Low-temperature Geothermal Resources Research Articles

Energy and exergy analysis of kalina cycle system (KCS) 34 with mass fraction ammonia-water mixture variation

Further utilization of waste heat produced by power plant system will increase the efficiency of the whole power plant system. The Kalina Cycle offers alternative solution to generate additional power from waste heat or from low temperature geothermal resources. The modeling application on energy system is used to study the basic design of thermal system, which uses Kalina Cycle for further utilization of geothermal brine water. If this geothermal brine water were not used in the Kalina Cycle, it would be reinjected to the geothermal reservoir and its remaining energy content would have been wasted. The study of this process is done by Cycle Tempo 5.0 simulation software, to obtain the data of efficiency, energy and exergy that could be generated from the heat source. An ammonia-water mixture is used as a working fluid on Kalina cycle system (KCS) 34. In order to obtain the maximum power output and maximum efficiency, the system will be optimized on the mass fraction of working fluid and also on the turbine output pressure. The result of the study shows that the maximum efficiency and power output are achieved at 78% ammonia-water mixture.

Subsurface thermal influence of experimental geothermal heat pump system operation for space cooling in Kamphaengphet, Thailand

Using natural sources of energy (solar, wind, biomass etc.) may potentially help to mitigate global warming. Low-temperature geothermal resources are among the more abundant natural energy sources. Methods of utilizing low-temperature geothermal resources include both direct use of warm groundwater and geothermal heat pump (GHP) systems. GHP systems may be subdivided into two basic types. One uses water circulated through a subsurface pipe without direct mass exchange between the pipe and the local groundwater aquifer (“closed system”). The other involves direct withdrawal of heated groundwater (“open system”). GHP systems are popularly used worldwide (Rybach et al., 2000; Fridleifson, 2001; Lund,2005). In Sweden, the number of GHP system installation per 100 people in 2005 is about two (Curtis et al., 2005). It is generally considered that GHP systems may be utilized everywhere because of stable temperature of the underground. However, the applicability of the GHP system is not clear for space cooling in tropical region where sufficient temperature difference between underground and atmosphere may not be expected. Aiming at grasping the applicability of GHP systems for space cooling in tropical region, an experimental operation of a GHP system was conducted at Kamphaengphet, Thailand from October, 2006 to March, 2008 (Yasukawa et al., 2009). The depth of the heat exchange borehole, in which U-tube was installed, was 56m. The authors set temperature sensors every ten meters inside the U-tube (at depths of 0, 6, 16, 26, 36, 46 and 56 meters, respectively). As the detail of the GHP system, the results of temperature measurements and calculation of system performances are presented in Yasukawa et al. (2009) in this issue, we attempted to estimate subsurface thermal influence of the GHP system for space cooling by acquiring temperature data of the underground from this test.

An assessment of renewable energy generation in a conventional steam power plant with geothermal feedwater preheating

Hybrid steam power plant with geothermal feedwater preheating enables conversion of low temperature geothermal resources into electricity. The paper presents results of calculation of some performance parameters for 200 MWe fossil power unit associated with geothermal well. The paper gives separation rule of renewable energy from conventional one at hybrid power plant output. An influence of geothermal fluid temperature on hybrid power plant performance is discussed in a study and illustrated in several charts.

Database on the geothermal resources of Algeria

The paper describes a database on the low-temperature geothermal resources of Algeria that includes information on thermal springs and wells, a description of hot water resources, and thematic maps.

Three-dimensional magnetotelluric surveys for geothermal development in Pohang, Korea

A three-dimensional (3D) magnetotelluric (MT) survey has been carried out to delineate subsurface structures and possible fractures, for development of low-temperature geothermal resources in Pohang, Korea. Quite good quality MT data could be obtained throughout the survey region by locating the remote reference in Kyushu, Japan, which is ~480 km from the centre of the field site.3D modelling and inversion are performed taking into account the sea effect in MT measurements near the seashore. The nearby sea in the Pohang area affects MT data at frequencies below 1 Hz ~0.2 Hz, depending on the distance from the seashore. The most severe sea effects were observed in the south-east parts of the survey area, closer to Youngil Bay. 3D inversion with and without the seawater constraint showed very similar results at shallow depths, roughly down to 2 km. At greater depths, however, a strong sea effect seems to form a fictitious conductive structure in ordinary 3D inversion, especially in the south-eastern part of the survey region.Comparison between drilling results and the resistivity profiles from inversions showed that five layered structures can be distinguished the subsurface beneath the target area. They are: (a) semi-consolidated mudstones with resistivity less than 10 Ω m, which are ~300 m thick in the northern part and ~600 m thick in the southern part of the survey area; (b) occasional occurrence of trachybasalt and lapilli tuff within the mudstone layer has resistivity of a few tens of Ω m, (c) intrusive rhyolite ~400 m thick has resistivity of several hundreds of Ω m, (d) alternating sandstone and mudstone down to 1.5 km depth shows resistivity of ~100 Ω m, (e) a conductive structure was found at a depth of ~3 km, but more geological and geophysical study should be carried out to identify this structure.

GEOTHERMAL POWER GENERATION: GLOBAL PERSPECTIVES; U.S.A. AND ICELAND; TECHNOLOGY, DIRECT USES, PLANTS, AND DRILLING

This paper discusses the state of the art in harnessing geothermal power for medium- and large-scale generation of electricity and for space heating worldwide. It reviews current, probable, possible, and potential developments in both developed and developing countries in the near future and long term. The author first reviews world energy consumption and then discusses relative contribution of energy sources in the world in OECD countries, summarizes installed geothermal capacities for electricity generation, and examines direct use of geothermal energy worldwide together with the technical potential of renewable energy sources. The central part of the article examines geothermal energy in the United States, highlighting heat flow, tectonic controls, types of geothermal systems, United States geothermal potential, geothermal energy in the United States, operating conditions for electricity generation, and environmental constraints. Then the author considers Iceland's primary power consumption, production of electricity in Iceland, low-temperature geothermal resources, and high-temperature geothermal resources. The paper then examines the Geothermal Technologies Programme in the United States, reviewing the goals of geo-science and supporting technologies, exploration and drilling research, and energy systems research and testing; enhanced geothermal systems, and direct use of geothermal energy, considering district heating, agriculture, and aquaculture applications and future developments. Finally, improving geothermal power plants is discussed and typical R&D projects are reviewed. Highlighted are such research and development projects as enhanced heat transfer in air-cooled condensers, materials research, instruments for real time monitoring of geothermal processes, plant optimization, removal of noncondensable gases from binary power plants, and silica and metals extraction. The article also discusses geothermal drilling R&D aimed at reducing drilling costs by 25∼50%.

地下温度に関する研究の現状と水文学的知見の貢献

Subsurface thermal regime is affected not only by thermal conduction but also by advection owing to groundwater flow. The effect of thermal advection is especially large in shallow sedimentary layer with active groundwater flow. Subsurface temperature distributions in some basins and plains in Japan are affected by regional groundwater flow systems. Both field observation and simulation results in the study area show that thermal transport conducted by regional groundwater flow system, driven by topographic effect, distorts subsurface temperature distributions. Moreover, subsurface temperature distributions in the Yonezawa Basin and Nagaoka Plain show effect of groundwater pumping. Subsurface temperatures in shallow layers in these areas have seasonal change due to groundwater pumping for snow melting in winter season.In recent years, subsurface temperature data have been used for reconstruction of ground surface temperature (GST) history as well. The effects of temperature change at the ground surface in the past have conducted into subsurface and have been recorded as transient temperature perturbations onto the background thermal field. Many studies on GST history in North America and Europe are inferred from inversion of borehole temperature profiles in log data.On the other hand, direct utilization of low-temperature geothermal resources, such as geothermal heat pump system, is important from the viewpoint of reduction of CO2 that causes global warming. Such systems are gradually increasing in Japan. To evaluate the influence of direct utilization onto subsurface temperature, an areal simulation, which numerical model was cut out from regional 3D groundwater flow and heat transport model of the Sendai plains, was conducted.Subsurface temperature observed with comparative ease includes important clues to understand global environment problems and/or hints for development of new energy to preserve global environment.It is hoped that hydrological knowledge contributes to understand many problems in various studies with subsurface temperature.

A study on modeling and performance assessment of a heat pump system for utilizing low temperature geothermal resources in buildings

Low and moderate geothermal resources are found in most areas of the world. A very efficient way to heat and air-condition homes and buildings is the utilization of ground source heat pumps (GSHPs), also known as geothermal heat pump (GHPs), to obtain heat energy from low temperature geothermal resources. The present study deals with the modeling and performance evaluation of a heat pump system utilizing a low temperature geothermal resource, which is approximated to a geothermal reservoir. The system was designed, constructed and tested in Nigde University, Nigde, Turkey and has been successfully operated since 2005. Energy and exergy analysis methods were used to assess the system performance based on the experimental data. Exergy destructions (or irreversibilities) as well as energy and exergy efficiency relations were presented for each component of the heat pump unit and the whole system, while some thermodynamic parameters, such as fuel depletion ratio, relative irreversibility, productivity lack, exergetic factor and improvement potential, were investigated for the system. Energy and exergy efficiency values on a product/fuel basis were found to range from 73.9% to 73.3% and 63.3% to 51.7% at dead (reference) state temperatures varying from 0 to 25 °C for the heat pump unit and entire system, respectively. It is expected that the model presented here would be beneficial to the researchers, government administration, and engineers working in the area of heat pump systems for residential applications.

Second Law assessment of binary plants generating power from low-temperature geothermal fluids

Binary-type energy conversion systems are typically used to exploit low-temperature geothermal resources. There are many different technical variations of binary plants, including those known as Organic Rankine Cycles (ORC) and proprietary systems known as Kalina cycles. Recent articles in the technical literature claim dramatic efficiency advantages for Kalina cycles over ORCs, thereby providing the motivation for this study. Claims of remarkable superiority for one type of technology relative to another ought to be verifiable by recourse to actual performance data. Since there is now an actual Kalina cycle in operation, it ought to be possible to make a comparison between it and ORC plants that have been in operation for some time. Comparisons between power plants must use an appropriate and consistent thermodynamic basis. It has been shown that the Second Law of thermodynamics is the best basis for such comparisons. This principle, employing the concept of exergy, is used here to shed light on these claims. Furthermore, we introduce a methodology to render the comparison of plant efficiencies on common input and environmental conditions, even though the plants being compared operate with somewhat different fluid inlet and ambient temperatures.

The Bad Blumau geothermal project: a low temperature, sustainable and environmentally benign power plant

The 250 kW geothermal project at Bad Blumau is the first geothermal project developed in Austria by the private sector following the deregulation of the electricity industry in this country. What makes the project unique besides its private ownership structure is its ability to generate electrical power and district heating for the Rogner Bad Blumau Hotel & Spa by using a low temperature geothermal resource. Installed in the record time of less than a week, the air-cooled ORMAT ® Energy Converter (OEC) CHP module has been in commercial operation since July 2001. With an annual availability exceeding 99%, between October 2001 and December 2002 the plant delivered 1,560,000 kWh to the local grid. The geothermal CHP module utilizes brine at ∼110 °C, available from a 3000 m deep production well. Exiting the OEC unit at a temperature of ∼85 °C, the brine is then fed into the district heating system, providing heat for the Rogner Bad Blumau Hotel & Spa. The geothermal brine is returned from the district heating system and injected into a 3000 m depth reinjection well. The system is a pollution-free, unattended operating power generation module, which has avoided more than 1100 kg of CO 2 emissions over its first operating year.

Model study of the thermal storage system by FEHM code

The use of low-temperature geothermal resources is important from the viewpoint of global warming. In order to evaluate various underground projects that use low-temperature geothermal resources, we have estimated the parameters of a typical underground system using the two-well model. By changing the parameters of the system, six different heat extraction scenarios have been studied. One of these six scenarios is recommended because of its small energy loss.

Reservoir engineering assessment of low-temperature geothermal resources in the Skierniewice municipality (Poland)

Reservoir engineering assessment of low-temperature geothermal resources in the Skierniewice municipality (Poland)

Reservoir engineering assessment of low-temperature geothermal resources in the Skierniewice municipality (Poland)

Low temperature geothermal resources and their production potential in the Skierniewice area of Poland were evaluated assuming conventional well doublet arrays. The reservoir engineering assessment was carried out, within the framework of a World Bank project, to study the feasibility of providing heat to the local district heating system, using data from two existing wells and from geophysical surveys, and by evaluating results of production, injection and interference well tests. Two options were simulated mathematically, using both semianalytical and numerical codes, considering a simplified reservoir model: one based on the two existing wells, the other considering four wells, two to be drilled. The injection of spent brines into a different reservoir was also studied.

Economic power generation from low-temperature geothermal resources using organic rankine cycle combined with vapour absorption chiller

Power generation with low temperature geothermal resources is not economically viable due to the poor thermal efficiency of organic Rankine cycles (ORC). A novel idea is proposed where a vapour absorption chiller (VAC) can be employed to lower the ORC condensing temperature, thus increasing its power output. This paper presents detailed analysis of a VAC that operates with water-lithium bromide to extract heat from the geothermal brine leaving the ORC vaporizer. The evaporator of the VAC serves as the ORC condenser. A computer program is coded to simulate the combined ORC-VAC performance and compare it with that of the conventional ORC. The results indicate that the ORC-VAC option would render power generation more economical. The organic fluid flow rate in the ORC per unit power output is cut by at least 50% in this case, thus reducing the ORC size and turbine cost. Moreover, even though the ORC-VAC includes more components, the total heat exchange area requirement per unit power output remains practically unchanged.

Geothermal investigations in Slovenia

The paper presents the methodology and the results of geothermal investigations, based on seventy-two boreholes in the territory of the Republic of Slovenia. The data of fundamental geothermal quantities: formation temperature, thermal conductivity, and radiogenic heat production of rocks as well as surface heat flow density are stored in a computerized data base. Their synthesis is given in the map of formation temperatures at 1000 m depth and in the map of surface heat flow density. In both maps the thermal difference between the Pannonian basin in the eastern and the Dinarides in the western part of Slovenia is clearly expressed. However, in the boundary area between these two tectonic units, for a distance of about 100 km in SW-NE direction, elevated horizontal gradients of formation temperature as well as heat flow density are evident. A small positive thermal anomaly in the Ljubljana depression is conspicuous. The low-temperature geothermal resources in Slovenia such as thermal springs and thermal water from boreholes, are estimated to have a flow rate of 1120 kg/s, corresponding to the ideal total heat production of 144 MWt. In the geothermally promising areas amounting to 3200 km2 the rate of accessible resource base (ARB) down to the depth of 3 km has been assessed to about 8.5 x 1020 J.

Geothermal activity in Italy: Present status and future prospects

In the Italian Peninsula the Apennines separata a relatively cold Po-Adriatic-Ionian “foredeep” external belt from a warmer Tyrrhenian “back-arc” internal tensional belt. The latter is characterized by high geothermal heat flow together with conspicuous recent or present-day volcanic phenomena. In this area, extending from Tuscany to Campania, lie the known steam- and water-dominated fields (Fig. 1). Other “warm” areas are located on some Tyrrhenian islands. Within the “cold” external belt, interesting locations for low enthalpy utilizations can be found in the Po river valley, particularly in the eastern part near Ferrara and Abano. Since 1977 ENEL (National Electric Energy Agency) and AGIP (State Oil Company) have been jointly conducting geothermal activities in Italy, with the exception of the Tuscan geothermal area where ENEL operates on an exclusive basis. At present the areas surveyed cover about 8250 km 2. As of December 1983 the geothermal installed capacity was 456.2 MW (net capacity 340 MW) and low-temperature geothermal resources equivalent to 100,000 OET ‡ ‡ Oil equivalent tons. /yr were being used. The National Energy Plant (PEN), issued on 4 December 1981, forecast for the year 1990 a geothermal power increment of 200 MW e, above the 449.1 MW e, already installed. The target in the low enthalpy non-electric sector is to save 300,000 OET/yr by 1990. This paper describes the activities carried out from March 1975 to December 1983 and the main projects in progress.

Investment in Geothermal Direct Heat Applications

An assessment of eight geothermal direct-heat projects for which confident cost and production data exists indicates that low-temperature geothermal resource can, in certain instances, provide an inexpensive, reliable source of direct-heat energy. The analysis examines the retrofit investment decision separately for private firm and local government investors. It compares the economics of geothermal and conventional energy supplies, and explores the sensitivity of these comparative results to changes in the underlying assumptions. Investors are warned that geothermal direct-heat applications projects have not been uniformly successful. Three of the eight projects do not appear to be economical when compared to conventional alternatives even though all eight are the most advanced of 22 demonstration projects originallly funded by DOE. 6 references, 1 figure, 6 tables.

Heat Flow as an Indicator of Regional Ground-Water Migration in Great Plains: ABSTRACT

Heat-flow and temperature-gradient measurements indicate a correlation between subsurface structures, regional ground-water flow, and heat flow in the Great Plains. Throughout the province, thick Cretaceous shales act as confining layers to aquifers, e.g., the Dakota (Cretaceous) and the Madison (Mississippian), which flow generally eastward in accord with the declivity of the plains. The vertical component of ground-water flow on the margins of the Denver, Kennedy, and Williston basins evidently exceeds the thermal diffusion rate in the confining layers overlying the aquifers, and causes significant disturbances in the surface heat flow. Heat flow along the eastern margin of the Denver basin in Nebraska may be about 50% higher than normal due to the water flow; the effec in the Kennedy basin in South Dakota and Nebraska may have doubled the surface heat flow. The Williston basin has anomalous heat flow on its eastern margin and may also show effects of intrabasin structures such as the Nesson anticline. These ground-water systems constitute a significant low-temperature geothermal resource that is estimated to exceed 20 × 1018 J of energy. Recognition of this geothermal resource and accurate estimation of the amount of available energy is best achieved by heat-flow studies. For example, estimates of geothermal resources in Nebraska based on heat-flow data and bottom-hole temperature data differ by 80%. End_of_Article - Last_Page 481------------

Geothermal Resources of Balcones-Ouachita Trend, Central Texas: ABSTRACT

The Balcones-Ouachita trend of central Texas is an often overlooked zone with great potential for widespread occurrence of low-temperature geothermal resources. The area with potential resources extends from north of Dallas to Del Rio. Thermal input to these systems is from the natural thermal gradient of the earth. Downdip movement of ground water from recharge zones to the west, or updip flow from overpressured zones within the Gulf Coast basin, are 2 possible sources for fluids. Permeability in these systems is typically stratigraphic, but local enhancement by fractures and faults aids fluid flow. Basal Cretaceous sandstones, such as the Hosston Formation and its lateral equivalents, and Cretaceous limestones, such as the Edwards formation, have identified resources. R source models developed to date indicate higher temperatures where updip flow from the basin is enhanced by fault permeability. Recent tests of these resources include a geothermal well in Marlin, where the Hosston Formation produces 67°C (153°F) fluids from a depth of 1,183 m (3,881 ft), and a program conducted in the fall of 1983 to assess the geothermal characteristics of the Hosston Formation in the San Antonio area. Results of this program are still being evaluated. In the San Antonio area, warm waters have been produced from the Edwards formation. End_of_Article - Last_Page 477------------

Geothermal resources of rifts: A comparison of the rio grande rift and the salton trough

The Rio Grande Rift and the Salton Trough are the best developed rift systems in the United States and both share many features common to rifts in general, including geothermal resources. These two rifts have different tectonic and magmatic histories, however, and these differences are reflected in the nature of their geothermal resources. The Salton Trough is a well developed and successful rift. It is the landward extension of the Gulf of California spreading center, which has separated Baja, California, from the remainder of Mexico. Quaternary silicic magmatization has occurred and several of the geothermal resources are associated with recent rhyolitic intrusions. Such resources tend to be high temperature (> 200°C). Greenschist facies metamorphism has been observed in several of the geothermal wells. Localized upper crustal melting is a distinct possibility and there is increasing speculation that very high temperature (> 300°C) geothermal fluids may underlie a large portion of the central trough at depths in excess of 4 km. Low temperature geothermal resources associated with shallow hydrothermal convection are less common and tend to be located on the flanks of the trough or in the Coachella Valley to the north of the zone of active rifting. In contrast, the Rio Grande Rift is less well developed. Recent volcanism consists primarily of mantle-derived basalts, which have not had sufficient residence time within the crust to generate significant crustal melting. The geothermal resources within the Rio Grande Rift do not correlate well with these young basalts. Rather, the quantity of geothermal resources are low temperature (< 100°C) and result from forced hydrothermal convection which discharges at constrictions within or at the end of the major sedimentary basins. High temperature resources are less common and the only discovered example is the Valles Caldera of northern New Mexico ( T = 250–300°C). The deep interiors of the sedimentary basins of the Rio Grande Rift do not appear to be major geothermal exploration targets.