FOSSIL FUELS &
ALTERNATIVE ENERGY SOURCES
4TH YEAR CHEM MAJOR
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FOSSIL FUELS &
ALTERNATIVE ENERGY SOURCES
4TH YEAR CHEM MAJOR
► FOSSIL FUELS
► ALTERNATIVE ENERGY SOURCES
► Fossil fuels are basically any carbon based substance that is used by mankind as a
source of energy. They are formed by natural processes such as anaerobic
decomposition of buried dead organisms.
► Fossil fuels contain high percentages of carbon and include coal, petroleum,
and natural gas . They range from volatile materials with low carbon : hydrogen ratios
like methane, to liquid petroleum to nonvolatile materials composed of almost pure
carbon, like anthracite coal.
► Fossil fuels are of great importance because they can be burned (oxidized to carbon
dioxide and water), producing significant amounts of energy per unit weight.
► Fossil Fuels are a nonrenewable resource because they were formed from the remains
of plant and animal matter from over 65 million years ago. Once they are gone, they
are gone forever!
FOSSIL FUEL COMBUSTION
Burning fossil fuels is responsible for environmental issues that are high on the political agenda
these days. Examples are greenhouse gas accumulation, acidification, air pollution, water
pollution, damage to land surface and ground-level ozone.
The principal air pollutants resulting from fossil fuel combustion are the following:
(a) carbon monoxide
(b) the oxides of sulfur, SO2 and SO3 (represented as SOx)
(c) the oxides of nitrogen, NO and NO2 (NOx)
(d) ‘particulates’, consisting primarily of very fine soot and ash particles.
► Carbon monoxide (CO) is a product of incomplete combustion of any fuel. It is both a
highly poisonous gas and the principal constituent of photochemical smog.
► Sulfur oxides arise during combustion from oxidation of sulfur in sulfur containing fuels (some
coals and some petroleum-based products). The principal product is sulfur dioxide:
S (in fuel) + O2 --> SO2
When it is released to the atmosphere, it can react with oxygen in the air to form sulfur trioxide:
2 SO2 + O2 --> 2 SO3
Sulfur trioxide can absorb moisture from the atmosphere or readily dissolve in rain water to form very fine droplets of sulfuric acid and fall to the earth as acid rain. Inhalation of these droplets can harm the respiratory system. Chronic exposure leads to a much greater likelihood of suffering from bronchitis.
► Nitrogen oxides have two sources : Fuel NOx is produced when nitrogen atoms chemically combined with the molecules of the fuel are oxidized during the combustion process to form nitric oxide:
2 N (in fuel) + O2 --> 2 NO
In addition, thermal NOx is produced in some combustion processes that operate at such high temperatures that nitrogen molecules in the air are oxidized to nitric oxide:
N2 (in air) + O2 --> 2 NO
2 NO + O2 --> 2 NO2
Nitrogen oxides will react further with water and oxygen to form nitric acid:
4 NO2 + 2 H2O + O2 --> 4 HNO3
Like sulfuric acid, nitric acid is a very strong acid that easily corrodes or attacks many materials. Nitric acid is also a component of acid rain.
► Particulate Matter emissions (soot and fly ash) are also a concern because they can contribute to long-term respiratory problems. Many of these particles are extremely small, of the order of 10 micrometer or less, and they are thus suspended in the air we breathe. After inhaling them, they get trapped in the very thin air passages inside the lungs. Over a period of years this reduces the air capacity of the lungs. Reduced air capacity leads in turn to severe breathing and respiratory problems. Chronic asthma or emphysema can result, as well as increased general susceptibility to respiratory diseases.
► The total fossil fuel used in the year 1997 is the result of 422 years of all plant matter that grew on the entire surface and in all the oceans of the ancient earth.
ALTERNATIVE ENERGY SOURCES
The nature of what constitutes an alternative energy source has changed considerably over time, as have controversies regarding energy use.
“Energy fueled in ways that do not use up natural resources or harm the environment “
- Oxford Dictionary.
“Energy derived from sources that do not use up natural resources or harm the environment “ - Princeton WordNet .
Energy generated from alternatives to fossil fuel. Need not be renewable.
► In a general sense, alternative energy as it is currently conceived, is that which is produced or recovered without the undesirable consequences inherent in fossil fuel use, particularly high carbon dioxide emissions, an important factor in global warming.
“I’d put my money on the sun and solar
energy. What a source of power! I hope
we don’t have to wait ‘til oil and coal run
out before we tackle that.”
- Thomas Edison
Solar energy is an energy source that involves tapping the radiant light energy that is emitted by the sun and converting it into other forms of energy, such as heat and electricity.
Solar energy reaching the earth is incredible. By one calculation, 30 days of sunshine striking the Earth have the energy equivalent of the total of all the planet’s fossil fuels, both used and unused! Solar technologies are broadly characterized as either Passive solar or Active solar depending on the way they capture, convert and distribute solar energy.
PASSIVE SOLAR HEATING
Passive solar design uses sunshine to heat and light homes and other buildings without mechanical or electrical devices . Heating the building through the use of solar energy involves the absorption and storage of incoming solar radiation, which is then used to meet the heating requirements of the space.
►The most common passive solar system is called direct gain. Direct gain refers to the sunlight that enters a building through windows, warming the interior space . A direct gain system includes south facing windows and a large mass placed within the space to receive the most direct sunlight in cold weather and the least direct sunlight in hot weather.
► If solar heat is to be used when the sun is
not shining, excess heat must be stored. In indirect gain the solar energy is collected and stored in one part of the house and use natural heat transfer to distribute heat to the rest of the house . Thermal mass ,materials with a high capacity for absorbing and storing heat (e.g., brick, concrete masonry, concrete slab, tile, adobe, water) are used for this purpose.
► It has been estimated that 40 to 90% of most homes’ heating requirements could be supplied by passive-solar heating systems.
The generation of voltage across the PN junction in a semiconductor due to the absorption of light radiation is called photovoltaic effect. The Devices based on this effect is called photovoltaic device.
Solar cell is a photovoltaic device that converts the light energy into electrical energy based on the principles of photovoltaic effect . Solar cell (crystalline Silicon) consists of a n-type semiconductor (emitter) layer and p-type semiconductor layer (base). The two layers are sandwiched and hence there is formation of p-n junction and an electric field within the cell.
SOLAR CELL [PHOTOVOLTAIC CELL]
During the incident of light energy, in n-type material, electrons can gain energy and move into the p-type region. Then they can no longer go back to their original low energy position and remain at a higher energy. The process of moving a light- generated carrier from p-type region to n-type region is called collection. These collections of carriers (electrons) can be either extracted from the device to give a current, or it can remain in the device and gives rise to a voltage.
► The surface receives about 47% of the total solar energy that reaches the Earth. Only this amount is usable. Still In principle, the amount of solar energy that reaches the Earth’s surface could provide for all human energy needs forever .
A hydroelectric plant uses the flow of water from a higher to a lower elevation to
generate power. Hydroelectric plants provide about 20% of the world’s electricity.
IMPOUNDMENT POWER PLANT
The most common type of hydroelectric power plant is an impoundment facility. An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level.
There's another type of hydropower plant, called the pumped-storage plant. In a conventional hydropower plant, the water from the reservoir flows through the plant, exits and is carried down stream. A pumped-storage plant has two reservoirs:
Upper reservoir - Like a conventional hydropower plant, a dam creates a reservoir. The water in this reservoir flows through the hydropower plant to create electricity.
Lower reservoir - Water exiting the hydropower plant flows into a lower reservoir rather than re-entering the river and flowing downstream.
Using a reversible turbine, the plant can pump water back to the upper reservoir. This is done in off-peak hours. Essentially, the second reservoir refills the upper reservoir. By pumping water back to the upper reservoir, the plant has more water to generate electricity during periods of peak consumption.
PUMPED – STORAGE POWER PLANT
In times of high energy demand, the pumped-storage plant releases water from the upper reservoir to the lower reservoir, turning the turbines along the way. When the energy demand decreases, the plant pumps water from the lower reservoir back to the upper reservoir. Some of the plant’s own power is used up during pumping. Droughts do not affect pumped-storage plants, because water can continually be pumped into the upper reservoir to keep the electricity production steady.
DIVERSION POWER PLANT
A diversion plant, sometimes called a run-of-river facility, in most cases does not use a dam. The plant diverts some of the river water through a canal or penstock, where the flow powers a turbine.
These plants rely entirely on the flow of the river to produce electricity. There is no dam to artificially raise the height of the water. A diversion plant depends solely on the landscape to create the head.
Magma rising from the mantles brings unusually hot material near the surface. Heat from
the magma, in turn, heats any groundwater. This is the basis for generating geothermal
Direct uses of geothermal energy is appropriate for sources below 150C. It includes :
• Space heating
• Air conditioning
• Industrial processes
• Hot water
• Resorts and Pools
• Melting snow
Geothermal energy can be used in a direct or indirect way. The choice is determined by the available temperature, the presence of a reservoir, the intended purpose and the economic context.
► Worldwide, there are now about 40 geothermal power plants and most
of them are built along plate tectonic boundaries .
Where temperatures are insufficient to meet the space heating requirements of residential or commercial buildings, Geothermal heat pumps can be used to boost the temperature to desired levels.
Space heating is provided by means of pumped wells or through the use of down hole heat exchangers.
► In fact using geothermal energy to heat is about 2-3 times as common as using it to create electricity.
Space heating can also be provided on a building by building basis or increasingly via a district heating network that supplies the needs of multiple consumers via an underground piping network connected to one or multiple wells or downhole heat exchangers.
The development of geothermal district heating, led by the Icelanders, has been one of the fastest growing segments of the geothermal space heating industry and now accounts for over 75% of all space heating provided from geothermal resources worldwide.
Given the proper circumstances, natural hot water may be used to space cool, too!
Absorption refrigeration is a cooling process that is efficiently employed to cool areas of human occupancy.
Geothermal absorption refrigeration units create "cold" by making use of a well known physical phenomena: the boiling temperature of a liquid depends on pressure; and heat is "robbed" from the environment when a liquid boils.
The use of geothermal space cooling wiII depend upon the location, temperature, production (flow) rates and chemical quality of hot water in prospective geothermal reservoirs.
INDIRECT USE : GENERATION OF ELECTRICITY
The indirect use of Geothermal energy includes the utilization of Super-heated water or steam from earth's interior in running the turbines of a conventional power plant to generate electricity. The water is then cooled and returned to the heat source. Generation of Electricity is appropriate for sources >150oC .
There are three types of geothermal power plants: Dry Steam, Flash Steam, and Binary Cycle.
DRY STEAM POWER PLANT
Steam is used directly from the wells to drive a turbine generator. Wastewater from the condenser is injected back into the subsurface to help extend the useful life of the hydrothermal system.
Resource temperature range :
220°C to 320°C.
FLASH STEAM POWER PLANT
Flash plants take super heated water out of the ground, allowing it to boil as it rises to the surface, then separates the steam from the water in a surface vessel (called a steam separator) and uses the steam to turn a turbine generator. The remaining water and steam are then injected back into the source from which they were taken.
Resource temperature range : 200°C to 300°C.
BINARY CYCLE POWER PLANT
In binary cycle geothermal power plants, pumps are used to pump hot water from a geothermal well, through a heat exchanger, and the cooled water is returned to the underground reservoir. A second "working" or "binary" fluid with a low boiling point, typically a Butane or Pentane hydrocarbon , is
pumped at fairly high pressure through the heat exchanger , where it is vaporized and then directed through a turbine. The vapor exiting the turbine is then condensed by cold air radiators or cold water and cycled back through the heat exchanger.
1- Wellheads , 2 - Ground surface , 3 -Generator
4 - Turbine, 5 -Condenser, 6 - Heat exchanger , 7 - Pump
Resource temperature range : 120°C to 190°C.
Wind Power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electrical power, windmills for mechanical power, wind pumps for water pumping or drainage, or sails to propel ships. It is predicted that by 2030, wind energy will supply at least twice the electricity it does now.
WIND POWER PLANT
A wind turbine or wind power plant is a device that converts kinetic energy from the wind into electric current . Modern wind turbine generators are highly sophisticated machines, taking full advantage of state-of-the-art technology, led by improvements in aerodynamic and structural design, materials technology and mechanical, electrical and control engineering and capable of producing several megawatts of electricity.
A wind turbine obtains its power input by converting the force of the wind into a torque (turning force) acting on the rotor blades. The rotor is connected to the main shaft, which spins a generator to create electricity. The amount of energy which the wind transfers to the rotor depends on the density of the air, the rotor area, and the wind speed.
The kinetic energy of a moving body is proportional to its mass (or weight). The kinetic energy in the wind thus depends on the density of the air, i.e. its mass per unit of volume. In other words, the "heavier" the air, the more energy is received by the turbine.
► One important factor is that with a doubling of wind speed, power output increases by a factor of 8.
Ocean energy or ocean power refers to the energy carried by ocean waves, tides, salinity, and ocean temperature differences. The movement of water in the world’s oceans creates a vast store of kinetic energy, or energy in motion. This energy can be harnessed to generate electricity to power homes, transport and industries.
Waves are caused by a number of forces, i.e. wind, gravitational pull from the sun and moon, changes in atmospheric pressure, earthquakes etc. Waves created by wind are the most common waves. Unequal heating of the Earth’s surface generates wind, and wind blowing over water transfers energy and thus generates waves.
The amount of energy transferred and the size of the resulting wave depend on the
Speed of wind : The faster the wind is traveling, the bigger a wave will be.
Time of wind : The wave will get larger the longer the length of time the wind is hitting it.
Distance of wind : The farther the wind travels against the wave (known as fetch), the
bigger it will be.
In order to extract energy from this never ending motion of waves, two technologies are mainly used They are : Tapered Channel Method and Floating Device Method.
FLOATING DEVICE METHOD
Floating wave energy devices generate electricity through the harmonic motion of the floating part of the device. The object can be mounted to a floating raft or to a device fixed on the ocean floor. In these systems, the devices rise and fall according to the motion of the wave and electricity is generated through their motion.
TAPERED CHANNEL METHOD
As a wave enters the collector, the surface of the water column rises and compresses the volume of air above it.
The compressed air is forced into an aperture at the top of the chamber, moving past a turbine.
As the wave retreats, the air is drawn back through the turbine due to the reduced pressure in the chamber.
Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power - mainly electricity.
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth.
Tidal power plants use the flowing water between low and high tides to generate electricity. When tides comes into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be let out just like in a regular hydroelectric power plant. In order for this to work well, you need large increases in tides.
An increase of at least 16 feet between low tide to high tide is needed.
Water speeds of nearly 1/10 the speed of wind can provide the same
energy output. A plant in France makes enough energy from tides to
power 240,000 homes.
Open-cycle OTEC uses warm surface water directly to make electricity. The water from the surface is put into a near vacuum. A near vacuum is a container which has had most of the air sucked out of it. This allows the water from the surface to turn into steam, because when water is in a near vacuum its boiling temperature is lower.
The expanding steam then drives a low-pressure turbine attached to an electrical generator. The steam, which has left its salt and other contaminants in the low-pressure container, is pure fresh water. It is condensed into a liquid by exposure to cold temperatures from deep-ocean water. This method produces desalinized
fresh water, suitable for drinking water, irrigation or aquaculture.
If both the open and closed systems are combined together, a hybrid system is created. This improves the amount of electricity and fresh water produced.
OCEAN THERMAL ENERGY CONVERSION (OTEC)
Ocean thermal energy conversion (OTEC) uses the temperature difference between cooler deep and warmer shallow or surface ocean waters to run a heat engine and produce useful work, usually in the form of electricity.
OTEC works best when the temperature difference between the warmer, top layer of the ocean and the colder, deep ocean water is about 20°C (36°F). These conditions exist in tropical coastal areas, roughly between the Tropic of Capricorn (northern Argentina to Madagascar to Australia) and the Tropic of Cancer (Mexico, Middle East, India, South of Taiwan).
CLOSED CYCLE OTEC
Biomass is organic material made from plants and animals. Biomass contains stored energy from the sun.
Most of the world still relies very heavily on fossil fuels, but slowly but surely,
attention is being diverted to alternative energy.
The most important aspects of most alternative energy sources is that they
promise clean, pollution-free energy.
Energy use in the future will not be dominated by a single source.
Bertani R., 2005: World geothermal power generation in the period 2001–2005. Geothermics, 34,651–690.