Tank & Suction Heating
U-Tube Bundles

Tank & Suction Heating U-Tube Bundles

Heating Inside the Vessel

An immersion bundle is a U-tube assembly on a mounting flange that bolts to a tank nozzle or manway. Steam or hot oil runs through the tubes and the tank contents are the shell side — there is no shell, because the tank is the shell. It is one of the few places a heat exchanger is bought without a pressure vessel around it.

Whole-tank heating. A bundle sized to raise the entire contents to temperature. Simple, slow, and the correct answer where the whole inventory genuinely has to be uniform: asphalt held for loading, tallow that must not stratify, or product being conditioned before a batch operation.

Suction heating. A smaller bundle located at the pump suction, conditioning only the volume about to be drawn off. It uses a fraction of the energy, reaches pumpable condition far sooner, and leaves the bulk cold. On heavy fuel oil and heavy crude storage this is very often the right answer, and it is frequently overlooked because whole-tank heating is the more obvious idea.

Fins belong on the tank side. The controlling resistance is outside the tubes, where a viscous product moves only by natural convection. Adding plain tube area helps a little; adding fin surface on that side helps a great deal, because it puts area where the resistance actually is. The exception is any product that carbonises or leaves residue, where fins clog faster than they earn their surface and plain tube with more of it is the more maintainable choice.

Watch skin temperature. Heating heavy product with high-pressure steam overheats the fluid at the tube surface and carbonises it onto the bundle. That deposit insulates, which raises surface temperature further, which makes the deposit worse. Lower-pressure steam or a hot oil medium at a controlled temperature keeps the surface below the product's degradation point and keeps the bundle clean.

Practical constraints. The bundle is cantilevered from its mounting flange, so support and vibration have to be considered rather than assumed. Removal means withdrawing it back through the same opening, which sets a clearance requirement outside the tank equal to the bundle length — worth confirming on a tank in a bunded area or hard against a structure before the order rather than at the first outage.

Related pages: tank-mounted and immersion bundles, thermal fluid heating, industrial U-tube exchangers and replacement bundles.