gas pressure dorp in pipelines

8/12/2019 Gas Pressure Dorp in Pipelines....

1/30

PRESSURE DROP IN GAS PIPELINES

Jn Steinar Gumundsson

TPG4140 Natural Gas

September 16, 2010

Importance of pressure drop and different pipes

Pressure drop in pipelines (depends on d5) Equations for liquid and gas flow

North Sea gas pipelines

Friction factor and roughness R&D on friction (roughness) and pressure drop

Summary


2/30

A: Wells, B: Flowlines, C: Risers, D: Process pipes, E: Off-Loading, F: Pipelines


3/30

Importance of pressure drop Transport capacity, we want to be able to push as much gas as

possible through existing pipelines to customers. Norwegian export

pipelines 100 BCM annually. Expensive gas compression (power and emissions) needed to give

sufficient inlet pressure to overcome pressure drop. Gas turbines

drive centrifugal compressors offshore (and on land?). Largest

consumption of power offshore.

Export pipelines have epoxy coating to make wall smoother to

reduce wall friction and hence greater production rate.

Production capacity (subsea-to-beach), we want to maintain

wellhead pressure as low as possible to sustain large production

rate from gas fields with time. Eventually we need subseacompression.

Large diameter pipelines used to avoid compression platforms along

export gas pipelines. On land, compressor stations along pipeline.


4/30

Pressure and Temperature With Distance

Booster compressor duty: 15.5 MW (most likely roughness)

sgard Transport (69.4 vs. 76.9 MSm/d)

110

120

130

140

150160

170

180

190

200

210

0 200 400 600 800Distance KP (km)

Pressur

e(barg)

0

5

10

15

2025

30

35

40

45

50

Tempera

ture(C)

Pressure Booster_press Temperature Booster_temp

Aamodt (2006)


5/30

Natural Gas Pipeline


6/30

Pressure Drop in Pipelines

where g (gravitation), a and f stand for hydrostatic, acceleration and

friction, respectively. The three terms can be expressed as

fag pppp

Lud

fp

uup

Lgp

f

a

g

21

2

sin

The total pressure drop in pipelines and wells consists of three terms

The angel is measured from horizontal and the lenght is the pipe lenght,

not height over/under the surface. The pressure drop due to friction is

the Darcy-Weisbach equation.


7/30

Darcy-Weisbach Equation


8/30

Darcy-Weisbach EquationLiquid Flow and When Gas Average Density Used

Lrrp 22

L

pr

2

2

8

1

uf

2

81

2uf

L

pr

2

2ud

Lfp


9/30

Darcy-Weisbach Equation

Force balance, steady-state pipe flow

wrdLrdp 22

dL

dprw2

2

8

1ufw

2

8

1

2uf

dL

dpr

2

2 ud

Lf

pf


10/30

North Sea Pipelines

Sletfjerding, E. (1999): Friction Factor in Smooth and Rough Gas Pipelines, Dr.Ing.,

Petroleum, NTNU.


11/30

North Sea Pipelines


Petroleum, NTNU.


12/30

North Sea Pipelines


Petroleum, NTNU.


13/30

North Sea Pipelines: Pressure Gradient


Petroleum, NTNU.

6,06

348,406,30812,895,5146,7H

167,6010,66227,0112,1136,3G

334,109,4448,567,4572,03F

334,106,95619,086,8129,85E

185,403,2648,563,6465,22D

185,402,23619,094,16107,97C

383,506,81303,5145,59166,26B

205,502,81812,485,59108,42A

kg/sbar/100 kmkmbarbar

m(p1-p2)/LLp2p1


14/30

Pressure Gradient in Gas Pipelines

6 (average 8 pipelines)

15-25

North Sea, Sletfjerding

(1999)

Canada, Hughes (1993)*

Gradient (bar/100 km)

* Mokhatab o.a. (2006, s. 419)


15/30

Maximum Gas Velocity*

*NORSOK P-001 (1999)

Sletfjerdings (1999) North Sea Pipelines A-H, uaverage (m/s), only 10-20 % av NORSOK umaximum


16/30

Pressure Drop Horizontal Gas Pipeline

0ln2

1

2

22

1

2

22

2

L

p

p

f

dpp

zRTfm

MdA


17/30

Frictional Pressure Drop Gas Pipeline

Horizontal Pipeline, Inclined Well

2

2ud

Lfpf 0Lp

plnfdpp

RTzmfMAd

2

1

2

221

222

2

Laggab

Lagpp

sin2exp1sinsin2exp 22

1

2

2

zRT

Ma

dA

fmb

2

2

2


18/30

Friction Factor in Pipelines


19/30

Nikuradses Sand-Grain Data


20/30

Moody Chart

Add reference to fluid mechanics text book.


21/30

Blasius Equation

000.100Re

Re316,025,0

rrglatteHydraulisk

f


22/30

Haalands Equation

vskeforn

gassforn

dk

nf

nn

1

3

75,3Re9,6log8,11

11,1


23/30

Wall Roughness in Pipes

5.1

12.5

30.033.0

35.1

38.1

53.3

0.20010-3

0.49210-3

1.1810-3

1.3010-3

1.3810-3

1.5010-3

2.1010-3

Internally plastic coated pipeline

Honed bare carbon steel

Electropolished bare 13CrCement lining

Bare carbon steel

Fiberglass lining

Bare 13Cr

Average

Absolut

Roughness(m)

Average

Absolut

Roughness(inch)

Material

Farshad og Rieke, JPT, oktober 2005, side 82-86.


24/30

Blasius, Colebrook-White and Haaland

d

k

ff 7,3Re

51,2log2

1

nn

d

k

nf

11,1

75,3Re

9,6log8,11

Haaland n=1 for liquids, same as Coolebrook-White

Haaland n=3 for gases, same as AGA data

25,0Re

316,0

f


25/30

Haaland Friction Factor

Gases, n=3, Hydraulically smooth and k/d=0.001

0,00000

0,00500

0,01000

0,01500

0,02000

0,02500

0,03000

0,03500

0 200000 400000 600000 800000 1000000 1200000

Reynolds-tall

Fri

ctionfaktor

Haaland for gas based on AGA data, lower than for liquids, transition different


26/30

Haaland Friction Factor

Liquid n=1 and gas n=3, k/d=0.001

0,00000

0,00500

0,01000

0,01500

0,02000

0,02500

0,03000

0,03500

0 200000 400000 600000 800000 1000000 1200000

Reynolds-tall

Friksjonsfaktor

Gas 3.8 % lower than liquid at Re=106


27/30

Nikuradses Sand Grain and Real Roughness


28/30

Sletfjerding

Ra = Arithmetic mean roughness

Rq = Root-mean-square roughness

Rz = Mean peak-to-valley roughness


29/30

Pipes Used by Sletfjerding

Sand-grain roughness ks, Measured roughness Rq , Hurste exponent H

4.5 < (ks/Rq) < 5.8

21 < ks

< 181


30/30

Summary Equation for pressure drop in horizontal gas pipelines; the

natural logarithm term can often be neglected (gentle

decrease in pressure)

Blasiuss equation used for smooth pipes and when Re

gas pressure dorp in pipelines

Documents