Geochemical characteristics of the Yufuin outflow plume, Beppu hydrothermal system, Japan

Thermal water at Yufuin (Kyushu Island, Japan) is tapped through about 820 shallow wells and used mainly for hot-spring bathing purposes. Chemical and isotopic data for fluids from wells and fumaroles in Yufuin and Beppu indicate that the thermal activity at Yufuin represents a dilute, westward-flowing hydrothermal outflow plume from the Beppu hydrothermal system. Two other (eastward-flowing) outflow plumes have long been recognized at Beppu, but the Yufuin outflow plume is first recognized here. The Yufuin outflow plume is apparently a mixture of two end-member fluids: (1) deep high-temperature (250–300°C) fluid from the Beppu system having high chloride concentration (1400–1600 mg/L) and a δ¹⁸O value near −6.0%, and (2) meteoric water having low chloride concentration (≤7 mg/L) and a δ¹⁸O value near −9.2%.A permeable conduit for the vertical and lateral transport of deep fluid from the Beppu system is provided by the Yufuin Fault zone, which extends westward from the southern flank of Mt. Tsurumi volcano to the town of Yufuin. Stable isotope ratios and chloride concentrations for shallow groundwaters near the eastern end of the fault, at an elevation near 700 m, are consistent with those required for the low-chloride meteoric end-member of the Yufuin thermal waters. Recharge of this meteoric water, as well as mixing with the Beppu deep fluid, may occur along the Yufuin Fault. Enthalpy-chloride relations indicate additional conductive heating of the Yufuin waters, in the amount of 350–500 kJ/kg beyond that which can be accounted for by mixing between Beppu deep fluid and meteoric water. This could be a result of conductive heating with convection to a depth of 1–2 km. Estimates of the magnitude of the heat source for the Beppu hydrothermal system should take into account the heat being discharged at Yufuin.     

Fluid geochemistry of the San Vicente geothermal field (El Salvador)

The volcano Chichontepeque (San Vicente) is one of the nine recent volcanoes making up the El Salvador sector of the WNW-ESE-trending active Central American volcanic belt. Thermal activity is at present reduced to a few thermal springs and fumaroles. The most important manifestations (Agua Agria and Los Infernillos Ciegos) are boiling springs and fumaroles located on the northern slope of the volcano (850 m a.s.l.) along two radial faults. The chloride acid waters of the Los Infernillos area are partly fed by a deep hydrothermal aquifer (crossed at 1100–1300 m by a geothermal exploration well), which finds a preferential path to the surface through the radial fault system. C0₂ is the most important gas (>90%) of the Los Infernillos Ciegos and Agua Agria fumaroles. Part of the Los Infernillos gases may also come from a deeper, hotter source, given their high HCl/S_tot. ratio and their more reducing conditions. The application of geothermometric and geobarometric methods to the gases and thermal waters suggests that both thermal areas are linked to the identified 1100–1300 m reservoir, whose temperature (250°C), lateral extension and chemical composition, as resulting from this study, are of interest for industrial development.     

Groundwater circulation in the Nea Kessani low-temperature geothermal field (NE Greece)

The low-temperature geothermal field of Nea Kessani, located in NE Greece, is characterized by a thermal reservoir made up of arkosic sandstones. The temperature distribution at depth, inferred from exploratory and productive wells, indicates that hot fluids rising from depth enter the arkosic reservoir in a restricted area of the field and flow towards local thermal springs. Well production tests have revealed the presence of hydrogeological boundaries within the arkosic reservoir.The geochemical characteristics of the thermal waters, which have an NaCl/HCO₃ composition and salinity varying between 5 and 6 g/L, indicate that these waters undergo conductive cooling within the reservoir. No admixture of waters from the aquifers in the cover has been observed. The slight chemical differences existing between the thermal waters are probably caused by CO₂, which represents about two thirds by volume of the discharged fluid. This CO₂, as indicated by its isotopic composition, could originate from decomposition of marbles of the Paleozoic basement underlying the arkosic reservoir and may also affect the isotopic composition of the thermal waters, which exhibit an interesting positive oxygen shift. However, such a shift could also be the result of water-rock exchange processes at low temperatures, since the water feeding the field comes from a regional circulation which, as indicated by its deuterium content, has recharge areas on the Rhodope Chain. Alternatively, the shift could be attributed to the contribution of a deep-seated high-temperature geothermal reservoir, but a present there is no evidence of high-temperature resources in the region. A maximum temperature of 110°C has been estimated by quartz geothermometry.The physical, chemical and hydrogeological data available so far have permitted us to formulate a fluid circulation model for the Nea Kessani geothermal field.     

Chemical patterns of thermal aquifers in the volcanic islands of the Aegean Arc, Greece

Thermal spring waters and associated gases discharging on several volcanic islands and on mainland Greece along the Hellenic Volcanic Arc (HVA) in the south Aegean sea have been investigated. The chemical characteristics of most of the spring waters suggest that the water in their feeding aquifers is largely derived from seawater that enters the hydrological circuits and mixes with local neutral low-salinity bicarbonate waters. There are however discrepancies between the simple theoretical mixing line between local meteoric waters and seawater, and the actual mixing line. This mixing is accompanied by partial Mg and SO₄ precipitation to secondary minerals and by the addition of K, Ca, HCO₃, B, NH₄, and SiO₂ to the solutions as a result of water-rock interaction processes.At Milos and Nisyros, where active hydrothermal systems are present at shallow depth, the silica content of the thermal springs is much higher than that of springs on the other islands and mainland Greece. This suggests higher thermal gradients at depth there, and the ascent of geothermal fluids to the surface along fractures prevalently located in the fumarolic fields within the latest eruptive centers and calderas. The fact that the springs are anomalously enriched in silica only at Milos and Nisyros suggests indirectly that, apart from Santorini island, where steam vents are present at the surface, the fluids from the active high-enthalpy geothermal systems do not rise to the surface anywhere else along the HVA. If present, they are well confined under thick and impermeable covers.     

Geochemical characteristics of upper Jurassic carbonate reservoir bitumen in the Eastern Kopeh-Dagh,NE Iran

Geochemical characteristics of solid bitumen in Upper Jurassic carbonate reservoir are investigated. Aromatic maturity parameters indicate peak to late oil window level of maturity for the bitumen samples. Regular sterane distributions, conical variable (CV), plots of δ¹³C_Sat versus δ¹³C_Aro and Pr/nC₁₇ against Ph/n_C18, predominance of C₂₃ tricyclic terpane, ratios of steranes/hopanes and C₂₃/C₂₁ tricyclic terpane indicate charging from clastic-rich anoxic marine source rocks. Ratios of C₂₉/C₃₀ hopane, Ts/Ts+ Tm, C₂₄ tetracyclic terpane/C_20-26 tricyclic terpanes and plot of C₂₂/C₂₁ versus C₂₄/C₂₃ tricyclic terpanes show influences of carbonate/marl facies. All these would throw crucial guiding light on the interpretation of the future exploration.     

Analysis of solar hydrogen production in Algeria: Case of an electrolyzer-concentrating photovoltaic system

The use of renewable energy and more particularly solar energy in hydrogen production is considered the most viable and the most environment protective. Electricity is required for water electrolysis to produce hydrogen. As photovoltaic modules enable the direct conversion of solar energy into electricity, photovoltaic systems are then the most indicated systems for this task.     

Performance analysis of a solar chimney power plant in the southwestern region of Algeria

In this paper, we present the performance analysis of a solar chimney power plant expected to provide the remote villages located in Algerian southwestern region with electric power. Solar energy and the psychometric state of the air in the south of Algeria are important to encourage the full development of solar chimney power plant for the thermal and electrical production of energy for various uses. We are interested in Adrar where solar radiation is better than other areas of Algeria. The obtained results show that the solar chimney power plant can produce from 140 to 200 kW of electricity on a site like Adrar during the year, according to an estimate made on the monthly average of sunning. This production is sufficient for the needs of the isolated areas.     

Geochemistry and groundwater contamination in the La Selva geothermal system (Girona, Northeast Spain)

Hot spring waters of the La Selva geothermal system show high concentrations of Cl, F, Ca, Na, K, Li, Si, As, Ba, and Rb, whereas cold waters show low salinity, high concentrations of NO₃, and significant As content when mixed with geothermal waters.Modeling of the geothermal fluids indicates that the fluid is supersaturated with aragonite and calcite, which matches the travertine precipitation close to the present discharge areas. Moreover, the barite and fluorite are also are near equilibrium levels, indicating possible control of Ba and F solubility by these mineral phases, which also precipitate in some discharge areas. Likewise, the fluid is supersaturated with respect to quartz, indicating the possibility of siliceous precipitation near the discharge areas of the present geothermal fluids.Taking into account the Na-K, Na-K-Ca, and SiO₂-temperature geothermometers, the temperature of the reservoir may be estimated to be about 135 °C.The chemistry of the geothermal fluids has changed from a recent high-enthalpy system, which precipitated siliceous deposits, to the present low-enthalpy system, which precipitates carbonated deposits (travertine).Multivariate analysis of the groundwater shows high correlations between K, Ca, As, Br, Ag, and Ba, suggesting that As is introduced to the environment via geothermal fluids. Moreover, As concentrations in hot groundwater are associated with high concentrations of Li and Si, as has been observed in other geothermal fields. Metal concentrations in the hydrothermal deposits show high values of Ag, As, Ba, Pb, Sb, and Zn, mainly in the siliceous deposits of the town of Caldes de Malavella, where the geothermal system deposited materials with high As concentrations (123-441 ppm).The similarities between the geochemical characteristics of the hydrothermal deposits and the groundwater suggest that the metals in these deposits and fluids have the same origin.     

Chemical description of spring waters from the Tutupaca and Rio Calientes (Peru) geothermal zones

Analysis of chemical data from 34 spring samples from the Tutupaca and Río Calientes (Republic of Perú) geothermal zones is presented in this paper. The main objective of the work was to characterize geothermal resources to be exploited in the future. The investigated zones were: Tutupaca and Río Calientes‐Ancocollo‐Challapalca. Thermal waters from Tutupaca showed low pH values and they were classified as sulphate type waters. Thermal springs from the Río Calientes zone showed almost neutral pH values and they were classified as sodium chloride type waters with a probably geothermal origin. Reservoir temperatures were estimated and the results indicated that water–rock equilibrium in the hydrothermal system was not completely attained. Taking into account the chemical composition of some equilibrated or ‘mature’ waters from the Río Calientes zone, reservoir temperatures in the range of 210–240°C were estimated. Mixing models based on silica, chloride and specific enthalpy of the samples were used to estimate the composition of the reservoir liquid. Isotopic data showed oxygen‐18 shift for the waters from Río Calientes‐Ancocollo regarding the waters from Tutupaca zone which were found on the world meteoric line. Copyright © 1999 John Wiley & Sons, Ltd.     

Geochemical modeling of the near-surface hydrothermal system beneath the southern moat of Long Valley Caldera, California

Geochemical reaction path and mass balance modeling techniques were used to test the hypothesis that an eastwardly flowing plume of thermal water in the southern moat of the Long Valley caldera system reacts with hydrothermally altered intra-caldera tuffs and mixes with non-thermal groundwater. Our conceptual model is based on hypotheses in the literature and published geochemical and petrologic data. Mixing of thermal and non-thermal waters and reaction with wall rock were simulated using the reaction path code EQ3/6. Mass balance calculations were conducted to estimate the extent of water-rock interaction between the intra-caldera tuffs and fluids. A mixing ratio of 82% thermal and 18% non-thermal water reacting with altered tuff minerals closely matches Casa Diablo fluid compositions and minerals observed in petrographic studies. Results of this study show that the mineralogy and fluid chemistry observed in the shallow reservoir at Long Valley caldera are formed in an open system. Further, calcite precipitated in the system serves as a sink for high levels of CO₂ generated by the deeper magmatic system. Our study serves as an example that processes acting in a geothermal system can be effectively quantified using geochemical modeling and mass balance calculations.     

Magmatic fluid input to the Kuju-Iwoyama hydrothermal system prior to the 1995 eruption of the Kuju volcano (Kyushu, Japan)

A schematic model showing the sources of hot waters being discharged at the surface in the Kuju-Iwoyama of the Kuju volcano has been developed. Based on the isotopic characteristics of these fluids it is inferred that deep magmatic fluid mixes with thermal waters derived from rainwater in a shallow geothermal reservoir, and with local groundwaters in a deeper reservoir. These thermal waters feed hot springs that discharge waters with Cl/SO₄ ratios that differ from that of the fumaroles on Kuju-Iwoyama, due to the addition of SO₄²⁻ ions produced by the decomposition of native sulfur and mixing with magmatic fluid of high Cl content.     

Chemical and isotope characteristics of the Chachimbiro geothermal fluids (Ecuador)

The parent geothermal water proposed for the Chachimbiro geothermal area has calculated values of 2250 mg/L Cl and approximately 5 bar P_CO2. It comes from a reservoir having an estimated temperature of 225–235 °C, although temperatures somewhat higher than 260 °C may be present at the roots of the system. The geothermal reservoir at Chachimbiro is recharged mainly by meteoric water (about 92%) and secondarily by arc-type magmatic water. Carbon and sulfur isotope data support a magmatic origin for the C and S species entering the geothermal system from below, consistent with indications provided by He isotopes.The thermal springs of Na–Cl to Na–Cl–HCO₃ type located in the Chachimbiro area originate through dilution of the parent geothermal water and have reached different degrees of re-equilibration with country rocks at lower temperatures.     

Model approach to the management of the tianjin hydrothermal field, China

The Tianjin hydrothermal field is located in the northeastern part of the North China basin, 130 km SE of Beijing, and covers an area of about 3500 km² including the city of Tianjin and its suburbs. The hot waters of the Tianjin field are contained in a four-aquifer/three-aquitard multilayered hydrothermal system.The quasi-three-dimensional finite element flow model of the field has been developed utilizing IGROSS (interconnected ground-water systems simulation program). The finite element grid network consists of 7514 triangular aquifer elements and 9160 linear aquitard elements. Steady-state model calibration was made with reference to the natural state of the system prior to its industrial exploitation (in 1970). Transient model calibration was made by reproducing the history of exploitation in the period 1970–1982. The good quality of the field data permitted an accurate system identification.The most suitable future exploitation of the hydrothermal system has been selected from five different exploitation hypotheses simulated over the period 1982–2010.     

Spatial distribution of temperature in the low-temperature geothermal Euganean field (NE Italy): a simulated annealing approach

The spatial distribution of groundwater temperatures in the low-temperature (60–86 °C) geothermal Euganean field of northeastern Italy has been studied using a geostatistical approach. The data set consists of 186 temperatures measured in a fractured limestone reservoir, over an area of 8 km². Investigation of the spatial continuity by means of variographic analysis revealed the presence of anisotropies that are apparently related to the particular geologic structure of the area. After inference of variogram models, a simulated annealing procedure was used to perform conditional simulations of temperature in the domain being studied. These simulations honor the data values and reproduce the spatial continuity inferred from the data. Post-processing of the simulations permits an assessment of temperature uncertainties. Maps of estimated temperatures, interquartile range, and of the probability of exceeding a prescribed 80 °C threshold were also computed. The methodology described could prove useful when siting new wells in a geothermal area.     

Hybrid energy system for hydrogen production in the Adrar region (Algeria): Production rate and purity level

The following work treat the prediction of the production rate and purity level of hydrogen produced by an alkaline electrolyzer fed by a renewable source in a hybrid energy system HES in the locality of Adrar in the south of Algeria. This work is made for different renewable energy penetration rate from 0% to 60% of conventional power (Genset generator). The cell electrolyzer model permits to predict the production rate of hydrogen with accuracy, according to operating parameters, climatic conditions and the load of the site of Adrar. The study permits to introduce a model of hydrogen purity level based on the operating parameters and the power supplying the alkaline electrolyzer. It also shows that the great influence of the intermittent energy supplying the electrolyzer on the production rate and purity level of hydrogen. The prediction of production rate and purity level by the models allow to obtain a distribution and storage of hydrogen produced according to predetermined selection criteria imposed by the operator.In the process of electrolysis, the oxygen is considered as by-product of the hydrogen production. The amount and purity level were estimated jointly.An HES-H₂ production program under MATLAB^®/SIMULINK^® has been developed to simulate the hourly evolution of the production rate and purity level of hydrogen and oxygen produced by an electrolyzer for different penetration rate of renewable energies in an HES.     

Wind-diesel hybrid power system integration in the south Algeria

In most isolated sites situated in south Algeria, the diesel generators are the major source of electrical energy. Indeed, the power supply of these remote regions still poses order problems (technical, economical and ecological). The electricity produced with the help of diesel generators is very expensive and responsible for CO₂ emission. These isolated sites have significant wind energy potential. Hence, the use of twinning wind-diesel is widely recommended, especially to reduce operating deficits. The objective of this paper is to study the global modeling of a hybrid system which compounds wind turbine generator, diesel generator and storage system. This model is based on the control strategy to optimize the functioning of the hybrid system and to consolidate the gains to provide proper management of energy sources (wind, diesel, battery) depending on the load curve of the proposed site. The management is controlled by a controller which ensures the opening/closing of different power switches according to meteorological conditions (wind speed, air mass, temperature, etc).     

An integrated approach for the production of hydrogen and methane by catalytic hydrothermal glycerol reforming coupled with parabolic trough solar thermal collectors

An integrated catalytic hydrothermal reforming process for the production of hydrogen and methane from wet biomass feedstock is proposed where the process heat is provided by molten salts previously heated by solar energy. The simulated reactor consists of double tubes in which the reactants and the heat transfer fluid (i.e. molten salts) are concurrently pumped through the inner and the outer tubes, respectively. The first section of the reactor essentially serves as a preheater to increase the feed temperature to 20 K below the desired reaction temperature (i.e. 773 K), while the second section is comprised of a catalyst appropriate for the reforming of glycerol and water-gas shift reaction (e.g. Ru and Ni catalysts). The required energy for heating up the reactants to the final reaction temperature in the preheating section as well as the heat of reaction needed throughout the catalyst bed is provided by a co-currently fed molten salts mixture previously heated to 823 K in parabolic trough solar collectors. After heat recovery, the product mixture is cooled down to ambient temperature and depressurized to form liquid and gas phases. The gas products are subsequently separated into hydrogen, methane, and carbon dioxide or can be alternatively used for electricity generation using solid oxide fuel cells (SOFC). Glycerol was considered as a biomass model compound throughout this study, but the same methodology with minor changes can be applied to other oxygenated biomass compounds such as carbohydrates. The simulation results indicated that the degree of heat recovery has considerable effects on the process efficiency, the required parabolic mirror area, and the corresponding molten salt flow rate. Also, the higher the extent of the heat recovery, the smaller the dependence of the overall efficiency to the feed concentration.     

Geochemistry of the surface and deep fluids of the Miravalles volcano geothermal system (Costa Rica)

The Miravalles high-temperature geothermal reservoir, located in the northwestern part of Costa Rica, is liquid-dominated. Reservoir temperatures generally range between 230 and 240 °C. The highest measured value is 255 °C. Bottom-hole measurements and solute geothermometry indicate that thermal conditions within the reservoir are very stable over time. The waters discharged from the wells have a neutral or slightly alkaline pH and are of the sodium-chloride type. Based on isotope data, the main recharge zone appears to be located on the northeastern side of the Guanacaste Cordillera. Several mixing trends have been identified between reservoir fluids and regional groundwaters. Gas discharges are dominated by CO₂, with minor amounts of H₂S and N₂. Relative N₂, Ar and He contents reveal a typical arc-type signature and significant inflow of meteoric-derived gases. Cl–SiO₂-enthalpy and δ¹⁸O–δ²H–Cl relationships suggest the existence of a maturation trend that is the result of both natural (i.e. direct drainage of deeper fluids) and anthropogenic causes (reinjection of Cl-rich waste waters). Acid fluids with SO₄-acidity (pH ranging between 2.4 and 3.7) have been encountered in three wells at the eastern border of the well field. Preliminary data assessment indicates two possible sources, either superficial H₂S oxidation or inflow of “immature” volcanic waters.     

Finite element method for computational fluid dynamics to design photovoltaic thermal (PV/T) system configuration

This study focuses on the optimal configuration and suitable flow rate in photovoltaic thermal (PV/T) system. Design and verification were carried out by finite element method (FEM) to solve computational fluid dynamic (CFD) problem and to determine the suitable flow in a collector system. COMSOL MULTIPHYSICS^® software was used for the analysis. The computed results were then comparatively evaluated against a set of result samples obtained from testing data of the 16 modules of PV/T system—a configuration with 4 strings (horizontal-axis) of 4 modules in-series (vertical-axis) (4×4). The redesign of PV/T system was further studied by changing the system configuration from a 4×4 configuration to simulate various configurations consisting of 8×2, 3×4, 4×3 and 6×2. For the same number of PV/T module (16), the 4×4 configuration provided better flow distribution, when compared with an 8×2 configuration. When decreasing to 12 modules, it was shown that the 3×4 configuration resulted in the most suitable flow distribution, compared with the 4×3 and 6×2 configurations. From these results, it can be concluded that the number of strings used was inversely proportional to the flow distribution quality. Experimental results have also shown that the optimized flow rate for the 4×4 configuration was approximately 1-3 L/min.