1. TPG 4140 NTNU Natural Gas Compression
Professor Jon Steinar Gudmundsson
Department of Petroleum Engineering and Applied Geophysics
Norwegian University of Science and Technology
Trondheim
October 8, 2013

2. Outline Compression in oil and gas production
Types of compressors (piston and centrifugal)
Characteristic curves
Adiabatic and reversible (=isentropic) compression
Real vs. ideal, isentropic head
Surge and stonewall
Compression in stages (inter-cooling)
System curves and parallel/series service

3. 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 (now being installed)

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

5. USA Natural Gas Industry

6. CO2 Emissions Norway
Oil and gas industry 29 %, Cars and trucks 22 %, Industry processes 18 %, Heating 16 %, Boats and ships 9 %, Other sources 6 %

7. Gas Turbines Offshore Norway 2007

9. Offshore Gas Turbines
The oil and gas industry in 2007 represented 25 % of CO2 emissions in Norway. 70 % is offshore (combustion, diesel and flaring)
Requirement for electricity offshore 2007 was 15 TWh (Norway’s total electricity production was then about 125 TWh).
In 2007 there were 167 gas turbines on offshore installations amounting to 3000 MW.
About 45 % of the power is for electrical equipment. The remaining power is gas turbines for compressors and other equipment.
The thermal efficiency of the gas turbines is in the range %.
Thermal recovery is used in most of the installations, increasing the thermal efficiency to about 40 %
Kraft fra land til norsk sokkel (2008), OD o.a.

10. 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

13. 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

14. Axial Flow Compressor

15. Radial Flow Compressor

16. Centrifugal Compressor

19. Reciprocating Compressor

20. Twin Screw Compressor for Subsea

21. Subsea Compressor

22. Usage of Compressors

25. Characteristic Curve

26. Characteristic Curve

27. Characteristic Curves
Left: Radial,
Middel: xxx,
Right:Axia
A: Centrifugal, B: Axial, C: Piston, D: Screw

29. Thermodynamic Processes
Condition
Exponent
Adiabatic
Isobaric
Isothermal
Isentropic
Polytropic
Isometric
dq=0
dp=0
dT=0
ds=0
∑ds=0
dV=0
k=Cp/Cv
k=0
k=1
k<n
k=∞
Reversible adiabatic process = Isentropic process

30. Compressor Work
A = Suction, B = Compression, C =Delivery, D = Expansion

31. Piston Compressor

32. The Carnot Cycle

33. Adiabatic/Isentropic Process

34. Adiabatic/Isentropic Compression
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

35. Surge and Stone Wall
A: Surge line, B: Stonewall line

36. Surge Control

37. Compression in Two Stages
Above pressures give minimum power

38. Intercooling

39. System Characteristic

40. Scaling Laws Isentropic Head Example
6000, 7000 and 8000 RPM

41. Parallel and Series

42. Hedne (2013)

43. Summary Recompression, export compression, reinjection compression
Reciprocating piston compressors and rotating centrifugal compressors (radial and axial)
Characteristic curves P [W] or h [J/kg] vs. q [m3/h]
Calculation of compression power (isentropic)
Surge (solved by recycle) and stonewall (speed of sound)
Compression in stages with intercooling (minimum power when equal power)
System curves (the need) and >1 compressor
Subsea compression