Natural Gas Compression

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COMPRESSION OF NATURAL GAS

Jn Steinar Gumundsson

TPG4140 Natural Gas

September 17, 2012

Compression in oil and gas production

Types of compressors (piston and centrifugal) Characteristic curves

Adiabatic and reversible (=isentropic) compression

Real vs. ideal, isentropic head, polytropic compression Surge and stonewall

Compression in stages (inter-cooling)

System curves and parallel/series service


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Compression in Oil and Gas Production

Recompression in separation train of gas and

condensate (same as in oil production).

Export compression (from platform to pipeline).

Reinjection compression (from platform to subsurface).

Various air compressors for control equipment in

processing facilities (offshore and onshore).

Export compression, from receiving and processing

terminal to pipeline.

Pressure boosting, onland compression. Gas storage in salt caverns.

Subsea compression (soon to be installed)


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A: Recompression, B: Gas Drying, C: Fuel Gas, D: Export Compression,E: Gas Pipeline, F: Injection Compression, G: Injection Well


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Compressor

Station

Compressor

Station

Production32,000 Compressors

Processing5,000 Compressors

Transmission & Storage

8,500 Compressors

Distribution 0 Compressors

Compressor

Station

USA Natural Gas Industry


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CO2 Emissions Norway

Oil and gas industry 29 %, Cars and trucks 22 %, Industry processes 18 %, Heating 16 %, Boats

and ships 9 %, Other sources 6 %


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Gas Turbines Offshore Norway 2007


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Offshore Gas Turbines The oil and gas industry in 2007 represented 25 % of CO2 emissions

in Norway.

At that time, the requirement for electricity offshore was 15 TWh(Norways total electricity production was then about 125 TWh).

In 2007 there were 167 gas turbines on offshore installationsamounting to 3000 MW.

About 45 % of the power is for electrical equipment. The remainingpower is for compressors and other equipment.

The thermal efficiency of the gas turbines is in the range 30-37 %.

Thermal recovery is used in most of the installations, increasing thethermal efficiency to about 40 %

Kraft fra land til norsk sokkel (2008), OD o.a.


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Simplistic Gas Turbines Working Principles

1-2 Isentropic compression (in a compressor)2-3 Constant pressure heat addition (in a combustor)

3-4 Isentropic expansion (in a turbine)

4-1 Constant pressure heat rejection


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6

Kristin Prosess

18.3 MSm/sd210 bar

50CPcric


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Types of Compressors

Reciprocating piston compressors

Low flow rate

High compression ratio

Rotating centrifugal compressors High flow rate

Low compression ratio each stage

Several stages higher compression ratio


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Axial Flow Compressor


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Radial Flow Compressor


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Centrifugal Compressor


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Reciprocating Compressor


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Twin Screw Compressor for Subsea


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Subsea Compressor


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Usage of Compressors


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Characteristic Curve


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Characteristic Curves

A: Centrifugal, B: Axial,C: Piston, D: Screw

Left: Radial,

Middel: xxx,

Right:Axia


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Thermodynamic Processes

k=Cp/Cv

k=0

k=1k=Cp/Cv

k


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Compressor Work

2

1

vdpW

A = Suction, B = Compression, C =Delivery, D = Expansion


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Piston Compressor


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The Carnot Cycle


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Adiabatic/Isentropic Process

nRTpV

RTpv

v

p

C

Ck

k

k

p

p

T

T1

1

2

1

2

kk vpvp 2211


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Adiabatic/Isentropic Compression

2

1

vdpW

11

1

1

211

k

k

p

p

k

kvpW

11

1

1

21

k

k

p

p

k

kRT

M

mP

v [m3/mol], p [Pa=N/m2], W [Nm/mol=J/mol] = Specific work

pv=RT, Wm/M [J/mol kg/s mol/kg=J/s=W] = Power

nRTpV

RTpv


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Ideal, Real, Efficiency, Head,

Polytropic

11

1

1

21

pk

k

p

pp

kkRT

MmP

8,06,0 p

11

1

1

21

k

k

spp

kk

MRTh

1idealreal PP

hs

[J/kg]

pk

k

n

n

11

P [W=J/s]


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Surge and Stone Wall

A: Surge line, B: Stonewall line


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Surge Control


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Compression in Two Stages

2

3

1

2

p

p

p

p

312 ppp

Above pressures give

minimum power


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Intercooling


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System Characteristic


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Scaling LawsIsentropic Head Example

0,0

10,0

20,0

30,0

40,0

50,0

60,0

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

q [m3/h]

h_

S

[kJ/kg]

11

2212

dNdNqq

2

11

2212

dNdNhh

3

11

2212

dN

dNPP

6000, 7000 and 8000 RPM


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Parallel and Series


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Summary Recompression, export compression, reinjection

compression

Reciprocating piston compressors and rotatingcentrifugal compressors (radial and axial)

Characteristic curves P [W] or h [J/kg] vs. q [m3/h]

Calculation of compression power (isentropic)

Efficiency and polytropic compression

Surge (solved by recycle) and stonewall (speed of

sound)

Compression in stages with intercooling (minimumpower when equal power)

System curves (the need) and >1 compressor

List of companies and their products


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List of companies and their products


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Industrial Aero-derivativesOverhaul Life 48,000 hours 30,000 hoursHot section inspection 8000 hours 6000 hoursOverhaul Life On-site Gas generator removalEngine weight Heavy Duty LightFast start capability No Yes

Tolerance to poor fuel Fair Poor Ease of automation Good GoodSuitable for off-shore Fair GoodPower Up to 325 MW Up to 55 MW

Thermal Efficiency 25-39% 25-42%

Difference between Heavy Duty and Aeroderivative Turbines


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Evolution of products : Uprates

Natural Gas Compression

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