(1) Coal Supply
Rugeley transports and uses up to 3,000,000 tonnes of fuel from coal fields in the UK and from around the world. Coal is shipped to British ports from as far afield as South Africa and Australia where it is loaded onto trains for delivery to the Station’s coal handling plant.
Coal laden rail wagons are unloaded automatically as the train moves slowly over gratings in the unloading house, the coal is taken by conveyor to bunkers inside the Station for immediate use, or to the stock pile which can hold up to 500,000 tonnes.
Raw coal is generally too coarse to burn efficiently in Rugeley’s large boilers, therefore it is ground or “pulverised” to the consistency of talcum powder in large Pulverised Fuel (PF) milling plant. Each of the Station’s boilers has seven such PF Mills, six of which are required for full load output.
(2) The Boiler House
After the coal is ground as fine as talcum powder in pulverising mills it is blown by air into the boiler to burn like a gas. The heat produced converts water to steam in the tubes that line the boiler. The steam passes through the boiler not once but twice. Each cycle helps the station to get as much electricity as possible from the coal. When the steam leaves the boiler it is at a high pressure – typically more than 163 times greater than atmospheric pressure – and at a temperature of 568°C. If the steam pipes were not heavily insulated, they would be seen at night glowing a cherry red.
(3) The Turbine
Steam from the Boiler passes to the high-pressure stage of the Turbine where some of its kinetic energy is converted into mechanical energy, helping to spin the blades. Steam then returns to the boiler where it takes in heat from the exhaust gases that would otherwise be lost up the chimney and then goes back to the turbine, passing through an intermediate pressure stage and three low-pressure stages. Each turbine stage converts energy from the steam, reducing its temperature and pressure. When it finally leaves the low-pressure turbines, the steam looks like a thick, wet fog. Its temperature is about 35°C and its pressure typically 55 millibars – effectively a vacuum – a little over a 20th of normal atmospheric pressure.
The turbine rotates at 3000 revolutions per minute and is connected via a solid shaft to the Alternator. The Alternator produces a high voltage field and generates 500MW of electricity to the National Grid system at 400,000 volts.
(4) The Condenser
The steam then passes through the condenser where it is cooled and condensed back into water to be used again in the boilers – it is so pure that it is far too valuable to be thrown away.
The condensers are cooled by water pumped from ponds beneath the cooling towers. After leaving the condenser this cooling water returns to the towers where it is sprayed over packing to be itself cooled by evaporation.
(5) The Generator
The energy that the turbines have taken from the steam turns the alternator. This is made up of a large rotor – a large cylindrical electromagnet – inside the stator (which is a giant coil of copper bars). The rotation of the electromagnet within the coil creates an electric voltage (22,000 volts are generated in the case of Rugeley) – using the same principle as Michael Faraday demonstrated circa 170 years ago.
(6) Ash and Dust
Burning coal produces ash. At full output the daily conversion of fuel to heat energy produces up to 1200 tonnes of ash and dust. Some falls to the bottom of the boiler where it is collected and sold for use in making roads and the building blocks that are used for constructing the inner walls of many modern houses. The remainder leaves the boiler with the exhaust gases as a fine dust – called pulverised fuel ash (PFA). More than 99% of this dust is extracted by electrostatic precipitators. A precipitator operates by electrostatically charging the dust particles in the gas stream. The charged particles are then attracted to and deposited on large metal plates. When enough dust has accumulated, the collecting plates are shaken to dislodge the dust that falls by gravity into hoppers. Pulverised fuel ash has many uses, including a partial substitute for cement in concrete manufacture.
(7) Control Room
Using modern systems the operators in the control room monitor the running of the plant and if necessary, make operational changes using the latest computer technology.
Staff in the control room are part of a power station team which keep the plant running 24 hours a day, 7 days a week. Care was taken in staff selection and great emphasis placed on their training. All the staff recognise the need for teamwork, flexibility and commitment to ensure Rugeley’s commercial success.