Heat Tracing for 3/4" drain from 12" Process pipe

[pbpower14]

I am looking for information to tackle heat tracing problem on 3/4" vents and drains.

Here is the situation:

12" Process pipe for steam at 1100 F and 2000 PSIG. Total length of pipe is 400ft with many bends because of expansion (pipe expands when heated)
There are many (lets say 50) vents and drains on this line.
I am looking for a solution to heat trace these line when the pipe is not in operation. (let's say for a week)

Design factors:
Temperature -5F (winter low) with 20 MPH wind.
Pipe should not fully freeze (72 hours)
12" line will not freeze in 72 hours with 2" insulation (because the 24 hour cycle -5F to 25F temperature never stays constant in real world)
3/4" drain however will freeze within 10 hours of temperature being lower than 25F.

Can someone help/suggest how to protect these 3/4" vents and drains from freezing and what kind of protective measures I can take.

Thanks in advance.

 

[racookpe1978]

Actually, your best solution to "never freezing" is to be able to completely drain every small bore line. Completely 100% dry lines below the isolation valves from the main line will never freeze. Do that by careful and thorough small bore piping routes to ALWAYS slope downhill to open drain points. Then you need to keep warm the short little stubs between the 12" main line and the isolation valves. Or just use the main line to re-melt those stub lines

Now - T100% drains are not easy, but your only other options is to completely and 100% heat-tape them and then hope that the heat tape and wrapping and insulation and heat-tape power supply and heat tape power regulator never fail during winter.

How are the drain lines operated, and where are their cutout (open/shut) valves?

 

[pbpower14]

Thanks for suggestion racookpe1978,
3/4" drain/vent has two isolation valves. I wanted less leaks through vents and drains. but these are manual drains and vents (i.e someone walks to them and open the drain).

Vents are placed at every high point in the line and drains at every low point. (12 vents and 14 drains total)

 

[StoneCold]

Ok I'll bite on this.
Why would the high point vents freeze if you shut of the steam line???
Open all the drains when you shut down the line. If they are plumbed with no pockets you should be fine, especially for only 72 hrs.

Regards
StoneCold

 

[pbpower14]

Thanks StoneCold,

I agree with you. I do not need to heat trace vents (since these are high points and water/condensate only collects at low points).

I was exploring if there is any technique used else where other than manual draining.

 

[StoneCold]

pbpower14
I think the problem with heat tracing and insulating is that you will have to pull all the heat tracing off before you start up. The heat trace wire will melt way before you get to 1100F.
You might consider blowing compressed air down the line once it cools off. Just to sweep out any pockets of water and to blow your drains dry.

Regards

StoneCold

 

[pbpower14]

Wow compressed Air is good alternative.

I will definately consider it because it makes sense economically.

Thanks for a great tip StoneCold.!!

 

[racookpe1978]

If so, permanently attach the air blowdown line to the highest vent point you have, but you MUST isolate the air supply with two isolation valves, and a bleed line between them, or a made up isolation flange: You cannot cross-connect the steam and air sides ever.

You appear to be manual, if so, have Manuel walk down and open all drain line valves. Go back and hook up the air supply to the vent line, then blow the air down through the vent to the main steam line and out through all the open drain lines.

 

[pbpower14]

I have an automatic isolation valve (12") on the boiler outlet and at the plant inlet. I am planning to design a flanged connection (1/2") with isolation valves for compressed air. That way my compressed air line is safe from heat and when operator shuts down the boiler, after 6-8 hrs later he/she can open the drain and blow the air through drain valves one by one.

Thanks for your genious idea.

It solved my problem....