An open feed system for an auxiliary boiler. 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.
Must read ➤Definition Of Open Feed System
➤Information About Boiler Operation
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 contaminated feed or drains.
The feedwater is then passed through charcoal or cloth filters to complete the cleaning process. Any overflow from the hotwell passes to the feedwater tank which provides additional feedwater to the system when required. The hotwell provides feedwater to the main and auxiliary feed pump suctions. A feed heater may be fitted into the main feed line. This heater may be of the surface type, providing only heating, or may be of the direct contact type which will de-aerate in addition.
De-aeration is the removal of oxygen in feedwater which can cause corrosion problems in the boiler. A feed regulator will control the feedwater input to the boiler and maintain the correct water level in the drum. The system described above can only be said to be typical and numerous variations will no doubt be found, depending upon particular plant requirements.
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