29C - Moisture Removal
Transcript of 29C - Moisture Removal
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The World of Energy
29.3. Moisture Removal
Chapter 29 LNG Technology Gas Treating
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Dehydration Unit
Dehydration is the removal of waterfrom the produced natural gas and is
accomplished by various methods:
Ethylene glycol
Triethylene Glycol dehydration
(TEG) and diethylene glycol (DEG) Dry-bed dehydrators using solid
desiccants
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Molecular Sieve
Molecular sieves areadsorbents composed ofaluminosilicate crystallinepolymers (zeolites).
They efficiently removelow concentrations ofpolar or polarizablecontaminants such asH2O, methanol, H2S,CO2, COS, mercaptans,sulfides, ammonia,aromatics and mercury
down to traceconcentrations.
Molecular sieve productsmanufactured in variousforms: beads, granulesand extrudates, includingstandard pellets and
TRISIVTM pellets. The molecular sieve type,
size and particle shapeselected for a particularcustomer are determinedby the application.
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Molecular Sieve vs Activated Alumina
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An Open Cycle Molecular Sieve Dehydration
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Molecular Sieve Applications
Natural gas dehydration Normal parameters: water saturated, 30-200F, 100-1500
psig. Regeneration is via dry or wet gas, yielding LNG orpipeline specifications, respectively.
Natural gas mercury removal (Combines with dehydration, one system, no additional
out.
Natural gas/LPG desulfurization H2S, mercaptans, COS and sulfides can be removed. Effluent
with H2O
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SE
RVICE
REGE
NERATION
GUARD
HOT
DRY GASDRY
SWEET GAS
WET GASWET
SWEET GAS H2O freezes and
blocked equipments
H20 is adsorbed by
Molecular Sieve (SilicaAlumina) catalyst
Regenerated by hotgas heating
H2O inlet : saturated
H2O oulet : 1 ppm Catalyst life : 4 ~ 6
years
Typical H2O (Moisture) Removal Unit
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Adsorption: Equilibrium & MTZ
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Feed Vapor Dryer & Molecular Sieves
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All LNG Plants use Molecular Sieve adsorption technology.The only technology can meet outlet moisture content below1 ppm (minus 110 Deg. C dew point)
Other dehydration technology such as Glycol Unit, Silica Gelor Activated Alumina cannot meet low moisture outlet
Adsorption/Desorption Scheme:
Pressure Swing Desorption
Heated Desorption (heat regenerated). Suitable for Gas Turbine
Plant. Various type of Molecular Sieve
Beads (Spherical). Sturdy, resistant to crushing and friction.High pressure drop, less surface area.
Pellet (Cylindrical). More surface area, higher efficiency. More
flow void space, less pressure drop. Clover Leaf (Triple Cylindrical). Highest surface area, high
efficiency. Prone to crushing and friction.
Dehydration Technology for LNG
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Causes of Molecular Sieve Aging
Causes of Aging Insoluble water
Liquid entrainment (hydrocarbon, water) High water partial pressure at high
temperature (above 150C)
Amine carryover
CO2 , Carbonic acid formation
H2CO3 + (Na+, Ca++, K+) Na2CO3 -NaHCO3 - CaCO3 - K2CO3
Decomposition of mercaptans during
regeneration Presence of chlorides
Mercury
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Multibed System: Dehydration
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Adsorption Mechanisms and Adsorbents
Adsorption is one of the many separationtechnologies used in treating natural gas. Adsorptioncan be broken down into several different
categories: Chemisorption (usually irreversible; no
regeneration) Mercury removal with promoted activated carbon, H2S
polishing with ZnO.
Physisorption (reversible adsorption on the surfaceof a material) Water or hydrocarbon removal with silica gel
regeneration by heat.
Size exclusion (the molecules of the contaminant fitinto the pores of the adsorbent, the rest passes by.) Removal of N2 or CO2 with Molecular Gate
regeneration with heat or pressure swing.
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Schematic of Adsorption Cycle