Improved Energy Efficiency in CDUs Through Fouling Control

Crude oil distillation accounts for a large fraction of the energy used in oil refining. Crude oil contains a variety of substances which tend to deposit as fouling layers in heat exchangers, and this results in decreased energy recovery and requires increased energy input to the furnace. CDU pre-heat train fouling is estimated to cost over $2 billion per annum in the US alone. In addition, non-reusable fuel savings from fouling mitigation would result in the reduction of CO2 emissions.

This paper outlines a holistic strategy for fouling mitigation and control consisting of:

• crude oil storage under non-oxidizing conditions • crude-oil blending to minimize fouling caused by asphaltene precipitation • revamping the HEN structure to keep tube wall temperatures below the fouling threshold • retrofitting the HX bundle and channels (eg. twisted tubes, “E-to-F” conversions) to increase velocities and shear rates • replacement of Shell & Tube HX with alternative designs that are inherently resistant to fouling and easy to clean in place • use of tube inserts to promote high shear rates • addition of chemicals to retard deposition of asphaltenes and other foulants • “smart HX cleaning” strategy, based on fouling rate models

Chemical analysis and visual observation of the deposits are key diagnostic tools that indicate the probable cause of fouling, and suggest the appropriate control/mitigation approach.

Case study results will be presented.