Some of the largest pumps you see in Australia may be at power stations. There are literally hundreds of different pump types and sizes for power station use. These can range from small submersible pumps to the giant pumps known as primary power station pumps: boiler feed pumps, condensate extraction pumps and cooling water pumps.
Boiler Feed Pumps
Boiler feed pumps are used to move water from the deaerator storage tank to the boiler. This is the phase of a power station that involves the highest water pressure. Usually, these are multi-stage pumps that have mechanical seals.
Many of the larger turbo-generators don’t use the multistage pumps; barrel-type pumps are used instead. These usually have an inner cartridge assembly that can be removed and replaced, decreasing downtime in case of a malfunction.
Condensate Extraction Pumps
These pumps draw warm water from a condenser at a pressure between 6 and 10kPa. They are usually multi-stage pumps, with a first stage impeller that has a low NPSH requirement. Many different combinations can be used, such as ring section pumps, vertical turbine pumps or horizontal multistage pumps.
These pumps are so important that they are usually installed in an arrangement that provides 2 x 100% capacity.
Cooling Water Pumps
Cooling water pumps move large quantities of water to a condenser, helping to condense the steam into water. When servicing a 660 MW unit, the flow of cooling water would be up to 20 m3/s for each unit fed by cooling water pipes varying from 2.0m to 2.6m in diameter.
There are two types of systems for cooling water: the once-through or open type and the cooling tower or closed type. The open type draws water from a large body, usually a lake or sea, and then returns it there after use. The closed type keeps all of the water within the system, recycling it through a condenser and pipework, eventually cooling it in an evaporative cooling tower.
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