Heat exchanger fouling
Heat exchanger fouling is the layer of deposit that builds on the heat transfer surface, and it costs duty and pressure drop long before it causes a failure.
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Types of heat exchanger fouling
Heat exchanger fouling is the deposit layer that builds on the heat transfer surface. Fouling costs duty and pressure drop long before it causes a failure, and the type of deposit decides the cleaning method.
- Scaling, or precipitation fouling
- Salts coming out of solution onto the surface, calcium carbonate most often. Scale is the usual deposit on water duties, and it favours the hottest surface.
- Particulate fouling
- Suspended solids settling out of the fluid. Particulate fouling builds where velocity is lowest.
- Corrosion fouling
- Corrosion products forming in place on the surface. Corrosion fouling matters more than the duty loss suggests, because the surface itself is being consumed.
- Chemical reaction fouling
- Product changing on a hot surface and sticking to it. Coking on refinery duties and protein deposits on food duties are both examples.
- Biofouling
- Growth of organisms on the surface, common in cooling water systems and particularly where water is stagnant.
What tells you fouling is costing you
- Approach temperature widening against its clean value
- Pressure drop rising across the unit at the same flow
- Downstream plant working harder to cover the shortfall, which is usually where the energy cost actually appears
- Cleaning intervals getting shorter, which points at something upstream rather than at the exchanger itself
Heat exchanger fouling questions
How do I know which type of fouling I have?
The deposit is identified when the unit is opened, and that decides the cleaning method. Guessing at it is how surfaces get damaged and how the deposit comes straight back.
Can fouling be prevented?
It can usually be slowed. Water treatment, flow velocity and surface temperature are the three levers, and which one applies depends on the deposit you actually have.
How often should a fouled unit be cleaned?
On condition rather than on a calendar. When the loss in duty costs more than the clean does, it is due, and trending the approach temperature is what tells you.