Nitrogen Rejection Unit Design Options

©2019 ConocoPhillips CompanyOptimized Cascade® is a registered trademark of ConocoPhillips Company

in the United States and certain countries

ConocoPhillips LNG Engineering & Operations

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ManagerFilippo Meacci

LNG Conceptual Process Engineering Supervisor

LNG Operations SupervisorLNG Process Engr. & Tech. Support Supervisor

Engineering FellowWes Qualls

Principal Process Engineer

Principal Process Engineer

Staff Process Engineer

Staff Process Engineer

Staff Process Engineer

Staff Process Engineer

Principal Process Engineer

Staff Process EngineerStaff Process Engineer

Senior Process Engineer

Presentation Overview

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What is a Nitrogen Rejection Unit (NRU)? When is an NRU Required? Where in the LNG Process is the NRU? Key Points Options

Warm NRU Cold NRU Refluxed Third Column

Nitrogen Rejection Unit – Key Points

What is an NRU A Nitrogen Rejection Unit (NRU) Separates and Vents Nitrogen (N2) to the Atmosphere, While

Returning Recovered Hydrocarbon Streams to the Main Liquefaction Process or Routing to Fuel Two to Three Fractionation Columns are Combined With two or More Multi-Pass Brazed

Aluminum Heat Exchangers, Usually Within a Cold Box. The Atmosphere Contains About 78 mol% N2

When do You Need and NRU An NRU is Typically Required When Feed N2 Concentrations Exceed the Amount that can be

Rejected to Fuel. Higher Fuel Gas Requirements Results in Greater Ability to Displace N2. Typically if Feed Gas Contains >1.5 mol% N2 (Downstream of Acid Gas Removal Unit),

Depending on Fuel Requirements

Where do You Place an NRU Typically Located on the End Flash of Competing LNG Technologies Integrated into the Methane Refrigeration System for the Optimized Cascade Process

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Cryogenic NRU Processes are Highly Heat Integrated

NRUs Within LNG Facilities are Typically Cryogenic Auto-refrigeration Processes.The Pressure Reduction of each Successive Column Bottoms Liquids Results in Lower

Temperatures, Which is Then Used to Condense the Successive Column Feed Streams.

Typical N2 Vent Purity Specifications for Methane (C1) are ≤1 mol%.Options to Reduce C1 in the Vent Include Additional NRU Equipment or Thermal or Catalytic

OxidationThe N2 Vent May be Further Processed to Recover Helium

Typical LNG Products Specifications for N2 are ≤1 mol%Typical Optimized Cascade Project LNG N2 Concentrations are Lower than 0.5 mol%.

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Nitrogen Rejection Unit – Key Points

NRU Options Within Optimized Cascade LNG Process

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Warm NRU High Efficiency No Dedicated Rotating Equipment for Feed or Product Streams Required

• Third Column Bottoms Pump Optional Less Heat Integration With Main Liquefaction Facility

• Ability to Bolt On at Later Date (Future N2 Case)

Cold NRU Higher Efficiency Higher Stability No Dedicated Rotating Equipment for Feed or Product Streams Required

• Third Column Bottoms Pump Optional Faster Controls Response More Heat Integration With Main Facility

• Rapid Startup Times• Responds Quickly to Changes in Feed N2

Option Available for All Stainless Steel Exchangers Refluxed Third Column

Strict Restrictions on C1 in N2 Vent

Auto-Refrigeration Provides Natural Process Feedback

With Feedback, NRU Feed Disturbances Can Result in Even Greater NRU Feed Disturbances

Variations in Temperature, Pressure, Concentration & Flow Should be Avoided if Possible

Auto-Refrigeration Processes are Time Consuming to Cooldown and Startup

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The Key to Successful NRU Design is Understanding & Mastering Feedback

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Variable NRU Feed Conditions Result in: Variable Vapor/Liquid Flows to HS Column Variable HS Column Levels

Variable HS Column Levels Results In: Variable HS Column Bottoms Liquid Flow Variable Condensing Duty For HS Column Feed Variable Flow Rates to IS Column Variable IS Column Levels

Variable IS Column Levels Result in: Variable IS Column Bottoms Liquid Flow Variable Condensing Duty for IS Column Feed Variable Flow Rates to LS Column Variable LS Column Levels

Variable LS Column Levels Result in: Variable LS Column Bottoms Liquid Flow Variable Condensing Duty for LS Column Feed Variable N2 Vent Flow & Composition

Traditional Warm NRU Feedback Cycles – Typical for Industry

Mastering Feedback

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Process Design Details Correctly Identify Stream Flow Regimes Layout Equipment to Avoid Slug Flow (Especially Riser Slugging) Include Sufficient Vessel Residence Time

Instrumentation & Controls Design Details Select Proper Control Valve Trim for Application Include Temperature, Pressure & Flow Indication for Controls Philosophy Select the Most Sensitive Locations for Temperature Control Include Sufficient Piping Straight-Run Distances for Equipment & Flowmeters Feed Forward Decouple Controls to Minimize Feedback Disturbances

Optimized Cascade Cold NRU Approach

Cold NRU Design

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US Patent 9,335,091 B2

Heat Integration with Main Liquefaction Plant to Avoid Auto-refrigeration Feedback

Cold NRU – Key Design Principles External Refrigerant From Main Liquefaction Unit Used to Condense HS Column Feed

Traditional NRUs Condense Feed with Recycled Column Bottoms Liquid. Feedback (Auto-refrigeration)

External Heat Source From Main Liquefaction Facility Used to Reboil HS Column Traditional Warm NRUs Utilize the NRU Feed to Provide HS Column Heat Duty

Condensed HS Column Reboiler Heat Duty Stream Routed to Main Liquefaction Plant The Heat Duty Stream Utilized Would Normally be Condensed & Routed to LNG Regardless Reboiler Duty Does Not Require Additional Process Heat Removal

HS Column Bottoms Liquids Routed to Main Liquefaction Plant With Little Pressure Loss Traditionally Bottoms Liquids are Flashed to a Lower Pressure to Utilize the Lower Temperatures as Feed Condensing Duty Traditionally the Liquids Flashed to Lower Pressures Requires Vaporization, Superheating, Compression & Recondensing

External Refrigeration & Heat Duty Provides Direct and Rapid Controls Response Condensing Duty for Traditional Warm NRUs Incurs Feedback Delay

External Refrigeration & Heat Duty Provides Better Control of the HS Column Overhead Composition Anchoring the Overhead Composition Minimizes Feedback Disturbances For Remaining Downstream Columns

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Variable NRU Feed Conditions DO NOT Result in: Variable Vapor/Liquid Flows to HS Column Variable HS Column Levels

STABLE HS Column Levels Results In: Variable HS Column Bottoms Liquid Flow STABLE Flow Rates to IS Column

Variable IS Column Levels Result in: Variable IS Column Bottoms Liquid Flow Variable Condensing Duty for IS Column Feed Variable Flow Rates to LS Column Variable LS Column Levels

Variable LS Column Levels Result in: Variable LS Column Bottoms Liquid Flow Variable Condensing Duty for LS Column Feed Variable N2 Vent Flow & Composition

NRU High Stage (HS), Interstage (IS) & Low Stage (LS) Feedback Cycles

HS Column Adjusts to Fix Composition to IS and LS Columns to Minimize LS Column Feedback

Summary Pros & Cons of Cold NRU

Pros Faster & Easier to Cool Down

Feed to NRU is Already Cold Cool Down as Quickly as LNG Facility

More Stable, Flexible & Reliable Downstream Column Feedback Eliminated Faster & More Direct Controls ResponseAbility to Anchor HS Column OH CompositionOne Multi-pass Exchanger EliminatedAllows for all Stainless Steel Equipment

Higher Thermal Efficiency Feed to NRU Already Cold Some Liquid Products Dumped to LNG Rather Than

Re-vaporized and Recycled

Cons Additional Equipment Required

External Feed Condenser External Bottoms Reboiler

Additional Integration With LNG Facility Less Conducive to Later Bolt-on Approach Than

Warm NRU Design (Future N2 Case)Higher Cost – Additional Equipment Equipment & Piping Layout and Hydraulics With

Remaining Facility Requires More Design Attention to Detail

Nitrogen Rejection Unit Design – Simplified Decision Chart

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Nitrogen Rejection Unit Options

Little Nitrogen Moderate Nitrogen

Stable Concentration

Significant Nitrogen

Reject to Fuel

Warm or Cold NRU

Cold NRU

Variable Concentration

Cold NRU

Future Nitrogen Case

Warm NRU

Optional Refluxed Third NRU Column Designs Available for Both Warm And Cold NRUs for Improved Vent Purity Control

Licensed Optimized Cascade Process – Warm & Cold NRUs

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Kenai LNG1.5 MTPA, 1969

Corpus Christi LNG13.5 MTPA, 2018

Atlantic LNG14.8 MTPA, 1999-2005

Egypt LNG7.2 MTPA, 2005

Darwin LNG3.7 MTPA, 2006

Equatorial Guinea LNG3.7 MTPA, 2007

Angola LNG5.2 MTPA LNG, 20131.7 MTPA NGL

Queensland Curtis LNG8.5 MTPA, 2014 -2015

Gladstone LNG7.8 MTPA, 2015

Wheatstone LNG8.9 MTPA, 2017 -2018

Australia Pacific LNG9.0 MTPA, 2015 - 2016

Sabine Pass LNG22.5 MTPA, 2015 -2018

Warm NRUCold NRU

Conclusions

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NRU Options Available for Wide Range of Compositions No Rotating Equipment on Feed or Product Streams

• Bottoms Pump on Third Column Optional Warm NRU Option

• Small Amounts of N2

• Future N2 Cases (Bolt-On Solution) Cold NRU

• Moderate to Large Amounts of N2 From Outset of Design Refluxed NRU Options

• Strict N2 Vent Purity Requirements

Stable Operation (All Options) Through Design Attention to Detail

• Equipment• Piping• Controls

N2 Vent Purity Requirements Achieved

Discussion