1.2   Functional needs of the system

 

To play its part in the boiler/turbine-generator cycle, the feedheating system has to perform the following functions:

  • Provide the required amount of feedwater to the boiler at a temperature dictated by cycle design.
  • Maintain a stable suction regime for the boiler feed pumps.
  • Contain a buffer store for water to allow for a short term mismatch between boiler demand and available feedwater.
  • In the longer term, to keep the water content constant.
  • Supply water to the boiler with an acceptable oxygen content.
  • Automatically cut off the supply of contaminated feedwater to the de-aerator, and hence to the boiler, in the event of ingress of chlorides due to inleakage of the condenser cooling water or chemicals from the polishing plant.
  • In the event of a turbine trip or sudden reduction of unit load, the stored energy within the feed system must not overspeed the turbine-generator.
  • Be so engineered as to protect the turbine from possible reflux of water or water/steam mixture from the feed system under all conditions of operation.

The above functions are the principal aims of feed system design: how they have been achieved by the systems installed in modern CEGB power stations is described in the following sections.

 

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