Low-temperature Geothermal Resources Research Articles

Second law analysis of a fossil‐geothermal hybrid power plant with thermodynamic optimization of geothermal preheater

AbstractThere is an urgent and compelling need to develop innovative and more effective ways to integrate sustainable renewable energy solutions into the already existing systems or, better yet, create new systems that all together make use of renewable energy. This study aims to establish the optimum working conditions of a geothermal preheater in a power plant that makes use of both renewable and nonrenewable energy resources, where renewable (geothermal) energy is used to boost the power output in an environmentally sustainable way. Hence, two models, one, a simplified model of a Rankine cycle with single reheat and regeneration, and another, with a geothermal preheater substituting the low‐pressure feedwater heater (LPFWH), were compared. The Engineering Equations Solver software was used to perform an analysis of the thermodynamic performance of the two models designed. An analysis was done to evaluate the energetic and exergetic effects of replacing a LPFWH with a geothermal preheater sourcing heat from a low temperature geothermal resource (100°C‐160°C). Results from the thermodynamic analysis reveal that the hybridization boosts the power output by approximately 4% and it is superior in terms of the second law. Entropy generation minimization analysis was then employed to establish optimal working conditions of the hybrid system (ie, the geothermal preheater modeled as a downhole coaxial heat exchanger).

Technologies of geothermal resources development in South of Russia

A technology has been proposed for the integrated development of low-temperature geothermal resources for using their thermal and water potentials for various purposes. The possibility is substantiated for efficient development of geothermal resources by construction of binary geothermal power plants (GeoPP) using idle oil and gas wells that will significantly reduce capital investments for their building. The East Ciscaucasian artesian basin situated in the South European part of Russia has a number of fields with idle wells that can be converted to thermal water production. Involving the entire fund of idle wells will make it possible to obtain up to 300 MW of summary net capacity at a geothermal power plant. This work proposes a deployment of hybrid technology of geothermal power plant coupled with combined cycle plant of gas turbine type (further GCP) for the effective utilization of medium-temperature thermal waters (80–100 °C). These technologies are shown to be promising for using such water for electricity generating with high efficiency. A comparative analysis was carried out for GeoPP and GCP operating on medium-temperature water, which has shown the advantage of the latter. According to the calculations, the implementation of hybrid technology at the Thernair field in Makhachkala town will make it possible to get a power plant capacity of up to 60 MW. The prospects of integrated processing of high-temperature geothermal brines are shown. The technological diagrams are presented where the electricity generated at a binary GeoPP is used in the unit for the chemical components extraction. The estimated parameters for the Berikey geothermal field are given. The proven reserves of the Berikey field thermal brines are shown to be promising for output more than 2000 tons of lithium carbonate annually. The prospects of integrated processing of high-temperature geothermal brines in the Tarumovka geothermal field have been presented. The thermal energy of the geothermal brine can be converted into electricity in a binary geothermal power plant using a low-boiling working agent. The Rankine thermodynamic cycles have been considered realized in the secondary circuit of the GeoPP at different temperatures of evaporation of the working agent isobutane. The most effective in terms of maximum power generation is a supercritical cycle, close to the so-called “triangular” cycle with an evaporation pressure pe = 5.0 MPa. The spent brine with a low temperature from the GeoPP will go to a chemical plant, where the main chemical components, namely, lithium carbonate, magnesia, calcium carbonate and sodium chloride will be extracted according to the developed by us technology for the integrated utilization of hydrothermal brines. For the production of valuable inorganic materials, the electricity generated at the GeoPP may be applied. The need is shown in the priority integrated processing the associated highly saline brines of the Yuzhno-Sukhokumsk group of oil and gas wells in Northern Dagestan. At present, the associated brines with a radioactive background exceeding permissible standards are dumped onto surface filtration fields. Technological solutions for their decontamination and development have been proposed.

Collocated geothermal resources of the South of Western Siberia (Russia) and prospects of their use

Low-temperature geothermal resources are widely distributed in the sedimentary cover of Western Siberia. In the southern part of the region the aquifer of the Pokur formation (K1-2), with temperatures up to 47° C at well heads, has the best prospects for direct heating. The energy extracted from this kind of geothermal resources must be used near the reservoir, that’s why collocation of the resource and a user is required. A new approach to the issue of using this energy potential is integrated use of existing water wells, drilled for domestic and drinking purposes, for heating of premises (including hot water supply) and water supply at rural communities in the south of Western Siberia. The research was aimed at the estimation of effectiveness of ground-source heat pump (GSHP) systems for extraction of energy from low-temperature groundwater, and their use for space heating of commercial buildings under the climatic conditions of the region. The computations were made by using NIBE AB (Sweden) software. It states that GSHP systems are very competitive with coal boilers, mostly used for hot water supply and space heating at domestic communities. The use of GSHP systems will also improve the ecological situation in the region.

Use of geothermal energy from abandoned oil wells

Abandoned oil wells, low-rate oil wells can be used as low-temperature geothermal resources. Geothermal power generation from abandoned wells is a new way to utilize geothermal energy. The paper presents a model for using geothermal energy from abandoned wells. The paper analyzes the use of freon as a main working fluid.

Study on Development and Utilization of Shallow Geothermal Energy in Jilin Province

Under the current trend of striving for economic, energy-saving, low-carbon and environmental protection, geothermal energy has received wide attention due to its advantages such as energy conservation and environmental protection. The so-called geothermal energy is a kind of energy from the interior of the earth. It has a strong vitality. The heat stored in the earth is about 170 million times of the global coal reserves, and the annual heat from the earth through the surface is about 100 billion barrels. The thermal equivalent of petroleum. Shallow geothermal energy is an important part of the earth's thermal energy. It usually refers to the low-temperature geothermal resources located in the shallow rock mass of the earth's crust, which is located at a depth of 15 to 200 meters above the Earth's surface. In new and renewable energy sources, shallow geothermal energy is a new energy source that is competitive with current trends. This paper introduces the utilization and development of shallow geothermal energy in Jilin Province to enrich the research results of shallow geothermal energy in Jilin Province.

Investigation energy, exergy and electricity production performance of an integrated system based on a low-temperature geothermal resource and solar energy

In this work, energy, exergy and electricity generation performance of an integrated system was conceptually investigated by using Engineering Equation Solver (EES) under 200–1000 W/m2 solar irradiation interval. The system comprises evacuated tube solar collectors (EVTSCs) with the surface area of 100 m2, an organic Rankine cycle (ORC) and a low-grade geothermal resource. The EVTSCs were used to enhance the temperature of the low-grade water coming from the geothermal source. The calculations were carried out for three geothermal sources in Kula (63 °C), Saraycık (74 °C) and Turgutlu (86 °C), respectively. N-hexane, n-pentane and n-butane were selected as a working fluid in the ORC. It was determined that the selection of the working fluid affected the performance of the ORC. And also, the waste heat is extracted from the ORC were used efficiently for space heating. As a result, the overall energy and exergy efficiencies of the system and power generation of the ORC were seriously affected by enhancing the water temperature of the geothermal resources by EVTSCs. The maximum overall energy and exergy efficiencies of the system were calculated as to be 6.92% and 21.06% by using n-butane for the source in Turgutlu, respectively. The minimum overall energy and exergy efficiencies of the system were calculated as 0.32% and 2.19% by using n-hexane for the source in Kula, respectively. The maximum and minimum generated electricity were calculated as to be 19.46 kW and 0.6168 kW for the sources in Turgutlu and Kula, respectively. It was seen that the best performance of the system was found for n-butane compared to n-pentane and n-hexane.

Developing low temperature Geothermal projects in Indonesia using pumped well technology

Indonesia’s installed electrical-grade geothermal capacity is currently limited to developments at high temperature geothermal areas; however, survey data from Badan Geologi (Geological Agency of Indonesia) suggests that a large reserve of medium and low temperature geothermal resources also exists in the country. Using electric line shaft or submersible pumps, low to medium temperature geothermal fluids can be pumped from relatively shallow depths and electricity can be generated using binary power plant technology. This has been proven to be a commercially viable development approach for geothermal systems hosted in a range of geologic settings (e.g., structural/sedimentary basins, volcanic flanks, and metamorphic terranes), and are usually situated in regions of geologic structural complexity. The heat sources for these systems can be the conductive/advective heat transfer from a magmatic body or simply related to deep circulation of fluids in a non-magmatic setting. Lateral outflows of higher temperature geothermal systems are another category of low and medium temperature geothermal resources that may be attractive development targets, potentially allowing for the expansion of presently developed systems. This paper considers the utilization of pumped wells to exploit low and medium temperature resources considering recent trends internationally and with specific regard for the Indonesian context of this technology. As discussed herein, the commercial viability of pumped wells depends on the resource characteristics (namely temperature, depth, well productivity, and gas content) as well as a number of economic and development factors. We present results of modelling the potential productivity in terms of MW/well (net) for pumped wells over a range of permeability and temperature conditions and compare the results with typical high temperature self-flow wells.

Geothermal resources complex utilization in russia

Thermal waters are used for many purposes - for development of electric power, for central heating and cooling, for hot water supply, in agriculture, animal industries, fish culture, in the food, chemical and oil-extracting industries, in balneology and spas, and for the recreational purposes.Geothermal energy use is a prospective way to achieve clean sustainable development of the world. Russia has rich high and low temperature geothermal resources and makes good steps in their use. In Russia the geothermal resources are used predominantly for heat supply, heating of several cities and settlements on Northern Caucasus and Kamchatka. In addition, in some regions of country the deep heat is used for greenhouses. The most active hydrothermal resources are used in Krasnodar territory, Dagestan and on Kamchatka.At the same time the problem of the most effective utilization of a natural source of raw materials is put forward in the category of actual tasks, including thermomineral waters and brines. Involving of these waters in economic activities can promote the decision of some social - economic and environmental problems.

Geothermal power based ULTDH for cooling and heating purposes

Ultra-low temperature district heating systems facilitate use of waste and renewable heat sources. The article presents a possible scheme of operation and optimisation of small ultra-low temperature district heating system consisting of waste heat source, a number of heated individual dwellings and borehole thermal energy storage plant. Optimisation performed for typical meteorological year for Kraków indicate significant potential of decreasing energy amount discharged to the environment and total length of borehole heat exchangers, compared to individual heat/cold production from low-temperature geothermal resources. Meanwhile, satisfied is a set of constrains providing borehole thermal energy storage sustainability and fulfilling entire heating and cooling demands.

Development of the Polish geothermal sector in the light of current possibilities of financial support for a geothermal investment

Geothermal energy is an internal heat of the Earth, that is a prospective and sustainable source of renewable energy. In Poland, despite having significant amount of low-temperature geothermal resources, its share in the national energy mix remains marginal but growing. Currently, the utilisation of geothermal resources is related to hydrogeothermal resources, that are used mainly in space heating, recreation and balneotherapy. Nevertheless, the indication of potential electricity production is under research. The utilisation of geothermal resources entails a plenty of environmental benefits that are particularly important in the context of the present pollution problem. Therefore, the development of the geothermal energy sector is of relevant importance and with appropriate legal and financial conditions it may have a bearing on improvement of the environment’s quality and, ipso facto, living in Poland. Thus, this paper presents numerous possibilities of obtaining a financial support for investments in geothermal energy sector. Selected funding and financial backing systems currently available in Poland are discussed. The importance of opportunity of obtaining a financial support for an investment as one of the crucial factors for the geothermal sector development is emphasised. Moreover, the examples of installations implemented in the country in the context of obtained funding are presented.

Economic appraisal and scoping of geothermal energy extraction projects using depleted hydrocarbon wells

This study offers a first step in examining a potential solution for what to do with the ever-increasing number of horizontal shale wells in the United States (and lately, Argentina and China), as they come to the end of their economic life. A comprehensive decision-making tool was developed for scoping assessments based on the technical and economic appraisal of abandoned hydrocarbon wells repurposed into enhanced geothermal systems. We specifically target near end-of-life oil and gas wells, re-commissioned to extract geothermal energy as opposed to hydrocarbons, because these potential geothermal resources are prevalent near a handful of major US population and energy demand centers, including Pittsburgh, Houston, Denver, Dallas, Oklahoma City and San Antonio. This study addresses some of the technical challenges associated with such projects. However, the main focus is on (1) the probabilistic evaluation of the economic net present value, and (2) specific solutions for possible commercial deal structures required for negotiation and project implementation. The backdrop for the test case in this study is the new Texas A&M RELLIS Campus being constructed in College Station, Texas. A successful commercial model for the use of abandoned oil and gas wells to extract low and medium temperature geothermal resources could spur further development and a pilot study is proposed for this green source of energy. Our estimations suggest a net present value of $1.2 billion could be unlocked in the US alone, through the repurposing of wells, previously used for hydrocarbon extraction only.

Determining the origin, circulation path and residence time of geothermal groundwater using multiple isotopic techniques in the Heyuan Fault Zone of Southern China

Medium–low temperature geothermal resources are abundant in Southern China, but their heat source and link to fault zones is poorly understood. Consequently, geothermal energy is only used at small scale. In order to broaden the footprint of geothermal energy use in Southern China, it is first necessary to understand and track the geothermal groundwater circulation pattern associated with fault zones. The Heyuan Fault Zone serves as a typical medium–low temperature geothermal system of South China. Here we show that the geothermal groundwater circulation pattern can be traced by using stable hydrogen and oxygen isotopes, helium and neon isotopes, carbon-13 and carbon-14 as well as hydrochemical parameters. The results show that: in the Heyuan Fault Zone, the main hydrochemical type of the hot springs is HCO3-Na + K, while the shallow cold groundwater is mainly enriched in HCO3-Ca. The results of the helium isotope and neon isotope indicate that the geothermal groundwater of this area is derived from the crust, thus excluding the possibility of extremely deep paths of groundwater tapping into mantle helium sources. Furthermore, the characteristics of the stable hydrogen and oxygen isotopes imply that geothermal groundwater is of local meteoric origin, and the recharge area located at the hilly area of the hanging wall of the Heyuan main fault, with the recharge elevations ranging from about 440 m to 670 m. The hot spring geothermometer shows that the highest reservoir temperature is about 157 °C, and the deepest circulation depth is about 6500 m. Carbon-14 isotope age dating suggests that the geothermal groundwater ages are mostly from 9.9 kyr BP to 12.3 kyr BP. According to the geological structural characteristics of the study area, the main upward channel for geothermal groundwater is the Heyuan main fault. Generally, the hot springs in this area are mixed with shallow cold groundwater and surface water, which raises the ratio of the Ca2+ in water and dilutes the heavy hydrogen and oxygen isotopes.

Conjunctive uses of the geothermal water resources from lower cretaceous formations in the Mogilno\u2013Lodz trough, Poland

The geothermal energy sector continues to develop dynamically in the world. Within this work, preliminary feasibilities of different geothermal applications were presented for the Lower Cretaceous formations for wider geothermal uses’ development in the Mogilno–Lodz trough, Central Poland. The Lower Cretaceous formations are one of the most prospective geothermal reservoirs in Central Poland. Geothermal waters that occur within them are mostly of Na–Cl type and contain specific elements like I, Br or Fe. These are low-temperature geothermal resources together with highly variable mineralization, from 0.4 to even more than 90 g/L. A simple estimation procedure for hydrogeological information, such as water and thermal conditions of the reservoir obtained from an archival chemical analysis and borehole temperature loggings was developed. The potential for geothermal applications was estimated for three zones of the Mogilno–Lodz trough. Possibilities of conjunctive geothermal applications, such as space heating, balneotherapy and balneorecreation, mineral extraction, electricity production in binary systems and aquifer thermal energy storage were examined for the Lower Cretaceous formations.

The Integration of 3D Modeling and Simulation to Determine the Energy Potential of Low-Temperature Geothermal Systems in the Pisa (Italy) Sedimentary Plain

Shallow, low-temperature geothermal resources can significantly reduce the environmental impact of heating and cooling. Based on a replicable standard workflow for three-dimensional (3D) geothermal modeling, an approach to the assessment of geothermal energy potential is proposed and applied to the young sedimentary basin of Pisa (north Tuscany, Italy), starting from the development of a geothermal geodatabase, with collated geological, stratigraphic, hydrogeological, geophysical and thermal data. The contents of the spatial database are integrated and processed using software for geological and geothermal modeling. The models are calibrated using borehole data. Model outputs are visualized as three-dimensional reconstructions of the subsoil units, their volumes and depths, the hydrogeological framework, and the distribution of subsoil temperatures and geothermal properties. The resulting deep knowledge of subsoil geology would facilitate the deployment of geothermal heat pump technology, site selection for well doublets (for open-loop systems), or vertical heat exchangers (for closed-loop systems). The reconstructed geological–hydrogeological models and the geothermal numerical simulations performed help to define the limits of sustainable utilization of an area’s geothermal potential.

Energetic and exergetic performance comparison of different polygeneration arrangements utilizing geothermal energy in cascade

In this paper, the energy and exergy performance of several polygeneration arrangements driven by low and medium temperature geothermal resource is investigated. The aim is to assess and compare different coupling schemes, identifying suitable thermally driven technologies for each type of arrangement. The polygeneration system is intended to produce power, cooling and heat for direct uses by considering variations of series and parallel coupling schemes along with different alternatives of ORC and absorption cooling machines. The study was conducted considering a temperature range of low-to-medium geothermal resource from 80 °C to 150 °C. Mathematical models are developed based on first and second law of thermodynamics and solved by means of an equation solver. The results show a threshold temperature that makes a shift between feasible polygeneration arrangements and the type of thermally driven technologies adopted, resulting in two different polygeneration arrangements with highest energetic and exergetic performance. The first arrangement correspond to a temperature range that lies between 80 °C and 110 °C, and the second one between 110 °C and 150 °C. The polygeneration arrangement with highest exergetic performance for the first range of temperatures was the hybrid parallel-series cascade arrangement (HPS2) having exergy efficiencies between 42.82% and 50.11%, while the one corresponding to the second temperature range was the series cascade arrangement (SC1) presenting exergy efficiencies from 51.44% to 52.9%. This effect is a consequence of the available temperature of the geothermal resource and the intrinsic energy performance of the different technologies considered. In regard to thermally driven technologies, arrangements where ORC and TDC subsystems are placed at the first thermal level, are the ones with the highest energetic and exergetic performance. Arrangements that have those components at the last level, present lowest performances.

Thermodynamics Analysis of Binary Plant Generating Power from Low-Temperature Geothermal Resource

The purpose in this research was to predict tendency of increase Carnot efficiency of the binary plant generating power from low-temperature geothermal resource. Low-temperature geothermal resources or less, are usually exploited by means of binary-type energy conversion systems. The maximum efficiency is analyzed for electricity production of the binary plant generating power from low-temperature geothermal resource becomes important. By using model of the heat exchanger equivalent to a power plant together with the calculation of the combined heat and power (CHP) generation. The CHP was solved in detail with appropriate boundary originating an idea from the effect of temperature of source fluid inlet-outlet and cooling fluid supply. The Carnot efficiency from the CHP calculation was compared between condition of increase temperature of source fluid inlet-outlet and decrease temperature of cooling fluid supply. Result in this research show that the Carnot efficiency for binary plant generating power from low-temperature geothermal resource has tendency increase by decrease temperature of cooling fluid supply.

Technologies for the Comprehensive Exploitation of the Geothermal Resources of the North Caucasus Region

Technology for the integrated development of low-temperature geothermal resources using the thermal and water potentials for various purposes is proposed. The heat of the thermal waters is utilized in a low-temperature district heating system and for heating the water in a hot water supply system. The water cooled in heat exchangers enters a chemical treatment system where it is conditioned into potable water quality and then forwarded to the household and potable water supply system. Efficient technologies for removal of arsenic and organic contaminants from the water have been developed. For the uninterrupted supply of the consumers with power, the technologies that use two and more types of renewable energy sources (RESs) have the best prospects. Technology for processing organic waste using the geothermal energy has been proposed. According to this technology, the geothermal water is divided into two flows, one of which is delivered to a biomass conversion system and the other is directed to a geothermal steam-gas power plant (GSGP). The wastewater arrives at the pump station from which it is pumped back into the bed. Upon drying, the biogas from the conversion system is delivered into the combustion chamber of a gas-turbine plant (GTP). The heat of the turbine exhaust gases is used in the GSGP to evaporate and reheat the low-boiling working medium. The working medium is heated in the GSGP to the evaporation temperature using the heat of the thermal water. High-temperature geothermal brines are the most promising for the comprehensive processing. According to the proposed technology, the heat energy of the brines is utilized to generate the electric power at a binary geothermal power station; the electric power is then used to extract the dissolved chemical components from the rest of the brine. The comprehensive utilization of high-temperature brines of the East-Precaucasian Artesian Basin will allow to completely satisfy the demand of Russia for lithium carbonate and sodium chloride.

Exergoeconomic analysis and comparison between ORC and Kalina cycles to exploit low and medium-high temperature heat from two different geothermal sites

The Organic Rankine (ORC) and Kalina (KC) Cycles represent two different technologies suitable to exploit low and medium temperature geothermal heat resources. In this work, the performances of KC, CO2 and ORC cycles, the latter using different working fluids, for power generation from two geothermal fluid reservoirs are compared from an energy and exergoeconomic perspective.Two different case studies are discussed: the first one referred to a medium-temperature heat source of 212 °C (Mt. Amiata, Italy), the second one to a low-temperature heat source of 120 °C (Pomarance geothermal basin, Italy).For each case study, cost rate balances and auxiliary equations for all components were evaluated, as well as the flow rate and unit exergy cost for each stream.The results for the medium temperature case study showed that, among the considered cycles, an ORC with R1233zd(E) achieves the best exergoeconomic performance. The cost of the produced electricity was found to be 8.85 c€/kW h, which is 3% lower than that of the KC. On the other hand, for the low temperature case study, the KC shows the best performance, being able to produce 22–42% more net power than the ORC; in this case, the cost of electricity produced by the KC was found at 12.5 c€/kW h, which is 24–34% lower than the typical value for an ORC with different working fluids.

Recent trends in the development of heat exchangers for geothermal systems

The potential use of geothermal resources has been a remarkable driver for market players and companies operating in the field of geothermal energy conversion. For this reason, medium to low temperature geothermal resources have been the object of recent rise in consideration, with strong reference to the perspectives of development of Organic Rankine Cycle (ORC) technology.The main components of geothermal plants based on ORC cycle are surely the heat exchangers. A lot of different heat exchangers are required for the operation of ORC plants. Among those it is surely of major importance the Recovery Heat Exchanger (RHE, typically an evaporator), in which the operating fluid is evaporated. Also the Recuperator, in regenerative Organic Rankine Cycle, is of major interest in technology. Another important application of the heat exchangers is connected to the condensation, according to the possibility of liquid or air cooling media availability. The paper analyzes the importance of heat exchangers sizing and the connection with the operation of ORC power plants putting in evidence the real element of innovation: the consideration of the heat exchangers as central element for the optimum design of ORC systems.

Research status of geothermal resources in China

As the representative of the new green energy, geothermal resources are characterized by large reserve, wide distribution, cleanness and environmental protection, good stability, high utilization factor and other advantages. According to the characteristics of exploitation and utilization, they can be divided into high-temperature, medium-temperature and low-temperature geothermal resources. The abundant and widely distributed geothermal resources in China have a broad prospect for development. The medium and low temperature geothermal resources are broadly distributed in the continental crustal uplift and subsidence areas inside the plate, represented by the geothermal belt on the southeast coast, while the high temperature geothermal resources concentrate on Southern Tibet-Western Sichuan-Western Yunnan Geothermal Belt and Taiwan Geothermal Belt. Currently, the geothermal resources in China are mainly used for bathing, recuperation, heating and power generation. It is a country that directly makes maximum use of geothermal energy in the world. However, China’s geothermal power generation, including installed generating capacity and power generation capacity, are far behind those of Western European countries and the USA. Studies on exploitation and development of geothermal resources are still weak.