Natural Gas Processing Dr. Stathis Skouras, Gas Processing and LNG RDI Centre Trondheim, Statoil, Norway
Schedule Thursday 9/11/2017, 11:45 13:30 Lecture 4 Hydrocarbon dew point control (HCDP) Examples from offshore/onshore gas processing Lecture 5 Low Carbon technologies and Future Value Chains (FVC) Kahoot quiz: Gas Processing 2
Hydrocarbon dew point - Phase envelope of natural gas Dense phase C Critical point Cricondenbar N M Cricondenbar Cricondentherm Liquid Cricondentherm Vapor + liquid Gas The phase envelope is ONLY a function of COMPOSITION 3
Gas quality specs along the value chain (1/2) Specifications for rich gas transport Designation and unit Specification Max operating pressure (barg) 210 Min operating pressure (barg) 112 Max operating temperature ( C) 60 Min operating temperature ( C) -10 Max cricondenbar pressure (barg) 105 Max cricondentherm temperature ( C) 40 Max water dew point ( C at 69barg) -18 Max carbon dioxide (mole%) 2 Max hydrogen sulphide and COS (ppmv) 2 Max O 2 (ppmv) 2 Max daily average methanol content (ppmv) 2.5 Max peak methanol content (ppmv) 20 Max daily average glycol content (LT/MSm 3 ) 8 Prepares gas for further transport Offshore processes Space and weight limitations Expensive labour Expensive utilities (cooling, water, chemicals, electricity) Escape issues Onshore processes 4
Gas quality specs along the value chain (2/2) Specifications for sales (dry) gas transport Designation and unit Specification Hydrocarbon dew point ( C at 50 barg) -10 Water dew point ( C at 69 barg) -18 Maximum carbon dioxide (mole%) 2.50 Maximum oxygen (ppmv) 2 Maximum hydrogen sulphide incl. COS (mg/nm 3 ) 5 Maximum mercaptans (mg/nm 3 ) 6.0 Maximum sulphur (mg/nm 3 ) 30 Gross Calorific Value (MJ/Sm 3 ) 38.1 43.7 Gross Calorific Value (MJ/Nm 3 ) 40.2 46.0 Gross Calorific Value (kwh/nm 3 ) 11.17 12.78 Wobbe Index (MJ/Sm 3 ) 48.3 52.8 Wobbe Index (MJ/Nm 3 ) 51.0 55.7 Wobbe Index (kwh/nm 3 ) 14.17 15.47 Onshore processes Prepares gas for end user Recovers valuable NGL products No space and weight limitations Access to utilities (cooling, water, chemicals, electricity) Easy escape Receiving terminals 5
Practical importance of phase envelopes Gas transport in pipelines b b a a Rich gas pipeline (a b) - Cricondenbar specification - Transport at high pressures - No liquid formation above cricondenbar (dense phase) - Manipulate phase envelope by removing NGL to reach a cricondenbar spec. Sales gas pipeline (a b ): - Cricondentherm spec - Transport at intermediate/low pressures - No liquid formation above cricondentherm (gas phase) - Manipulate phase envelope by removing NGL to reach a cricondentherm spec. 6
Effect of composition on phase envelopes Effect of heavy ends (C 7+ ) Manipulate phase envelope by removing NGL and heavy ends (C 7+ ) Source: A. M. Elsharkawy / Fluid Phase Equilibria 193 (2002) 147-165 7
Manipulation of phase envelopes along the Value Chain- HC dew point control Manipulate phase envelope by removing NGL or heavy ends (C 7+ ) Source: A.O. Fredheim, E. Solbraa, Compendium Industrial Processes, TEP4185 NTNU 8
NGL recovery processes Joule-Thompson valve Sales gas Expander process Sales gas S2 S2 S1 PRODUCT-FLAS GAS S1 GAS EX1 VALVE PRODUCT-FLAS S3 FEED-FLASH S3 FEED-FLASH FEED FEED LIQUID LIQUID NGL NGL JT-valve (isenthalpic process) moderate NGL recovery Expander (isentropic process) achieves lower temperatures (deep NGL recovery) Expander creates shaft work combination with compressor (energy recovery) 9
Moderate NGL recovery - Thermodynamic path 10 -
NGL recovery processes Pre-cooling and expansion Heat integration between feed and product (gas/gas HX) Heat integration with cold products and extra refrigeration S2 S2 S1 S1 S3 S4 EX1 PRODUCT-FLAS S5 S4 EX1 PRODUCT-FLAS NGL E2 E1 GAS S5 E1 Sales gas S3 FEED-FLASH GAS S7 Sales gas FEED-FLASH FEED FEED NGL LIQUID LIQUID Lower temperatures achieved deep NGL recovery More robust scheme wrt. feed disturbances 11
Deep NGL extraction process Thermodynamic path 12 -
NGL recovery processes Pre-cooling, expansion and fractionation Sales gas NGL Distillation column (de-methaniser) to increase NGL recovery Robust scheme to adjust C2 recovery according to market prices 13
NGL fractionation C2+ from NGL recovery Feed Propane 4 3 1 2 NGL fractionation in series of distillation columns Make high added value products (C2, C3, C4, C5+) C2 Sea water 5 7 Steam 8 6 5 De-etanizer C3 Sea water Sea water Steam ic4 De-propanizer Steam De-butanizer Steam C5+ Butane splitter nc4 14
Examples: Offshore and onshore processing
Snøhvit Offshore processing Melkøya Norne Åsgard Heidrun Kristin ÅTS Haltenpipe Ormen Lange Statfjord Tjeldbergodden Troll Nyhamna Frigg Vesterled Sleipner Kollsnes Kårstø St Fergus Ekofisk Europipe I Europipe II Langeled Zeepipe I Norpipe Easington Franpipe Emden Zeebrugge Dunkerque 16
Subsea Gas train WDP control: Hg removal TEG plant 31 C Offshore process HCDP control: Cooling and separation Fuel Gas Meter Rich Gas CricoP <105 barg Åsgard Transport Mercury Removal Units w/filters 25 C GT Export gas compressor 26 C H2S Scavenger 2nd stage separator Recompressor-train with 3 stages 1st or 2nd stage separator 30 C 30 C 30 C Feed 121 C, 87 bar Separation train (3-phase) Test 1 st stage separator LP Mod. 2 nd stage separator 3rd stage separator 3rd stage separator Oil stabilization train Recompression train 2 nd stage separator Test-separator 26 bar 3 rd stage separator Stabilised Oil 2 bar Meter TVP = 0.965 bar 17
CO 2 /H 2 S removal Åsgard B Process RICH GAS EXPORT FEED Oil stabilization train Water treatment plant STABILISED OIL 18
Onshore processing: Kårstø plant Snøhvit Melkøya Norne Åsgard Heidrun Kristin ÅTS Haltenpipe Ormen Lange Statfjord Tjeldbergodden Troll Nyhamna Frigg Vesterled Sleipner Kollsnes Kårstø St Fergus Ekofisk Europipe II Europipe I Langeled Zeepipe I Norpipe Easington Franpipe Emden Zeebrugge Dunkerque 19
Kårstø gas processing plant 94 MSm 3 /d rich gas feed 72 x 10 6 ton/d feed gas 74 MSm 3 /d sales gas export 8 500 x 10 3 ton/yr liquid products Njord Alve Draugen Heidrun Norne Åsgard Mikkel Kristin Åsgard Transport 42 707 km Europipe II 42 650 km Snorre Statfjord Ø Gullfaks Tordis Sleipner Ø/V Gudrun Gungne Sigyn Volve Statpipe 30 308 km Sleipner 20 light oil/condensate 245 km Statpipe 28 228 km 20
Kårstø: Feed pretreatment 111 bar 5,8 C Mercury removal H 2 S removal H2S filters LP steam Feed from Åsgard Pig trap Cyclone separator Feed preheater Let-down station Crossover/ backflow Filter separator Mercury Removal Coalescers NET1 inlet module Driers To warm turbo expander Raw gas filters Water dew point
HCDP control unit (DPCU) Cooling and expansion COOLING NGL RECOVERY Gas/Gas HX LT separator De-C1 JTvalves column Turbo-expander Expansion/compression C2+ to NGL fractionation 22
Thank you Presenters name: Dr. Stathis Skouras Presenters title: Principal Researcher efss@statoil.com, tel: +47 97 69 59 62 www.statoil.com 23