We have selected Geothermal Energy as this group topic because it was interesting to learn about existing renewable energy alternatives. As us young people are very concerned about the environment and this was a great opportunity to know about how energy can be obtained from earth’s core. This report consists of four parts: system design and operation; investigation of the energy source used, how that energy is converted, losses incurred during conversion and the environmental impact of using such energy; the advantages and disadvantages of the conversion process; and the feasibility of using bio-power as a source of electricity in Trinidad and Tobago in the future.
For over 4 billion years, the earth has been creating energy from its core. It has been projected that the Earth’s core produces a similar temperature to the sun’s surface. Geothermal energy is energy resultant from the earth’s internal heat or thermal energy. The energy acquired is dependent on the depth at which it is harnessed as well as the method used.
Beneath the earth’s crust contains rock and fluids, this is where the thermal energy is sequestered. This thermal energy is produced because of abrasion or sliding of continental tectonic plate boundaries as well as the radioactive decay of elements such as thorium and uranium. If utilized successfully, these repositories of steam and hot water can produce energy which can further be employed into electricity, heat, etc. Geothermal energy is considered a renewable resource because its source is immeasurable, the earth is constantly producing thermal energy ensuring an inexhaustibly sustainable natural resource. The use of geothermal energy is not dependent on the utilization of fossil fuels which has been implicated in a plethora of environmental issues.
Geothermal energy uses may vary but they are sectioned into three groups: Geothermal Heat Pumps (GHPs),direct-use applications, and electric power generation. Direct-use applications are most common as there isn’t a need for any specialized equipment. They utilize low-temperature geothermal assets, between to 50 and 150 degrees Celsius or to about 122- and 302-degrees Fahrenheit. Geothermal heat pumps exploit reasonable temperatures, between 10 to 16 degrees Celsius or to about 50 to 60 degrees Fahrenheit at the first 300 metres of the surface. The electrical power generation requires specialized equipment as well as competent personnel. There are three systems by which electricity can be produced: flash steam, dry steam, and binary cycle.
System design and operation
Geothermal energy has three (3) different plant designs by which the energy is taken from the earth and converted. These include:
1. Dry Steam Geothermal Plant
2. Flash Steam Geothermal Plant
3. Binary Cycle Geothermal Plant
Some of the equipment associated with these three (3) plant designs are:
3. Heat Exchangers (shell and tube or plate)
5. Cooling Towers (wet, humid or dry)
7. Production Well
8. Injection Well
10. Power Cycle Pumps (centrifugal multistage)
In the dry steam geothermal process, you have underground steam flowing directly to a turbine from the production well to drive a generator which produces electricity.
In the flash steam geothermal process, a pump pushes pressurised hot fluid into a flash tank at the surface where it cools. As it cools, the fluid flashes or vaporize into a vapour. The vapour then drives a turbine which then powers a generator.
In the binary cycle geothermal process, it uses two (2) types of fluid. The hot fluid from underground heats a second fluid called a heat transfer fluid in a giant heat exchanger. The second fluid has a much lower boiling point that than the first fluid, so it flashes into a vapour at a lower temperature. When the second fluid flashes, it spins a turbine which drives a generator.
It is reminded that the fluids that aren’t used or flash within the system is transferred back into the geothermal reservoirs via the injection wells.
Some other equipment found in a geothermal power plant are:
1. Industrial silencers
2. Blow off silencers
3. Industrial mufflers
4. Exhaust silencers
5. Pipeline compressor station silencer
The equipment listed above all play an integral part in reducing unwanted negative noise which can be created by the wide range of industrial processes.
Investigation of energy source, conversion and losses incurred
Geothermal energy is the use of heat which comes from deep beneath the earth’s surface. The earth’s outer layer is fragmented into portions which is called Tectonic Plates. In geographical theory states, lithosphere of the earth’s surface is separated into many amounts of plates which drift and independently travel over on the earth’s mantle. Near the edges of the tectonic plates’ magma comes very close to the earth’s surface, where which many volcanoes occur and erupt. Rocks goes through a slow deterioration of radioactive atoms in the earth’s core, with this process the heat is absorbed from the rocks deep underground which have the highest temperatures. Geothermal Energy comes deep beneath the earth’s surface, which engineers have industrialized many ways to generate power from the geothermal wells which has been drilled into the ground and pumping the steam or underground water that is hot or to the earth’s surface. People now can use this clean renewable energy to power and heat their homes with use of stable temperatures to heat and cool buildings.
Generating geothermal electricity, wells are made into the underground reservoirs up to miles or kilometres deep or more just to tap steam and hot water to power the turbines which are connected to electricity generators. There are three types of geothermal power plants:
• Dry steam plants
• Flash steam plants
• Binary cycle plants
Dry Steam plants were the very first geothermal power generating plants to be built, by Lardarello in Italy in 1904. Energy is converted, or electricity is generated using hydrothermal fluids which is water that is naturally heated or, primarily steam. With this steam obtained from the underground reservoir it travels directly into the turbine, this powers the generator which produces electricity. The problem with this conversion from steam to energy/electricity have a few losses occurred such as excess steam and little amounts of gases emits from these plants.
In Flash steam plants they are the most common geothermal power generating plants. Hot water at temperatures larger than 360°F (182°C) is pumped under extreme pressure into a tank at the surface till the pressure is lowered. During this process the water changes into steam or vaporized, this can then drive the turbine, which can power the generator giving you energy and electricity into buildings. If there’s any liquid remaining in the tank it can be vaporized or flashed again but with this extra process more energy is extracted.
Binary cycle plants are closed-loop structures and, differs from Flash geothermal steam and Dry geothermal steam plants, the reason for the difference is that the hot water or steam from the underground reservoirs never encounters the turbine or generator. Geothermal fluid with a low temperature about below 400°F and binary/secondary fluid with a low boiling point in which that water passes through a heat exchanger. The binary fluid vaporizes from the heat from the geothermal fluid, which then operates the turbines creating power in the generators.
Factors affecting energy conversion and losses incurred during conversion are:
• Non-condensable gas (NCG) content
• Heat loss from equipment, turbine and generator efficiency
• And power plant load e.g. fans
When cooling the water or steam in these geothermal plants, the condenser requires equipment such as fans and pumps. In cooling towers, they consume as twice as much more electricity which can be at a disadvantage. There also heat lost in pipes due to the transport of hot water or geothermal fluids.
Environmental impact using Geothermal Energy
The environmental impacts on using geothermal energy are:
• The water use and quality
In these plants water have major impacts on the system since hot water from the reservoir are have high amounts of sulphur and minerals, the water can be pumped directly back to the reservoir after its used from generating energy or electricity, to prevent contamination. Geothermal plants need gallons of water to generate energy, freshwater or geothermal fluid can be used for cooling, and using geothermal fluid rather freshwater can reduces the plant’s general water impact.
• Air Pollutions
In some Geothermal plants can let out small amounts of air pollutants such as Carbon Dioxide, Hydrogen Sulphide, Ammonia, Sulphur Dioxide, Mercury emissions. As these are cause by Open-loop systems in geothermal plants whereas the closed-loop system is not all exposed to the atmosphere. These toxins can cause lung and heart diseases and cause acid rain which can harmfully damage crops and soils and can run off to streams and lakes affecting the aquatic life. Even though the plant has Scrubbers which can reduce the air emissions, but the scrubbers can also produce sludge that capture and comprises with toxic compounds.
• Land Use
In some cases, the land surface sinks and its sometimes caused by the deduction of hot water from geothermal reservoirs. Geothermal plants are sited on geological locations which can have greater stages of an earthquake. Earthquake risk can be minimized by locating the plants a suitable distance away from the fault lines. If when a geothermal plant is located at a near profoundly inhabited area, constant monitoring and communication with the local societies necessary.
• Global Warming Emissions
In the process of drilling a well for kilometres or miles into the earth and pumping hot water can release little source of Carbon Dioxide whereas coal generated electricity produces more CO2 in the atmosphere.
Advantages and disadvantages
Geothermal energy systems are to be told the most efficient alternating energy source and here are some advantages of Geothermal Energy:
1. Geothermal Energy is environmentally friendly
The power generated to create electricity or energy can be obtained without the use of burning fossil fuels like gas or oil and even coals. In the Geothermal sector there’s no amounts of emissions especially in the closed cycle operations also known as the Binary Cycle plants, as this is very Eco-friendly.
2. It is a reliable Source of alternating renewable Energy
Yes, Geothermal energy is renewable but other than wind, solar or bioenergy it is neither dependant on the sun nor it is dependent on the wind. Geothermal source is beneath us and that energy is accessible all year long.
3. Little or no maintenance to the system/plant
Since geothermal structures are protected on the inside of the plant, the maintenance is at a low giving a geothermal heat pump to last for years creating a relatively high life span which have warranties to about 30 to 50 years of service.
4. Geothermal systems have a high efficiency
Even though the Geothermal system generates electricity some of the equipment uses electricity also e.g. the heat pump systems uses less electricity than any conventional heating or cooling systems.
5. In Economic factors
Geothermal energy is an independent renewable energy source which is reducing the intake of fossil fuels, gas and crude oil. With this in mind the carbon footprint stems into a reduction.
Some disadvantages of Geothermal Energy:
1. Environmental problems
Even though Geothermal Energy have the status of being an Eco-friendly Energy source there are still some minor issues when it comes to the environment. When drilling the well for extraction of hot water and steam from the reservoirs, it releases greenhouse gases like methane, carbon dioxide and many other air pollutants, Although, the amount of greenhouse gases released are far lower than fossil fuels.
2. High Costs for Geothermal plants
Even though geothermal systems generate power it is at a disadvantage to build or to install at homes where there is a high initial cost for equipment and installing and drilling near one’s home will be a hassle which put the home owner in more expense.
3. Land and Space Requirements
Other than it’s costly to install but finding land and space would be even harder for drilling and instalment of a Geothermal system or even a plant.
4. Possibility of future outcomes of reduction of Geothermal Sources
Notwithstanding being considered as a reliable and renewable alternating energy, there may be chances at specific locations of Geothermal plants may have some cooling down over the years which would make obtaining geothermal energy problematical in the future.
Feasibility for Trinidad and Tobago in the future
Geothermal is a renewable, reliable and alternating energy source which can be very useful on hot sunny days. It can also reduce the amount of greenhouse gases emitted into the atmosphere which will slow down the process of global warming. Geothermal energy is much cheaper compared to using fossil fuels to generate electricity and will be easy to implement in Trinidad and Tobago to cut down cost and dealing with the economic crisis its facing. Even though countries abroad implement geothermal energy for heating it can also take away the heat in exchange for cooling at hot periods, and in this country, we may have two seasons and its almost hot daily it doesn’t mean we cannot have some enjoyment of cooling systems at our homes with the works of geothermal energy.
In Trinidad and Tobago the energy consumption rate are at an all-time high and our dependence on fossil fuels have become mind boggling. The implementation and utilization of geothermal energy can be a more sustainable avenue, which ensures the fulfilment of energy needs for generations to come. The islands of the Lesser Antilles, which includes Trinidad and Tobago are immensely susceptible to volcanic activity. This can be beneficial because high levels of volcanic activity are proportional to high levels of geothermal energy which can then be extracted.
Our reliance of fossil fuels has contributed to our continued paralysis of the environment, the shift to geothermal energy decreases this as it is environmentally friendly and is not dependent on the utilization of fossil fuels. It is also naturally replenished which makes it renewable. The earth is constantly and continuously producing thermal heat thus creating an inexhaustible supply.
However, the capital investment required for the implementation of the plant is high. There is specialized equipment which must be utilized, and staff must be employed as well. There are no economic incentives which makes the economic aspect of setting up a plant extremely precarious. In Trinidad and Tobago, the economy is unstable, so it would be difficult to implement a geothermal plant. Also, there is also a potential environmental risk as there is a vast amount of greenhouse gases below the surface of the earth. These can potentially enter the atmosphere and emissions are particularly higher in areas where geothermal plants are present.