Electricity generation

Gas turbine

Steam turbine

Energy

The Two-Drum Water-Tube Boiler

A typical small two-drum water-tube boiler is fired by a spreader stoker equipped with a dump grate. By means of baffles, the gases are forced to follow a path from the furnace to the boiler exit. This arrangement of gas flow is known as a "three pass" design. A water level is maintained slightly below the midpoint in the steam drum. Water circulates from the steam drum to the lower or mud drum through the six rows of tubes in the rear of the boiler-tube bank where the comparatively low gas temperature results in a low heat-transfer rate. Circulation is from the mini drum to the steam drum through the front boiler tubes and the side-wall furnace tubes. The side-wall furnace tubes are supplied with water from the mud drum by means of circulators connected to rectangular water boxes located in the side walls at the level of the grate. Water for the front-wall tubes is supplied to a round front nail header by down-comer tubes connected to the steam drum and insulated from the furnaces by a row of insulating brick. Most of the steam is generated in the furnace-wall tubes and in the first and second rows of boiler tubes which can “see” the flame in the furnace and absorb energy by radiation.

Boilers of this type have been standardized in a range of sizes capable of generating 8,000 to 50,000 lb of steam per hr.

The position of the drums and the shape of the tubes result in a compact unit having a well-shaped and economically constructed furnace. By simple changes in the arrangement of furnace-wall tube, the design can be adopted to almost any kind of firing equipment and fuel.

Energy is the property (or the quantity of the property) of changing the state of a system or doing work. The expressions energy and power have different meaning in different scientific and non-scientific fields. Physics aims to explain quantitatively this property and gives a definition that makes it possible to consider energy as a description of the whole state and the different ways jobs are done are unified in this treatment.

Energy is a fundamental quantity that every physical system possesses; it allows us to predict how much work the system could be made to do, or how much heat it can exchange. In the past, energy was discussed in terms of easily observable effects it has on the properties of objects or changes in state of various systems. Basically, if something changes, some sort of energy was involved in that change. As it was realized that energy could be stored in objects, the concept of energy came to embrace the idea of the potential for change as well as change itself. Such effects (both potential and realized) come in many different forms; examples are the electrical energy stored in a battery, the chemical energy stored in a piece of food, the thermal energy of a hot water heater, or the kinetic energy of a moving train. To simply say energy is "change or the potential for change", however, misses many important examples of energy as it exists in the physical world.

Energy can be used not only to produce observable change, it also is used to prevent change in which case unaided observation of this kind of energy can be difficult. For example, looking at a statue holding a 50 pound weight, the presence of energy needed to do so may not be observable. However, if you are holding up the fifty pound weight instead of the statue the need for energy to accomplish this becomes apparent. You can feel the gravitational force on you both when you are moving the weight up and when you are not moving it. Energy can be readily transformed from one form into another; for instance, using a battery to power an electrical heater converts electrical energy into thermal energy. In the previous example of holding the fifty pound weight, the work you perform to raise the weight is observed as kinetic energy of motion which is converted to potential energy and added to the weight's potential energy as you continue to hold the weight up against the pull of gravity. Letting go of the weight once again transforms this stored potential energy back into kinetic energy as the weight falls under the force of gravity. The law of conservation of energy states that the total amount of energy, corresponding to the sum of a system's constituent energy components, remains constant. Scientists have also defined several forms of energy that are not easily measured by the unaided observer.

A steam turbine extracts the energy of dry pressurized superheated steam as mechanical movement. In a Parsons-Westinghouse steam turbine nozzles apply supersonic steam to a curved blade. The blade whips the steam back in the opposite direction, simultaneously allowing the steam to expand a bit. A stationary blade then redirects the steam towards the next blade. The process repeats until the steam is completely expanded. The moving blades are mounted radially on the rotor. The stationary blades are mounted to the case of the turbine.

Turbines usually consist of a number of stages, with each stage being specifically optimized for the pressure and volume of steam that it will operate with.

Steam turbines of this type have some weak spots. First, some steam leaks through the annulus where the journal of the shaft penetrates the casing. Usually this is limited by some sort of rotating labyrinth seal, but it can be a problem, especially on the high-pressure end of the turbine. Also, most steam turbines are very particular about what they expect in their feed. Water droplets can quickly damage a steam turbine if the turbine blades have not been designed to withstand the presence of water droplets.

The turbine described above was invented by Charles A. Parsons, and improved by George Westinghouse.

A number of other types of turbines have been developed that work effectively with steam. The de Laval turbine (invented by Gustaf de Laval) accelerated the steam to full speed before running it against a turbine blade. This was good, because the turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam. It is also, however, less efficient.

Problems with turbines are quite rare but any imbalance of the rotor blades can lead to vibration, which in extreme cases can lead to a blade letting go and punching straight through the casing. If water gets into the gas and is blasted onto the blades rapid erosion of the blades can occur, possibly leading to imbalance and failure. The control of a turbine with a governor is essential, as turbines need to be run up slowly, to prevent damage. Uncontrolled acceleration of the turbine rotor can lead to the over-speed trip being activated to shut off the activating gas supply to the turbine. If this fails then the turbine may continue accelerating until it breaks apart, often spectacularly, probably extremely dangerously. The high pressures inside the casing lead to problems in sealing the output shaft. Turbines are expensive to make, requiring precision manufacture and special quality materials. This purchase cost is offset by much lower maintenance requirements and the small size of a turbine when compared to its shaft power output.

Electrical power stations around the world use large steam turbines driving turbo-generators to produce vast amounts of electricity. Other uses of steam turbines are in ships, pumps and motors at land based plant where steam is often available as a production by-product. Steam turbines were tested on railways, without success, although gas turbines

are now commonly used. (From Wikipedia, the free encyclopedia)

http://en.wikipedia.org/wiki/Steam_turbine

The world's first commercial, oil-free gas turbine is manufactured by Capstone. This machine has a single-stage radial compressor and turbine, a recuperator, and foil bearings.

A gas turbine is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.)

Energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity and volume of the gas flow. This is directed through a diffuser (nozzle) over the turbine's blades, spinning the turbine and powering the compressor.

Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power airs\craft, trains, ships and generators.

Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems. The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated building. They can be particularly efficient – up to 60% - when waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle configuration. They can also be run in a cogeneration configuration, where the exhaust is captured to heat steam which is then used to heat buildings or run air-conditioners through a steam turbine.

Simple cycle gas turbine in the power industry require smaller capital investment than combined cycle gas, coal or nuclear plants and can be designed to generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for base-load plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Large simple cycle gas turbines may produce several hundred megawatts of power and approach 40%

thermal efficiency. (From Wikipedia, the free encyclopedia). http://en.wikipedia.org/wiki/Gas_turbines

Electricity generation is the first process in the delivery of electricity to consumers. The other three processes are electric power transmission, electricity distribution and electricity retailing.

The importance of dependable electricity generation, transmission and distribution was revealed when it became apparent that electricity was useful for providing heat, light and power for human activities. Decentralized power generation became possible when it was recognized that alternating current (was recognized to be able to transport) electric power lines can transport electricity at low cost across great distances by taking advantage of the ability to transform the voltage using power transformers.

Electricity has been generated for the purpose of powering human technologies for at least 120 years from various sources of potential energy. The first power plants were run on wood, while today we rely mainly on oil, natural gas, coal, hydroelectric and nuclear power and a small amount from hydrogen, solar energy, tidal harnesses, and wind generators. The generation and distribution of electricity has mostly been in the hands of either privately owned or state owned public

utilities. In recent years some governments have started to privatise or corporatise these utilities as part of a move to introduce market forces to monopolies. The New Zealand Electricity Market is a typical example.

The demand for electricity can be fed in two different ways. The primary method thus far has been for public utilities to construct large scale projects to generate and transmit the electricity required to fuel growing economies. Many of these projects have unpleasant environmental effects such as air or radiation pollution and the flooding of large areas of land.

Increasingly, distributed generation is seen as a new way to supply the electrical demand close to the users. Smaller, distributed projects can: Protect from blackouts caused by the closure of de-centralized power plants or transmission lines for maintenance, market manipulation or emergency shut downs Reduce pollution Allow smaller players to enter the energy markets

Rotating turbines attached to electrical generators produce most commercially available electricity. Turbines are usually rotated by using steam, water, wind or other fluids as an intermediate energy carrier.

Fuel cells produce electricity using a variety of chemicals and are seen by some people to be the most likely source of power in the long term, especially if hydrogen can be used as the feedstock. However, hydrogen is usually only an energy carrier, and must be formed by some other power source.

Small mobile generators are often driven by diesel engines, especially on ships, remote building sites or for emergency standby. (From Wikipedia, the free encyclopedia). http://en.wikipedia.org/wiki/Electrical generation

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