Heat Tracing 5

[kptx171]

I have 20 pipe lines of average lengths about 100 ft and dia of 2 in with liquid temp 150F to be freeze protected above 40F.Can i use one thermostat and have ambient set at 40F and switch all 20 heat tracing circuits(Self regulating heat tapes) from a powersupply panel?

 

[itsmoked]

You have stated nothing about the power or current required by these 'tapes' which makes an answer hard.

Generally if the tapes are self limiting then you could use an ambient thermostat physically located at the absolute coldest area you want to protect. You then control a handful of relays with the the thermostat which will in turn run the HTs.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[quark]

Should we require a thermostat for self regulating tracer tapes?

 

[waross]

Hi quark
Heat tapes are often de-energised in warm weather when they are not needed. The self regulating feature limits the maximum temperature but does not turn them off completely. You can waste a lot of energy trying to heat cold water a couple of degrees.
yours

 

[rcw retired EE]

Check the sizing of the supply feeder and the contactor against the sum of inrush currents or cold starting currents of the heat tapes. The initial current when the thermostat controlled contactor turns all circits on at once can trip your feeder breaker. The heat up current may last a few minutes. We had to subdivide circuits on 2 or 3 thermostats to cure that.

Otherwise, what you describe works OK with self-limiting cables.

 

[quark]

Waross,

Thanks. That idea didn't strike me becuase the tracers I used, so far, are not for freeze protection but to heat fuel oil to boilers. Anyhow, it is right time for me to take some classes in lateral thinking

BTW, can you please let me know, what percentage of power we waste, once the fluid temperature reaches the set temperature of the tracers, on an average.

 

[waross]

Hello quark
I'm sorry. I missed the point of the fluid temperature at 150F
I should have said "You can lose some energy" rather than "A lot of energy"
I just did a little checking and found;
Self regulating tapes have a maximum temperature and a maximum de-energised temperature. The actual temperatures vary with the type, but 150F is dangerously close to the limit for some types.
The temperature/wattage curves do not go to zero wattage. The curves end at the maximum temperature and show a small output at maximum rated temperature.
If you can get some performance curves for the particular tape you are using you will be able to make a guess as to the losses.
The application instructions recomend using thermostats but self regulating tape may be used without thermostats.
rcwilson's warning concerning inrush currents is noted in the installation instructions for self regulating tape.
See

http://www.heat-trace.com/index.html

respectfully

 

[danw2]

1) The principle I learned about heat trace is that heat trace is used to provide heat to guard against freezing in an "insulated" pipe.

On previous projects, I ran a Windows program from the heat trace vendor that calculated heat loss at a minimum expected ambient temperature X in Y mph wind with a pipe with Z" of insulation with factor Ra to be maintained at b°C.

Are your pipes insulated? Have you calculated heat loss under assumed conditions? Is the self regulating tape of sufficient rating to make up the heat loss?

2) I'm not sure what you mean by 'freeze protected above 40F'. One is usually concerned about freeze protection below a certain ambient temperature, not above an ambient, like 40°F. Can I ask how you picked 40°F?

Dan

 

[itsmoked]

I'm wondering why pipes that are at 150F would need any help preventing freezing.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[davidbeach]

He says liquid, not water. Maybe the liquid isn't water and has a higher freezing point.

 

[waross]

Hi Keith
I have seen caustic solutions in a waste oil reclamation facility that froze at a higher temperature than water. We used a freeze point temperature of 40 F. (I got the figure from the chemical dept. They may have added a few degrees safety factor to the actual freeze point but it was definitely above 32 F.) The heat tracing on the caustic lines was on our "watch" list in cool weather. In a batch operation, the fluid may be standing and cooling down at times.
respectfully

 

[BJC]

IME with heat tapes I have learned to install redundant tracing. That will vary depending on the critically of the system and the cost of downtime. Heat trace is cheap compaired to pulling off insulation in the middle ofwinter looking for a bad tape.
Most ot the bunkerC i have seen traced was with steam trace. When the traceing system goes down it turns to roofing tar.
Second install current monitors to alarm on failure of the system. Some people use indicating light with signs to call someone if the light is out, but they never seem to. I am not up on the latest monitoring systems but I am sure there are some better ones out there.

 

[itsmoked]

Thanks waross.. Funny how I make assumptions.

Excellent points BJC. I would certainly follow your suggestions.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[BJC]

I left out one of the current monitors tha I found to work well. Check out their Hawkeye units. I have had MCCs vendors install them in buckets.

I just mention them in another thread on agitators but I don work for them or have stock in the company <%^)

http://www.veris.com/