Geothermal Brine Research Articles

Lithium extraction from geothermal brines: Adsorption-desorption studies on 226Ra (228Ra) and 210Pb on lithium-titanium-oxides (LTO)

Extracting lithium from geothermal brines contributes to meet the growing demand for lithium-ion batteries and other energy applications. Deep geothermal brines of the Upper Rhine Graben (URG) contain up to 200 mg L−1 of lithium and a wide range of dissolved elements, including Th–U series radionuclides. This study presents data from a radiochemical monitoring conducted as part of pilot tests for lithium extraction at the Bruchsal geothermal site under site-specific thermodynamic conditions (T = 60 °C; p = 18 bar). The results show an uptake of the long-lived radionuclides 226Ra (228Ra) and 210Pb by the granulated lithium-titanium-oxide (LTO) sorbent employed. Increasing pH values favor the adsorption of the naturally occurring radionuclide, due to increasing negative charge of the LTO surface. The radioactive uptake of radium was found to be nearly in adsorption equilibrium state after 12 extraction cycles performed. In contrast, 210Pb is permanently removed from the Bruchsal brine by more than 96 % reflecting its high capability to approach the adsorbent surface during adsorption compared to the competing cations. Radioactive load of both radium and lead isotopes on the LTO adsorbent could be reduced using 0.5 M HCl as desorption agent. In this context, desorption percentages ranging from 50 to 100 % per extraction cycle were obtained.

Lithium recovery from geothermal brines: An investigation into radioactive nuclide uptake on lithium‑manganese-oxide (LMO) granules

Due to the growing demand for lithium, the exploitation of non-conventional lithium sources such as Li-bearing geothermal brines is currently on the rise. These brines contain up to 200 mg L−1 of lithium along with a diverse range of other dissolved elements, including naturally occurring radionuclides. In this study, data from a radiochemical monitoring process performed during the pilot plant testing of direct lithium extraction (DLE) at a geothermal site in the Upper Rhine Graben (URG) are presented. The tests were conducted under thermodynamic p-T conditions of the geothermal plant (T = 60 °C, p = 18 bar). The results present an uptake of the long-lived radionuclides 226Ra (228Ra) and 210Pb by the granulated lithium‑manganese-oxides (LMO) sorbent employed. Elevated pH values enhance the sorption of nuclides formed in the Th-U decay series, due to the increased negative charge on the LMO surface. The radioactivity uptake on the sorbent was found to be time-dependent. Experiments with a 5-min contact time resulted in relatively low sorption capacities, while extending the sorption time to 30 min significantly increased the accumulation of Ra isotopes and 210Pb on the sorbent surface. During the regeneration phase, the radioactive load on the LMO sorbent could be reduced using 0.5 M HCl. The mass balance analysis of the investigated radionuclides demonstrates desorption percentages ranging from 16% to 100% per extraction cycle.

Rare earth element extraction from geothermal brine using hybrid capacitive-deionisation process

Rare Earth Elements (REE) in geothermal brine include pollutants such as dissolved Lanthanum, Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, lithium, and other ions. These REEs in geothermal brine, also popularly known as “Vitamins of the modern industry”, are vital for industries such as new energy vehicles, wind turbines, radar systems, laser crystals, etc., and harmful for agriculture and drinking purposes. Hence, identifying, quantifying, and extracting these REEs are essential and economical for a geothermal plant. The present study systematically investigates identifying and quantifying the REE and other essential ions in geothermal brine sources from Gujarat regions. For the extraction of REE from geothermal brine, geothermal brine treatment systems and their integration with automation control are designed in the present work. The proposed system filters geothermal brine and extracts REE through a hybrid filtration setup using capacitive deionization. Solar photovoltaic Water Filtration uses a hybrid Capacitive De-Ionization (CDI) treatment-based prototype to purify water and extract REE. The CDI method is an emerging technology in the desalination systems. It has far greater leverage over other desalination methods such as electrodialysis. The proposed design allows the simultaneous removal of various dissolved organic and inorganic contaminants in geothermal brine.

Battery Electrode-Based Lithium Recovery from Geothermal Brines

Driven by the electrification of transport sector the demand of lithium for battery application is increasing exponentially. The major sources for lithium are continental brines and hard minerals where the production comes along with consumptive water requirements and energy intensive processing and extraction. Therefore, it is of tremendous importance to consider alternative, non-conventional, sources and to develop more efficient and environmentally benign Li extraction methods. Geothermal brines can have significant Li concentrations (150–240 mgLi+ L−1)[1] and could represent an attractive sustainable lithium source. Implementing electrochemical methods for lithium extraction offers further advantages of high Li-selectivity, minimal waste production and low water consumption.[2] Here, we present a dual-ion battery type setup for the selective electrochemical Li-adsorption and desorption from geothermal brines. The chloride concentration in brines is a thousand times higher than that of Li+, hence, both species can be captured at opposite electrode sides. In the dual-ion setup presented in this work, Li+ are stored in a Li-selective LiFePO4(LFP) battery electrode and Cl− are stored using bismuth oxychloride (BiOCl) as counter electrode that has shown excellent Cl− storage capabilities and chemical stability in chloride-ion batteries and desalination batteries.[3] In the second step, both ions are released in a recovery solution to yield a Li-rich solution that could be further processed into battery-grade lithium hydroxide or carbonate. The stability of LFP in aqueous solutions and high Li -selectivity makes it a favored candidate for the electrochemical recovery of Li from natural solutions, where a diverse mixture of cations and anion is present.[4] Therefore, we examined the stability of the electrodes in brine solutions by XRD, indicating good reversibility and no intercalation of competitor ions. In addition, the Li-selectivity in extraction/recovery experiments was analyzed by ICP-OES and influences of different process parameters (e.g. current density, pH, temperature) were investigated. The results demonstrate that the LFP/BiOCl dual-ion battery setup is a feasible and promising low cost method for environmentally friendly Li extraction from geothermal brines.

(Invited) Transforming Metal-Containing Secondary Resources into Functional Materials for Electrochemical Energy Applications

Transforming metal-containing waste into functional materials for electrochemical energy applications presents an innovative and sustainable solution to address the growing issue of waste management and resource conservation. By utilizing end-of-life products, off-specification materials, waste materials, and spent materials as secondary resources, this approach can effectively reduce environmental impacts and promote the development of clean energy technologies.Gas-diffusion electrocrystallization (GDEx) is a novel electrochemical technology that can be used as a step to selectively recover and convert valuable metals from metal-containing waste streams into functional materials for electrochemical energy applications. By leveraging the electrochemical reduction of gases, such as O2 or CO2, for the in-situ production of oxidizing (H2O2) or reducing agents (H2 and CO)—which may also result in the formation of other chemical species, e.g., alkali (OH–) in aqueous media, GDEx facilitates the precipitation of soluble metal precursors. This process results in the formation of metal nanoparticles with controlled compositions, crystal structures, sizes, morphologies, and compositions, tailored for specific electrochemical applications.In this talk, the principles of the GDEx process will be explained and examples will be provided of its applicability in the direct transformation of metals contained in secondary resources for the production of functional materials for electrochemical applications. Specifically, the production of electrocatalysts for methanol oxidation from the recycling of automotive catalysts leachates will be conveyed, as well as the production of active battery materials for Li-ion batteries, and the recovery of lithium from geothermal brines.Gas Diffusion Electrocrystallization (GDEx) is a novel and sustainable approach to transform waste materials into functional materials for electrochemical energy applications. This innovative method enables the recovery and synthesis of valuable metal nanoparticles (NPs) from waste streams, such as end-of-life products and industrial leachates, for use in electrocatalysis, energy storage, and fuel cells.GDEx will be conveyed as a sustainable and scalable technology for the recovery of critical metals, contributing to a circular economy and reducing the environmental impact of mining and refining activities. The opportunity for producing materials with enhanced performance will be portrayed, together with the portent of a customizable and flexible solution which can be integrated with existing recycling chains.AcknowledgementThis research has received funding from the European Union’s Horizon 2020 and Horizon Europe research and innovation programmes under grant agreements 958302 (PEACOC Project), 101069685 (Rhinoceros Project), 101069644 (LICORNE Project), 101058163 (CRM-Geothermal Project), and 101091715 (FIREFLY Project).ReferencesPrato M.R.A., Van Vught V., Chayambuka K., Pozo G., Eggermont S., Fransaer J., Dominguez-Benetton X. (2020) Synthesis of material libraries using gas diffusion electrodes. J. Mater. Chem. A, 8:11674-11686. DOI:10.1039/D0TA00633E.Martinez Mora O., Pozo G., Leon-Fernandez L.F., Fransaer J., Dominguez-Benetton X. (2023) Synthesis of platinum group metal nanoparticles assisted by CO2 reduction and H2 cogeneration at gas-diffusion electrodes. RSC Sustain., 2023, Accepted Manuscript. DOI: 10.1039/D3SU00046J

Economic Analysis of Gas Turbine Using to Increase Efficiency of the Organic Rankine Cycle

In this research, a modified organic Rankine cycle (ORC) system has been presented and examined. This system incorporates a gas turbine as an additional subsystem to boost the enthalpy of geothermal brine. The primary objective of this study is to perform an economic evaluation of the modified ORC system, wherein a gas turbine is utilized to enhance the quality of geothermal steam. The suggested modified ORC system is particularly well-suited for areas abundant in geothermal resources with low to medium temperatures. It offers a more effective utilization of such resources, resulting in improved efficiency. The study considered 10 different working fluids and 8 types of gas turbines used to heat the geothermal water brine witch, the temperature vary of which varies between 80–130 °C. Various flue gas temperatures behind the heat exchanger, as well as temperatures of the return of the geothermal water to the injection hole, were examined. Based on that, 990 variations of configuration have been analyzed. The research showed that the lowest simple payback time (SPBT) values were achieved for the SGT-800 gas turbine and the working fluid R1336mzz(Z), for example, for an electricity price equal 200 USD/MWh and a natural gas price equal to 0.4 USD/hg, resulting in a SPBT value of 1.45 years. Additionally, for this variant, the dependence of SPBT on the price of electricity and the depth of the geothermal well was calculated; assuming the depth of the geothermal well is 2000 m, SPBT changes depending on the adopted gas prices and so for 150 USD/MWh it is 2.2 years, while at the price of 100 USD/MWh it is 5.5 years. It can be concluded that a decrease in SPBT is observed with an increase in the price of electricity and a decrease in the depth of the geothermal well. The findings of this study can help us to better understand the need to utilize low and medium temperature geothermal heat by using combined cycles (including gas turbines), also from an economic point of view.

Geochemical modelling of heavy metal deposition in a geothermal heat exchanger

Heavy metal deposition and corrosion of carbon and low alloy steels exposed to geothermal two-phase fluids and brine solutions under acidic fluid conditions have been widely reported. Similarly, near neutral conditions can result in the precipitation of arsenic and antimony scales that can limit heat exchange. Geochemistry modelling has been undertaken to explain observed deposition and scaling in a two-phase geothermal fluid heat exchanger with a view to predicting the risk of heavy metal deposition and corrosion and heavy metal scaling in geothermal process fluids for new and existing energy facilities. Understanding of the geochemical parameters that control deposition, scaling and corrosion will allow the prediction of the risk of heavy metal deposition and scaling at the design stage for geothermal energy plants and assist in the selection of materials and processes that will give reliable long-term performance. The developed models have application in other industries for prediction of risk of scaling and corrosion and for process development support for example for the gettering of heavy metals from contaminated liquids and soils.

Multi-criteria thermoeconomic optimization of a geothermal energy-driven green hydrogen production plant coupled to an alkaline electrolyzer

Among the various technologies for hydrogen production, the renewable energy driven water electrolysis has emerged as a favorable method. In this respect, the present research proposes and analyses a novel and efficient medium-temperature driven geothermal system for green hydrogen production. An alkaline electrolyzer is deployed for hydrogen production which is powered by a double flash steam geothermal power cycle. To boost the power generation (and hence the hydrogen production amount) the double flash cycle is equipped with a self-superheating process, which superheats the saturated vapor at turbine inlet without using another external heat source. Thermodynamic evaluations, based on exergy concept, along with economic analysis are carried out to assess the hydrogen production amount, plant exergy efficiency and total cost rate, and the unit hydrogen price. In order to represent a comprehensive investigation of the plant performance, parametric analyses along with single- and multi-criteria optimizations were conducted. The results revealed that, for 1kg/s of geothermal brine, the capacity of hydrogen production of the proposed plant is ∼1.5−3kg/h under various operating conditions. It is found that, under multi-objective optimum operating conditions, the plant yields 12.63% exergy efficiency and its total cost rate is calculated to be 10.42 $/h. However, if the plant is to be optimized for maximum exergy efficiency, the value of 14.25% is achievable which will result in increment of total cost rate to 11.97 $/h.

Separation Performance of Lithium and Calcium from Synthetic Geothermal Brine Using Electric Field-assisted Membrane

Green low-carbon technology development has spurred an increased demand for lithium. Brine, including geothermal brine, is the world’s largest source of lithium. However, the low lithium content and the presence of other ions pose challenges in concentrating lithium. An electric field-assisted membrane is a separation approach combining nanofiltration membranes with an electric field as an additional driving force, effectively separating lithium from magnesium and strontium. This study was conducted to separate lithium and calcium from synthetic geothermal brine using an electric field-assisted membrane. The separation process is conducted for lithium (50 ppm) and calcium (300, 800, and 2,000 ppm) with variations in electrical voltage (0V, 2V, and 3V). The decrease in lithium rejection reaches up to 50% at an electrical voltage of 2V. Conversely, the increase in electrical voltage does not significantly impact calcium rejection (calcium rejection remains at 89% with an electrical voltage of 3V) and the permeate flux for lithium and calcium. The increasing calcium concentration affects permeate flux significantly but does not notably affect calcium rejection, with the rejection remaining above 85%. The findings suggest the feasibility of concentrating lithium through electric field application without compromising calcium rejection within a single salt solution system.

Geothermal Energy and Its Potential for Critical Metal Extraction—A Review

In an era of accelerating energy transition and growing demand for critical metals essential for clean technologies, the innovative integration of geothermal energy with critical metal extraction stands as a paradigm shift in sustainable resource utilization. This comprehensive review unravels the synergistic potential of coupling geothermal energy systems with critical metal extraction, thereby transforming a dual crisis of energy and resource scarcity into an opportunity for circular economy. Through rigorous analysis of existing geothermal technologies, and extraction methodologies, the study establishes a coherent framework that merges energy production with environmental stewardship. It scrutinizes current extraction techniques, and evaluates their compatibility with geothermal brine characteristics, proposing optimized pathways for maximum yield. Through detailed case studies and empirical data, the paper elucidates the economic and environmental advantages of this multifaceted approach, from reduced carbon footprint to enhanced energy efficiency and resource recovery. It concludes that combined heat and mineral production technology can open new, unexplored resources, increasing the supply of previously untapped resources, while the potential of geothermal energy for sustainable mineral extraction and energy production is in line with Sustainable Development Goal 7, which aims to ensure access to affordable, reliable, sustainable and modern energy for all.

Microbial desalination cell treated spent geothermal brine as a nutrient medium in hydroponic lettuce cultivation: Health risk assessment

The scarcity and contamination of freshwater resources are extremely critical issues today, and the expansion of water reuse has been considered as an option to decrease its impact. Therefore, the reuse of microbial desalination (MDC)-treated spent geothermal brine for agricultural purposes arises as a good solution to prevent water contamination and provide sustainable water usage. In this study, the potential of treated spent geothermal water from MDC system as a nutrient solution for the hydroponic cultivation of lettuce was evaluated. The effects of different water samples (Hoagland solution (R1) as a control, MDC-treated water (R2), 1:1, v/v mixture of MDC-treated water and Hoagland solution (R3), 4:1, v/v mixture of MDC-treated water and Hoagland solution (R4), and tap water (R5)) on lettuce growth were considered. The application of R3 and R4 samples for hydroponic lettuce cultivation was promising since the lettuce plants uptake sufficient nutrients for their growth and productivity with low toxic metal concentrations. In addition, the chlorophyll-a, chlorophyll-b, and carotene contents of lettuce were in the range of 1.045–2.391 mg/g, 0.761–1.986 mg/g, and 0.296–0.423 mg/g in different water samples, respectively. The content of chlorophyll-a was highest in R1 (2.391 mg/g), followed by R3 (2.371 mg/g). Furthermore, the health risk assessment of heavy metal accumulations in the lettuce plants cultivated in the various water samples was determined. Results showed that heavy metal exposure via lettuce consumption is unlikely to suffer noticeable adverse health problems with values below the permissible limit value.

Anisotropic gypsum scaling of corrugated polyvinylidene fluoride hydrophobic membrane in direct contact membrane distillation

Membrane distillation (MD) technology has gained a lot of attention for treatment of geothermal brine, high salinity waste streams. However, mineral scaling remains a major challenge when treating complex high-salt brines. The development of surface-patterned superhydrophobic membranes is one of the core strategies to solve this problem. We prepared flat sheet membranes (F-PVDF) and hydrophobic membranes with micron-scale corrugated pattern (C-PVDF) using a phase separation method. Their scaling behavior was systematically evaluated using calcium sulfate solutions and the impact of the feed flow was innovatively investigated. Although C-PVDF shows higher contact angle and lower sliding angle than F-PVDF, the scaling resistance of C-PVDF in the perpendicular flow direction has worst scaling resistance. Although the nucleation barrier of the corrugated membrane is the same at both parallel and perpendicular flow directions based on the traditional thermodynamic nucleation theory, experimental observations show that the C-PVDF has the best scaling resistance in the parallel flow direction. A 3D computational fluid dynamics (CFD) model was used and the hydrodynamic state of the pattern membranes was assessed as a determinant of the scaling resistance. The corrugated membrane with parallel flow mode (flow direction in parallel to the corrugation ridge) induces higher fluid velocity within the channel, which mitigated the deposition of crystals. While in the perpendicular flow mode (flow direction in perpendicular to the corrugation ridge), the solutions confined in the corrugated grooves due to vortex shielding, which aggravates the scaling. These results shed light on the mechanism of scaling resistance of corrugated membranes from a hydrodynamic perspective and reveal the mechanism of anisotropy exhibited by corrugated membranes in MD.

Lithium recovery from brines by lithium membrane flow capacitive deionization (Li-MFCDI) – A proof of concept

The demand of lithium for electric vehicles and energy storage devices is increasing rapidly, thus new sources of lithium (such as seawater and natural or industrial brines), as well as sustainable methods for its recovery, will need to be explored/developed soon. This work presents a novel electromembrane process, called Lithium Membrane Flow Capacitive Deionization (Li-MFCDI), which was tested to recover lithium from a synthetic geothermal brine containing a much higher mass concentration of sodium than lithium (more than 650 times). Specifically, a ceramic lithium-selective membrane was integrated into a flow capacitive deionization (FCDI) cell, which was specifically designed, and 3D printed, to allow simultaneous charging and regeneration of the employed flow electrodes. Despite the extremely high Na+/Li+ mass ratio in the feed stream, 99.98% of the sodium was rejected and the process selectivity for lithium over other monovalent cations was 141 ± 5.85 for Li+/Na+ and 46 ± 1.46 for Li+/K+. The Li-MFCDI process exhibited a stable behaviour over a 7-day test period, and the estimated energy consumption was 16.70 ± 1.63 kWh/kg of Li+ recovered in the draw solution. These results demonstrate promising potential of the Li-MFCDI for the sustainable lithium recovery from saline streams.

Challenges and Opportunities for Lithium Extraction from Geothermal Systems in Germany—Part 3: The Return of the Extraction Brine

Lithium (Li) is considered a crucial element for energy transition due to its current irreplaceability in Li-ion batteries, particularly in electric vehicles. Market analysis indicates that Germany’s future automotive sector and planned battery cell production will necessitate significant quantities of global lithium production. At the same time, only 1% of the world’s Li production is currently sourced from Europe. Recently, geothermal brines in Germany have gained attention as a potential local raw material source. These brines exhibit elevated Li concentrations and substantial flow rates in geothermal plants, suggesting the possibility of viable local production. However, a comprehensive full-scale Li extraction process from geothermal brines is yet to be established, and uncertainties persist regarding its long-term behavior. To address this, a generic model based on the geothermal settings of the Upper Rhine Graben was developed, simulating a 30-year operational period for Li extraction. The simulation revealed a 40% depletion of lithium during the observation period, while heat production remained constant. Nonetheless, the model also demonstrated a mean Li production of 231 t per year (equivalent to 1230 t per year of lithium carbonate equivalent), which could significantly enhance the economic prospects of a geothermal power plant and, if applied to multiple plants, reduce Germany’s dependence on global lithium imports. The primary factor influencing productivity is the achievable flow rate, as it directly impacts access to the raw material, hence, emphasizing the importance of detailed reservoir exploration and development in optimizing future lithium production from geothermal brines.

Lithium Extraction from Geothermal Brine Using Electrodialysis Method

The global market share of electric vehicles is expected to increase significantly. The lithium-ion battery is one type of battery that can power electric vehicles because light, inexpensive, has a high energy density, and has a long service life. Lithium may be obtained economically from hard rock ores and brines. Indonesia has a huge geothermal potential and lithium concentration in geothermal brine can reach 70 mg L−1. With the high concentration of lithium in brine, this is a great opportunity for Indonesia to produce lithium independently. The separation of lithium from brine can be separated by various methods. One method that has high effectiveness is by using the electrodialysis method. This study will extract lithium from geothermal brine with the electrodialysis method using monovalent membranes. Anion exchange membrane (AEM) and cation exchange membrane (CEM) are used in this system. The recovery solution to collect lithium from brine is HCl 0,1 M. We variate the voltages (2 volt and 3 volts) to see the effect on flux and conductivity. From the experiment, the 3 volts give more flux and conductivity than the 2 volts. The 3 volts has 10 mL cm−2 h−1 of flux and 2110 μS cm−1 of conductivity while the 2 volts has 4 mL cm−2 h−1 of flux and 1770 μS cm−1 of conductivity. The higher voltages given to the system, the easier separation can be done.

Thermodynamic Analyses of Sub- and Supercritical ORCs Using R1234yf, R236ea and Their Mixtures as Working Fluids for Geothermal Power Generation

Organic Rankine cycles (ORCs) have been widely used to convert medium-low-temperature geothermal energy to electricity. Proper cycle layout is generally determined by considering both the thermo-physical properties of the working fluid and the geothermal brine temperature. This work investigates saturated, superheated and supercritical ORCs using R1234yf/R236ea for brine temperatures of 383.15 K, 403.15 K and 423.15 K. The evaporation and condensation pressures were optimized to maximize the net power outputs. The thermodynamic characteristics of the cycles at the optimal conditions were analyzed. The saturated ORCs produced slightly more net power than superheated cycles for the R1234yf mole fraction less than 0.2 due to lower exergy losses in the evaporator and condenser; however, the limited evaporation pressure by the turning point at the higher R1234yf mole fraction led to excessive exergy losses in the evaporator. Two R1234yf mole fractions maximized the net power and exergy efficiency in a superheated cycle, with the maximum net power output occurring at the R1234yf mole fraction of 0.8 for brine temperatures of 383.15 K and 403.15 K. The exergy losses for evaporation were reduced by 6–12.7% due to the use of an IHE, while those for condensation were reduced up to 42% in a superheated cycle for a brine temperature of 423.15 K, resulting in a 1–17.8% increase in the exergy efficiency. A supercritical cycle with an IHE using R1234yf/R236ea (0.85/0.15) generated the maximum net power output for a brine temperature of 423.15 K, 8.2–17.5% higher than a superheated cycle with an IHE.

Lithium extraction from geothermal brines in the Upper Rhine Graben: A case study of potential and current state of the art

Increasing demand for lithium is leading to a rising focus on alternative, non-conventional lithium sources. These include geothermal brines, among others. The geothermal brines of the Upper Rhine Graben are characterized by comparatively high lithium concentrations of up to 200 mg L−1. To exploit this untapped potential, various direct lithium extraction (DLE) techniques can be used including adsorption and ion exchange.Several laboratory experiments on lithium extraction using inorganic sorbents such as lithium‑manganese oxides (LMO), lithium‑titanium oxides (LTO) and lithium‑aluminum-layered double hydroxide chloride (LDH) have been conducted in the past. Based on the promising results, various research projects are currently working on the development and implementation of the first pilot plants on existing geothermal sites.Before lithium extraction from geothermal brines can be commercialized, not only the sustainability of the resource must be investigated, but also the DLE process must be adapted to the respective site conditions. Finally, improved sorbent performance will be the main driver for future cost reductions and enhanced economics in lithium extraction from geothermal brines.

Possibilities for the industrial use of cooled geothermal brines by borehole salt mines in the Polish Lowlands

Possibilities for the industrial use of cooled geothermal brines by borehole salt mines in the Polish Lowlands

A techno-economic assessment of sCO2 Brayton cycles for low-grade geothermal reservoirs

CO2-based power cycles have recently received much attention because they have several advantages over traditional power cycles in a wide variety of applications. For low-grade heat sources such as geothermal energy, the research has focused on the transcritical CO2 Rankine cycle (TCRC). However, the TCRC requires relatively low-temperature heat sinks to condense the CO2 and operate properly, preventing its deployment in many locations. A straightforward solution is to use a supercritical CO2 Brayton cycle (SCBC) instead. Nonetheless, in the context of binary cycle geothermal power plants, there is a lack of information about the feasibility of implementing SCBCs. Therefore, to elucidate the viability of employing SCBCs for power generation using geothermal heat, this paper presents an assessment of the thermodynamic and economic performances of four SCBC configurations. For this purpose, thermodynamic and economic models of the system, along with a thermal-hydraulic model of the heat exchangers, were developed. Net power output and net present value were used as technical and economic performance indicators, respectively. Subsequently, base case simulations were conducted, and multi-objective optimization using NSGA-II was performed. Results show that, using 20 kg/s of geothermal brine at 150 °C as the heat source and cooling water at 25 °C as the heat sink, an intercooled recuperated Brayton cycle (IRBC) is superior to the other considered configurations. It can achieve up to 932.07 kW of net power output at the optimal thermodynamic conditions and 4.45 × 103 USD of net present value at the optimal economic conditions. Besides, balancing the thermodynamic and economic performances, the IRBC attains the highest overall performance. In conclusion, using SCBCs in binary cycle geothermal power plants could be feasible, and the IRBC is a suitable layout.

CO2 Dissolution in the reservoir brine: An experimental and simulation-based approach

This study benefits from carbon dioxide gas (CO2) dissolution experiments to mimic CO2 dissolution behavior under reservoir conditions. A unique experimental setup, consisting of a batch reactor, gas flow meter, and a sampling separator, was used to measure CO2 dissolution in the geothermal brine at various temperatures (20 °C to 142 °C) and pressures (1 barg to 13 barg). The CO2 was measured using a gas flowmeter and alkalinity tests. It was observed that the experiments’ results matched with a PHREEQC model and empirical correlations available in the literature with R-square values more than 0.86. Water salinity and gas impurity effects on CO2 dissolution were investigated using a calibrated PHREEQC model. CO2 dissolution enhanced mineral solubility such as gypsum, calcium, dolomite, and halite. The study also investigated CO2 dissolution kinetics using batch experiments. The pressure behavior of the gas-brine mixture showed the importance of complete mixing to reach the maximum gas dissolution in the brine. The mixing process showed that at least 2000 s of mixing is required to achieve the maximum dissolving capacity of the geothermal brine at the experiment conditions. The novelty of the study is using real reservoir gas and reservoir brine for CO2 dissolution experiments in a unique experimental setup. Therefore, it will provide insight for CO2 sequestration in geothermal reservoirs.