Design Of Geothermal Power Plants Research Articles

Performance and economic analysis of various geothermal power plant systems: Case study for the Chingshui geothermal field in Taiwan

Geothermal power plants are a source of sustainable energy. However, their performance is influenced by various factors, including production temperature and well locations, and few studies have investigated the relationships between these factors. To address this research gap, the present study developed integrated models of a geothermal reservoir and a variety of power plant systems. By using COMSOL and MATLAB, we conducted simulations for the Chingshui geothermal field in Taiwan to investigate the performance and economic feasibility of five common types of geothermal power plant systems over their operational lifetime under different well configurations. The key findings of this investigation are as follows. First, the locations of production wells are a primary factor influencing production temperature. Constructing wells in low-permeability zones results in considerable increases in the pressure differential in the injection pump; thus, wells should not be constructed in such zones. Second, as system flow rate and well depth decrease, production temperature remains relatively stable, net power output decreases, and system efficiency increases. This efficiency increase is caused by decreases in pumping power requirements at lower flow rates and shallower well depths. Finally, among the investigated systems, the organic Rankine cycle system had the lowest electricity production cost and shortest payback period within the enthalpy range of 500–1000 kJ/kg. Double-flash (DF) and DF–binary systems are also viable options when the mass flow rate is 10–20 kg/s and the enthalpy is 700–800 kJ/kg. Overall, the results of this study offer valuable insights for the design of geothermal power plants, thereby contributing to the optimization of renewable energy systems.

Optimal design of geothermal power plants: A comparison of single-pressure and dual-pressure organic Rankine cycles

Four variants of the Organic Rankine Cycle (ORC) applied to geothermal power plants are optimized by means of numerical tools. These variants are: (i) the subcritical ORC with single-pressure heater (ORC/S/SC), (ii) the transcritical ORC with single-pressure heater (ORC/S/TC), (iii) the subcritical ORC with dual-pressure heater (ORC/D/SC), and (iv) the transcritical ORC with dual-pressure heater (ORC/D/TC). All the systems are recuperative and include a wet cooling tower. The objective function is the specific work output and design variables include operating pressures, mass flow ratios between the brine and the working fluid, superheaters effectiveness and cooling tower range. The systems are optimized for 20 different potential working fluids. The optimization is performed for inlet brine temperatures from 80 to 180 °C, and for ambient air wet bulb temperatures from 10 to 32 °C. The results show: (i) the superiority of ORC/D/TC for most of the cases, (ii) the relevance of using a dual-pressure heater at high sink temperature and low brine temperature, and (iii) the importance of choosing the right cooling tower range for an optimal power plant design.

Testing of Early Stage of BPPT-3MW Condensing Type Small Scale Geothermal Power Plant – Kamojang - Indonesia

Geothermal power plant (GPP) technology is one of the prospective renewable energy technologies and a priority in the development of national electricity today. The Electricity Supply Business Plan (RUPTL) 2018-2027 shows the plan to increase GPP capacity in the period of 4.583 GW, or 8% of all national power plants development, and 30% of all new & renewable energy-based power generation. Until 1st quarter 2018, the installed GPP capacity of 1.924 GW and all of them are imported technology. So efforts to develop national GPP technology are very strategic to support national energy independence in the future. AgencyfortheAssessmentandApplicationof Technology(BPPT) has developed and operated a 3 MW GPP of condensing type technology in Kamojang - Indonesia, which is the first prototype GPP manufactured by national company. The GPP design is based on KMJ-68 well data characteristics, owned by Pertamina Geothermal Energy, and steam turbine specifications designed in reverse engineering. The manufacturing process of the main components of the plant such as turbines, generators, condensers, etc. carried out by the national industry. In this paper it is discussed about the process of test operation in the early stage, starting from the preparation of SOP, conducting free load generator test, dummy load testing, and load testing. Until early 2018, the BPPT’s GPP has generated 15,572 kWh of electricity, with the highest load of 1.3 MW. During testing all process parameters, particularly vibrations, bearing temperatures and lubricants, all within safe limit. The thermal efficiency of the turbine-generator system reaches 13% for loads of about 1 MW.

Optimization of geothermal power plant design for evolving operating conditions

The main goal of this work is to determine optimal geothermal power plant designs by taking into account the transient evolution of the plant/reservoir system. To do so, a geothermal reservoir model is developed, where the permeability of the ground is represented by a series of parallel pipes inside which the underground water can flow. The reservoir model is coupled to an evolving Organic Ranking Cycle (ORC), where the pressure at the condenser adapts to the conditions in the geothermal reservoir (temperature of the brine and mass flow rate) based on the Stodola equation. The system is then optimized in order to maximize the total energy output of the power plant over its lifetime. A series of parametric analyses was performed for relevant design parameters (e.g., overall conductance of the heat exchanger at the evaporator, turbine sizes, number of years of operation, etc.), while other parameters were optimized, namely the working fluid to geofluid mass flow rate ratio, the pressure at the evaporator, and the geofluid mass flow rate. The optimal values that were found were values that yielded viable cycles over the entire exploitation period of the plant and that did not deplete the thermal reservoir prior to the end of the plant lifetime. ORC cycles that were optimized by considering the time evolution of the system were then compared against cycles optimized under the assumption of constant geothermal reservoir properties. It was also demonstrated that by allowing key design parameters to change over the course of the exploitation of the plant, it was possible to further increase the plant performance.

Improvement of Double-Flash geothermal power plant design: A comparison of six interstage heating processes

In this paper, six different modifications of the Double-Flash power plants are proposed. These modifications are named “interstage heating” and consist of additional heat exchangers properly located in the system. The six interstage heating designs are analysed, optimized and then compared to an optimized Double-Flash reference power plant. The objective function is the power plant specific output (kJ/kg), and the design variables are the separator temperatures (°C) and the split fraction. Optimizations are performed for a wide range of reservoir temperatures (i.e., from 140°C to 240°C). Results show that interstage heating processes may increase the specific output of the plant by about 5%, decrease the liquid content in the low pressure turbine by about 50%, and decrease the required cooling capacity of the plant by about 10%. On the other hand, the analysis showed that the new designs proposed have negligible influence on the high pressure turbine liquid content or on the silica saturation coefficient.

The constrained design space of double-flash geothermal power plants

This paper investigates the constrained double-flash geothermal power plant design space across a range of brine and condenser temperatures. Silica deposition and/or turbine exhaust quality constraints reduce specific work output at most brine temperatures. Some combinations of brine temperature and condenser temperature are also shown to be infeasible. Reducing condenser temperature is shown to improve specific work output up to 47% with diminishing effect as brine temperature increases. Relaxing the silica constraint is shown to yield up to an 8% increase in specific work output. These results are useful to a plant designer in determining the value of installing improved condensing or silica control equipment.

Self-Superheating: A new paradigm for geothermal power plant design

In this paper, a new thermodynamic concept for improving the Single-Flash and the Double-Flash cycles in geothermal power plants is presented. This process, named Self-Superheating, uses a part of the heat contained in the geothermal fluid at the well-head to increase the temperature of the steam that enters the turbines. When optimal separator temperature is used, the results of this novel process are an increase of the specific output (approximately 5%) of the geothermal power plant and a reduction (approximately 20–40%) of the liquid content in the last stages of the turbines. The optimal separator temperature for the cycles using Self-Superheating is about 5°C lower than the optimal separator temperature of the Single-Flash and Double-Flash cycles. The simple but fundamental process of Self-Superheating opens the route for more complex thermodynamic cycles in geothermal power plants.

An integrated “Reservoir-Plant” strategy for a sustainable and efficient use of geothermal resources

A multidisciplinary approach for the design of geothermal power plants for water dominant resources is here proposed. The importance of a strategic approach is underlined, considering all the connections between the analysis of the geothermal potential of the reservoir (geophysical exploration and geochemical analysis) with the design of the plant based on thermodynamic and energy considerations, mainly regarding ORC (Organic Rankine Cycles) power plants. This multidisciplinary approach is fundamental for the objective of a sustainable exploitation of medium to low enthalpy sources. The aim of this study is to propose the optimization and management of the global system “reservoir-power plant” as the task of geothermal projects. This approach can be pursued only in a multidisciplinary perspective in which both Engineering and Geological aspects are involved. Numerical simulation appears to be an essential interacting step. After analyzing the problems caused by an incorrect characterization of geothermal source, reinjection temperature and strategy, a method for the numerical simulation of geothermal reservoirs long-term behavior/capacity is discussed. This could be the key instrument to synthesize the strategy inputs. A numerical modeling is performed, using as reference data the history matching of a well known and completely analyzed geothermal field.

3D-Modellierung der tiefengeothermischen Potenziale von Hessen - Eingangsdaten und Potenzialausweisung

Within the scope of the research project “3D-modelling of the deep geothermal potentials of Hesse” the deep geothermal potential of the Federal State of Hesse was quantifi ed and assessed in a qualitative analysis. The quantifi cation of the heat stored under ground and the qualitative analysis was done for different geothermal systems. These are hydrothermal and petrothermal systems, as well as fault zones and deep borehole heat exchangers. For the assessment of the deep geothermal potential, knowledge of the geological structure and the geothermal properties of the potential reservoir rocks are indispensable. Therefore, a 3D model of the deep geothermal potential of the Federal State of Hesse (Germany) has been developed (cf. Arndt et al. 2011). Systematic measurements of thermophysical and hydraulic rock properties such as thermal conductivity, heat capacity and permeability of relevant geologic formations have been combined with in-situ temperature measurements, hydrothermal upwelling zones, characteristics of geological faults and were added to the 3D geological structural model. Using a multiple criteria approach, the various rock and reservoir properties were assessed incorporating their relevance for the different geothermal systems to allow the qualitative analysis. Therefore, threshold values for each parameter were defi ned specifying whether the potential is very high, high, medium, low or very low. This method was tested for the one-dimensional case (virtual drilling) and the two-dimensional case (geological-geothermical cross-sections) before being applied to the 3D model. The resulting geothermal model, which incorporates the quantifi cation and the qualitative analysis, is an important tool, which can be used at an early stage of the planning phase for the design of geothermal power plants. Furthermore, it allows quantifi cation of the deep geothermal potential and is intended to be an instrument for public information. Schlusselworter: Geothermie, geothermisches Potenzial, thermophysikalische Gesteinseigenschaften, hydraulische Kennwerte, geologisches 3D-Modell, Oberrheingraben, Hessen, Deutschland, GOCAD

Geothermal Power Generation Worldwide: Global Perspective, Technology, Field Experience, and Research and Development

This article discusses the state of art in harnessing geothermal power for medium- and large-scale generation of electricity (and for space heating) worldwide. It reviews technology, field experience, research, and development, together with current, probable, possible and potential developments in the USA, developed, and developing countries in near future and long term.First, world consumption of geothermal energy is discussed. Here, worldwide installed capacities for geothermal electricity, the countries with the highest share of electricity generated from geothermal power, capacity factors, and direct use of geothermal energy is reviewed. Then, cost of renewable energy, i.e., current installation cost for electricity generation and heat generation, for biomass, solar photovoltaic, solar thermal, hydro, geothermal, wind, and tidal power is reviewed. Geothermal power in the United States is examined. Highlighted is heat flow, tectonic controls, types of geothermal systems, United States geothermal potential, geothermal energy in the United States, operating conditions for electricity generation, and environmental constraints.The central part of the article discusses field experience with innovative geothermal plants considering geothermal power plant analysis and design (optimization in design of geothermal power plants, optimization of prime movers, heat cycle considerations, resource considerations, and environmental considerations). A review of experimental plants (proposed systems and tested systems), and innovative power plants in commercial operation (low, moderate, and high enthalpy resources) is then discussed.The article goes on to examine R&D programs that are underway to significantly enhance the use of geothermal power. Highlighted is typical research and development projects such as enhanced heat transfer in air-cooled condensers, materials research, instruments for real time monitoring of geothermal processes, plant optimization, removal of non-condensable gases from binary power plants, silica and metals extraction, and small-scale power plant field verification projects. Geothermal drilling R&D is also reviewed.

New trends in the planning and design of geothermal power plants

The amount of endogenous fluid which can be extracted from a steam area is restricted and bound to diminish in time, though at a slow rate. In order to re-integrate the decrease and, if possible, to improve the productivity, it is necessary to expand the research area with drillings which are progressively more distant from the production centres. Almost invariably the characteristics of the steam jets which are found at the peripheral areas are remarkably different from those of the existing ones (higher pressure, greater amount of gas, etc.) and slowly evolve in time before they are almost completely stabilized. A common finding is that of sources having moderate steam deliveries, which cannot conveniently be connected to the distant operating power plants. The above considerations, confirmed by the research and statistics concerning the Larderello steam fields, have prompted Italian planners and builders to: • - achieve simple and easily removable units of 1000 to 1500 kW, with counterpressure turbines, with automatic or remote-controlled operation, for the exploitation of moderate peripheral steam jets which would remain otherwise unexploited; • - install at the head of the wells turbo-alternators of 3000 to 4000 kW which can be easily removed and operated like the preceeding ones, for immediate, even though not rational, exploitation of new peripheral sources in the required period of time (a few years) for the investigation of the properties and behaviour of the new steam jets, before more suited fixed systems could be achieved: • - improve the machinery to be used in fixed condensation-type geothermal power plants, making some more flexible and adaptable to the varying conditions of pressure, temperature and gas contents, to obtain optimum values in the long-term operation of a steam basin; • - adapt the main ancillary equipment of a geothermal power plant (gas extractors, atmospheric refrigerators, and condensation water circulation pumps, etc.) to the requirements of the system, which vary in time. Technical and constructive details of some geothermal power plants erected in Tuscany are then examined, in particular the condensation power plant of Gabbro and the counter-pressure power plant of Piancastagnaio, with two 15,000 kW units, which started operation in 1969.