Glycol Heat Tracing

[ONEPOINT]

Hi,

I am wondering if someone knows about the Glycol Heat Tracing Systems? I need to find the number of tubes and the size of them for 24",12" 30" NPS? Any idea about a refernce manual or a handbook that would show the design procedures?

Regards,

One Point

 

[TD2K]

I don't recall seeing anything on glycol tracing design methods in the general literature. I worked in a plant that used it but I wasn't involved in the original design nor did we trace anything that large so it was always one tracer and a moot point. You might check with Dow Chemical as they sell a lot of glycol and they have some good information and may have some literature.

Barring that, you are back to developing them yourself. You have a hot tracer that is conducting heat from its surface to the pipe/air/insulation it's installed in. I'd try the following:

1. Pick a reasonable figure for your glycol tracing system for dP to estimate the flow through your tubing (50 psi?). 1/2" tubing is common, 0.049" wt is a common wt. Copper tubing is often used.

2. Determine how much flow you can get through various lengths, 100 to 200 feet is a typical maximum for inplant tracing. Using that flow, estimate the inside heat transfer coefficient through the tracer. At this point, you'll have to assume negligible dT.

3. Now, estimate the heat transfer from the tubing surface to the air and pipe. I'd likely assume natural convection with a heat transfer resistance from the tracer to the air and then from the air to the pipe, say in the range of 1/4 to 1/2 BTU/hrft2F. There was also an article in Chemical Engineering magazine a few years ago on sizing steam tracers (size and numbers), I'll see if I can find the correlations from the tracer to the pipe to pass on because they should be in the range of what you are dealing with other than temperature.

What the purpose of the above calculations is to determine whether the heat transfer from the hot glycol to the pipe is a significant portion of the overall heat transfer coefficient or if it can be neglected (I suspect the latter but I haven't run the numbers). Once you have an overall heat transfer for your tubing lengths, you can also see if the dT of the glycol along the length is significant and has to be taken into account. If it is, it would be a good reason to limit the tracer lengths on more critical tracing applications.

Once you have an idea what the heat transfer is you can see how many tracers you need for whatever it is you want to achieve, freeze protection, temperature maintenance at a higher temperature during a shutdown, etc.

 

[ONEPOINT]

Hi,TD2K (Chemical)

Thank so much for your advice. I would be intersted in finding that article from Chemical Engineering Magazine that shows how to do the sizing. Could you give me a hint of where could I get that article?

Could you please explain to me more specifically about the following advice that you have sent to me?

"Pick a reasonable figure for your glycol tracing system for dP to estimate the flow through your tubing (50 psi?). 1/2" tubing is common, 0.049" wt is a common wt. Copper tubing is often used.

What "dP" stands for and what does "a reasonable figure" refers to?

Looking forward to hearing from you,

Best Regards,
One Point

 

[TD2K]

It was from Chemical Engineering magazine, 1986, a little more than a few years back I'm afraid.

A glycol heat tracing system usually consists of a tank, heat exchanger to maintain the glycol at temperature and a circulation pump. The dP refers to the pressure produced by the pump and 50 psi to me would seem a reasonable value (I can't remember the exact value).

 

[ONEPOINT]

Hi TD2K (Chemical),

What do you mean by "you'll have to assume negligible dT."

What does "dT" refer to? Look forward to hearing from you.

Kindly Regards,

One Point