Low-temperature Geothermal Water Research Articles

Carbon-Free Heat Production for High-Temperature Heating Systems

The article presents a new carbon-free heat production technology for district heating, which consists of a combined heat and power generation fuel cell (FC CHP) with CO2 capture and a two-stage cascade high-temperature heat pump (TCHHP). The FC generates heat and electricity, the latter being used to drive the compressors of the TCHHP. During the winter period, the water temperature achieved can occasionally be too low, so it would be heated up with hydrogen gas boilers. The hydrogen would be produced by reforming natural gas, synthetic methane, or biogas. The results are presented with natural gas utilization—the ratio between the obtained heat flow transferred directly to the water for district heating and the input heat flow of natural gas. In the case of a return water temperature of 60 °C and district heating temperature of 85 °C, the TCHHP, whose heat source is groundwater, achieves plant efficiency of 270.04% in relation to the higher heating value (HHV) and 241.74% in relation to the lower heating value (LHV) of natural gas. A case with a TCHHP whose heat source is low-temperature geothermal water achieves a plant efficiency of 361.36% in relation to the HHV and 323.49% in relation to the LHV.

Hydrogeochemistry and Formation of Low Temperature Geothermal Waters in South Hunan, China

Hydrogeochemistry and Formation of Low Temperature Geothermal Waters in South Hunan, China

Analysis of the Formation Mechanism of Medium and Low-Temperature Geothermal Water in Wuhan Based on Hydrochemical Characteristics

Wuhan and its surrounding areas have obvious geothermal spring outcrops, which are unexplored potential geothermal resources. The degree of geothermal resource development in Wuhan is low, and there is a lack of systematic research on their hydrochemical characteristics and formation mechanism. The Wuhan area is bounded by the Xiang-Guang fault, the South Qinling-Dabie orogenic belt in the north, and the Yangtze landmass in the south, with Silurian and Quaternary outcrops and little bedrock outcrops. The Silurian is the main water barrier in the region, which separates the upper Triassic and Paleogene as shallow aquifers and the lower Cambrian and Ordovician as deep aquifers. Different strata are connected by a series of fault structures, which constitute Wuhan’s unique groundwater water-bearing system. Eleven geothermal water (23~52 °C) and six surface water samples (around 22 °C) were collected from the study area. The geothermal water in the study area is weakly alkaline, with a pH of 7.04~8.24. The chemical type of geothermal water is mainly deep SO42− with a higher TDS and shallow HCO3− type water with a lower TDS. Isotopic analysis indicates that atmospheric precipitation and water-rock interaction are the main ionic sources of geothermal water. The chemical composition of geothermal water is dominated by ion-exchange interactions and the dissolution of carbonates and silicates. The characteristic coefficients, correlation analysis, water chemistry type, recharge elevation, geothermal water age, reservoir temperature, and cycle depth were also analyzed. The performance was similar in the same geothermal reservoir, which could be judged as an obviously deep and shallow geothermal fluid reservoir, and the genetic conceptual model of Wuhan geothermal was preliminarily deduced. DXR-8 and DXR-9 had the best reservoir conditions, hydrodynamic conditions, rapid alternation of water bodies, and large circulation depth, which is a favorable location for geothermal resource development and will bring considerable economic and social benefits.

Geochemical and isotope constraints on the hydrogeology and geochemistry of the geothermal waters in the Shandong Peninsula, China

Utilization of low-temperature (< 150°C) geothermal waters plays an increasingly important role in the space heating and other direct uses in China, providing an alternative energy source to fossil fuels. In the Shandong Peninsula several local geothermal areas with low temperatures were discovered by drilling over 90 boreholes. The geothermal waters have surface temperatures ranging from 28 to 89°C, pH values between 6.8 and 8.5, and total dissolved solid contents between 150 and 10,000 mg/L. The mobile element systematics (B, Sr, and Cl) and isotope ratios (δ2H, δ18O) reveal that the geothermal waters are predominantly of meteoric origin with occasional minor seawater mixing and/or mineral salt leaching followed by modification through water–rock interactions and mixing with shallow non-thermal groundwaters. By applying multiple mineral-water equilibria geothermometry, higher subsurface water temperatures ranging from 70 to 160°C were obtained indicating conductive cooling and/or mixing with non-thermal groundwater as the geothermal waters ascends to the surface. Two types of geothermal waters were identified in the Shandong Peninsula. The type I geothermal waters are characterized by deep water circulation (∼2–5 km) associated with large and deep faults, low Cl concentrations (57.7–1781 mg/L), variable and often low 14C activity (6.94–82.6 pMC) and 3H activity (< 1–8.3 TU), and reasonably high reservoir temperatures (70–160°C). These results indicate mixing between reacted and “old” water components at depth and modern meteoric water sourced from the surface. The type II geothermal waters are associated with shallower fractures located away from the major granite intrusions. The geothermal waters have a narrow range of 3H activity (5.9–6.9) revealing a modern meteoric origin, whereas the 14C (54.26–131.78 pMC) activity ranges from modern to “old”. This is the result of input from multiple carbon sources rather than the input of only “old” water. The calculated reservoir temperatures (50–160°C) are generally lower than those of the type I geothermal waters and the water commonly display more elevated Cl concentrations (254–5316 mg/L) and a lower degree of water–rock interactions and rock leaching based on the B, Cl, and Sr systematics. Based on these findings, further prospects for geothermal exploration and exploitation may be feasible in the Shandong Peninsula in terms of deeper boreholes that may discharge higher temperature water.

Hydrochemical characteristics and geothermometry applications of thermal waters inthe Çürüksu Graben, western Turkey

In this study, we investigate chemical and isotopic characteristics of low-temperature geothermal waters issuing from carbonate reservoirs in the Çürüksu Graben within the eastern termination of the Büyük Menderes Graben in western Turkey. Temperatures and pH values of geothermal waters vary from 20.1 to 24.6 °C and 6.62 to 7.11 and those of cold waters are 17.1 to 19.9 °C and 6.85 to 7.72, respectively. Geothermal waters are of Ca-HCO3 and Ca-SO4 types whereas cold waters are characterized by these two types and Mg-HCO3 as well. δ18O and δD values of samples vary from ?9.27‰ to -7.69‰ (VSMOW) and -58.06‰ to -52.2‰ and indicate a meteoric origin with local recharge. Tritium contents are from 0.12 to 2.17 TU for thermal waters and 0.28 to 4.85 TU for the cold waters implying relatively longer residence time for the hot waters. Thermal water samples mostly have positive δ13C values (varying from ?0.32‰ to +1.99‰) and carbon in these waters is likely derived from marine limestone or metamorphic CO2. δ34S and δ18O values of dissolved sulfate in the waters indicate that sulfur originates from dissolution of marine evaporite deposits (e.g., gypsum). Çürüksu waters are generally oversaturated with respect to calcite, dolomite and quartz but undersaturated with respect to gypsum. Common ion effect exerted a strong control for the formation of travertine deposits in the area. Chemical and isotopic evaluations indicated that the diversity in the water chemistry of samples is attributed to a combination of processes including water-rock interaction, ion exchange and mixing of various types of waters. Çürüksu thermal waters are immature and not in chemical equilibrium with the reservoir rock. Among the various geothermometers applied to Çürüksu thermal waters, temperatures computed by chalcedony, quartz and Ca- Mg geothermometers are 21-52 °C, 49-83 °C and 73-96 °C, respectively. HCO3-SO4-F and anhydrite-chalcedony (quartz) diagrams estimated a temperature range of 63?86 °C and δ18O(SO4-H2O) isotope geothermometer yielded 67-78 °C.

Hydrochemical characteristics and geothermometry applications of thermal waters inthe Çürüksu Graben, western Turkey

In this study, we investigate chemical and isotopic characteristics of low-temperature geothermal waters issuing from carbonate reservoirs in the Çürüksu Graben within the eastern termination of the Büyük Menderes Graben in western Turkey. Temperatures and pH values of geothermal waters vary from 20.1 to 24.6 °C and 6.62 to 7.11 and those of cold waters are 17.1 to 19.9 °C and 6.85 to 7.72, respectively. Geothermal waters are of Ca-HCO3 and Ca-SO4 types whereas cold waters are characterized by these two types and Mg-HCO3 as well. δ18O and δD values of samples vary from ?9.27‰ to -7.69‰ (VSMOW) and -58.06‰ to -52.2‰ and indicate a meteoric origin with local recharge. Tritium contents are from 0.12 to 2.17 TU for thermal waters and 0.28 to 4.85 TU for the cold waters implying relatively longer residence time for the hot waters. Thermal water samples mostly have positive δ13C values (varying from ?0.32‰ to +1.99‰) and carbon in these waters is likely derived from marine limestone or metamorphic CO2. δ34S and δ18O values of dissolved sulfate in the waters indicate that sulfur originates from dissolution of marine evaporite deposits (e.g., gypsum). Çürüksu waters are generally oversaturated with respect to calcite, dolomite and quartz but undersaturated with respect to gypsum. Common ion effect exerted a strong control for the formation of travertine deposits in the area. Chemical and isotopic evaluations indicated that the diversity in the water chemistry of samples is attributed to a combination of processes including water-rock interaction, ion exchange and mixing of various types of waters. Çürüksu thermal waters are immature and not in chemical equilibrium with the reservoir rock. Among the various geothermometers applied to Çürüksu thermal waters, temperatures computed by chalcedony, quartz and Ca- Mg geothermometers are 21-52 °C, 49-83 °C and 73-96 °C, respectively. HCO3-SO4-F and anhydrite-chalcedony (quartz) diagrams estimated a temperature range of 63?86 °C and δ18O(SO4-H2O) isotope geothermometer yielded 67-78 °C.

Hydrogeochemical Characteristics and Formation of Low-Temperature Geothermal Waters in Mangbang-Longling Area of Western Yunnan, China

Numerous low-temperature geothermal waters are distributed extensively in Mangbang-Longling of western Yunnan in China, whose formation mechanism has not been completely investigated yet. This study focused on the hydrogeochemical evolution, reservoir temperature, and recharge origin of geothermal waters using hydrogeochemical and deuterium-oxygen (D-O) isotopic studies. The low-temperature geothermal waters were characterized by HCO3-Na type, while shallow cold spring was of the hydrochemical type of HCO3-Ca. The hydrogeochemical characteristics of low-temperature geothermal waters were mainly determined by the dissolution of silicate minerals based on the geological condition and correlations of major and minor ions. The reservoir temperatures of low-temperature geothermal waters ranged from 111°C to 126°C estimated by silica geothermometry and the silicon-enthalpy graphic method. Low-temperature geothermal waters circulated at the largest depth of 1794–2077 m where deep high-temperature geothermal waters were involved. The data points of δD and δ18O of the hot spring water samples in the study area show a linear right-up trend, indicating the δ18O reaction between the water and rock and a possible mixture of magmatic water from below. The low-temperature thermal waters were recharged by meteoric water at the elevation of 2362–3653 m calculated by δD values. Upwelling by heating energy, low-temperature geothermal waters were exposed as geothermal springs in the fault and fracture intersection and mixed by up to 72% shallow cold waters at surface. Based on acquired data, a conceptual model of the low-temperature geothermal waters in the Mangbang-Longling area was proposed for future exploitation.

Influence of low temperature tail water reinjection on seepage and heat transfer of carbonate reservoirs

Seepage and heat transfer in the carbonate reservoir under low-temperature tail water reinjection is a complex coupling process, which is an important basis for scientific and reasonable evaluation of geothermal resource sustainability. This study based on the tracer test of double-well reinjection for carbonate heat reservoir, a coupling model of seepage field and temperature field of fracture network is established by using the finite element software COMSOL. The uncertainty analysis is carried out to study the fluid-thermal coupling process of carbonate fracture under the condition of low-temperature tail water reinjection.The variation law of seepage field and temperature field of thermal reservoir under low-temperature geothermal tail water reinjection is revealed, The variation of measured temperature of thermal reservoir pumping side under different reinjection conditions is predicted. The results show that the dominant fracture channels between wells of the fractured heat reservoir in Xian county geothermal field play an important role in controlling the seepage heat transfer. Under the coupling action of the seepage field, pressure field and the temperature field of the heat reservoir, the low-temperature tail water reinjection forms a preferential flow along the dominant channels, which is one of the important factors to consider in the prediction of thermal breakthrough. Reinjection pressure, temperature and well spacing are the main factors for artificial control of geothermal production and reinjection system. In the pumping and reinjection system of Xian county geothermal field, under the conditions of 0.5 MPa reinjection pressure, 30 °C reinjection tail water temperature and 270 m spacing between pumping and reinjection wells, the heat reservoir temperature at the pumping side decreased by 1.5 °C in 100 years.

Geochemical Survey of low- temperature geothermal resource of the Reşadiye Spa (Tokat, Northern Turkey)

The low-temperature geothermal area of Reşadiye is located within the Kelkit Valley in the middle of the Black Sea region of Turkey. The area is covered with widespread travertine deposits which are acquired immediately on deposition from hot spring waters. Thermal waters have temperatures between 42 °C and 49 °C and the discharge rate is 3 L/sec. Total dissolved solids range from 3686 to 4204 mg/L. These thermal waters are of Na-HCO3-Cl type. A geothermal reservoir having probable temperature of about 100° is the source of thermal water for the springs. Before emerging along the margins of exposed carbonate formations through the faults and fractures, the waters interacts sometimes with Na-rich Neogene sediments and/or with B-rich rising geothermal fluids as confirmed by high concentrations of Cl, and, to a greater degree, by the presence of B. The conductive process along with the mixing of thermal waters with shallow groundwaters is the main cooling mechanism. Deuterium and oxygen-18 signatures of thermal groundwater indicate its meteoric origin. Equilibrium states of the Reşadiye thermal waters studied by means of the Na–K–Mg triangular diagram, K–Mg–Ca geoindicator diagram, and finally the activity diagrams in the systems composed of Na2O–CaO–MgO-K2O–Al2O3–SiO2–CO2–H2O phases indicate that the springs and low-temperature geothermal well waters in the area can be classified as shallow or mixed waters which are likely to be equilibrated with muscovit at temperature similar to those calculated from the chemical geothermometers. It was also observed that mineral equilibrium in Reşadiye waters is largely controlled by CO2 concentration. Based on acquired data, a conceptual model of the geothermal system of Reşadiye is proposed.

Sustainable Utilization of Low Enthalpy Geothermal Resources to Electricity Generation through a Cascade System

The article presents an assessment of the potential for using low temperature geothermal water from the C-PIG-1 well (Małopolskie Voivodship, southern Poland) for electricity generation, as the first stage in a geothermal cascade system. The C-PIG-1 well is characterised by a temperature of geothermal water of 82 °C and a maximum flow rate of 51.22 kg/s. Geothermal water is currently only utilised for recreation purposes in swimming pools. In such locations, with the potential to use renewable energy for energetic purposes, the possibility of comprehensive management of the geothermal waters extracted should be considered both in the first stage of the cascade and after recreational use. Thermodynamic calculations were conducted assuming the use of the Organic Rankine Cycle (ORC) or Kalina Cycle. Two variants were analysed—the use of the maximum flow rate of geothermal waters and partial use with an assumption of a priority for recreational/heating purposes. The analysis and calculations indicate that the gross capacity in the most optimistic variant will not exceed 250 kW for the ORC and 440 kW for the Kalina Cycle. As far as the gross electricity generation is concerned, for ORC this will not exceed 1.9 GWh/year and for the Kalina Cycle it will not exceed 3.5 GWh/year.

Integration of geothermal water into secondary network by absorption-heat-pump-assisted district heating substations

Integrating renewable energy into District Heating (DH) systems can significantly save the consumption of fossil energy and receive environmental benefits. The 4th Generation District Heating (4GDH) is the most promising technique for future DH systems by decreased supply temperature and use of low-temperature renewable thermal sources. As current district heating networks are mostly designed with supply temperature around 100°C, high hydraulic resistance and large pressure loss may often occur if decreasing the supply temperature to 30–70°C. This paper has proposed a Composite District Heating Substation (CDHS) with integrated geothermal water into the secondary network by Absorption Heat Pump (AHP). This has been demonstrated to be a feasible and effective solution for using low-temperature geothermal water in DH systems, without decreasing supply temperature of the primary network. The AHP is driven by hot water from the primary network, and the heat of the geothermal water could be used more intense by reducing its return temperature by the AHP and the plate heat exchanger. In this study, both the AHP and the whole substation were simulated by MATLAB, and the results indicated that the heating capacity of AHP increased when increasing the temperature or the mass flow rate of geothermal water, the mass flow rate of the primary network, or when decreasing the return temperature of the secondary network. Additionally, it was found that using temperature regulation with flow changing in stages in the secondary network could receive a higher COP of the AHP and a higher ratio of geothermal energy used in the substation. A case study was carried out as well and its results showed that comparing to conventional DH substations, the CDHS could save 8.0% of the annual cost and reduce 25.6% of the pollutant emissions for a heating season.

Theoretical and Experimental Research on a novel adsorption refrigerator based on low temperature geoethermal water

In view of the problems existing in adsorption refrigeration based on low temperature geothermal water, the adsorbent with high mass transfer performance was prepared by carbonization activation method. The specific methods are as follows: firstly, Chinese fir sawdust is immersed in calcium chloride solution, then taken out and dried, and the mixture is carbonized and activated at high temperature to form a porous activated carbon/calcium chloride composite adsorbent, and then expanded graphite is added to enhance the thermal conductivity of the composite adsorbent.The results show that: The proportion of calcium chloride in the composite adsorbent can be significantly increased by carbonization activation method, which makes the composite adsorbent have abundant microporous structure and uniform element distribution. The thermal conductivity of the composite adsorbent can be improved by adding expanded graphite.

Isotope (δD, δ18O, 3H, δ13C, 14C) and chemical (B, Cl) Constrains on water origin, mixing, water-rock interaction and age of low-temperature geothermal water

The isotope (δD, δ18O, 3H, δ13C, 14C) and chemical (B, Cl) compositions of cold (streams, rivers, soil- and groundwater) and low-temperature geothermal water from northern Iceland were investigated in order to delineate the origin, mixing, water-rock interaction and the age of the waters. The waters showed a large range in temperature (0–104 °C) and chemical composition (TDS 7–954 ppm). Based on the δD (−54.9 to −125‰), δ18O (−7.8 to −16.7‰), B (0.001–1.57 ppm), Cl (0.3–500 ppm) content the waters were of meteoric origin that have been modified by primary rock leaching corresponding to rock to water ratio (ξ) of ∼0.001–0.1 kg of basalt dissolved per kg of water. At temperatures above ∼50 °C close to saturation was observed between the waters and common secondary minerals like clays, zeolites and oxides indicating these reactions control the concentrations of reactive elements. At lower temperatures deviation from equilibrium saturation was evident. The water age was constrained by 3H and 14C, the latter corrected for rock carbon using B, Cl and δ13CDIC relations. Most waters displayed modern age. Exceptions were 1) some waters at high ground having lower tritium content and older radiocarbon age; the trend considered to result from mixing between old glacial melt water and modern meteoric water, and 2) some low-temperature geothermal waters in lowland areas considered to be a mixture of old ʽice-ageʼ water, originating from last glacial times >12,000 years ago and modern and/or few decades old meteoric water. Thus, the chemical and isotope composition of cold and low-temperature geothermal waters in the region display a complex story, with waters originating from different conditions and of different age and later mixed and affected by water-rock interaction. These processes need to be considered and understood in order to develop a hydrogeological model of a groundwater system.

Exergoeconomic comparison and optimization of organic Rankine cycle, trilateral Rankine cycle and transcritical carbon dioxide cycle for heat recovery of low-temperature geothermal water

Depleting fossil fuel resources and the horrible environmental impacts due to burning fossil fuels emphasize the importance of using renewable energy resources such as geothermal and solar energies. This paper compares performance of CO2 transcritical cycle, organic Rankine cycle, and trilateral Rankine cycle using a low-temperature geothermal heat source. Thermodynamic analysis, exergetic analysis, economic analysis, and exergoeconomic analysis are applied for each of the aforementioned cycles. In addition, a sensitivity analysis is performed on the system, and the effects of geothermal heat source temperature, evaporator pinch point temperature, and turbine inlet pressure on the cycle's performance are evaluated. Finally, the systems are optimized in order to minimize product cost ratio and maximize exergetic efficiency by using the genetic algorithm. Results indicate that the maximum thermal efficiency is approximately 13.03% which belongs to organic Rankine cycle with R123 as working fluid. CO2 cycle has the maximum exergetic efficiency, equals to 46.13%. The minimum product cost ratio refers to the organic Rankine cycle with R245fa as working fluid. Moreover, sensitivity analysis shows that increasing geothermal heat source temperature results in higher output power, product cost ratio, and exergy destruction ratio in all cycles.

Electrochemical Studies on Local Corrosion Behavior Mechanism of Super Ferrite Stainless Steel in Low-temperature Geothermal Water Environment

Super ferrite stainless steel as a new material in heat transfer equipment has applied widely in foreign coastal power plants because of its high strength, low coefficient of thermal expansion, and corrosion resistance. In this paper, stainless steel materials with S44660 super ferrite and 316L were selected as research objects. The corrosion and scaling of S44660 and 316L in model geothermal water (environmental conditions of geothermal water in the central plain of China) were studied by the electrochemical tests, weight loss method. The electrochemical results show that the corrosion resistance of S44660 is better than that of 316L in geothermal water. Weight loss tests and microscopic analysis indicate that S44660 is easier to form scale than 316L.

Exergo-economic analysis of a low-temperature geothermal-fed combined cooling and power system

In this work, a novel cogeneration system is analyzed. The system consists of an organic Rankine cycle and a hybrid GAX cycle, and uses a source of 100 kg low-temperature geothermal water at 133.3 °C to produce power and cooling at −50 °C. The ammonia-water mixture is used as the working fluid of the system. The “Parallel-Series” configuration of the system produces more power output, higher exergy efficiency, and lower unit product costs as compared to the “Parallel” configuration. For 1000 kW cooling load while other conditions are the same, the “Parallel-Series” configuration produces 1897 kW power with 42.8% exergy efficiency and 4.192 $/GJ total unit product cost. The exergo-economic analysis also shows that the boiler has the lowest exergetic factor, and the regenerator has the highest relative cost difference.

Development of a compression-absorption heat pump system for utilizing low-temperature geothermal water

Heat pump is an effective way to use the low temperature geothermal water with temperature lower than 50℃ for building heating. Compared to the conventional vapour compression heat pump, the compression-absorption heat pump (CAHP) can obtain higher heat sink temperature with lower compression ratio. Besides, the temperature glide in the generator and absorber of CAHP can be fitted to the heat source and heat sink, which achieves better coefficient of performance. Two models, respectively, for the generator and whole system using ammonia-water (NH3-water) as the working fluid are proposed, and the effects of different concentration of strong solution, cycle ratios, heat source temperature and spray density on the generator are investigated. The objective is to analyse the performance of CAHP system driven by low temperature geothermal water. The results show that the maximum of overall heat transfer coefficient of the vertical out-tube falling film generator can be obtained with the optimum spray density of around 0.16 kg/ms and there is an optimum concentration of around 65% for the CAHP system. When the low heat source temperature between 30℃ and 40℃, the high heat sink temperature can reach to 65-70℃.

Radon in Icelandic Cold Groundwater and Low-Temperature Geothermal Water

Samples of hot and cold water for radon analysis were collected from boreholes and springs in Iceland in 2014 and 2015. The majority of the samples was collected from municipal district heating services or potable water utilities. The total number of samples was 142, covering most towns and villages in Iceland. Radon activity is generally rather low, in most cases less than 5 Bq/L. Only 12 samples had a measured radon activity higher than 5 Bq/L, with a maximum activity of 10.8 Bq/L. The hot water samples generally have a higher radon activity than cold water samples, but samples from boiling borholes have a lower radon activity as radon fractionates into the vapour phase. The geographical distribution of the samples indicates that radon activity is generally lower within the active rift zones. This is most likely due to the very low uranium content of the tholeiites typically erupted within the rift zones. Higher radon values (> 5 Bq/L) are in most cases close to extinct central volcanoes and thus it seems plausible that the water sampled has been in contact with felsic rocks.

Thermo-economic comparison of Kalina and CO2 transcritical power cycle for low temperature geothermal sources in China

Over 3200 geothermal spots have been discovered in China. With purpose of evaluating the performance of enhanced geothermal systems, a thermal-economic comparative analysis is conducted between CO2 transcritical power cycle (CTPC) and Kalina cycle driven by the low temperature geothermal water. The two cycles are compared through six indicators: net power output, thermal efficiency, exergy efficiency, total heat exchanger area, cost per net power (CPP) and the percentages that heat exchangers occupied in the total cost (PHC). Moreover, the single indicator is optimized by means of genetic algorithm (GA) and the optimum value of each indictor is compared between the CTPC and Kalina cycle. Geothermal water with the same temperature and mass flow rate is chosen as the heat source for both the systems. The results show that the Kalina cycle presents a higher net power output and thermal efficiency while the exergy efficiency of the Kalina cycle is less than that of the CTPC. In addition, the Kalina cycle presents a lower CPP and PHC which represent a better economic performance than the CTPC. Therefore, the adoption of the Kalina cycle may be reasonable in the low-temperature geothermal sources due to the better thermo-economic performance in contrast to the CTPC.

Design and simulation of a geothermal–solar combined chimney power plant

The solar chimney power plant (SCPP) is dominated by the solar radiation, and therefore its discontinuous operation is an unavoidable problem. In this paper, low temperature geothermal water is introduced into the SCPP for overcoming this problem. Based on a developed transient model, theoretical analyses are carried out to investigate the performance of the geothermal–solar chimney power plant (GSCPP) with main dimensions the same as the Manzanares prototype in Spain. Three operation models, viz. the full solar model, the full geothermal model and the geothermal–solar combined model are compared in typical summer and winter days and throughout the year. It is found that the GSCPP can attractively run in the GSM to deliver power continuously. Due to the ambient-dependant geothermal water outlet temperature, introducing the geothermal water makes greater contribution in winter days than in summer days, in the night than in the daytime. Power generation under GSM is larger than the sum of FSM and FGM. GSM is not the simple superposition of FSM and FGM, but makes better utilization of solar and geothermal energy. In addition, introducing high temperature and mass flow rate geothermal water can doubled and redoubled improve the GSCPP’s power capacity.