With a capacity to generate 1460 megawatts, Stanwell Power Station is a major supplier of electricity to the National Electricity Market, to ensure your lights stay on when renewable sources of energy (like solar and wind) are unavailable.
At the time it became fully operational in 1996, Stanwell Power Station – located 22 kilometres west of Rockhampton – was one of the largest industrial developments ever undertaken in Queensland.
The highly automated station’s performance has been recognised both nationally and internationally. Demonstrating its reliability, it currently holds the world record for the longest stretch of continuous operation (1087 days 21 hours, spanning from 16 August 2012 to 9 August 2015 for Stanwell Unit 1).
So, how does it do it?
First, low sulphur black coal – sourced from the Curragh Mine, near Blackwater in Central Queensland – is transported via rail to the power station. This coal is stockpiled in huge mounds within the power station complex, until it’s required in boiler bunkers capable of holding approximately 350 tonnes of coal each.
When operating at full load, Stanwell Power Station burns about four million tonnes of coal a year. But because of its innovative design, it’s also one of the most efficient conventional coal-fired power stations in the country.
Regulated by the coal feeder, the coal flows from boiler bunkers to the pulverisers (sometimes called mills). Inside these pulverisers – of which there are six for each of the station’s four generating units – steel balls the size of large beach balls roll around, crushing the coal until it’s ground as fine as talcum powder.
Full steam ahead
After being pulverised, the finely ground coal is mixed with warm air and burnt inside a boiler. Each of the station’s four units has one of these boilers, which is essentially a large room with about 200 kilometres of boiler tubing attached to its inside walls.
The burning coal heats the water flowing through the boiler tubes, and when the temperature gets high enough, it converts to steam. The boilers are fitted with low nitrogen oxide burners, one of the key environmental controls at the station.
The steam from the boiler then gets even hotter in the superheater, and passes through high pressure pipework to the turbine. The steam is actually hot enough, at 541°C, to make the steam pipe glow a dull red (yes, just like in the cartoons). These high temperatures help to make the process more efficient.
Within the turbine, the steam pressure drops from about 17,000 kilopascals to about 8kPA absolute, depending on ambient conditions. This causes the turbine to rotate at 3,000 revolutions per minute. The used steam is then condensed to water, which is pumped back to the boiler, and the process of creating steam begins all over again.
Heat from the condensing steam is removed by recycled water, which then flows back to one of two 130-metre-high cooling towers, both designed to withstand cyclonic winds. Here, water is cooled by air, and then falls to the bottom of the cooling tower, where it will be recycled through the condenser. The absorbed heat from the water is released into the atmosphere – the plumes you’ll see emerging from the cooling towers are made up of water vapour (or steam) lost through evaporation during the cooling process.
Meanwhile, the ash and dust emissions from the burnt coal are kept within regulatory limits through the use of electrostatic precipitators. There are two of these precipitators in each generating unit – they use large plates to collect ash, dust and fine particles. The particles are attracted to the plates, then collected in hoppers and carried away by a conveyor to silos, where they are mixed with water and ash.
This process creates a slurry which is pumped to the ash disposal area, where it dries hard like cement. Low amounts of water in the ash keep the risk of groundwater contamination to a minimum.
The gases that pass through the electrostatic precipitators are discharged up a 210-metre-high chimney. There are four flues – one for each unit – within the chimney.
Each of the station’s four units has a generator, the main components of which are the rotor and the stator. A turbine drives the rotor, while the stator remains still. An electric current is then applied which creates a magnetic field, similar to the workings of an electric magnet. The rotation of the magnetic field causes an alternating electric current to flow through the stator and out to the generator transformer.
The last step in the electricity generation process is the generator transformer. The transformer increases the electricity voltage from the stator from 20,000 volts to 275,000 volts, which allows the power to be transported efficiently through the electricity grid to the customer at the end of the distribution system.
Finally, it’s your turn. You use the electricity generated by the station to power your lights, air conditioner, fridge, appliances and so on – but now, you’ll know the process it went through to get there.
In addition to generating energy to power your lights, fridges, air conditioners and more, Stanwell Power Station also delivers essential services to the network . The site provides frequency management, voltage management and system restoration services which ensure there are enough power reserves in the systems so that the network can cope with any unexpected events (like a sudden sharp increase in demand or a power station suddenly going offline). These services ensure the security and reliability of the network in North Queensland.
Stanwell Power Station into the future
Stanwell Power Station is needed now to supply reliable and affordable energy around the clock when intermittent sources aren’t available. Stay tuned to see how Stanwell Power Station’s role is changing and how it will support industry as we move towards a low carbon future.