chapter 12 based on presentation by prof. art kidnay...hydrocarbon recovery chapter 12 based on...
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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
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Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
Plant Block Schematic
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Adapted from Figure 7.1, Fundamentals of Natural Gas Processing, 2nd ed.Kidnay, Parrish, & McCartney
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
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
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Updated: January 4, 2019Copyright © 2017 John Jechura ([email protected])
Fundamentals
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
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
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Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
Retrograde Condensation
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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
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Operating Conditions Depend on Type of NGL Recovery
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Process Components
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
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
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Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
Basic Single-Stage Refrigeration System
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Condenser
Chiller/ Evaporator
J-T Valve
Receiver
Compressor
Suction
Drum
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Single-Stage Refrigeration cycle
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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
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1-Stage Propane Refrigeration System
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Condenser
Chiller/ Evaporator
-40°F, 16 Psia
J-T Valve
Receiver
~120°F
240 Psia
Compressor
Suction
Drum
250 Psia
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Refrigeration cycle
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A
BC
D
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2 Stage C3 Refrigeration System
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~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
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2 Stage C3 Refrigeration System
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~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
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Refrigeration cycle
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A
BC
D
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Benefits of Staging
Condenser Temp = 100oF Chiller Temp = -40oF
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Number of Stages 1 2 3
Reduction in Compression Power 0 19% 23%
Reduction in Condenser Duty 0 8% 10%
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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
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Methane Expansion – Isentropic vs. Isenthalpic
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Recovery Processes
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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
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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)
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Dew Point Control (No External Refrigeration)
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Condensate
Stabilizer
Glycol
Regenerator
Condensate
Rich Glycol
Low
Temperature
Separator
J-T
Valve
Water
Gas from
Field
Water
Knockout
Residue Gas
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Dew Point Control (With External Refrigeration)
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Fig. 16-5, GPSA Engineering Data Book, 14th ed.
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
Example Dew Point Control Package
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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
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Membrane for Fuel Conditioning
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Rich
Gas
Compressor Cooler
C3+ Lean
Fuel GasMembrane
Compressor
Engine
Fuel Gas
Slipstream
C3+ Enriched
Gas Permeate
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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
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http://twisterbv.com/PDF/resources/Twister_-_How_Does_It_Work.pdf
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
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
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Refrigerated Process
Cold Separator
C3 Chiller
Fractionator
CompressorAir Cooler
Inlet Gas
NGL
Product
Reboiler
Residue
Gas
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Effect of Composition on C3+ Recovery
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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
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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
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Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
Refrigerated Lean Oil
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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
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
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
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Considerations for Cryogenic Distillation
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1st Generation Cryo Process
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Brazed Aluminum Heat Exchanger – “Cold Box”
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http://hub.globalccsinstitute.com/publications/co2-liquid-logistics-shipping-concept-llsc-overall-supply-chain-optimization/53-co2
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
Effect of Inerts on Max C2 Recovery
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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
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Propane Recovery Processes
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GPSA Engineering Data Book, 14th ed.
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
Ethane Recovery Processes
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Updated: January 4, 2019Copyright © 2017 John Jechura ([email protected])
Summary
Updated: January 4, 2019Copyright © 2019 John Jechura ([email protected])
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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