#6 FW generator Flashcards
Domestic FW Usage
70 litres per day per crew
15-20 tonnes for a crew of 20
Domestic Uses
Bathing, drinking, washing, cooking
Machinery
Boiler steam plant 50t/ day
engine cooling
engine room cleaning
S
Shore supply water
minimum amount of water from shore
produce rest onboard
has impurities like chlorine and suspended particles (not suitable for machinery)
scale to form on heat transfer surface area and reduce efficiency
500 ppm (engine requires 2.5 ppm)
Boiling type
boiled till evaporation
condensed into fw
Flash type
heated sea water led into a chamber with sub-atmospheric pressure
water instantly flashed into steam
Reducing boiling point
reduce pressure
done by creating a vacuum
ejector
Scaling
impurities left behind
calcium carbonate
calcium sulfate
magnesium hydroxide
calcium carbonate
seawater contains 180 ppm of calcium bicarbonate
calcium sulfate
seawater inside evaporator maintained at high density
occur frequently in brine solutions
Magnesium hydroxide
seawater boiled above 80 degree celcius
very hard to remove
Prevention of scaling
mantain boiling point below 80 degree celcius
prevent brine by continually introducing new seawater
Why Water treatment
condensate cannot be used as it is only boiled at 30 degree
bacteria will not be killed, hence need to be treated
Water treatment methods
ultraviolet light
chlorination
sand bed
activated carbon filter bed
ultraviolet light
treated with ultraviolet light to kill all bacteria
