Chapter 12 Based on presentation by Prof. Art...

Hydrocarbon Recovery

Chapter 12Based on presentation by Prof. Art Kidnay

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

Plant Block Schematic

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

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

Retrograde Condensation

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

Temperature, °F

Liquid Vapor

Rich Gas Phase Diagram

Operating Conditions Depend on Type of NGL Recovery

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

Basic Single-Stage Refrigeration System

Condenser

Chiller/ Evaporator

J-T Valve

Receiver

Compressor

Suction

Single-Stage Refrigeration cycle

Enthalpy

Critical Point

Liquid

Condenser

Chiller/ Evaporator

J-T Valve

Receiver

Compressor

Suction

1-Stage Propane Refrigeration System

Condenser

Chiller/ Evaporator

-40°F, 16 Psia

J-T Valve

Receiver

~120°F

240 Psia

Compressor

Suction

250 Psia

Refrigeration cycle

2 Stage C3 Refrigeration System

~120°F

240 Psia

- 40°F

16 Psia

60 Psia 250 PsiaCondenser

JT-Valve

Receiver

62 Psia

Interstage

Economizer

Chiller / Evaporator

-40°F, 16 Psia

JT-Valve

62 Psia

Chiller/

Evaporator

2 Stage C3 Refrigeration System

~120°F

240 Psia

- 40°F

16 Psia

60 Psia 250 PsiaCondenser

JT-Valve

Receiver

62 Psia

Interstage

Economizer

Chiller / Evaporator

-40°F, 16 Psia

Refrigeration cycle

Benefits of Staging

Condenser Temp = 100oF Chiller Temp = -40oF

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

Methane Expansion – Isentropic vs. Isenthalpic

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

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)

Dew Point Control (No External Refrigeration)

Condensate

Stabilizer

Glycol

Regenerator

Condensate

Rich Glycol

Temperature

Separator

Gas from

Knockout

Residue Gas

Dew Point Control (With External Refrigeration)

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

Example Dew Point Control Package

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

Membrane for Fuel Conditioning

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

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

Refrigerated Process

Cold Separator

C3 Chiller

Fractionator

CompressorAir Cooler

Inlet Gas

Product

Reboiler

Residue

Effect of Composition on C3+ Recovery

-40 -30 -20 -10 0 10 20

Process Temperature, °F

Recovery Efficiency of C2 and C3

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

Process Temperature, °F

7 GPM 3 GPM

Refrigerated Lean Oil

Inlet Gas

Residue Gas

Cold C3 Liquid

Absorber Rich Oil

Demethanizer

Low Pressure

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

Considerations for Cryogenic Distillation

1st Generation Cryo Process

Brazed Aluminum Heat Exchanger – “Cold Box”

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

GSP Schematic

Effect of Inerts on Max C2 Recovery

0 2 4 6 8 10 12 14

Nonhydrocarbon Content, mol %

Propane Recovery Processes

GPSA Engineering Data Book, 14th ed.

Ethane Recovery Processes

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

Chapter 12 Based on presentation by Prof. Art...

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