heat loss through insulated pipe line 1

[pradeep4u]

Dear all
We encountering a problem of increase of 10-12 tonnes of steam load during heavy rains. I want to know how can we calculate heat loss of long pipeline. We are supplying 12kg/cm2 steam at 280 degree celcius. Pipeline size is 6" and of carbon steel and insulation we use is Light resin bonded matress of 65mm thickness and 140 kg/cm3 density and aluminium cladding. Pipeline is about 1.8 km long. Please guide me
Regards
A.Pradeep

 

[pierreick]

Hi ,
To add to my previous reply

https://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/steam1_traps.pdf

Pierre

 

[LittleInch]

Pradeep,

]Like a few others have been saying, you don't need calculations - you already have the answer in the form of energy lost between dry and rainy periods.

That insulation is basically rockwool but supplied in pre formed sheets enclosed by thin wire mesh. It is clear in your 1.8km the external cover is not able to to fully water proof your line and hence over time water gets in and increases significantly the thermal conductivity. Given that the rain will probably take this extra heat away, you will need to wait for the dry periods in the rainy season to measure surface temperature to find the worst locations. I've seen Indian monsoons and any external cover will be very lucky to prevent a slow ingress of water over the many weeks of the heaviest rain.

Or you need to replace with some sort of closed cell insulation, either Foam Glas or PUF, though the temperature might be a bit high for the PUF. Then you don't need to worry anymore - that should last for decades if you install it right.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pradeep4u]

Dear georgeverghese
FTs are DP type with flow orifice and we checked they are working fine. I did not understand the point (cooling of steam due to expansion from the initial pressure to the pressure at the end of the pipe that may be considered as an intermediate expansion between the isenthalpic and the isentropic) as explained by casflo. Please explain it. Littleinch sir and all other respected sirs thanks for your guidance
Regards
Pradeep

 

[georgeverghese]

FTs' will work fine even when impulse lines are badly installed. In addition, in this case, impulse lines may be getting wet in the rain. Are the impulse lines sloping continuously down to the source pipe so that any condensate in the impulse line will drain back to the source pipe? If not sloping correctly, condensate will accumulate at low points in the impulse tubing and readings will be in error.

 

[casflo]

Dear pradeep4u,
I only want to say that the steam and whichever other compressible fluid, has a pressure drop (expansion) flowing along the pipe, that cools it. This expansion along the pipe is close to an intermediate value between the isentropic and the isenthalpic expansions.
If the expansion were through a nozzle, it is close to isentropic. If the expansion were through a valve, it is close to isenthalpic.

 

[pradeep4u]

Dear Georgeverghese
Impulse lines are sloped downwards from source to transmitter as per required guidelines. I think FT problem is not there.
Thanks and regards
Pradeep

 

[LittleInch]

If they slope down to the TX then you need to regularly drain it. Does this happen or do you mean it slopes back down to the pipe?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

The FT should be above the pipe.

 

[chicopee]

If you can answer my first inquiry, you can then APPLY THE FIRST LAW OF THERMODYNAMICS as long as you know the initial(from steam generator) and final(receiving end of pipeline) states of steam. For initial and final states either use a steam table or a Mollier diagram to determine the enthalpy, internal energy and specific volume for the two states. There is one catch and that is you have to know the quality of steam at the initial and final states which normally require sampling. If sampling is not possible then an educated guess will be needed for steam quality at the initial and final conditions. Steam quality values are needed because you may have to interpolate for more accurate values of enthalpy, internal energy and specific volume (interpolation may not be needed if the initial and final states are in the superheated region which I doubt).

 

[pradeep4u]

Dear Chicopee
Steam at receiving end is at 11.5 kg/cm2 and temperature at receiving end is 210 degree celcius and flow is about 40 tonnes per hour. Again I thank each and everyone for sharing valuable information. I will be grateful for that.
Regards
A.Pradeep

 

[chicopee]

There are two ways to solve your problem but I have to know if you had classes in thermodynamics and heat transfer. If you did not then my presentations will be too overwhelming.

 

[pradeep4u]

Dear Cicopee sir
Please provide presentations. I studied Thermodynamics and Heat transfer. I will be grateful for this.
Regards]
Pradeep

 

[berkshire]

One other item to check is the aluminum covers over the insulation. Where are the joints in the wrap? If the overlaps are in the wrong direction, then water instead of being shed off the cover will run inside wetting the insulation, giving you all of the problems previously described.
B.E.

You are judged not by what you know, but by what you can do.

 

[chicopee]

My first attachment is the application of the first law of thermodynamics. I noted from your OP that you are dealing with metric units however my presentation is in English units so it is up to you to figure out the equivalency. English units are a bit messy when compared to metric units so I have included a little bit more information for your edification. The unit for heat lost Q is BTU/hr. Note mass in metric is kg or grams but in the english unit it is pound mass (Lbm). Force in metric is Newton but in the english unit it is pound force (Lbf). You'll note mass rate dm/dt or m dot is in (Lbm/hr). Note the other units used for pressure, specific volume, enthlapy and steam quality being in %. To know the steam quality if you deal with saturated steam field testing with a calorimeter is needed.
In due time, my second presentation on your OP will be a little more difficult when using the heat transfer approach.

 

[pradeep4u]

Dear Chicopee sir
Thanks for your solution
Regards
Pradeep

 

[MortenA]

There is a free and good web calculator here:

https://checalc.com/calc/inshoriz.html

but its does not consider wet insulation. I would agree with others and say that you need to improve your insulation shell.

Best regards, Morten

--- Best regards, Morten Andersen

 

[FMJalink]

Dear pradeep4u,
I am afraid that determining a more economical insulation material and thickness is quite elaborate.
If I understood your point well, the problem is with heavy (tropical) rains. During such rains the heat transfer on the sheeting outside will be high due to the refreshing water layer, which will be higher than with wind.
You could make spreadsheet dividing the pipeline in segments of some meters length. Per segment a heat balance and heat transfer should be determined. The heat transfer coefficient inside in the pipe and outside on sheeting should be estimated. The condition inside pipe should be determined using the vapor-condensation curve. Also the pipe resistance should be taken into account. A lot of work. Your above mentioned insulation thickness seems somewhat small, but increase of the insulation thickness will bring also additional cost, which could outweight the extra steam cost during heavy rains,