Freezing Steam Coil
Freezing Steam Coil
(OP)
I need to install an air preheater for an air cooled exchanger such that the winter air here in Northern Alberta is preheated to avoid over cooling of the process fluid. If i install a steam bundle, the bundle at some point will simply freeze with -30F air. Is there a type of steam bundle that will not freeze and crack?





RE: Freezing Steam Coil
The condensate must be able to gravity drain to a vented receiver, and the coil must have vacuum breaker. Check out "Hook Ups" by Spirax Sarco for some excellent info on this.
RE: Freezing Steam Coil
RE: Freezing Steam Coil
We used a steam heater to preheat H2 and that hydrogen came off at about -75C in the cold train. So, it can be done but you need to ensure you remove the condensate as soon as it forms.
Get some user names and talk to them, steam coils as you've described are pretty commonly used and they do work well, if selected properly.
For a steam coil, that shouldn't be difficult. You are just going to turn the steam on full I assume and the coil needs to be sloped to the steam trap (or traps). If you need turndown capability (for when the air is 0F rather than -30F), put in parallel steam coils with their own traps rather than throttling the steam pressure to one big coil.
RE: Freezing Steam Coil
I've seen many problems (I'm also in Alberta) of breaking steam coils (or hydrocarbon coils with water) due to freeze-up during cold weather. Waste steam condensers can be a particular problem because they are usually designed wrong for our climate.
The only design that I've seen that works well for waste steam condensers is to add ducting to recirculate warmer exaust air from the fin-fan back to the inlet plenum. on a forced draft fan, this would involve "boxing in" under the fan with louvers that would open based on the fan inlet temperature. Warm air from the outlet could be routed back under the fan or exhaust to atmos (again using automated louvres).
This may even work for you instead of using a steam coil.
I've often seen finfans in hydrocarbon service tarped to keep heat in. One site I worked at had a pretty good method to "roll" tarps in place. I'd rather do this than have a steam coil...
I hope this helps....cause I understand the mess and hassle broken steam coils can be when it's 30 below.
Regards,
Bob