Temp loss gas pipe to ground for buried pipe

[jruby]

My company is in the process of building a new natural gas supply station. This station will serve a large volume customer located 2000' away. This customer will be served via 200' of 6" SCED-40 buried piping from station. We are taking pipeline gas at 750 PSIG - preheating - then reducing to 200 PSIG. This customer will be using at 275 PSIG - 300,000 Cubic Feet per hour. Their contract mandates a minimum gas temperature of 60 Degrees F. I have been asked to determine the temperature drop across the buried piping so as we can determine the required preheat temp. This pipeline will be in an area where frost depths are up to 3 feet. The pipe depth will be 3 feet.

There was a paper written in 1981 that was submitted to PSIG (Pipeline Simulation Interest Group)

http://www.psig.org

named "8101 - A Closer Look at Transient Heat Transfer from Pipeline Gas to Nearby Ground". I believe this paper focuses on the Jacobs Two-Phase Soil method. I have found the equation for this method, but am not comfortable with all the variables- particularly the soil conductivity which is in units of BTU/HR*Ft*F. I've been trying to get this paper - no luck yet.

Anyway, I was hoping someone could give me some advice on this.

 

[CRG]

BTU/(Hr*ft*degF) is not very useful for most equations; however, BTU/(Hr*ft*degF)*(12*in/1*ft) will give you BTU*in/(Hr*ft^2*degF). The second form will make your calculations dimensionally correct for many applications.

 

[zdas04]

I'm a little confused about the details of your problem. If the customer is 2,000' away then 200' of pipe won't reach them. If the customer is expecting 275 psig gas your 750 to 200 reduction won't work for him.

Assuming that you keep the gas close to 300 psig, then 7.2 MMCF/d in 6-inch pipe is 22 ft/s with 3.5 psi dP over 2,000 ft. That gives you a residence time of 91 seconds.

You have to calculate your thermal entry length to determine how much pipe would be required to cool the gas to reach 20% of original dT. With the thermal entry length you can determine how much you need to preheat the gas.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[TD2K]

This is a scanned copy of the equations Pipephase uses for buried piping

http://s17.yousendit.com/d.aspx?id=2WQY1XRIZ33PK1A6FYQ8WOI16A