this aim. In the present study, a multi-generation system driven by geothermal energy, which produces electrical power, hydrogen, oxygen, and cooling, is proposed, appraised from thermodynamic and economic standpoints. Due to today's importance of hydrogen production, pure hydrogen production is one of the primary purposes of the system here described and analyzed. The subsystems include an organic Rankine cycle (ORC), a polymer electrolyte membrane (PEM) electrolyzer, and a lithium/bromide absorption refrigeration cycle. The model is implemented in the Engineering Equation Solver software and a multi-objective optimization is performed with NSGA-II.The results indicate that the parameters mostly affecting system performance include geothermal fluid mass flow rate, geothermal fluid temperature, ORC turbines inlet temperature, and evaporator pinch-point. The highest exergy destruction is pertinent to evaporators and the PEM electrolyzer, respectively. Moreover, the results reveal that the higher the geothermal well temperature, the higher the output parameters of the system. Also, a case study was carried out to implement the proposed system in Sabalan geothermal wells; the results indicate that the system can support the energy need of 160 families during one year by producing 4,696 MWh of electrical power. Lastly, the multi-objective optimization lead to a optimal scenario with 37.85 % exergy efficiency and 15.09 USD/h system cost rate.

Energy and Exergy analysis and selection of the appropriate operating fluid for a combined power and hydrogen production system using a Geothermal fueled ORC and a PEM electrolyzer

This research aims to introduce an efficient power cycle that simultaneously produces power and hydrogen by PEM electrolyzer. This cycle is driven by geothermal energy. Comprehensive thermodynamic modeling (energy and exergy) has been performed to compare four different operating fluids' performance on the proposed system. EES software was used for modeling. A parametric study has also been applied to investigate the effect of important parameters on the system's energy and exergy performance. As a brief novelty statement, the unique model can be mentioned in which both power and chemicals can be produced, and hydrogen output can be used as a storage system that transforms energy into an energy carrier. The results showed that R245fa operating fluid with 3.5% and %67.6 of energy and exergy efficiency had the highest performance. The operating fluids R114, R600, and R236fa are also in the next ranks of performance characteristics. As the geothermal fluid temperature increases, the production of power and hydrogen increases, but the energy and exergy efficiency decrease. Also, it can be noted that the hydrogen unit significantly increases the exergy efficiency of the plant. As an example, in the R245fa case, it increases from 36% to 67.6%.

A Sustainable model for the integration of solar and geothermal energy boosted with thermoelectric generators (TEGs) for electricity, cooling and desalination purpose

In this research paper, an integrated energy system for the production of cooling, hot water, and electricity along with desalinated water is proposed, simulated, assessed, and optimized. This integrated energy system is composed of a geothermal well, a single-effect Li/Br and water absorption chiller, parabolic trough collectors (PTCs), a steam Rankine cycle (SRC) and, a reverse osmosis desalination unit. Instead of the condenser, thermoelectric generators (TEGs) are used to increase the generated electricity by the SRC. The system's performance is evaluated in terms of energy, exergy, and exergoeconomic, and the cases with the TEG is compared to the system with the condenser, and results are discussed and investigated. Using the TEG instead of a condenser, results in reducing the total cost rate and enhancing the system's exergy efficiency. Also, the performance of the system was evaluated for four different days in Shiraz city. For the selected days in spring, summer, fall, and winter, the highest generated electricity of the system with the thermoelectric generator is 1087 kW, 1158 kW, 1133 kW, and 766.5 kW, respectively. Thus, the system with thermoelectric is selected for optimization. To optimize the system, seven decision variables are selected namel, the geothermal fluid temperature, the total solar aperture area, the collector outlet temperature, the inlet pressure of the turbines, the TEG figure of merit, the turbine outlet pressure, and the evaporator pinch point temperature difference. Total cost rate and system exergy efficiency are considered as two objective functions. To determine optimum values of the objective functions, a multi-objective genetic algorithm is applied, and also the Pareto frontier figure is obtained. In this figure, the best point is chosen from the technique for order of preference by similarity to ideal solution (TOPSIS) decision-making criterion, where the cost rate is 10.41 ($ / GJ), and the exergy efficiency is 20.52%.

A review of geothermal energy-driven hydrogen production systems

This paper presents a review of hydrogen production systems using geothermal energy, showing the importance and potential of this technology in addition to the main obstacles facing this domain. The effect of several parameters was taken into consideration, such as geothermal fluid temperature, water electrolysis temperature, working fluid, and type of power cycle. The different types of geothermal power plants were also compared, namely, flash, binary, flash-binary, recuperative, regenerative, and organic Rankine flash cycles. This study covers a wide range of investigations regarding hydrogen production rate, hydrogen production cost, energetic efficiency, exergetic efficiency, exergetic cost, and electricity generated. Hydrogen production rate is one of the most important mentioned parameters in which it was found to vary from 5.439 kg/h to 13958 kg/h. Multigeneration systems have shown great potential to enhance the overall system’s efficiency, leading to reduced production costs. The integration of another energy source was found to be interesting in geothermal-driven hydrogen production systems. This would promote the adoption of multigeneration system as well as increasing the geothermal fluid’s temperature before entering the power cycle.

Experimental Investigation of Organic Rankine Cycle (ORC) for Low Temperature Geothermal Fluid: Effect of Pump Rotation and R-134 Working Fluid in Scroll-Expander

Organic Rankine Cycle (ORC) is one of the solutions to utilize a low temperature geothermal fluid for power generation. The ORC system can be placed at the exit of the separator to extract energy from brine. Furthermore, one of the main components of the system and very important is the pump. Therefore, in this research, the pump rotation is examined to investigate the effect on power output and energy efficiency for low temperature geothermal fluid. The rotation is determined by using an inverter with the following frequencies: 7.5, 10, 12.5, 15 and 17.5 Hz, respectively. R-134 working fluid is employed with 373.15 K evaporator temperature in relation to the low temperature of the geothermal fluid. Furthermore, the condenser temperature and fluid pressure were set up to 293.15 K and 5 × 105 Pa, respectively. This research uses a DC generator with a maximum power of 750 Watt and the piping system is made from copper alloy C12200 ASTM B280 with size 1.905 × 10−2 m and a thickness of 8 × 10−4 m. The results showed that there is an increase in mass flow rate, enthalpy and generator power output along with increasing pump rotation. In addition, it showed that the maximum generator output power was 377.31 Watt at the highest pump rotation with a frequency of 17.5 Hz.

Thermodynamic Optimization of a Geothermal Power Plant with a Genetic Algorithm in Two Stages

Due to the harmful effects and depletion of non-renewable energy resources, the major concerns are focused on using renewable energy resources. Among them, the geothermal energy has a high potential in volcano regions such as the Middle East. The optimization of an organic Rankine cycle with a geothermal heat source is investigated based on a genetic algorithm having two stages. In the first stage, the optimal variables are the depth of the well and the extraction flow rate of the geothermal fluid mass. The optimal value of the depth of the well, extraction mass flow rate, and the geothermal fluid temperature is found to be 2100 m, 15 kg/s, and 150 °C. In the second stage, the efficiency and output power of the power plant are optimized. To achieve maximum output power as well as cycle efficiency, the optimization variable is the maximum organic fluid pressure in the high-temperature heat exchanger. The optimum values of energy efficiency and cycle power production are equal to 0.433 MW and 14.1%, respectively.

Jeotermal Enerji Kaynaklı Multi-Jenerasyon Enerji Sisteminin Termodinamik ve Performans Değerlendirmesi

In this study, a new integrated geothermal energy based plant is proposed for multigeneration purposes such as hydrogen, electricity, hot water, drying, cooling and heating. Therefore, this proposed integrated system is consisted of proton exchange membrane electrolyzer, hydrogen compression unit, organic Rankine cycles, single effect absorption cooling cycle, hot water storage tank and a drying unit. Thermodynamic analyses including of energy and exergy analyses have been performed for general evaluation of the proposed system. Energy and exergy efficiencies of whole plant are found as 37.65% and 39.26%, respectively. In addition to these analyses, parametric analyses have been carried out to see how some variables affect system performance and useful product generation. For this reason, the impacts of dead state temperature, geothermal mass flow rate, geothermal source temperature and pinch point temperature of heat exchanger 1 are investigated. Any increase in dead state temperature, geothermal mass flow rate and geothermal source temperature has positive impact on system performance and useful product generation. Increase in pinch point temperature of heat exchanger 1 decreases the system performance. Hydrogen production rate reaches maximum point (0.0024 kg/s) when geothermal mass flow rate is 8.125 kg/s or when geothermal working fluid temperature is 168 °C for this paper.

Energy, economic and environmental evaluation of a novel combined cooling and power system characterized by temperature and humidity independent control

A novel combined cooling and power system with independent control of temperature and humidity was presented to meet the energy supply demand in buildings. The energy, economic and environmental characteristics of the organic Rankine cycle powered two-stage vapor compression cycle with sixteen organic working fluids were discussed at variable geothermal fluid temperature. The results showed that organic Rankine cycle powered two-stage vapor compression cycle had certain advantages in improving refrigeration performance. Taking the critical mass flow rate as the boundary, the cooling and electricity output of the system could be controlled by adjusting the mass flow rate of refrigeration device. As far as the output power of the system was concerned, R1234yf, R134a, R600a, R600, R123 and R601 were suitable for different temperature ranges of geothermal fluids, while in terms of refrigeration performance, R1234ze, R245fa, R123, and R601 were respectively suitable for different geothermal fluid temperatures. The system with N-heptane had the optimal techno-economic performance, which electricity production cost decreases from 0.1543 $/kWh to 0.0484 $/kWh. Therefore, the novel combined cooling and power system can meet the seasonal cooling and electricity demand of the building and maximize the use of dry hot rock resources.

Development of a Geothermal-Based Integrated Plant for Generating Clean Hydrogen and Other Useful Commodities

Abstract In this study, geothermal energy is considered as a renewable energy source to finally provide various useful outputs such as electricity, hydrogen, fresh and hot water, drying, heating, and cooling. In this regard, a new geothermal power-based multigenerational system is proposed to meet these demands in an environmentally benign manner and studied thermodynamically by considering energy and exergy approaches and investigating parametrically. A combination of geothermal energy is used to achieve the most promising hydrogen generation rates and high plant performances. The results of this study indicate that the energy and exergy efficiency values of the entire plant for the selected operating conditions become 38.41% and 42.57%. In addition to the thermodynamic analysis performed, numerous parametric studies are performed to reveal how operating conditions and state parameters affect the overall system performance. According to the parametric analyses results, for given ranges, an increase in ambient temperature, separator working temperature, geothermal fluid temperature, and geothermal fluid mass flowrate have positive impact on both energy and exergy efficiency of the integrated system and useful products generation rate as well.

Optimum Design of Shell and Tube Heat Exchangers using Modified Kinetic Gas Molecule Optimizer for the use of Low Temperature in Organic Rankine Cycles

Shell and Tube Heat Exchangers (STHEs) plays a crucial role in an effective design of Organic Rankine Cycle (ORC) power plants.The main aim of this research work is to design a cost-effective ORC in order to exploit low to medium temperature geothermal fluid or low grade industrial waste heat. In this research work, modified Kinetic Gas Molecule Optimization (KGMO) algorithm was developed forfinding the optimized parameter settings of the power plant. In modified KGMO algorithm, feedback learning stage was included for improving the fitness of individual worst particles. In addition, the proposed optimization algorithm was tested on two dissimilar fluids such asR245fa and R134a in order to show the effectiveness of proposed scheme. The experimental investigation showed that the proposed scheme effectively improved the heat exchanger performance as related to the existing schemes.The enhancement factor of proposed scheme was 2.8063 for R245fa fluid and 1.9346 for R134a fluid, which was better compared to the existing schemes; KGMO and Bell-Delaware method.

Synergetic mechanism of fracture properties and system configuration on techno-economic performance of enhanced geothermal system for power generation during life cycle

Enhanced geothermal system is one of the most commonly used geothermal power generation systems for hot dry rock. In order to illuminate the life cycle performance, the fracture spacing is coupled with cycle configuration in this study. The typical fracture properties and three enhanced geothermal system configurations are considered, the optimal operating conditions of each system in different periods are obtained, and the techno-economic performance during the life cycle, in 30 years, is compared. The results show that the optimal operating conditions are constantly changing in the life cycle. With the decrease of the geothermal fluid temperature, the optimal evaporation temperature decreases. Double-stage flash system exhibits better power generation performance and techno-economic performance. During the life cycle of double-stage flash system, the net power output decreases 17.41%, while the leveling cost of electricity increases 17.11%. Moreover, the fracture spacing and fracture permeability of hot dry rock have an evident impact on the techno-economic performance and power generation performance. Lower fracture spacing and higher fracture permeability are beneficial for system performance. This study lays a theoretical basis for enhanced geothermal system in engineering applications.

Potential of thermoelectric waste heat recovery in a combined geothermal, fuel cell and organic Rankine flash cycle (thermodynamic and economic evaluation)

The present work aim is performance improvement of an integrated geothermal system by proposing the integration of organic Rankine flash cycle (ORFC) with the Proton exchange membrane fuel cell (PEMFC) and waste heat recovery from condensers using thermoelectric generator (TEG) modules. To achieve this goal, a novel integrated system is proposed, thermodynamically modeled, investigated, and compared with the conventional system. To assess the performance of proposed system, thermodynamic and economic evaluations are performed. The results indicate that R123 as working fluid, has the best performance for the conventional and proposed systems. The findings demonstrate that with employing TEG modules an increase of 2.7% and 2.8%, for the first and second law efficiencies can be obtained respectively. Additionally, the results of parametric analysis indicate that however the geothermal fluid temperature increment decreases the first and second law efficiencies of the system, it leads to the net output power enhancement. Also, enhancement of the flash vessel pressure ratio increases the first and second law efficiency as well. Additionally, the simple payback method showed that a payback time between 1.25 years and 25 years according to the TEG modules cost can be achieved.

Multi-objective design optimization of a multi-generation energy system based on geothermal and solar energy

In this paper, a multi-generation system based on geothermal energy and parabolic trough solar collectors is proposed for the simultaneous generation of power, cooling, freshwater, hydrogen, and heat. Power is generated by a combined steam Rankine cycle and an organic Rankine cycle. Ten different refrigerants are used for the organic Rankine cycle, among which R123 has the best performance. In addition, four fluids are used as the geothermal fluid, among which Therminol 59 has recorded the best performance. Solar intensity, geothermal mass flow rate, geothermal fluid temperature, and steam turbine inlet pressure have proven to be the most prominent parameters affecting the exergy efficiency and cost. After analyzing the proposed system from the energy, exergy and exergoeconomic points of view, a multi-objective-optimization-genetic-algorithm is applied for improving the performance of the system. In order to apply the multi-objective optimization, Engineering Equation Solver and MATLAB software are linked together by the Dynamic Data Exchange method. According to the obtained results. The results show that the exergy efficiency of the system and the total unit cost respectively reach to 29.95% and 129.7 $/GJ at the optimum point.

Techno-economic performance comparison of enhanced geothermal system with typical cycle configurations for combined heating and power

The hot dry rock contains abundant heat, which can be exploited by enhanced geothermal systems, being one of the most commonly used geothermal power generation solutions. To enhance the power generation efficiency and utilization of geothermal resource, four combined heating and power systems are presented for geothermal fluids temperature ranging from 120 °C to 220 °C and dryness between 0 and 0.9. The operating parameters of four enhanced geothermal systems are respectively optimized, and the system performances are analyzed and compared. The results showed that the system performances as well as the optimal operating conditions varied with the temperature and dryness of the geothermal fluid. The double-flash organic Rankine cycle based combined heating and power system exhibited the highest power generation efficiency under geothermal fluid temperature and dryness coupling. The double-flash organic Rankine cycle based combined heating and power system had the highest techno-economic performance in the practical application, which the levelized cost of electricity was 0.0831 $/kWh and the payback period was 9.43 years. The organic Rankine cycle subsystem using n-Octane showed preferable power generation performance, while using n-Decane showed preferable techno-economic performance. Moreover, the enhanced geothermal system configuration and its operating parameters should match with actual local geothermal fluid conditions and the double-flash organic Rankine cycle based combined heating and power system was recommended in most cases.

Techno-Economic Analysis of Hybrid Binary Cycles with Geothermal Energy and Biogas Waste Heat Recovery

In Germany, enhancing renewable power generation represents a leading step to comply with the requirements of the Energiewende agenda. The geothermal reservoir in Oberhaching is assumed as a case study, with a gross electric power equal to 4.3 MWel. The intent of this work is to design a hybrid binary geothermal power plant and to integrate it into the German energy market. Biogas waste thermal power equal to 1350 kWth is assumed as a secondary source. Two different layouts are defined for the hybrid solution: increasing the geothermal fluid temperature before entering the organic Rankine cycle (ORC) unit and superheating the working fluid after the evaporator. Stationary and quasi-stationary simulations have been performed with Aspen Plus V8.8. Results demonstrate how hybridization allows a maximum electric power increase of about 240 kWel. Off-design conditions are investigated regarding both the switch-off of exhaust gases and the annual ambient temperature fluctuations. In spite of the additional secondary source, the selected case studies cannot comply with the Minute reserve requirements (MRL). Moreover, economic results for both power-only and combined heat and power (CHP) configuration are provided. In the power-only configuration, the new-build hybrid system provides 15.42 €ct/kWh as levelized cost of electricity (LCOE), slightly lower than 16.4 €ct/kWh, as calculated in the geothermal-only solution. A CHP hybrid configuration shows a +19.22% increase in net cash flow at the end of the investment on the CHP geothermal solution.

Off-design performance analysis of a novel hybrid binary geothermal-biomass power plant in extreme environmental conditions

A novel configuration of a hybrid binary geothermal biomass power plant is proposed that generates electricity through the Organic Rankine Cycle (ORC), which receives the thermal power provided by a biomass heat source through intermediate geothermal fluid. The plants are located in regions with extreme environmental conditions where water is not available, making the use of air-cooled condensers in the ORC necessary, and the seasonal variations of the ambient air temperature are remarkable. As a further novel aspect, the modification of the biomass mass flow rate is used to overcome the simultaneous harmful effects of a considerable reduction in the geothermal fluid temperature during the operative life of the plant and the more significant seasonal change of the ambient air temperature. Our original approach involves developing a simulation model of the proposed plant using the commercial software Aspen® to determine the energy performance in off-design conditions, i.e., in the presence of the simultaneous changes of the biomass flow rate, ambient air temperature and geothermal fluid temperature. The biomass flow rate is controlled to maximize the net electric power or net thermodynamic efficiency of the plant with varying ambient air and geothermal fluid temperatures. In comparison to the first operating mode, the second enables a saving of the biomass used annually in the range of 28.3%–42.6%, corresponding to the maximum and minimum geothermal fluid temperature, respectively, with the resulting detrimental effect on the yearly produced electric energy in the range of 9%–23.6%.