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Cryogenic Sour Gas Process

Cryogenic Sour Gas Process Attractive for Acid Gas Injection Applications P. Scott Northrop ExxonMobil Upstream Research Rene F. Bialek Imperial Oil Resources. Cryogenic Sour Gas Process. The following items will be discussed: Controlled-Freeze Zone (CFZ ™ ) process overview and background

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Cryogenic Sour Gas Process

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  1. Cryogenic Sour Gas Process Attractive for Acid Gas Injection ApplicationsP. Scott NorthropExxonMobil Upstream ResearchRene F. BialekImperial Oil Resources

  2. Cryogenic Sour Gas Process • The following items will be discussed: • Controlled-Freeze Zone (CFZ™) process overview and background • Earlier pilot plant results • CFZ™- why now? • New case study • Experimental program

  3. CFZ™ Overview/Background • Problem: CO2 Freezing in Cryogenic Separations • Solid CO2 plugs standard distillation equipment • CO2 is present in many natural gas streams • Solution: • Instead of trying to avoid CO2 freezing, induce it in a specially-designed part of the distillation column • CFZ™ was originally conceived for methane/CO2 separation, but it has general application to cases where a solid phase forms in a distillation column

  4. CFZ™ Process Schematic CH4 Vapor (N2, He) From Pump Spray nozzles Liquid level Feed Gas Liquid CO2, H2S (C2+, Trace sulfur compounds)

  5. Clear Lake Pilot Plant • Test Parameters • Feed rates: 200-600 kscfd • Feed CO2: 15-65% • Overhead CO2: 700-2500 ppm • Bottoms CH4: 0.5-2% • Demonstrated • Concept and operability of unit • Multiweek operation at 600 psig • Performance predicted by tools • Two start-up procedures • Spray temperature key • Reflux to spray line helped • Problem - Inadequate insulation • Limited test to high pressure • Limited tests that could be run

  6. Why Now? CH4, N2 CFZ™ is easily integrated with acid gas injection (AGI)! PI CFZ Dry Gas • H2S/Sulfur: • - Eliminates Claus/TGT units, sulfur blocks •  Saturated sulfur markets •  Slow development of alternative uses • CO2: • - Canadian producers may have Kyoto limits • - Enhanced oil recovery possible H2S, CO2

  7. Case Studies: General Remarks • CAPEX and OPEX savings can be in the 10-20% range over commercial technologies • At moderate to high CO2 concentrations, CFZ is competitive • Major benefits: • Fewer processing steps • Reduction in acid gas injection costs • Total contaminant removal • Economic issues: • Higher refrigeration loads than solvents • Means of CO2/C2+ separation required in some cases

  8. Case Study - Gwillim • Several processing options evaluated • Gas composition & reinjection requirement are good fit for CFZ™ • Basis: 100 MCF/D Feed,. Pipeline spec. (4 ppm H2S)

  9. Gwillim Resource Overview Est’d. CH4 Resource: Approx. 1 TCF psig Initial Reservoir Pressure 4500 Reservoir Temp 203F Average Well Depth: 11,000 ft Wells drilled to date 4 (mol %) Gas Composition Methane 58.3 H2S 24.5 CO2 16.8 C2 & C3 0.08 C4+ 0.00 N2 0.3 Elemental sulfur Trace Reservoirs with similar acid gas content are being produced by other operators in the area

  10. Gwillim: Existing Infrastructure • Duke Pine plant • Duke Kweon acid gas stripper plant • Burlington sweet plant (Noel) • High pressure sour gas gathering system to Pine & Kweon • No sweet fuel line • 240 KV power line nearby • Challenges: • Insufficient existing plant capacity for entire development • Processing fees Pine Noel Kwoen Gwillim

  11. Detailed Sweetening Process Screening Relative Comparison Completed by an independent consultant 100 MCF/D, 40% Acid gas & 950 psig plant inlet Selexol CFZ™ Capital Investment 1.3 1.0 Annual Operating Cost 1.19 1.0 Plant Horsepower 1.41 1.0 Gas sales 0.93 1.0

  12. Reflux/Sales Comp. Aerial Cooler CFZ Tower Reboiler Expander (Optional) Sales Gas Chiller Raw Gas Dehy. Spray Pump CFZ Tower Liquid Acid Gas to disposal <1% CH4 Preliminary Conceptual CFZ™ Processing Plant Cross Exchanger

  13. Increasing H2S Impact of H2S • Shrink freezing zone • - Liquid H2S dissolves solid CO2 • Relative volatility • - 4 ppm H2S spec achievable, • drives reflux/tray req. • Other solids • - Elemental sulfur, other contaminants may freeze ahead of column • Metallurgical requirements • - Since liquefied acid gas is dry, no special materials needed After Fig. 16-32 of GPSA Databook

  14. Experimental Program • Cold depletion experiments • Collected wellhead sample, cooled to -80°C, expelled gas • Identified presence of elemental sulfur • CO2 adhesion in the presence of H2S • “Cold finger” experiments in progress • H2O solubility in liquid acid gas at low T • Experiments planned • CO2, H2S K-values at infinite dilution in liquid methane • verify numerical models, simulation results at top of column

  15. Summary CFZ™ best fits include: • Lean gases where hydrocarbon liquids recovery is not needed • Total acid gas and mercaptan removal, e.g, pre-LNG • Acid gas injection (acid components are already liquefied) CFZ AGI

  16. Back-up Slides

  17. CO2/CH4 Phase Behavior T vs. x,y for CO2/CH4 at 600 psia

  18. CO2/CH4 Phase Behavior T vs. x,y for CO2/CH4 at 800 psia

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