Chapter 11 Based on presentation by Prof. Art Kidnayjjechura/GasProcessing/08_Dehydration.pdf · Reasons for Gas Dehydration Field Operations Prevent hydrate formation Minimize corrosion

Gas Dehydration

Chapter 11Based on presentation by Prof. Art Kidnay

Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])

Plant Block Schematic

2

Adapted from Figure 7.1, Fundamentals of Natural Gas Processing, 2nd ed.Kidnay, Parrish, & McCartney


Reasons for Gas Dehydration

Field Operations▪ Prevent hydrate formation

▪ Minimize corrosion

• Need to dry gas to dew point below lowest operating temperature

Plant Operations▪ Need 4 to 7 lb/MMscf (85 to 150 ppmv) in pipeline

• Glycol dehydration most common to produce water contents down to 10 ppmv

▪ Need to have less than 1 ppmv H2O in gas to cryogenc units

• Glycol dehydration cannot get to these low water levels – mole sieves used for this service

3


Topics

Water Content of Hydrocarbons

Gas Dehydration Processes▪ Absorption processes

▪ Adsorption processes

▪ Non regenerable desiccant processes

▪ Membrane processes

▪ Other processes

▪ Comparison of dehydration processes

Safety and Environmental Considerations

4


Water Content of Hydrocarbons


Equilibrium considerations

Equal fugacities for each component in each phase. Between gas & water phases:

For a gas in contact with pure water:

Formation of the water phase will control the water content in the gas phase

▪ Increasing water in the feed increases the amount of free water, not the concentration of water in the gas.

▪ Can decrease the gas water content by adding compounds that are water soluble

6

= = =

, ,

, ,

where expsat

i

Pvapi L i Li i

i i i i

i V i V P

vPy x K K dP

P RT

=H2OH2O H2O since 1

vapPy x

P


Water content of natural gasBased on “typical” gas composition

▪ Separate corrections for actual composition & acid gas content

Takes into account non-idealities

Take care if gas is specified as “wet” or “dry” basis – dry basis does not include the amount of water in the MMscf

▪ When less than 5,000 lb/MMscf the wet & dry values are within 0.5%

7

Fig. 20-4, GPSA Engineering Data Book, 13th ed.

Figure 11.1 in Kidnay et. al. text book

=+

=−

H2O H2OH2O H2O H2O

HC H2O

H2O H2O H2O H2OH2O

HC H2O

/Wet Basis: /

/ /Dry Basis:

1

N MX y M

N N

N M y MX

N y


Water content of natural gas – typical pipeline specs

8

GPSA Engineering Data Book, 13th ed.


Water content of natural gas

9


Figure 11.1 (b) & (c) in Kidnay et. al. text book


Applicability of dehydration processes

10

1

10

100

1000W

et G

as W

ater

Co

nte

nt,

lb/M

Msc

f

Dry Gas Water Dew-Point, degrees F

806040200-20-40-60-80 100 120 140

Compression and Cooling

Liquid Desiccants

Glycol & Methanol

Molecular

Sieves

Enhanced Glycol

Alumina and

Silica Gel


Dehydration by Absorption


Equilibrium considerationsGlycols tend to be only in the water phase (i.e., non-volatile & very low solubility in the hydrocarbon liquid phase)

For a gas in contact with water/glycol mixture:

Water content in the gas phase is less than that for a pure water phase since x’H2O < 1

Away from glycol, must reduce temperature to create a free water phase.

12

H2OH2O H2O

vapPy x

P


Typical Glycols

EG DEG TEG

Name Ethylene Glycol

DiethyleneGlycol

TriethyleneGlycol

Formula C2H6O2 C4H10O3 C6H14O4

Molecular Weight 62.1 106.1 150.2

Boiling Point (°F) 386.8 473.5 550.4

Vapor pressure @ 77°F (mmHg) 0.12 < 0.01 < 0.01

Density @ 77°F (lb/gal) 9.26 9.29 9.34

Viscosity @ 77°F (cP) 16.9 25.3 39.4

Decomposition temperature (°F) 329 328 404

13



Glycol molecular structure

Ethylene glycol HO-CH2-CH2-OH

Diethylene Glycol HO-CH2-CH2-O-CH2-CH2-OH

Triethylene Glycol HO-CH2-CH2-O-CH2-CH2-O-CH2-CH2-OH

14

Chemical structures drawn using http://molview.org/

http://molview.org/


Equilibrium water content above TEG solutions

15

Based on Fig 20-59 GPSA Data Book 13th ed. & Figure 11.3 in Kidnay et. al. text bookBased on 1,000 psia contactor pressure


Example – Equilibrium water content above TEG solutions

Operate a TEG contactor @ 100oF & 1,000 psiawith 99.9 wt% TEG introduced at the top

Dried gas is protected to a dew point of -40oF

16

Fig. 20-59, GPSA Engineering Data Book, 13th ed.Figure 11.3 in text book


Equilibrium water content for TEG solutions

17


Typical Glycol Dehydration UnitSystem

▪ 2 – 5 gal TEG per lb water removed

Absorber / Contactor

▪ 60 – 100oF inlet

▪ Can operate up to 2,000 psia

▪ Typically 4 – 10 bubble cap trays

• 25 – 30% efficiency

▪ 5 – 10 psi pressure drop

Flash tank

▪ 10 – 20 minute residence time

▪ 150oF, 50 – 75 psig

Regenerator

▪ Packed equivalent to 3 – 4 trays

▪ 375 – 400oF

18

Fig. 20-58, GPSA Engineering Data Book, 13th ed.Basis for Figure 11.2 in text book


Typical Glycol Dehydration UnitSystem

▪ 2 – 5 gal TEG per lb water removed

Absorber / Contactor

▪ 60 – 100oF inlet

▪ Can operate up to 2,000 psia

▪ Typically 4 – 10 bubble cap trays

• 25 – 30% efficiency

▪ 5 – 10 psi pressure drop

Flash tank

▪ 10 – 20 minute residence time

▪ 150oF, 50 – 75 psig

Regenerator

▪ Packed equivalent to 3 – 4 trays

▪ 375 – 400oF

19

H2O H2O H2Ovapy P x P


Example based on GPSA Data Book example 20-11

30 MMscfd of a 0.65 gravity natural gas enters a TEG contactor at 600 psia and 100oF. The outlet water content specification is 7 lb H2O/MMscf and the TEG circulation rate is 28 lb TEG/ lb H2O absorbed (3 gal TEG/lb H2O). How much water is to be absorbed? What is the rich TEG concentration? What is the lean TEG concentration?

▪ Water content at inlet conditions?

70 lb/MMscf

▪ How much water is removed?

20

lb H2O lb TEG1890 28

day lb H2O

lb TEG52920

day




▪ How much TEG is circulated?

21

lb H2O lb TEG1890 28

day lb H2O

lb TEG52920

day

lb H2O gal TEG1890 3

day lb H2O

hr min24 60

day hr

gal TEG3.9

min


Example based on GPSA Data Book example 20-11 (#2)


▪ Dew point temperature at thecontactor pressure (600 psia)?

~ 24oF

22




▪ What is the minimum TEG concentration for a 24oF dew point & the contactor temperature (100oF)? ~98.5 wt%

• Lean TEG has 806 lb/day water

▪ Rich TEG content (after absorbing the water from the wet gas)

23

( )

+ +

lb TEG52920

day

lb H2O lb TEG1890 806 52920

day day

95.2 wt% TEG


Solubility of hydrocarbons in glycol solutions

Methods to control BTEX emissions from Regenerator

▪ Condense overhead & recover

▪ Burn vent gas through flare or thermal oxidizer

▪ Recycle back to process

24



Field Glycol Dehydrator

25

reboiler

contactor

gas burner

heat exchanger,surge tank

Flash separator3-phase, gas,glycol,condensate

Inlet separatorglycol pump

stripper

From Sivalls, “Glycol Dehydration Design,” LRGCC, 2001


Common Operational Problems

Contactor foaming▪ Contaminates: hydrocarbons, salts, particulates, inhibitors, O2

Poor dehydration (from source other than foaming)▪ Gas rate too low - 80% flow reduction = 20 % tray eff

▪ Glycol rate low - 75% flow reduction = 33% tray eff

▪ Glycol inlet temperature too high

Flash drum / Foaming in Still▪ Presence of heavy hydrocarbons

26


Dehydration by Adsorption


Absorption vs Adsorption

28

Absorption Adsorption


Physical absorption

29


Adsorption fundamentals

Two types of adsorption▪ Chemisorption

• Chemical interaction between adsorbate and adsorbent

• May not be completely reversible

▪ Physical adsorption

• Only physical interaction between adsorbate and adsorbent

• Completely reversible

-ΔHChem >> -ΔHPhys

30


Physical Adsorption Fundamentals

Factors affecting selectivity ▪ Size – adsorbent pore diameter major factor

▪ Volatility – less volatile displaces more volatile (e.g., C3 displaces C2)

▪ Polarity

• For desiccants, more polar displaces less polar (e.g., CO2 displaces C2, MeOH displaces CO2, water displaces MeOH)

31


Adsorption Isotherms

32

From UOP

1.0 E-8 1.0 E-7 1.0 E-6 1.0 E-5 1.0 E-4 1.0 E-3 1.0 E-2 1.0 E-1 1.0 E0 1.0 E+1 1.0 E+2 1.0 E+3 1.0 E+4

5

0

10

15

20

25

600 °F

500 °F

400 °F

150 °F

100 °F

77 °F

32 °F

Partial Pressure of Water, psia

Lb W

ate

r A

dso

rbed /

100 lb A

ctiv

ate

d A

dso

rbent


Solid Desiccant Dehydrator – Twin Tower System

33



Typical Vessel Loading

6 in of 1/2 in

diameter

ceramic balls

3 in of 1/4 in

diameter

ceramic balls

3 in of 1/2 in

diameter

ceramic balls

floating screen

fixed screen

32,200 lb

MS 4A

4x8 mesh

(1/8 inch)

bed diameter,

7.5 ft

bed height,

16.2 ft

Possible configuration for drying 100 MMscfd to a dew pointof -150ºF, adsorption time ~12 hours

Sample packing of catalyst/dessicant on top of supports

Model prepared by Enterprise Products


Concentration Profile

35

Equilibrium Zone (Saturated)

Mass Transfer Zone (Partially saturated)

Active Zone (Unsaturated)


Concentration Profile

36

Time

Vap

or

Co

nce

ntr

atio

n

yIn

0yOut

Dry Break-Through Saturated


Regenerating Bed Temperature History

37

Heat On

Inlet Temperature

Desorption

Bed Heating Bed Cooling

Outlet Temperature

0 1 2 3 4 5 7 86

Time, Hours

Tem

per

atu

re, º

F

100

200

300

400

600

500

0

Tem

pe

ratu

re, º

C

50

100

150

200

250

300


Common Adsorbents for Drying

In order of increasing cost:

Silica gel (SiO2)▪ Min exit water content 10 to 20 ppmv (~-60oF)

▪ Inert and used for inlet concentrations of > 1 mol%

Activated Alumina (Al2O3)▪ Min exit water content 5 to 10 ppmv (~-100oF)

▪ High mechanical strength but more reactive

Molecular Sieve (4A and 3A)▪ Min exit water content below 0.1 ppmv (~-150oF)

▪ Highest surface area

▪ Composite of sieve and clay binder

38


Design stepsDetermine size of vessels for adsorption

▪ Determine the bed diameter based on superficial gas velocity / allowable pressure drop

• Too small – pressure drop will be too high & can damage the sieve

• Too large – need too high a regeneration gas rate to prevent channeling

• Typically use (-P/L) < 0.33 psi/ft with a total pressure drop of 5 – 8 psi max

▪ Choose an adsorption period & calculate the mass of desiccant

• Sets the bed height – contributions from saturation zone & mass transfer zone heights

• 8 to 12 hour periods with 2 or 3 beds are common

o Too long – more desiccant & larger vessels needed than necessary

o Too short a time – shorter desiccant life

Regeneration

▪ Calculate heat required to desorb water while also heating the desiccant & vessel

▪ Total amount of regeneration gas flow calculated based on heating phase about 50-60% of total regeneration time

▪ Regeneration gas flowrate should give a pressure drop gradient of at least 0.01 psi/ft

39


Design equations (#1)

Determine gas velocity for bed diameter

▪ Modified Ergun equation for pressure drop

• Viscosity [cP] & density [lb/ft³] determined at inlet conditions

• Solve quadratic equation for maximum superficial velocity (Vmax [ft/min]) for 0.33 psi/ftpressure drop

• Pressure drop gradient in units of psi/ft

▪ Minimum diameter

▪ Adjust diameter upwards to nearest ½ foot increment

• Recalculate superficial linear velocity & pressure drop using adjusted diameter

40

= + 2P

B V C VL

=

min

max

4 mD

V



Determine bed length (method 1)

▪ Amount of desiccant in saturation zone

Assumes 13 lb water per 100 lb dessicant

▪ Amount of desiccant in the mass transfer zone (MTZ) (GPSA EDB method)

where CZ is 1.70 ft for 1/8 inch sieve & 0.85 for 1/16 inch sieve

… or Trent method for MTZ

41

= =

water satsat sat 2

bulk

4

0.13 SS T

m SS L

C C D

=

0.3

MTZ

ft/minft

35Z

VL C

( )= +0.636 0.0826 ln %satSSC

( )= − 1.20 0.0026 FTC = +MTZ ft 2.5 0.025 ft/minL V



Determine bed length (method 2)

▪ Calculate “effective desiccant capacity” which includes the MTZ effect, temperature, and relative humidity corrections. An effective capacity of 8–10% is typically assumed.

Finalize bed length

▪ Total bed height (Lsat+LMTZ or Lbed) but should not be less than the bed diameter or 6 ft, whichever is greater

▪ Total bed pressure drop should be 5 – 8 psi max

• If too large increase the bed diameter

Determine vessel height & weight

▪ Total bed height plus other allowances – at least 3 ft (for inlet distributor on top and bed support & hold down balls underneath)

42

= =

water bedbed bed 2

bulk

4

eff

m SS L

C D



Regeneration calculations

▪ Used to determine the required regeneration gas flow & the fuel gas requirements

• If regeneration gas recycled back to inlet of mole sieves then you must add this rate to that of the feed gas for the bed calculations

▪ Heat loads

• Heat to desorb water – increase water to its desorption temperature, break adherence to surface, & vaporize

o Use 1,800 Btu/lb water adsorbed for conservative design

• Heat to increase sieve to regeneration temperature

• Heat to increase vessel to regeneration temperature

• Heat losses – typically estimated as 10%

43



Regeneration Calculations (cont.)

▪ Calculation of vessel weight for heating calculations

where the 0.75D term accounts for the weight of the vessel heads

• Design pressure in psig. Usually 10% greater than operating pressure (minimum 50 psig)

▪ Usually have to heat the regeneration gas 50oF hotter than the desired regeneration temperature (e.g., 500oF gas needed to regenerate at 450oF)

▪ Total regeneration load 2.5 times the minimum load

• Assumes only 40% of the heat is transferred from gas to mole sieve system.

• The remainder exits as hot gas. Need to size downstream coolers appropriately.

▪ Regen gas flowrate. Check that pressure drop gradient at least 0.01 psi/ft

44

( )( )= + = + +−

design

steel vessel

design

12in 0.0625 and lb 155 0.125 0.75

37600 1.2

D Pt m t L D D

P

( )= =

−

Total Regen rg

Regen Gas rg 2hot bed rg

4

P

Q mm V

C T T D



100 MMscfd natural gas (molecular weight of 18) is water saturated at 600 psiaand 100oF & must be dried to –150oF dew point. Determine the water content of the gas (inlet & outlet) & amount of water that must be removed.

Do preliminary design of a molecular-sieve dehydration system consisting of two towers with down-flow adsorption in one tower and up-flow regeneration in the other. Use 4A molecular sieve of 1/8″beads (i.e., 4x8mesh). The regeneration gas is part of the plant’s residue gas (at 600 psia and 100oF) & has a molecular weight of 17. The bed must be heated to 500oF for regeneration. Base this on a 24-hour cycle consisting of 12 hours adsorbing and 12 hours regenerating (heating, cooling, standby, and valve switching; the heating time is 60% of the regeneration time).

45



100 MMscfd natural gas (molecular weight of 18) is water saturated at 600 psiaand 100oF & must be dried to –150oF dew point. Determine the water content of the gas (inlet & outlet) & amount of water that must be removed.

▪ Water content at inlet conditions?

70 lb/MMscf

▪ Water content at outlet conditions?

Essentially 0 lb/MMscf

▪ How much water is to be removed?

46

( ) 70 0 lb/MMscf 100 MMscfd

7,000 lb/day

−



… Do preliminary design of a molecular-sieve dehydration system consisting of two towers with down-flow adsorption in one tower and up-flow regeneration in the other. Use 4A molecular sieve of 1/8″ beads (i.e., 4x8 mesh)…

▪ Determine bed diameter. Velocity criteria not given so determine from allowable pressure drop (0.33 psi/ft max)

• Ideal gas flowrate at inlet conditions (600 psia and 100oF)

• Real gas flow much different? Estimate: Z=0.93

47

( )

( )

+ = =

+

3 36 6

IG

100 460 °Rft 14.7 psia ft100 10 2.6 10

day 600 psia 60 460 °R dayV

( )

= = =

3 3 36 6

IG

ft ft ft0.93 2.6 10 2.5 10 1700

day day minactV Z V



… Do preliminary design of a molecular-sieve dehydration system consisting of two towers with down-flow adsorption in one tower and up-flow regeneration in the other. Use 4A molecular sieve of 1/8″ beads (i.e., 4x8 mesh)…


• Real gas density at inlet conditions (600 psia and 100oF)

• Gas viscosity at inlet conditions (600 psia and 100oF). Estimate 0.015 cP.

• Velocity vs. pressure gradient. For given beads & gas properties:

48

( )( )

( )( )( ) = = =

3

600 18 lb1.93

0.93 10.7316 560°R ft

PM

ZRT

( )( ) ( )( )−

= +

= + =

2

5 2 ft0.33 0.056 0.015 8.89 10 1.93 41.4

min

PB u C u

L

u u u



… Do preliminary design of a molecular-sieve dehydration system consisting of two towers with down-flow adsorption in one tower and up-flow regeneration in the other. Use 4A molecular sieve of 1/8″ beads (i.e., 4x8mesh)…


• Minimum diameter is ratio of volumetric flowrate to maximum velocity. Scale up to next 6”.

49

= = = =

2

min

ft4 1700

min7.2 ft D=7.5 ft

ft441.4

min

actVDA D

u



… Do preliminary design of a molecular-sieve dehydration system consisting of two towers with down-flow adsorption in one tower and up-flow regeneration in the other. Use 4A molecular sieve of 1/8″ beads (i.e., 4x8mesh)…


• Determine actual gas velocity & pressure drop in absorbing bed

50

( )( )

= = = =

3

22

4 1700 ft /min438.5 ft/min

7.5 ft

V Vu

A D

( )( )( ) ( )( )( )−

= +

= + =

2

25 psi0.056 0.015 38.5 8.89 10 1.93 38.5 0.29

ft

PB u C u

L



… Base this on a 24-hour cycle consisting of 12 hours adsorbing and 12 hours regenerating (heating, cooling, standby, and valve switching; the heating time is 60% of the regeneration time).

▪ Since the overall removal rate is 7,000 lb/day we must have enough adsorbent to safely contain 3,500 lb of water (corresponding to the adsorbing time).

▪ No other criteria given for amount of water to be contained by desiccant –determine size using the zone analysis (method 1)

• Size saturation zone to contain all water for the cycle. Use a typical sieve bulk density of 45.0 lb/ft3

51

( ) ( )

( ) ( )

= = =−

= = =

watersat

satsat 22

bulk

350028,600 lb sieve

0.13 0.13 1 1.20 0.0026 100

4 4 2860014.4 ft

7.5 45.0

SS T

mS

C C

SL

D




▪ … determine size using the zone analysis

• Add appropriate length for the mass transfer zone (MTZ) to ensure no breakthrough of water. CZ=1.7 for this size sieve

• Total bed height is the sum of these two zones. Total vessel height adds 3 ft for supports, …

52

( )

= = =

0.3 0.3

MTZ

38.61.7 1.74 ft

35 35Z

uL C

= + = + = = + =Bed sat MTZ vessel Bed14.4 1.74 16.1 ft 3 19.1 ftL L L L L




▪ … determine size using the zone analysis

• Check that the bed length is at least the bed diameter (here 7.5 ft) or 6 ft, whichever is greater.

o This bed depth does not need to be adjusted

• Check that total pressure drop is 5 – 8 psi. If too small, add bed height; if too large, add diameter

53

( )( )

= =

bed 0.29 16.1 =4.7 psi (close enough)p

p LL



… The regeneration gas is part of the plant’s residue gas (at 600 psia & 100oF) & has a molecular weight of 17. The bed must be heated to 500oF for regeneration…

▪ Determine amount of heat needed for regeneration

• Heat to desorb water

• Heat the sieve to regeneration temperature

54

( ) ( )( )= = =3500 1800 6,300,000 Btuw w wQ m H

( ) ( )

( ) ( )( )( )( )

= − = −

= −

=

2

, ,

2

4

7.5 16.1 45.00.24 500 100

4

3,070,000 Btu

bed bulksi si p si regen ads p si regen ads

D LQ m C T T C T T




▪ Determine amount of heat needed for regeneration (cont.)

• Heat the steel to regeneration temperature

55

( )( )( )( )

= −

= −

=

,

50620 0.12 500 100

2,430,000 Btu

steel steel p steel regen adsQ m C T T

( ) ( ) ( )

( )( )

( )( )( )

= +−

−= + =

− −

= + +

= + + =

design

design

steel vessel

12in 0.0625

37600 1.2

12 7.5 1.1 600 14.70.0625 1.636 in

37600 1.2 1.1 600 14.7

lb 155 0.125 0.75

155 1.636 0.125 19.1 0.75 7.5 7.5 50620 lb

D Pt

P

m t L D D




▪ Determine amount of heat needed for regeneration (cont.)

• Total regeneration heat needed

▪ Determine amount & rate of regen gas needed

• Heat that must be transferred to the regeneration gas

56

( )( )

( )( )

= + + + = + + +

= + + +

=

1

6,300,000 3,070,000 2,450,00 1 0.10

13,002,000 Btu

regen w si steel loss w si steel lossQ Q Q Q Q Q Q Q f

( )= =2.5 2.5 13,002,000 =32,505,000 Bturg regenQ Q




▪ Determine amount & rate of regen gas needed (cont.)

• Determine amount regen gas needed

• Determine rate of regen gas needed

57

( ) ( ) ( )= = =

+ −−,

32,505,000111,100 lb

0.65 500 50 100

rg

rg

p rg rg cold

Qm

C T T

( )= = =

111,10015,430 lb/hr 257 lb/min

0.6 12

rg

rg

mm

t

, 0.65 Btu/lb F (based on Fig. 23-48 in GPSA EDB averaged between 100 & 550 F)o op rgC




▪ Verify there is sufficient pressure drop during regeneration to prevent channeling (i.e., pressure drop is above 0.01 psi/ft)

• For the hot regen gas (@ 550oF):

Flow rate is sufficient

58

( )( )

( )( )( ) = = =

+ 3

600 17 lb0.94

1 10.7316 550 460 ftrg

PM

ZRT

= 0.023 cP (from Fig. 23-23 in GPSA EDB)

( )( )( ) ( )( )( )−= + = + =

22 5 psi0.056 0.023 6.2 8.89 10 0.94 6.2 0.011

ft

PB u C u

L

( )= = = =

22

4 4 2576.2 ft/min

0.947.5

rg rg

rg

rg

V mu

A D


Common Mole Sieve Operational Problems

Loss of bed capacity▪ Aging, rapid initial loss then

gradual loss over years

▪ Coking by partial oxidation of heavy hydrocarbons

▪ Coking by conversion of H2S to elemental sulfur

▪ Poor regeneration

Increased pressure drop▪ Attrition

▪ Caking at top of bed

Fines▪ Attrition

▪ Failed bed support

COS formation▪ Chemical equilibrium

H2S + CO2 COS + H2O

59


Other Dehydration Processes


Other processes

Consumable salts (CaCl2)

Refrigeration with MEOH addition, more complex

Membranes, ideal for remote sites when low pressure permeate gas can be used effectively

If drying high pressure gas:▪ Vortex tube – one application known

• Simple but poor turndown ratio and efficiency

▪ Twister Supersonic Separator one known offshore application

• Simple, poor turndown ratio but better efficiency

61


Twister Operating Principle

Acceleration to Mach >1 cools gas (typically 60 – 80oC) ΔP = 30%

Cooling causes condensation (water and heavier hydrocarbons)

Swirl centrifuges liquid droplets to the tube wall

Drainage section removes liquid film from the wall + ~20% gas

Diffuser section recompresses the gas

62

http://twisterbv.com/PDF/resources/Twister_-_How_Does_It_Work.pdf

http://twisterbv.com/PDF/resources/Twister_-_How_Does_It_Work.pdf


Comparison of Dehydration Processes

For < 1 ppmv H2O need mole sieve.

For higher concentrations:▪ Glycol (usually TEG) widely used

• Minimal manpower requirements

• High turndown

▪ Regenerative desiccants (silica gel, alumina) more costly

▪ Membranes, and Twister(?) where pressure drop acceptable

▪ Nonregenerative desiccants (CaCl2) for remote, low water content gas

63


Summary


Summary

Water content can be estimated from Fig. 20-4▪ Units of lb/MMscf

▪ Wet & dry bases essentially the same below 5,000 lb/MMscf

Three primary separation technologies▪ Bulk removal by cooling & separation

▪ TEG dehydration to pipeline specs (4 – 7 lb/MMscf)

▪ Mole sieves required upstream of cryogenic applications

65


Supplemental Slides


Glycol Dehydration Unit

67

contactor

stripping still

reboiler

http://www.kirkprocess.com/products/highspeed-gas-dehydration/

http://www.kirkprocess.com/products/highspeed-gas-dehydration/


Glycol Dehydration Unit

68

contactor

stripping still

reboiler

http://www.en-fabinc.com/en/glycol_dehydration_system.shtml

http://www.en-fabinc.com/en/glycol_dehydration_system.shtml


Mole Sieve Dehydration Unit

69

http://www.enerprocess.com/processing-&-treating-units/gas-conditioning-&-treating/mol-sieve-dehydration-units

http://www.enerprocess.com/processing-&-treating-units/gas-conditioning-&-treating/mol-sieve-dehydration-units


Zeolite structures

Zeolite A Zeolite X

70

Documents

Chapter 11 Based on presentation by Prof. Art Kidnayjjechura/GasProcessing/08_Dehydration.pdf · Reasons for Gas Dehydration Field Operations Prevent hydrate formation Minimize corrosion