THE IMPACT OF CHANGING PIPELINE CONDITIONS ON COMPRESSOR EFFICIENCY BRANDON RIDENS SOUTHWEST RESEARCH INSTITUTE (SWRI) 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 Source: Energy Information Administration Not All Shale Gas Is Equal
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) Barnett Shale Play Source: Ed Bowles Natural Gas Composition in the U.S. and Impact of Shale Gas (2014)
SHALE GAS COMPOSITIONS AT THE SAME LOCATION Eagle Ford (Texas) Station 1 Station 2 Well 1 Well 2 Well 3 Well4 Well 5 Well 1 Well 2 Well 3 Well4 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 19.53 Relative Density (SG) 0.72 0.72 0.71 0.69 0.65 0.76 0.76 0.75 0.75 0.67 Δ16% Δ13% 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 Head, H (m) 9000 8000 7000 6000 5000 4000 3000 2000 1000 0.85 50% 60% 70% 0.81 0.78 0.75 0.72 0.69 105% 100% 80% 90% 0 10000 20000 30000 40000 Flow, Q (m 3 /h) Base Case Case 2 Case 3 Case 4B Case 4 Case 5 Case 5B Isentropic Head [ft lbf/lbm] 11.3 16.3 21.3 26.3 31.3 36.3 41.3 46.3 9000 8000 7000 6000 5000 4000 3000 2000 1000 Compressor Map with Performance Data 19800 RPM Test 17800 RPM Test Theoretical Surge Line 17800 RPM Prediction 19800 RPM Prediction MEASURED SURGE LINE Actual Flow [m 3 /min] 0 0 400 600 800 1000 1200 1400 1600 1800 Actual Flow [cfm] 19800 RPM 17800 RPM 25000 20000 15000 10000 5000 Isentropic Head [J/kg]
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 applications Defined 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 Amplitude (psi) 25 20 15 10 5 0 Helmholtz response (two-bottle system) Fixed Speed Compressor Orders at 300 RPM Choke tube pass-band frequency above 4x Cylinder gas passagenozzle response (7x to 8x) 0 5 10 15 20 25 30 35 40 45 50 Frequency (Hz)
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 Brandon.ridens@swri.org 210-522-3459 Adrian Alvarado Adrian.alvarado@swri.org Augusto Garcia Hernandez Augusto.garciahernandez@swri.org Eugene (Buddy) Broerman III Eugene.broerman@swri.org