Heat optimisation of recycled oil production from waste oils and oily waste waters

Waste oils, bilge water and oily waste waters are more and more being processed into recycled oil products. Producing marketable recycled oil with a sufficiently low content of water, sulphur, heavy metals and other trace elements requires energy-intensive processing of oil/water mixtures containing up to 90% water. This paper addresses the energy economy of a processing plant that suffers from significant heat losses as a result of electricity use for heating and the time-delays between receiving the raw material and its actual processing. An assessment is made of the scale of the energy dissipation and how these can be reduced, for example, by replacing input of electricity by a heat source; by reducing on the heat losses to the environment during product and raw material storage; by making better use of the heat of the incoming raw material when it is delivered; and by using heat storage volumes for "hot" streams of raw material, product oil and water separated from the oil/water mixtures. Exergy analysis is used to calculate the energy losses to the environment and the efficiency of the heat exchange steps. Minimising the use of electricity and fuel oil for heating purposes is the main target in this work. Also included in the analysis are seasonal effects. An example shows how batch-wise receiving of raw material could be integrated with a continuous process where hot water is one of the by-products.