Design of Compabloc exchangers to mitigate refinery fouling

This paper describes the thermo-hydraulic performance of welded plate heat exchangers like the Compabloc™ units (offered by Alfa Laval). Two case studies are investigated in this paper. The first involves an exchanger in which heat from the residues leaving a vacuum distillation unit is used to heat crude oil. The physical properties of the residues are very sensitive to temperature and the heat transfer coefficient on the hot side of the unit is very much lower than that on the crude side. The second case study involves a heat recovery match between a column pump around stream and crude oil. In this example the heat transfer coefficient on the hot side of the unit is high. A thermo-hydraulic modelling of the exchangers is investigated and it has included a consideration of the variation of the physical properties across the length of the exchanger since some complex combinations of flow passes are possible. Modelling and integration of the fouling behaviours in these exchangers shown to be great instrument to their subsequent design since the fluid shear stresses generated in these exchangers can be high to minimise fouling but at a cost of pressure drop. A model developed for analysing fouling has also been applied to these exchangers and results show that operation of these welded plate exchangers at certain fluid shear stress values can result in excessive fouling.