(94b) Overview of the Mechanisms of Fouling In Pre-Heat Trains and Conclusions Regarding Operating Practice

The fouling of heat exchanger surfaces in exchangers used in pre-heat tarins can be the result of a variety of mechanisms.

Below the de-salter fouling can be the result of wax deposition, particulate deposition, or the deposition of salts.

The exchangers positioned immediately after the de-salter should exhibit little fouling. However, if the de-salter is not operating properly the depsoition of inorganic salts can be a significant problem. If slops are being inappropriately handled, then polymer gum formation can lead to high fouling rates.

At the hot end of the deposition of asphaltenes is the most likley cause of fouling.

If insufficient heat recovery has been achieved in the pre-heat train then high fouling rates can be encountered in the convective section of the fired heater. This can give rise to excessive coke production. With VDU's excessive fouling in the fired heater can result in excessive quanities of coke being fed top the distillation column and fouling of the clumn itself.

These various mechanisms and problems are reviewed.

Suggestions regarding operating practice are made.