IAPG Natural Gas CongressMolecular Sieves:is your regenerationprocedure optimized?CECA – VETEKAuthor Peter MeyerPresenter Bob Davenport
IAPG 2008
A non optimized regeneration procedure can harm themolecular sieves and reduce significantly their life time
New unit: if the regeneration gas is recycled therecycled water content has to be taken in account, ifthe regeneration gas flow rate is too short the unit willnot work
Knowing how to optimize the procedure can helpdebottlenecking a unit
Why optimize the regeneration procedure?
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cap TSA
cap PSA
Industrialunits
Regeneration: how does it work?
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TSA Regeneration: how does it work?
This presentation will focus on Natural Gas Dryingregenerated by Thermal Swing Adsorption (TSA).
Regeneration procedure:
1)Switch including possibly pressure change (depress.)
2)Heating (Purge? Two step heating? Heating ramp?)
3)Cooling (dry/wet gas?)
4)Switch including possibly pressure change (repress.)
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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
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Regeneration: temperature influence
The quantity of regeneration gas depends on the inlet temperature during theheating. Below a minimum temperature the water dew point spec could notbe reached (too high residual water content), the maximum temperaturedepends on the type of molecular sieve.
Regeneration temperature
Quantity ofregenerationgas
Minimum!!
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Regeneration: uncomplete regeneration
A sudden decrease of adsorption time is the sign for a badregeneration (accumulation of water) happens veryoften shortly after start up, possibility to recover sieves
Adsorption cycles
Adsorptiontime
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Regeneration: uncomplete regeneration
Make sure to have a plateau at the outlet during heating.
Make sure to have a small temperature difference betweeninlet and outlet during heating.
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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) withprecautions
For information
5A/13X: 300°C (572°F) in case of sweetening, but ifthere is NO water on the sieves
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Regeneration: pressure influence
More regeneration gas (quantity) is needed if the regenerationpressure 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 anddesorption (regeneration temperature above boiling temperatureof water at regeneration pressure)
High pressure – stripping limited
The regeneration gas has additionally to strip off (push out) thedesorbed water.
The limit between both is around 30-35 bars. Example: aregeneration at 60 bar (870 psia) may require perhaps25% more regeneration gas quantity.
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CASE STUDY
3 adsorber system, 2 inadsorption, 1 in regeneration
500 MMSCFD, 60 bar (870psia), 30°C (86°F),
Saturated gas, 4A molecularsieve,
Adsorption time 16 hrs,
Regeneration recycled (aircooler sat. @ 55°C (131°F),30 bar (435 psia))
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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 hydrothermaldamage and improve molecular sieves performance.
(Case 5: Correction of case 2 supposing only case 1 flow rateavailable, internal heat insulation)
Fixed: pressure drop during adsorption, no stand-by time.
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CASE 1
Case 1:Regenerationat 250°C,482°F and 30bar, 435 psia
Procedure
Depress 15 min
Heating
Cooling
Repress 15 min
7 hrs 30 minavailable
100% FP
Case 1
Vessel diameter : 100%
Adsorbent weight : 100%
100% FR1
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CASE 2
Case 2:Regenerationat 250°C,482°F and 60bar, 870 psia
Procedure
Depress 0 min
Heating
Cooling
Repress 0 min
8 hrs 00 minavailable
30 min more
Case 2
Vessel diameter : 100%
Adsorbent weight : 104%
Regengasquantity : 123%
Heater /
Compressor -
Capacity ??
100% FP
115% FR1
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CASE 3
Case 3
Vessel diameter : 100%
Adsorbent weight : 102%
Regengasquantity : 115%
Case 3:Regenerationat 290°C,482°F and 60bar, 870 psia
Procedure
Depress 0 min
Heating
Cooling
Repress 0 min
8 hrs 00 minavailable
Steel: max.designtemperature ??
100% FP
108% FR1
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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: ???
MS Quantity
Regengas
quantity
Regengas
Flow rate
CASE 1
100%
100%
100% FR1
CASE 2
104%
123%
115% FR1
CASE 3
102%
115%
108% FR1
HYDROTHERMAL DAMAGING
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End of Adsorption
Hydrothermal damaging
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Start of Heating
Cold saturatedsection
Heated section
Hydrothermal damaging
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Heating proceeds ...
Steam FogFormation
Cold SaturatedSection
Hot Section
Hydrothermal damaging
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Water Retro-condensation
during Heating
Vaporization Zone
Condensation Zone
REFLUX
Water Droplets
Crust and Lumpsformation
Hydrothermal damaging
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CASE 4
Case 4:Regenerationat 290°C,482°F and 60bar, 870 psia
Procedure
Depress 0 min
30 min intermediateheating
Heating
Cooling
Repress 0 min
7 hrs 30 minavailable
Case 4
Vessel diameter : 100%
Adsorbent weight : 102%
Regengasquantity : 123%
100% FP
115% FR1
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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.
MS Quantity
Regengas
Quantity
Regen flow rate
CASE 1
100%
100%
100% FR1
CASE 2
104%
123%
115% FR1
CASE 3
102%
115%
108% FR1
CASE 4
102%
123%
115% FR1
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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 heatinsulation , diameter 3.5 m, increase feed flow rate, decrease adsorptiontime
MS Quantity
Regengas
quantity
Regen flow rate
CASE 1
100%
100%
100% FR1
CASE 2
104%
123%
115% FR1
CASE 3
102%
115%
108% FR1
CASE 4
102%
123%
115% FR1
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CASE 5 (versus case 2)
Case 2:Regenerationat 250°C,482°F and 60bar, 870 psia
Procedure
Depress 0 min
Heating
Cooling
Repress 0 min
4 hrs 30 minavailable
Adsorption 9 hrs
Case 2
Vessel diameter : 94.6%
Adsorbent weight : 88%
Regengasquantity : 61%
Pressure drop0.7 bar
(233%)
140% FP
100% FR2
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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)
MS Quantity
Regengas
quantity
Regen flow rate
CASE 2
100%
100%
100% FR2
CASE 5
88%
61%
100% FR2
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How to prevent hydrothermal damaging?
Hydrothermal damaging happens when liquid water is present on themolecular sieves at high temperature:
One should try to change the regeneration procedure in order toprevent desorption of water when the molsieve bed is not yetheated up almost homogenously thus limiting water condensationat top layers
intermediate heating step + higher regeneration gas flow rate
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How to prevent hydrothermal damaging?
Original procedure:
- int. temperature too high, toomuch water desorbed
- plateau of outlet temperatureshowing water re-vaporization
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How to prevent hydrothermal damaging?
New procedure:
- int. temperature lower
- smoother increase of outlettemperature
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How to prevent hydrothermal damaging?
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Conclusion
When looking at your molecular sieve unit and itsregeneration procedure:
-Don’t underestimate the pressure influence on theregeneration gas quantity
-Think about hydrothermal damaging
-Optimization does not cost a lot but lengthens the lifetime of the molecular sieves
Don’t hesitate to ask the nice and knowledgeable guysfrom CECA to help you.
THANK YOU!