Geothermal Energy

I certify that this assignment is entirely my own work, except where I have given fully documented references to the work of others, and that the material in this assignment has not previously been submitted for assessment in any formal course of study.

This paper examines the present condition of geothermal energy and its conceivable enhancement. To meet this criteria the assistance of present foundations were examined referencing its quality and shortcoming both. Moreover the examination of the arrangement towards sustainable power source and individuals’ criticism are represented.

Renewable energy is the main choice to limit the CO2 emissions from the power plants. Solar,Wind,tidal and hydro-power are the diverse assets of renewable source of energy. Anyway there is a lot of utilization of non-renewable energy source in the development of a power plant and the utilization of machinery. Thus the net CO2 emission per unit of energy production characterizes which renewable energy source is better for the future. Hydro-power and Tidal energy can not be utilized in small scale however wind,solar and geothermal can be scaled down to desired requirement.

Why Geothermal?

The choice of renewable energy is predicated on certain factors like the supply of resources and technology, modification of climate throughout the year, government encouragement, duration of the need and environmental impacts. The geothermal energy eliminates the issue with climate change during the year and colonization of the energy resources. The spontaneous flow of heat is spreading radially from the core of the earth by conduction and convection processes and the energy resource is available for billions of years to come. However it’s easier to get access to the unlimited heat supply near active volcanoes. The technology is divided into two main aspects. One is deep geothermal (more than 1500 meter from the earth crust) and the shallow geothermal energy (limited to mostly 200m).The deep geothermal is majorly used for electricity production whereas shallow is employed for direct use and heat pumps.Initial investment, reluctance of state, motivation issue of public interest  the most important challenges towards plant procurements.

How geothermal energy is captured?

Presently, the most broadly perceived technique for catching the energy from geothermal sources is to take advantage of normally happening ‘hydro warm convection’ frameworks, where cooler water saturates Earth’s hull, is warmed up, and after that ascents to the surface. When this warmed water is compelled to the surface, it is a generally basic issue to catch that steam and use it to drive electrical generators. Geothermal power plants drill their very own openings into the stone to all the more adequately catch the steam.

There are three fundamental structures for geothermal power plants, all of which pull high temp water and steam from the ground, it, and after that arrival it as warm water to prolong the life of the warmth source. In the simplest design, known as dry steam, the steam goes specifically through the turbine, at that point into a condenser where the steam is condensed into water. In a second methodology, high temp water is depressurized or ‘flashed’ into steam which would then be able to be utilized to drive the turbine.

In the third methodology, called a paired cycle framework, the high temp water is gone through a warmth ex-changer, where it warms a second fluid, for example, ISO-butane in a shut circle. ISO-butane bubbles at a lower temperature than water, so it is all the more effectively changed over into steam to run the turbine.

The decision of which configuration to utilize is dictated by the asset. On the off chance that the water leaves the well as steam, it tends to be utilized straightforwardly, as in the main plan. In the event that it is boiling water of a sufficiently high temperature, a flash system can be utilized; else it must experience a warmth ex-changer. Since there are more boiling water assets than unadulterated steam or high-temperature water sources, there is more development potential in the binary cycle, heat ex-changer structure.

Direct use of geothermal heat. 

Geothermal springs can also be used directly for heating purposes. Geothermal hot water is used to heat buildings, raise plants in greenhouses, dry out fish and crops, de-ice roads, improve oil recovery, aid in industrial processes like pasteurizing milk, and heat spas and water at fish farms.

District Heating. Geothermal district heating systems are capital-intensive.

Major spendings are on initial investment costs, for production and injection wells, down-hole and transmission pumps, pipelines and distribution networks, observance and management. Simplified flow diagram of the geothermal district heating system of Reykjavik

Source: Gudmundsson, 1988.

equipment, peaking stations and storage tanks. Operating expenses, are however, relatively lower than in conventional systems, and comprises of pumping power, system maintenance, control and management. A crucial factor in calculating the initial cost of the system is the thermal load density, or the heat demand divided by the ground area of the district. A high heat density determines the economic practicability of a district heating project, since the distribution network is expensive. Some economic profit can be achieved by combining heating and cooling in areas where the climate permits. The load factor in a system with combined heating and cooling would be higher than the factor for heating alone, and the unit energy value would consequently improve.

Space Cooling.

Space cooling is a feasible option wherever absorption machines can be adapted to geothermal use. The technology of these machines is well known, and they are easily available on the market. The absorption cycle is a process that uses heat in place of electricity as the energy source. The refrigeration effect is obtained by utilizing two fluids: a refrigerant, that circulates, evaporates and condenses, and a secondary fluid or absorbent. For applications above 0 °C (primarily in space and process conditioning), the cycle uses LiBr as absorbent and H2O as refrigerant. For applications below 0 °C an ammonia/water cycle is adopted, with NH3 as refrigerant and H2O as absorbent. Geothermal fluids provide the thermal energy to drive these machines, though their potency decreases with temperatures lower than 105 °C.The various systems of heat pumps available permit us to economically extract and utilize the heat content of low-temperature bodies, such as the ground and shallow aquifers, ponds and so on.

Simplified schemes of ground source heat pumps. Agricultural Applications

The main agricultural applications of geothermal fluids consist of open-field agriculture and greenhouse heating. Thermal water can be employed in open-field agriculture to irrigate and heat the soil. The greatest hitch in irrigating with warm waters is that, to obtain any worthy variation in soil temperature, such huge quantities of water are required at temperatures low enough to prevent damage to the plants that the fields would be flooded. One potential solution to this problem is to adopt a subsurface irrigation system coupled to a buried-pipeline soil heating device. Heating the soil in buried pipelines without the irrigation system could decrease the heat conductivity of the soil, because of the humidity around the pipes, and consequent thermal insulation. The best solution seems to be to combine soil heating and irrigation. The chemical composition of the geothermic waters employed in irrigation must be monitored carefully to avoid adverse effects on the plants. The main benefits of temperature management in open-field agriculture are: (a) it prevents any damage ensuing from low environmental temperatures, (b) it extends the growing season, increases plant growth, and boosts production, and (c) it sterilizes the soil.

The most common application of geothermal energy in agriculture is, however, in greenhouse heating, which has been developed on a huge scale in several countries. The cultivation of vegetables and flowers out of season, or in an unnatural climate, can now draw on a widely tested technology. Various solutions are there for obtaining optimum growth conditions, based on the optimum growth temperature of each plant,and on the quantity of light, the CO2 concentration in the greenhouse environment, the humidity of the soil and air, and air movement. The walls of the greenhouse can be made of glass, fibreglass, rigid plastic panels or plastic film. Glass panels are transparent than plastic and will let in much more light, but will provide less thermal insulation, are less resistant to shocks, and are heavier and more expensive than the plastic panels. The simplest greenhouses are constructed using single plastic films, but recently some greenhouses have been constructed with a double layer of film separated by an air space. This system reduces the heat loss through the walls by 30 to 40 per cent, and thus greatly enhances the overall efficiency of the greenhouse. Greenhouse heating are often accomplished by forced circulation of air in heat exchangers, hot-water circulating pipes or ducts located in or on the floor, finned units located along the walls , or a combination of these methods. Exploitation of geothermal heat in greenhouse heating can significantly decrease their operating price, which in some cases account for 35 per cent of the product costs (vegetables, flowers, house plants and tree seedlings).

Farm animals and aquatic species, as well as vegetables and plants, can benefit in quality and quantity from optimum conditioning of their environmental temperature. In many cases geothermal waters could be used profitably in a combination of animal husbandry and geothermal greenhouses. The energy required to heat a breeding installation is about 50 per cent of that required for a greenhouse of the same surface area, so cascade utilization could be adopted. Breeding in a temperature-controlled environment improves animal health, and the hot fluids can also be utilized to clean, sanitize and dry the animal shelters and waste products.

Growth curves for some crops Effect of temperature on growth or production of food animals

Aquaculture, which is the controlled breeding of aquatic forms of life, is gaining worldwide importance nowadays, because of an increasing market demand. Control of the breeding temperatures for aquatic species is of much greater importance than for land species, as can be seen in, which shows that the growth curve trend of aquatic species is completely different from that of land species. By maintaining a ideal temperature artificially we can breed more exotic species, improve production and even, in some cases, double the reproductive cycle. The species that are usually raised are carp, catfish, bass, tilapia, mullet, eels, salmon, sturgeon, shrimp, lobster, crayfish, crabs, oysters, clams, scallops, mussels and abalone. Aquaculture also involves alligator and crocodile breeding, as tourist attractions and for their skins, which could prove a lucrative activity. Past experience in the United States has shown that, if its growth temperature is maintained at about 30 °C, an alligator can be grown to a length of about 2 m in three years, whereas alligators bred under natural conditions will reach a length of only 1.2 m over the same period. These creatures have been bred on farms in Colorado and Idaho for some years now, and the Icelanders are planning something similar. The temperatures required for aquatic species are generally in the 20 to 30 °C range. The size of the installation will depend on the temperature of the geothermal source, the temperature required in the fishponds and the heat losses from the latter. The cultivation of Spirulina is also a form of aquaculture. This acellular, spiral-shaped, blue-green micro-algae is frequently called ‘super-food’ because of its nutrient density; it has also been proposed to solve the problem of famine in the poorest countries of the planet, although at the moment it is being marketed as a nutritional food supplement. Spirulina is now being farmed in a number of tropical and sub-tropical countries, in lakes or artificial basins, where conditions are ideal for its fast and widespread growth (a hot, alkaline environment rich in CO2). Geothermal energy has been utilized effectively to provide the heat needed to grow Spirulina throughout the year in temperate countries. The entire temperature range of geothermal fluids can be exploited in industrial applications.

The different forms of utilization include process heating, evaporation, drying, distillation, sterilization, washing, de-icing and salt extraction. Industrial process heat has applications in nineteen countries,where the installations tend to be large and energy consumption high. Examples includes concrete curing, bottling of water and carbonated drinks, paper and vehicle parts production, oil recovery, milk pasteurization, the leather industry, chemical extraction, CO2 extraction, laundry use, diatomaceous Earth drying, pulp and paper processing, and borate and boric acid production. There are also plans to utilize low-temperature geothermal fluids to de-ice runways and disperse fog in some airports. A cottage industry has developed in Japan that utilizes the bleaching properties of the H2S in geothermal waters to produce innovative and much admired textiles for ladies’ clothing. In Japan they have also tested a technique for manufacturing a lightweight ‘geothermal wood’ that is particularly suited to certain types of construction. During treatment in the hot spring water the polysaccharides in the original wood hydrolyze, rendering the material more porous and thus lighter.

Economic considerations

The elements that have to be considered in any cost estimate, whether they are assigned to plant or operating costs, and the price of the ‘products’ of geothermal energy, are numerous and are complicated than for other forms of energy. All these elements must be evaluated carefully before a geothermal project is launched. We can only offer a few indications of a more general character, which, together with information on local conditions and on the value of the geothermal fluids available, should help the potential investor to reach a decision. A resource-plant system (geothermal power facility) consists of the geothermal wells, the pipelines carrying the geothermal fluids, the utilization plant, and frequently a re-injection system as well. The interaction of all these elements bears heavily on investment costs, and must therefore be subjected to careful analysis. To give an example, in the generation of electricity, a plant that discharges to the atmosphere is the simplest solution, and is therefore cheaper than a condensing plant of the same capacity. It will, however, require almost twice as much steam as the condensing plant to operate, and consequently twice as many wells to feed it. Geothermal Background 19 Since wells are very expensive, a condensing power plant is effectively a cheaper option than the discharge-to-atmosphere plant. The latter is, in fact, typically chosen for reasons apart from economy.

Geothermal fluids can be transported over fairly long distances in thermally insulated pipelines. In ideal conditions, the pipelines can be as long as 60 km. However, the pipelines, the ancillary equipment needed (pumps, valves and so on), and their maintenance are all quite expensive, and could weigh heavily on the capital cost and operating costs of a geothermal plant. The distance between the resource and the utilization site should therefore be kept as small as possible. The capital cost of a geothermal plant is usually higher, and sometimes much higher, than that of a similar plant run on a conventional fuel. Conversely, the energy driving a geothermal plant costs far less than the energy from a conventional fuel, and corresponds to the cost of maintaining the geothermal elements of the plant (pipelines, valves, pumps, heat exchangers and so on). The savings in energy costs should recover the higher capital outlay. The resource-plant system should therefore be designed to last long enough to amortize the initial investment and, wherever possible, even longer. Appreciable savings can be achieved by adopting integrated systems that offer a higher utilization factor (for example, combining space heating and cooling) or cascade systems, where the plants are connected in series, each utilizing the waste water from the preceding plant (for example, electricity generation + greenhouse heating + animal husbandry). In order to reduce maintenance costs and shutdowns, the technical complexity of the plant should be on a level that is accessible to local technical personnel or to experts who are readily available. Highly specialized technicians or the manufacturers should ideally be needed only for large-scale maintenance operations or major breakdowns. Finally, if the geothermal plant is to produce consumer products, a careful market survey must be carried out beforehand to guarantee an outlet for these products. The necessary infrastructures for the economic transport of the end product from the production site to the consumer should already exist, or should be included in the initial project.

ENVIRONMENTAL IMPACT

During the 1960s, when our environment was healthier than it is today and we were less aware of any threat to the Earth, geothermal energy was still considered a ‘clean energy’. There is actually no way of producing or transforming energy into a form that can be utilized by humankind without making some direct or indirect impact on the environment. Even the oldest and simplest form of producing thermal energy, that is, burning wood, has a detrimental effect, and deforestation, one of the major problems in recent years, first began at the point when our ancestors chop down trees to prepare their food and warmth their homes. Abuse of geothermal energy additionally affects the earth, however there is no uncertainty that it is a standout amongst the least contaminating types of energy.

In most cases the degree to which geothermal exploitation affects the environment is proportional to the scale of its exploitation .The table summarizes the probability and relative severity of the effects on the environment of developing geothermal direct-use projects. Electricity generation in binary cycle plants will affect the environment in the same way as direct heat uses. The impacts are possibly more prominent on account of conventional back-pressure or consolidating power plants, particularly in respect of air quality, yet can be kept within acceptable limits.Any adjustment to our condition must be assessed cautiously, in reverence to the significant laws and guidelines (which in a few nations are extreme), yet in addition on the grounds that an obviously insignificant change could trigger a chain of events whose impact is hard to completely assess beforehand. For example, a mere 2 to 3 °C increase in the temperature of a body of water as a result of discharging the waste water from a utilization plant could damage its ecosystem. The plant and animal organisms that are most sensitive to temperature variations could slowly disappear, leaving a fish species without its food source. An increase in water temperature may impair the development of the eggs of other fish species. If these fish are edible and provide the necessary support for a fishing community, then their disappearance could be critical for the community at large.

The principal recognizable impact on nature is that of boring, regardless of whether the boreholes are shallow ones for estimating the geothermal slope in the investigation stage, or exploratory/creating wells. Establishment of a boring apparatus and all the extra gear involves the development of access streets and a drilling pad. The last will cover a zone running from 300 to 500 square meter for a little truck-mounted apparatus (max. depth 300 to 700 m) to 1,200 to 1,500 square meter for a little to-medium apparatus (max. depth of 2,000 m). These activities will alter the surface morphology of the region and could harm nearby plants and wildlife. Blowouts can pollute surface water; blowout preventers ought to be introduced when boring geothermal wells where high temperatures and weights are involved. During boring or stream tests undesirable gases might be released into the air. The effect on nature brought about by boring for the most part closes once boring is finished. The following stage, establishment of the pipelines that will transport the geothermal liquids, and development of the usage plants, will likewise influence animals and vegetation and the surface morphology. The picturesque view will be changed, in spite of the fact that in a few territories, for example, Larderello (Italy) the system of pipelines confusing the field and the power-plant cooling towers have turned into a basic piece of the scene and are undoubtedly a celebrated vacation destination. Ecological issues likewise emerge amid plant task. Geothermal liquids (steam or heated water) for the most part contain gases, for example, carbon dioxide (CO2), hydrogen sulfide (H2S), alkali (NH3), methane (CH4), and follow measures of different gases, whose concentrations usually increase with temperature. For instance, sodium chloride (NaCl), boron (B), arsenic (As) and mercury (Hg) are a wellspring of contamination whenever released into the earth. Some geothermal liquids, for example, those used for region warming in Iceland, are fresh water, yet this is extremely uncommon. The waste water from geothermal plants additionally have a higher temperature than the earth and accordingly establish a potential thermal pollutant.

Air pollution may become a problem when generating electricity in conventional power plants. H2S is one of the main pollutants. The odour threshold for H2S in air is about 5 parts per billion by volume, and subtle physiological effects can be detected at slightly higher concentrations. Various processes, however, can be adopted to reduce emissions of this gas. CO2 is also present in the fluids used in the geothermal power plants, although much less CO2 is discharged from these plants than from fossil-fuelled power stations: 13 to 380 g for every kWh of electricity produced in the geothermal plants, compared with the 1,042 g/kWh of the coal-fired plants, 906 g/kWh of oil-fired plants and 453 g/kWh of natural gas-fired plants. Binary cycle plants for electricity generation and district-heating plants may also cause minor problems, which can virtually be overcome simply by adopting closed loop systems that prevent gaseous emissions. Discharge of waste water is also a potential source of chemical pollution.Spent geothermal liquids with high concentrations of synthetic substances, for example, boron, fluoride or arsenic ought to be dealt with, re-infused into the supply, or both. In any case, the low-to-moderate temperature geothermal liquids utilized in most direct-use applications contain low levels of synthetic substances,and the discharge of spent geothermal fluids is seldom a major problem. A portion of these liquids can frequently be released into surface waters after cooling. The waters can be cooled in special storage ponds or tanks to avoid modifying the ecosystem of natural bodies of water (rivers, lakes and even the sea). Extraction of large quantities of fluids from geothermal reservoirs may give rise to subsidence, that is, a gradual sinking of the land surface.This is an irreversible phenomenon, yet in no way, shape or form calamitous, as it is a moderate process distributed over huge zones. Over various years the bringing down of the land surface could achieve noticeable dimensions, now and again of the request of a couple of several centimeters and even meters, and ought to be checked methodically, as it could harm the stability of the geothermal structures and any private homes in the area. In many cases subsidence can be prevented or reduced by re-injecting the geothermal waste water. The withdrawal and re-injection of geothermal fluids may trigger or increase the frequency of seismic events in certain areas. However these are micro seismic events that can only be detected by means of instrumentation. Exploitation of geothermal resources is unlikely to trigger major seismic events, and so far has never been known to do so. The commotion related with working geothermal plants could be where the plant being referred to creates power.During the production phase there is the higher pitched clamor of steam going through pipelines and the occasional vent release. These are typically satisfactory. At the power plant the main noise pollution originates from the cooling tower fans, the steam ejector, and the turbine ‘hum’ . The clamor created in direct warmth applications is normally negligible.

Conclusions

If exploited correctly, geothermal energy could certainly assume an important role in the energy balance of many countries. In specific conditions even small scale geothermal assets are fit for taking care of various local issues and of raising the expectations for everyday comforts of little disconnected networks. In the first passages, we have featured the different advantages that can gather from using this type of energy. It would be a mistake, to assume that it can take care of all energy issues and that its abuse will be an achievement in any area and under any conditions. We certainly have no wish to discourage potential users of geothermal energy; quite the contrary, it is our mission and our wish to promote this energy form as much as possible. But at the same time we have to emphasize the importance of making a careful evaluation, with the backing of reliable data, of the physical, technical, economic and social situation, before taking any action. We should also like to recall a few other important points that must be considered beforehand. Exploitation nearly always triggers certain physical and chemical processes in the underground that, added to naturally occurring processes, could lead to the depletion of the geothermal resources. In order to avoid unpleasant surprises at a later date, it is therefore of crucial importance that we begin by modelling the geothermal system, to obtain some indication of how long our resources can be expected to last. The smaller the resources and the financial investment involved, the simpler this model will be. This preliminary evaluation and a rational programme for developing the resources should guarantee that the funds spent on research and construction of the utilization plants will prove a worthwhile investment. Even in the simplest, and admittedly somewhat rare, case of the utilization of thermal fluids emerging naturally at the ground surface (a hot spring), where no artificial extraction by wells or pumps is involved, a few preliminary studies should still be carried out on the quality of the fluid and on the surrounding hydrogeological conditions. Fluids that exhibit scaling or corrosion properties will create severe problems in a utilization plant within a short time. The extraction of large quantities of underground water or any other operations that modify the hydrological conditions in the area could also change the characteristics of the resource and even lead eventually to its depletion. The engineering of geothermal plants and the materials used in their construction are often more expensive than in plants that use traditional fuels. Similarly, maintenance operations can in some cases prove more expensive. The environmental impact of geothermal energy can be kept within fairly acceptable limits and is generally less harmful than that of other energy sources. Nevertheless, these effects cannot be ignored altogether, and their elimination or mitigation may require expensive operations and the installation of auxiliary plants. All these factors (the need for accurate preliminary evaluations, the higher cost of the utilization plants and of their maintenance, environmental impact), and others that we have already discussed, could weigh against geothermal energy in a balance of the pros and cons of different energy sources. Their influence on the final choice could, however, be reduced by basing the geothermal programme and operative decisions on the information and recommendations of qualified geothermal experts. It would be difficult to find geologists, engineers or teams of consultants willing to admit that they are incapable of planning and implementing a geothermal project. Yet the research and utilization of geothermal energy actually pose a series of specific problems that can be anticipated and overcome only by individuals with the relevant know-how and experience. There are many factors that must be considered before opting for the geothermal solution and launching a research and development programme, and not all of them are positive ones. Having warned you, as a potential user, of the pitfalls lying in wait for the unwary, we feel that it is only right that we also present some of the positive aspects that make geothermal energy such a valuable asset for many nations: • Geothermal is a ‘national’ energy that could, in favourable circumstances, lead to a reduction in the import of the more expensive conventional fuels or, on the contrary, an increase in the export of the latter.

• In certain areas and in certain situations geothermal energy may be the only energy source available.
• The ‘fuel’ itself costs nothing.
• The utilization of geothermal energy contributes to the reduction of greenhouse gas, as recommended by the UN Framework Convention on Climate Change (Kyoto, 1997).