Bilge Water Heating

Once in a while the question is asked about the need of heating bilge water for processing. The question is asked, because some makers offer heaters in their bilge separators.

Anyone who cooks pasta knows that it takes quite a while to heat a pot of water on the electric stove. Let me demonstrate on hand the old British system how much heat is required to heat bilge water while processing. By definition 1 British Thermal Unit (BTU) is the energy required to raise the temperature of 1 lb of water by 1 degree Farenheit. Applying this to a small 1 ton/hr bilge separator, the size of the heater can be determined as follows:

To raise the temperature of the 1,000 liters (2,200 lbs) process water by 1 degree Centigrade (1.8 deg.F), we need to apply 1.8 x 2.2 x 1000 = 3,960 BTU/hr; which factors out to a heater capacity of 1.16kW. - To get a meaningful 10 deg C (18 deg F) temperature rise in a 1 ton/hr unit we'd need to install an 11.6kW (15HP) heater, with a 2.5 ton/hr separator a 29kW heater is required!

The other side of the coin in bilge water heating is heat density of the heating element. Oil has roughly half the heat value of water, therefore when heating the oily water mixture the oil will "bake" to the high density heating surface of the element, causing the electric heater to burn out.

All this to say that in my personal opinion, whether the ship is burning HFO or distillate, it is not really possible to heat the bilge water significantly while processing. A heating element in the bilge separator may very well be practical as a freeze protection.