How We Generate Electricity
Coal arrives at the Station by rail and road. It is then delivered by conveyor to bunkers in the boiler house. From there it is fed to pulverising mills where it is ground as fine as face powder and blown into the boilers to burn like a gas.
The heat produced converts water to steam in the pipes that line the boiler. Steam passes through the boiler twice – each cycle helps the Station to generate as much electricity from the coal as possible.
The steam first goes to the high-pressure turbine where this energy is converted into mechanical energy, which turns the turbine blades at up to 3000 rpm.
The steam then returns to the boiler where it takes in heat from the exhaust gases, which would otherwise be lost through the chimney. It then goes back to the turbine, passing through the intermediate and low pressure stages.
Each turbine stage removes energy from the steam, reducing its temperature and pressure. When the steam finally leaves the turbine, it looks like a thick, wet fog – its temperature is 35 degrees centigrade.
The Station has four boilers, each producing steam at a temperature of 568 degrees centigrade. Each boiler is as tall as a 15-storey tower block.
Each of the four turbines comprises a high pressure turbine, an intermediate pressure turbine and three low pressure turbines. When the turbine rotates, the electrical rotor coupled to the turbine shaft rotates with it at 3000 revolutions per minute.
Once the steam has passed through the turbines, it is cooled back into water before being returned to the boilers to be turned once again into steam.
The condensers are cooled by water which has been cooled as it passes through the eight cooling towers; this water is continually recirculated ensuring that only small quantities of river water are required. The plume visible from the cooling towers is a fine water vapour. Winter’s low temperatures increase condensation making the plume larger.
Ash and dust
Burning coal produces ash, some of which falls to the bottom of the boiler. This is collected and sold to produce building blocks.
The rest of the ash leaves the boiler with the exhaust gases as pulverised fuel ash (PFA). More than 99% of the PFA is prevented from reaching the atmosphere by electrostatic precipitators which give the fine particles a static charge of electricity and attracts them to screens. The cleaned flue gases are then discharged up the chimney.