Chapter 12 Based on presentation by Prof. Art Kidnayjjechura/GasProcessing/09_Hydrocarbon_Recovery.pdfPropane refrigeration (unless high inlet gas pressure) Multipass heat exchangers

Hydrocarbon Recovery

Chapter 12Based on presentation by Prof. Art Kidnay

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

Reasons for Hydrocarbon Recovery

Field Operations▪ Reduce liquid content of high GPM gases in gathering systems

▪ Eliminate or reduce potential for condensation (dew-pointing)

▪ Reduce Btu content of gas for use in engines (fuel conditioning)

Plant Operations▪ Reduce Sales gas Btu content to spec (950 to 1150 Btu/scf)

▪ Eliminate possible condensation

▪ Recover valuable C2+ liquids

2


Plant Block Schematic

3

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


Topics

Fundamentals▪ Retrograde Condensation

Process Components▪ Refrigeration System

▪ Turboexpansion

▪ Heat exchange

▪ Gas-Liquid Separators

▪ Fractionation

Recovery Processes▪ Dew Point Control and Fuel

Conditioning

▪ Low C2+ Recovery

▪ High C2+ recovery

4


Fundamentals


LNGNGLLPG

Reminder – Liquids Composition

What are Natural Gas Liquids (NGL vs LPG vs LNG)?

Methane

Ethane

Propane

Butane

Pentanes+

What is the GPM of a gas?▪ Gallons of NGL components per 1000 scf (Mscf) of gas

▪ Either C2+ GPM or C3+ GPM

6


Retrograde Condensation

7

0

250

500

750

1000

1250

1500

-300 -250 -200 -150 -100 -50 0 50 100

Pre

ssu

re, P

sia

Temperature, °F

C

B

A

Liquid Vapor


Rich Gas Phase Diagram

8


Rich Gas Phase Diagram

9


Operating Conditions Depend on Type of NGL Recovery

10


Process Components


External Refrigeration

When inlet pressures to Hydrocarbon Recovery are too low to provide required cooling by expansion we can obtain additional refrigeration by:

▪ Compressing inlet gas to higher pressure

▪ Compressing propane in refrigeration cycle

Compressing propane is usually the best choice

12


Basic Single-Stage Refrigeration System

13

Condenser

Chiller/ Evaporator

J-T Valve

Receiver

Compressor

Suction

Drum


Single-Stage Refrigeration cycle

14

Enthalpy

Pre

ss

ure

Critical Point

Vapor

Phase

Liquid

Phase

A*

BC

D

Condenser

Chiller/ Evaporator

J-T Valve

Receiver

Compressor

Suction

Drum

A

B C

D


1-Stage Propane Refrigeration System

15

Condenser

Chiller/ Evaporator

-40°F, 16 Psia

J-T Valve

Receiver

~120°F

240 Psia

Compressor

Suction

Drum

250 Psia


Refrigeration cycle

16

A

BC

D


2 Stage C3 Refrigeration System

17

~120°F

240 Psia

- 40°F

16 Psia

60 Psia 250 PsiaCondenser

JT-Valve

JT-Valve

Receiver

25°F

62 Psia

Interstage

Economizer

Chiller / Evaporator

-40°F, 16 Psia

JT-Valve

25°F

62 Psia

Chiller/

Evaporator


2 Stage C3 Refrigeration System

18

~120°F

240 Psia

- 40°F

16 Psia

60 Psia 250 PsiaCondenser

JT-Valve

JT-Valve

Receiver

25°F

62 Psia

Interstage

Economizer

Chiller / Evaporator

-40°F, 16 Psia


Refrigeration cycle

19

A

BC

D


Benefits of Staging

Condenser Temp = 100oF Chiller Temp = -40oF

20

Number of Stages 1 2 3

Reduction in Compression Power 0 19% 23%

Reduction in Condenser Duty 0 8% 10%


Turboexpanders

Provide▪ Maximum possible cooling

▪ Work which can drive compressors

Operate▪ Over wide temperature range

▪ At high speeds, > 15,000 rpm

Require clean gas

Can handle up to 50 wt % liquid formation provided droplet size less than 20 μm

21


Methane Expansion – Isentropic vs. Isenthalpic

22


Recovery Processes


Recovery Processes

Dew Point Control and Fuel Conditioning▪ High recovery not needed

▪ Operating temperatures ~0oF for fractionation

Low C2+ Recovery

▪ < 60% C2+ recovery needed

▪ Operating temperatures ~ -35oF for fractionation

High C2+ recovery

▪ ~ 90% C2+ recovery needed

▪ Operating temperatures ~ -165oF for fractionation

24


Dew Point Control and Fuel Conditioning

Traditional technology▪ Low Temperature Separators (LTS or LTX)

• Standard technology (>60 years old)

Newer technologies▪ Membrane System

• Newer technology (~10 years old)

▪ Twister

• Newest technology (~5 years old)

25


Dew Point Control (No External Refrigeration)

26

Condensate

Stabilizer

Glycol

Regenerator

Condensate

Rich Glycol

Low

Temperature

Separator

J-T

Valve

Water

Gas from

Field

Water

Knockout

Residue Gas


Dew Point Control (With External Refrigeration)

27

Fig. 16-5, GPSA Engineering Data Book, 14th ed.


Example Dew Point Control Package

28

http://www.enerflex.com/Oil-and-Gas-Solutions/Gas-Processing/Dew-Point-Control/index.php

Propane Condenser

De-Ethanizer Tower

Water Separator

Low Temperature Separator

Gas-Gas Heat Exchanger

Gas Chiller

http://www.enerflex.com/Oil-and-Gas-Solutions/Gas-Processing/Dew-Point-Control/index.php


Membrane for Fuel Conditioning

29

Rich

Gas

Compressor Cooler

C3+ Lean

Fuel GasMembrane

Compressor

Engine

Fuel Gas

Slipstream

C3+ Enriched

Gas Permeate


TwisterModular, flow dependent

Depends upon pressure ratio, ΔP ~ 20 to 30%

Slip gas is 10 to 15%

Used for dehydration and liquids removal

Is being tested in subsea application

30

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

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


Low C2+ Recovery

Two major processes

▪ Refrigerated Lean Oil

• Lean Oil Absorption first process for liquids recovery

• Existing plants now use refrigerated system

▪ Refrigerated Process

• Simpler than Lean Oil process

• Lower recoveries

31


Refrigerated Process

Cold Separator

C3 Chiller

Fractionator

CompressorAir Cooler

Inlet Gas

NGL

Product

Reboiler

Residue

Gas

32


Effect of Composition on C3+ Recovery

20

30

40

50

60

70

80

90

-40 -30 -20 -10 0 10 20

Process Temperature, °F

C3

+ R

ec

ov

ery

, %

3 GPM

5 GPM

7 GPM

33


Recovery Efficiency of C2 and C3

10

20

30

40

50

60

70

80

90

-30 -25 -20 -15 -10 -5 0 5 10

Process Temperature, °F

Re

co

ve

ry,

%

3 GPM

5 GPM

7 GPM 3 GPM

5 GPM

7 GPM

C2

C3

34


Refrigerated Lean Oil

35

Inlet Gas

Residue Gas

Cold C3 Liquid

Absorber Rich Oil

Demethanizer

Low Pressure

Still

NGL

Fuel Gas

Cold C3 Vapor

Cold C3 Liquid

Cold C3 Vapor


High C2+ Recovery

Requires cryogenic separation

Processes involve:▪ Propane refrigeration (unless high inlet gas pressure)

▪ Multipass heat exchangers (gas-gas)

▪ Expansion, turbo and JT

▪ Demethanizer column

Two processes:▪ “1st Generation” – simplest

▪ Gas Subcooled Process (GSP) – more efficient, higher recoveries and commonly used

36


Considerations for Cryogenic Distillation

37


1st Generation Cryo Process

38


Brazed Aluminum Heat Exchanger – “Cold Box”

39

http://hub.globalccsinstitute.com/publications/co2-liquid-logistics-shipping-concept-llsc-overall-supply-chain-optimization/53-co2

http://hub.globalccsinstitute.com/publications/co2-liquid-logistics-shipping-concept-llsc-overall-supply-chain-optimization/53-co2


GSP Schematic

40


Effect of Inerts on Max C2 Recovery

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12 14

Nonhydrocarbon Content, mol %

Ma

xim

um

Eth

an

e R

ec

ov

ery

, %

1.5

GPM

3.0

GPM

5.0

GPM

8.0

GPM

41


Propane Recovery Processes

42

GPSA Engineering Data Book, 14th ed.


Ethane Recovery Processes

43


Summary


Summary

Primary liquids’ production from cold separation▪ Produced gas at dew point condition at last conditions in contact with

hydrocarbon liquid

Lower liquid content of produced gas has a lower dew point requiring lower temperatures

Propane refrigeration loop▪ Typical low temperatures to -40oF

▪ Intermediate pressures reduce compression power & can make chilling temperatures about 10oF

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Documents

Chapter 12 Based on presentation by Prof. Art Kidnayjjechura/GasProcessing/09_Hydrocarbon_Recovery.pdfPropane refrigeration (unless high inlet gas pressure) Multipass heat exchangers