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Cryogenic Sour Gas Process for Acid Gas Injection: Innovation & Efficiency<br>

Explore the benefits of Controlled-Freeze Zone (CFZ™) process for methane/CO2 separation, cost savings, and operational efficiency in acid gas injection applications. Learn from case studies and experimental programs.<br>

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Cryogenic Sour Gas Process for Acid Gas Injection: Innovation & Efficiency<br>

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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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