Environmental impact of gas turbines
One of the primary advantages of gas turbines is that they produce relatively little pollution, at least compared with coal-fired power plants. In the developed countries of the world where emission control has become a high-profile issue this has had a significant effect on the choice of technology for new generating capacity. Most gas turbine power plants burn natural gas which is a clean fuel. Gas turbines are, anyway, extremely sensitive to low levels of impurities in the fuel, so fuel...
Storage caverns
The most important part of a CAES plant is somewhere to store the compressed air. Small-scale CAES plants - with storage capacities of up to 20 MWh - can use overground storage tanks but large, utility-scale plants need underground caverns in which to store the air. The natural gas industry has used underground storage caverns for years to store gas these same caverns can provide ideal storage facilities for a CAES plant. However the demand for such a cavern limits the development of CAES to...
Traditional combustion plants
The traditional method of converting waste to energy is by burning it directly in a special combustion chamber and grate, a process which is often called mass burning. The dominant European technologies use this system. These involve specially developed moving grates, often inclined to control the transfer of the waste, and long combustion times to ensure that the waste is completely destroyed. Designs have evolved over 20-30 years and are generally conservative. More recently, fluidised-bed...
Solar photovoltaic technology
The solar cell is made from a thin layer of semiconducting material. The key feature of this semiconductor layer is that it will absorb photons of radiation in the visible region of the electromagnetic spectrum. Each photon of light energy is absorbed by an electron within the solid material. In absorbing the energy, the electron acquires an electrical potential. This potential can be made available as electrical energy, as an electric current. The current is produced at a specific fixed...
Gasification and pyrolysis
In recent years a number of companies have attempted to develop new waste-to-energy technologies based on both gasification and pyrolysis. These technologies are derived from the power and the petrochemicals industries. Pyrolysis is a partial combustion process carried out at moderate temperatures in the absence of air, which usually produces a combustible gas and a combustible solid residue. Gasification uses higher temperatures and converts most of the solid material into a combustible gas....
Impulse turbines
The main type of impulse turbine in use today is the Pelton turbine, patented by the American engineer Lester Allen Pelton in 1889. It is found mainly in applications where a high head of water is available. Another type, called the Turgo turbine, has also been developed, again for high-head applications. In both cases, the head of water will normally be greater than 450 m, although the Pelton turbine is applicable for heads of between 200 and 1000 m. For heads higher than 1000 m there will...
Types of energy storage
Electricity normally has to be used as soon as it has been generated. This is why grid control and electricity dispatching systems are important they have to balance the demand for electricity with the supply. Once one fails to match the other, problems occur. It would seem obvious, given this situation, that some reservoir of saved electricity would be a major boon to grid operation. Yet storing electricity has proved difficult to master. Storing electricity in its dynamic form, amperes and...
Canadian deuterium uranium reactor
The Canadian deuterium uranium CANDU reactor was developed in Canada with the strategic aim of enabling nuclear power to be exploited without the need for imported enriched uranium. Uranium enrichment is an expensive and highly technical process. If it can be avoided, countries such as Canada with natural uranium reserves can more easily exploit their indigenous reserves to generate energy. This has made the CANDU reactor, which uses unenriched uranium, attractive outside Canada too. The CANDU...
End notes Lgs
1 In fact the Californian plants have achieved 20 conversion efficiency. 2 This is a World Bank estimate. 3 Photovoltaics come down to earth, Bill Yerkes, Modern Power Systems July 2004 p. 30. 4 Renewable Energy Technology Characterization, The US Department of Energy and the Electric Power Research Institute Topical Report 109496 1997, available at http www.eere.energy.gov power pdfs techchar.pdf 6 Solar Thermal Power 2020, Greenpeace, 2004. 7 PV Market Update, Paul Maycock, Renewable Energy...
Molten carbonate fuel cells
The MCFC has an electrolyte which is composed of a mixture of carbonate salts.5 These are solid at room temperature but at the cell operating temperature of 650 C, they have become liquid. Work on high-temperature MCFCs began during the 1950s. The US army tested cells during the 1960s and in the 1970s the US Department of Energy began to support research. Japanese companies also picked up the technology. By the end of the 1990s pilot units of up to 250 kW had been tested, mainly in the USA....
Pistonenginebased power plants
Piston engines or reciprocating engines the two terms are often used interchangeably to describe these engines are used throughout the world in applications ranging from lawn mowers to cars, trucks, locomotives, ships, and for power and combined heat and power generation. The number in use is enormous the US alone produces 35 million each year. Engines vary in size from less than 1 kW to 65,000 kW. They can burn a wide range of fuels including natural gas, biogas, LPG, gasoline, diesel,...
Small hydropower
Small hydropower projects are those under 10 MW in size, though this classification can vary from country to country. In China, for example, any project under 25 MW is considered small. While small projects operate on essentially the same principles as large projects and use similar components, there are differences that need to be considered separately. There are three types of small hydropower project, designated small, mini and micro. According to a United Nations Development Programme UNDP...
Fluidisedbed combustion
If a layer of sand, of finely ground coal, or of another fine solid material is placed in a container and high-pressure air is blown through it from below, the particles, provided they are small enough, become entrained in the air and form a floating, or fluidised, bed of solid particles above the bottom of the container. This bed behaves like a fluid in which the constituent particles constantly move to and fro and collide with one another. As a type of reactor, this offers some significant...
Horizontal or vertical
As outlined above, the standard wind turbine has a vertical rotor attached to a horizontal shaft. This arrangement imposes certain restrictions on the wind turbine design. With a horizontal shaft, the rotor turns in a vertical plane and must be raised on a tower so that the blades are clear of the ground and of the turbulent layer of air next to it. Gearbox and generator are attached directly to the turbine shaft so these, too, must be placed on the tower, high above ground. This raises the...
Boiler technology
A power plant boiler is a device for converting the chemical energy in coal into heat energy and then transferring that heat energy to a fluid, steam. The efficiency of a coal-fired power plant increases as the pressure and temperature of the steam increases. This has led to a demand for higher temperatures and pressures as technology has developed and this has required, in turn, the development of materials with higher performance under increasingly stressful conditions. The most advanced...
Piston engine technology
In its most basic form, the piston engine comprises a cylinder sealed at one end and open at the other end. A disc or piston which fits closely within the cylinder is used to seal the open end and this piston can move backwards and forwards within the cylinder. This it does in response to the expansion and contraction of the gas contained within the cylinder. The outside of the piston is attached via a hinged lever to a crankshaft. Movement of the piston in and out of the cylinder causes the...
Advanced gas turbine design
A gas turbine aeroengine must remain light and compact so it is not possible to add to it significantly in order to improve its performance. The stationary turbine for power generation does not suffer this restriction. Taking advantage of this greater freedom, engineers have explored a number of strategies that can be applied to stationary gas turbines in order to provide significant performance enhancements. In large steam-turbine-based power plants it is traditional to split the turbine into...
Bunded reservoir
As an alternative to a barrage across an estuary, it is theoretically possible to enclose an area of a tidal estuary or tidal region of the sea with an embankment or bund see the St Malo project discussed above . The principle involved is the same, creating a reservoir that can be filled at high tide and then allowed to empty when the tide has fallen. The environmental effect of such a structure would probably be less dramatic than complete closure of an estuary but costs are likely to be...
Direct firing
The direct firing of biomass involves burning the fuel in an excess of air inside a furnace to generate heat. Aside from heat the primary products of the combustion reaction are carbon dioxide and a small quantity of ash. The heat is absorbed by a boiler placed above the main furnace chamber and water in tubes within the boiler is heated and eventually boiled, producing steam which is used to drive a steam turbine. The simplest type of direct-firing system has a fixed grate onto which the fuel...
Combined cycle power plants
A single gas turbine connected to a generator can generate electricity with a fuel-to-electricity conversion efficiency of perhaps 38 using the best of today's technology. New developments, such as those falling under the auspices of the US DOE's ATS programme aim to push the simple cycle efficiency as high as 41 without cycle adaptation, 43 with adaptation such as recuperation. This is still marginally lower than a modern coal-fired power plant can hope to achieve. Part of the reason for this...
Flashsteam plants
Most high-temperature geothermal reservoirs yield a fluid which is a mixture of steam and liquid brine, both under high pressure typically up to 10 atmospheres . The steam content, by weight, is between 10 and 50 . The simplest method to exploit such a resource is to separate the steam from the liquid and use the steam alone to drive a steam turbine. However this throws away much of the available energy, particularly where the proportion of steam in the fluid is small. A more productive...
Open and closed cycle ocean thermal energy conversion
The siting of an OTEC plant, either onshore or offshore, represents one of the key decision for any proposed project. The other key decision is the type of cycle to use. There are two principle options, an open cycle plant or a closed cycle plant. Hybrids of the two have also been proposed. A closed cycle OTEC plant employs a thermodynamic fluid such as ammonia or a refrigerant like freon. This is contained in a completely closed system including the plant turbine. Hot surface seawater is used...
Liquid fuels
Biomass is already used extensively to produce liquid fuels. The most important of these are ethanol, made from the fermentation of grain or sugar cane and biodiesel produced from oil-rich crops such as sunflower and oil-seed rape. Biodiesel is produced extensively in Europe where the total production was over 850,000 tonnes in 2001. Production is now on target to reach 2 of the liquid fuel market by 2005 though 5.75 by 2010 may be harder to attain. Europe also produces ethanol but the largest...
Propeller and Kaplan turbines
The propeller turbine looks like the screw of a ship, but its mode of operation is the reverse of the ship's propulsion unit. In a ship a motor turns the propeller which pushes against the water, forcing the ship to move. In the hydropower plant, by contrast, moving water drives the propeller turbine to generate power. Propeller turbines are most useful for low-head applications such as slow running, lowland rivers. Their efficiency drops off rapidly when the water flow drops below 75 of the...
Shore and nearshore wave converters
Perhaps the most widely tested of shore and near-shore devices is the oscillating water column. If a tube, sealed at one end, is placed so that its open end is just beneath the surface of the sea, as waves pass the tube, the level of water inside the tube will rise and fall, alternately compressing and expanding the air column within the tube. If, instead of a seal, the upper end of this tube is open and houses a device that acts like a wind turbine, then the moving water will cause the air to...
Ocean thermal energy conversion
OTEC relies on the principle exploited in most forms of electricity generation that a source of heat and a source of cold5 can be used to drive an engine. In the case of OTEC the source of heat is the surface of a tropical or subtropical sea while the source of cold is the deep sea. The possibility of extracting energy from the sea in this way was recognised in the latter half of the nineteenth century and the first practical system was proposed by the French inventor D'Arsonval in 1881....
Protonexchange membrane fuel cell
The PEM fuel cell uses a polymer membrane as its electrolyte. The cell was invented by US company General Electric and tested for US military use in the early 1960s. After development for the US Navy it was adopted by the British Navy in the early 1980s. Since then it has attracted most attention as a possible replacement for the internal combustion engine for automotive applications. However a number of companies are also developing stationary power applications. The membrane which forms the...
Offshore devices
The three types of device discussed above can all be exploited offshore provided they can be moored so that they remain stationary relative to the waves. However most offshore devices try to exploit the wave motion in different ways. The hosepump, developed in Sweden, is based on an elastic tube that changes its internal volume as it is stretched. One end of the tube is sealed and attached to a float while the other end is open and, is connected to a moored plate close to the bottom of the sea....
Integratedgasification combined cycle
The second type of advanced coal-burning plant, the IGCC plant, is based around the gasification of coal. Coal gasification is an old technology. It was widely used to produce town gas for industrial and domestic use in the USA and Europe until natural gas became readily available. Modern gasifiers convert coal into a mixture of hydrogen and carbon monoxide, both of which are combustible. Gasification normally takes place by heating the coal with a mixture of steam and oxygen or, in some cases,...
Fundamentals of nuclear power
A nuclear power station generates electricity by utilising energy released when the nuclei of a large atom such as uranium split into smaller components, a process called nuclear fission. The amount of energy released by this fission process is enormous. One kilogram of naturally occurring uranium could, in theory, release around 140 GWh of energy. 140 GWh represents the output of a 1000 MW coal-fired plant operating a full power for nearly 6 days. There is another source of nuclear energy,...
Gas turbine technology
A gas turbine is a machine which harnesses the energy contained within a fluid - either kinetic energy of motion or the potential energy of a gas under pressure - to generate rotary motion. In the case of a gas turbine this fluid is usually, though not necessarily, air. The earliest man-made device for harnessing the energy in moving air was the windmill, described by Hero of Alexandria in the first century ad. The early windmill was a near relative of today's wind turbine. Closer in concept to...
Engine size and speed
The speed at which a piston engine operates will depend on its size. In general small units will operate at high speed and large units at low speed. However since in most situations a piston-engine-based power unit will have to be synchronised to an electricity grid operating at 50 or 60 Hz, the engine speed must be a function of one or other of these rates. Thus a 50 Hz high-speed engine will operate at 1000, 1500 or 3000 rpm while a 60 Hz machine will operate at 1200, 1800 or 3600 rpm....
Biomass gasification
For dedicated biomass combustion to become a major source of electricity, higher-efficiency conversion is required. The best means of achieving this may well prove to be biomass gasification. Gasification involves the partial combustion of biomass in either air or oxygen to produce a gas that contains combustible organic compounds, carbon monoxide and hydrogen. The gasification process is well tested and the product gas will have a calorific value of between one-fifth and one-half that of...
Types of solar cell
Microchips and transistors are universally fabricated using slices cut from perfect crystals of silicon. These crystals are carefully grown under controlled conditions and are expensive to produce. Solar cells can be made with single crystal silicon too. Indeed, cells using this material have provided the best performance of any silicon solar cells, with solar-to-electrical conversion efficiencies of up to 24 . Long-term performance of single crystal silicon cells is good too, but the cost of...