Heat recovery units are used in some vessels with propulsion diesel engines or auxiliary diesel engines. Two variations of the recovery type are used; both use the heat from one or more engines as a source of heat to evaporate seawater. Supplemental water heaters may also be used to provide an additional heat source as needed. In one model of a heat recovery plant, the heat of the diesel engine jacket water is transferred to the seawater in a feedwater heat exchanger. When it enters the distilling plant, the heated seawater flashes into steam, hence the name flash-type distilling unit. In another design, the hot diesel engine jacket water is circulated through a tube bundle that is submerged in seawater. The seawater is boiled in a chamber that is under vacuum, hence the name submerged-tube distilling plant.

SUBMERGED-TUBE DISTILLING PLANT

The unit shown in figure 15-2 is a submerged-tube heat recovery distilling plant. Figure 15-2

Figure 15-2.-Model S167ST heat recovery (submerged-tube) distilling plant.

shows the major components that we are going to discuss. The main source of heat for the feedwater is a continuous flow of diesel jacket water. The hot jacket water flows through the heating tube bundle and transfers its heat to the feedwater. In the event that the heat of the jacket water is not sufficient to maintain the temperature through the tube bundle between 168 and 172F, supplemental heaters (electric or steam) are provided in the system and are energized to provide additional heat as required.

When properly operated, this unit is capable of producing 4,000 gallons of distillate per day with a purity of 0.065 epm chloride, 2.3 ppm chloride, or 9.43 micromhos/cm.