Turbo-Generators
Mt Piper operates two 660 megawatt generating units. The turbo-generators are tandem compound reheat with single-flow high pressure, double-flow intermediate pressure and low-pressure exhaust cylinders. Operating speed is 3,000 rpm (50Hz). Each turbo-generator is about 50 meters long and weighs 1,342 tonnes. A bypass system allows short shutdowns of the plant, and subsequent re-tarting reduced stress on the turbine due to steam to turbine metal temperature mismatch. The bypass system is basically 2 pipe systems, one bypassing steam around the HP turbine, and the other bypassing steam past the IP and LP turbines. Water sprays help cool the steam as it bypasses the turbine. Main turbine lubricating and power oil is supplied off a shaft driven oil pump, with AC and emergency DC pumps providing runup and rundown oil supplies and protection of the oil supply to the bearings in the event of a loss of all AC supplies. A small, high pressure jacking oil pump provides oil supply when the turbine is placed on barring (slow rotation to stop the turbine from sagging or hogging).
Boilers
The boilers are single-furnace, twin drum type, using natural circulation with divided back pass and balanced draught. Boiler steam pressure is 16,550 kPa, steam temperature is 540 degrees Celsius, and steam flow rate is 560 kilograms/second. The main boiler, turbine and auxiliary plant at Mt Piper have a proven record for design and reliability. The plant is automated, with few items needing manual operation.
Cooling Water
Two natural draught hyperbolic cooling towers cool the circulating water after it has passed through the turbine steam condenser. Water for cooling is pumped from Lyell Dam on the Coxs River, about 20 km from the power station to the Thompsons Creek dam, close to Mt Piper. Waste water from the plant processes is treated and recycled to restrict discharges into the environment. Most water is recycled by an elaborate water treatment plant, but any water discharges are monitored and treated to prevent contaminants from entering the Coxs River.
Transmission
The high voltage switchyard located south of the power station directs station supply on 330 kV transmission lines running to Bayswater, Marulan, Wellington and Wallerawang. The very high voltages used by Delta Electricity are necessary because of the long distances and large amounts of electricity transmitted.
Coal Supply
Coal is an abundant source of energy in Australia. Mt Piper converts coal into electricity in a very efficient way. The sophisticated power station is designed to achieve a thermal efficiency rate of 36%, depending on the weather conditions.
Coal is crushed in large coal mills, grinding the 25mm pieces of coal down to powder roughly the same as talc(baby powder), using 80 tonnes of steel balls in a large rotating steel cylinder. In this state, the coal dust (called pulverised fuel, or PF) burns like a gas, and gives off large amounts of heat in a very short time. When both generating units are operating at full load, approximately 14,000 tonnes of coal are consumed daily, leaving some 3,500 tonnes of ash to be disposed of each day. The ash is collected in large fabric filters which ensure that airborne emissions are cut to no more than 0.08 grams per cubic metre. Ash from the bottom of the boilers and dust trapped by the filters are transported by conveyor to a nearby disused open-cut mine for dry disposal. This is environmentally preferable to using ash dams as it lessens the chance of water seeping into the local ground water. The infilled mounds will be covered with earth and gradually revegetated as part of Mt Piper's extensive landscaping program.