Single Stage Heat Transformer Used to Recover Energy in an Oil Distillation Column

Abstract

Abstract This paper presents the theoretical analysis of the use of a single stage absorption heat transformer operating with the water-lithium bromide mixture coupled to an oil distillation column installed in a Mexican refinery. The distillation column is used to produce mainly C5H12-1 and C5H12.2. Actually, the heat load in the condenser column is delivered to the atmosphere at 82°C while heat is supplied to the reboiler of the column at 115°C to distill the oil products. In order to reduce the heat load supplied to the reboiler a single stage heat transformer may be coupled of the way that the heat delivered in the condenser may be used as heat input in the generator and evaporator of the heat transformer which increases the heat to a more useful level in the absorber to preheat the stream entering to the reboiler. To do this, a mathematical model of a heat transformer was developed in FORTRAN and introduced to the software ASPEN PLUS. Both components coupled were modelled on steady state conditions. The results showed that the coefficient of performance of the heat transformer which is directly related with the energy saving in the column is highly dependent of the condenser and absorber temperatures of the heat transformer. At a condenser temperature of 22°C (cooling water temperature of 14°C and ΔT = 8°C) which can be obtained in winter time in that part of Mexico, up to 43% of the energy supplied to the reboiler of the distillation column may be saved by using the heat transformer, but in general at a condenser temperature of 30°C, which is a more representative temperature during a whole year, up to 30% of the energy may be saved. Also, it was shown that the reboiler’s area may be reduce considerably if the distillation column was built since the beginning integrating a heat transformer, which may helps to reduce the extra capital costs caused by the use of the heat transformer.