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B R A N D O N R I D E N S – S O U T H W E S T R E S E A R C H I N S T I T U T E ( S W R I )
THE IMPACT OF CHANGING PIPELINE CONDITIONS ON COMPRESSOR
EFFICIENCY
2015 GAS/ELECTRIC PARTNERSHIP CONFERENCE XXIII
OVERVIEW
• Shale Gas Deposits and Production• Gas Compositions and Comparison• Centrifugal Compressor Performance• Simulations with Varying Gas Compositions• Performance and Efficiency Impacts• Reciprocating Compressor and Piping System
Impacts• Pulsation and Vibration Case Study• Summary
SHALE GAS DEPOSITS
• US and Canada largest producers of shale gas
• Predicted 46% of US NG supply will come from shale by 2035
• Hydraulic fracturing and horizontal drilling increasing production
Not All Shale Gas Is Equal
Source: Energy Information Administration
SHALE GAS COMPOSITIONS AROUND THE UNITED STATES
Barnett (Texas) Marcellus Shale (New York) Fayetteville (Arkansas)
New Albany (Indiana, Illinois, Kentucky)
Haynesville (Louisiana)
Well 1 Well 2 Well 3 Well 4 Well 1 Well 2 Well 3 Well 4 Avg Well Well 1 Well 2 Well 3 Well 4 Ave Well
Nitrogen 7.9 1.5 1.1 1 0.4 0.3 0.3 0.2 0.7 0.1
CO2 1.4 0.3 2.3 2.7 0.1 0.1 0.9 0.3 1 8.1 10.4 7.4 5.6 4.8
Methane 80.3 81.2 91.8 93.7 79.4 82.1 83.8 95.5 97.3 87.7 88 91 92.8 95
Ethane 8.1 11.8 4.4 2.6 16.1 14 12 3 1 1.7 0.8 1 1 0.1
Propane 2.3 5.2 0.4 0 4 3.5 3 1 0 2.5 0.8 0.6 0.6 0
Molar Mass 19.161 19.42 17.547 17.282 19.499 19.052 18.855 16.852 16.547 19.248 19.288 18.421 17.918 17.411
Relative Density (SG) 0.66 0.67 0.61 0.60 0.67 0.66 0.65 0.58 0.57 0.66 0.67 0.64 0.62 0.60
Source: Keith Bullin - Composition Variety US Shale Gas (2008)
SHALE GAS DEPOSITS (TEXAS)
Source: Ed Bowles – Natural Gas Composition in the U.S. and Impact of Shale Gas (2014)
Barnett Shale Play
SHALE GAS COMPOSITIONS AT THE SAME LOCATION
Eagle Ford (Texas)
Station 1 Station 2
Well 1 Well 2 Well 3 Well 4 Well 5 Well 1 Well 2 Well 3 Well 4 Well 5
Nitrogen 0.1191 0.1571 0.1377 0.1199 0.1331 0.1111 0.1669 0.0968 0.0791 0.1059
CO2 1.7376 1.726 1.875 2.2574 2.2266 1.4261 1.3454 1.2863 1.3558 2.2998
Methane 79.9909 78.8998 80.9187 83.3418 88.7402 74.6498 74.4652 76.2094 75.2332 85.6547
Ehtane 10.4649 11.1471 9.803 8.4465 5.2514 13.8239 13.9161 12.9318 13.7304 7.2385
Propane 4.7834 4.9585 4.2409 3.4283 2.0159 6.3995 6.423 5.691 5.8157 2.4488
Isobutane 1.2568 0.8767 0.8286 0.6683 0.4264 0.9978 1.0194 1.0275 1.0852 0.6438
n‐Butane 0.7993 1.3513 1.2441 0.9357 0.5306 1.6245 1.6925 1.628 1.6021 0.671
i‐Pentane 0.3373 0.3575 0.3768 0.2972 0.2104 0.3842 0.3845 0.4331 0.4304 0.2949
n‐Pentane 0.2766 0.278 0.2913 0.2227 0.1514 0.3082 0.3081 0.3412 0.4318 0.2858
Hexanes 0.2341 0.248 0.2839 0.2822 0.314 0.2749 0.2789 0.3549 0.2363 0.3568
Molar Mass 20.727 20.967 20.594 20 18.809 21.874 21.918 21.625 21.769 19.53Relative
Density (SG) 0.72 0.72 0.71 0.69 0.65 0.76 0.76 0.75 0.75 0.67
Δ13%Δ16%Source: Ed Bowles – Natural Gas Composition in the U.S. and Impact of Shale Gas (2014)
COMPRESSOR PERFORMANCE
• Performance and efficiency are significantly tied to suction and discharge conditions• Suction and Discharge pressure/temperature• Head• Molecular Weight (molar mass)• Density and Compressibility• Ratio of Specific Heats
• Common conditions to change• Suction and Discharge pressure/temperature• Head
COMPRESSOR MAPS
0.85
0.810.78
0.750.72
0.69
50%60%
70%
80%
90%
100%105%
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000 20000 30000 40000
Head, H (m
)
Flow, Q (m3/h)
Base Case
Case 2
Case 3
Case 4B
Case 4
Case 5
Case 5B
0
5000
10000
15000
20000
25000
11.3 16.3 21.3 26.3 31.3 36.3 41.3 46.3
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
400 600 800 1000 1200 1400 1600 1800
Isen
trop
ic Head [J/kg]
Actual Flow [m3/min]
Isen
trop
ic Head [ft‐lbf/lbm]
Actual Flow [cfm]
Compressor Map with Performance Data19800 RPM Test 17800 RPM Test Theoretical Surge Line17800 RPM Prediction 19800 RPM Prediction MEASURED SURGE LINE
19800 RPM
17800 RPM
SIMULATION AND PARAMETRIC STUDY
• Stoner (Synergi) Pipeline Simulator (SPS)• Transient fluid flow simulator of natural gas pipeline networks• Types of analyses
• Control systems• Equipment (compressor/pump) performance analysis• Pressure-Flow capacity
• Equations of State (EOS): BWRS, CNGA, AGA-8, and specify unique gas properties
• Model Conditions• Gas Composition (SG)• Pressure Ratio and Temperature• Compressor Speed• Gas Flow Rate• Compressor map and polytrophic efficiency• Gas turbine power, heat rate, and speed
COMPRESSOR MODEL
• Singular variable speed centrifugal compressor with defined suction and discharge conditions
• No suction/discharge piping or equipment• Nuovo Pignone Compressor with GE Frame 3 Gas Turbine• Case Studies:
• Process and pipeline applicationsDefined Conditions
Case 1 Fixed Pressure Ratio Fixed Compressor Speed
Case 2 Fixed Pressure Ratio Fixed Flow Output
Case 3 Fixed Suction Pressure
Fixed Compressor Speed
Fixed Flow Output
FIXED SPEED CASE STUDY
• Set (constant) conditions:• Suction and Discharge
Pressure• Suction Temperature• Compressor Speed
Suction Pressure
(psig)
Discharge Pressure
(psig)
Suction Temperature
(F)
Speed (RPM)
580.2 855.7 63.8 5200
FIXED SPEED CASE (EFFICIENCY)
• Decrease in efficiency as specific gravity increases• SG change of 0.23 ~ 10% change in Efficiency
FIXED SPEED CASE (HEAD & FLOW)
• A decrease in initial Head as SG increases (38%)• An increase in flow as head decreases (32%)
FIXED SPEED CASE (POWER & FUEL CONSUMPTION)
• Increase of power utilization as SG increases• Fuel is the same as the process gas
VARIABLE SPEED CASE STUDY
• Set (constant) conditions:• Suction and Discharge
Pressure• Suction Temperature• Flow Output
Suction Pressure
(psig)
Discharge Pressure
(psig)
Suction Temperature
(F)
Flow (MMSCFD)
580.2 855.7 63.8 423.8
VARIABLE SPEED CASE (EFFICIENCY)
• Decrease in efficiency as specific gravity increases• SG change of 0.23 ~ 2% change in Efficiency
VARIABLE SPEED CASE (HEAD)
• Decrease in initial Head as specific gravity increases• 38% decrease in head with a fixed flow rate
VARIABLE SPEED CASE (POWER & FUEL CONSUMPTION)
• Very little change in power utilized• Decrease in fuel consumption as SG increases (28%)
FIXED SPEED/FLOW CASE STUDY
• Set (constant) conditions:• Suction Pressure• Suction Temperature• Compressor Speed• Flow Output
Suction Pressure
(psig)
Suction Temperature
(F)
Flow (MMSCFD)
Speed(RPM)
580.2 63.8 398.4 5200
FIXED SPEED/FLOW CASE (EFFICIENCY)
• Increase in efficiency as specific gravity increases• SG change of 0.23 ~ 3% change in Efficiency
FIXED SPEED/FLOW CASE (HEAD)
• Increase in initial head as specific gravity increases• 21% increase in head with a fixed speed and flow rate
FIXED SPEED/FLOW CASE (POWER & FUEL CONSUMPTION)
• Increase of power utilization (38%) and fuel consumption (20%) as SG increases
• Approaching surge conditions
PULSATION AND VIBRATION ISSUES
• Changes in gas compositions can cause harmful resonances from reciprocating compressors• Pulsations caused by periodic
pulsations (pressure & velocity)• High amplitude pulsations
(resonance) caused when frequencies of pulsations coincide with acoustic natural frequencies
• Horsepower losses and increases with pressure drop associated with pulsation mitigations (increase fuel consumption)• Pulsation bottle• Orifices
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40 45 50Frequency (Hz)
Ampl
itude
(psi
)
Fixed Speed Compressor Orders at 300 RPM
Helmholtz response (two-bottle system)
Cylinder gas passage-nozzle response (7x to 8x)
Choke tube pass-band frequency above 4x
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40 45 50Frequency (Hz)
Ampl
itude
(psi
)
Fixed Speed Compressor Orders at 300 RPMFixed Speed Compressor Orders at 300 RPM
Helmholtz response (two-bottle system)
Cylinder gas passage-nozzle response (7x to 8x)
Choke tube pass-band frequency above 4x
VIBRATION SAFETY & RELIABILITY CONCERNS
• Vibration Stress Failure• Noise Operation/Environmental Safety Issues
• Cracks and fatigue failures• Insulation deterioration• Compressor cylinder vibration and nozzle failures• Valve failures• Loosening or breaking of piping clamps• Foundation damage or failure• Elevated noise• Flow measurement inaccuracies• Overall reduction of compressor performance
PULSATION ANALYSIS CASE STUDY
• Existing reciprocating compressor station operating with new shale gas using initial pulsation mitigations for older gas composition
• Operating with the same conditions (compressor speed)
Existing Future
% mol %mol
CO2 0.958 1.761
Nitrogen 0.347 0.081
Methane 97.909 77.947
Ethane 0.494 11.782
Propane 0.19 4.718
Iso‐Butane 0.036 1.167
N‐Butane 0.042 1.35
Iso‐Pentane 0.01 0.523
N‐Pentane 0.007 0.34
N‐Hexane 0.007 0.248
N‐HEPTANE 0 0.052
N‐OCTANE 0 0.011
N‐NONANE 0 0.001
BENZENE 0 0.002
METHYLBENZENE 0 0.002
Molecular Weight 16.511 21.288
COMPARISON OF SPEED OF SOUND
RESPONSE SHIFTING
• All acoustic natural frequency responses shift down• 6.5 Hz response (Helmholtz or piping length response)• 17 Hz response (lateral length or other piping response)• 35 Hz response (cylinder nozzle or piping length response)
• Issues seen in field• Floor vibrations• Pulsation on Discharge• Pulsation on Suction
(potential baffle failures)
SUGGESTED MODIFICATIONS
• Option 1• Orifice installation in discharge cylinder nozzle• Rerouting of discharge piping• Implementation of more rigid piping restraints• De-coupling of cylinder supports
• Option 2• Combined with Option 1• Modify internal and external
components of the existing pulsation bottles• Suction and discharge internal
and external choke tubes• Suction and discharge baffles
• Option 3• Combined with Option 1• Fabricate and install new pulsation bottles
SUMMARY
• Notable impact on efficiency and performance• Efficiency change upwards of 10%• Head change upwards of 40%• Power utilized change upwards of 38%• Fuel consumption change upwards of 28%
• Possibility of reaching surge under certain conditions• Pulsation and vibration issues may be experienced causing
potential damage, loss of performance, and/or need for modifications
THANK YOU
• Brandon Ridens• [email protected]• 210-522-3459
• Adrian Alvarado• [email protected]
• Augusto Garcia Hernandez• [email protected]
• Eugene (Buddy) Broerman III• [email protected]