Overview Gas Processes

1

Design of Natural Gas Handling Equipment

Course prepared for Offshore Oil and Gas Engineering program

ENG 8976

by Majid A. Abdi, Ph.D., P.Eng.

Faculty of Engineering and Applied ScienceMemorial University of Newfoundland (MUN)

Winter 2004

2

Schedule and Evaluation Breakdown

• Instructional hours per week: 3 lecture hours; • Midterm exam: March 1st, 2004;• Evaluation:

– Assignments: 10% – Midterm: 25%– projects (term papers): 15%– Final: 50%

3

Course Outline

1. Introduction2. Fluid Properties3. Inlet separator design4. Prevention of hydrate formation and dehydration of

natural gas 5. Natural gas dew point control and liquid recovery6. Natural gas transmissions systems7. Natural Gas Compression8. Natural gas measurement*9. Heat exchange equipment*10. Overview of natural gas sweetening processes*11. Natural gas transportation**Optional sections; will be covered only if time allows

4

References1. Beggs H.D., Gas Production Operation, OGCI publications, 1985, ISBN: 0-930972-

06-62. Kumar S., Gas Production Engineering, Gulf Publishing, 1987, ISBN: 0-87201-577-73. Rojey A., Jaffret C., Natural Gas Production Processing Transport, Editions

Technip; (1997), ISBN: 2710806932 4. Manning F. and Thompson R., “Oil Field Processing of Petroleum, Volume 1:

Natural Gas”, Pennwell Publishing, 1991, ISBN:0-87814-343-2 5. 11th Edition GPSA Engineering Data Book, FPS and SI Versions, 1998, by Gas

Processors Suppliers Association 6. Arnold K. and Stewart M., Surface Production Operations; Volume 2; Design of

Gas-Handling Facilities, 2nd Edition, 1999, Butterworth-Heinemann, ISBN: 0-88415-822-5

7. Kohl A., Nielsen R., “Gas Purification”, 5th Edition, Pennwell, 1997, ISBN 0-88415-220-0

8. Mohitpour M., Golshan H., and Murray A. "Pipeline Design & Construction, A Practical Approach", 2nd edition, ASME Press, 2003, ISBN 0-7918-0156-X

9. Manning F. and Thompson R., Oil Field Processing of Petroleum, Volume 1: Crude,Pennwell Publishing, 1991, ISBN: 0-87814-354-8

10. Arnold K. and Stewart M., Surface Production Operations; Volume 1; Design of oil Handling Facilities, 2nd Edition, 1999, Butterworth-Heinemann ISBN: 0-88415-821-7

11. Skinner, D.R., Introduction to petroleum production: well site facilities, Gulf Publishing Co., 1981, ISBN: 0872017699

12. Brian Research and Engineering (BR&E) technical papers, 2002; see web site at: http://www.bre.com/technicalpapers/technicalpaper-home.asp

13. Instructor’s notes on personal field and design experiences

http://www.bre.com/technicalpapers/technicalpaper-home.asp

5

World Natural Gas Occurrence and Production - International Gas Statistics

• Natural gas is a major world energy source.

• World natural gas reserves are estimated at 5893 TCF.

• About 72 percent of the world’s natural gas reserves are found in the Middle East and the former Soviet Union.

• Canada is a major exporter of natural gas.

6

Natural Gas Origin

• Biogenic methane• Thermogenic methane • Metamorphism• Abiogenic methane

7

History of Natural Gas

• Dates back to thousands years ago• Persians and Indians used it for religious

practices• Chinese used it to desalt sea water• British commercialized natural gas

8

Source: BP

9

World Natural Gas Reserves (2002)

Source: BP

10

World Natural Gas Reserves (2002)

Source: BP

11

World Natural Gas Production (2002)

Source: BP

12

World Natural Gas Production (2002)

Source: BP

13

World Natural Gas Consumption (2002)

14

World Natural Gas Consumption (2002)

15Source : BP

16

Global Stranded Gas Reserves

17

North American Natural Gas Reserves (2001)

18

Canadian natural gas production/demand by region (2001)

19

Canadian Natural Gas

20

Canadian Natural Gas (2001)

21

Natural Gas Value Chain

22

Natural Gas Processing

23

Gas Processing Facility Block Diagram

Acid Gas Management SystemsControlled Release of

emission gases to Atmosphere

SulphurSales

Sulphur Production

Natural Gas Well Gas

High Pressure

Separation

Intermittent solid removal

Water VapourRemoval -

Dehydration

NGL Recovery -Dew Point Control

(DPC)

Acid Gas RemovalHeating

SALES GAS

Cooling

Stabilization Condensate Sales

Water disposal

Water handling Facilities

Compression

LPG Recovery

(C3 & C4)

Propane and Butane

Sales

24

FLUID PROPERTIESFLUID PROPERTIESCharacterization of Natural Gas and Its Products

colorless---Dry gas

colorless>50>50,000-Wet gas

Water white50-603,300-50,000>0.35Retrograde gas – gas condensate

Colored –dark brown

>402,000-3,300<0.5

Very dark –black oil

<45<2,000>0.5Associated gas from:•Low Shrinkage crude (Low GOR) –Ordinary crude•High Shrinkage Oil (high GOR) –volatile oil

COLOROAPISCF/BSTOBSTO/BRF

STOCK-TANK LIQUIDTYPICAL GORSPECTRUM OF PRODUCED SPECTRUM OF PRODUCED HYDROCARBONSHYDROCARBONS

FLUID TYPE

25

Fluid Properties – Natural Gas Constituents

N2

C6+

nC5

iC5

nC4

iC4

C3

C2

C1

Abbreviation

variableFeSReservoir fines and iron sulfidevariable-Millscale or rustSolidsvariableCH3OH(MeOH), EG, etc.Methanol and glycolvariable-Corrosion inhibitorsvariableH2OFree water or brineWater vapour/Liquid

slugs

1.0-10.0ppmR-S-S-RDisulfides1.0-10.0ppmR-S-RSulfides10-1000ppmR-SHMercaptansSulphur compouns

0.2-10.0CO2Carbon Dioxide0.01-10.0H2SHydrogen sulfideAcid gasesa few ppmO2Oxygena few ppmH2Hydrogena few ppmArArgon0.01-0.1HeHelium0.2-5.0N2NitrogenInert Gases1.0-3.0-Hexanes and heavier0.1-2.0nC5H12n-Pentane

0.1-2.0iC5H12i-Pentane

0.3-7.5nC4H10n-Butane

0.3-2.5iC4H10i-Butane1.0-15.0C3H8Propane3.0-10.0C2H6Ethane59.0-92.0CH4MethaneHydrocarbons

Typical composition(volume %)

FormulaComponentsClass

26

Fluid Properties – Natural Gas physical properties

• PVT behavior and equations of state • Molecular weight• Density and specific gravity• Critical pressures and temperatures • Gas compressibility factor• Viscosity• Specific heat (heat capacity)• Heating value (Wobbe number/index)• Thermal conductivity

27

Fluid Properties – Equations of State

• Behavior of ideal gas • Behavior of a real (non-ideal) gas• Compressibility factor approach• Important equations of state

Van der WaalsBenedict-Webb-Rubin (BWR)Saove-Redlich-Kwang (SRK)Peng-Robinson (PR)Virial

28

Principal Equation of States

29

Fluid Properties – Molecular Weight – Mole concept

Weight of a mole of any substance Different units in Imperial, SI and CGS systemsMoles = Weight of a gas component divided by its molecular weightAverage molecular weight =

]).([ NN MWyMW ∑=

30

Fluid Properties – Density and Specific Gravity

• Density = mass of a unit volume (lb/ft3 or kg/m3)

• S = MW/29 (for gases)

or

• S.G.= density of liquids/density of pure water @ 60oF

• oAPI =141.5/S.G. -131.5 (for liquid hydrocarbons such as crude oil)

TZSP

g 7.2=ρTZ

PMWg

)(093.0=ρ

31

Fluid Properties – Critical Pressures and Temperatures

• Critical temperature= the maximum temperature at which the component can exist as a liquid

• Critical pressure= vapour pressure of a substance at its critical temperature

• Beyond critical temperature and pressure there is no distinction between a liquid and a gas phase

PCN and TCN from Figure 23-2 GPSAPPC = Σ yNPCN and TPC = Σ yNTCN

PPC = 709.604 – 58.718 S

TPC = 170.491 + 307.344 SThomas et al. equation

32

Physical Property Tables

33

Physical Property Tables

34

Fluid Properties – Gas Compressibility Factor

• Standing-Katz compressibility charts (Figures 23-3, 23-4, and 23-5 GPSA)

• Brown-Katz-Oberfell-Alden charts (Figures 23-7, 23-8, and 23-9 GPSA)

• Acid gas content consideration by Wichert-Aziz correction factors

ε from Figure 23-10 GPSA• Compressibility from equations of state

)1(

'''

BBTTPPandTT

PC

PCPCPCPCPC −+=−=

εε

35

Compressibility charts Brown-Katz-Oberfell-Alden Z charts

Standing-Katz compressibility charts

36

Fluid Properties – Gas Viscosity

• Carr et al. correlation (Fig. 23-32 and 23-33 GPSA)• Viscosity of gas mixture from single component data:

• Lee et al. for natural gas:

• GPSA charts – Fig.s 23-30 through 23-38• Dean and Stiel method

∑

∑

=

== n

NNN

n

NNNgN

g

MWy

MWy

1

5.0

1

5.01

1

µµ

XyandMWTXTMW

TMWKwhereXK ygg

2.04.201.0/9865.319209

)02.04.9(10,)exp(5.14

−=++=++

+==

−

ρµ

[ ]

9/8Pr

5Pr

9/5

Pr5

Pr3/22/1

6/1

)10(0.34,5.1

,0932.01338.0)10(8.166,5.1;)(

4402.5

TTforand

TTforPMWy

T

g

gPCNN

PC

−

−

=≤

−=>=∑

ξµ

ξµξ

37

Viscosity Charts

38

Fluid Properties – Specific Heat

• Definition: amount of heat required to raise the temperature of a unit mass of a substance through unity

• Cp and Cv and their relationships (Maxwell’s equation)

• Cp determination– Hankinson’s gravity C op = A + B.T + C.S + D.S2 + E(T.S) + F.T2

– Kay’s mixing rule

• Cp of natural gas mixture, pressure corrections (GPSA Figure 13-6 and Kumar’s Book – Table 3-3, Figures 3-17 and 3-19)

RCCgasesidealforvPTPTCC vp

T

vvp =−

∂∂∂∂

−=−)/()/( 2

∑=

=n

N

opNN

op CyC

1

39

Heat Capacity Data

40

Fluid Properties – Heating Value/Wobbe Index

• Definitions:– Gross Heating Value (GHV) or Higher Heating Value

(HHV):Total energy transferred as heat in an ideal combustion reaction at a standard temperature and pressure in which all water formed appears as liquid

– Net Heating Value (NHV) or Lower Heating Value (LHV):Totalenergy transferred as heat in an ideal combustion reaction at a standard temperature and pressure in which all water formed appears as vapour

• Heating value determination: Hv = Σ yNHvN

• Wobbe Index: WO=HHV /S1/2

41

Fluid Properties – Thermal conductivity

• Significance of thermal conductivity – Heat transfer calculations and heat exchanger (line heater, shell and tube, air cooler, etc.) design

• Determination of thermal conductivity – gas and liquid (GPSAFig.s 23-40 through 23-45)

• Lenoir et al. pressure corrections• Gas mixture thermal conductivity

∑∑=

).().(

3

3

NN

NNNm MWy

MWkyk

42

Thermal conductivity Charts

43

Thermal conductivity Charts (cont.)

44

Phase Behavior - Fundamentals

• Single component fluid• Two component fluid• Multi-component fluid• Phase diagrams (envelopes)

– Pressure-Temperature-Volume (PVT)– Pressure-Temperature (PT)– Pressure composition – Composition-composition

• Phase ruleN=C-P+2

45

Phase Behavior – Single Component Systems

B

A

CD

a b c de h

Dense Fluid region-supercritical fluid

gf

• Phase Equilibrium – gas-liquid– gas-solid– Liquid-solid

• Triple point • Critical point

46

Phase Behavior: Two-Component Systems

• Concept of phase envelope

• Equilibrium lines– Bubble point– Dew point

• Critical point• Cricondentherm• Cricondenbar• Rertrograde phase

change

Pres

sure

Cricondenbar

Cricondentherm

Dew-Point L

ine

Bubble

-Poin

t Line

Vapo

urpr

essu

re

of p

ure

A

Vapour pressure

of pure B

C

a bd e

h

j

klPC

TC

Two component phase envelop

90% va

p’d

g

f

Temperature

47

Phase Behavior: Multi-Component Systems

C

Condensate reservoirOil reservoir

Gas reservoir

A

A’

B

B’

C

C’

D

D’

E

E’

Temperature

Pres

sure Two-Phase Region

(Gas+Liquid)

Cric

onde

nthe

rm

Wet Gas

Dry

Gas

• Full wellstream• Source of phase

diagrams• Quantitative phase

behavior • Phase behavior in

separators

48

Phase Behavior: Vapour-Liquid Equilibria

• Thermodynamic criteria for equilibrium-equality of fugacities: fN,v= fN,l

• Equilibrium ratio (K values): K=yN / xN

• Equilibrium calculations– Equilibrium flash:

– Bubble point: ΣyN =Σ zN . KN = 1.0Σ zN . KN > 1.0 guarantees vapour is

present– Dew point: ΣxN =Σ zN / KN = 1.0

Σ zN / KN > 1.0 guarantees liquid is present

N

NNN KLV

FKV+

=)//(1

V, yN

F, zN

L, xN

A gas-liquid flash separator

49

Phase Behavior: Water Hydrocarbon Systems• Water and hydrocarbons are insoluble in liquid phase• Problems with water saturated gas

– Excessive pressure drop – Plugging due to ice and hydrate formation– Sever corrosion in acid and sour gas lines

• Water content of natural gas – McKetta and Wehe charts: Fig. 20-3, GPSA– Robinson et al. correlation for sour gases: Fig.s 20-10 and 20-

11, GPSA– Campbell charts: W = yhc Whc + yCO2 WCO2 + yH2S WH2S and

Fig.s 20-8 and 20-9, GPSA)– Equation of state methods; SRK, PR and commercial process

simulators (e.g. HYSYS, ASPEN, PROSIM, PROII, AMSIM, AQUASIM, SSI, DESIGNII, PROCESS, etc.)

50

Phase Behavior: Water Hydrocarbon Systems–Natural Gas Hydrates

• Gas hydrate - pipeline trouble maker or ?

• Prediction of hydrate formation conditions

– Katz Gas gravity– Wilson-Carson-Katz equilibrium-

constant method – Baillie and Wichert method– Equation of state methods

• Comparison of techniques to predict hydrate formation conditions

51

Water Hydrocarbon Systems: Overall Phase Behavior of Natural Gas- Hydrates Systems

Wat

er

Dew

-poi

nt

Curv

e

Hydr

ocar

bon

Phas

e En

velo

pe

Hydrate Formation Curve

Lhc+Lw+G+H Lhc+Lw+G

Lw+G

G

Pres

sure

B. High Water Content

Hydr

ocar

bon

Phas

e En

velo

pe

Lhc+Lw+G+H Lhc+Lw+G Lhc+G

Pres

sure

Wat

er

Dew-

poin

t cC

urveHy

drat

e Fo

rmat

ion

Curv

e

G

Lw+G

A. Normal Case

A

Temperature Temperature

52

Phase Behavior: Carbon Dioxide Frost Point

• Significance of CO2 freezing- design of turbo-expansion facilities and cryogenic NGL recovery systems

• CO2-methane equilibrium (Liquid-solid-vapour systems) (see Ref.1, also Fig.s 25-5 and 25-6 of GPSA data book)

• Natural gas-CO2 systems (see Ref. 1)

• Predicting CO2 formation conditions (GPSA charts vs. process simulators)

53

Natural Gas Properties/Phase Behavior and

Scope of Natural Gas Field Processing• Process objectives

– Transportable gas– Salable gas– Maximized condensate (NGL) production

• Gas type and source– Gas-well gas– Associated gas– Gas condensate

• Location and size of the field– Remoteness– Climate– size

54

Scope of Natural Gas Field Processing: Process objectivesProcess objectives

• Transportable gas– Hydrate formation– Corrosion– Excessive pressure drop (two-phase flow)– Compression requirement (dense phase flow)

• Salable gas– Sales quality-pipe line spec. (see Fig. 2-4, GPSA)– Heating value-inert gas and condensate recovery

• Maximized condensate (NGL) production– Maximizing crude production– Retrograde condensate gas processing– Inherent value of NGL

55

Scope of Natural Gas Field Processing: Type and Source of Natural GasType and Source of Natural Gas

1. Gas-well gas– Wet or dry– Lean or rich– Sour or sweet

2. Associated gas– Enhanced oil recovery (EOR)– Enhancement crude production

3. Gas condensate– Pressure maintenance– Gas cycling operations

56

Scope of Natural Gas Field Processing: Filed Location, Size, and OperationFiled Location, Size, and Operation• Remoteness

– Offshore vs. onshore (land) reservoirs– Platform design– Floating gas processing (a new concept)

• Climate– Design consideration for harsh environment– Cold vs. warm– Dry vs. humid

• Size– Reservoir capacity– Production rate: small vs. large

• Gas handling facilities operations

57

GAS AND LIQUID SEPARATIONGAS AND LIQUID SEPARATION

•• Purpose, principles and terminologyPurpose, principles and terminology• Separation equipment- common

components • Types of separators • Separation principles • Separator design• Factors affecting separation • Operational Problems

58

Gas and Liquid Separation: Separation Equipment- Major Parts

A - Primary Separation

B - Gravity Settling

C - Coalescing

D - Liquid Collecting

59

Gas and Liquid Separation - Types of Separators

• Gravity (vertical vs. horizontal)• Centrifugal• Filter coalescing• Impingement• Comparison of separators –

advantages vs. disadvantages

60

Gas and Liquid Separation: Separation Equipment- vertical separator

Source: Natco

61

Gas and Liquid Separation: Separation Equipment- Horizontal separators

62

Gas and Liquid Separation: Separation Equipment, Two-Barrel (Double-Tube) horizontal separator

63

Gas and Liquid Separation: Separation Equipment- horizontal filter separator

Filter elements

64

Gas and Liquid Separation: Separation Equipment- mist eliminator arrangement

65

Gas and Liquid Separation: Separation Equipment-Vane (radial/axial) mist extractor arrangement

Vertical Radial Flow (VRF) separator

A

BC

D

Downcomer

J=ρg .Vt2 = 20 lb/(ft.sec2)

NatcoTM radial vanes

66

Gas and Liquid Separation: Separation Equipment- Centrifugal separator

67

Gas and Liquid Separation: Separation Equipment- Swirl/cyclonic separators

Porta-Test Whirlyscrub ITM

Source: Natco

68

Gas and Liquid Separation –Separation principles

]2

[2

gV

ACF tDD ρ= Drag force

Stock’s termonalvelocity for:

Re < 1.0µ

26 .).(1078.1 mt

dGSV

∆×=

−

Re for actual natural gas and crude operations are much larger than 1.0, therefore the following equations should be iteratively used to calculate the terminal velocity and drag coefficient:

34.03242/1 ++=

ReReCD

2/1])[(0119.0D

m

g

glt C

dVρρρ −

=

69

Gas and Liquid Separation –Separation principles: Terminal Velocity/Residence Time calculations

• Terminal velocity iterative calculations:

1. Start calculating CD using:

2. Calculate Re as:

3. Calculate new values for CD :

4. Calculate new values for CD :

5. Go to step 2 and iterate until CD,new – CD,old ≤ 0.001

• Residence time definition: Effective vessel volume/flow rate or:

t = V /Q

2/1])[(0204.0 mg

glt dV

ρρρ −

=

µρ tmg Vd

Re 0049.0=

34.03242/1 ++=

ReReC D

2/1])[(0119.0D

m

g

glt C

dVρρρ −

=

70

Gas and Liquid Separation – Separator Design

• Gas capacity• Liquid capacity• Gas Capacity Calculations: Souders-Brown’s

Technique• Vessel design considerations• Separator design using manufacturers

separator performance charts• Computer based techniques -

Computational Fluid Dynamics (CFD), etc.

71

Gas and Liquid Separation – Sizing Equations• Horizontal separator

– Gas Capacity:

Or: , where, from Fig. 4.10 Ref.8

– Liquid Capacity:

– Seam to seam length: Lss = Leff + d/12 for gas capacity and Lss = 4/3 Leff for liquid capacity

• Vertical Separators– Gas capacity:

– Or: , where K is defined as above and found from Fig. 4.10 Ref. 8

– Liquid capacity:

– Seam-to-seam length:

2/1

420

−

=

m

D

gl

ggeff d

CP

TZQdL

ρρρ

=

PTZQ

KdL geff 42

2/1

−= D

gl

g CKρρ

ρ

7.02 lr

effQt

Ld =

2/1

2 040,5

−

=

m

D

gl

gg

dC

PTZQ

dρρ

ρ

=

PTZQ

Kd g4202

12.02 lr Qthd =

1240......;........

1276 ++

=+

=dhLorhL ssss

72

g

glSBt KV

ρρρ −

=

Gas and Liquid Separation: Sizing Equations-Souders-Brown Technique

2/1])[(0119.0D

m

g

glt C

dVρρρ −

=

Terminal Velocity Equation

Souders-Brown Equation

0.4-0.5(L/10)0.565

0.40-0.50

0.18-0.35

0.12-0.24

API Recom’d. KSB, (ft/sec.)

-Other lengths

0.38 with mist extractor10Horizontal

0.18 without and 0.3 with mist extractor

10

0.12 without and 0.2 with mist extractor

5Vertical

Most commonly used KSBValue(ft/sec.)

Height, H or Length, L (ft)

Separator type

API Spec. 12 J (1989) Recommendations for KAPI Spec. 12 J (1989) Recommendations for KSBSB valuesvalues

73

Gas and Liquid Separation: Vessel design considerations

• Liquid residence time: 2-4 min• Liquid-gas interface (minimum

diameter/height): 6 ft. vertical height; 26 in. horizontal diameter

• Gas specification: 0.1 gal/MMscf• Liquid re-entrainment: API Spec. 12J• Pipe connections:• Fabrication cost• Optimum length to diameter (L/D) or

aspect ratio

2 to 410-20

1 to 220-30

1Above 35

API recom’ndLiquid retention

time (min)

Oil gravityoAPI

API Spec. 12J (1989API Spec. 12J (1989)

74

Gas and Liquid Separation: Separator Design-manufacturers charts

Source: Natco

75

Gas and Liquid Separation: Separator Design-CFD modelling

76

Gas and Liquid Separation: Factors Affecting Separators Performance

• Operating and design pressure and temperature

• Fluid composition and properties (density, Z-factor, etc.)

• Fluid (gas and liquid) flow rates

• Degree of separation• Two vs. three phase• Gas vs. oil - sand and solids?• Surging/slugging tendencies• Foaming and Corrosive

tendencies• Offshore floating vs. land base

static facilities

Sway Surge

Heave

Roll PitchYaw

◘◘Articulated tower

◘◘Guyed tower platforms

◘◘Tension-leg platforms

◘◘◘Semi-submersibles

◘◘◘◘Single point anchored

tanker

YawPitchRollHeaveSwaySurge

Angular motionLinear motionMotion

77

Gas and Liquid Separation: Operations

• Potential Problems– Foaming– Fouling –

• Solid/sand deposition • Hydrate, paraffin, wax

– Corrosion– Liquid carryover and gas blowby– Flow variations

• Maintenance• Troubleshooting

78

Gas and Liquid Separation: Operations-Troubleshooting

1. Low liquid level2. High liquid level3. Low pressure in separator4. High pressure in separator5. All the oil going out gas line6. Mist going out gas line7. Free gas going out oil valve8. Gas going out water valve on three-phase9. Too much gas going to tank with the oil10.Condensate and water not separating in 3-phase11.Diaphragm operated dump valve not working

79

NATURAL GAS DEHYDRATIONNATURAL GAS DEHYDRATION

• Introduction- purpose of gas dehydration• Pipeline specification• Hydrate prevention• Methods of dehydration

– Absorption dehydration using glycol – Solid bed adsorption– Expansion refrigeration (LTX units)

• Design techniques• Operations of dehydration facilities

80

Natural Gas Dehydration- Hydrate Prevention

• Line heating and Low Temperature Exchange Units (LTX

• Inhibition by additives– Types and selection of additives– Inhibitor requirements––– Prediction of inhibitor requirementsPrediction of inhibitor requirementsPrediction of inhibitor requirements––– Injection techniquesInjection techniquesInjection techniques––– Operations and troubleshootingOperations and troubleshootingOperations and troubleshooting

81

Natural Gas Dehydration-Hydrate Prevention

Typical Glycol injection system

82

Natural Gas Dehydration- Hydrate Prevention

• Inhibition by additives––– Types and selection of additivesTypes and selection of additivesTypes and selection of additives– Process consideration– Injection techniques ––– Prediction of inhibitor requirementsPrediction of inhibitor requirementsPrediction of inhibitor requirements––– Operations and troubleshootingOperations and troubleshootingOperations and troubleshooting

83

Natural Gas Dehydration- Hydrate Prevention: Inhibitor Requirements

• Inhibition by additives––– Types and selection of additivesTypes and selection of additivesTypes and selection of additives––– Process considerationProcess considerationProcess consideration––– Injection techniques Injection techniques Injection techniques – Prediction of inhibitor requirements

• Hammerschmidt’s equation• Computer simulation

––– Operations and troubleshootingOperations and troubleshootingOperations and troubleshooting

3210662MW

233540004000KH

MethanolDEGEG

HKMWdMWdW

+=

))(()100)()((

84

Natural Gas Dehydration- Hydrate Prevention: Operations and Troubleshooting

• Operations– Vapour losses– Corrosion– Glycol losses– Glycol-water-oil separation

• Troubleshooting– Preventing freeze-offs– Improving Glycol-Condensate Separation

85

Natural Gas Dehydration- Glycol Absorption

• Advantages over other methods of dehydration:– Solid desiccant– Expansion refrigeration (LTS or LTX units)

• Choice of glycol (EG and DEG vs. TEG)• Process description and elements• Design methods• Process operations

86

Natural Gas Dehydration- Glycol AbsorptionSource: Natco

A typical glycol absorption process

87

Process Elements:1.1. Inlet scrubberInlet scrubber2.2. Absorber (glycol contactor)Absorber (glycol contactor)3.3.3. Flash tankFlash tankFlash tank4.4.4. FiltersFiltersFilters5.5.5. Glycol pumpGlycol pumpGlycol pump6.6.6. Surge tankSurge tankSurge tank7.7.7. Heat exchangersHeat exchangersHeat exchangers8.8.8. Regeneration system (tower and Regeneration system (tower and Regeneration system (tower and reboilerreboilerreboiler)))9.9.9. InstrumentationInstrumentationInstrumentation


Natco bubble cap

88

Process Elements:1.1.1. Inlet scrubberInlet scrubberInlet scrubber2.2.2. Absorber (glycol contactor)Absorber (glycol contactor)Absorber (glycol contactor)3.3. Flash tankFlash tank4.4. FiltersFilters5.5. Glycol pumpGlycol pump6.6. Surge tankSurge tank7.7.7. Heat exchangersHeat exchangersHeat exchangers8.8.8. Regeneration system (tower and Regeneration system (tower and Regeneration system (tower and reboilerreboilerreboiler)))9.9.9. InstrumentationInstrumentationInstrumentation


89

Process Elements:1.1.1. Inlet scrubberInlet scrubberInlet scrubber2.2.2. Absorber (glycol contactor)Absorber (glycol contactor)Absorber (glycol contactor)3.3.3. Flash tankFlash tankFlash tank4.4.4. FiltersFiltersFilters5.5.5. Glycol pumpGlycol pumpGlycol pump6.6.6. Surge tankSurge tankSurge tank7. Heat exchangers8. Regeneration system (tower and reboiler)9. Instrumentation


90

• Required information– Inlet gas flow rate, T and P and

composition– Required water dew point– Available utilities– Safety/environmental

regulations

• Required TEG reconcentration

• Process flow sheeting (M&EB)

• Equipment sizing

Natural Gas Dehydration- Glycol Absorption: Design Guidelines

Equipment Specification

Tables from NatcoNatco

91

Equipment sizing:• Contactor

– Height (2 to 3 theoretical stages or GPSA Figures 20-53 to 20-58)

– Diameter (Sauders-Brown)• Pump (70-80% mechanical efficiency

Pump BHP=(0.000012) (gph) (psig)


92

Regeneration package• Flash Tank• Stripping column

– Three theoretical stages

– Diameter: 9.gpm0.5

• Reboiler– Duty: 1500.gph– Temp.: 370-390oF– Firetube flux: 6000-

8000 Btu/hr.ft2


93

• Heat Exchangers– Reflux condenser– Lean-rich glycol HX– Lean glycol cooler


94

Natural Gas Dehydration- Glycol Absorption: Operations

Contactor• Inlet gas flow rate• Inlet gas T and P• Len TEG T and

concentration• TEG flow rate• Contactor T

<200 (pefer 180)TEG entering pump380-400 (prefer 380)Reboiler

210Top of stripping column

300-350TEG to stripping column

100-150 (prefer 150)TEG to filters100-150 (prefer 150)TEG to flash tank

5-15 warmer than inlet gas

TEG to contactor80-100Inlet gas

Tempearture (oF)Process location

95

• Regenerator– Reboiler T– Stripping gas– Column T


Drizo® Process

96

• Glycol care– Oxygen– Thermal decomposition– Low pH– Salt contamination– Liquid HC– Sludge accumulation– Foaming


97

• Glycol pump• Sour gas • Startup/shutdown


98

Preventive maintenance– Daily – Weekly– Monthly– Annual inspections


99

Natural Gas Dehydration- Glycol Absorption: Troubleshooting

• High exit gas dew-point• High glycol loss (should

be < 0.1 gal/MMscf)– Loss from contactor– Loss from stripping column– Loss from separator– Leaks and spills

• Glycol contamination• Poor glycol regeneration

• Low glycol circulation• High pressure drop across

contactor• High stripping column

temperature• High reboiler pressure• Firetube fouling/ hotspots/

burnout• Low reboiler temperature• Flash separator failure

100

Natural Gas Dehydration- Solid desiccants

Example Solid Desiccant Dehydrator Twin Tower System (Source: GPExample Solid Desiccant Dehydrator Twin Tower System (Source: GPSA)SA)

101

Natural Gas Dehydration- Solid desiccants

Natco’s solid desiccant beds

102

Natural Gas Dehydration- Solid desiccants: Design• Allowable gas superficial velocity• Pressure drop - vessel diameter: Ergun’s eq.

• Cycle time (6-8 hours)• Bed length: Saturation Zone (LS) and Mass Transfer Zoneheights (LMTZ)

)(4

))((13.0 2 densitybulkDSLand

CCWS s

sTss

rs π

==

2VCVBLP ρµ +=

∆

0.0002100.2381/16” extrudate

0.0001360.1521/16” bead

0.0001240.07221/8” extrudate

0.00008890.0561/8” bead

CBParticle type Allowable Velocity for Mole Sieve Dehydrator

103

Natural Gas Dehydration- Solid desiccants: Design (cont.)

• Length of mass transfer zone LMTZ = (V/35)0.3 (Z)

• Bed regeneration– Heat duty– Regeneration gas rate

• General comments ondsing

104

Natural Gas Dehydration- Solid desiccants: Operations

• Desiccant installation• Startup• Switching• Operating data• Energy conservation

105

Natural Gas Dehydration- Solid desiccants: Troubleshooting

• Proper design-Design considerations

• Bed contamination• High Dew point• Premature Breakthrough

106

Natural Gas Dehydration- Refrigeration and Membrane

A typical JT unit for water and NGL removal (source: Natco)

Manufacturer selection guide (source: Natco)

Membrane systems (Source: Air Products)

107

Natural Gas Dehydration- Process Selection

• Dehydration methods advantages and disadvantages– TEG (glycol dehydration)– Solid desiccants– Low temperature– Membranes

• Selection recommendations

108

NATURAL GAS LIQUID RECOVERYNATURAL GAS LIQUID RECOVERY

• Why NGL recovery?• NGL components and specifications• Introduction to low temperature processes• Processing objectives

– Transportable gas– Sales gas– Maximum NGL recovery

• Value of NGL• Liquid Recovery Porcesses

109

Natural Gas Liquid Recovery- Processes

• Refrigeration• JT-Valve expansion (LTS)• JT-Turbine Expansion• Oil absorption• Solid bed adsorption

Hyd

roca

rbon

Ph

ase

Enve

lope

Liquid

Gas

Pres

sure C B A

C’’

C’

RefrigerationInterchange JT and

Expander

Expander JT

Gas-Gas HX

Temperature

110

Natural Gas Liquid Recovery- Processes: Joule-Thompson (JT) Valve Expansion

Hyd

roca

rbon

Ph

ase

Enve

lope

Liquid

Gas

Pres

sure

C

B A

C’’

C’

RefrigerationInterchange JT and

Expander

Expander JT

Gas-Gas HX

A simplified JT Expansion Process

Temperature

111

Natural Gas Liquid Recovery- Processes: LTS Units

112

Natural Gas Liquid Recovery- Processes: LTS Units

113

Natural Gas Liquid Recovery- Processes: Refrigeration

114

Natural Gas Liquid Recovery- Processes: Refrigeration

115

Natural Gas Liquid Recovery- Processes: Oil absorption

Flow Diagram of a Refrigerated Lean Oil Absorption Process

116

Natural Gas Liquid Recovery- Processes: JT Turbine Expansion

Hyd

roca

rbon

Ph

ase

Enve

lope

Liquid

Gas

Pres

sure

C

B A

C’’

C’

RefrigerationInterchange

JT and Expander

Expander JT

Gas-Gas HX

Temperature

A Simplified Turbo Expansion Flow Diagram

117


Conventional Turbo-expansion System

118


Residue Recycle (RR) Turbo-expansion Process

119


120


121


122

Natural Gas Liquid Recovery- Processes: Mixed Refrigerant

123

Natural Gas Liquid Recovery- Processes: Solid Bed Adsorption

Solid Bed Adsorption Dew Point Control Units

124

Natural Gas Liquid Recovery- Process Selection

• NGL content of the gas– Low: expander process– High: external refrigeration

• Inlet gas pressure– High: LTS – Low: Turbine expansion or refrigeration

• Gas flow rate– Low: simple valve JT unit, solid adsorption or

membranes– Large: more complex plants

• Location (offshore, onshore, or remote areas)

125

Natural Gas Liquid Recovery - Process Design

• Process flowsheeting/simulation – EOSs (SRK, PR, etc.)– Software packages (BR&E PROSIM®, Hyprotech

HYSYS®, Aspen®, Chemshire Design II®, SSI PROCESS® and PRO/II® etc.)

• Equipment selection– HXs– Towers– Turboexpanders– Pumping and storage

126

Natural Gas Liquid Recovery – Equipment Selection: Heat Exchangers

Basic Components of a Three Stream Counterflow Brazed Aluminum Heat Exchanger Typical Fin Arrangements for Gas/Gas

Exchanger

127

Natural Gas Liquid Recovery – Equipment Selection: Towers, Pumps, and Storage

128

Natural Gas Liquid Recovery – Refrigeration Cycle

Simple Cycle

• Process flow diagram

• Vapour compression P-H diagram

1. Expansion

2. Evaporation

3. Compression

4. Condensation

129

Natural Gas Liquid Recovery – Refrigeration Cycle

130

Natural Gas Liquid Recovery – Refrigeration Cycle: Single, vs Multistage Systems

131

Natural Gas Liquid Recovery – Refrigeration Cycle: Single, vs Multistage Systems

132

Natural Gas Liquid Recovery – Refrigeration Cycle: Refrigerant Cascading

133

134

Natural Gas Liquid Recovery – Design and Operating considerations

• Oil removal

• Liquid surge and storage

• Vacuum systems (air leaks and corrosion)

•Vacuum considerations

135

Natural Gas Liquid Recovery – Design and Operating considerations

• Material of construction

no copper in presence of ammonia and sulfur compounds

Steel is preferred (CS down to -20oF)

Aluminum alloy and SS for very low Ts

ANSI B31.3 and B31.5 design codes

• Refrigeration purity

Lube oil

Light and heavy ends

Process fluid leak

Air leak and humidity (use drier or methanol wash/purge)

136

Natural Gas Liquid Recovery – Refrigeration Compressors

Compressor types

• Centrifugal (>450 HP)

• Reciprocating (higher efficiency, multistage)

• Screw (high compression ratios up to 10, less noise)

• Rotary (low capacity)

137

Natural Gas Liquid Recovery – Mixed refrigerant

138

• Kettle type Allowable refrigerant load in lb/hr per ft3 vapor space =

• Plate fin

Natural Gas Liquid Recovery – Refrigeration Chillers

VL

VFSρρ

σρ−)869.0(

)3980)(.)(.(

139

Natural Gas Liquid Recovery –Refrigeration Control System

• Level displacer-type

internal float

differential pressure

• PressureCompressor suction and discharge

• Temperature

Chiller (by controlling compressor suction pressure)

Low ambient

140

• High Compressor Discharge Pressure• High Process Temperature• Inadequate Compressor Capacity• Inadequate Refrigerant Flow to Economizer or Chiller

Natural Gas Liquid Recovery – Refrigeration Operations and trouble shooting

Documents

Overview Gas Processes