Electricity Generation

The process of converting energy stored in fuels or drawn from the environment into electrical energy.

It embraces numerous complex technologies.

Energy appears in nature in two forms, disordered and ordered (See Physics: The Second Law of Thermodynamics). The disordered form, of which heat is a prime example, can be converted into other forms, such as mechanical energy, through a heat engine. Typical heat engines are piston engines, as used in cars, or gas turbines, as used in jet aircraft. The efficiency of practical heat engines is rather low-in general, less than 40 per cent.

This means that less than 40 per cent of the energy output from the engine is in a useful form.

The ordered form of energy, of which mechanical and electrical energy are prime examples, is high-grade energy, as one type can be converted to other types at nearly 100 per cent efficiency. For example, electrical energy can be converted into mechanical energy in a motor at an efficiency of over 90 per cent.

The reasons why electricity is universally employed as a medium of energy transfer and use are that: (1) It can be efficiently transported from generators to the point of use in the consumers premises through a simple-to-install network of wires. (2) It can be converted at high efficiency into heat, mechanical, and chemical energy.

It powers electronic devices. It provides light. (3) It is instantly controllable at the point of use-it takes only a flick of a switch to turn an electrical device on or off.

In a typical coal-fired power station the coal is ground to fine powder in a mill, mixed with pre-heated air and blown into a furnace, where it burns like a gas. The furnace, or boiler, is the largest structure in a power station, as its walls are lined with several kilometres of water pipes which are designed to extract as much heat as possible from the burning fuel. The hot gases boil the water in the pipes and convert it into high-pressure, high-temperature steam. Afterwards, the low-temperature gases are forced through dust extractors to collect as much of the ash as possible. In modern stations they pass through specialized equipment to extract the environmentally harmful sulphur products of combustion. Finally, the flue gases are forced up a tall chimney stack and discharged into the atmosphere.

The steam generated by the boiler is supplied to a turbine, in which its heat energy is converted into mechanical energy by making a shaft rotate. It is here that the inefficiency of heat engines takes its toll. The low-temperature, low-pressure steam at the output of the turbine has to be condensed into water and pumped back into the boiler to close the cycle. Large quantities of cooling water are needed for this task-perhaps 230, 000 cubic metres (50. 6 million gallons) per hour for a 2, 000 MW station (1 MW equals 1 megawatt). If the power station is built on a river estuary, the river can supply the water; otherwise, the cooling water has to be recycled. ...