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Why optimize the regeneration procedure?

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Why optimize the regeneration procedure?

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  1. IAPG Natural Gas CongressMolecular Sieves:is your regeneration procedure optimized?CECA – VETEKAuthor Peter MeyerPresenter Bob Davenport

  2. Why optimize the regeneration procedure? • A non optimized regeneration procedure can harm the molecular sieves and reduce significantly their life time • New unit: if the regeneration gas is recycled the recycled water content has to be taken in account, if the regeneration gas flow rate is too short the unit will not work • Knowing how to optimize the procedure can help debottlenecking a unit

  3. cap PSA cap TSA Industrial units Regeneration: how does it work?

  4. TSA Regeneration: how does it work? This presentation will focus on Natural Gas Drying regenerated by Thermal Swing Adsorption (TSA). • Regeneration procedure: • Switch including possibly pressure change (depress.) • Heating (Purge? Two step heating? Heating ramp?) • Cooling (dry/wet gas?) • Switch including possibly pressure change (repress.)

  5. Regeneration: parameters • Heating step: how much heat? • Heat up the molecular sieves • Heat up the vessel (internal/external insulation) • Remove water • Push out desorbed water

  6. Minimum!! Regeneration: temperature influence Quantity of regeneration gas Regeneration temperature The quantity of regeneration gas depends on the inlet temperature during the heating. Below a minimum temperature the water dew point spec could not be reached (too high residual water content), the maximum temperature depends on the type of molecular sieve.

  7. Regeneration: uncomplete regeneration Adsorption time Adsorption cycles A sudden decrease of adsorption time is the sign for a bad regeneration (accumulation of water)  happens very often shortly after start up, possibility to recover sieves

  8. Regeneration: uncomplete regeneration Make sure to have a plateau at the outlet during heating. Make sure to have a small temperature difference between inlet and outlet during heating.

  9. Regeneration: Maximum temperature 3A: 230°C (446°F) for saturated gases, up to 260°C (500°F) for unsaturated gases 4A: normally 250°C (482°F), up to 290°C (554°F) with precautions For information 5A/13X: 300°C (572°F) in case of sweetening, but if there is NO water on the sieves

  10. Regeneration: pressure influence More regeneration gas (quantity) is needed if the regeneration pressure is at a high pressure. Two cases for pressure range: Low pressure – heating limited The regeneration gas has to bring in the energy for heating and desorption (regeneration temperature above boiling temperature of water at regeneration pressure) High pressure – stripping limited The regeneration gas has additionally to strip off (push out) the desorbed water. The limit between both is around 30-35 bars. Example: a regeneration at 60 bar (870 psia) may require perhaps 25% more regeneration gas quantity.

  11. CASE STUDY 3 adsorber system, 2 in adsorption, 1 in regeneration 500 MMSCFD, 60 bar (870 psia), 30°C (86°F), Saturated gas, 4A molecular sieve, Adsorption time 16 hrs, Regeneration recycled (air cooler sat. @ 55°C (131°F), 30 bar (435 psia))

  12. CASE STUDY Case 1: Regeneration at 250°C, 482°F and 30 bar, 435 psia Case 2: Regeneration at 250°C, 482°F and 60 bar, 870 psia Case 3: Regeneration at 290°C, 555°F and 60 bar, 870 psia Case 4: Regeneration optimization to minimize hydrothermal damage and improve molecular sieves performance. (Case 5: Correction of case 2 supposing only case 1 flow rate available, internal heat insulation) Fixed: pressure drop during adsorption, no stand-by time.

  13. CASE 1 Case 1: Regeneration at 250°C, 482°F and 30 bar, 435 psia Procedure Depress 15 min Heating Cooling Repress 15 min 7 hrs 30 min available 100% FR1 100% FP Case 1 Vessel diameter : 100% Adsorbent weight : 100%

  14. CASE 2 Case 2: Regeneration at 250°C, 482°F and 60 bar, 870 psia Procedure Depress 0 min Heating Cooling Repress 0 min 8 hrs 00 min available 30 min more 115% FR1 Heater / Compressor - Capacity ?? 100% FP Case 2 Vessel diameter : 100% Adsorbent weight : 104% Regengasquantity : 123%

  15. CASE 3 Case 3: Regeneration at 290°C, 482°F and 60 bar, 870 psia Procedure Depress 0 min Heating Cooling Repress 0 min 8 hrs 00 min available 108% FR1 Steel: max. design temperature ?? 100% FP Case 3 Vessel diameter : 100% Adsorbent weight : 102% Regengasquantity : 115%

  16. CASE STUDY Case 1: Regeneration at 250°C, 482°F and 30 bar, 435 psia Case 2: Regeneration at 250°C, 482°F and 60 bar, 870 psia Case 3: Regeneration at 290°C, 555°F and 60 bar, 870 psia (possibility to reach lower dew point) Case 4: ??? HYDROTHERMAL DAMAGING

  17. Hydrothermal damaging End of Adsorption

  18. Hydrothermal damaging Start of Heating Cold saturated section Heated section

  19. Hydrothermal damaging Heating proceeds ... Cold Saturated Section Steam Fog Formation Hot Section

  20. Water Droplets Condensation Zone Crust and Lumps formation Vaporization Zone Hydrothermal damaging Water Retro-condensation during Heating REFLUX

  21. CASE 4 Case 4: Regeneration at 290°C, 482°F and 60 bar, 870 psia Procedure Depress 0 min 30 min intermediate heating Heating Cooling Repress 0 min 7 hrs 30 min available 115% FR1 100% FP Case 4 Vessel diameter : 100% Adsorbent weight : 102% Regengasquantity : 123%

  22. CASE STUDY Case 1: Regeneration at 250°C, 482°F and 30 bar, 435 psia Case 2: Regeneration at 250°C, 482°F and 60 bar, 870 psia Case 3: Regeneration at 290°C, 555°F and 60 bar, 870 psia Case 4: Regeneration at 290°C, 555°F and 60 bar, 870 psia, interm. heating Advantage of case 4: lower water dew point at outlet.

  23. CASE STUDY Case 1: Regeneration at 250°C, 482°F and 30 bar, 435 psia Case 2: Regeneration at 250°C, 482°F and 60 bar, 870 psia Case 3: Regeneration at 290°C, 555°F and 60 bar, 870 psia Case 4: Regeneration at 290°C, 555°F and 60 bar, 870 psia, interm. heating Case 5: keep regeneration gas flow rate and MS height of case 2, internal heat insulation , diameter 3.5 m, increase feed flow rate, decrease adsorption time

  24. CASE 5 (versus case 2) Case 2: Regeneration at 250°C, 482°F and 60 bar, 870 psia Procedure Depress 0 min Heating Cooling Repress 0 min 4 hrs 30 min available Adsorption 9 hrs 100% FR2 Pressure drop 0.7 bar (233%) 140% FP Case 2 Vessel diameter : 94.6% Adsorbent weight : 88% Regengasquantity : 61%

  25. CASE STUDY Internal insulation, 3.7m  3.5 m internal diameter Higher feed flow rate : 140% Higher pressure drop during adsorption : 233% Adsorption time down from 16hrs to 9hrs (shorter life time)

  26. How to prevent hydrothermal damaging? Hydrothermal damaging happens when liquid water is present on the molecular sieves at high temperature: One should try to change the regeneration procedure in order to prevent desorption of water when the molsieve bed is not yet heated up almost homogenously thus limiting water condensation at top layers  intermediate heating step + higher regeneration gas flow rate

  27. How to prevent hydrothermal damaging? • Original procedure: • int. temperature too high, too much water desorbed • plateau of outlet temperature showing water re-vaporization

  28. How to prevent hydrothermal damaging? • New procedure: • int. temperature lower • smoother increase of outlet temperature

  29. How to prevent hydrothermal damaging?

  30. Conclusion • When looking at your molecular sieve unit and its regeneration procedure: • Don’t underestimate the pressure influence on the regeneration gas quantity • Think about hydrothermal damaging • Optimization does not cost a lot but lengthens the life time of the molecular sieves Don’t hesitate to ask the nice and knowledgeable guys from CECA to help you. THANK YOU!