Academic literature on the topic 'Closed-loop geothermal plant'

Geothermal energy is a clean resource, which could significantly contribute to the reduction of greenhouse and other gas emissions by replacing fossil fuels for power generation. In many geothermal sites, the resource contains substantial Non-Condensable Gases (NCGs: CO2 and contaminants), whose emissions can be limited to developing power plant schemes suitable for complete resource reinjection. Organic Rankine or other closed-loop cycles are definitely favored in this light. This work investigates a solution for complete NCG reinjection in the liquid-dominated reservoir conditions typical of the Monte Amiata area (Italy), referring to the specific site of Torre Alfina (IT) which presents a specific attractiveness because of its high pressurization. The solution considered avoids flashing the resource and thus presents an appealing environmental performance. The power plant models include energy and exergy balances, as well as exergo-environmental analysis. The overall environmental performance is evaluated by a simplified (preliminary) Life Cycle Analysis (LCA). Different solutions are compared, considering the possibility of sub- or super-critical power cycles.

Although its use is declining, oil heating is still used in areas not covered by the methane grid. Oil heating is becoming more and more expensive, requires frequent tank refill operations, and has high emissions of greenhouse gas (GHG) and air pollutants such as SOx. In addition, spills from oil underground storage tanks (USTs) represent a serious environmental threat to soil and groundwater quality. In this paper, we present a comprehensive analysis on technical alternatives to oil heating with reference to the Aosta Valley (NW Italy), where this fuel is still often used and numerous UST spills have been reported in the last 20 years. We assess operational issues, GHG and pollutant emissions, and unit costs of the heat produced for several techniques: LPG boilers, wood boilers (logs, chips, pellets) and heat pumps (air-source, geothermal closed-loop and open-loop systems). We examine the investment to implement such solutions in two typical cases, a detached house and a block of flats, deriving payback times of about 3–8 years. Wood log boilers turn out to be the most economically convenient solutions; however, heat pumps provide several benefits from the operational and environmental points of view. In addition, including solar thermal panels for domestic hot water or a photovoltaic plant would have payback times of about 6–9 years. The results highlight the economic feasibility and the multiple benefits of a rapid phase-out of oil heating in Italy.

Abstract The existing effective domestic regional development framework requires analyses for increasingly wider areas (micro, meso and even macro regions) before operational – short-term – local developments to be prepared and implemented. Such comprehensive complex studies or larger-term programmes may demonstrate the profitability of the given project and can complement it with combined utilization technologies; in the case of Himesháza several locally known renewable energy sources could facilitate geothermal heat, later electricity supply, e.g. local biomass (biogas-based) recovery technology (organic waste of the local pig farm) and, for example, the construction of a low-power “dwarf” hydroelectric power plant chain based on rich watercourses of the region (the “southern dwarves” in Hungary) and the connection of existing solar utility facilities to a modern “smart grid” system in the longer term. Himesháza, located in southern Hungary in Baranya county, is developing; it has a detailed feasibility study of a thermal energy supply network and an energy supply development plan. Based on the geothermal characteristics of Baranya county it would be reasonable to encourage the development of smaller-scale, decentralized heating systems for dynamic settlements. Several settlements in close proximity to Himesháza have already explored thermal wells. Power generation with a small scale, closed-loop system can be used in the project region for thermal water with an outflow temperature of 90 °C. The heating system may also be able to fulfill the needs of recreational, vacation-based or complex thermal spa facilities formerly planned in the region. Moreover, the system could also be capable of utilizing a larger spectrum of renewable energy through its combination with photovoltaic technology. Due to the country's favorable agricultural characteristics, Hungary's biomass potential is higher than the European average. The utilization of organic waste from agricultural and farming sectors is highly recommended in Baranya county; biogas production seems to be the most suitable in the region of Himesháza too, broadening the utilization of renewable resources. The realization of the current project could contribute to shifting the energy resource sector in a more modern, environmentally conscious direction. The background for shorter-term plans and investment (carried out within the framework of operational programs) necessary for the optimal operation and maintenance of longer-term (25–50 years) energy development strategies is created by the analysis (at multiple scales) of complex regional characteristics and future potential, and the selection of optimal sites.

Abstract A closed-loop geothermal well design is presented which incorporates both wellbore configuration and completions components as well as a strategy for well operations which together achieve meaningful production of thermal energy. Planning and optimization of intermittent circulation enable "thermal soak" periods to thermally charge the working fluid while mitigating thermal depletion in the reservoir. Technical challenges of a viable closed-loop downhole heat exchanger scheme are discussed. Advantages of Closed-loop Geothermal Systems (CLGS) compared to Enhanced Geothermal System (EGS) designs are also considered. Fully transient and closely coupled thermal-hydraulic simulations using an industry standard software model were performed on a representative well design and schedule of well circulation operations. The simulation model accounts for detailed conduction, forced and natural convection and radiative heat transfer modes in both the wellbore and the formation as appropriate. Detailed thermophysical characteristics are incorporated into the model for all wellbore completion components which include industry available OCTG grades and sizes, specialized variations such as Vacuum-Insulated-Tubing (VIT), insulating fluids including nitrogen, conventional and foamed cements and syntactic foam as well as the variation in the earth formation. Water is used as a demonstration working fluid and the full spectrum of fluid behavior for all potential phase and quality regimes are accounted for throughout the circulation flow path and at the surface wellhead. Resultant transient temperatures over an extended sequence of flow and shut-in periods are reported inclusive of near-by earth formation temperatures out to the far-field boundary. Comparisons with analytical reference models are also considered. Well simulations presented herein achieve repeatable and extended return fluid temperatures in the range of 200°F to over 400°F. In combination with a pad well concept, this allows for long-term steady energy generation. Clearly the generation of useful temperatures and ultimately justifiable enthalpy delivery with closed-loop configurations is a challenge. Further work on innovative design concepts, refinements such as integration with surface plant processes to optimize surface pressures and pump requirements as well as the recycling of heated water, and identification of optimal locations for deployment will progress this work. Advantages of fully closed-loop well systems include avoidance of potential problems associated with traditional geothermal and EGS wells such as induced seismicity and bedding plane slippage, formation interface skin quality, reservoir degradation over time and introduction of corrosive formation species into the wellbore, and disposal thereof. Combined optimization of both wellbore configuration components and staged circulation and thermal soak periods is shown here to provide a realistic option for significant steady heat generation. Impact of various completion components on operational efficiency can be quantified. In particular, the optimal staging of intermittent circulation operations and their associated thermal soak periods is a featured design option which has not received wide consideration in the literature.

The Queensland Geothermal Energy Centre of Excellence is investigating the use of supercritical CO2 closed loop Brayton cycles in the Concentrated Solar Thermal power cycle plant. One of the important components in the turbomachinery within the plant are seals. As the cycle is closed loop and operating at high pressures, dry gas seals have been recommended for future use in these systems. One of the main challenges of using supercritical CO2 dry gas seals is that operating conditions are near the critical point. In the supercritical region in the vicinity of the critical point (304 K, 7.4 MPa), CO2 behaves as a real-gas, exhibiting large and abrupt non-linear changes in fluid and transport properties and high densities. To correctly predict the seal operation and performance, the interaction between this real gas and the seal rotor (primary ring) and the seal stator (mating ring) need to analysed and investigated in detail, as they can lead to significant changes in flow and seal performance. Results from this paper show that increased centrifugal effects caused by higher gas densities can reduce the pressure in the sealing dam region. This adversely affects the loading capacity of the dry gas seal. However, it also benefits seal performances by reducing the leakage rate. The current work presents an investigation of the supercritical CO2 dry gas seals operating close to the critical point with an inlet pressure and temperature of 8.5Mpa and 370K respectively and a speed of 30000 RPM. Results highlighting the effects of the groove length or dam to groove ratio on the performance of the dry gas seal are presented. The seal is simulated using Computational Fluid Dynamics to study the flow behaviour of the supercitical CO2 in the dry gas seal. Supercritical CO2 fluid properties are based on the fluid database REFPROP. The numerical model was validated with previous work and good agreement was demonstrated.

Abstract One emerging application in geothermal energy is that of closed-loop systems, where two laterals are intersected so that a working fluid can be pumped down one wellhead and up another. These solutions are attractive because they do not rely on the natural permeability of a formation or a reservoir of heated water already in place, they simply require a high enough downhole temperature. While a great deal of discussion exists on wellbore intersection, most applications are by their nature heavily constrained by tight geologic requirements (e.g. coal-bed methane) or have one wellbore trajectory rigidly defined (e.g. relief well drilling). These intersection operations require extensive use of specialized ranging technologies and control drilling at the intersection point which can be time-consuming. Closed-loop geothermal presents a unique opportunity, with relatively few constraints to satisfy (e.g. target depth, lateral length). This study uses this freedom in trajectory design and quantifies the extent that various wellbore positioning techniques can increase the probability of intersection while minimizing the need for ranging workflows. A baseline scenario is described, with wells originating from differing pad locations, drilling with standard practices and active magnetic ranging. Using Monte Carlo techniques, the probability of successful intercept is evaluated for alternate trajectory combinations and compared to the baseline. These include well pairs originating from the same pad and pairs from differing pad locations. Major factors contributing to relative survey errors are identified and the impact of uncertainty reducing techniques are explored for each trajectory type. Techniques include survey corrections, variation of the trajectory profiles, incidence angle at intersection, and the use of alternative solutions to control relative vertical uncertainty. For each scenario, the probability of intercept was evaluated for cases without using ranging tools and for both passive and active ranging technologies. A cost-benefit comparison is conducted, and an optimal combination of factors is identified. For the baseline scenario, low probabilities of collision imply that extensive use of ranging is required for a successful operation. Positional uncertainty reduction techniques and multiple target intervals can greatly increase the collision probability and reduce the need for ranging. Of importance to increasing the probability of successful interception are techniques that maximize the uncertainty reduction along a single axis (e.g. the vertical plane). This enables a "sweep" across the other plane to achieve intersection. Value provided by additional uncertainty reduction techniques depends on the assumed costs of drilling additional footage, performing ranging operations, and rig spread rate. The application of sophisticated wellbore positioning techniques at scale to the closed-loop geothermal problem has not been previously explored. The relatively low number of constraints compared to traditional wellbore intersections enables strategies not otherwise available for successful project construction.

Abstract There are large regions of the subsurface where the temperature is sufficiently hot to generate geothermal electricity within reasonable drilling depths, but the formation does not have enough permeability to create heated water productivity. The primary bottleneck is the difficulty of achieving adequate flow rate in such geothermal reservoirs. These formations are referred as hard dry rock (HDR). In these formations two common applications are conducted: Enhanced (or Engineered) geothermal systems (EGS) and Advanced geothermal systems (AGS). AGS is a closed-loop system that are built on wells drilled that connect with each other allowing a heat exchange-type to set up beneath the surface. There has recently been a lot of attention to the concept of ‘closed-loop geothermal’. The concept is still evolving and few startups such as E2E Energy Solutions, Eavor Technologies, and Green Fire Energy suggested different types of the closed-loop to optimize the technology. Since the technology only relies on conduction as the only source of heat transfer to improve the economics of the closed-loop E2E Energy Solutions suggested to use the hydraulic fracture to increase the surface area between the well and the geothermal reservoir. Such process is called Enhanced Geothermal Reservoir Recovery System (EGRRS). In the E2E's EGRRS process, a fluid would be produced from an existing hot subterranean aquifer reservoir, close to a favorable geothermal zone, instead of creating the whole loop from the surface. The fluid withdrawn from a hot subterranean reservoir would be contacted with a hydraulically fractured zone in the geothermal zone, which would result to additional energy transfer and therefore a higher enthalpy once the fluid reaches the surface. The plan is to reach temperatures above 200°C that greatly increasing the electrical generation potential. Although to implement the EGRRS process we are using the common oil and gas practice but to optimize and design the process using current modelling techniques is not achievable. Current simulation schemes cannot model such complex system, and to resolve this, a new framework must be designed to resolve the challenge. In this paper we present a new method that calculate rate to each branch by a new iterative approach that resolve the problem on how fractions of different pipe should be solved. Since the closed-loop wells are connected to the subterranean aquifer reservoirs and operator required to keep the WHP at constant pressure, there is another layer of iteration that required to solve for fraction on each pipe and BHP at the aquifer. Finally, to model the heating in the fractured zone, a new resistance is added to the model to mimic the heating exchange between the fracture and the fluid? and also the fracture and the radiator formation.

The merit of using supercritical CO2 (scCO2) as the working fluid of a closed Brayton cycle gas turbine is now widely recognized, and the development of this technology is now actively pursued. scCO2 gas turbine power plants are an attractive option for solar, geothermal and nuclear energy conversion. Among the challenges which must be overcome in order to successfully bring the technology to the market, the efficiency of the compressor and turbine operating with the supercritical fluid should be increased as much as possible. High efficiency can be reached by means of sophisticated aerodynamic design, which, compared to other overall efficiency improvements, like cycle maximum pressure and temperature increase, or increase of recuperator effectiveness, does not require an increase in equipment cost, but only an additional effort in research and development. This paper reports a three-dimensional CFD study of a high-speed centrifugal compressor operating with CO2 in the thermodynamic region slightly above the vapor-liquid critical point. The investigated geometry is the compressor impeller tested in the Sandia scCO2 compression loop facility [1]. The fluid dynamic simulations are performed with a fully implicit parallel Reynolds-averaged Navier-Stokes code based on a finite volume formulation on arbitrary polyhedral mesh elements. The CFD code has been validated on test cases which are relevant for this study, see Ref. [2,3]. In order to account for the strongly nonlinear variation of the thermophysical properties of supercritical CO2, the CFD code is coupled with an extensive library for the computation of properties of fluids and mixtures [4]. Among the available models, the one based on reference equations of state for CO2 [5,6] has been selected, as implemented in one of the sub-libraries [7]. A specialized look-up table approach and a meshing technique suited for turbomachinery geometries are also among the novelties introduced in the developed methodology. A detailed evaluation of the CFD results highlights the challenges of numerical studies aimed at the simulation of technically relevant compressible flows occurring close to the liquid-vapor critical point. The data of the obtained flow field are used for a comparison with experiments performed at the Sandia scCO2 compression-loop facility.