4 replies to this topic

[Tommy]

Hi,

I am a new user, this is the first time I write on this forum but I think it is very useful to exchange ideas and suggestions.

I have to do a heat tracing on a K.O. Drum drainage line (water only) to avoid freezing. Minimum ambient temperature is -10°C (14°F). I thought to ensure a costant temperature of +5°C (41°F).

Could you give me any suggestions? Do you think the temperature I chase it is correct?

Thank You

[Art Montemayor]

Tommy:

I've done this several times in Chemical processing plants and the results turned out very well each time. What I've done is the following:

1. Strip the vertical drum (I have to assume it's vertical, you don't say anything - the orientation is important in order to have drainage of steam condensate) of any insulation and clean the drum of all surface paint and rust;

2. Obtain & apply a mortar-like paste called "Thermite" ( a special, heat-transfer cement made by a company in San Antonio, TX) and on top of the mortar wind a 1/2" copper tube in a spiral coil - starting at the bottom cylindrical seam and stopping at the top horizontal seam. The coil should be tightly wound and tight so that the contact between the drum's surface, the mortar and the coil will be as close as is possible. You will be depending on CONDUCTION as the primary heat transfer, so you want the surfaces to be intimate.

3. When the mortar sets, you can insulate the results. Introduce low pressure (waste) steam at the top of the coil and put a small, thermostatic steam trap at the bottom exit. You can control the steam flow automatically or manually. The drum will be heated and winterized.

If you ever maintain a low level in the drum (below the lower cylindrical seam, then you should also put a coil on the bottom head. This coil would be a flat, pancake shape formed around the head such that the top inlet is just below the lower cylindrical seam and the outlet is near the center, bottom of the head. Again, introduce steam at the top and put a steam trap at the bottom. Insulate the results and be sure to vapor seal.

I hope this helps you out. You can find the Thermite cement source by asking for it in the industry or searching on the Google database engine. Go to: http://www.thermon.com/ and click on "Catalog". You can download a lot of useful information on heat tracing.

Art Montemayor
Spring, TX

[ShaunHill]

Art's suggestion is a good one on how to install tracing on the vessel to prevent freezing.
I would like to add a few suggestions on alternatives.

First of all, if you are just preventing the liquid from freezing due to ambient conditions, you don't need to heat trace the entire vessel. Just go from the bottom of the vessel up to a high liquid level. I've also used a similar approach for horizontal vessels where we've heat traced the bottom 1/3 of the vessel. The entire vessel will still be insulated of course.

Also, you haven't stated what kind of utilities your plant has. Even low pressure steam is quite hot, and dealing with the condensate can be a concern depending on how far away from the steam source you are.
I've seen glycol (ethylene glycol/ water mix) used as a heat medium in many plants. It generally runs at a lower temperature than steam and unlike steam condensate, it does not freeze in ambient conditions down to -40C.

Electric heat tracing is another option that is worth looking at. It runs at minimal temperatures. I can safely put my hand on it and it feels only maderately warm. If you are a long distance from a suitable heat source it may be an easier installation. It can use a surprising amount of electricity (depending on how much tracing you require), so it is worth getting an electrical person involved to estimate the requirements. You will want to consider how this will impact your electrical bill and utility supply. However, the advantage is that it can be easily controlled by automatic temperature controls, so you don't need to run it when the temperature is above freezing.

Another option is to not use tracing on the vessel, but build an insulated enclosure around the bottom section of the vessel. The part of the vessel that is inside the enclosure is not insulated, outside the enclosure, the vessel is insulated. Put an explosion proof heater inside the enclosure. Depending on how big the enclosure is and what is inside that requires access for maintenance, you should consider if it may need to be classified as a confined space. To get around this, make sure it is fitted with properly located removable panels or doors for access. However, be clear that this is not a building. It is an insulated box.

You should also heat trace the liquid line out of the vessel, particularly if flow is intermittant. Same options on tracing medium apply as above. However, another option that can be used is a utilidor. This is an insulated box that contains your piping. you also run other piping that is hot (waste heat source) in the utilidor to keep it warm. Of course, this requires that you have such piping in the immediate area.

[chemtiger]

ShaunHill is very professional. In fact it is very easy to do that. If it is ok to add some additives in the water. All will be ok.

[Tommy]

Thank you all for answers.

I think it will be better an electrical heat tracing with isolation of the vessel and of the drainage pipe because the plant is off-shore and there is not any waste steam available.