Low Temperature Geothermal Energy Research Articles

Configuration of Organic Rankine Cycles for Geothermal Applications: An Industrial Perspective

Abstract Geothermal resources represent a valuable option to reduce fossil fuel-based power production because they feature an unmatched capacity factor among other renewable energy sources (RES). Geothermal resource availability reduces with the temperature. Therefore, developing cost-effective solutions to exploit low-temperature geothermal energy is mandatory to expand technology utilization. The standard solution for converting low-temperature thermal sources into power is organic rankine cycles (ORCs). ORC basic layout (subcritical) is well-known, but the more advanced alternatives, such as transcritical and two-pressure level cycles, are much less widespread, and it is unclear whether the higher efficiency justifies the higher capital cost. The paper focuses on the exploitation with ORC of geothermal resources (hot water) with a temperature lower than 200 °C and mass flow rates between 200 and 1400 m3/h for a target power production ranging from 3 to 30 MW. The paper compares three ORC layouts, subcritical, transcritical, and two pressure-level, from thermodynamic and economic points of view to map the most cost-effective solutions in the investigated size ranges. The techno-economic comparison considers the impact of the operating conditions and fluid on the machine's expected performance and the heat exchangers' size. As expected, more complicated layouts yield higher conversion efficiencies, with the two pressure-level cycles achieving the highest power output for the same geothermal source conditions. However, the economic analysis showed that the most efficient solutions are not always preferable when considering the cost-efficiency tradeoff.

Jeotermal Enerji Destekli Güç ve Hidrojen Üretim Tesisinin Termodinamik ve Çevresel Etki Değerlendirmesinin Modellenmesi

In this proposed study, hydrogen and power generation by low-temperature geothermal energy supported Kalina cycle is thermodynamically investigated with an energy and exergy efficiencies approaches. This combined plant includes a Kalina cycle and a PEM electrolysis for power and hydrogen generation. The key purpose of this paper is to generate power and hydrogen in an environmentally benign way. Furthermore, environmental impact analysis is discussed to investigate the carbon dioxide emission that will be released if the power and amount of hydrogen obtained are produced with natural gas. As coming to the examination results, the energy and exergy performance of the overall plant 7.94% and 37.64%, respectively. Also, the net power and hydrogen production rates are computed as 100.5 kW and 0.0001191 kgs-1.

Assessment of possibility of finding geothermal energy resources around Mount Meru in northern Tanzania using classical solute geothermometry

This study uses classical solute geothermometry analysis to estimate the temperature and circulation depth of the geothermal reservoir around Mount Meru. Five springs affected by magmatic gases from a deep magmatic heat source are investigated; these include two hydrothermal springs. Results from silica geothermometers show that estimated reservoir temperatures range from 70 to 110 °C; this corresponds to a low-temperature hydrothermal system. Since Mount Meru is an active volcano, one would expect a high-temperature hydrothermal system; the low temperatures are ascribed to the mixing of hydrothermal and cold recharge waters. The geothermal reservoir is estimated to be about 1.3–1.4 km deep. Thus, the study shows that a low-temperature geothermal energy resource can be found on the eastern flank of Mount Meru.

A hybrid machine learning-assisted optimization and rule-based energy monitoring of a green concept based on low-temperature heating and high-temperature cooling system

This article aims to support the targeted worldwide green transition process by introducing and thoroughly analyzing a low-temperature heating and high-temperature cooling, smart building system. This concept allows for greater use of renewable energy while utilizing less input energy than conventional heating and cooling techniques. The proposed system consists of a reversible water-to-water heat pump driven by low-temperature geothermal energy. A rule-based control strategy is developed to establish an intelligent connection with the regional energy grids for peak shaving and compensating for the building's energy costs over the year. The dynamic simulation is carried out for a multi-family building complex in Stockholm, Sweden, using TRNSYS. The most favorable operating condition is determined via an artificial neural network-assisted tri-objective optimizer based on the grey wolf algorithm in MATLAB. The comparison of the proposed smart model with the conventional system in Sweden results in 332%, 203%, and 190% primary energy reduction, cost saving, and carbon dioxide emission mitigation, respectively. As indicated by the parametric results, the conflicting fluctuation between desirable and unfavorable indicators highlights the importance of multi-objective optimization. The grey wolf optimizer obtains 12% higher efficiency, 1.2 MWh lower annual bought energy, 24 $/MWh lower unit cost, and 5.1 MWh more yearly sold energy than the design condition. The scattered distribution reveals that tank volume and subcooling degree are sensitive parameters. According to the transient results, the suggested smart system can independently satisfy the building's heating, cooling, and electricity demands for more than 81% of the year, thanks to the two-way connection with the electricity and heating networks via the rule-based controller.

Assessment of the Thermal Power of Groundwater Intakes in the Kielce District

Abstract The purpose of the article was to estimate the thermal power of groundwater intakes of the Kielce district within the sheets of hydrogeological maps with the serial numbers MHP 813-817, MHP 850-851, and to indicate in this area prospective areas for the development of low-temperature geothermal energy supported by water/water heat pumps. Based on the calculations on the basis of 147 groundwater intakes, it was determined that the estimated values of thermal power resources are in the range of 3.47 kW to 5757.34 kW. The created map of the low-temperature geothermal potential for groundwater intakes indicates the towns of Bodzentyn, Morawica and the villages of Piekoszów, Wolica and the area around the village of Górno as prospective areas.

Innovative numerical procedure for simulating borehole heat exchangers operation and interpreting thermal response test through MODFLOW-USG code

In recent years, among renewable energies, the geothermal resource exploitation shows a constant growth; specifically, in countries engaged in CO2 emissions reduction and dependent on energy from abroad, the low-temperature geothermal energy (geo-exchange) for air conditioning of buildings represents a cost-effective and green solution. In closed-loop systems borehole heat exchangers (BHE) are coupled with ground-source heat pumps (GSHP) constituting the key component of the heating ventilation air-conditioning (HVAC) system. Therefore, the design of the BHE and the correct interpretation of in situ Thermal Response Tests (TRT) are essential to supply the building energy demand. To support the design, Modflow-USG Connected Linear Network (CLN) and Drain Return Flow (DRT) packages are adapted and improved to reproduce the operation of one or more BHE in aquifers and to analyze the TRT. The improvements are compared with a previously developed numerical model and two different analytical solutions (infinite line source and moving line source) by imposing a constant heat rate injection into the aquifer. The results show good agreement between the new approach and previous ones (discrepancy lower than 2% for models with highly refined grid), but the new approach is much more accurate and expeditious in both implementation and execution, also allowing for an easy numerical simulation of multiple BHE.

Modelling and control strategy of a distributed small‐scale low‐temperature geothermal power generation system

At present, commercial geothermal power stations are mainly high-temperature and medium-temperature geothermal energy, while the large number of low-temperature geothermal energy resources are rarely used for power generation applications. This paper proposes a new model for energy conversion in low-temperature geothermal power systems. The basic structure and working principle of this new model are analysed, in detail, a low-temperature geothermal model and a Stirling engine model for geothermal energy conversion are established, and the control strategies on the rotor and stator sides of the Stirling-driven doubly-fed generator are discussed. Finally, the simulation analysis is carried out, and its results show that the thermal conversion efficiency of Stirling’s engine can reach 38%, the output AC voltage of the power generation system reaches the set value 50Hz, 190V, and the DC bus voltage is constant at 300V, which verified the validity of the proposed power generation model and related control strategies. This system expands the range of available heat sources in geothermal power generation, makes geothermal power generation more flexible in terms of site selection, power generation capacity and control, and provides a new idea for geothermal power generation structure.

The Standard Geothermal Plant as an Innovative Combined Renewable Energy Resources System: The Case from South Poland

Geothermal energy, as one of the more well-known renewable energy sources (RES), is used in many operating installations around the world. Depending on the temperature of the geothermal waters in question, the choices range from installations for generating electricity (high-temperature geothermal energy), to the production of thermal energy for use in recreational complexes, to fish farming (low-temperature geothermal energy). Lindal’s diagram determines the possibilities of using warm groundwater for many investment projects. In light of the drive to avoid climate change, it seems that the conventional “one-way” use of geothermal water resources is insufficient. Therefore, this article presents an optimal innovative solution wherein geothermal water is fully utilized in a geothermal cogeneration installation to produce heat and electricity and to provide cooling. In addition, it was proposed to expand the investment with photovoltaic and hydropower plants to ensure greater energy independence by diversifying energy sources and increasing the share of energy supplies based on renewable energy sources. Such a broad approach allows for the implementation of a sustainable development strategy in the field of environmental protection. The proposed solution involves the modernization and expansion of the existing energy generation sources by a heating plant and a geothermal power plant in Chochołowskie Termy (South Poland), as well as the construction of a power plant based on a photovoltaic installation, hydropower setup, and energy storage. The presented innovative solution may be an excellent example of implementation for similar geothermal facilities in the world. The novelty of the system is the approach of assessing and combining the different RES in one project, based on a geothermal plant. Popularizing this solution in the wider scientific environment may have a real impact in terms of the reduction of pollutant emissions.

Techno-economic assessment for heating cattle feed water with low-temperature geothermal energy: A case study from central Alberta, Canada

There are over 450,000 registered oil and gas wells in the province of Alberta, Canada. A recent increase of the number of inactive wells creates significant environmental risk and financial liability in cleanup costs. By retrofitting wells for direct use geothermal heat energy production, these wells can produce clean, renewable energy and offset these risks and liabilities. This research is the first to create a model of well retrofit costs and power/benefits and to consider direct use of heat energy for ranching applications in Canada. We estimate the average cost to retrofit a suspended well to be $50,000 less than an identical abandoned well. The cost of retrofitting suspended wells varies little (<$11,000). The greatest variance in cost (>$120,000/well) is related to the distance between the well and user and resulting pipe/materials necessary to transport the hot water. Our model of well retrofit costs can be expanded to other geothermal re-purposing projects in North America and worldwide.

Performance of Kalina cycle with single-screw expander for low-temperature geothermal energy utilization

Recovering the expansion work by replacing throttle valve with expander may improve the performance of a thermodynamic cycle. Based on Kalina Cycle System 11, 34, and 34 g, different redesigned cycles with single-screw expander are proposed in this paper. I-redesigned cycle has a single-screw expander which replaces the throttle valve and is located between absorber and regenerator. In II-redesigned cycle, the single-screw expander is located between regenerator and separator, and the original throttle valves is removed. The thermodynamic performance of two redesigned cycles is analyzed and compared with their corresponding original cycle. It can be found that two redesigned cycles perform better than their corresponding original cycle system. II-redesigned cycle is better than I-redesigned cycle. When comparing the redesigned cycle of the same type, the performance ranking from good to bad is Kalina Cycle System 34, 11, and 34 g. II-redesigned cycle for Kalina Cycle System 34, 11 and 34 g can reach the maximum thermal efficiency of 11.44%, 11.14%, and 10.85% respectively at the evaporation pressure of 3.0 MPa. It can be seen that the series connection of regenerator and evaporator is better than the parallel connection and the increase in the number of regenerators can improve the thermodynamic performance of the cycle.

Energy-Saving Thermal Stabilization System and Assessment of Temperature Loadings of a Bridge Deck Pavement

To improve the general traffic safety in conditions of winter ice at traffic interchanges and to extend the overall service life of the roadway, it is proposed to use energy-saving thermal stabilization of a bridge deck pavement by transferring the low-temperature geothermal energy by heat pumps. The practical and computational parts of the pilot plant work are demonstrated and discussed. In order to analyze the need to use additional thermal joints, computer simulation was performed in the LIRA-CAD-2018 software package with subsequent extrapolation to a real bridge span.

ОПЫТ ИСПОЛЬЗОВАНИЯ ГЕОТЕРМАЛЬНОЙ ЭНЕРГИИ ПРИПОВЕРХНОСТНОГО МАССИВА ДРЕВНИХ ГРАНИТОИДОВ ДЛЯ ЦЕЛЕЙ ТЕПЛОСНАБЖЕНИЯ (ЮГ ЗАПАДНОЙ СИБИРИ)

An example of transition of the heating- and hot-water supply system to a low-temperature geothermal energy source from the Paleozoic granitoid massif is given for a secondary school building in Novosibirsk. The necessity for change the source of heat supply arose in 2018 due to wear and tear of the coal boiler house old equipment, which has provided the school with heat since it was built in 1964. At the time of the geothermal project implementation, there were already several cases of successful use of underground heat-producing probes arranged in specially drilled geothermal wells for heating public facilities in neighboring Siberian cities (Tomsk, Barnaul). However, loose sedimentary rocks there served for the source of heat energy, that greatly simplified and accelerated the tasks implementation. The described experience of heating – and hot-water supply of building due to the low energy from a shallow lying massif of ancient rocky grounds with intrusive genesis is unique for Russia and can serve as a platform for the implementation of geothermal projects in regions with complicated ground conditions and moderately cold climate.

The Study of Soil Temperature Distribution for Very Low-Temperature Geothermal Energy Applications in Selected Locations of Temperate and Subtropical Climate

The publication presents the results of research on soil temperature distribution at a depth of 0.25–3 m in three measurement locations. Two boreholes were located in Białystok in the temperate climatic zone and one measuring well was installed in Belmez in the subtropical climatic zone. Measurements were made in homogeneous soil layers in sand (Białystok) and in clay (Białystok and Belmez). Based on the results of the measurements, a simplified model of temperature distributions as a function of depth and the number of days in a year was developed. The presented model can be used as a boundary condition to determine heat losses of district heating pipes located in the ground and to estimate the thermal efficiency of horizontal heat exchangers in very low-temperature geothermal energy applications.

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.

Harvesting the low-temperature geothermal energy for agricultural drying with two-phase closed thermosyphon: An experimental study

Due to the decline in the availability of fossil fuel and its destructive impact on the environment, there is a need to accelerate the use of more sustainable and safer environmental energy. The geothermal energy is one of renewable energy with abundant sources, especially in Indonesia where the source of low-temperature geothermal energy (LTGE) spreads around the country. However, several challenges exist in regard to its use, such as expensive investment to drill the source of energy and issues of silica scaling. To solve these challenges and boost the utilization of LTGE, a technology that can easily harvest is needed. A potential technology that is capable of handling this issue is the two-phase closed thermosyphon (TPCT). Therefore, this study aims to investigate the thermal performance of TPCT as a heat pipe heat exchanger (HPHE) to harvest LTGE for agricultural drying. The TPCT was made from a copper tube with a 1-inch diameter and 700 mm in length. Demineralized water with a 55% filling ratio was used as the working fluid. The vacuum pressure inner TPCT was -50 cmHg and -70 cmHg. A total of 18 pcs of TPCTs were used, with 30 fins made from a copper plate. Furthermore, the LTGE source was simulated using hot water that can be adjusted and flowed by a pump. The experimental results showed that the vacuum pressure on the TPCT greatly affected the heat transfer performance of the system. Also, the highest TPCT-HPHE effectiveness was 0.31, obtained with a vacuum pressure at TPCT, hot water temperature, and air velocity of -70 cmHg, 80 °C, and 0.2 m/s, respectively. From the results, it was concluded that TPCT can be proposed as a good candidate technology to harvest and accelerate the utilization of the LTGE resource.

Enhancing the performance of conventional coffee beans drying with low-temperature geothermal energy by applying HPHE: An experimental study

Abstract The unpredictable weather in Indonesia results in a less effective conventional coffee beans drying process, which usually uses solar energy as a heat source. This experiment aimed to examine the performance of the coffee beans drying using low-temperature geothermal energy (LTGE) with solar energy as the energy source. Heat pipe heat exchanger, which consists of 42 straight heat pipes with staggered configuration, was used to extract the LTGE. The heat pipes have 700 mm length, 10 mm outside diameter with a filling ratio of 50%, and added by 181 pieces of aluminum with a dimension size of 76 mm × 345 mm × 0.105 mm as fins. LTGE was simulated by using water that is heated by three heaters and flowed by a pump. Meanwhile, to simulate the drying process with conventional methods, a system of solar air collectors made of polyurethane sheets with a thickness of 20 mm and dimensions of length × width × height = 160 cm × 76 cm × 10 cm, respectively, was used in this study. Zinc galvalume sheet with 0.3 mm thickness was installed and coated by the black doff color throughout the inner of the container wall. The result showed that the drying process with LTGE and solar energy is faster than with solar energy or geothermal energy only. The drying coffee beans using the hybrid system can speed up the drying coffee beans time by about 23% faster than the solar energy only.

Heat setting system development of bridge floor surface using low temperature geothermal energy

Multilevel transport interchanges play a decisive role in the road infrastructure both throughout the world and in Russia. Significant problems of the safe operation of multi-level highways in the general metropolitan traffic system and the country territory, in general, are associated with the need to thoroughly clear them of snow and ice during winter and off-season periods. The simplest, most obvious, and historically proven non-mechanical ice control method is using the chemical reagents mixtures. Despite the fact that the quality of the original anti-ice chemical products is constantly being improved, the reagents composition is updating, the target operation remains unchanged — a decrease in the ice and snow melting temperature point. Unfortunately, in the process of melting with heavy snowfall, the concentration and, accordingly, the brine viscosity increases, leading to «oiling» of the asphalt pavement, thereby worsening the already difficult situation on the road. One of the attractive ways to keep the roadway in proper condition is to heat it to get rid of ice. Direct heating methods such as central heating or electric heating are too costly and economically unfeasible. It seems promising to use low-temperature geothermal energy, which will significantly reduce energy costs and increase the transport projects’ economic attractiveness. This work is devoted to the study of the practical applicability of the bridge floor surface heat setting technology using low-temperature geothermal energy as part of the «Best available technologies» concept implementation in accordance with GOST R 56828.15-2016 in terms of infrastructure facilities energy efficiency. Based on the work results, the authors provide the study results and numerical modeling, as well as their comparison. The results presented in this article are a part of the dissertation research «New technological solutions development for the bridge floor surface at transport interchanges» Kostenko S.А.

Research on Fresh and Hardened Sealing Slurries with the Addition of Magnesium Regarding Thermal Conductivity for Energy Piles and Borehole Heat Exchangers

Currently, renewable energy is increasingly important in the energy sector. One of the so-called renewable energy sources is geothermal energy. The most popular solution implemented by both small and large customers is the consumption of low-temperature geothermal energy using borehole heat exchanger (BHE) systems assisted by geothermal heat pumps. Such an installation can operate regardless of geological conditions, which makes it extremely universal. Borehole heat exchangers are the most important elements of this system, as their design determines the efficiency of the entire heating or heating-and-cooling system. Filling/sealing slurry is amongst the crucial structural elements. In borehole exchangers, reaching the highest possible thermal conductivity of the cement slurry endeavors to improve heat transfer between the rock mass and the heat carrier. The article presents a proposed design for such a sealing slurry. Powdered magnesium was used as an additive to the cement. The approximate cost of powdered magnesium is PLN 70–90 per kg (EUR 15–20/kg). Six different slurry formulations were tested. Magnesium flakes were used in designs A, B, C, and magnesium shavings in D, E and F. The samples differed in the powdered magnesium content BWOC (by weight of cement). The parameters of fresh and hardened sealing slurries were tested, focusing mainly on the thermal conductivity parameter. The highest thermal conductivity values were obtained in design C with the 45% addition of magnesium flakes BWOC.

Thermodynamic performance and economic feasibility of Kalina, Goswami and Organic Rankine Cycles coupled to a polygeneration plant using geothermal energy of low-grade temperature

Low-temperature geothermal energy is an abundant and renewable resource, but with technical and economic limitations for the generation of electricity. Currently, the polygeneration systems are an alternative for effective use of energy resources, geothermal energy included. In this paper a comparative analysis of the thermodynamic and economic performance of Kalina (KAC), Goswami (GOC) and Organic Rankine (ORC) cycles coupled to a polygeneration plant that uses geothermal energy of low-grade temperature to produce electricity, refrigeration and dehydrated products, simultaneously, is presented. It is proposed that the system design operates sequentially at different thermic levels under the concept of cascade utilization. The KAC, GOC and ORC cycles are analyzed as candidates for electricity generation, placed in a first thermal level. In a second thermal level, a cooling technology activated with thermal energy for fresh product conservation is included. Finally, a fresh product dehydrator is included in the last thermal level. To carry out the analysis, a standard structure has been proposed, to which the laws of mass and energy conservation apply. In addition, an exergy analysis is performed to know the performance of the system from the perspective of the second law of thermodynamics. The results indicate that the KAC and ORC cycles are more flexible to integrate, since the systeḿs products can adjust to the predefined needs. However, a better energy and exergetic efficiency of the polygeneration plant is obtained with the ORC, having 30.68 and 27.43%, respectively. From economic perspective the ORC has also the lowest Simple Payback Period (3.36 years) and the highest NPV (1.684 × 106 USD) among power cycles studied.

Comparative thermoeconomic analysis of trigeneration systems based on absorption heat transformers for utilizing low-temperature geothermal energy

Two novel trigeneration cycles are proposed based on Absorption Heat Transformers (AHTs) to generate power and produce freshwater, and heating effect from low-temperature geothermal energy. Simulation models are developed to examine the thermodynamic and thermoeconomic performances of the systems based on the single-stage, double and double-effect AHTs. The power is generated in an Organic Rankine Cycle (ORC) and a single-stage evaporation desalination system is employed to produce freshwater. The exergy performance parameters are determined, and the levelized cost of energy (LCOE) and water (LCOW) are considered as the criteria for the thermoeconomic assessment. According to the results, a maximum of 191.1 kW of power can be generated by the proposed systems, for a geofluid with a temperature of 95 °C and mass flow rate of 50 kg/s, that belongs to the double-effect AHT based system. This is 18.6 and 60.9 kW more than the single-stage and double AHT based systems power, respectively. Also, the energy and exergy efficiencies, as well as LCOE and LCOW for this system, are calculated to be 40.07%, 57.38%, 0.04636 $/kWh, and 34.85 $/m3, respectively. Moreover, a parametric study revealed the notable influences of temperatures of AHT components on the performance parameters of the systems.