Design of Compabloc Exchangers to Mitigate Refinery Fouling

Design of Compabloc Exchangers to Mitigate Refinery Fouling

E. Tamakloe & G.T.Polley

Dept. of Chemical Engineering, University of Guanajuato

Welded plate heat exchangers (such as Compabloc^TM units offered by Alfa Laval) are finding wide application in the oil and process industries.

Quite complex flow arrangements can be used in such units. For instance, the authors know of one case in which a hot stream flowed through twelve passes whilst being matched against a cold stream that flowed through just 3 passes.

It is also common to find that the physical properties of the fluids being handled exhibit quite large changes between inlet and outlet of the exchanger. This means that the individual film heat transfer coefficients are different for each individual pass.

In this paper the authors describe how the performance of such exchangers can be analysed.

Since, an important application of such exchangers is improved heat recovery at the hot end of crude oil pre-heat trains, analysis of fouling behaviour of such units is also addressed.

 

MODELLING BEHAVIOUR OF A BASE CONFIGURATION

DEALING WITH VARIABLE PROPERTIES

OVERALL ALGORITHM

FOULING IN WELDED PLATE EXCHANGERS

EXAMPLE APPLICATION

CONCLUSIONS

In order to get good performance out of a welded plate heat exchanger it is often necessary to use multiple passes. A range of possible configurations is possible. Some of these configurations are complex.

The behaviour of multi-pass units has now been modelled. The modelling has included consideration of the variation of physical properties over the length of the exchanger.

The shear stresses developed in this type of exchanger can be much greater than those possible in shell-and-tube heat exchangers. This has led to interest in the application of this type of exchanger in crude oil pre-heat trains.

Examination of monitoring data has indicated that fouling models currently used to predict fouling rates in shell-and-tube heat exchangers may also apply to welded plate exchangers. Consequently, such a model has been incorporated into the modelling of welded plate exchanger behaviour.

Examination of an example application has demonstrated the importance of considering fouling behaviour during the design of this type of heat exchanger.

REFERENCES

Colburn A. P. 1933, “Mean Temperature difference and heat transfer coefficient in liquid heat exchangers”, Ind. Eng. Chem. Vol 25 873-877

Kern D. Q. 1950, Process Heat Transfer, McGraw-Hill, New York.

Polley G.T., Tamakloe E. & Picon Nunez M. “Models for chemical reaction fouling”, paper presented at AIChE Spring Meeting, Chicago, March, 2011

McCartney T. & Smith S. “Advancements in large scale application of ultrasonic cleaning in removal of refinery fouling”, 11^th Annual Intnl. Conf. on Petroleum Phase Behaviour and Fouling, June, 2010, Jersey City

Yeap B.L., Wilson D.I., Polley G.T. & Pugh S.J. “Mitigation of crude oil refinery heat exchanger fouling through retrofits based on thermo-hydraulic fouling models”, Trans.I.Chem.E.,2004,82A,53-71