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September 26, 2006

September 26, 2006. NATURAL GAS DEHYDRATION. WHAT IS GAS DEHYDRATION? The removal of particulate water and water vapor from a produced gas stream. GAS DEHYDRATION. Water in pipelines causes corrosion Water reduces pipeline efficiency Water reduces accuracy in measurement

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September 26, 2006

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  1. September 26, 2006

  2. NATURAL GAS DEHYDRATION

  3. WHAT IS GAS DEHYDRATION? The removal of particulate water and water vapor from a produced gas stream. GAS DEHYDRATION

  4. Water in pipelines causes corrosion Water reduces pipeline efficiency Water reduces accuracy in measurement Water can form hydrates and cause plugging Why Dehydrate

  5. Calcium Chloride Branded desiccants Molecular Sieve Membrane Units Glycol Diethylene Triethylene Types of Dehydration

  6. Glycol is a hygroscopic liquid. Which simply means GLYCOL has the ability to absorb water. Glycol

  7. Diethylene Glycol Lower Cost 328° Thermal Decomposition 474° Boiling Point 92% - 94% Regeneration Higher Operating Cost Higher Capital Cost Diethylene Glycol

  8. Triethylene Glycol Higher Cost 404° Thermal Decomposition 550° Boiling Point 928% - 99.5% Regeneration Lower Operating Cost Lower Capital Cost Triethylene Glycol

  9. Fixed Minimum and Maximum gas capacity at a given pressure and temperature Gas composition Minimum and Maximum heat input into the regenerator Fire Tube surface area Vapor capacity of the still column Liquid and gas capacity of the inlet scrubber Parameters of a Dehy

  10. Variable Gas flow into the absorber Water content of the dehydrated gas Glycol circulation rate Glycol concentration Parameters of a Dehy

  11. Gas Flow Rate Gas Temperature Gas Pressure Pipeline Specifications Utilities Available Pad Size and Location Dehydrator Sizing

  12. Water Content of Natural Gas Temperature Differences Dehydrator Sizing

  13. Water Content of Natural Gas Pressure Differences Dehydrator Sizing

  14. Dehydrator Sizing Water Removal

  15. Natural Gas Dehydrator Contactor Tower Glycol Cooler Reboiler Dry Gas Outlet Inlet Scrubber Surge Tank Wet Gas Inlet High Pressure Filter Condensate Outlet Excess Separated Gas Outlet Three Phase Gas, Glycol & Condensate Separator Wet Glycol from Absorber (High Pressure) Wet Glycol to Reboiler (Low Pressure) Dry Glycol from Reboiler (Low Pressure) Dry Glycol to Absorber (High Pressure) Condensate Outlet

  16. Inlet Scrubber • First stage of liquid removal for the dehydration process • Eliminates free liquids from gas stream • Requires liquid level controller and high pressure dump valve • Used with pre-contactor • Mist Eliminator

  17. Absorber with Integral Scrubber • Lower capital cost than separate scrubber. • Requires liquid level controller and high pressure dump valve • Reduces footprint of dehydrator • Can not be used with pre-contactor • Mist eliminator

  18. Natural Gas Dehydrator Dry Gas Out Dry glycol Reboiler Absorber (Contactor) Wet glycol Wet Gas In Pump Dry glycol Heat exchanger surge tank Wet glycol

  19. Absorber or Contact Tower • Vessel where glycol and natural gas make contact • Concurrent flow • Gas flows up • Glycol flows down • Packed type • Structured Packing • Pall Ring Packing • Tray type • Bubble Cap • Nutter Valve

  20. Absorber with Scrubber • Gas temp 60°-135° F • Pressure 100 – 2600 psi • Inlet glycol should be 10° F higher than inlet gas • Lower temp than gas will cause foaming • Higher temp might increase glycol loss • 5 psig maximum pressure drop between inlet and outlet • Liquid seal must be established • Glycol circulation established on tray type tower • Gas flow should be gradually increased

  21. Absorber with Scrubber • pH of Glycol should be 7.0 – 7.5 • Absorber must have an adequate glycol/gas heat exchanger • Gas flow must be kept in turn down range or “channeling” may occur • Mist pad or mist extractor should be used • Glycol loss should be .1 gal per MMSCF • Tower should be level and secure

  22. Surge or Storage Tank • Holding tank for the dry or lean glycol before it goes to the glycol pump • Level must be maintained for pump head pressure • Can be separate vessel or integral to the reboiler. • Individual surge tanks may have glycol/glycol heat exchanger internally • Integral surge tanks have panel or tube type glycol/glycol exchangers

  23. Reboiler • Vessel where water is “cooked” out of the glycol • Temp range 375°- 400° for TEG • Fire tube heat flux • 6000-8000 BTU/Hr. per Sq./Ft • Fire tube must be free of deposits • salt • tar or coke • Stripping Gas • sparger style • spillover style • Stahl column • Temperature Control deadband should be as small as possible • Pressure should be at a minimum

  24. Still Column (where wet or “rich” glycol is injected for water removal) Packed with ceramic saddles 225°F Ideal Temperature Temperatures below 218°F will cause reboiler to flood Temperatures above 250°F will cause excess glycol loss out vent. Still Column

  25. Pump piping should be correctly sized A High pressure filter MUST be used and maintained Charcoal filters used for high condensate wells Inlet strainer MUSTbe installed and maintained Pump should be secured on a level surface Glycol Pump

  26. 3 Phase Glycol/Gas/CondensateSeparator • Separates any liquids that might get carried over with the glycol such as condensate or compressor oils • Used to reclaim some of the gas that would ordinarily lost through the still column • Flash separator pressure should be kept as low as possible to prevent pump stalling

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