Drying boiler tubes

[CGarfield]

Good day;
We are in the process of preparing for hydrotesting some OTSG units. The client will not be using them for quite some time after hydrotesting. The AI wants to see a procedure for drying the waterside of the tubes before we button everything up. Our intention is to use an oil free compressor and desiccant dryer to blow any moisture from the tubes. I'm wondering if anyone can give me a guideline as to what velocity of air we should target through the tubes? We intend to use a piece of cardboard to determine when the drying is complete. Any moisture on the cardboard means we have to keep drying. I'm wondering if anyone has any experience with drying boiler tubes? I'm looking for a rough idea how long the process will take. I'm guessing the drying time is a function of air flow and waterside volume, but would appreciate any insight you may have. I figured a couple of days for drying, but I'm just guessing.

Thanks in advance.

Brian

 

[macmet]

What is your target moisture level? If you use compressed air you will on,y get it as dry as the air.

I have seen boilers dried with hot air from a trailer sized compressor which worked fairly well and took about a day. Can you use the gas turbine to dry it?

Is freezing a concern for you?

 

[CGarfield]

The client specification is for a dewpoint of -40C. We are considering a trailer mounted unit. However, I thought it was coming with a desiccant dryer.... I will contact the vendor again to confirm.
I will have to investigate the turbine option. I'm not sure if our client will allow it or not.
Yes, freezing is major concern. There are a lot of eyes on this project right now. I want to make sure we allow enough time in the schedule to properly dry the units.
Thanks

 

[macmet]

If this is the initial hydro, I would suggest that you ask the AI about postponing the hydro until after the winter season. Button the unit up with some desiccants and nitrogen and wait.

I think that for storage, getting the unit down to -40C dewpoint is good enough, assuming it is an accurate reading. But I am always worried about tubes with water standing in low points and the air passing over the surface and leading you to believe it is dryer than you believe.

 

[CGarfield]

Good points. I have a similar concern. We are currently developing a procedure to blow from every high point vent and opening each low point drain. We are anticipating this will take two to three days to accomplish.

Yes it is initial hydro. I don't think the AI would have a problem with postponing. Our client is pushing to do it right away. The client is considering a nitrogen pad or just leaving dry air in it. Still waiting for a decision.

 

[macmet]

If this is a new boiler you "should" be fine, but no guarantees. It should be obvious that you make absolute certain that there is no way water can get by a valve and into the boiler. I have seen that happen on a relatively new boiler myself. Good luck.