Geothermal Energy Lecture - Dec 14

‫محاضرة االسبوع العاشر‬ Dec 14 Geothermal Energy Introduction Geothermal energy is defined as heat from the earth’s internal heat underneath the earth surface. Heat from the Earth or geothermal Geo (Earth) + thermal (heat) energy is ob...

‫محاضرة االسبوع العاشر‬ Dec 14 Geothermal Energy Introduction Geothermal energy is defined as heat from the earth’s internal heat underneath the earth surface. Heat from the Earth or geothermal Geo (Earth) + thermal (heat) energy is obtained by drilling water or steam wells in a process similar to drilling for oil. 1 Planet earth Fig. 1: Planet earth Fig 2: Earth structure. 2 Geothermal Temperature Gradient Temperatures within the Earth's interior increase with depth: The average temperature gradient is about 20~30°C per 1 km depth, and much higher in the areas of high structural activity. Examples of geothermal gradient in some typical areas: 10 – 20 °C/km in shield crust 30 – 60 °C/km in platform areas >100 °C/km in volcanic areas 3  Fig.3: Temperature in the earth. Where does geothermal energy come from? Geothermal energy is the heat that comes from the sub-surface of the earth. It is contained in the rocks and fluids beneath the earth’s crust and can be found as far down to the earth’s hot molten rock, magma )‫ (رواسب‬. Heat has been radiating from the Earth's core for billions of years. This heat is originated since the formation of the Earth and it is continuously regenerated by the decay of radioactive elements. The rate of this regeneration of geothermal heat is so high that it makes the geothermal energy a renewable resource. Near the Earth's core, the temperature ranges about 5500 degree Celsius. This heat is basically the thermal energy stored inside the Earth's core and the Earth's crust acts like an insulator and keeps the heat trapped inside. The heat trapped inside the core (by the Earth's crust) is transferred to the surface by the following ways: 4  1. Direct heat conduction 2. Bubble like magma that buoys up to the surface 3. Rapid injection of magma into deep, natural rifts )‫(شقوق‬ Direct heat conduction does not produce much heat on the surface. Also, magma buoys up to the surface only at selected locations like active volcanoes. Whereas magma is injected into deep rifts and causes heating of the underground water. This geothermal energy rises upwards due to one of the above reasons and causes large amounts of underground water to be heated on or below the surface of the Earth. Such locations are called geothermal reservoirs. Such reservoirs are either on the surface in the form of hot springs or underground reservoirs which are reached by drilling wells. The heat energy in geothermal reservoirs can be carried up to the surface and utilized to produce electricity by geothermal power plants. Although areas with signs like hot springs are more obvious and are often the first places , geothermal resources are used, the heat of the earth is available everywhere. It is considered a renewable resource because the heat emanating from the interior of the Earth is essentially limitless. Geothermal wells are drilled into the earth’s crust at a depth of about 3 to 10 km. The heat is extracted from inside the earth’s crust using different methods, but the most popular one is using water and steam. Hot water from the hot water reservoir below may be extracted and directly channeled to heat homes and buildings. This is achieved by circulating the hot 5 water throughout the building or pumping the hot water via a heat exchanger, which emits the heat insides the building. How to access heat? Drill 2 holes, one to inject cold water, another to extract hot water. Circulate fluid uses hot water to generate steam that turns turbine of more-or-less standard design Fig.4: Regions of the earth interior. 6 Advantages of Geothermal Energy: Geothermal energy has many advantages, especially when compared to conventional sources of energy: 1. Geothermal Energy Sourcing is good for the Environment First and foremost, geothermal energy is extracted from the earth without burning fossil fuels, and geothermal fields produce practically no emissions. What’s more, geothermal energy can be very beneficial, as you can achieve savings of up to 80% over conventional energy usage. 2. Geothermal is a Reliable Source of Renewable Energy Geothermal energy also has many advantages when compared to other renewable sources like solar, wind or biomass. It is an exceptionally )‫( استثنائي‬constant source of energy, meaning that it is not dependent on neither wind nor sun, and available all year long. When looking at the availability factor, which shows how reliable and constant specific energy sources are, geothermal is ranking on the top way above the other groups, which supports the argument of its independence on inconstant external circumstances when delivering energy. 7  ‫المحاضرة الثانية‬ Dec 16 3. High Efficiency of Geothermal Systems Geothermal heat pump systems use 25% to 50% less electricity than conventional systems for heating or cooling, and with their flexible design they can be adjusted to different situations, requiring less space for hardware as opposed to conventional systems. 4. Little Geothermal System Maintenance Due to the fact that geothermal systems only have few movable parts which are sheltered inside a building, the life span of geothermal heat pump systems is relatively high. Heat pump pipes even have warranties of between 25 and 50 years, while the pump can usually last for at least 20 years. Disadvantages of Geothermal Energy: However, there are always two sides of the coin so let’s have a look at the cons of geothermal energy: 1. Environmental Concerns about Greenhouse Emissions Unfortunately, no matter its reputation of being an environmentally friendly alternative energy source, geothermal energy also causes some minor concerns in regards to the environment. The extraction of geothermal energy from the grounds leads to a release of greenhouse gases like hydrogen sulfide, carbon dioxide, methane and 8 ammonia. However, the amount of gas released is significantly lower than in the case of fossil fuels. 2. Depletion of Geothermal Sources Furthermore despite being considered a sustainable and renewable energy, the chances are that specific locations might cool down after time, making it impossible to harvest more geothermal energy in future. The only non depletable option is sourcing geothermal energy right from magma ( hot fluid below of within the earth crust)but the technology for doing so is still in the process of development. 9 3- High Investment Costs for Geothermal System Another disadvantage is the high initial cost for individual households. The need for drilling and installing quite a complex system into one’s home makes the price climb quite high. Nevertheless )‫( مع ذلك‬, the return on such investment is very promising, being able to earn the investment back within 2 to 10 years. 4. Land Requirements for Geothermal System to Be Installed In case of geothermal systems, having a piece of land next to the house is required in order to be able to install one. That makes geothermal systems hard to be implemented for homeowners in big cities, unless a vertical ground source heat pump is used. Types of Geothermal Systems There is a number of different geothermal systems available. Which system to choose depends on a variety of factors such as soil conditions, climate, local installation costs on site, available land and applications? Geothermal energy can be used for electricity production, for commercial, industrial, and residential and for thermal energy applications, such as efficient home heating and cooling and domestic hot water through geothermal heat pumps. First: Geothermal systems for electricity generation: To develop electricity from geothermal resources, wells are drilled into a geothermal reservoir. The wells bring the geothermal water to the surface, where its heat energy is converted into electricity at a geothermal power plant. 10  Power production needs temperatures well above 100 deg-C a- Dry steam power plant This is the simplest and oldest type of geothermal plant. It directly uses steam from the reservoir to operate the turbine. The steam is collected from the production well and used to operate low-pressure turbines. Hence, the working fluid is steam. The used steam is then condensed and injected back through the injection well as shown in Fig. (5 ).Dry Steam Power Plant: Uses the superheated, pressurized steam (180°-350°C) Fig.(5): Dry steam power plant. b- Flash steam power plant Flash steam power plants are the most commonly employed geothermal plants today. They operate on the geothermal reservoirs having water temperature greater than 180 degree Celsius. The high pressure hot water from the reservoir flows up through the production well due to its own pressure. The pressure decreases as the water flows upwards and, hence, some of it gets converted into steam. 11 The steam is separated from the water by steam separator and sent to drive the steam turbine. The unused water as well as the condensed steam are injected back through the injection well. In another word, in a flash steam power plants take high-pressure hot water from deep inside the earth and convert it to steam to drive generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used again. Most geothermal power plants are flash steam power plants. In other ward, extremely hot water flows up through the wells via the pressure gradient created by the temperature difference between the earth’s surface and the underground reservoir. As it travels through the wells, the some of the water turns to steam that can be separated from the liquid water and used to power a steam turbine. This is the most common type of geothermal power plant as shown in Fig.(6 ). Flash Steam Power Plant: use hot water above 182°C (360°F) from geothermal reservoirs. Fig.6: Flash steam power plant. 12  c- Binary cycle (ORC) power plant, Ordinary Rankine cycle Binary power plants transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam, which is used to drive a generator turbine. Generally, most geothermal areas contain moderate-temperature water (below 400°F). Energy is extracted from these fluids in binary-cycle power plants. In this case, the proper selection of the fluid allows to obtain comparatively higher efficiency. Hot geothermal fluid and a secondary (hence, "binary") fluid with a much lower boiling point than water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to vapor, which then drives the turbines. Because this is a closed-loop system, virtually nothing is emitted to the atmosphere. Moderate-temperature water is by far the more common geothermal resource, and most geothermal power plants in the future will be binary-cycle plants as shown in Fig. (7). It uses hot water in the 110-160 °C range from geothermal reservoirs. 13  Fig.(7): Binary cycle (ORC) power plant. Second: Geothermal heat pumps (GHP) for thermal energy applications such as space heating and domestic hot water: Definition: A geothermal heat pump is a heat pump that uses the earth’s thermal capacity as an energy sources to add heat to a system or as an energy sink to cool a system. It utilizes constant temperature of upper 5 feet of the Earth’s surface. Geothermal heat pumps take advantage of the Earthís relatively constant temperature at depths of about 5 ft to 300 ft. GHPs can be used almost everywhere in the world, as they do not share the requirements of fractured rock and water as are needed for a conventional geothermal reservoir. 14 GHPs circulate water or other liquids through pipes buried in a continuous loop, either horizontally or vertically, under a landscaped area, parking lot, or any number of areas around the building. Summary Geothermal heat pumps Promising alternative to heating/cooling systems. Ground below the frost line (about 5 feet) is kept around 55oF year-round. During winter: The ground is warmer than the outside. Heat can be pumped from the ground to the house. During summer: The ground is cooler than the outside. Heat can be pumped from the house to the ground. 15 The Environmental Protection Agency considers them to be one of the most efficient heating and cooling systems available. Animals burrow underground for warmth in the winter and to escape the heat of the summer. The same idea is applied to GHPs, which provide both heating and cooling solutions. To supply heat, the system pulls heat from the Earth through the loop and distributes it through a conventional duct system. For cooling, the process is reversed; the system extracts heat from the building and moves it back into the earth loop. It can also direct the heat to a hot water tank, providing another advantage of free hot water. GHPs reduce electricity use 30-60% compared with traditional heating and cooling systems, because the electricity which powers them is used only to collect, concentrate, and deliver heat, not to produce it. 16 There are four types of pumps, three closed-loop systems (Horizontal, Vertical and Pond) and one open-loop systems. Each depends on the type of soil, climate conditions and land available. a- Ground coupled (closed-loop) GHP, Horizontal, vertical and pond Closed loop horizontal systems are the most cost-effective for residential areas. For larger commercial buildings, closed loop vertical systems are more often used. These can sometimes go down 400 feet deep. Closed loops constructed under or in a pond or lake are usually the cheapest as shown in Fig. (8). In closed loop systems, a water/antifreeze mixture circulates through a loop of pipes underground (or beneath a body of water) and into a building. In the winter , the temperatures underground are warmer than the air, so the fluid pumping in is warmer. Then the electric compressors and heat exchangers transfer the heat through ducts in the building. In the summer, the pipes draw heat away from the building and it is absorbed into the earth or water. Since the fluid is already cool in the summer and warmer than the air in the winter, the heater/AC system doesn’t have to work nearly as hard. 17  Fig.8: Closed loop system. b- Ground coupled (open-loop) GHP , (Pond) In open loop systems, the water is taken directly from a water source and into the heat pump where it then can either be recycled back into the same source or pumped into another water source (without polluting). The only difference with the water going in and out is a slight change in temperature. These four types of geothermal heat pumps can be used all over the country due to the constant temperature below the surface, but they vary in efficiency and cost savings. 18  Fig.9: Open loop system. These systems differ mainly in the installation of the pipes, depending on the structure and size of the land available. One of the big advancements for the future of geothermal energy is called an Enhanced Geothermal System (EGS). Traditionally, geothermal power must be taken where geothermal reservoirs exist, which is mainly in the Western United States. In fact, geothermal energy already provides around 60% of the power along the Northern California coast, according to the U.S. Department of Energy. So, EGS creates engineered geothermal reservoirs by pumping cold water thousands of feet underground to gain access to hot water and produce steam needed to power plants on the surface. 19 Since geothermal energy is a renewable natural resource, think of it like a gift from the earth that keeps giving. Although over time it is often necessary to drill additional wells to maintain levels of energy production, the earth is constantly giving off heat that was generated when our planet was formed billions of years ago. Third: Direct Heating Uses: Geothermal heat is used directly, without involving a power plant or a heat pump as shown in Fig. (10), for a variety of applications such as space heating and cooling, food preparation, hot spring bathing and spas )‫( المنتجعات الصحية‬, agriculture, aquaculture )‫ (تربية االحياء المائية‬, greenhouses, and industrial processes. Uses for heating and bathing are traced back to old Roman times , Currently, geothermal is used for direct heating purposes at sites across the United States. U.S. installed capacity of direct use systems totals 470 MW or enough to heat 40,000 average-sized houses. This system of direct heating can be performed by: - Using hot water from springs or reservoirs near the surface. - Hot water near the earth's surface can be piped directly into buildings and industries for heat. 20  Fig.10: Direct heating system. Numerous alternative techniques are being currently explored to achieve thermal comfort conditions inside buildings. The earth–air heat exchanger is one of these promising techniques which can effectively be used to preheat the air in winter and vice versa in summer. The temperature of earth at a depth of 1.5 to 2 m remains fairly constant throughout the year. This constant temperature is called earth’s undisturbed temperature (EUT). The EUT remains higher than ambient air temperature in winter and lower than ambient air temperature in summer. The concept of earth–air heat exchanger (EAHE) is very simple as shown in Fig. (11). The ambient air is drawn through the pipes or ducts of the EAHE buried at a particular depth, moderated to EUT, and gets heated in winter and vice versa in summer. In this way, the heating and cooling load of building can be reduced passively. 21 Fig.(11): One-dimensional model of earth–air heat exchanger system. 22 Geothermal energy in Jordan: Geothermal resources in Jordan can be considered as one of those resources related to deep circulation of meteoric )‫( نيزكي‬water along crack and fractures. They can be subdivided into two groups. The first: Is connected with natural springs in sandstone rocks Outcrops)‫ ( نتوءات‬. These springs from the main surface appearance of geothermal energy of Jordan. Other geothermal appearance such as boiling and mud pools are not observed thus there is no surface evidence that would indicate the existence of high temperatures at shallow depths. The second: Group of geothermal resources are these discovered during oil and groundwater exploration within the deep aquifers )‫( المياه الجوفية‬in the eastern deserts and along to eastern margin of the Dead Sea Rift. The location of nearly all the thermal springs and the hot boreholes are dictated by their proximity to the Dead Sea cracks. Most of the springs have temperature below 45°C except in two localities the temperature reaches up to 63°C (Zarqa Ma’in and Zara springs). 23 Thermal springs have been used for bathing and irrigation for many years. Recently several hotels (spas) were constructed at the thermal springs sites, for example Zarqa Ma’in spa. In the near future it is planned to use the available thermal water to heat greenhouses for growing various types of plants. Especially flowers and for fish farming, to provide the local market with fresh fish. 24 Geothermal Resources in Jordan: The geothermal investigations revealed a rich geothermal potential in low enthalpy resources spread amongst several geothermal fields. The geothermal gradient map of Jordan shows two distinct regions of high geothermal gradients up to 50 °C/km. - The first region is in immediate vicinity of the east Dead Sea escarpment, where many springs discharge thermal water originates from the Lower Cretaceous Sandstone forming three main geothermal fields. These fields are: Mukhiebeh thermal springs, Zara and Zarqa Ma’in thermal springs and Afra and Burbeitta thermal springs. - The second one is near the border with Syria and Iraq. In this region several thermal wells discharge water from the Upper Cretaceous Limestone. In both regions there are many wells (shallow and deep) discharging thermal water such as; shallow wells near Queen Alia airport, North shuneh well and Mukheibeh well field. 25 Typical Field Development Costs The percentage cost for geothermal power plant is shown in Fig. (11). Notes that, the dominant cost will in the wells drilling. 26