P OWER GEN ER AT I O N Fig 7 - ‘Can-type’ double suction condensate pump (Flowserve) Boiler feed pumps require a booster pump to provide sufficient suction pressure, and the booster pump is usually driven by the same motor or turbine drive. Sometimes the booster pump may be appended to the nondrive end of the existing motor, or driven by an extension shaft from the non-drive end of the pump. In the latter case a reduction gearbox would be needed for the booster pump, to bring it back to 4 pole speed. In some cases the booster pumps can have their own drive motor, but this is not usual in Australia where it is customary have the booster pump driven by the same turbine or motor that drives the main pump. Each boiler feed pump would have its own separate leak-off line (minimum flow protection line), fitted with a throttling control valve. The leak-off line would open at all flow rates below approximately 20% of full flow. Boiler feed pumps have close internal clearances, and require protection from grit and debris, by the provision of a filter usually situated before the booster pump.
Fig 8 (above) - Barrel type boiler feed pump (KSB) Fig 9 (right) - Ring section boiler feed pump (KSB) The standby pump would need to be in readiness to start at any time, and would have its suction and discharge isolating valves open (and non return valve closed). The water temperature is about 190 deg C at this point in the cycle, and the pump must be pre-warmed and ready to operate. ■ About the author John McAndrew has extensive experience in the design of cooling water systems, pumping stations, and associated plant for both Power Stations and Major Water Supply Projects including production of associated specifications. His experience includes feasibility studies, specification of plant and equipment, hydraulic design and waterhammer studies of all types of pumping systems including power station feed and condensate pumping systems. He is currently a senior mechanical engineer with Aurecon.
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pump industry | November 2013 | Issue 5
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