(14c) Crude Unit Fouling: What's Normal? Why is it Important?

Comparing actual crude unit heat integration performance to predicted performance or best-practice expectations hinges upon understanding crude unit fouling. Based on long industrial experience a fouling factor summarizes heat exchanger fouling tendencies. This approach has many drawbacks. Recent work has focused on probabilistic and statistical methods of evaluating fouling systems. Nevertheless, fouling factors remain in common use. They have the advantage of simplicity, wide-acceptance, and a long historic baseline for comparison purposes.

Common perceptions of acceptable fouling in crude units come from the TEMA (Tubular Exchanger Manufacturers Association) values. The genesis of these fouling factors is unclear. The purpose of these factors was to establish a baseline for design of new heat exchangers. Over time, the values have increased – but questions about their reasonableness persist.

Plant data makes the complexity of fouling factors clear. Fouling varies with:

• crude types, blends, and processing history,
• interaction of multiple fouling mechanisms,
• exchanger type and configuration,
• temperatures and pressures in individual exchangers,
• flow rates, pressure drops, and other operating conditions,
• desalting effectiveness,
• contaminants and additives in use, and
• cleaning history.

Published values of fouling factors (and fouling rates) often lack basic information on many of the factors affecting fouling. Nevertheless, data from typical plants show the TEMA values are extremely low compared to experience in many units.

This presentation includes:

• an analysis of fouling factors extracted from published reports of crude units,
• initial publication of fouling factor data from several crude unit performance tests, and
• a review of the importance of using the right fouling factor in design and operating optimization.