5 replies to this topic

[krishanan]

Dear All,


Subject:
I have to design steam jacketing system for natural gas piping to rise natural temperature from 10 Deg.C to 45 Deg.C in one of our project.

Technical Parameters:
Following are the natural gas & LP steam parameters

Cold Fluid:
Natural Gas flow – 45612 kg/hr
Inlet Gas Pressure – 45 kg/cm2(g)
Inlet Gas Temperature – 10 Deg.C
Outlet Gas temperature – 45 Deg.C

Hot Fluid:
Inlet Steam Pressure – 6.0 - 6.5 Kg/cm2(g)
Inlet Steam Temperature – 190 Deg.C
Outlet condition – Condensate

Concerns/Problems:
Here is the following concern where in i am looking for your valuable suggestion.

1. Inside Heat transfer coefficient as per my calculation (Natural gas side) is ~ 1500 Kcal/Hr/m2/k. I am doubting that this is on higher side for gases(may be due to first of its kind for me), hence i request you all experties to suggest the optimum inside heat transfer coefficient which usually consider for these type of applications.

Arrived calculation result is based on following parameters

Nu = 0.023 * (Red)^4/5 * (Pr)^0.4

Reynolds No. (Red) = r*V*D/u
r - Density of natural gas @ 45 Kg/cm2(g)
u - Dynamic viscosity - 0.00002 N-s/m2
Diameter of pipe(D) = 260.3 mm

Prandtl no.(Pr) = u*Cp/k
k - 0.03 w/m/k @ 25 Deg.C
Cp - 0.5 Kcal/kg/k

Inside heat transfer coefficient(Hi) = Nu*k/D

I am seeking your valuable opinion/suggestion to design this.

Your quick response is highly appreciable

Rgds
krishna

[ankur2061]

krishna,

 

Value of overall HTC in your case (Heater with Steam-Gas fluids) should be in the range of 30-300 W/m²-K (26-260 kcal/h/m²/°C). Refer the links below:

 

http://www.engineeri...l/transfer.html

 

http://blackmonk.co....r-coefficients/

 

Regards,

Ankur.

[krishanan]

Thank you very much Mr. Ankur for your reply,

 

I have gone through your links where in values given typically for heat exchanger, where as my requirement is pipe jacketing(I.e inner pipe - natural gas & Outer Pipe - Steam), hence can we use same values as mentioned in heat exchangers (i.e Steam to Gas)

 

Rgds

krishna

[ankur2061]

Krishna,

 

Yes, with the value to be considered on the lower side of the range given due to less flow turbulence in the pipe-in-pipe type of heat exchanger.

 

Regards,

Ankur.

[breizh]

http://www.thermon.c...ignsupport.aspx

This resource may help you .

Breizh

[PingPong]

Inside Heat transfer coefficient as per my calculation (Natural gas side) is ~ 1500 Kcal/Hr/m2/k.

You would need to post your calculation if you want to know where you went wrong.

Maybe it is simply because you seem to work with a mix of metric and SI units.

 

When I do a calculation for inside inside heat transfer coefficient h_i using your data and method, I find

h_i = ~ 500 W/m².K = ~ 430 kcal/h.m².K

Combined with condensing steam this would give an overall heat transfer coefficient U = ~ 350 W/m².K = ~ 300 kcal/h.m².K

 

That U value is at the upper end of the range of the typical U's published in various books and websites, but if I would have used more realistic values for natural gas physical properties the calculated h_i and U would have been even higher.

 

Duty = ~ 1100 kW (based on C_p = 2.5 kJ/kg.K) and LMTD = ~ 135 ^oC so you can estimate required A and L. Make sure you add plenty of overdesign.

Edited by PingPong, 04 October 2014 - 06:31 AM.