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

 

[casflo]

Probably the problem is due that in the heavy rains, the pipe is wet and with much water in the external surface. In this case the heat loss transmission from the pipe to the water is higher than in the case of the transmission to the air when the pipe is dry. The thermal conductivity of the water is higher than the air.
In any case, you must take into account that the cooling of the steam along the pipe is due to the transmission loss and also to the 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.

 

[3DDave]

The heat loss is 10-12 tonnes of steam. What's important is how much extra fuel had to be burned - ask the plant manager for that information.

 

[pierreick]

Hi ,
Share with us some more information , what is the normal steam flowrate and what is the over consumption ,both in tons/hour ?
Regarding pressure , is it gauge or absolute pressure ? Confirm that your steam is overheated (+90 to 100 C) !
Regarding insulation and cladding , please confirm the condition .
How the steampipe is routed cross country , any pipe rack to support ? Will it be covered with water during rainy season (flood)?
You may want to share a picture with us.

Pierre

 

[IRstuff]

Water has both good thermal conductivity and specific heat, so wetting the insulation is easily 10x more efficient at removing heat than natural convection.

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[georgeverghese]

Ask a piping insulation inspector to survey this line for water ingress - some sections may need to be reinsulated.

 

[pradeep4u]

Dear Pierre
Normal flow rate is 40 tones/hr now during rains it flow rate increased to 55 tones per hour. It is absolute pressure. Yes sir steam is superheated to 280 degree Celsius. Insulation and cladding is ok. We renew insulations based on thermography report. Steam line layed about 10 meters above ground supported on pipe rack. Sir how we can measure heat loss from pipeline of such great length of 1.8 km. Is there any formula for calculation.
Regards
A.Pradeep

 

[LittleInch]

What is "light resin bonded mattress?? That is meaningless I'm afraid and could mean anything
We need some technical details (material, thermal conductivity etc), photos etc

Ten metres above ground?? Really??
How do you go about inspecting that?

What is the skin temperature of the cladding?

Are there any exposed sections in the plant? Or how do you know it is the pipeline which is responsible and not some other part of the steam process?

Can something else cause the increase in steam when it rains?

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

 

[pierreick]

Hi Pradeep ,
Calculation is not an issue I can provide an excel sheet , I have difficulty to understand that rain can be responsible for steam overconsumption (+30%). Definitely you need some one to inspect your insulation and cladding , all the pipe must be checked (1.8 km) for defect and may be leaks.
By the way you did not mention steam traps, did you check them ? Please consider to read the link underneath about the consequences of cold weather .

https://www.chemicalprocessing.com/articles/2007/013/

As suggested , let you measure the skin temperature of the cladding , Infra red thermometer should be good enough to confirm the condition of the insulation material and its efficiency.
Good luck
Pierre

 

[3DDave]

You don't need better insulation - you need a rain cover.

 

[georgeverghese]

How do you know steam flow has increased to 55t/hr - is the FT located at some point where there is 2phase flow, like a piping low point ?
Presume your insulation contractor has given you assurance this insulation is water proof all through 1.8km length.

 

[MintJulep]

You can review the fundamentals of the calculation from any of many web sites or any heat transfer text.

For example a lecture on the fundamentals:

https://youtu.be/Vy9OW-14iw8

A legally downloadable heat transfer text:

https://ahtt.mit.edu/

But equations are not going to solve your problem. Finding the cause of your problem is the first step of solving your problem.

Does the steam flow increase instantaneously when it starts to rain, or does it take some time?

Does the steam flow return to normal instantaneously when the rain stops, or does it take some time?

LittleInch already hinted at this, are any of the steam consumers sensitive to rain?

 

[georgeverghese]

Some steam traps work by sensing saturated condensate temp on a cooling leg upstream of the trap. So if the cooling leg is exposed to rain and cools the condensate more than it should, the trap will continue to blow and not close when it should. Hence check the steam trap arrangements also on this line - cooling legs may be left uninsulated, but they should be shielded from rain.

 

[matias correa]

For the first few meters install an anti-rain roof, choose the cheapest roof that you can install. Moreover, you may install temperature sensors in that area so that you may obtain the temperature differential obtained without and with a roof, with this information you may calculate the economic benefits of this initiative

 

[pradeep4u]

Dear All
I am attaching technical sheet of LRB as required by Littleinch Sir. Skin temperature of Insulated pipe are checked before rainy season. Actually insulation is very old about 20 years old we want replace it with new insulation after rainy seaon. . Thats why I asked calculation sheet[/u]. We want to compare steam load before and during rainy season. Mintjulep uploaded video but it is about heat loss at any particular cross section, as heat loss is steady along the length of pipeline temperature is getting changed. We want to put proposal to management about savings in replacing it with new insulation. Sir there is problem with working of steam traps because when steam gets transported from such long pipes there is always chance of 2 phases instead of single phase steam, so steam trap very frequently blows during rainy season. Trap line is insulated. What is purpose of Aluminium cladding if we require another rain protection. Steam load gradualy increases during rains and reduces to normal when rain stops. FLow transmitters are installed at outlet of boilers. It is not located at low piping point. It is located at midpoint. Average skin temperature is 45 degree celcius. It is considered normal considering ambietn temperature is 30 degree celcius. I hope i provided all details you all asked. Please guide us.
Regards
A.Pradeep

 

[pierreick]

Hi Pradeep ,
You said your insulation last for 20 years ! Probably a very good time to replace it .. Regarding overconsumption of steam during rainy season , is it a recent problem or has it been always the case ?
To me this is typically a lack of maintenance of your insulation system ,probably soaked with rain with issue with steam traps , lack of management.
Prior to rainy season , you should perform an inspection of the insulation and regularly check for malfunction of steam traps.
I've attached a spreadsheet to help you for your calculation of normal heat loss during steam transportation .
Good luck
Pierre

 

[pradeep4u]

Dear Pierre sir and all other respected sirs,
Thanks for your valuable and precious suggestions. These suggestions enhanced our knowledge and will help us maintaining steam line in best possible ways. I am grateful to all of you.
Regards
A.Pradeep

 

[MintJulep]

We want to compare steam load before and during rainy season.

But you have already done this. "Normal flow rate is 40 tones/hr now during rains it flow rate increased to 55 tones per hour."

Steam load gradually increases during rains and reduces to normal when rain stops.

This strongly supports everyone's guess that your insulation gets wet when it rains.

We want to put proposal to management about savings in replacing it with new insulation.

(15 tones per hour x cost of fuel/tone of steam x number of hours that it rains) + something for new insulation being better year round than whatever old insulation you have = annual savings.

 

[chicopee]

At the delivery end of the 1.8 km long of the 6" pipe do you know the pressure and temperature of the steam and of the mass rate of steam being supplied?

 

[georgeverghese]

Just to be sure, you may check these FTs' also. What type are they? If they are dp cells with flow orifice, check that impulse lines are not collecting condensate in the rain - are they installed correctly?