Page 112 - Introduction to Marine Engineering

Chapter 5
Feed systems

The feed system completes the cycle between boiler and turbine to
enable the exhausted steam to return to the boiler as feedwater. The
feed system is made up of four basic items: the boiler, the turbine, the
condenser and the feed pump. The boiler produces steam which is
supplied to the turbine and finally exhausted as low-energy steam to the
condenser. The condenser condenses the steam to water (condensate)
which is then pumped into the boiler by the feed pump.
Other items are incorporated into all practical feed systems, such as a
drain tank to collect the condensate from the condenser and provide a
suction head for the feed pump. A make-up feed tank will provide
additional feedwater to supplement losses or store surplus feed from the
drain tank. In a system associated with an auxiliary boiler, as on a motor
ship, the drain tank or hotwell will be open to the atmosphere. Such a
feed system is therefore referred to as 'open feed'. In high-pressure
watertube boiler installations no part of the feed system is open to the
atmosphere and it is known as 'closed feed'.

An open feed system for an auxiliary boiler is shown in Figure 5.1. The
exhaust steam from the various services is condensed in the condenser.
The condenser is circulated by sea water and may operate at
atmospheric pressure or under a small amount of vacuum. The
condensate then drains under the action of gravity to the hotwell and
feed filter tank. Where the condenser is under an amount of vacuum,
extraction pumps will be used to transfer the condensate to the hotwell.
The hotwell will also receive drains from possibly contaminated systems,
e.g. fuel oil heating system, oil tank heating, etc. These may arrive from
a drains cooler or from an observation tank. An observation tank, where
fitted, permits inspection of the drains and their discharge to the oily
bilge if contaminated. The feed filter and hotwell tank is arranged with
internal baffles to bring about preliminary oil separation from any

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