Steam Tracing vs. Electric Tracing (Sizing for Steam Tracing) 2

[jcurtis]

thread124-200052

Hi,

I've been tasked with the problem to weigh the pros and cons of Steam vs. Electric tracing on a #6 Fuel Oil line.

Some background information. We are a thermal generating station. We burn #6 Fuel Oil in our Boiler to make steam. A question posed to me was: is steam tracing a better option for heating out fuel oil line?

We currently run electric tracing on the fuel oil line up to our tank farm. From the Jetty to the tank farm is roughly 1700m long. The diameter of the fuel oil line to the tank farm is 0.46m (18"). Two phases are currently working and are doing the job of keeping the fuel oil warm, but since we are a thermal generating station someone asked if steam was a better option. The coldest it would get here is -20C (which is rare, and we wouldn't pump oil at that temperature anyway).

Personally, I'm of the mind if it's not broken, don't fix it, but I'd like to give my seniors a better answer than that.

I noticed these questions were asked in a pervious thread:

How long is the pipeline? As total, 2000m at most (including the run from the plant to the tank farm, then from the tank farm to the Jetty).
What diameter is the pipeline? 18"
Is there steam available at either end of the pipeline? Yes, we can provide steam at 700kPa (100psig). There is currently a pressure regulator to prevent steam above that pressure to be sent to the tank farm and beyond. Yes, removing it can be an option.
How often is the pipeline used? As needed, as much as daily.
What is the desired flow rate of the pipeline? Unsure.
Will the pipeline be used for other products? No.

I've done some calculations for the condensate loading and at +20C I've determined we would need roughly 2300kg/hr of condensate removal. Since I'm new to steam tracing, I'm not sure what to think of that number.

It seems like a costly venture to replace the working electrical heat trace with steam (albeit readily available). Being a junior guy, I'd like to get thought from a more senior level. With the numbers I've presented, is it even possible?

Thanks.
Jamie.

 

[ione]

Good stuff in the link below (a spreadsheet coupled with theory background). Hope it could help.

http://www.cheresources.com/steam_tracing.shtml

 

[rmw]

Steam tracing what are the pros and cons.

1. It requires a live steam source. Can you guarantee that you will always have a steam generator of some type on line? Maybe that is not an issue, but I have seen the same issue at single unit stations and the unit wasn't always on the line.

2. Do you have a supply of relatively low pressure waste steam, or will you be taking steam that you could be making your market product (power) with?

3. Are you going to waste or try to recover the condensate, and if the latter, how will you get it back and the condensate lines will need to be traced too at that temperature.

4. Trap maintenance.

5. Supply valving and valve maintenance.

6. Freezing of steam lines when steam tracing system is off and it drops below freezing.

Pros and cons of electric tracing.

1. You basically always have plant auxiliary power available (except during black outs and you don't have steam generation then either.)

2. Electric circuit device maintenance.

3. When you want it, switch it on, when you don't, switch it off and forget it.

I can't think of a lot of downsides to electric tracing, but if it were my decision to make, unless the answer to #1 and #2 above were a resounding yes and #3 was no, I'd go electric. Even if the steam were free and always there, I'd still go electric not to have to mess with the condensate.

rmw

 

[rneill]

If the electric system is already up and running then I think you would be hard pressed to come up with an economic justification to change it. I think it's usually the capital cost of the electric tracing that tends to make it look unattractive compared to steam. Since it's already there, you are comparing the operating cost of electric tracing vs. the capital + operating cost of the steam tracing (which needs to consider the opportunity cost of the steam in terms of lost power output as mentioned by rmw).

If you aren't already doing it, you can provide temperature control on the electric tracing circuits so they only operate when necessary and you are not wasting excess power. This will significantly reduce the cost of the electric tracing.

 

[unclesyd]

Here is link to The Thermon Site. At one time they had some good technical information and design aids. We used a lot of their products keeping organic acids liquid.

http://www.thermon.com/us/default.aspx

We also used a lot of bolt-on steam tracing from controls Southeast.

http://www.csiheat.com/

 

[eadwine]

Check into the Armstrong International site. They have software on line or did at one time for calculating the number and size of tracers required and insulation requirements. There is also softwre for doing the economics analysis.

 

[jcurtis]

Thanks for the help so far.

I will have a look at those websites and report back with any questions or concerns. Lots of good information so far.

Cheers,
Jamie.

 

[jcurtis]

1. It requires a live steam source. Can you guarantee that you will always have a steam generator of some type on line? Maybe that is not an issue, but I have seen the same issue at single unit stations and the unit wasn't always on the line.
--Excellent thought (and I echo it). We obviously do maintenance in the summer when the load requirements are low. When we have a total plant outage, there is no steam. However, there is also no requirement for fuel oil either and the lines are drained before hand.

2. Do you have a supply of relatively low pressure waste steam, or will you be taking steam that you could be making your market product (power) with?
--We would have to use aux. steam from our boiler. So we would have to increase the demand from it to meet the needs for the steam tracing line.

3. Are you going to waste or try to recover the condensate, and if the latter, how will you get it back and the condensate lines will need to be traced too at that temperature.
--Another solid point which I never thought of. From what I've seen around the plant so far (I have only been here for 2 months) it looks as if we would discharge the condensate and not recover it.

4. Trap maintenance.

5. Supply valving and valve maintenance.

6. Freezing of steam lines when steam tracing system is off and it drops below freezing.

 

[ione]

If you don't collect and recover condensate you will have multiple issues:

1. Waste of energy.
2. Waste of water
3. Need for fresh water makeup also implies adequate water treatment. Be aware it is not a good practice to feed a steam generator with cold water.

 

[jcurtis]

Right now in our Tank Farm we do not recover any condensate. However, to our advantage, we are located on the Avalon Peninsula of Newfoundland (ie: right next to Conception Bay which is for the most part the Atlantic Ocean) so water supply isn't an issue. The treatment of this water (salt) is a concern, which would also have to be factored into consideration. A condensate return line (which as mentioned would also need to be heated) would significantly add to the cost of this project. Seems to me that adding steam tracing would have been a viable study in the initial design of the plant and not so much now where we have 2 phases of electrical heat tracing doing the job.

I appreciate all the help so far!

 

[ione]

Water treatment for steam generator’s feeding involves more than just salt removal (softening process). Depending on working pressures, deeper treatments are more than an option. Demineralization or reverse osmosis, coupled with TDS control, oxygen and carbon dioxide removal are some of available processes. Please be aware that cold water makeup produces detrimental effects due to thermal shocks and corrosion (oxygen solubility in water is inversely proportional to water temperature). Likewise steam generator’s efficiency is affected by the use of cold water makeup.

One consideration on condensate return line. During heating process the condensate line doesn’t need further heat to prevent risk of freezing, it just needs to be lagged. If the heating system doesn’t work because of ordinary or extraordinary maintenance procedures it would be enough to drain the condensate line.

Jamie, please considerate a full condensate recovery system will allow you to save about 15% in terms of thermal power (i.e. money) if compared with a waste steam plant.

Finally, I agree with you that to retrofit the heat tracing system with steam tracing is not probably the best choice.

 

[jcurtis]

Hi again,

I finished reading through the document that Spirax Sarco published and found it to be very helpful for someone knew to the steam game.

To correct myself, we do recover condensate in the thermal plant, however, the condensate is sent to drain in the tank farm. After reading the document from Spirax Sarco I now fully understand why.

"One consideration on condensate return line. During heating process the condensate line doesn't need further heat to prevent risk of freezing, it just needs to be lagged. If the heating system doesn't work because of ordinary or extraordinary maintenance procedures it would be enough to drain the condensate line." -- from ione.

Good point. Another added cost that will add significant cost to the project total. Since the total traceable length of 18" pipe line is roughly 5500ft, this is a big cost even though the line would be smaller.

I'm going to prepare a document for my supervisor and his superiors to weigh the pros and cons. I'm also going to try and do a cost analysis as well. When I am done, I will post what I have taken from here and give back for comments and opinions.

Please feel free to continue to comment. Junior engineers need all the help we can get!

Thanks again.
Cheers.
Jamie.

 

[jcurtis]

I'm not sure how to edit postings (I do not see the button). But knew = new.

And I fully understand why sending condensate to drain is such a bad idea. Perhaps next time I should preview my posting.