Heat loss in steam piping. 1

[murphymok]

Hi,

When calculating heat loss through underground steam distribution piping, do I use sensible heating valve or total (sensible+latent) heating valve?

Thanks in advance.

 

[quark]

How does it matter at all? Important factor to you is the temperature of steam.

 

[25362]

Is your steam superheated or saturated ?

 

[murphymok]

Hi,

Saturated steam at 200 psig. We have a 10% steam loss each month. I am looking at the heat loss through the distribution piping network. Another possible loss I am thinking about is the steam traps. Any thoughts?

Thanks in advance.

 

[rmw]

If your steam leaves the source saturated, it can do one of two things.

If the pressure drops along the piping system are "just right" then the steam will tend to superheat as it loses pressure, minimizing losses due to moisture.

However, I doubt that to be the case, because Peter Pan doesn't work here, Murphy does, (sorry murphymok), and Murphy's laws govern.

So, if your saturated steam is losing heat, then it is getting wetter and wetter as it travels from the source to the users. Since the velocities probably aren't high enough to meet the conditions of my first suggestion, they are low enough to permit the moisture to drop out along the piping, or be separated out every time it goes around an elbow, or any other fitting that causes a momentum change in the steam flow, probably doing a number on the elbows, etc., in the process.

Therefore, checking all the traps would be a good idea. I suspect that if you are able to determine a reasonable flow from all or almost all of the traps, and figure the latent heat of this amount of water, you will find the majority of your steam losses.

rmw

 

[friartuck]

I assume your condensate goes back to a 'hotwell' or boiler feed tank. These are usually vented to atmosphere so when your condensate enters at the higher pressure it will 'flash off' and you will lose a lot here.

You need to recover the flash somehow. Do you have need for hot water or hot water heating. A flash vessel would utilise the waste....alternatively pre-heat the boiler feed water to help reduce the waste.

Friar Tuck of Sherwood

 

[rmw]

Good call, Friartuck.

Flash loss back to atmospheric or DA pressure from 200psig would account for a lot of the loss, at the boiler end, or at the traps of the individual users.

Murphymok has another active thread in this forum regarding Hx sizing that indicates that he might have just what you suggested.

rmw

 

[MintJulep]

Murphymok,

Could you define what you mean by "a 10% steam loss each month"?

Your initial question implied a concern about energy loss, but now I am wondering if you are also concerned about mass as well.

Going back to quark's reply, assuming that the pipe doesn't leak, heat transfer out of the pipe is an energy thing only, there will be no change of mass associated. If the steam is truely saturated, the energy loss will result in condensation.

To the other potential energy and mass loss points noted above, add continual blow-down, if your boilers are so equipped.

 

[rmw]

Mintjulip,

If he has a large steam distribution system, but the traps along the route are not piped back into the condensate return but rather to the ditch or sewer or whatever, then this would represent a mass loss to his system caused by an energy loss.

In my experience I have probably, doing a mental inventory, seen more traps in isolated locations along long and large steam distribution systems blowing both their condensate and/or leakage steam to the surroundings.

Murphymok should consider this as a loss source if this is the case with him. He is getting double whammied. He has the energy loss for whatever reason, and then he loses the mass and latent heat in the condensate along his system.

rmw

 

[murphymok]

Hi all,

I am talking about steam mass loss. For example, the steam plants send out 1000 lbs and the metered steam from the buildings is 900 lbs. The pressure drop from the plants to the buildings is minimal. I have looked at possible metering loss/inaccuracy, but it is very small. I am thinking that steam mass might be loss to condensate forming at the traps. There are about 500 TD traps in the distribution network.

Any thoughts will be appreciated, I am running out of clues on the steam loss.

Thanks

 

[MintJulep]

rmw,

I just wanted to focus the picture a bit.

Murphymok,

rmw is right on, if some of your 500 traps are discharging to drain that is likely a contributor, especially if some are not working correctly and are constatly blowing live steam.

How closed is your system? Are you metering your make-up water? If you are dumping lots of steam/water to atmosphere/drain that should show up as high make-up consumption. If your make-up does not match the difference between the steam you send out and sum of the steam entering the buildings then you may be moving a lot of steam out, and condensate back without having it perform any useful work.

 

[rmw]

Murphymok,

You did not clarify whether or not your TD traps are discharging to atmmosphere, or to the condensate return header. If it is the former, 500 traps at even a small flow rate, notwithstanding TD traps are notorious steam wasters, letting out "X" amount of steam with each load of condensate that they let out, could mount up to a fairly large sized mass loss.

Go time a few traps, get the number of times per hour they pass flow, and look at our trap data, and see how much they are rated to pass at 200 Psi delta P, (again assuming that they are discharging to atmosphere) and multiply that number by 500, and see if you get anywhere close to your loss rate.

Now, are your steam flow measurement flow devices at the user end pressure compensated. Notwithstanding that you have minimum pressure loss (which tells me in a run that has 500 traps, that you have some pretty slow velocities) your flow measuring devices might have a compensation error in them.

Also, have you any idea, or any way of measuring what the quality of the steam is at the measurement point at the users end. You may be delivering the steam, but it may just be sloppy wet, (poor quality), which also would throw off the measurement, if not properly compensated for.

Your measurement device is probably calibrated for D&S (dry and saturated) steam.

The system that you describe to me would indicate that steam quality could be a problem.

rmw