Geothermal Energy最新文献

The expanding geothermal energy sector still faces performance issues due to scalings in pipes and surface level installations, which require elevated operation pressure levels and costly maintenance. For facilities in the North Alpine Foreland Basin, the precipitation of ({hbox {CaCO}}_{3}) is the main problem which is a consequence of the disruption of the lime-carbonic acid equilibrium during production. The formation of gas bubbles plays a key role in the scaling process. This work presents experiments in a bubble column to quantify the effects of gas stripping on carbonate precipitation and an extension of PhreeqC to include kinetic exchange between a gas phase and water for the simulation of the experimental results. With the same hybrid model not only precipitation of ({hbox {CaCO}}_{3}) but also the dissolution of scalings by the injection of ({hbox {CO}}_{2}) could be quantified. The bubble column was filled with tap water and brine. By varying the ionic strength of the solution, a wider range of geothermal waters was covered. Air and ({hbox {CO}}_{2}) were introduced at the bottom. The precipitates built on the column wall were analyzed with Raman spectroscopy: injecting air into tap water at low ionic strength led to the formation of aragonite with 59.8% of the precipitates remaining at the column wall and the rest as particles in dispersion. At moderate ionic strength the dominant polymorph was calcite and 81.5% of the crystals were attached to the wall. At high ionic strength precipitation was inhibited. The presence of crystallization nuclei reduced the time for precipitation, but not the amount of scalings formed. Injecting ({hbox {CO}}_{2}) into the solution completely removed the scalings from the column wall. The model and its experimental backup lay the foundation for a process-based prediction of the scales (not only) in geothermal systems.

Geothermal heat pumps are one of the most growing and cost-effective renewable energy technologies based on the temperature difference between the ground and the environment. In the cold seasons, the temperature inside the soil or water is higher than the ambient temperature. Therefore, the heat pump is used to extract the warm temperature of the ground into the house or any other controlled space. In the summer, the air temperature is higher than the temperature of the soil or water. This temperature difference is used again to cool the house or any other environment. This paper examines the energy and exergy assessments of a hybrid system in Shanghai, China, that employs a geothermal heat pump with an economizer for winter heating and a wind turbine to provide clean electricity. The complete set of procedures, as well as every component and every aspect of the hybrid system, have all been carefully examined. The heat pump's coefficient of performance is 3.916, its net power output is 22.03 kW, its overall energy efficiency is 77.2%, and its exergy efficiency is 25.49%.

Graphical Abstract

Open-loop borehole heat exchanger (OBHE) is a single well geothermal heat exchanger with an open-loop structure that can realize the geothermal energy extraction without mining the geothermal water. In this paper, a sandbox experiment is designed to simulate the convective heat transfer process in the reservoir area of OBHE. The mechanism of convective heat transfer in the reservoir area is studied, and the key factors that affect the convection heat transfer intensity are analyzed. The results show that the convection heat transfer of OBHE in the reservoir area is affected by both the driving effect of fluid flow inside the screen tube and the buoyancy effect. In the forward flow mode, the two effects have the opposite direction. While in the backward mode, the two effects have the same direction. The backward flow mode is more conducive to convective heat transfer. In addition, many factors influencing significantly the convective heat transfer of OBHE include inlet temperature, inlet flow rate, reservoir temperature, fluid flow direction and inner tube diameter.

Recent researches have proposed the use of enhanced geothermal system reservoirs consisting of dense networks of microfractures, created by hydraulic and/or thermal fracturing in superhot/supercritical geothermal environments, because of their suitability for thermal energy harvesting. During fracturing and energy extraction, the fracture networks are exposed to cooling due to the injection of cold fluid into the reservoirs. Previous studies showed such cooling enhanced reservoir permeability in conventional geothermal environments. However, the cooling may result in a higher risk of seismicity, owing to decreased normal stress on the fractures. Nevertheless, it is unclear whether cooling-induced permeability enhancement and a higher risk of seismicity occurs within networks of microfractures which consist of numerous interconnected microfractures at various orientations to the in situ triaxial stress. Thus, no dominant fractures have the possibility to cause permeability enhancement/induced seismicity. In this study, results are presented for borehole cooling experiments on a dense network of microfractures in granite, at 400 °C, under true triaxial stress. Permeability and acoustic emissions were measured with decreases in borehole temperature (up to ~ 90 °C). Results showed that permeability increased with increasing temperature drop at relatively low stress levels (15 and 20 MPa). The permeability enhancement occurred without intensive failure, and was reversible. However, permeability was almost constant at a higher stress level (65 MPa). Results showed that permeability enhancement required a thermal stress equivalent to the mean stress, so that the normal stress was reduced to near-zero, for a considerable amount of the microfractures. Additionally, the permeability of dense microfracture networks can be increased by cooling primarily through thermo-elastic deformation (without intensive failure), which may be useful to compensate for the reduction in injectivity due to cooling-induced fluid property changes.

The presence of non-condensable gases (NCGs) in a geothermal fluid disrupts the vacuum process in the condenser, reducing turbine efficiency and decreasing the total power output of the geothermal power plant (GPP). Therefore, to optimize the thermodynamic efficiency of a GPP, NCGs should be removed using a gas removal system. Since there is a substantial lack of design and simulation software for a GPP including NCG removal alternatives, in this study, we aimed to model and develop a software-based interface to simulate mass and energy balance involving an NCG fraction in a single-flash GPP as well as examine the thermodynamic performance of the gas removal system, which is the most important step in the planning and designing phase of a GPP. This software was validated using outputs of Kamojang GPP Units 2, 3, and 4 located at Kamojang geothermal field, Garut, West Java, Indonesia. Units 2 and 3 use two ejectors which are installed in series, and Unit 4 utilizes a hybrid system (HS) that is mostly a combination of vacuum pumps and a steam jet ejector (SJE). Our results showed that Kamojang GPP Units 2 and 3 generate 55.295 MW of power with an absolute error of 0.53%, whereas Unit 4 generates 60.218 MW of power with a 0.36% absolute error concerning the field data. These results correspond with the expected minimum error; therefore, our model’s parameters are considered valid and can be used for simulation. We found that using the simulation, the total steam saved by the HS at Kamojang GPP Units 2 and 3 was 534 kW. Furthermore, the net power production was reduced by 1.6% for the HS and 2.03% for the SJE with every 1% increase in the NCG fraction. The power requirement of the vacuum pumps remained less than the power generated by the motive steam which the ejector requires to dispose of the same amount of NCG, indicating that Kamojang GPP Units 2 and 3 will be more efficient if an HS is used.

In the foreseeable future, the geothermal exploitation from hot dry rocks (HDR) using a horizontal well will bear potential. Thus, in-depth studies should be conducted on the selection of injection-production scheme (IPS) and working fluid, design of reinjection parameters, optimization of wellbore structure and materials, and analysis of geological settings. This paper proposed a fully coupled model to study the above scientific questions. For Model A, the working fluid was injected into the annulus and then flowed out of the thermal insulation pipe (TIP). Its temperature passes through two stages of temperature rise and two stages of temperature decline. But for model B, the working fluid was injected into the TIP and then flowed out of the annulus. Its temperature undergoes five stages, four stages of temperature rise and one stage of temperature decline. The results show that the Model A is the best IPS owing to its high outlet temperature, stable thermal recovery, and low fluid injection volume. In Model A, when the working fluid was supercritical carbon dioxide and the liquid injection volume was 135.73 m³/d, the heat recovery ratio (HRR) was as high as 85.40%, which was 17.85% higher than that of the Model B whose working medium was water, and its liquid injection volume was only 25% of that. Meanwhile, over ten years of continuous production, the outlet temperature decreased by 7.5 °C and 18.38 °C in the latter. The optimal working fluid has a low volume heat capacity and thermal conductivity for any IPS. Sensitivity studies showed that for the area that met the HDR standard, the effect of reinjection temperature on the outlet temperature can be ignored. As for Model A, HRR drops sharply by 6.74–9.32% when TIP goes from completely adiabatic to nonzero thermal conductivity. Meanwhile, the horizontal segment length of the TIP is shorter when Model A obtains the optimal outlet temperature compared with Model B. In addition, the correlation between the outlet temperature and different formations of thermophysical properties was seriously affected by the IPS and exploitation period, which was summarized in detail.

Compared with conventional fossil fuel sources, geothermal energy has several advantages. The produced geothermal energy is safe for the environment and suitable for meeting heating power needs. Because the hot water used in the geothermal process can be recycled and used to generate more steam, this energy is sustainable. Furthermore, the climate change does not affect geothermal power installations. This study suggests a combined power generation cycle replicating using the EES software that combines a single flash cycle with a trans-critical carbon dioxide cycle. The findings demonstrate that, in comparison to the BASIC single flash cycle, the design characteristics of the proposed system are greatly improved. The proposed strategy is then improved using the Nelder–Mead simplex method and Genetic Algorithm. The target parameter is exergy efficiency, and the three assumed variable parameters are separator pressure, steam turbine outlet pressure, and carbon dioxide turbine inlet pressure. The system’s exergy efficiency was 32.46% in the default operating mode, rising to 39.21% with the Genetic Algorithm and 36.16% with the Nelder–Mead simplex method. In the final step, the exergy destruction of different system components is calculated and analyzed.

Graphical Abstract

Renewable energy sources are key to achieve the transition toward clean energy system. Among them, the geothermal energy has a production whose effectiveness requires sufficient understanding of the temperature distribution and fluid circulation at depth, as well as of the lithological and petrophysical properties of the crust. The focus of this paper is twofold: first, we summarize the main advances in the development of new methodologies and numerical codes to characterize the properties of the thermal lithosphere in terms of its, temperature, density and composition; second, based on the compilation of available thermal modelling results, we present the depth of the thermal Lithosphere–Asthenosphere Boundary (LAB) of the Iberian Peninsula and the temperature distribution at crustal depths of 5, 10, and 20 km, in addition to at Moho level. At 5 km depth, the temperature is above 110 °C with local anomalies (> 130 °C) located in the Iberian Massif and Cenozoic volcanic provinces. A similar pattern is observed at 10 and 20 km depth, where temperatures are above 190 °C and 350 °C, respectively. At 20 km depth, anomalies above > 500 °C, delineate the SE and NE Cenozoic volcanic provinces. At Moho depths, temperature ranges from 450 to 800 °C with hot regions mainly located along the Iberian Massif and the SE and NE volcanic provinces. The compiled results do not show any lithospheric anomaly that could give rise to high temperatures at shallow depths, but they do show an acceptable exploitation potential at intermediate depths. With regard to the direct use of district and greenhouse heating and for industrial processes, the potential is great throughout the Peninsula, the main challenges being the availability of groundwater and drilling costs.

One key aspect in the energy transition is to use the deep geothermal energy stored in sedimentary basins as well as in igneous and metamorphic basement rocks. To estimate the variability of deep geothermal potentials across different geological domains as encountered in the Federal State of Hesse (Germany), it is necessary to understand the driving processes of fluid flow and heat transport affecting subsurface temperature variations. In this study, we quantify the stored energy in a set of geological units in the subsurface of Hesse with the method of “heat in place” (HIP, sensu Muffler and Cataldi in Geothermics 7:53–89, 1978)—HIP is one proxy for the geothermal potential of these units controlled by their temperature configuration as derived from a series of coupled 3D thermo-hydraulic numerical models. We show how conductive, advective and convective heat transport mechanisms influence the thermal field and thereby the HIP calculations. The heterogeneous geology of the subsurface of Hesse ranges from locally outcropping Paleozoic basement rocks to up to 3.8 km thick Cenozoic, porous sedimentary deposits in the tectonically active northern Upper Rhine Graben. The HIP was quantified for five sedimentary layers (Cenozoic, Muschelkalk, Buntsandstein, Zechstein, Rotliegend) as well as for the underlying basement. We present a set of maps allowing to identify geothermally prospective subregions of Hesse based on the laterally varying thermal energy stored within the units. HIP is predicted to be highest in the area of the northern Upper Rhine Graben in the Cenozoic unit with up to 700 GJ (text {m}^{-2}) and in the Rotliegend with up to 617 GJ (text {m}^{-2}). The calculations account for the variable thicknesses and temperatures of the layers, density and heat capacity of the solid and fluid parts of the rocks as well as porosity.