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 Science Memorial University of Newfoundland (MUN)

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. Introduction

2. Fluid Properties

3. Inlet separator design

4. Prevention of hydrate formation and dehydration of natural gas

5. Natural gas dew point control and liquid recovery 6. Natural gas transmissions systems

7. Natural Gas Compression 8. Natural gas measurement* 9. Heat exchange equipment*

10. Overview of natural gas sweetening processes* 11. Natural gas transportation*

4

References

1. Beggs H.D., Gas Production Operation, OGCI publications, 1985, ISBN: 0-930972-06-6

2. Kumar S., Gas Production Engineering, Gulf Publishing, 1987, ISBN: 0-87201-577-7 3. 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

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.

Natural Gas Origin

• Biogenic methane

• Thermogenic methane

• Metamorphism

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

9

World Natural Gas Reserves (2002)

10

11

World Natural Gas Production (2002)

12

13

15 Source : BP

17

Canadian natural gas production/demand by

region (2001)

19

21

23

Gas Processing Facility Block Diagram

Acid Gas Management Systems Controlled Release of emission gases to Atmosphere Sulphur Sales Sulphur Production Natural Gas Well Gas High Pressure Separation Intermittent solid removal Water Vapour Removal -Dehydration NGL Recovery -Dew Point Control

(DPC) Acid Gas Removal Heating SALES GAS Cooling Stabilization Condensate Sales Water disposal Water handling Facilities Compression LPG Recovery (C₃ & C₄) Propane and Butane Sales

FLUID PROPERTIES

FLUID PROPERTIES

Characterization of Natural Gas and Its Products

colorless -Dry gas colorless >50 >50,000 -Wet gas Water white 50-60 3,300-50,000 >0.35

Retrograde gas – gas condensate

Colored – dark brown >40 2,000-3,300 <0.5 Very dark – black oil <45 <2,000 >0.5

Associated gas from:

•Low Shrinkage crude (Low GOR)

–Ordinary crude

•High Shrinkage Oil (high GOR) –

volatile oil COLOR O_API SCF/BSTO BSTO/BRF STOCK-TANK LIQUID TYPICAL GOR SPECTRUM OF PRODUCED SPECTRUM OF PRODUCED HYDROCARBONS HYDROCARBONS FLUID TYPE

25

Fluid Properties – Natural Gas Constituents

N₂ C₆+ nC₅ iC₅ nC₄ iC₄ C₃ C₂ C₁ Abbreviation variable FeS

Reservoir fines and iron sulfide

variable

-Millscale or rust

Solids

variable CH₃OH(MeOH), EG, etc.

Methanol and glycol

variable

-Corrosion inhibitors

variable H₂O

Free water or brine

Water vapour/Liquid slugs 1.0-10.0ppm R-S-S-R Disulfides 1.0-10.0ppm R-S-R Sulfides 10-1000ppm R-SH Mercaptans Sulphur compouns 0.2-10.0 CO₂ Carbon Dioxide 0.01-10.0 H₂S Hydrogen sulfide Acid gases a few ppm O₂ Oxygen a few ppm H₂ Hydrogen a few ppm Ar Argon 0.01-0.1 He Helium 0.2-5.0 N₂ Nitrogen Inert Gases 1.0-3.0

-Hexanes and heavier

0.1-2.0 nC₅H₁₂ n-Pentane 0.1-2.0 iC₅H₁₂ i-Pentane 0.3-7.5 nC₄H₁₀ n-Butane 0.3-2.5 iC₄H₁₀ i-Butane 1.0-15.0 C₃H₈ Propane 3.0-10.0 C₂H₆ Ethane 59.0-92.0 CH₄ Methane Hydrocarbons Typical composition (volume %) Formula Components Class

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

9 Van der Waals

9 Benedict-Webb-Rubin (BWR) 9 Saove-Redlich-Kwang (SRK) 9 Peng-Robinson (PR)

29

Fluid Properties – Molecular Weight – Mole

concept

ƒ Weight of a mole of any substance

ƒ Different units in Imperial, SI and CGS systems

ƒ Moles = Weight of a gas component divided by its molecular weight

ƒ Average molecular weight =

]

)

.(

[

y

_N

MW

_N

MW

=

∑

Fluid Properties – Density and Specific Gravity

• Density = mass of a unit volume (lb/ft3 _{or kg/m}3₎

• S = MW/29 (for gases)

or

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

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

crude oil)

TZ

SP

g

=

2

.

7

ρ

TZ

P

MW

g

)

(

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

P_CN and T_CN from Figure 23-2 GPSA

P_PC = Σ y_NP_CN and T_PC = Σ y_NT_CN

P_PC = 709.604 – 58.718 S T_PC = 170.491 + 307.344 S

33

Fluid Properties – Gas Compressibility Factor

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

23-5 GPSA)

• Brown-Katz-Oberfell-Alden charts (Figures 7, 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

(

' ' '

B

B

T

T

P

P

and

T

T

PC PC PC PC PC PC

−

+

=

−

=

ε

ε

35

Compressibility charts Brown-Katz-Oberfell-Alden Z charts

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 N N N n N N N gN g MW y MW y 1 5 . 0 1 5 . 0 1 1 µ µ X y and MW T X T MW T MW K where X K y g g 2 . 0 4 . 2 01 . 0 / 986 5 . 3 19 209 ) 02 . 0 4 . 9 ( 10 , ) exp( 5 . 1 4 − = + + = + + + = = ρ − µ [ ] 9 / 8 Pr 5 Pr 9 / 5 Pr 5 Pr 3 / 2 2 / 1 6 / 1 ) 10 ( 0 . 34 , 5 . 1 , 0932 . 0 1338 . 0 ) 10 ( 8 . 166 , 5 . 1 ; ) ( 4402 . 5 T T for and T T for P MW y T g g PC N N PC − − = ≤ − = > = ∑ ξµ ξµ ξ

37

Fluid Properties – Specific Heat

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

• C_p and C_vand their relationships (Maxwell’s equation)

• C_p determination

– Hankinson’s gravity C o_p = A + B.T + C.S + D.S2 _{+ E(T.S) + F.T}2

– Kay’s mixing rule

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

R C C gases ideal for v P T P T C C _{p v} T v v p _{∂ ∂} − = ∂ ∂ − = − ) / ( ) / ( 2

∑

= = n N o pN N o p y C C 1

39

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):Total energy 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: H_v= Σ y_NH_vN • Wobbe Index: W_O=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 (GPSA Fig.s 23-40 through 23-45)

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

∑

∑

=

)

.

(

)

.

(

3 3 N N N N N m

MW

y

MW

k

y

k

43

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 rule N=C-P+2

45

Phase Behavior – Single Component Systems

B A C D a b c d e h Dense Fluid region-supercritical fluid g f • Phase Equilibrium – gas-liquid – gas-solid – Liquid-solid • Triple point • Critical point

Phase Behavior: Two-Component Systems

• Concept of phase envelope • Equilibrium lines – Bubble point – Dew point • Critical point • Cricondentherm • Cricondenbar • Rertrograde phase change Pressure Cricondenbar Cricondentherm De w-Poin t Lin e Bub ble-P oint Lin e Vapo urpr essu re of p ure A Vapour pressu re of pure B C a _b d e h j k l P_C T_C

Two component phase envelop

90% vap’ d g f Temperature

47

Phase Behavior: Multi-Component Systems

C Condensate reservoir Oil reservoir Gas reservoir A A’ B B’ C C’ D D’ E E’ Temperature Pressure Two-Phase Region (Gas+Liquid) Cricondentherm Wet Gas Dry Ga s • Full wellstream • Source of phase diagrams • Quantitative phase behavior • Phase behavior in separators

Phase Behavior: Vapour-Liquid Equilibria

• Thermodynamic criteria for

equilibrium-equality of fugacities: f_N,v= f_N,l

• Equilibrium ratio (K values): K=y_N/ x_N • Equilibrium calculations

– Equilibrium flash:

– Bubble point: Σy_N =Σ z_N . K_N = 1.0

Σ z_N . K_N > 1.0 guarantees vapour is present – Dew point: Σx_N =Σ z_N / K_N = 1.0 Σ z_N / K_N > 1.0 guarantees liquid is present N N N N K L V F K V + = ) / /( 1 V, y_N F, z_N L, x_N

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 10 and 20-11, GPSA

– Campbell charts: W = y_hc W_hc + y_CO2 W_CO2 + y_H2S W_H2S 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,

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 -po int Cu rve Hydr ocar bon Pha se Env elop e Hydrate Formation Curve L_hc+L_w+G+H L_hc+L_w+G L_w+G G Pressure

B. High Water Content

Hydr ocar bon Pha se Env elope L_hc+L_w+G+H L_hc+L_w+G L_hc+G Pressure Wate r Dew -poi nt cC urve Hyd rate For mat ion Cur ve G L_w+G A. Normal Case A Temperature Temperature

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

Scope of Natural Gas Field Processing:

Process objectives

Process 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 Gas

Type 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

Scope of Natural Gas Field Processing:

Filed Location, Size, and Operation

Filed 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 SEPARATION

GAS AND LIQUID SEPARATION

•

•

Purpose, principles and terminology

Purpose, principles and terminology

• Separation equipment- common

components

• Types of separators

• Separation principles

• Separator design

• Factors affecting separation

• Operational Problems

Gas and Liquid Separation: Separation

Equipment- Major Parts

A - Primary Separation B - Gravity Settling

C - Coalescing

59

Gas and Liquid Separation - Types

of Separators

• Gravity (vertical vs. horizontal)

• Centrifugal

• Filter coalescing

• Impingement

• Comparison of separators –

Gas and Liquid Separation: Separation

Equipment- vertical separator

61

Gas and Liquid Separation: Separation

Equipment- Horizontal separators

Gas and Liquid Separation: Separation

Equipment, Two-Barrel (Double-Tube)

horizontal separator

63

Gas and Liquid Separation: Separation

Equipment- horizontal filter separator

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 B C D Downcomer J=ρ_g .V_t2 _{= 20 lb/(ft.sec2)}

Gas and Liquid Separation: Separation

Equipment- Centrifugal separator

67

Gas and Liquid Separation: Separation

Equipment- Swirl/cyclonic separators

Porta-Test Whirlyscrub ITM

Gas and Liquid Separation –Separation

principles

] 2 [ 2 g V A C F t D D = ρ Drag force Stock’s termonal velocity for: Re < 1.0 µ 2 6_{( . .)} 10 78 . 1 _m t d G S V = × ∆ −

Refor 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 . 0 3 24 2 / 1 + + = Re Re C_D 2 / 1 ] ) [( 0119 . 0 D m g g l t C d V ρ ρ ρ − =

69

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

•

Terminal velocity iterative calculations: 1. Start calculating C_Dusing:

2. Calculate Re as:

3. Calculate new values for C_D :

4. Calculate new values for C_D :

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

•

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

t = V /Q 2 / 1 ] ) [( 0204 . 0 _m g g l t d V ρ ρ ρ − = µ ρ_gd_mV_t Re=0.0049 34 . 0 3 24 2 / 1 + + = Re Re C_D 2 / 1 ] ) [( 0119 . 0 D m g g l t C d V ρ ρ ρ − =

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

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: L_ss = L_eff+ d/12 for gas capacity and L_ss = 4/3 L_eff 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 g l g g eff d C P TZQ dL ρ ρ ρ       = P TZQ K dL_eff 42 g 2 / 1                 − = _D g l g C K ρ ρ ρ 7 . 0 2 r l eff Q t L d = 2 / 1 2 _5,040                 −       = m D g l g g d C P TZQ d ρ ρ ρ       = P TZQ K d2 420 g 12 . 0 2_h trQl d = 12 40 ... ;... 12 76 ₌ + + + =h or L h d L_{ss ss}

g g l SB t K V

ρ

ρ

ρ

− =

Gas and Liquid Separation: Sizing

Equations-Souders-Brown Technique

2 / 1 ] ) [( 0119 . 0 D m g g l t C d V ρ ρ ρ − =

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. K_SB, (ft/sec.)

-Other lengths

0.38 with mist extractor 10

Horizontal

0.18 without and 0.3 with mist extractor

10

0.12 without and 0.2 with mist extractor

5 Vertical

Most commonly used K_SBValue

(ft/sec.)

Height, H or Length, L (ft) Separator type

API Spec. 12 J (1989) Recommendations for K

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 4 10-20 1 to 2 20-30 1 Above 35 API recom’nd Liquid retention time (min) Oil gravity o_API API Spec. 12J (1989 API Spec. 12J (1989)

74

Gas and Liquid Separation: Separator

Design-manufacturers charts

75

Gas and Liquid Separation: Separator

Design-CFD modelling

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 Pitch Yaw ◘ ◘ Articulated tower ◘ ◘ Guyed tower platforms ◘ ◘ Tension-leg platforms ◘ ◘ ◘ Semi-submersibles ◘ ◘ ◘ ◘ Single point anchored tanker Yaw Pitch Roll Heave Sway Surge Angular motion Linear motion Motion

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

Gas and Liquid Separation:

Operations-Troubleshooting

1. Low liquid level 2. High liquid level

3. Low pressure in separator 4. High pressure in separator 5. All the oil going out gas line 6. Mist going out gas line

7. Free gas going out oil valve

8. Gas going out water valve on three-phase 9. Too much gas going to tank with the oil

10.Condensate and water not separating in 3-phase 11.Diaphragm operated dump valve not working

79

NATURAL GAS DEHYDRATION

NATURAL 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

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 requirements

Prediction of inhibitor requirements

Prediction of inhibitor requirements

–

––

Injection techniques

Injection techniques

Injection techniques

–

81

Natural Gas

Dehydration-Hydrate Prevention

Natural Gas Dehydration- Hydrate Prevention

• Inhibition by additives

–

––

Types and selection of additives

Types and selection of additives

_{Types and selection of additives}

– Process consideration

– Injection techniques

–

––

Prediction of inhibitor requirements

Prediction of inhibitor requirements

Prediction of inhibitor requirements

–

83

Natural Gas Dehydration- Hydrate Prevention:

Inhibitor Requirements

• Inhibition by additives

–

––

Types and selection of additives

Types and selection of additives

_{Types and selection of additives}

–

––

Process consideration

Process consideration

Process consideration

–

––

Injection techniques

Injection techniques

Injection techniques

– Prediction of inhibitor requirements

• Hammerschmidt’s equation • Computer simulation

–

––

Operations and troubleshooting

Operations and troubleshooting

Operations and troubleshooting

32 106 62 MW 2335 4000 4000 K_H Methanol DEG EG H

K

MW

d

MW

d

W

+

=

)

)(

(

)

100

)(

)(

(

Natural Gas Dehydration- Hydrate Prevention:

Operations and Troubleshooting

• Operations

– Vapour losses

– Corrosion

– Glycol losses

– Glycol-water-oil separation

• Troubleshooting

– Preventing freeze-offs

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

86

Natural Gas Dehydration- Glycol Absorption

Source: Natco

87

Process Elements:

1.

1. Inlet scrubberInlet scrubber 2.

2. Absorber (glycol contactor)Absorber (glycol contactor) 3.

3.3. Flash tankFlash tankFlash tank 4.

4.4. FiltersFiltersFilters 5.

5.5. Glycol pumpGlycol pumpGlycol pump 6.

6.6. Surge tankSurge tankSurge tank 7.

7.7. Heat exchangersHeat exchangersHeat exchangers 8.

8.8. Regeneration system (tower and Regeneration system (tower and Regeneration system (tower and reboilerreboilerreboiler))) 9.

9.9. InstrumentationInstrumentationInstrumentation

Natural Gas Dehydration- Glycol Absorption

Process Elements:

1.

1.1. Inlet scrubberInlet scrubberInlet scrubber 2.

2.2. Absorber (glycol contactor)Absorber (glycol contactor)Absorber (glycol contactor) 3.

3. Flash tankFlash tank 4.

4. FiltersFilters 5.

5. Glycol pumpGlycol pump 6.

6. Surge tankSurge tank 7.

7.7. Heat exchangersHeat exchangersHeat exchangers 8.

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 scrubber 2.

2.2. Absorber (glycol contactor)Absorber (glycol contactor)Absorber (glycol contactor) 3.

3.3. Flash tankFlash tankFlash tank 4.

4.4. FiltersFiltersFilters 5.

5.5. Glycol pumpGlycol pumpGlycol pump 6.

6.6. Surge tankSurge tankSurge tank

7. Heat exchangers

8. Regeneration system (tower and reboiler) 9. Instrumentation

• 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)

Natural Gas Dehydration- Glycol Absorption:

Design Guidelines

Regeneration package • Flash Tank • Stripping column – Three theoretical stages – Diameter: 9.gpm0.5 • Reboiler – Duty: 1500.gph – Temp.: 370-390o_F – Firetube flux: 6000-8000 Btu/hr.ft2

Natural Gas Dehydration- Glycol Absorption:

Design Guidelines

93

• Heat Exchangers

– Reflux condenser

– Lean-rich glycol HX

– Lean glycol cooler

Natural Gas Dehydration- Glycol Absorption:

Design Guidelines

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 pump

380-400 (prefer 380) Reboiler 210 Top of stripping column 300-350 TEG to stripping column 100-150 (prefer 150) TEG to filters 100-150 (prefer 150)

TEG to flash tank

5-15 warmer than inlet gas TEG to contactor 80-100 Inlet gas Tempearture (o_F) Process location

95

• Regenerator

– Reboiler T

– Stripping gas

– Column T

Natural Gas Dehydration- Glycol Absorption:

Operations

• Glycol care

– Oxygen

– Thermal decomposition

– Low pH

– Salt contamination

– Liquid HC

– Sludge accumulation

– Foaming

Natural Gas Dehydration- Glycol Absorption:

Operations

97

• Glycol pump

• Sour gas

• Startup/shutdown

Natural Gas Dehydration- Glycol Absorption:

Operations

Preventive maintenance

– Daily

– Weekly

– Monthly

– Annual inspections

Natural Gas Dehydration- Glycol Absorption:

Operations

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

Natural Gas Dehydration- Solid desiccants

Example Solid Desiccant Dehydrator Twin Tower System (Source: GP

101

Natural Gas Dehydration- Solid desiccants

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 (L_S) and Mass Transfer Zone

heights (L_MTZ) ) ( 4 ) )( ( 13 . 0 D2 bulk density S L and C C W S s s T ss r s = = _π 2 V C V B L P _{= µ + ρ} ∆ 0.000210 0.238 1/16” extrudate 0.000136 0.152 1/16” bead 0.000124 0.0722 1/8” extrudate 0.0000889 0.056 1/8” bead C B

103

Natural Gas Dehydration- Solid desiccants:

Design (cont.)

• Length of mass transfer zone

L

_MTZ

= (V/35)

0.3

_(Z)

• Bed regeneration

– Heat duty

– Regeneration gas rate

• General comments on

dsing

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

106

Natural Gas Dehydration- Refrigeration and

Membrane

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

107

Natural Gas Dehydration- Process Selection

• Dehydration methods advantages and

disadvantages

– TEG (glycol dehydration)

– Solid desiccants

– Low temperature

– Membranes

NATURAL GAS LIQUID RECOVERY

NATURAL 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

109

Natural Gas Liquid Recovery- Processes

• Refrigeration

• JT-Valve expansion (LTS) • JT-Turbine Expansion • Oil absorption

• Solid bed adsorption

Hy dro car bo n Ph ase En vel op e Liquid Gas Pressure C B A C’’ C’ Refrigeration Interchange JT and Expander Expander JT Gas-Gas HX Temperature

110

Natural Gas Liquid Recovery- Processes:

Joule-Thompson (JT) Valve Expansion

Hyd roca rbo n Ph ase En velo pe Liquid Gas Pressure C B A C’’ C’ Refrigeration Interchange JT and Expander Expander JT Gas-Gas HX A simplified JT Expansion Temperature

111

113

Natural Gas Liquid Recovery- Processes:

Refrigeration

Natural Gas Liquid Recovery- Processes:

Refrigeration

115

Natural Gas Liquid Recovery- Processes:

Oil absorption

Natural Gas Liquid Recovery- Processes:

JT Turbine Expansion

Hyd roca rbo n Ph ase En velo pe Liquid Gas Pressure C B A C’’ C’ Refrigeration Interchange JT and Expander Expander JT Gas-Gas HX Temperature

117

Natural Gas Liquid Recovery- Processes:

JT Turbine Expansion

Natural Gas Liquid Recovery- Processes:

JT Turbine Expansion

119

Natural Gas Liquid Recovery- Processes:

JT Turbine Expansion

Natural Gas Liquid Recovery- Processes:

JT Turbine Expansion

121

Natural Gas Liquid Recovery- Processes:

JT Turbine Expansion

Natural Gas Liquid Recovery- Processes:

Mixed Refrigerant

123

Natural Gas Liquid Recovery- Processes:

Solid Bed Adsorption

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

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

126

Natural Gas Liquid Recovery – Equipment

Selection: Heat Exchangers

Basic Components of a Three Stream

127

Natural Gas Liquid Recovery – Equipment

Selection: Towers, Pumps, and Storage

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

Natural Gas Liquid Recovery – Refrigeration

Cycle: Single, vs Multistage Systems

131

Natural Gas Liquid Recovery – Refrigeration

Cycle: Single, vs Multistage Systems

Natural Gas Liquid Recovery – Refrigeration

Cycle: Refrigerant Cascading

Natural Gas Liquid Recovery – Design and

Operating considerations

•

Oil removal

•

Liquid surge and storage

•

Vacuum systems (air leaks and corrosion)

135

Natural Gas Liquid Recovery – Design and

Operating considerations

•

Material of construction

9no copper in presence of ammonia and sulfur compounds 9Steel is preferred (CS down to -20o_F)

9Aluminum alloy and SS for very low Ts 9ANSI B31.3 and B31.5 design codes

•

Refrigeration purity

9Lube oil

9Light and heavy ends 9Process fluid leak

Natural Gas Liquid Recovery – Refrigeration

Compressors

Compressor types

•

Centrifugal (>450 HP)

•

Reciprocating (higher efficiency, multistage)

•

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

137

Natural Gas Liquid Recovery – Mixed

refrigerant

• Kettle type

Allowable refrigerant load in lb/hr per ft3 _{vapor space =}

• Plate fin

Natural Gas Liquid Recovery – Refrigeration

Chillers

V L V F S ρ ρ σ ρ − ) 869 . 0 ( ) 3980 )( .)( . (

139

Natural Gas Liquid Recovery –

Refrigeration Control System

• Level

9 displacer-type 9 internal float

9 differential pressure

• Pressure

9 Compressor suction and discharge

• Temperature

9 Chiller (by controlling compressor suction pressure) 9 Low ambient

• 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