Use Of Geothermal Resources Research Articles

Defining Optimal Configurations of Geothermal Systems Using Process Design and Process Integration Techniques

The use of geothermal resources for the polygeneration of energy services has recently gained interest and is expected to know an important development in the future. Major research questions concern the increase of the efficiency in the usage of geothermal resources, as well as the increase of their economical profitability and the minimization of the generated life-cycle environmental impacts. This can be achieved by applying process design and process integration techniques to the overall geothermal system, formed by the subsystems of resources harvesting, energy conversion systems and demand. This paper presents a systematic methodology for the optimal design of geothermal systems configurations. In a first step, the different components of the system superstructure are separately modeled using a flowsheeting software. The superstructure includes not only the potential conversion technologies, but as well the different types of potential resources and the demand profiles for the district heating and cooling. It covers a wide pannel of conventional resources and technologies like deep and shallow aquifers, heat pumps, flash systems or organic Rankine cycles, as well as emerging resources and technologies, like Enhanced Geothermal Systems, Kalina cycles, supercritical cycles or organic Rankine cycles using fluid mixtures. Then, resources, technologies and demand profiles models are integrated together using process integration techniques. The resolution of the mixed integer linear programming problem extracts the configuration of the geothermal system from the superstructure. The state variables of the final configuration are then used to define the size of the equipment in the system. Based on these results, the economic, energetic and environmental performances of the integrated system are finally calculated. Performance indicators considered include energy and exergy efficiency, investment costs, operating costs and profitability. Life cycle impact assessment is as well performed by fully integrating the life cycle inventory in the process design framework. To account for the seasonal variation of the demand in energy services, a multi-period optimization model of the integrated system is proposed. The calculation sequence is implemented in a multi-objective optimization framework to calculate the optimal system configurations with their associated technologies, resources and process operating conditions, choosing the objective functions in the different considered performance indicators. This results into the thermo-economic Pareto Frontier that includes the set of the most attractive configurations of the system. The methodology is illustrated by an application to a case study of a city of Switzerland. The results are discussed, as well as their practical implications in terms of technological orientations to be favored in the development of geothermal energy.

Harnessing the geothermal resources of sedimentary basins for electricity production

Use of geothermal resources for generating electricity is briefly analyzed. Results obtained from optimization of the thermodynamic cycle implemented in the secondary coolant circuit of a binary geothermal power station and the parameters of its primary heat carrier circuit are presented.

Thermodynamic analysis of models used in hydrogen production by geothermal energy

Four models are developed for the use of geothermal energy for hydrogen production. These include using geothermal work output as the work input for an electrolysis process (Case 1); using part of geothermal heat to produce work for electrolysis process and part of geothermal heat in an electrolysis process to preheat the water (Case 2), using geothermal heat to preheat water in a high-temperature electrolysis process (Case 3), and using part of geothermal work for electrolysis and the remaining part for liquefaction (Case 4). These models are studied thermodynamically, and both reversible and actual (irreversible) operation of the models are considered. The effect of geothermal water temperature on the amount of hydrogen production per unit mass of geothermal water is investigated for all four models, and the results are compared. The results show that as the temperature of geothermal water increases the amount of hydrogen production increases. Also, 1.34 g of hydrogen may be produced by one kg of geothermal water at 200 °C in the reversible operation for Case 1. The corresponding values are 1.42, 1.91, and 1.22 in Case 2, Case 3, and Case 4, respectively. Greater amounts of hydrogen may be produced in Case 3 compared to other cases. Case 2 performs better than Case 1 because of the enhanced use of geothermal resource in the process. Case 4 allows both hydrogen production and liquefaction using the same geothermal resource, and provides a good solution for the remote geothermal resources. A comparison of hydrogen production values in the reversible and irreversible conditions reveal that the second-law efficiencies of the models are 28.5%, 29.9%, 37.2%, and 16.1% in Case 1, Case 2, Case 3, and Case 4, respectively.

Utilisation of geothermal resources

For centuries, geothermal energy has been used for bathing, cooking and space heating. More recently, district heating, industrial processing and geothermal heat pumps have become part of the direct-use mix. Geothermal electric power generation began in Italy in 1904, with the first commercial plant operational in 1913. Presently, the total installed global capacity for direct use is 29 000 MWt, producing 76 000 GW h/year in 72 countries; the installed capacity for electric power is 9700 MWe, generating 60 000 GW h/year in 24 countries. Recent trends are to maximise the use of geothermal resources in a combined heat and power project. Geothermal resources of around 100°C have been used in binary (organic Rankine) cycle plants and then cascaded for district heating. Geothermal energy is considered to be both renewable and sustainable as a ‘green energy’ resource, but certain environmental aspects must be considered and mitigated.

Geyser Decline and Extinction in New Zealand—Energy Development Impacts and Implications for Environmental Management

Geysers are rare natural phenomena that represent increasingly important recreation, economic, and scientific resources. The features of geyser basins, including hot springs, mud pots, and fumaroles, are easily damaged by human development. In New Zealand, the extinction of more than 100 geysers provides important lessons for the environmental management of the world's remaining geyser basins. The impacts on New Zealand's geysers are described in sequential "phases," including the following: the first use of geothermal resources by the indigenous people-the Maori; early European-style tourism and spa development; streamside geyser decline caused by river level modification at the Spa geyser basin; multiple geyser basin extinctions caused by industrial-scale geothermal well withdrawal at Wairakei; the drowning of geysers at Orakeikorako after the filling of a hydroelectric reservoir; and geyser decline caused by geothermal well heating systems in Rotorua City. The crisis in Rotorua prompted preservation of the few remaining geysers at Whakarewarewa -- the last major geyser basin in New Zealand. The New Zealand government ordered the geothermal wells within 1.5 km of Pohutu Geyser, Whakarewarewa, to be closed, which was a locally controversial measure. The well closure program resulted in a partial recovery of the Rotorua geothermal reservoir, but no extinct geysers recovered. The implications of recent geothermal computer modeling and future planning are discussed. The New Zealand case suggests that the protection of geysers requires strong regulations that prevent incompatible development at the outset, a prescription that is especially relevant for the future management of the geothermal fields adjacent to the geyser basins of Yellowstone National Park, U.S.A.

Environmental impact of geothermal energy utilization

Abstract Presently geothermal energy accounts for 0.25% of the annual world-wide energy consumption. Extraction of heat from geothermal reservoirs involves drillings. Exploitation of geothermal resources is generally far less a cause of pollution than fossifuel combustion, making it preferable as a source for power and heat. Geothermal energy exploitation has locally some adverse environmental effects. Possible effects include scenery spoliation, drying out of hot springs, soil erosion, noise pollution, and chemical pollution of the atmosphere and of surface- and groundwaters. Exploitation may enhance seismic activity and cause land subsidence. The development of geothermal fields must sometimes be evaluated against the value of tourism. Various measures have been successfully employed to reduce the adverse environmental effects of geothermal energy utilization. The most important ones are directional drilling and injection of spent geothermal fluid. Future use of geothermal resources should specifically consider further use of geothermal heat pumps, extraction of chemicals from spent geothermal fluids to yield useful byproducts, integrated multiple use of high-temperature systems, and furthering of technology to develop hot-dry-rock systems including those occurring in the roots of active volcanic geothermal systems.

Geothermal space heating

The use of geothermal resources for space heating dominates the direct use industry, with approximately 37% of all direct use development. Of this, 75% is provided by district heating systems. In fact, the earliest known commercial use of geothermal energy was in Chaudes-Aigues Cantal, France, where a district heating system was built in the 14th century. Today, geothermal district space heating projects can be found in 12 countries and provide some 44,772 TJ of energy yearly. Although temperatures in excess of 50 °C are generally required, resources as low as 40 °C can be used in certain circumstances, and, if geothermal heat pumps are included, space heating can be a viable alternative to other forms of heating at temperatures well below 10 °C.

The silica heat flow interpretation technique: application to continental Australia

The silica heat flow interpretation technique [Swanberg, C.A. and Morgan, P., J. Geophys. Res. 117 (1979) 227–241; J. Geophys. Res. 85 (1980) 7206–7214] has been applied and tested in mainland Australia, using a database of approximately 41 000 Australian groundwater analyses. The silica geotemperature of the groundwaters was obtained by substituting the dissolved silica content of a groundwater into the quartz geothermometer equation of Truesdell [(1976) Proceedings of the Second United Nations Symposium on the Development and Use of Geothermal Resources. San Francisco, CA, USA, 20–29 May, 1975, Vol. 1]. The average silica geotemperature value for 1×1° (latitude×longitude) grid cells has been calculated and the results plotted against published traditional heat flow values for those grid cells [Cull, J.P. (1982) BMR J. Aust. Geol. Geophys. 7, 11–21], to form silica heat flow estimation models. Data exclusion criteria, based upon data quantity and statistical spread have been applied to both the groundwater data and the traditional heat flow data. This was done in order to exclude areas that were poorly categorized in terms of data quality and quantity. For the remaining data, a significant linear relationship between the groundwater geotemperature estimates and traditional heat flow measurements has been identified for four of the models with a t-test on the correlation coefficient. Estimates of regional heat flow were then made by applying the calibration models in areas with no traditional heat flow measurements but adequate groundwater data. A silica heat flow map has been constructed using one of the models and the differences between it and the traditional heat flow map evaluated. Good correlations exist between the silica heat flow map and the traditional heat flow map, except for the northwest Yilgarn, of WA, Australia, where silica heat flow data give significantly higher values than traditional data. The silica heat flow map identifies areas of high heat flow associated with some large-scale geological features such as the granite belt in southeastern Australia. The calibration models result in some silica heat flow estimates exceeding natural likely values. This suggests that the calibrations need further refining for Australian conditions.

Calculated heat flow for the Ensenada region, Baja California, Mexico

Due to the scarcity of heat flow data in the region of Ensenada, Baja California (Mexico), the present study calculated them using the silica geothermometer technique. The average heat flow value determined was 123.33 ± 35.57 mW m–2 (2.95 ± 0.85 HFU). Four zones within the study area, related to the main fault systems of the region, were found to have high hydrothermal activity. The potential use of geothermal resources in the area is feasible as it is considered a low geothermal system with water temperature values, above the static water level, that vary from 30ºC to 108ºC.

The 15th New Zealand geothermal workshop : Long-term Use of Geothermal Resources: Problems and Solutions 10,11,12 November 1993

The 15th New Zealand geothermal workshop : Long-term Use of Geothermal Resources: Problems and Solutions 10,11,12 November 1993

Training in industrial uses of geothermal energy

Specialized training in industrial uses of geothermal energy is available in Iceland. The Geothermal Training Programme of the United Nations University (UNU) has operated in Iceland since 1979 with six months' annual courses for professionals in either Geological Exploration, Borehole Geology, Geophysical Exploration, Borehole Geophysics, Reservoir Engineering, Chemistry of Thermal Fluids, Geothermal Utilization, or Drilling Technology. The trademark of the training is to give university graduates with some practical experience in geothermal work, intensive on-the-job training in their specialization. Industrial applications of geothermal resources is one of the options open to participants in the Geothermal Utilization course. Participants selecting this option have mainly been trained in drying processes and how to adapt the design of conventional steam or hot water/air drying systems to the specific characteristics of the geothermal fluids. One participant studied food drying using low-temperature geothermal energy, and two dealt with heat exchanger selection for geothermal applications and the merits of the combined use of geothermal resources for electricity production and industrial utilization. Of other options directly relevant to industrial applications can be mentioned the selection, installation, and operation of downhole pumps in geothermal wells, the prediction of calcite scaling, and materials selection.

Geothermal energy stirs worldwide action

Geothermal energy activities are progressing on a broad front worldwide. So far, however, the practical results in usable energy are few, relative to the need. Although locally significant even now in a few places, and soon to become so in a few more, geothermal energy faces numerous obstacles, some of them formidable, before it achieves a significant overall energy role in the world. Such was the picture that emerged from the Second United Nations Symposium on the Development and Use of Geothermal Resources. The 10-day meeting was held in San Francisco last month under sponsorship of the UN, the Department of the Interior, and the state of California. Some 1300 scientific, industrial, and governmental experts from 59 nations gathered to assess the current status of geothermal energy activities and where they are headed. For the experts, who last met under UN auspices at the first symposium, held in Pisa, Italy, in 1970, there was a ...