(119a) Crude Unit Heat Exchangers and Fouling: Engineered Solutions

Engineered Solutions

Andrew W. Sloley

All heat exchangers in refinery crude distillation units foul. Fouling on the crude oil side of the preheat train imposes significant capital, maintenance, and operating costs on the crude unit. The conventional approach has been to use fouling factors that account for enough fouling for the unit to have a reasonable duration between exchanger cleaning. Fouling factor use suffers from:

• Difficulty in execution – many fouling factors are either too high or too low for specific services. This leads to higher operating costs of over-use of capital.
• Lack of explicit understanding of extra capital involved.
• Over-sized exchangers with low fluid velocities – increasing fouling rates and defeating the purpose of fouling factor allowances.

Enough fouling will shut crude units down, increasing maintenance costs and opportunity costs of lost production.

Of course, the best fouling is the fouling the plant doesn’t have. Engineered approaches to decreasing fouling in crude unit exchangers include:

• Valves and piping to allow for cleaning during operation.
• Optimized baffle-cut and baffle-spacing configurations coupled with high shear-stress designs (the ‘no fouling’ approach).
• Alternate shell-and-tube exchanger geometries
  • Helical baffle
  • Rod baffle
  • EMbaffle®
  • Twisted Tube®
• Surface treatments (polishing)
• Tube inserts
• Non-shell-and-tube exchangers
  • Spiral plate
  • Welded plate

All these options are reviewed and best practices recommendations for crude unit exchangers are made.