High-temperature Geothermal Resources Research Articles

Potential areas of interest for the development of geothermal energy in La Réunion Island based on GIS analysis

La Réunion Island has been considered an attractive target for geothermal exploitation since the 1970s. However, to date, the island's geothermal resources are not being used. Here we use for the first time, a Geographic Information System (GIS) as a decision-making tool to target the most favorable zones for exploitation of moderate and high temperature geothermal resources. All data acquired since the 1970s (geology, geophysics, geochemistry) in addition to environmental constraints such as protection of the National Park that was recently classified as a UNESCO World Heritage Site, were analyzed using the weighted overlay method to delineate favorable areas for local geothermal exploration. Three thematic maps were constructed: geological and structural indicators, thermal indicators, and geophysical indicators. Cross-analysis of these maps highlights two zones that have high geothermal potential; six zones with unconfirmed geothermal potential; and two zones located within the National Park protected area and thus subject to stringent exploitation regulations. It appears that, while thermal anomalies exist in several areas, permeability of the geological formations is low or insufficient for traditional geothermal utilization. Future exploration phases should assess the feasibility of using enhanced geothermal system (EGS) technologies to obtain a satisfactory economic return.

Geochemical evidence for the nonexistence of supercritical geothermal fluids at the Yangbajing geothermal field, southern Tibet

Exploring and exploiting high-temperature (even supercritical) geothermal resources are significant to meet energy demands and reduce carbon emissions. The Yangbajing geothermal field is the most exploited in China, with the currently highest temperature (329.8 °C) measured in a geothermal well. However, whether there are supercritical geothermal fluids beneath the deep parts of this geothermal field is under controversy. In this paper, the water isotope, chemical compositions, and C–He isotopes of gas samples were collected and analyzed. The geothermal water originated from the mixing of meteoric water and magmatic water (25%). The sources of CO2 in the geothermal field were dominated by the thermogenic degassing of carbonates and metasediments in the crust while the radioactive decay of U and Th in granite is the dominated source of He. The temperatures of three different reservoirs are 150 ± 15 °C, 250 ± 10 °C, and ∼320 °C (with a depth of ∼8 km), respectively. These were obtained using dissolved gas, soil CO2 flux, and noble gas geothermometers. Unlike other supercritical geothermal fields worldwide with larger, shallower, basaltic magma chambers, the Yangbajing geothermal field has a deep-seated, small-scale, granitic magma chamber. Thus, its geological conditions are not conducive for gestating supercritical fluids. These results are of great significance for exploring and developing high-temperature (even ultra-high-temperature) geothermal resources in China.

Existence of High Temperature Geothermal Resources in the Igneous Rock Regions of South China

Large areas of Yanshan period granites with high heat production values (3–10 μW/m3) and mantle plume around Hainan province co-exist in Igneous Rocks Regions of South China (IRRSC). Surface manifestations are mainly warm/hot springs with temperatures below 90 °C and no typical phenomenon of high temperature resources have been observed. The main objective of this paper is to discuss the existence of high temperature geothermal resources and their possible locations under this kind of geothermal and tectonic background by analysis of high temperature heat sources, borehole temperature measurement, and reservoir temperature estimation. Two possible partial melts of the magma chamber were detected as high temperature heat sources in the Southern Leizhou Peninsular and North Hainan Island at a depth of 8–15 km. Other low resistivity zones in the upper crust are more likely caused by fluid in the formations or faults but not high temperature heat sources. This was also verified by borehole temperature measurement in these two areas, with maximum formation temperatures of 211°C and 185°C found, respectively. Reservoir temperatures from fluid geothermometers show lower temperatures of between 110–160°C for typical geothermal fields over the IRRSC but not in the Southern Leizhou Peninsular and Northern Hainan Island. In all, high temperature geothermal resources may be found in the Southern Leizhou Peninsular and on Northern Hainan Island.

Magmatic origin of geothermal fluids constrained by geochemical evidence: Implications for the heat source in the northeastern Tibetan Plateau

The northeastern Tibetan Plateau (NETP) represents the growth front of the Tibetan Plateau (TP) system. This region has long been recognized as a key in understanding the topographic response and crustal thickening of the entire TP. A heat flow anomaly (Gonghe Basin, 102 mW/m2) was found in the NETP. However, the heat-generation mechanism and the heat source of the Gonghe Basin are still debated as it is unclear whether they are related to magmatic melting activities. Herein, we provide systematic hydrogeochemical data of two types of geothermal waters (type I and II: geothermal waters sampled from within the basin and the mountainous regions, respectively) found in the region. Type I high δD (−85.0‰ to −59.0‰), δ18O (−11.1‰ to −8.0‰), Cl− (mostly range from 300 to 900 mg/L), and trace element, whereas type II has low δD (−97.1‰ to −89‰), δ18O (−13.0‰ to −11.8‰), Cl− (30 to 180 mg/L) and trace elements. Furthermore, we identified the existence of a high-temperature parent geothermal fluid based on the chloride – enthalpy model, it was estimated to possess a temperature of 310 °C and a circulation depth of 6.8–7.8 km. The parent geothermal fluid originated from snowmelt water, which later mixed with a magmatic fluid. The helium (He) ratios of geothermal gas ranged from 0.01 Ra to 0.18 Ra and indicated that the source of He was primarily from a crustal source. In addition to the heat flow analysis and magnetotelluric (MT) data, we suggested that the magmatic nature of the geothermal fluid is caused by a partial melt zone, which is ubiquitous in the middle to lower crust and serves as the heat source in the NETP. Finally, a conceptual model was built to illustrate the occurrence of magmatic fluid and its genesis. The findings will help to improve the understanding of the uplift of the TP and reveals the important role of deep groundwater circulation in the formation of high-temperature geothermal resources.

Performance enhancement and multi-objective optimization of a double-flash binary geothermal power plant

Initiating cost-effective and technological frameworks to exploit geothermal energy is a fundamental incentive for scientists and engineers; in this regard, flash-binary geothermal power plants are plausible for high-temperature geothermal resources. Stemming from an in-depth literature review, it is conspicuous that the thermal and exergy losses of the expansion process are significant. To shed light on this matter, an ejector-expander is integrated into the conventional expansion valve of a double-flash binary geothermal power plant to enhance the plant performance. The feasibility of the contrived notion is scrutinized from energy, exergy, thermal, and cost balance standpoints and results converged in the increase in turbine output power, energy efficiency, and exergy efficiency of approximately 7.66%, 7.64%, and 7.69%, respectively. Among all components, the condenser constituted a 45.06% share of the overall exergy destruction, whilst the turbine had an exergy destruction ratio of 22.07%. An intensive parametric study is implemented that outlined that the turbine output power, energy efficiency, and exergy efficiency of the ejector-expander power system have a maximum in a specified pressure value of the first and second separator. Another merit was a marked decrease in the unit cost of power when ejector-expander is employed.

Geological controls on geothermal resources for power generation

Threats posed by the climate crisis have created an urgent need for sustainable green energy. Geothermal resources have the potential to provide up to 150 GWe of sustainable energy by 2050. However, the key challenge in successfully locating and drilling geothermal wells is to understand how the heterogeneous structure of the subsurface controls the existence of exploitable fluid reservoirs. In this Review, we discuss how key geological factors contribute to the profitable utilization of intermediate-temperature to high-temperature geothermal resources for power generation. The main driver of geothermal activity is elevated crustal heat flow, which is focused in regions of active magmatism and/or crustal thinning. Permeable structures such as faults exercise a primary control on local fluid flow patterns, with most upflow zones residing in complex fault interaction zones. Major risks in geothermal resource assessment and operation include locating sufficient permeability for fluid extraction, in addition to declining reservoir pressure and the potential of induced seismicity. Advanced computational methods permit effective integration of multiple datasets and, thus, can reduce potential risks. Future innovations involve engineered geothermal systems as well as supercritical and offshore geothermal resources, which could greatly expand the global application of geothermal energy but require detailed knowledge of the respective geological conditions. Successful discovery and operation of geothermal resources requires a thorough understanding of the heterogeneous geological subsurface. This Review discusses the key geological factors that contribute to the effective exploration of intermediate-temperature to high-temperature geothermal resources used for power generation and direct use applications.

Performance Prediction of a Turbodrill Based on the Properties of the Drilling Fluid

High-temperature geothermal well resource exploration faces high-temperature and high-pressure environments at the bottom of the hole. The all-metal turbodrill has the advantages of high-temperature resistance and corrosion resistance and has good application prospects. Multistage hydraulic components, consisting of stators and rotors, are the key to the turbodrill. The purpose of this paper is to provide a basis for designing turbodrill blades with high-density drilling fluid under high-temperature conditions. Based on the basic equation of pseudo-fluid two-phase flow and the modified Bernoulli equation, a mathematical model for the coupling of two-phase viscous fluid flow with the turbodrill blade is established. A single-stage blade performance prediction model is proposed and extended to multi-stage blades. A Computational Fluid Dynamics (CFD) model of a 100-stage turbodrill blade channel is established, and the multi-stage blade simulation results for different fluid properties are given. The analysis confirms the influence of fluid viscosity and fluid density on the output performance of the turbodrill. The research results show that compared with the condition of clear water, the high-viscosity and high-density conditions (viscosity 16 mPa∙s, density 1.4 g/cm3) will increase the braking torque of the turbodrill by 24.2%, the peak power by 19.8%, and the pressure drop by 52.1%. The results will be beneficial to the modification of the geometry model of the blade and guide the on-site application of the turbodrill to improve drilling efficiency.

Geochemical evaluation of geothermal resources in Toyama Prefecture, Japan, based on the chemical and isotopic characteristics of hot spring waters

The chemical compositions, including hydrogen and oxygen isotopes, of 35 hot spring waters in Toyama Prefecture, central Japan, were analyzed to examine their geochemical characteristics and geothermal resources. The hot spring water samples were classified into two groups: low and high chloride (Cl−) concentrations of less than and greater than 2000 mg/L, respectively. The samples in the low-salinity group were determined to be of meteoric origin and Ca2+–HCO3− type. The samples in the high-salinity group were determined to be of Na+–Ca2+–Cl− type and assumed to contain a mixture of fossil seawater and meteoric water. In the eastern area of the study region, the Na+/K+ and SiO2 concentrations were lower and higher, respectively, than those in other areas, which corresponded to high-temperature geothermal resources. Thus, the subsurface information obtained in this study enabled effective use of the low to medium geothermal resources in Toyama Prefecture.

Heat extraction analysis of a novel multilateral-well coaxial closed-loop geothermal system

We propose a novel multilateral-well coaxial closed-loop geothermal system (CCGS) to help realize the commercial exploitation of hot dry rock. Compared with the enhanced geothermal system, it avoids the high-cost fracturing and environmental problems by closed-loop circulation. Also, the multilateral-well CCGS can significantly increase heat production than traditional vertical-well or horizontal-well CCGSs via lateral wellbores. Then, we establish a new 3D transient model and validate it with experimental data. The temperature field is studied. The Influences of injection flow rate, number of lateral wellbores, wellbore size, thermal conductivity of insulation pipe, and reservoir temperature are analyzed. Results show that the lateral wellbores are vital to improving heat extraction, and a viable lateral-wellbore spacing is determined. The total energy output rises linearly with time, while the extracted heat in the initial stage is limited though the thermal power is high. There is an appropriate injection flow rate by comparing the total energy output and dissipation. A smaller wellbore size is preferred due to the minor effect. A reasonable thermal conductivity exists for the insulation pipe. Particularly, the high-temperature geothermal resources at various depths can be efficiently developed through the multilateral-well CCGS given the effect of reservoir temperature.

Radiogenic heat production variations in the Gonghe basin, northeastern Tibetan Plateau: Implications for the origin of high-temperature geothermal resources

Hot dry rock is an almost inexhaustible source of geothermal energy. Since the first attempt to extract thermal energy from hot dry rock in America in the 1970s, successive studies have been conducted in many countries. Recently, high-temperature rock (exceeding 180 °C) was drilled in the Gonghe basin, northeastern Tibetan Plateau, marking a significant breakthrough in the exploration of hot dry rock resources in China. A proper understanding of the origin of the hot dry rock in the Gonghe basin is essential to the evaluation of the geothermal resource potential and to the establishment of an enhanced geothermal system in the basin.In the present research, we attempt to seek clues from the radiogenic heat production of the rocks. In all, 52 core samples collected from the main boreholes in the Gonghe basin were measured for the concentrations of radioisotopes. The heat production values were determined to be 1.21–2.02 μW m−3 for the sedimentary rocks, yielding an arithmetic mean of 1.67 ± 0.29 μW m−3, and 1.17–5.81 μW m−3 for the basal granitic rocks, yielding a mean of 3.20 ± 1.07 μW m−3. The results show that the radiogenic heat production of the granitic rocks is approximately that of global Mesozoic-Cenozoic granites, which is further corroborated by an extensive compilation of heat production data for granitic rocks in the immediate vicinity of the study area (average of 2.07 ± 0.97 μW m−3, n = 136). Based on the heat production data sets combined with available geological and geophysical information, the crustal heat production contribution is determined. The results show that the heat contribution from the crust is about 48.3 mW m−2, accounting for ∼47.3% of terrestrial heat flow. Compared with the regional background heat flow, the high heat flow in the Gonghe basin may be attributed to an additional heat flow contribution (∼27 mW m−2) from a heat anomaly (probably related to partial melting) at shallow depth, which is evidenced by the low-resistivity anomalies in the magnetotelluric survey results. Thus, this study emphasizes that the anomalous heat flow and the hot dry rock geothermal resources in the Gonghe basin may be the combined effects of the radiogenic heat contribution from the thickened crust and the heat contribution from a local heat anomaly beneath the Gonghe basin.

The use of super-critical carbon dioxide as the working fluid in enhanced geothermal systems (EGSs): A review study

Naturally-occurring high-temperature geothermal energy resources contribute significantly to the world’s emerging energy demand by allowing renewable and clean power generation, and the technology of enhanced geothermal systems (EGSs) continues to progress at deeper levels, providing the ability to extract heat stored in deep underground at 2–5 km depths, which would have previously been considered impractical. Water-based EGSs are fairly well established, and a number of research studies have been carried out on the performance of water as the working fluid in geothermal reservoirs. Besides, the applicability of super-critical carbon dioxide (ScCO2) as the working fluid in EGSs by replacing water was recently investigated by research studies due to a number of advantages accompanied in CO2 as the working fluid in EGSs. The aim of this review study is to comprehensively investigate the applicability of ScCO2 as a working fluid in EGSs by summarising the recent research studies conducted on the operation of CO2-based geothermal systems. The study is further intended to highlight the advantages of ScCO2 in the EGS environment compared to conventional water-based methods. Of the advantages, a reduction of the external power requirement for the pumping of ScCO2 due to enhanced injectivity and flowability is the most attractive. In terms of heat extraction, higher mass flowrates can be achieved using ScCO2 as a working fluid, depending on the density-to-viscosity ratio, and the ratio is doubled with ScCO2 compared to water in the temperature range of 200–250 °C. Moreover, an accelerated energy recovery can be achieved through the higher thermal extraction rates of ScCO2, which are 50% greater than for water. Importantly, ScCO2 has the ability of inducing an interconnected fracture network with multiple secondary branches under comparatively low breakdown pressures compared to water. ScCO2 being a linear molecule with lower viscosity has the percolation ability into microcracks of the rock matrix, and thereby, the pressurisation of these microcracks induce multiple flow paths long the rock matrix by interconnecting the microcracks. In addition, the use of ScCO2 eliminates the problems associated with silica dissolution followed by precipitation, takes place in surface piping, heat exchangers and other surface equipment, because dry ScCO2 is less reactive in hot-dry reservoirs. However, in water-based EGSs, enhanced reactivity of water with the increase of pH accelerates the dissolution and precipitation of minerals, and is a critical issue in water-based EGSs. The enhanced reactivity of ScCO2 in the presence of pore fluid may also affect the long-term integrity of EGSs, because it alters the internal pore structure, due to the dissolution and precipitation of primary and secondary rock minerals, resulting in altered porosity and permeability, which ultimately affect the energy extraction process.

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.

Classification of geothermal resources in Indonesia by applying exergy concept

Indonesia is well-known for its reputation for possessing the world's largest geothermal potential, which has been characterized by high temperature geothermal resources' concentration. The geothermal energy potential of Indonesia has been estimated to be 28,617 MW, which is about 40% of the world's geothermal potential. However, only about 4.5% is being utilized as electrical energy supply in this country. This paper comprises the Indonesian geothermal resources, based on their capability of doing work and efficiency. In this study, currently operating geothermal power plants in Indonesia have been classified, based on the exergy concept and the Specific Exergy Index (SExI). The results of SExI values show that nine geothermal fields are classified as high exergy resource with their SExI values exceeding 0.5, and two remaining power plants with SExI values between 0.05 and 0.5 are classified as medium geothermal resources.

Deep-seated Geothermal Resources of the Parana Basin

Updated data sets on terrestrial heat flow and thermal springs have been employed in outlining the nature of deep-seated geothermal resources of the Parana basin. A 1o x1o grid system was adopted for data processing and in determinations of vertical distributions of excess temperatures. The results obtained have led to an improved understanding of the occurrence of high temperature geothermal resources and allowed estimates of associated resource base. It has been possible to identify more than 20 crustal blocks where the resource base per unit area, referred to the accessible depth limit of 6 km, are in the range of 2x1011 to 9x1011 Joules. There are indications pointing to occurrence of medium temperature geothermal resources at depths of 4 to 6 km in several sectors of the central and western parts of the basin. The area extent of such blocks has dimensions of several tens of kilometers. Most high temperature resources occur within the well-known sectors of fault-controlled magmatic activity associated with the eruption of Serra Geral flood basalts. In addition, isolated pockets of high enthalpy geothermal resources are found to be present along the northwestern border. The results have also allowed better assessments of low temperature resources of the Guarani aquifer system, which span over large areas of southern Brazil, western Uruguay and northern Argentina.

Numerical investigation on the implications of spring temperature and discharge rate with respect to the geothermal background in a fault zone

Geothermal springs are some of the most obvious indicators of the existence of high-temperature geothermal resources in the subsurface. However, geothermal springs can also occur in areas of low average subsurface temperatures, which makes it difficult to assess exploitable zones. To address this problem, this study quantitatively analyzes the conditions associated with the formation of geothermal springs in fault zones, and numerically investigates the implications that outflow temperature and discharge rate from geothermal springs have on the geothermal background in the subsurface. It is concluded that the temperature of geothermal springs in fault zones is mainly controlled by the recharge rate from the country rock and the hydraulic conductivity in the fault damage zone. Importantly, the topography of the fault trace on the land surface plays an important role in determining the thermal temperature. In fault zones with a permeability higher than 1 mD and a lateral recharge rate from the country rock higher than 1 m3/day, convection plays a dominant role in the heat transport rather than thermal conduction. The geothermal springs do not necessarily occur in the place having an abnormal geothermal background (with the temperature at certain depth exceeding the temperature inferred by the global average continental geothermal gradient of 30 °C/km). Assuming a constant temperature (90 °C here, to represent a normal geothermal background in the subsurface at a depth of 3,000 m), the conditions required for the occurrence of geothermal springs were quantitatively determined.

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.

Modern geothermal power: GeoPP with geothermal steam turbines

The first part of the review presents information on the scale and specific features of geothermal energy development in various countries. The classification of geothermal power plant (GeoPP) process flow diagrams by a phase state of the primary heat source (a geothermal fluid), thermodynamic cycle, and applicable turbines is proposed. Features of geothermal plants using methods of flashing and steam separation in the process loop and a flowsheet and thermodynamic process of a geothermal fluid heat-to-power conversion in a GeoPP of the most widespread type using a double-flash separation are considered. It is shown that, for combined cycle power units, the specific power-to-consumption geothermal fluid ratio is 20–25% higher than that for traditional single-loop GeoPP. Information about basic chemical components and their concentration range for geothermal fluids of various formations around the world is presented. Three historic stages of improving geothermal energy technologies are determined, such as development of high-temperature geothermal resources (dry, superheated steam) and application of a two-phase wet-steam geothermal fluid in GeoPP power units with one or two expansion pressures and development of binary cycle GeoPPs. A current trend of more active use of binary power plants in GeoPP technological processes is noted. Design features of GeoPP’s steam turbines and steam separating devices, determined by the use of low-potential geothermal saturated steam as a working medium, which is characterized by corrosion aggressiveness and a tendency to form deposits, are considered. Most promising Russian geothermal energy projects are determined. A list of today’s most advanced geothermal turbine performance technologies is presented. By an example of a 25 MW steam turbine design, made by JSC Kaluga Turbine Works, advantages of the internal moisture separation with a special turbine-separator stage are shown.

Petrogeothermal energy resources within low-temperature areas of Iceland

Iceland remains one of the leading countries in the field of the utilization of geothermal energy worldwide. Despite its knowledge and tremendous experience in the exploitation of mostly high-temperature geothermal energy resources (water and steam), it has been interested in the possibility of harnessing heat from hot rock formations with the implementation of the Enhanced Geothermal System (EGS). This paper presents the main outcomes of the feasibility study of EGS technology within the low-temperature area of the country. It includes broad geological research that constitutes the background for finding a suitable site for an EGS installation and to determine the local thermal parameters together with rock characteristics. To calculate the amount of heat stored within the preordained HDR formation and ascertain that the deployment of the EGS within the lowtemperature area of Holmavik town (NW Iceland) is plausible, the term of static resources of energy was applied. Considering the geological issue, it emerged that within the low-temperature areas of Iceland, there are excellent lithological (mainly porous lava layers) as well as thermal conditions (relatively high heat flow and geothermal gradient values) for the implementation of EGS technology for providing heat for small district heating networks. The amount of energy stored within the designed rock formation turned out to be significant and more than sufficient to cover the energy demands of Holmavik town. The authors also emphasize the importance of running several exchange programs between Polish and Icelandic research and academic centers, with the indication of possible benefits for the Polish geothermal energy sector.

Extracting lithium from Tibetan Dangxiong Tso Salt Lake of carbonate type by using geothermal salinity-gradient solar pond

Given their unique resources, the carbonate salt lakes in Tibet offer significant advantages in the extraction of lithium, but some disadvantages are being exposed in production. These disadvantages include the long period of lithium extraction and the low grade of lithium carbonate caused by geographical conditions and climate factors of the Qinghai–Tibet plateau. Based on the above reasons, we rebuilt the traditional solar ponds by introducing a kind of heat exchanger in a bid to speed up the temperature rise of brine, whereby we planned to make use of the high-temperature geothermal resources around the lakes to produce lithium carbonate in large-scale applications. We carried out a small lithium-extraction experiment with hot water as the heat source for the purpose of verifying the feasibility of lithium extraction by geothermal-salinity gradient solar pond (G-SGSP). In the experiment, the contrastive analysis method was employed as a means to study the relationship between ion diffusion and temperature, as well as salinity in G-SGSP and these controllable factors’ impact on the precipitation of lithium carbonate. The results of the experiment show that it is highly feasible to extract lithium through G-SGSP, thus enhancing the efficiency of lithium extraction and generating higher-grade lithium carbonate. Thus, the experiment serves as a dramatic reference for extracting lithium from Dangxiong Tso Salt Lake through the application of geothermal resources.

The geothermal heating system at Taupo Hospital, New Zealand

Taupo Township is located in the south western apex of the Taupo Volcanic Zone (TVZ), in the centre North Island of New Zealand, which has an abundance of high temperature geothermal resources. The Taupo Hospital sits in the south-east of the Taupo township located on the outflow zone from the Wairakei–Tauhara geothermal system. The direct-use of geothermal energy in the hospital was commissioned in August 2010 to provide space heating and domestic hot water supplies. Previously, two coal fired boilers that consumed around 340t/year of coal were used. By converting to geothermal energy, significant savings were made in terms of operation (fuel) and maintenance costs, while no greenhouse gases are emitted to the environment. Geothermal fluid production fluctuates depending on the season. Minimum production during summer is 59t/day and maximum production during winter is 279t/day. The geothermal and heat exchanger system has now been running for more than four years, with no issues pertaining to scaling and corrosion. This is due to a combination of good maintenance practices and the favourable chemical composition of the geothermal fluid.