Fouling Precursor
- Precipitation on blending that changes solubility characteristics – asphaltenes, polycyclic aromatics, polymers
- Inorganic fouling precursors – salts, iron sulfides, ammonium chlorides, dissolved soluble catalysts
- Coke formation on heated surface - thermal instability and cracking
- Deposition of insoluble converted asphaltens, polycyclic aromatics, polymers on cooling
- Polymerization of olefins – autoxidation or metal-induced polymerization
- Oil-water emulsions due to aqueous phase carry over – desalter problem
- Corrosion products – upstream vs in-situ corrosion
Physical and Chemical Mechanisms
Interactive effects of physical and chemical mechanisms depend on three fouling cases:
- Case 1: Precursor formation in the bulk flow or carried over followed by deposition on the heat transfer surface
- Case 2: Precursor generation in the thermal boundary layer followed by deposition on the heat transfer surface
- Case 3: Precursor formation on heated or cooling surface
Root Cause Analysis to identify appropriate solutions:
- Selective foulant analysis to validate chemical mechanisms
- Fouling trend under different process conditions that affect the interactive effects of physical and governing chemical mechanisms
- Heat exchanger design and off-design performance, particularly for two-phase flows
- Laboratory tests:
- Fouling rates with incremental addition of fouling precursor – iron naphthenate
- Fouling rates- effects of velocity and temperatures