The main reason for the adoption of double evaporation boilers in tankers is that oil majors are concerned of damage caused by oil and sulphur which enters the feed systems through leaky steam heating coils used for heating the oil in cargo tanks. The double evaporation boiler is proof against this by virtue of the fact that the boiler proper operates on a closed circuit, its initial charge of high quality water being continuously evaporated in the boiler and condensed in a heat exchanger producing low pressure steam ,and requiring occasional make-up to replace incidental losses.
All the feed necessary to produce the low pressure steam is fed into the heat exchanger and ,as this is not fired. Dangers of damage to boilers by oil contamination and sulphur are eliminated in
this non-fired heat exchanger.
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