max flowrate for natural gas

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irprocess
Posts: 2
Joined: Sat Feb 18, 2012 12:29 pm

max flowrate for natural gas

Post by irprocess » Sat Feb 18, 2012 1:47 pm

Hi everyone;

In our plant,we transfer natural gas between two locations with 16" pipeline(carbon steel).Now,we want to know it is possible to use 12" pipe instead of 16" existing pipe:

distance: app. 800 meter
elevation: app. 10-15 m
flowrate : 217000 kg/hr
density: 60 kg/m3
p1=70 bar, p2= 69.5bar

also let me know about max gas will be applicable in order to transfer between two locations with 12".

Regards
Irprocess

PipeFlowCalcs
Posts: 57
Joined: Sat Sep 17, 2011 8:50 am

Re: max flowrate for natural gas

Post by PipeFlowCalcs » Sat Feb 18, 2012 3:49 pm

Here is the report that I have with natural gas flow calculator:

Compressible natural gas flow calculator

1. volumetric flow rate (q):
q : 361666.66 m3/h

2. mass flow rate (w):
w : 217000 kg/h

3. length (L):
L : 800 m

4. diameter (D):
D : 12 in

5. density (ρ):
ρ : 0.60 kg/m3

6. temperature (T):
T : 288 K

7. volumetric flow rate at the start (q1):
q1 : 5519.736 m3/h

8. volumetric flow rate at the end (q2):
q2 : 5668.8965 m3/h

9. pressure on the pipe start (p1):
p1 : 70 bar

10. pressure on the pipe end (p2):
p2 : 68.15816 bar


11. pressure drop (p1-p2):
p1-p2 : 1.8418375 bar

12. velocity at the start (V1):
V1 : 21.0134 m/s

13. velocity at the end (V2):
V2 : 21.581245 m/s


This means that you will have 68.16 bar with 12" instead of 69.5 bar for 16" pipe. and it is ok.
Also you will have 21 m/s speed of gas which is also ok (on the upper lever of recommendation, but it is ok).
Pipe flow calculations - free fluid flow calculators

irprocess
Posts: 2
Joined: Sat Feb 18, 2012 12:29 pm

Re: max flowrate for natural gas

Post by irprocess » Sat Feb 18, 2012 5:14 pm

Dear Sir,

Please pay attention that density is 60 kg/m3
T=54.2 oC
MW=18.82
composition (mol FRAC)
C1=.874
C2=0.037
C3=.0142
C4=.0073
CO2=.0054
H20=.0028
N2=.05
and let me know how much roughness is considered in your calculator.

PipeFlowCalcs
Posts: 57
Joined: Sat Sep 17, 2011 8:50 am

Re: max flowrate for natural gas

Post by PipeFlowCalcs » Sun Feb 19, 2012 10:32 pm

When you say 60 kg/m3 you mean that is the density on real conditions at 70 bar?

In natural gas calculator Renouard equation is used. There is used density at standard conditions (t=15 C, p=101325 Pa) which is about 0.78 kg/m3, for most common gas composition and I think that minor changes of density due to change of gas composition will not have too big influence on the result.
So, for 0.78 kg/m3 and other values same, pressure drop is:

Compressible natural gas flow calculator

1. volumetric flow rate (q): - at standard conditions
q : 278205.16 m3/h

2. mass flow rate (w):
w : 217000 kg/h

3. length (L):
L : 800 m

4. diameter (D):
D : 12 in


5. density (ρ): - at standard conditions
ρ : 0.78 kg/m3

6. temperature (T):
T : 54.2 C

7. volumetric flow rate at the start (q1):
q1 : 4823.873 m3/h

8. volumetric flow rate at the end (q2):
q2 : 4928.1704 m3/h

9. pressure on the pipe start (p1):
p1 : 70 bar

10. pressure on the pipe end (p2):
p2 : 68.51855 bar

11. pressure drop (p1-p2):
p1-p2 : 1.4814478 bar


12. velocity at the start (V1):
V1 : 18.364277 m/s

13. velocity at the end (V2):
V2 : 18.761333 m/s
Pipe flow calculations - free fluid flow calculators

expressfire
Posts: 7
Joined: Wed Feb 08, 2012 3:13 am

Re: max flowrate for natural gas

Post by expressfire » Wed Mar 21, 2012 10:58 am

The capacity of a low pressure natural gas (less than 1 psi, 6.9 kPa) pipe line with a small pressure drop can be calculated with the Spitzglass formula

q = 3550 k ( h / l SG)1/2 (1)

where

q = natural gas flow capacity (cfh)

h = pressure drop (in Water Column)

l = length of pipe (ft)

k = [d5/(1 + 3.6/d + 0.03 d)]1/2

d = inside diameter pipe (in)

SG = specific gravity

For natural gas the nominal BTU/cf varies from about 900 to 1100 BTU/cf. In general it is common to set

* 1 Cubic Foot (CF) = approx 1,000 BTUs
* 1 CFH = 1 MBH

The specific gravity of natural gas varies from 0.55 to 1.0.

The downstream pressure in a houseline after the meter/regulator is in general in the range of 7 to 11 inches Water Column, or about 1/4 psi.
Example - Natural Gas Pipe Capacity

The capacity of a 100 ft natural gas pipe with a nominal diameter 0.5 inches (actual ID 0.622 in) and 0.5 inches WC pressure drop can be calculated as

k = [(0.622 in)5/(1 + 3.6 / (0.622 in) + 0.03 (0.622 in))]1/2

= 0.117

q = 3550 0.117 ( (0.5 in) / (100 ft) 0.60 )1/2

= 37.9 cfh

Specific gravity of natural gas is set to 0.60.

Teritor
Posts: 1
Joined: Fri Apr 13, 2012 11:54 pm

Re: max flowrate for natural gas

Post by Teritor » Sat Apr 14, 2012 12:01 am

Before transferring natural gas from your plant between two location's have you measured the distance between two locations using a distance calculator? If not then you should measure them again by a distance calculator to get right calculation.

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