Read this term paper to learn about:- 1. Introduction to Fossils and Alternative Energy Sources 2. Global Power Generation Scenario 3. Carbon Dioxide Generation by Fossil Fuel based Power Plants 4. Renewable Sources for Power Generation 5. Nuclear Power 6. Mini or Micro-Generation Facilities.
Term Paper # 1. Introduction to Fossils and Alternative Energy Sources:
The basic science has taught us that ‘the energy cannot be created nor destroyed but can be transformed from one type to another’. For example, the stored energy in carbon can be released by burning fossil fuel, and the heat energy thus formed can be used to produce either steam or high energy gas, which in turn can be used to drive steam or gas turbines for power generation or to utilize as motive power for driving transport systems. Energy transformation from one form to another involves dissipation (loss) of substantial quantity of energy in some other form. The transformation or power generation efficiency is always below 100%.
The major source of GHGs till date is that produced by burning of fossil fuel to generate electricity and to run transports. Thus the thrust areas to be managed include, apart from development of alternatives, the improvement in power generation and utilization efficiency. Asia has the fastest projected regional growth in electric power generation worldwide, averaging 4.4 percent per year from 2006 to 2030, which is led by China and India’.
Alternative sources of energy based on natural resources, such as wind, solar beam and water are free from GHG emissions. The reduced GHG fuels, such as biofuels produce less GHG than the normal fossil fuels like coal. Biofuels are made from renewable and sustainable sources, but not free from GHG emissions. However biofuel sources can be made carbon neutral by growing plants with capacities to absorb carbon dioxide of equivalent to that of emitted amount. Liquid biofuels are mostly used in transportation sector.
Excepting few, such as, hydroelectric, major alternatives are yet to enter in a big way in the commercial arena. However smaller alternatives, such as, wind, solar and biofuel collectively are growing at a fast rate, and expected to play major role in the energy generation. These renewable and sustainable alternatives should provide longtime energy security with no or negative effect on global warming.
Term Paper # 2. Global Power Generation Scenario:
The US Energy Information Administration’s figure of global energy consumption in 2004 is estimated to be 15TW (in SI units, T = tera = 1012 = trillion). (Tab.12.1).Fossil fuels supply 86% of world’s energy. Major share belongs to oil (37.33%); followed by coal (25.33%) and then gas (23.33%). The proportion varies with the availability of resources. In China & India, coal has the major share in fossil fuel based power generation industries. Improvement in power generation efficiency is the major task involved in reducing GHG emissions in the fossil fuel based power generation industries.
Amongst the alternative resources, hydro and nuclear accounts for 12% and rest 1% belong to wind, solar and biofuel. The energy conversion efficiency in alternate energy segment is equally important to cater to growing need to energy at a lower average emission figure.
Term Paper # 3. Carbon Dioxide Generation by Fossil Fuel based Power Plants:
In the last forty years, the use of fossil fuels has continued to grow and their share of the energy supply has increased. In the last couple of years, coal, which is one of the dirtiest sources of energy, has become the fastest growing fossil fuel. China plans to build or expand 199 coal-fired facilities in the next decade, compared with 83 in United States. India plans to build 25 coal based mega- power plants of 4000MW each by 2012.
The International Energy Agency predicts that fossil fuels will continue to be heavily used for many years to come. In 2006, coal’s share of generation was an estimated 79 percent in China and 71 percent in India, which are likely to decline to 56 percent in India and 75 percent in China in 2030. The achievement of the emission target would be possible with the use of energy efficient thermal plants and alternate energy sources in this fast growing sector.
The recent IEA report (1a) includes estimated energy related carbon dioxide emissions in 2010 as record 30.6 Gigatonnes (Gt), compared to CO2 emission of 29.3 Gt in 2008, which was followed by a dip in 2009 due to the global recession. To achieve the goal of 2°C limitation, as agreed in Cancun in 2010, global energy-related emissions in 2020 must not be greater than 32 Gt.
This means that over the next 10 years, emissions rise should be less in total than they did between 2009 and 2010. In terms of fuels, according to IEA, 44 percent of the estimated CO2 emissions in 2010 came from coal, 36 percent from oil, and 20 percent from natural gas. There is thus a greater need to manage emissions in the energy front.
Power plants account for 40 percent of U.S. greenhouse gas emissions and 25 percent of the world. China, South Africa and India host the world’s five dirtiest utility companies in terms of global warming pollution. The world’s top-ten power sector emitters in absolute terms are China (no. 1), the United States, India (no.3), Russia, Germany, Japan, the United Kingdom, Australia, South Africa, and South Korea (no. 10). If the 27 member states of the European Union are counted as a single country, the E.U. would rank as the third biggest CO2 polluter, after China and the United States.
Reduction of Carbon Dioxide Emission in Fossil Fuel Plants:
Coal-based power plants have the major share in producing electricity compared to any other single source. The life of a thermal power plant ranges between 50 to 100 years. Hence it is not possible to close down these plants just because they are the worst emitters of carbon dioxide. The improvement in the generating efficiency of coal-based power plants holds the key to minimizing emissions per unit of electricity generated.
The strategy involved in this sector is to address the following issues:
i. Improvement in Energy Generation Efficiency by Prolonging Plant Life:
The hard minerals (ash) content of coal (around 40% in Indian coal) cause damage to grinding equipments and boiler tubes by wear of surface materials. In Europe, coal contains high sulphur which leads to damage of the boiler tubes by corrosion. The progressive wear and corrosion of the power plant components would result in malfunctioning of equipments leading to premature failure.
As a result of poor plant performance, the energy generating efficiency can be substantially reduced. The direct and consequential losses in the production can be anywhere between 20% to 45% in a year. Tribo-science based wear prognosis and surface engineering have in recent past, been able to provide solutions to minimize wear & corrosion and thus enabling improvement in the plant performance and energy generating efficiency. Plant life cycle analysis and extension through appropriate maintenance and repair technology are being increasingly used to further improve the plant efficiency.
ii. Improvement of Thermal Energy Generating Efficiency: Through Innovative Practices:
In a thermal power plant, heat or thermal energy’ produced by burning fossil fuel or nuclear fission is used to convert water into steam in a boiler. The steam is used to drive a turbine (in the generator) to generate electricity. In a thermal power plant out of 100 units of heat produced, typical heat loss figures include 10% in stack gases, 50% in cooling water, and 3% in transmission.
Therefore the resultant efficiency of conversion is 37% maximum under normal conditions of operation. The average global efficiency of coal-fired plants is currently 27% compared to 45% for the most efficient plants.
Improvements in the efficiency of thermal power plant using coal can be achieved with the adoption of following technological innovations:
a. Fluidized Bed Combustion:
In fluidised bed combustion, pulverized coal is burnt in a reactor comprised of a bed through which gas is fed to keep the fuel in a turbulent state. The fluidised state of the coal powder improves combustion efficiency, heat transfer and recovery of waste products. The higher heat exchanger efficiencies and better mixing in FBC system allows operation at lower temperatures than conventional pulverised coal combustion (PCC) systems.
b. Integrated Gasification Combined Cycle:
An alternative to use of pulverized coal as ‘fluid’ in a fluidized bed reactor is to convert coal into a fluid (gas) in a gasifier where carbon from coal reacts with oxygen and steam to produce the syngas, which is mainly H2 and carbon monoxide (CO). IGCC plants use a gasifier to convert coal to syngas, which drives a combined cycle turbine. Waste heat from the gas turbine is recovered to create steam which drives a steam turbine, producing more electricity. Hence a combined cycle system produces more power with same quantum of coal.
c. Supercritical & Ultra Supercritical Boilers:
The term ‘supercritical’ refers to thermodynamically equilibrium conditions where both liquid (water) and gaseous (steam) phases exist together as a homogenous fluid.
The supercritical stage in water exists at a pressure over 22.1 MPa (3207 psi) at the boiling point. Up to an operating pressure of around 19 MPa in the evaporator part of the boiler, the cycle is subcritical.
This means, that there is a non-homogeneous mixture of water and steam in the evaporator part of the boiler. In this case, a drum-type boiler is used because the steam needs to be separated from water in the drum of the boiler before it is superheated and led into the turbine.
In the evaporator, at an operating pressure greater than 22.1 MPa, the cycle medium is a single-phase homogeneous fluid. Once-through boiler without drum seperator is therefore used in supercritical cycle. Since the once through boiler does not rely on the density difference between steam and water to provide proper circulation and cooling of the furnace enclosure tubes, it can be operated at pressures above the supercritical point.
Supercritical power generation units feature once- through boilers designed to operate with pressures from 3,500 to 4,000 psi, versus 1,800 to 2,500 psi for subcritical boilers. The temperature in subcritical, supercritical and ultra supercritical range are approximately at 538°C, 566°C & upto 700°C respectively. Ultra-supercritical power generation uses higher pressures in the supercritical range.
Higher firing temperatures and pressures improve conversion efficiency; defined as more electricity generated per BTU of coal consumed. The significantly high energy conversion efficiency and results in similar reduction in fuel consumption, carbon dioxide, SO2 and NOx (acid rain) emissions per megawatt of power output. The increased efficiencies translate into reduced fuel costs and emissions.
The average efficiency of a coal-fired power plant operating in subcritical range (19 MPa, 2757 psi) is around 27% with ah emission figure of 1259gm CO2 per kWh of electricity generated. In a supercritical operation (24 MPa, 3500 psi), the efficiency can be as high as 45% and the corresponding emission figure can be as low as 750gm CO2 per kWh of electricity generated.
In ultra-supercritical operation (27.5 MPa, 4000 psi) the efficiency can go up beyond 55% and carbon dioxide emission figures can be lower than 500g per kWh of electricity generated. The improvement in percent efficiency in supercritical from subcritical is 18% with reduction in emission figure by 40.4%.
Similarly from super to ultrasuper (27. 5 MPa, 4000 psi) efficiency improves by 10% and corresponding emission reduction by 33.33%. One percentage point, improvement in the efficiency of a conventional pulverized coal combustion plant results in a 2-3% reduction in CO2 emissions.
A series of fossil fuel based, high efficiency Ultra- Mega-power generating units has been a part of the ambitious project, to narrow the gap between supply and demand in India, a country of chronic power deficit. This would entail a creation of an additional capacity of at least 100,000 MW by 2012.
The UM plant is considered as belonging to ‘Clean Development Mechanism’ by the organization that administers the Kyoto Protocol. This allows industrialized nations to invest in the plant as an alternative to domestic emissions reductions (2).The first UM-plant, the Tata Ultra Mega, a $4.2 billion power plant is being built near at Mundra, Gujrat, India.
iii. Use of Clean Coal Technology & Capping of Carbon dioxide.
Term Paper # 4. Renewable Sources for Power Generation:
The renewable resources/sources for generating electricity can be divided in two-groups, as follows:
i. No-GHG Sustainable Natural Energy Sources:
The energy sources belonging to this group are Omni-present in nature and replenished by nature as soon as depleted, hence also called perpetual resources. Major alternate sources, such as, water (hydel power), sunlight (solar), geothermal and wind (wind power) do not, in real sense, get depleted, when used for power generation. Also one need not pay for getting access to and utilizing these resources, unlike fossil fuels or even alternative like bio-mass.
These sources do not directly emit GHGs while used for power generation. However even in this non-GHG emitting segment, the improvement in energy conversion efficiency is important to make the process techno-economically viable, to derive maximum benefit by producing more of clean energy utilizing less resources and to have minimum effect on the ecology per unit of power produced.
ii. Reduced- GHG Sustainable Alternate Fuels:
Biomass producing biofuels belongs to this group. GHG emissions on burning biofuel are less than that of fossil fuels. However, the biomass energy require wise management if they are to be used in a sustainable manner. Biofuels based on plantation can be possibly made carbon neutral, only if, carbon dioxide absorbed by plants in their growth process becomes equal to carbon dioxide emitted by biofuel made from same quantity of plants.
Renewable energies are also sustainable energy as they generally contribute to world energy security, reducing dependency on fossil fuel resources, and providing opportunities for reducing GHGs.
The International Energy Agency has defined three generations of renewable energy technologies, as follows:
First-generation technologies resulting from the industrial revolutions at the end of the 19th century include hydropower, biomass combustion, and geothermal power & heat. Some of these technologies are still in widespread use. Second-generation technologies include solar heating & cooling, wind power, modern forms of bioenergy and solar photovoltaic. Since 1980s, these are gradually being introduced in the commercial markets.
Third-generation technologies include advanced biomass gasification, biorefinery technologies, concentrating solar thermal power, hot-dry-rock geothermal power, and ocean energy. Some of them, like solar thermal have grown rapidly from the beginning of new century.
i. Water Power- Hydropower:
Hydroelectric power, which underwent extensive development during growth of electrification in the 19th and 20th centuries, is experiencing resurgence of development in the 21st century. The areas of greatest hydroelectric growth are the booming economies of Asia.
China is the development leader; however, other Asian nations are installing hydropower at a rapid pace. This growth is driven by much increased energy costs – especially while using imported raw materials (coal, oil) — and widespread desires for more domestically- produced, clean, renewable, and economical generation.
Energy in water in the form of motive energy can be used for power generation by running a turbine. Since water is about 800 times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy. The total world production of hydroelectric power in 2005 is 2994 TWh. China, Canada & Brazil are top three amongst the top ten producers.
The production in India is around 25% of that of China. However Norway leads the world with clean hydro-electricity constituting virtually the total domestic power production (98.9%).Although rich in fossil fuel resources, Brazil and Venezuela have made significant contribution in using clean energy by having share of hydro in domestic power generation as 83.7% and 73.9% respectively. Canada (57.9%) and Sweden (46.9%) have around half of their domestic production in hydro.
All other countries have less than 19% share of domestic generation. In India, hydroelectric has a share of around 14% of total power generating capacity (tab.12.3) Northern states in India and the adjoining countries like Nepal and Bhutan are major producers on hydroelectric power in the sub-continent.
Renewable Energy (Excluding Big Hydro):
The renewable energy, excepting big hydro plants, which have joined the mainstream production processes include, wind, biofuel, geothermal, solar PV and solar Thermal. The installed capacities in top six countries for five types of green resources in terms of gigawatts GW are shown in table 12.4. The total installed capacity in six top countries is around 80 GW, for the five green resources.
In 2006, overall renewable power capacity from all green resources, expanded from 160 GW in 2004, to 182 GW in 2006, and then to 240GW in 2007, excluding large hydropower. Global power capacity from new renewable energy sources (excluding large hydro) reached 280 GW in 2008 – a 16 percent rise from the 240 GW in 2007 and nearly three times the capacity of the United States nuclear sector.
The small scale power generation plants based on renewable resources face the difficulty of using transmission grids operated by big power generating plants based on conventional sources. Apart from competition high price of the power based on renewable resources is also a factor in this denial of access to grid.
However renewable energy regulations introduced by various countries have resulted in granting access to transmission grids to power generated from renewable sources. For example, German law encourages investment by cross-subsiding renewable electricity fed into the grid. America’s renewable energy boom and the solution to grid sharing problem are due to state laws requiring utilities to generate a certain share of power from renewable resources with generous tax incentive to abider.
ii. Wind Power:
In generating power from wind, the driving speed of airflow is used to run wind turbines. Modern wind turbines range from around 600 kW to up to 5 MW of rated power, although turbines, with rated output of 1.5-3 MW, have become the most common for commercial use. The power output of a turbine is a function of the cube of the wind speed.
Therefore with the increase in wind speed, power output increases dramatically. Areas where winds are stronger and more constant, such as offshore and high altitude sites are preferred locations for wind farms. Wind power is based on renewable & sustainable resource and produces no greenhouse gases during operation.
Wind strengths near the Earth’s surface vary and thus cannot guarantee continuous power and due to intermittent wind strengths, the capacity factor is 25%. It would mean that a typical 5 MW turbine in the EU would have an average output of 1.7 MW. It is best used in the context of a system that has significant reserve capacity such as hydro, or reserve load, such as a desalination plant, to mitigate the economic effects of resource variability.
Wind power is one of the fastest growing of the renewable energy technologies, though it currently provides less than 0.5% of global energy. Over the past decade, global installed maximum capacity increased from 11 GW in 2000 to 64.7 GW in 2006, grew by 28% to 95 GW by 2007, to 121 GW in 2008, another 28% growth—a trend that is projected to continue into the future.
Wind power in USA grew 45% in 2007. Wind power accounts for around 1% electricity generated in USA. This figure is expected to rise to 15% by 2020. It currently produces less than 1% of world-wide electricity use, but accounts for approximately 20% of electricity use in Denmark, 9% in Spain, and 7% in Germany.
iii. Solar Energy:
The total resources of ail fossil fuels amount to about 0.4 YJ total, while the availability of solar energy is 3.8 YJ per year. Solar constant is the average amount of incoming solar radiation per unit area on the outer surface of Earth’s atmosphere is approximately 1,367 watts per square meter.
The average incoming solar radiation or the solar irradiance, taking into account the half of the planet not receiving any solar radiation at all, is one fourth the solar constant or 342 W/m2. Of all the total incoming sunlight that passes through the atmosphere annually, 51% is available at the Earth’s surface.
If the 51% of solar energy amounting to 174.4 W per sq. meter absorbed by the Earth’s surface can be utilized for power generation instead of currently used energy from burning fossil fuels, there would not be any global warming due to anthropogenic emissions.
Solar heating capacity has increased by 15 percent to 145 gigawatts-thermal (GWth), while biodiesel and ethanol production showed an increase of 34 percent.
The energy collected from solar beam, called solar energy, can be used in many ways for direct heating of materials. A 20 MW per sq.in solar flux needs a fraction of seconds to melt materials like silicon carbide with a melting temperature of 3630°C. The development of solar furnaces has made it possible to utilize direct sunlight as concentrated high energy beams for heat treatment and fusion processes of materials. The process is yet to be commercialised. The current practice is to utilise electricity or fossil fuels for the heat treatment and fusion of materials.
Two most widely used commercial processes to generate electricity are as follows:
i. Solar Thermal or Concentrating Solar Power (CSP):
In this process the solar beam is concentrated by mirrors of different designs, and the concentrated beam is allowed to focus onto boiler tubes containing water. The concentrated heat source makes superheated steam in the boiler to drive a turbine generating electricity.
Solar radiation used for heating covers almost entire spectrum range, including near ultraviolet (305nm) through visible (700nm) to near infrared (2500nm). Many materials absorbs visible radiation better than infra-red. Solar radiation can be concentrated to produce solar flux at peak energy of 16MW to 100MW per square inch by using different types and numbers of concentrators.
Solar thermal concentrators are of different designs, including:
(i) Long curved mirrors, called parabolic troughs, to focus light on a tube of fluid running just above them. This is the one used in ‘Nevada Solar One’ generating up to 64MW capacity;
(ii) A large number of smaller mirrors to focus light on a tower in their midst. This system is used in an 11 MW Spanish plant;
(iii) Others using long flat mirrors and devices resembling satellite dishes.
The three major problems in solar thermal power generation include the need for steam generating water in the favored water scarcity area like deserts, intermittent power generation depending on day light, and the non-availability of power transmission grids set up by big power plants based mostly on fossil fuels.
The water scarcity in areas with plenty of sunshine like desert is a problem in CSP plants. A project to build a plant in Nevada needs 20% of the water available in the area. Another project in the Californian desert faces difficulty in appropriate water rights, since California water law prohibits use of potable water for cooling.
Newer designs require less water by using air- cooling to convert the steam back into water. The water is then returned to the boiler in a closed process which is environmentally-friendly. Compared to conventional wet- cooling, this results in a 90 percent reduction in water usage. The proposed Ivanpah Solar Power Facility in southeastern California will use this new design.
In order to make the electricity generation process continuous, it is essential to generate and store sufficient amount of heat during bright sunny days. Heat is transferred to a thermal storage medium in an insulated reservoir during the day, and withdrawn for power generation at night.
Thermal storage media include pressurized steam, concrete, a variety of phase change materials, and molten salts such as sodium and potassium nitrate. Heat storage allows a solar thermal plant to produce electricity at night and on overcast days. Additionally, the utilization of the generator is higher which reduces cost.
This allows the use of solar power for base load generation as well as peak power generation, with the potential of displacing both coal and natural gas fired power plants. While only 600 megawatts of solar thermal power is up and running in 2009, a 400 megawatts is under construction, and another 14,000 megawatts CST projects being developed.
ii. Solar Photovoltaic:
Photovoltaic systems use conventional solar panels, where directly convert sunlight into energy using the principles of the photovoltaic effect. The photovoltaic effect takes advantage of the properties of semiconductor materials, with silicon being the primary material used in photovoltaic solar cells.
When photons strike the solar cell, electrons in the semiconductor material are shaken loose, allowing them to flow as electricity. This electricity is direct current (DC), and can be directly used to charge batteries, or can be connected to an inverter to power alternating current (AC) components, or to be connected to the local electrical grid.
Traditional photovoltaic systems are based on silicon. Silicon ingots are sliced into wafers -that are fabricated into cells. Cells are combined into modules, which are packaged into end-user systems. Silicon-based solar cells have efficiencies of approximately 14-19%. However, newer systems that use gallium arsenide, another semiconductor material, can be made into thinner and more flexible modules. These “thin film” modules can presently produce efficiencies up to 30%, but currently cost more to fabricate than traditional silicon-based modules.
Photovoltaic production has been doubling every 2 years, increasing by an average of 48 percent each year since 2002, making it the world’s fastest-growing energy technology. At the end of 2008, the cumulative global PV installations reached 15,200 MW. The world’s largest solar-photovoltaic plant with 46 MW capacities is in Portugal, and another 40MW in Germany, both built in 2008. The proposed larger plants have capacities ranging from 100 to 600 MW.
Advanced technologies to convert biomass in the electricity, gaseous and liquid biofuels, and even hydrogen are in the process of development. Some of the advanced technologies and the available commercial processes for conversion of biomass into biofuel.
Plants use photosynthesis to grow and produce biomass or biomatter. Biomass, like other organic matters, such as fossil fuels is basically comprised of organic compounds of carbon and hydrogen. Therefore they can be used directly as fuel or can be converted to liquid or gas fuel. Biofuels are based on biomass, which is renewable and thus sustainable source of energy.
The plants specifically grown for use as renewable and sustainable source for biofuels include corn & soybeans (in USA), flux seed and rapeseed (in Europe) sugarcane (Brazil), palm oil (Indonesia), and jatropha (India). Other sources of biofuel include biodegradable wastes, sewage, manure etc., which are converted to biogas by anaerobic digestion.
First generation biofuels, mainly bioethanol, biodiesel, and biogas which are produced from food crops (sugar or oil crops) and other food based feed stocks (e.g. food waste) are now commercially available, with almost 50 billion litres (39.5 million tons) of bioethanol and 5.4 billion litres (5.4 million tons) of biodiesel produced worldwide in 2006.
Second generation biofuels make use of a wider range of feedstocks, mainly non-food crops. For example, the whole plant biomass can be used or waste streams that are rich in lignin and cellulose, such as, wheat straws, grass, or wood.
Third generation biofuels make use of biotechnological processes to engineer the properties of plants so as to derive maximum amount of intermediate and /or final product with easier processing techniques. For example, plant scientists trying to develop trees that can be triggered to change the strength of the cell walls so that breaking them down become easier with faster release of sugar. This area is now being explored.
The total biofuel production of six top producers in 2006 was amounting to 16.4 GW in terms of energy, and was the second largest energy producer in the alternate energy sector (excluding big hydro-power), next only to fastest growing wind energy.
The liquid biofuel (mainly biodiesel and alcohols) forms the bulk, followed by biogas (mainly mixtures with ethane or carbon monoxide) and some amount in solid biofuel (mainly charcoal).
Biomass is converted to biofuels by thermo-chemical, physical- chemical and bio-chemical processes (tab. 12.5). Thermo-chemical processes include carbonization, gasification and pyrolysis. Physical- chemical processes consist of pressing/extraction, and trans esterification. Bio-chemical processes include alcoholic fermentation, anaerobic fermentation and composting.
Biofuels, such as, biodiesel and ethanol can be burned in internal combustion engine to generate motive power (thus to run car) or in boilers to generate electricity. Liquid biofuels are mostly used in the transport industry because of their lower carbon emissions than that of petrol and diesel.
a. Liquid Biofuel:
Liquid biofuel constitutes the bulk of the biofuel produced by all the three process routes. All the products of physical-chemical processes, alcoholic fermentation products in bio-chemical processes, and part of gasification conversion products in thermo-chemical belong to liquid biofuel. Liquid biofuel is usually either a bio alcohol such as ethanol or a bio-oil such as biodiesel and straight vegetable oil.
Biodiesel can be used in modem diesel vehicles with little or no modification to the engine and can be made from waste, virgin vegetable, animal oil and fats (lipids). Virgin vegetable oils can be used in modified diesel engines. The use of biodiesel reduces emission of carbon dioxide and other hydrocarbons by 20 to 40%.
In some areas corn, cornstalks, sugar beets, sugar cane, and switch grasses are grown specifically to produce ethanol (also known as grain alcohol) a liquid which can be used in internal combustion engines. Ethanol is being phased into the current energy infrastructure. E85 is a fuel composed of 85% ethanol and 15% gasoline that is sold to consumers. Biobutanol is being developed as an alternative to bioethanol.
Syngas can be directly used in internal combustion engines, or to produce methanol and hydrogen, or converted via the Fischer- Tropsch (FT) process into synthetic fuel. The principal purpose of this FT process is to produce a synthetic petroleum oil or synthetic petroleum substitute, such as synthetic lubrication oil for running trucks, cars, and some aircraft engine.
The combination of biomass gasification (BG) and FT synthesis is considered by some as very promising route to produce renewable transportation fuels. Using natural gas as a feedstock, the ultra-clean, low sulfur fuel has been tested extensively by the US Department of Energy, the Department of Transportation, and most recently, with US Air Force to develop a synthetic jet fuel blend.
Pitfall in Biofuels Making:
The conversion of biomass into biofuel in the form of liquid or gas involves consumption of energy. In some cases the energy consumed in the conversion process can be more than the saving in energy by substituting fossil fuels. In the case of corn-ethanol fuel making, if all the corn produced in USA were converted to ethanol this would save only 12% of gasoline demand. However, one gallon of corn ethanol requires four-fifth of a gallon of fossil fuels and 1,700 gallons of water to produce. The net advantage tends to be negative.
Use of Liquid Biofuel:
Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18 percent of the country’s automotive fuel. As a result of this, together with the exploitation of domestic deep water oil sources, Brazil, has recently reached complete self- sufficiency in oil. Most cars on the road today in the U.S run on blends of up to 10% ethanol, and some up to 85% ethanol (E85).
b. Solid Biomass:
Solid biomass is mostly used directly as a combustible fuel, producing 10-20 MJ/kg of heat. The sources include wood fuel, the biogenic portion of municipal solid waste, or the unused portion of field crops. Two billion people currently cook every day, and heat their homes in the winter by burning biomass, which is a major contributor to man-made climate change.
The black soot that is being carried from Asia to polar ice caps is causing them to melt faster in the summer. Wood and its byproducts can now be converted into biofuels such as woodgas, methanol or ethanol fuel. Further development may be required to make these methods affordable and practical.
White Coal from Biomass in India:
The white coal is produced from agricultural waste, like mustard sticks and sesame seed oilcake. After mixing and grinding, the powder is shaped as briquettes, and sold as white coal, for use in boilers and brick kilns. The product has become popular in Rajasthan in India where more then 50 units are producing the biofuel with low level of carbon emission. During last three to four years, an investment of around 200 million rupees (approximately over 4 million USD) has been made in the white coal production from the bio waste.
Biogas can easily be produced from current waste streams, such as, paper production, sugar production, sewage & animal waste. The various waste streams have to be flurried together and allowed to naturally ferment, producing methane gas. This can be done by converting current sewage plants into biogas plants. When a biogas plant has extracted all the methane, the remains work better as fertilizer than the original biomass.
Alternatively biogas can be produced via advanced waste processing systems such as mechanical biological treatment. These systems recover the recyclable elements of household waste and process the biodegradable fraction in anaerobic digesters. Renewable natural gas is a biogas which has been upgraded to a quality similar to natural gas. By upgrading the quality to that of natural gas, it becomes possible to distribute the gas to the mass market via gas grid.
Gasification process is used to convert any type of organic material, such as coal, petroleum, or more recently biomass or organic waste into carbon monoxide and hydrogen by controlled combustion with oxygen. The gas mixture produced is called synthetic gas or syngas and is itself a fuel.
Gasification is a very efficient method for extracting energy from many different types of organic materials, and also has applications as a clean waste disposal technique. The gasification may be an important technology for renewable. In particular biomass gasification can be carbon neutral.
Gasification relies on chemical processes at elevated temperatures >700°C, which distinguishes it from biological processes such as anaerobic digestion that produces biogas. Liquids are more portable because they have high energy density, and they can be pumped, which makes handling easier. This is why most transportation fuels are liquids.
Biofuels from Seaweeds by Aquaculture:
Seaweeds have the potential of not only countering global warming but also providing bio-fuels to cater the growing energy needs. Large-scale cultivation of biofuels on land has serious environmental costs, including deforestation, water use and generation of greenhouse gases. In recent years, the use of agriculture land & resources has led to growing increase in food scarcity and corresponding price increase. These could be avoided by seaweed cultivation.
Technology for Aqua- or Sea- or Mari-Culture:
Seaweeds are marine plants and protists (a diverse group of eukaryotes that cannot be classified as animals, plants, or fungi) belonging to the category of benthic algae and often found in the seashore biome. The main components of seaweed are fucoidan and alginic acid. While an enzyme for breaking down fucoidan to sugar has already been discovered, the scientists are looking for an enzyme that breaks down alginic acid. They are also looking at the possibility of using genetic modification technology.
The sequences in making ethanol from seaweeds are as follows:
Seaweed (fucoidan + alginic acid) → Fucoidan + Enzyme → Sugar → Ethanol
Proposed Giant Plant in Japan:
Tokyo University, along with Mitsubishi Heavy Industries and several other private-sector firms envision a 10,000 square kilometer (3,860 square mile) seaweed farm at Yamatotai, a shallow fishing area in the middle of the Sea of Japan, to cultivate seaweed, which grows rapidly, a floating reactor for converting seaweed to ethanol at sea, and to transport by tankers. They claim a farm of this scale could produce about 20 million kiloliters (5.3 billion gallons) of bioethanol per year, which is equivalent to one-third the 60 million kiloliters (16 billion gallons) of gasoline that Japan consumes each year.
The researchers claim that in addition to serving as a source of fuel, the seaweed would help clean up the Sea of Japan, by removing some of the excess nutrient salts that flow into the sea from the surrounding land masses. Along with Japan, seaweed fanning has been established in Costa Rica; with R&D inputs from World Bank funded Sea Gardens Project at the University of Costa Rica.
Less than three per cent of world’s oceans or about 20% of agricultural land used in agriculture would be needed to fully substitute for fossil fuel. The former is a much more superior alternative than the later. One concern of harvesting naturally occurring seafood could have comparable GHG emission effects due to habitat loss or fragmentation. The effect may be as good as that of large scale deforestation.
Seaweeds from Waste Water:
Growing large seaweed fields for energy by using wastewater nutrients could be economically sound, for millions of tons of untreated wastewater are dumped daily into seas and seaweeds help clean it up. This idea has been tested successfully using human waste water in experiments in USA.
A biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, and value-added chemicals from biomass. Similar to petroleum refinery, a biorefinery produces multiple products such as, chemicals, biodiesel or bioethanol, and simultaneously generating electricity and process heat, through combined heat and power (CHP) technology, for its own use and perhaps enough for sale of electricity to the local utility. Although some facilities exist that can be called bio-refineries, the bio-refinery has yet to be fully realized.
According to the International Energy Agency, amongst the new bioenergy (biofuel) technologies, most promising one is cellulosic ethanol biorefineries. Cellulosic ethanol can be made from inedible cellulose fibers that form the stems and branches of plants. Crop residues (such as corn stalks, wheat straw and rice straw), wood waste, and municipal solid waste are potential sources of cellulosic biomass. Dedicated energy crops, such as switchgrass, as sources for cellulose can be sustainably produced in many regions.
Royal Society on Biofuel:
Theoretically biofuel produces lower carbon dioxide, which would get absorbed by the growing plants and the recycling process continues. Farmers hope to make more money by growing crops for biofuels than other agricultural products.
The Royal Society, UK’s national science academy, based on the analyses of a wide range of commercially available biofuels have published a report, in which it was concluded that some biofuels may in effect cause more global warming than petrol due to emissions of greenhouse gases from fertilizers and processing. Royal Society argues for a worldwide strict certification system, similar to that used for eco-friendly wood, to let consumers know just how green is the biofuel they would be using.
Development of such a system would require exhaustive analysis of every step of a firm’s supply chain, a difficult, if not an impossible task, in view of fiercely protected indigenous biofuel industries in USA and Brazil.
v. Geothermal Energy:
Geothermal energy is obtained by tapping the heat of the earth itself, usually from kilometers deep into the Earth’s crust. It is expensive to build a power station but operating costs are low resulting in low energy costs for suitable sites. It should be stressed that the geothermal resource is not strictly renewable in the same sense as the hydro resource.
However, the International Energy Agency considers geothermal power as renewable. It estimates that Iceland’s geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW. Geothermal is the first generation sustainable energy source.
Three types of power plants are used to generate power from geothermal energy; dry steam, flash, and binary. Dry steam plants take steam out of fractures in the ground and use it to directly drive a turbine that spins a generator. Flash plants take hot water, usually at temperatures over 200 °C, out of the ground, and allows it to boil as it rises to the surface then separates the steam phase in steam/water separators and then runs the steam through a turbine.
In binary plants, the hot water flows through heat exchangers, boiling an organic fluid that spins the turbine. The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat.
Alcoa, US-based aluminum giant, is evaluating the feasibility of building the world’s first big geothermal power plant in Iceland for running a proposed aluminum production plant.
Term Paper # 5. Nuclear Power:
Fission of uranium atom by accelerated neutron generates large quantity of energy. Thorium can also be used. Fission power’s long-term sustainability depends on the amount of uranium and thorium that are available to be mined. It is said that nuclear has the potential to be sustainable.
However, this is often qualified with the argument that there are serious challenges with respect to nuclear hazards that must be dealt with before it can drastically increase its role. Nuclear fission is generally not regarded as renewable, as indicated by the U.S. DOE on the website. Both fission and yet to be developed commercially fusion process, create radioactive waste in the form of activated structural material, which is one of the sustainability issues.
Currently, there are 440 commercial power generating nuclear reactors operating in 30 different countries. The total installed capacity is 372,000 Mw, which supplies 16% of global electricity consumption. Proponents, claim that nuclear power is at least as environmentally friendly as traditional sources of renewable energy, making it part of the solution to global warming and the world’s growing need for energy.
Due to high energy cost and environmental problem, some of the major nuclear energy generating countries, like USA and UK has stalled the further expansion projects. US have 104 nuclear power reactors at 65 power plants, and no newer one under construction. After 1995, no new nuclear power plant has been commissioned in U.K. In 2020 nuclear energy would provide only 7% of the requirement, from existing 18%.
The nuclear establishments in UK are opting for improving lifetime of efficiency and updating nuclear waste management rather than going for new plants. Large part of electricity supply in Germany is from nuclear power plant, but they are rapidly making stride to replace the need by green renewable resources. Aim is to maintain existing plants and keep the show on road. However in Europe, a total of 197 European nuclear power plants are in operation and another 13 under construction in five countries in Europe.
The recent revival of interest in nuclear energy is more due to spiraling oil and gas price combined with increasing demand rather than environmental concern. Also the economics on nuclear power has changed due to high fossil fuel price, making the cost to consumer similar to conventional power. Thirdly new designs of future nuclear power plant are being explored to make it more techno-economically viable. So far as fusion energy is concerned it is still in laboratory, and commercial production may take another 30 years or more.
Term Paper # 6. Mini or Micro-Generation Facilities:
The ‘climate change and sustainable energy act 2006’ in UK aims to boost the number of electricity microgeneration installations in the country, so helping to cut carbon emissions and reduce fuel poverty. For the purposes of the Act, microgeneration technologies include, biomass, biofuels, fuel cell, photovoltaic, water (including wave and tidal), wind power, solar power, geothermal sources and combined heat and power systems.
Some Third-Generation Technologies:
Hot-dry-rock power unit uses geothermal source, where the very high temperature of rocks just a few kilometers below ground, is used to produce steam and run a turbine to generate electricity.
Ocean energy is another third-generation technology. Portugal has the world’s first commercial wave farm, the Agucadora Wave Park, under construction in 2007, shall generate 2.25 MW initially and based on the success, there would be further expansion to a generation capacity of 525 MW. A wave farm in the world’s first commercial tidal power station (2007) in the narrows of Strangford Lough in Ireland shall generate 1.2 megawatt underwater tidal electricity.
Solar power panels that use nanotechnology can create circuits out of individual silicon molecules may cost half as much as traditional photovoltaic cells. Nanosolar, USA has built a factory for nanotechnology thin-film solar panels and reported to make roll- print solar cells that require only 1/100th as thick an absorber as a silicon-wafer cell. Company’s plant has a planned production capacity of 430 megawatts peak power of solar cells per year.
Renewable energy and energy efficiency are sometimes said to be the “twin pillars” of sustainable energy policy. Both resources must be developed in order to stabilize and reduce carbon dioxide emissions. Renewable energy (and energy efficiency) is no longer niche sectors that are promoted only by governments and environmentalists. The increased levels of investment and the fact that much of the capital is coming from more conventional financial sectors suggest that sustainable energy options are now becoming mainstream.
India is rich in green energy resources – clean, renewable and sustainable energy resources like, solar, wind, water and biofuels (jatropha, sugarcane) – which promise significant future potential. The efforts to develop energy from these resources shall pay rich dividend both financially and creating a truly green country.
High Silt Erosion of Hydro Turbines in Himalyan Regions- Nature’s Revenge:
The extensive deforestation in the northern Himalayan region of India and Bhutan has resulted in severe soil erosion by rain water and falls. (fig 12.1).The silts (mainly anthropogenic) formed by erosion of deforested soil, are carried by flowing water jets or columns to join the downstream river.
The hydroelectric power plants on these rivers are subjected to severe erosion by high concentration of silts (with high proportion of quartz) in the water. The runner blades and guide vanes are subjected to heavy damage, leading to substantial reduction in power generating capacities. The silt erosion damage scar on worn turbine in fig 12.2 is similar to that of deforested soil erosion scar fig. 12.1.
In the hydroelectric power plants in the Himalayan regions in India and Bhutan, the erosion can be so severe as to remove half of the turbine’s runner blades in six months’ time. With the decreasing size of the runner blades there is a proportionate drop in power generation. The downtime for repair and re-blading is around three months in a year, the period in which there is no power generation. The total loss in generating capacity can be as high as 40% per year in the worst affected plants.
The solution to this problem lies on producing durable wear- resistant coating on the turbine blades, so as to not only increase the original design life when used in OEM (original equipment manufacturing) but can also be coated, several times during scheduled maintenance and repairs (M&R), thus extending the life of the turbine several times the original designed life.
The published literatures on this particular problem indicate vast improvement in the life cycle of turbine runners with anti-wear overlays on the blades. However, the nodal agencies like NHPC (National Hydro Power Corporation) in India and some of the overseas suppliers choose to conduct research in various alternatives. Based on their research findings, the field trials conducted so far have failed miserably.
Hence, instead of developing antiwar coatings, the NHPC have signed an agreement recently (September, 2008) for a new material of construction with a national laboratory, to replace the currently used base material. This being a long term project, and vested normally to a turbine manufacturer, hence the saga would likely to continue.