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Showing posts with label Kalina Cycle. Show all posts
Showing posts with label Kalina Cycle. Show all posts

Friday, May 11, 2012

Solar thermal for base load power

The city of Athens hosted its oldest tradition of lighting the Olympic torch for the 2012 London Olympic Games on Thursday in Olympia. The torch was lit by solar power; using parabolic mirror to redirect the sun’s light in order to light the flame with purest natural light. The thermal energy of sun’s light can be powerful when focused to a point and it can reach a temperature more than 600C.The parabolic trough with reflective mirror focuses the sunlight on the tube called ‘collectors’ in which a fluid with high boiling point is circulated. The hot fluid in turn is used to convert water into steam in boiler. The hot oil transfers its heat to the water in a heat exchanger and returns back to the parabolic trough. It is a closed circuit system. The hot oil at 390C generates steam at 370C at 100 bar pressure, which is used to run a HP steam turbine. The standard steam condensing cycle generates power similar to fossil fuel fired power plant. A 50 Mw Trough plant in Israel (Negev Desert) is already in operation. The capacity of such plant can be easily expanded by adding modular parabolic troughs and collectors and the plant can be designed to meet specific power demands. This is a straight forward method to generate base load power using standard steam cycle. The efficiency of such system will be 41% maxium.However recently few companies are trying use a combined cycle. This increases the solar to heat efficiency from 50.5% to 53.6%.This nominal 50Mw power plant generates a total peak power of 57.10Mw using a solar collection area of 310,028m2 with annual solar to electrical efficiency at 16.3% using a water cooled condenser in the steam cycle. The cost of energy works out to $0.23 to $ 0.25 /kwhrs. By using a central solar collection tower (Heliostat) and bottoming with Rankin/kalina cycle ,it is estimated that the total installed cost can be reduced by 10%.The system can be configured from 2Mw up to 100Mw using both trough and tower system. The system can be installed in any remote, arid locations using air condensers, where cooling water is a problem. The estimated annual specific energy cost is less than 6 cents/kwhrs, comparable to low cost fossil energy but with zero pollution and with zero carbon emission. Solar thermal is a potential clean energy of the future for many countries around the world with yearlong sunshine with good intensisty.The solar thermal energy can also be used in many process industries where thermal heating is required. Solar salt pans can use solar thermal energy very efficiently to reduce their production cycle. The concentrated brine can be used as a circulation fluid in solar collectors and also be used to generate power using low heat technologies like Kalina cycle, because concentrated salt brine can store thermal heat. Gemasolar power in Spain is a base load power station supplying power for 25,000 homes 24x7 using molten salt (60% KNO3+40% NaNO3) as a thermal storage medium instead of batteries. Nine plants were built in 1980 in Mojave Desert with a combined capacity of 354 Mws. Other examples of solar base load power plants are Blythe solar with capacity of 968Mw at Riverside County, California and Ivanpah power station with capacity of 370 Mw capacities in US,both under construction. Large scale solar base load plants are no longer a theory but a commercial reality. Direct solar lighting is also being introduced using fiber optics. The sun light is collected at a central point and directed through fiber optics to various rooms inside the building supplying direct sun light. This saves not only electricity but also provides natural light to work places because human body requires certain amount of UV light exposure. Solar energy is here to stay and offer various clean energy solutions in the future.

Tuesday, February 28, 2012

Ocean-the largest source of Clean energy

Water makes up seventy one percent of the planet earth and ninety eight percent of it constitutes the ocean. It is a single source of water for all forms of life on earth and it also plays an important role in climate changes in the atmosphere. Ocean is the biggest heat sink and absorbs sun’s heat and also a carbon sink absorbing excess carbon dioxide from atmosphere. The surface temperature of seawater is warmer than the temperature at the bottom of the ocean. Sun supplies solar energy to the ocean. In fact the water temperature in Deep Ocean is about 15-20C less than the surface temperature, and it is used as a working fluid to cool buildings by evaporative cooling without using any electricity like commercial air-conditioning. OTEC (ocean thermal energy conversion) system is a potential method of generating power using the temperature gradient between ocean’s surface water and ocean’s deep water. A temperature difference, as small as 15 -20C is sufficient to generate power using Kalina cycle, similar to geothermal energy systems. Commercial plants using this technology are already in operation in few countries. The biggest advantage with open cycle ocean thermal energy conversion system is the fresh water (desalinated ocean water) as a by-product. This technology is unique because it can generate not only power but also drinking water from sea without polluting the air with greenhouse gas emissions. In fact this technology should be deployed commercially is many islands around the world, where there is always a demand for power and drinking water. “Water, water, everywhere but not a drop to drink”. It is the situation in many islands and many parts of the world. Islands like Maldives and Mauritius should adopt this technology to generate power and supply drinking water without burning fossil fuels like diesel or setting up desalination plants. Of course, the economy of scale and finance is an issue in many islands. PNG (Papua New Guinea) is one of the biggest islands in Pacific Ocean where there is s severe shortage of power and water. The country is endowed with rich minerals, oil and gas but the basic necessity like power and water are in short supply. OTEC will be an ideal solution for such islands. Fresh water supply is going to be a major issue in parts of the world due to global warming and climate changes. In countries like India, drinking water is in short supply and a number of seawater desalination plants are coming up. Bottled waters are expensive and unaffordable to a common man. This will only increase the power requirements in the country when there is already a massive shortage of power. OTEC is an ideal solution for India with its long coastal line. One of the major issues with current power generation technologies is the pollution. In any combustion process involving fossil fuel the combustion products like carbon dioxide, carbon monoxide and Oxides of Nitrogen (the greenhouse gases) will contribute global warming. What is the level of such emission and how fast the globe is warming is a futile argument. The pollution can be small in term of PPM (parts per million) but the cumulative effects over several decades is a major issue and that cannot be simply dismissed. There are many places where the Arsenic content in drinking water is above certain acceptable levels (only in ppms) but such small excess cause debilitating health conditions. This is the same argument with greenhouse emission and global warming. It can be gradual and insignificant but it will reach a tipping point and dramatic changes can happen all of a sudden. Nature has got its own mechanism to adjust any imbalances and maintain certain equilibrium. But humans cannot take them for granted and pollute the air and water indiscriminately. There will be a price to pay. Ocean is the largest and inexhaustible source of Hydrogen. Currently Caustic soda plants use sodium chloride (salt) brine as the raw material for conversion into Caustic soda; the by-products are Hydrogen and Chlorine. Caustic soda plants are currently using Hydrogen as a fuel or use to manufacture Hydrochloric acid. They can generate onsite power using Hydrogen to offset their energy cost. In both water electrolysis as well as brine electrolysis, Hydrogen is a product and Ocean water is the largest source of such Hydrogen. In fact countries should generate Hydrogen using desalinated water and OTEC power. The stored Hydrogen is a stored energy that can be used as and when required. That is why we believe ‘water and energy are two sides of the same coin’.