Free Thesis About Geothermal Energy

Omer Bese

Supervised
Asst. Prof. Fusun Tut Haklidir

Energy Systems Enginering

Istanbul Bilgi University
2014

LIST OF FIGURES

LIST OF TABLES
LIST OF SYMBOLS/ABBREVIATIONS
1. Introduction 3
1.1. Goal of the Study 3
1.2. Renewable Energy Sources 3
1.3. Geothermal Energy 3
1.3.1. What is Geothermal Energy? 3
1.3.2 Geothermal Reservoirs 4
1.3.3 Present Status of Geothermal Energy 7
1.4 Geothermal Applications around the World 7
1.4.1Geothermal Applications in Turkey 8

Flash steam power plants 10

Single Flash 10
Double Flash 11
Triple Flash 11
Binary Steam Power Plants 11
Binary Cycle Types and Differences 11
/> Organic Rankine Cycle 12
Kalina Cycle 12
Positive and Negative Ways 12
Companies that Produce Binary Plants 13
Pure Cycle Power Plant 13

REFERENCES 16

LIST OF FIGURES
LIST OF TABLES
LIST OF SYMBOLS/ABBREVIATIONS
- ABSTRACT
Renewable energy is a form of energy taken from sustainable natural resources including geothermal, hydro, wind, solar, tidal, and biomass. Wind energy is taken from wind turbines that are responsible in transforming the kinetic energy of the wind into mechanical energy through the use of gigantic blades. Solar energy makes use of sunlight and heat to produce electricity. Hydropower is acquired from the kinetic energy of water in a method that is the same with the wind energy. Hydroelectricity is generated from rivers, streams, and waterfalls that pour downhill along with the immense kinetic energy transforming huge turbines that change the flow of energy into electricity. Biomass is a renewable energy resource that can be produced from organic materials such as garbage, wood, alcohol fuels, and landfill gases. Geothermal energy is the thermal energy produced by the Earth. It is made up of fluids, a heat source, faults, and reservoir rocks. The primary purpose of this research is to examine the geothermal systems as a whole, along with power-generation forms, to recognize the best generation systems in Turkey. In addition, this paper also presents a case study for Seferihisar field.
- Introduction
- Goal of the Study
The aim of the study is to investigate geothermal systems, together with power-generation types, to determine the best generation systems for middle- and low-enthalpy geothermal systems in Turkey. And then generate a case study for Seferihisar field. And make financial analyses.
- Renewable Energy Sources
Renewable energy is any energy derived from sustainable natural resources such as wind, solar, geothermal, hydro, biomass, and tidal. These energy resources are known to be clean, infinite, and domestically derived. Through the energy crises in the 1970s, governments realized the importance of renewable and alternative energy sources, and many implemented new legal regulations leading to more renewable energy generation. With the current focus on climate change and extreme weather events, governments are encouraging companies to invest in green energy alternatives.
Wind energy is obtained via wind turbines, which convert the wind’s kinetic energy into mechanical energy using gigantic blades. This mechanical energy is then converted into electricity with a simple generator. Wind potential depends on the direction, density, and speed of wind in the region. These parameters are used in feasibility analyses to estimate potential economic returns and draw in new investors. Difficulties include legal permissions and transporting wind turbines, especially the gigantic blades, to wind farms. Environmental issues (such as bird migration) and other technical issues (such as aircraft radars) are also highly critical in the selection of wind farm sites.
Solar energy is the use of radiant sunlight and heat to generate electricity. Solar panels are widely used in Turkey for heating purposes. Solar technologies are characterized as either passive or active depending on their capture of shine and the way radiant energy is used. Although solar energy is a renewable resource, fabrication of some of the parts like photovoltaic panels and solar thermal collectors can leave a high carbon footprint and may require chemical constituents that are not environmentally friendly.
Hydropower is obtained from the kinetic energy of falling or running water in a process similar to the capture of wind energy. Hydroelectricity is produced from streams, rivers, and waterfalls that flow downhill—with the tremendous kinetic energy turning large turbines, which convert the flow into electricity.
Biomass, which can be considered a renewable energy resource if derived from materials that can be regenerated, is formed from organic materials like garbage, wood, landfill gases, and alcohol fuels. The important elemental constituents of biomass are carbon, hydrogen, and oxygen. Bioenergy can be broken down into four main categories: biogas (breakdown of organic matter in the absence of oxygen), biodiesel (vegetable oils, animal fats), bioethanol (sugar fermentation from plants), and gasification.
- Geothermal Energy
- What is Geothermal Energy?
Geothermal energy (GE) is defined as the thermal energy generated by the Earth. Scientists estimate that the temperature at the center of the Earth is more than 6650oC (1).As a result of this, heat is conducted outwards to the outer rock layer, commonly known as the mantle. In some places, the mantle melts into magma just beneath the Earth’s surface. Meteoric water oozes down via fault lines and then becomes superheated upon reaching the heated rocks (2). This highly heated water finds its way out to the Earth’s surface, where it surfaces as hot springs or geysers. This hot water below the Earth’s surface forms a geothermal reservoir.
A geothermal system consists of a heat source, fluids, faults, and cap and reservoir rocks (Figure 2.1). In a geothermal system, geothermal fluids (brine, gas, and steam) carry the heat from the depths of the Earth to the surface by fault systems.
2.3.2 Geothermal Reservoirs
Geothermal systems can be classified by reservoir equilibrium state, fluid type (water or steam-dominated),and enthalpy type (low or high enthalpy)in geothermal fields (Nicholson, 1992).The reservoir equilibrium state depends on how heat is transferred along the system: by convection and circulation of fluids (dynamic systems) or by conduction (static systems). Reservoir enthalpies are mainly described as low temperature (<150oC) or high temperature (>150oC).These values are extremely important to know when using geothermal fluids for different applications.
The term “geothermal resource” refers to the accessible resource base, i.e.,the thermal energy stored between the Earth’s surface and a specified depth in the crust, beneath a specific area, which is measured from the local mean annual temperature. This includes the accessible resource base, which is apart of the resource that can be extracted legally at a cost competitive with other commercial energy sources. Geothermal resources can be classified into three main groups—low enthalpy, <900oC; intermediate enthalpy, 900–1500oC; and high enthalpy, >1500oC—based on their reservoir temperatures (3).
A low-enthalpy resource is best suited for direct applications of GE. These resources are available at depths of 1200–1600 m and water temperatures of 900–1500oC. Intermediate enthalpy is used in electricity generation using binary-cycle power plants. A high-enthalpy resource can also be used to generate electricity, but has a high water temperature range:> 1500oC. A single bore of a high-enthalpy resource can generate about 5 MW of electricity.
Classification of geothermal resources is vital in that it helps in the characterization, assessment, and development of energy resources (4).Characterization of geothermal resources is determined by geologic settings, intrinsic properties, and viability for commercial utilization. The classification also requires coherent frameworks, which include assessment of resources, exploration, development, and reporting (4). Classification requires a specific methodwith simple and logical definitions that can be understood by experts and non-experts alike. Similarly, the classification should be valid from scientific and technical perspectives and meet the needs that are clearly identified for categorized resource information (5). The classification method should also be easily translatable into other classification systems to avoid misconceptions,which may unintentionally adversely affect commercial activities. There should also be no gaps or overlaps between categories.
Additionally, the classification should avoid unnecessary predictions by focusing on fundamental physical and chemical properties of resources rather than on aspects of utilization that can be altered by evolving technological, regulatory, and economic factors. Various examples of classification of geothermal resources include assessment confidence and definitions, temperature and other thermodynamic properties, geologic setting and fluid type, and convective/advective versus conductive (5). Geothermal resources classified in terms of reserves specify the GE extracted through legal and economic means. Similarly, a geothermal resource is the energy that can be recovered through technical means and added to reserves for future purposes (3).
However, the classification does not address the development of a clear and concise definition of a geothermal system. The assessment of oil and gas defines petroleum systems that expand the natural hydrocarbon fluid system in the lithosphere mapped to include the important elements and processes necessary for oil and gas existence through their accumulation (5). The classification relies on temperature, which has been accepted as a classification parameter because of it being a simple measured quantity. However, classification of geothermal resources through its reservoir fluid temperature is regarded as irrelevant because it requires two distinctive properties for the definition of the thermodynamic state of fluids (6).
The classification should specify the way the resources are capable of doing thermodynamic work. Thus, they can be classified into low-, medium-, and high-quality resources in accordance with their specific energy indices. These indices are, however, limited by demarcations of energies of saturated water and dry saturated steam at 1bar absolute (6). The classification follows various criteria that utilize the enthalpy of geothermal fluids that transport heat from deep rocks to the surface. Enthalpy, in this case, expresses the heat contained in the fluids, which determines the value. The criteria require standard methods that eradicate any ambiguity (5).
It is this form of GE that is harvested and utilized in various ways (7).
GE has gained popularity recently because of various characteristics. For instance, it is perceived as being environmentally friendly since its use generates little pollution. Also, it is a sustainable source of energy, unlike other energy sources such as fossil fuels. Furthermore, GE can be utilized in various ways, as described by the Lindal Diagram (Figure 2.2), which describes its application as a function of fluid temperature(8).
Figure2.2.The Lindal Diagram, which describes usage of GE as a function of fluid temperature.
A common application of GE is electricity generation. Subject to the features of geothermal resources, electricity can be generated in binary plants with conventional steam turbines. GE is considered the best alternative to generating electricity from fossil fuels (2).
Perhaps the most resourceful and common use of GE is for direct heat, including space and district heating for different types of buildings, including individual homes(8). Engineers have developed a sophisticated temperature-control system that can be used not only for heating but also for cooling homes. This has contributed to energy cost reductions in countries that experience temperature variations throughout the year (9).
Another direct use of GE is in greenhouses, as a source of warmth and moisture for plants. A third direct use is in industry and agriculture. For instance, it is used in paper mills to dry timber. It is also used to dry crops after harvesting. Another industrial use is in food processing, particularly to sterilize facilities processing food, to produce powders and concentrates, and to cook food (9).
2.3.3 Present Status of Geothermal Energy
Following World War II, several countries became interested in developing geothermal resources, believing it to be economically viable compared with other energy forms. For particular countries, it did not have to be imported, and in a number of instances, these countries believed it to be their only domestic energy source.
Now, every country in the world uses GE to provide some amount of electricity. The electrical power generated by GE (measured in MWe) in 1995 stood at nearly 6800 MWe; by 2000, it reached about 8000 MWe (10). The total capacity at the conclusion of 2003 stood at 8402 MWe. Power created from GE in third-world countries represented 38% and 47% of the world’s total in 1995 and 2000, respectively.
The use of GE in third-world countries has shown a remarkable upward trend for the last several years. In the period 1975–1979, the power derived from GE in these countries rose from 75 to 462 MWe; by the conclusion of the subsequent 5-year period, the number touched 1495 MWe, showing a significant rise (11). From 1984 to 2000, it increased by about 150%. In particular countries, GE is used for a major portion of the domestic power; for instance, in 2001,electrical power generated from GE stood at about 30% of the total electrical energy created in the Philippines, about 12% in Kenya, nearly 11% in Costa Rica, and just about 4% in El Salvador.
Regarding the non-electrical use of GE (measured in MWt, where t denotes thermal),the energy consumption of 190,699 was anticipated worldwide for the year 2000. Throughout that year, fifty-eight nations reported its direct use, in contrast with twenty-eight in 1995 and twenty-four in 1985. The number of countries directly using GE has risen considerably since then, in addition to the total installed power and energy consumption.
The most frequent non-electric utilization of GE globally is heat pumps, followed by bathing, space heating, greenhouses, aquaculture, and industrial applications (12).
2.4Geothermal Applications around the World
GE usage is rapidly increasing globally, as Asian-Pacific countries incline toward green energy. Geothermal resources are abundant around volcanic and plate-boundary settings, and are considered the least expensive energy option in terms of future marginal costs. Its low CO2 emissions, low environmental impact, and low surface footprint encourage governments to provide incentives, as GE efficiently provides on-demand heating and cooling and direct process-heat applications (13). The installed geothermal capacity and produced energy has escalated since the mid-20th century, with different production ways and trends in various regions.
The United States is among the leading countries producing and consuming GE. It is argued that the country produces about 3 GW. More plants are being constructed, and upon completion, they are expected to produce about 2.4GWmore (14). California has the highest number of GE plants, followed by Nevada, Utah, Hawaii, Idaho, Alaska, Oregon, New Mexico, and Wyoming, in that order. Approximately 80% of geothermal projects in the United States currently are located in California and Nevada (14). Globally, it is estimated that the United States produces about 29% of the total GE used worldwide. The country has the potential to harvest more GE, based on the argument that it has a total of about two million square kilometers of geothermal areas, especially in the western states (15). Furthermore, the Government Performance and Results Act (GPRA) was passed in 2010 to improve U.S. Federal Government’s performance. Federal agencies have set outcome-focused High Priority Performance Goals (HPPGs) to implement the Act (Trends in Geothermal Applications Survey Report, 2011, 26).
The Philippines is the second-highest harvester of GE—about 18% of the global GE power, and utilizes this energy source to produce about 27% of its national electricity (14). It is followed by Indonesia, with a capacity of about 11% of global GE. Mexico, Italy, New Zealand, Iceland, and Japan, in that order, are the other top users of GE in the world. Other countries produce GE, but have a low capacity to influence the global market (7). In 2010, New Zealand passed an emissions trading scheme to assist geothermal projects and help reduce future costs relative to fossil fuel power generation. However, as a result of financial swings in the electricity market, the market rate for carbon dropped in 2011, and the government incentives for GEwere reduced.In 2011, a new energy strategy was introduced with a more balanced recognition of the role of renewable energy. As the 2008 NZ National Policy Statement on Renewable Electricity Generation was being discussed, this strategy was introduced to guide implementation for 90% renewable energy by 2025(Trends in Geothermal Applications Survey Report, 2012).
In summary, GE has emerged as an important energy source in the modern era, especially regarding efforts to deal with increasing environmental challenges. It is a source of energy that is obtained from the Earth; hence, it is renewable. It can be used indirectly to generate electricity, and can be used directly as well. The United States is the leading harvester of this energy, responsible for about 29% of the total GE used globally. The Philippines is ranked second, followed by Mexico, Italy, New Zealand, Iceland, and Japan.
2.4.1Geothermal Applications in Turkey
Turkey, with a potential 31,500 MWt geothermal heat in 185 geothermal sites, has a geothermal electricity production potential of 3100 MWe(MTA website).The western Anatolian region is divided into three parts in terms of its geothermal potential, with the mid-region (Part II) being the most efficient because of its high geothermal temperatures. Kızıldere (242oC), Germencik (232oC), Salavatli (174oC), and Alaşeir (191oC) are the five regions with reservoir temperatures above 150oC. Common direct applications include district heating/cooling, heating greenhouses (a total of 635,000 m2), solid CO2 production, industrial drying, thermal tourism, and balneology. The İzmir Balçova district, 9th of September University, and the Thermal Spa (Agamemnon) are all examples of geothermal district heating systems. Some other district heating applications, geothermal power plants, and heating greenhouse applications are shown in Tables 2.1, 2.2, and 2.3.
( http://lisans.epdk.org.tr )
Flash Steam Power Plants
Flash steam power plants are the most common type of geothermal power plants. The plant is designed such that hot water is forced to the Earth’s surface under high pressure. On reaching the surface, a significant amount of this water turns into steam as a result of reduced pressure. The cooled water is then returned to the reservoir, and the entire process begins again. This form of technology was invented in New Zealand to pull deep, high-pressure hot water into lower-pressure tanks such that the resulting flashed steam drives turbines (16). Flash steam power plants utilize water at temperatures greater than 182oC to generate electricity. When the hot water flows up through the wells in the ground, it gets collected in flash tanks, where it drops in pressure and causes the liquid to boil into steam. After this, the steam is separated from the liquid and is used to run turbines, which generate power (16).
The condensed steam is returned to the reservoir. The cycling of the flash steam power plant occurs such that the high-temperature pressurized fluid is passed through low-temperature tanks, which allows some portion of the flow to flash off as steam (16). This steam generates electricity, while the remaining spent geothermal fluid is either returned for reinjection, or in some instances, used for generating more energy in either a double flash cycle or in a binary bottoming cycle power unit, where second flash tanks are used in the separation of fluids at a lower pressure. The main parts include turbines, the generating facility, the condenser, the production well, and the injection well (16).
Single flash and double flash cycles are common systems that use pressure change to detach steam from a liquid-dominated source. Single flash systems are preferred for fluids with temperatures above 2600oC, whereas the double flash system is used if the fluid temperature ranges between 1750oC and 2600oC (17).
Single Flash
A single flash cycle plant comprises a turbine-generator unit, a separator, a condenser, a circulation water pump, cooling tower, and a gas removal system. The geothermal fluid enters into the separator from the reservoir before proceeding to a two-phase flow, which is separated into liquid and steam phases using minimum pressure loss within the separator (17). The liquid phase is redirected into the injection line, while the steam phase goes via a ball check valve into the turbine at high pressure, turning the turbine blades to generate electricity (18). Thereafter, the pressure of the steam reduces, allowing it to flow into the condenser through the liquid phase. Water from the condenser is pumped into the reinjection well using the separated liquid phase to maintain production.
The Kızıldere, Denizli power plant, operated by Zorlu energy, with a production capacity of 15 MWe, is the first single flash steam power plant in Turkey. This power plant was first operated at 500 kWe by the government in 1974 as a prototype for the innovative process. In 1984, EUAS constructed a power plant with a design capacity of 17.4 MWe; however, itcould only produce 6–10 MWe due to in-well scaling. Zorlu Energy took over the plant in 2008 and increased its capacity to 17.4 MWe in the first 6 months of ownership after necessary design revisions and the use of inhibitors along with reinjection systems. Three years after the takeover, Zorlu Energy implemented add-on power plants to increase the plant’s capacity to 80 MWe.
Figure 2.3.Singleflash schematic showing the geothermal power plant cycles and main components.
(Dr. PállValdimars son University of Iceland Reykjavik ICELAND )
Figure 2.4. T–s diagram of a single flash cycle.
Figure 2.5. T–h diagram of a single flash cycle.
Double Flash
A double flash plant differs from a single flash plant in that it has an additional turbine and a low-pressure separator (17). From the first phase separation, the liquid phase is directed to the low-pressure separator. The liquid and steam phases are separated, and steam enters via the low-pressure turbine into the condenser, which gets steam from the high-pressure turbine. From there, a process similar to that in the single flash cycle occurs (1).
In 2009, GurmatElektrikÜretim AŞ brought online a double flash power plant with a capacity of 47.4 MWe in Germencik, Aydın, making it the largest double flash power plant in Turkey.
Figure 2.6. Double flash cycle schematic.
Figure 2.7. T–s diagram of a double flash cycle.
Figure 2.8. T–h diagram of a double flash cycle.
Triple Flash
Similar to the double flash process, in triple flash steam power plants, brine is separated into different pressure groups; however, this process ends after three operations for triple flash, as compared with two in double flash. After the different pressure groups—HP, IP, and LP—are separated, these steams are diverted to their corresponding steam entrances in the turbine (KAYNAK!!!!).
Binary Steam Power Plants
A binary power plant is used in generating electricity in cases where the water reaching the Earth’s surface cannot produce steam because it is not hot enough. First, the water is passed into a heat exchanger. A liquid, like isopentane, absorbs heat from the hot water and vaporizes. Isopentane is typically used because it has a lower boiling point than other liquids. The Isopentane vapor is passed through turbines to generate electricity. The liquid is then condensed using cold water or a cold air radiator, and the cycle starts over again (19). Other liquids that could be used, other than isopentane, include pentane and butane. All these liquids have a low triple-point temperature, high thermal conductivity, high decisive temperature, high pressure, and a high enthalpy of vaporization.
Note that binary power plants are used in geothermal regions containing water of moderate temperature. Nothing is discharged into the atmosphere because the entire process isa closed-loop system. The binary power plant is likely to be the most common geothermal power plant in the future because moderate-temperature water is the largest and most common geothermal resource. The main difference between a binary power plant and flash and dry steam systems is that water transmitted from the geothermal reservoir does not directly enter the turbine/generator units (19); heat is transferred via heat exchangers.
Binary Cycle Types and Differences
Planning of power plants for GE needs consideration of the system optimization as a whole. Attributes of the geothermal fluid and selection of the optimum power conversion cycle need to be considered (1). This is accompanied by other considerations, such as simplicity of the system, maintenance requirements,the reservoir, as well as environmental considerations. Steam cycles are used for higher-enthalpy wells, while binary systems are used for lower enthalpies. In most cases, the brine is rejected to the environment, orusually,reinjected and flashed again at a lower pressure. This simply describes the single and double flash cycles (1). The binary cycle, on the other hand, uses a secondary working fluid in a closed power generation cycle. It utilizes a heat exchanger in the transfer of heat from the geothermal fluid to the working fluid. The cooled brine is then rejected to the environment(or reinjected). The organic Rankine cycle and the Kalina cycle model this type of power generation.
Organic Rankine Cycle
The Organic Rankine cycle (ORC) is a power generation cycle that converts heat energy to mechanical work via a turbine that drives agenerator to produce electricity. Unlike typical Rankine cycles,which use wateras the working fluid, anORC uses an organic working fluid,such as isooctane, isopentane, and isobutene. The boiling point of these organic fluids is less than that of water. Thus, ORCsenable the extraction of power from waste heat in industrial processes. They are also used in most geothermal power plants of low enthalpy (20).
A typical ORC used in a low-temperature geothermal power plant is shown in Figure 2.9. The ORC starts at point 1, with the organic working fluid in the liquid state at low pressure. Through the action of the pump, the working fluid ispreheatedand then moved to the evaporator. The working fluid is converted into high-pressure and high-temperature vapor after passing through the vaporizer. The high-temperature,high-pressure vapor expands through the turbine, which is coupled to a generator. Because of the expansion, the vapor loses energy and is converted into a low-pressure vapor at the turbine exit (point 3). The low-pressure vapor then passes through the condenser, where it cools further and is finally pumped back to the vaporizer. The condenser creates a partial vacuum thatlowers the pressure at the turbine exit—hence increasing the efficiency of the turbine and consequentlyincreasing the turbine work or power generated (21).
Figure 2.9.
Kalina Cycle
Binary power plants can also run viathe Kalina cycle, in whichthe secondary or motive liquid is ammonia. The heated secondary fluid is the motive fluid that drives the turbine or generator unit. The Kalinacycle uses a mixture that results in a good geothermal match in the boiler due to the non-isothermal boiling created by the shifting mixture composition. The system has been proven to perform substantially better than a steam Rankine cycle system, becausethe second law analysis indicates that by using a binary fluid, the Kalina cycle reduces the irreversibility in the boiler (1). This causes an improvement in the efficiency of the cycle. However, the Kalinacycle requiresa high vapor fraction in the boiler. Nevertheless, the surface of the heat exchanger becomes dry when exposed to high vapor fractions, which contributes to low heat-transfer coefficients and a larger heat-exchange area. Another limitation of the Kalina cycle is the corrosiveness of ammonia because of impurities found in liquid ammonia, ranging from air to carbon dioxide.
Figure 2.10. Flow diagram of a saturated Kalina cycle.
Advantages and Disadvantages of Power Cycles
The advantage of using power cycles for GE production arethat they are highly reliable, the reservoir is sustainable, and they are environmentally friendly. DiPippo has also presented approaches of optimizing and maximizing the simplicity and high reliability of ORCs through power conversion cycles (1). This is achieved through the maintenance of the simplicity and high reliability of the ORC equipment. The binary cycle has the benefit that the geothermal fluid can be maintained under a sufficiently high pressure during the heat-exchange process, avoiding boiling and release of non-condensable gases. The fluid can then be reinjected into the reservoir,which contains all minerals and dissolved gases (1).
However, the binary cycle has a secondary working fluid,which is often expensive, toxic, and flammable. This also means more expenses in terms of the required safety measures.
Summarizing the types of geothermal power plants,they range from flash cycles to binary cycles, and all of them usesteam turbines to generate electricity. Water or working fluids are heated via a heat exchanger by GE, orin the case of geothermal dry steam power plants, the reservoir fluid is used directly and the heated fluid is sent through a turbine,so the thermal energy is converted into electricity. This occurs through generators in a process called electromagnetic induction. The advantage of binary cycles over flash steam power plants is that the hot geothermal water is passed through a heat exchanger,which transfers the heat energy to a second liquid,often an organic fluid that vaporizes and drives aturbine (22). This secondary fluid has a lower boiling point and higher vapor pressure than steam at the same temperature. After passing through the turbine, the organic vapor gets condensed and re-circulated in the plant. The partiallycooled geothermal water gets pumped back underground down an injection well. Binary cycle geothermal power plants can be environmentally superior compared with flash steam cycles, as the geothermal hot water or steam may contain dissolved salts and gases that canbe exposed to the environment (22).
The binary cycle is so-named because the geothermal fluid circulates in a closed loop underground,while the lower-boiling-point working fluid heated by the geothermal fluid circulates in a separate closed loop in the power plant at the surface. Also, binary cycles can use geothermal fluid at temperatures below about 190oC, while flashed steam plants require higher temperatures.
Geothermal Binary Plant Companies
Some of the companies that have received recognition by the GE Association for their work in bringing new geothermal plantsto places such as the United States includeOrmatTechnologies, Inc., andEnel Green Power S.p.A.Ormat received this recognition for the expected completion of the new Don A. Campbell geothermal power plant, formerly known as the Wild Rose geothermal power plant (22) in Mineral County, Nevada (22). Ormat and Enel are responsible for bringing an additional 25 MWeof geothermal power to the United States. The Surprise Valley ElectrificationCorporation was also recognized for the creation of a 3MWe power plant in Oregon. Other companies include the Gradient Resources,which successfully obtained $155M in bank financing in December 2012 for construction of the first phase of the Patua Project near Fernley, Nevada.By the time this financing was approved, it had been three years since a bank had financed a geothermal project in the United States (22).
In New Zealand, the Kawarau geothermal field is recognized as a world-class high-temperature resource. The operators of the geothermal field joined forces with NST todevelop a 25 MW Ormat binary plant on its industrial site forproviding electricity directly to the NST mill. This helps in reducing losses from the electrical grid (22).
Also, Ormat’sNgatamarikipower plant in New Zealand is an extreme example of the capacity possible with a binary power plant. The Ngatamariki plant, which costs about $475 million to build, is one of the largest binary power plants in the world. It comprises seven geothermal wells and produces about 100MWe.
Pure Cycle Power Plant
Pure cycle is a type of power plant designed to generate electricity from a renewable energy source with zero emissions. The plant can usefluid resource temperatures starting from as low as91oC (1). The pure cycle plant usesanORC to change low- to moderate-temperature resource fluids into electricity by vaporization and expansion of a working fluid within the system.
The pure cycle power plant differs from the binary system in several ways. First, the binary power plant can only be used withgeothermal resources with temperatures above 182oC, whilethe pure cycle power plant can use geothermal resources of low to moderate temperatures—91 to 300oC (1). Second, unlikethe pure cycle power plant, the binary power plant requires a secondary fluid with a lower boiling point than water. Third, unlike the binary cycle power plant, the pure cycle power plant has no emissions; hence, it is environmentally friendly (24). Last, the cost of operating a pure cycle power plant is relatively low compared with the cost of operating a binary power plant.
The pure cycle power plant has various benefits. For instance, it has zero emissions, which means it is environmentally friendly. Besides, it uses renewable power. In addition, no fuel is required, which is one of the factors that make its operation relatively cheap compared with other systems (1). It is also readily available. Moreover, it is easy to monitor at any given time through remote monitoring technology. Finally, it has a standardized mechanism and assembly process.
MEDIUM-ENTHALPY gEOTHERMAL sYSTEMS IN tURKEY FOR POWER GENeRATION
High-enthalpy geothermal resource fields in the west Anatolia region, found on GREBENS??, like Büyük Menderes and GedizSimav, already have electricity-generating plants operated by various companies. Construction of these plants, located at various resource fields around Aydın and Denizli, started with the Germencik plant (47.4 MWe) in 2009. By 2016, the region aims to have an electricity generation capacity of 600 MWe.
Western and mid-Anatolian geothermal fields consist of mid-enthalpy fields. These resources do not have the required heat to operate high-capacity systems, but can be utilized efficiently usingbinary and purecycle-type power plants.
Figure: Turkey’s potential
Especially in western Anatolia at aydindenizlikutahya, it is advised to use ORC systems or pure cycle technologies
Description of the Seferihisar geothermal field
Seferihisar is located southwest of İzmir in the Aegean Region, 45 km from the city center. It is bordered by Urla and Guzelbahce in the north and Menderes in the east. The county centre is located 18 m above sea level.
The geothermal field of Seferihisar stretches from Doğanbeyburnu tosouth-west of Menderes in the north.
(Geophysical investigations of the Seferihisar geothermal area, Western Anatolia, Turkey
Mahmut G. Drahor ∗, Meric ̧ A. Berge)