joe,

I'll be damned if I know. I've never cleaned one.

You don't say what size? We used to clean the heat exchangers in the
refinery with steam lances and then Hot water. Any solids were removed
with a large steel blade but i don't think your into that size.

They required riggers to pull them and move them to a cleaning area were
exchanger cleaners would work on them.

http://community.webtv.net/tassail/ILLDRINKTOTHAT