The main problems of today's society are; the increasing demand in energy, a possible source lack and environmental pollution. Therefore a lot of money is put in in research to find different means of producing energy using Earth's natural resources like wind, sunshine and the sea. This record is a report on Ocean Thermal Energy Conversion (OTEC) which might be the response to the energy and environmental problem our world has to face. A simple explanation and an launch to the types and key points of operation of closed pattern, open routine and hybrids of OTEC technology is given in this survey. Emphasis is shown on the cross types cycle which includes advantages in comparison to other single purpose vegetation for fresh drinking water production or electricity generation. The procedure of desalination of sea drinking water can prove vital for countries that have water shortage. This report is targeted on the technology that would be suited for a hybrid cycle OTEC plant situated in Cyprus.
Contents
Table of Figures
1. Goals and Objectives
The goal of this project is to investigate the characteristics of an dual purpose vegetable for simultaneous production of desalinated normal water and energy. An attempt will be produced to convey the conditions and standards for adjusting the percentage of desalinated drinking water to power production and also how this percentage is affected by way of a variant in seawater heat and pressure. In addition, different design things to consider of the cross cycle particularly suited to an OTEC vegetable operating in Cyprus will be talked about.
2. Introduction
''The ocean surface absorbs more heating from the sun in one square mile than could be produced by losing 7000 barrels of olive oil'' (Avery & Wu, 1994). Which means solar energy absorbed each day by the top waters may be used to provide a renewable, zero-emission creation of electricity. Ocean Thermal Energy Alteration or OTEC is the technology that meets the technological requirements and it is economically feasible for harvesting the solar energy assimilated by the ocean. OTEC plants make use of the thermal gradient that is out there between your surface of the ocean and the deep frosty waters to start a power producing pattern. The warm tropical surface waters (at a temperature of 22C) and the deep ocean waters (at a depth of 1000m a heat of 4C) are being used as a source of thermal energy to vaporize and condense the working smooth of a turbine-generator system. The thermodynamic routine for this heating engine is the called the Rankine routine. OTEC systems maybe either shut cycle, open cycle or a combo of both also known as hybrid systems. Within the closed routine, seawater is employed to vaporize and condense a working liquid, such as ammonia, which drives a turbine-generator in a closed down loop, producing electricity. On view cycle, surface drinking water is flash-evaporated in a vacuum chamber. The ensuing low-pressure steam can be used to drive a turbine-generator. Freezing seawater is used to condense the vapor after it has transferred through the turbine. The wide open cycle can, therefore, be configured to create fresh normal water as well as electricity. The cross types cycle involves both the closed down cycle system and the open up cycle system. The machine is interconnected and arranged in such a manner that the ex - pattern provides electricity and the last mentioned yields desalinated water. Such a system has encouraging potential in countries which have issues with insufficient water.
3. Literature Review
3. 1 Closed Circuit OTEC System
3. 1. 1 Theory of Operation
The closed pattern was first suggested in 1881, by D'Arsonval in France, and was demonstrated in 1979, when a little plant mounted on a barge off Hawaii (Mini-OTEC) produced 50 kW of gross vitality, for several calendar months, with a world wide web output of 18 kW (Vega, 1992). The principle of operation of the sealed OTEC system is confirmed in physique 1 below.
Figure : Rule of operation of your closed cycle OTEC system (Country wide Renewable Energy Laboratory)
In the shut down pattern, the OTEC system utilizes the warm surface seawater to vaporize an operating fluid, such as ammonia, which moves through a heat exchanger (evaporator). The vapor expands at moderate pressures and drives a turbine which is coupled to a generator that produces electricity. The vapor then goes by through another temperature exchanger (condenser) where it is condensed back to a liquid using cold seawater from pumped from the ocean's depths by using a cold water tube. A pressurizer or feed pump is utilized to pump the condensed working fluid back to the evaporator to complete the circuit, producing continuous vitality generation as long as the tepid to warm water and cold water continue to stream.
The sealed OTEC cycle is actually exactly like the conventional Rankine cycle used in steam engines, where the steam is condensed and came back to the boiler after driving a car a piston or steam turbine, OTEC differs by using a different working fluid and lower pressures and heat (Avery & Wu, 1994). The four functions of the ideal Rankine cycle are the following:
1. Isentropic growth (Turbine)
2. Isobaric high temperature rejection (Condenser)
3. Isentropic compression (Pump)
4. Isobaric heating addition (Evaporator)
3. 2 Open up Routine OTEC System
3. 2. 1 Rule of Operation
The open circuit concept was initially proposed in the 1920's and proven in 1930, off Cuba by its inventor, a Frenchman by the name of Georges Claude (Vega, 1992). In the wild routine, the warm seawater is the working fluid. The warm seawater is pumped into vacuum pressure chamber where it is ''flash''- evaporated to create steam at an absolute pressure around 2. 4kPa. The vapor passes through a minimal pressure turbine which in turn drives a generator to create electricity. The heavy steam exiting the turbine flows is condensed by chilly seawater pumped from the ocean's depths through a cold-water pipe. In this particular open cycle configuration a surface condenser can be utilized and then the condensed vapor remains separated from the cold seawater and a way to obtain desalinated water. Amount 2 below shows the rule of procedure of the wide open routine OTEC system.
Figure : Rule of operation of any open cycle OTEC system (Country wide Renewable Energy Lab)
3. 2. 2 Negatives of the Open Cycle Configuration
This kind of configuration produces less electricity than the shut cycle choice but it is of interest in places where normal water shortage can be an issue. Furthermore, the very low pressure at which the system performs means that associations must be carefully sealed to prevent atmospheric air from stepping into the system, that could bring the operation to a halt. Another disadvantage compared to the closed circuit system is that the specific volume of the low-pressure steam is very large compared to the pressurized working fluid used in the closed routine system. Therefore the components must have large stream areas to ensure that vapor flow will not reach a higher enough velocity which could harm the turbine. Also, a huge turbine must accommodate the high volumetric move rates of the low-pressure heavy steam in order to create enough electrical energy.
3. 3 Cross types Cycle OTEC System
3. 3. 1 Basic principle of Operation
A hybrid circuit combines the features of both closed-cycle and open-cycle systems. In a cross types OTEC system, warm seawater gets into vacuum pressure chamber where it is flash-evaporated into heavy steam, which is comparable to the open-cycle evaporation process. The vapor vaporizes the working smooth of an closed-cycle loop on the other hand of any ammonia vaporizer. The vaporized fluid then drives a turbine that produces electricity. The vapor condenses within the heat exchanger and desalinated water. Amount 3 can be an illustration of the hybrid cycle OTEC system.
Figure : Theory of operation of a hybrid pattern OTEC system (Country wide Renewable Energy Lab)
The electricity made by the system can be delivered to a computer program grid or used to create methanol, hydrogen, enhanced metals, ammonia, and similar products.
3. 4 OTEC Components
The main the different parts of an OTEC system are referred to below- namely, temperature exchangers, evaporators, turbines and condensers.
3. 4. 1 Temperature Exchangers for Closed Routine OTEC Systems
The design of temperature exchangers to meet professional requirements for efficiency, durability, ease of production, packaging, system integration consistency and cost has led to an extensive technology devoted just to this subject. The special requirements of OTEC can be satisfied by heat exchangers with different operating characteristics than normal designs. Also, research has been done to improve the overall heat copy coefficients in ways that will reduce the heat exchanger costs per kilowatt of world wide web power generated. This has resulted in the investigation of varied potential types of high temperature exchangers with features designed to be best for OTEC applications. Some of these are briefly defined below.
Shell and Pipe Heat Exchangers: This is the most widely used type of heating exchanger for commercial evaporator and condenser applications. As the name means, this type consists of a shell and a lot of money of tubes inside it. Specifically for OTEC applications, normal water flows through the tubes and the working substance flows across the tube bank in the middle section. In conventional ones, seawater moves through the pipes, and the working fluid evaporates or condenses in a shell around them. This design can be enhanced by using fluted pipes: the working smooth flows into the grooves and over the crests, creating a thin film that evaporates more effectively.
Plate Warmth Exchangers: A different type of heat exchanger that would offer advantages in performance and cost is the plate heating exchanger. The plate type temperature exchanger is more compact than the shell and tube configuration. In this type, the seawater and the working smooth flow in different channels separated by parallel plates. Suitable manifolds are being used to guide the fluid in to the proper programs. With this kind of high temperature exchanger the gains in heat copy coefficient can be up to 100-200%, weighed against the conventional shell and pipe designs.
The material which warmth exchangers are made of is very important in terms of cost and performance. Titanium was the original material chosen for closed-cycle temperature exchangers since it resists corrosion. However, it can be an expensive option for vegetation that use large high temperature exchangers. Therefore other cheaper materials such as corrosion-resistant copper-nickel alloys may be used to protect system and cold-water pipes, but are not compatible with ammonia, the most frequent working fluid. The right solution is aluminium which works well under sea conditions and results reveal that picked aluminium alloys may keep going twenty years in seawater (Thomas & Hillsides, 1989). Marine organisms and slime can quickly grow on floors exposed to warm seawater- a accumulation known as biofouling- which reduces the heat copy efficiency. Laboratory tests point out that the addition of chlorine in the pipes can prevent biofouling (Panchal, Larsen-Basse, & Little, 1984).
3. 4. 2 Evaporators for Open Routine OTEC Systems
Open-cycle flash-evaporators include those with open-channel flow, slipping films, and dropping jets. These classic evaporators typically perform to within 70% to 80% of the maximum thermodynamic performance at acceptable hydraulic deficits. The scientific development resulted in a vertical-spout evaporator that can perform to within 90% of the thermodynamic limit (Country wide Renewable Energy Lab). In this evaporator, water is drawn upward through a vertical tube (a spout) and violently sprayed outward by escaping steam (Bharathan & Penney, 1984). To enhance performance, the aerosol may fall on monitors that further break up the droplets and increase the evaporation rate. To avoid pressure reduction, the evaporator has simple absorption and leave systems that distinguish the steam from the release. Steam remains through the machine, and the rest of the seawater is discharged from underneath of the evaporator. Violent blinking in a spout evaporator causes seawater droplets to be entrained by the vapor. If they are not removed, these droplets can cause erosion and stress-corrosion breaking in turbine blades and contaminate the desalinated normal water discharge as well. Transferring the steam through the commercially available mist eliminators used in the process industry removes a sufficient level of these seawater droplets (Bharathan & Penney, 1984).
3. 4. 3 Turbines
In the open cycle process, after the droplets are removed, heavy steam flows through large, low-pressure turbines, going into at a pressure around 2. 4 kPa. These turbines must have the ability to handle the top steam flows essential to create a significant amount of electric power. Multistage turbines used in nuclear or coal-fired ability plants are already available. The low-pressure levels of these turbines typically operate at conditions near to those needed within an open-cycle OTEC herb. In close routine OTEC systems the turbine needs not be so large because it works together with vapor at enhanced pressures.
3. 4. 4 Condensers for Open Circuit OTEC Systems
Once the heavy steam goes by through the turbines, it could be condensed in direct-contact condensers or surface condensers. A surface condenser consists of an intermediate brick wall, which is absent in direct-contact condensers and therefore the latter provides more effective condensation (Bharathan, Parsons, & Althof 1988). In a single design-a two-stage condenser (see shape 4 below) developed at Solar Energy Research Institute-cold seawater is sent out through two open-ended vessels filled with a commercially available structured packing materials. About 80% of the heavy steam is condensed as it flows through the first vessel in the same direction as the chilly seawater. The remaining vapor is routed into the bottom of the second vessel and moves through it in the opposite route to the seawater. At the top of the second vessel, a vacuum system pumps out the non-condensable (inert) gases along with any uncondensed steam (National Renewable Energy Lab).
Figure : Illustration of the two stage condenser (National Renewable Energy Laboratory)
Surface condensers keep carefully the cooling seawater separate from the put in vapor during condensation. Through the use of indirect contact, the condensers produce desalinated drinking water that is relatively free of seawater impurities. The top condensers considered for use in OTEC systems act like those found in conventional power crops; however, these surface condensers must operate under lower stresses and with higher levels of non-condensable gases in the vapor. These non-condensable gases which are present in the wild circuit system are released from the seawater when it's subjected to low pressures under vacuum and are namely oxygen, nitrogen and carbon dioxide. Air can also get into the open circuit vacuum chamber through leaks therefore decent building techniques can decrease the rate of air leakage to very low levels. These gases, if are not removed from the vacuum vessel, they can build up enough pressure to stop evaporation. An exhaust compressor is usually used to remove these non-condensable gases. The compressor however requires about 10% of the full total power made by the machine (Parsons, Bharathan, & Althof, 1985).
4. Methodology
In this section, pending work and project plan brief summary will be defined. For the final project, the literature review might be broadened a little more to add the many types of working essential fluids that can be used. Furthermore, a section describing the thermodynamics behind the procedure of the OTEC routine (Carnot efficiency and Rankine cycle) will be added, accompanied by a more natural calculation on the OTEC genuine thermal efficiency, online power output and production of desalinated drinking water. Once these computations are completed, a sensibly concise section on the use of solar heating up on OTEC will be written. Then a study on the result of increasing normal water inlet temperatures on power generation and fresh normal water creation will be completed. In addition, the effect of a rise in pressure on electricity technology and fresh water production may also be included. Computational software such as 'Wolframalpha' or 'Matlab' will help in determining the partnership between variable temperature and pressures on power technology and desalinated normal water creation. If time allows it, simulation software such as 'Simul8' will be utilized to find the ideal conditions for the cross cycle OTEC place. A section of discussion and examination of results will observe detailing the obtained results, including suggestions for improving the look. Finally, a section explaining by what means the proposed hybrid cycle OTEC place is ideal for procedure in Cyprus. This portion includes the economic factors engaged (dependence on finance, administration subsidies etc. ), disadvantages and benefits such a herb will have on the island.
5. Gantt Chart
The Gantt Graph below represents the program for conclusion of the job including important deadline schedules for presentations and distribution of the article.
Figure : Shape exhibiting the Gantt Chart
6. Conclusion
Water and energy are essential for human life. A reliable supply of energy and normal water is essential for enhancing the living standard and economic steadiness of any country, especially countries which face water lack problems like Cyprus. The purpose of this record is to demonstrate the characteristics of the dual goal OTEC vegetable and through various design things to consider find the most effective conditions for such a flower to be as beneficial and as efficient as is feasible and at the same time be economically viable to attract investors.
