In general, tube banks with gas flowing externally and perpendicular to the tube axis is frequently used. If the pot gas contains contaminants, such as particles and/or condensables (alkali metals, salts etc) mechanical cleaning such as hammering or shot cleaning (using steel balls or wire-cuts) are used. I have seen such soulutions in the steel and silicone (and Si-metal) industries, as well as in Municipal Waste Applications. If the deposit consist of dry particles, acoustic cleaning may be used (albeit I don't think it is very efficient), and finned tubes can also be applied to reduce heat exchanger volume/cost/pressure drop.

For the aluminum electrolysis industry, there are patents out there that have the pot gas flowing inside tubes (Alstom) and also having external crossflow using finned tubes (preferably elliptical tubes) (Solios), using proprietary techniques to maintain the surfaces clean.

Thank you for your answer Prof. Erling Næss