Open vessels containing heated fluids should be covered to minimize losses.
Open vessels that contain heated liquids often have a high loss due to surface evaporation. This idea though commonly known is often not implemented on the plant floor. An open surface of area 50m2 looses 14940Kcal of energy per hour! Both energy and liquid losses are reduced by covering open vessels with insulated lids.
The table below shows the amount of heat lost per m2 of open surface in Kcal/hr. The losses are dependent on the difference between the ambient temperature and the liquid temperature.
A tank 5m wide and 10m long, is maintained at a constant temperature of 65oC. The evaporative heat loss from the tank if ambient temperature is 30oC would be:
Area of evaporating surface = 5m x 10m = 50m2
Total heat loss for uncovered liquid surface = 298.8Kcal/hr/m2 x 50m2 = 14940Kcal/hr = 5.4KL of FO / yr