New Zealand The University of Auckland Modelling Dual

New Zealand The University of Auckland Modelling Dual Reflux Pressure Swing Adsorption for Methane and Nitrogen Separations in LNG Production Yechun Zhang 1 yechun. zhang@auckland. ac. nz Thomas Saleman 2, Eric May 2 and Brent Young 1 1: The Department of Chemical and Materials Engineering, The University of Auckland, Auckland 1010, New Zealand 2: School of Mechanical and Chemical Engineering, The University of Western Australia, Crawley WA 6009, Australia

WA's North West Shelf Project 29 October 2021 Pluto Gorgon Prelude Wheatstone The University of Auckland New Zealand Ichthys Resource 5. 0 TCF 47. 3 TCF 295 MMbblc 2. 8 TCF 120 MMbblc 4. 5 TCF 12. 8 TCF 527 MMbblc Estimated Start-up Proposed Capacity Concept [mmtpa] 2012 4. 3 2014 15 2016 3. 6 2016 8. 9 2018 8. 4 LNG Plant at Burrup Peninsula LNG Plant on Barrow Island Floating LNG Plant at Onslow LNG Plant at Darwin Significant offshore gas fields with production since 1989 Estimated $140 B investment in next 10 years (most committed) N 2 vent streams from plants contain 3% CH 4: 435000 CO 2 e tonnes per annum in greenhouse emissions Page 2

New Zealand 29 October 2021 Conventional PSA to Capture the CH 4 • Consider conventional PSA cycles to achieve 100 ppm CH 4 in N 2 vent Lean Product (< 100 ppm CH 4) • Challenges - Low CH 4 selectivity for current adsorbents - Waste stream barely enriched HP LP Feed Waste (CH 4 enriched) - Unviable numbers of beds required The University of Auckland • Solutions - Require a new adsorbent with high selectivity (6 -10) - Process engineering design Page 3

New Zealand 29 October 2021 Dual Reflux PSA • Theoretically produces 2 pure products from binary mixture 1 -3 • Experimental demonstrations show: 1. Enrichment ratios well beyond The University of Auckland standard thermodynamic limit 2. Lean products with <100 ppm contaminants possible 1 Diagne, D. , Goto, M. , Hirosi, T. , 1994. . Journal of Chemical Engineering Japan 27 (1), 85– 89. 2. A. Ebner and J. Ritter AICh. E Journal. Volume 50, Issue 10, pages 2418– 2429. 3. J. A. Mc Intyre, C. E. Holland, and J. A. Ritter. Ind. Eng. Chem. Res. 2002, 41, 3499 -3504. Page 4

Possible Process Design Solution: Dual Reflux PSA 29 October 2021 Lean Product (N 2) The University of Auckland New Zealand • Intermediate feed position HP LP • Feed to HP or LP Stripping PSA HP LP Feed Enriching PSA Rich Product (CH 4) Page 5

29 October 2021 Evaluating DR-PSA Viability Question: How to evaluate DR-PSA for N 2/CH 4 separation required by LNG industry? New Zealand Strategy: a) Conduct modelling to establish whether DR-PSA solution is economically viable The University of Auckland b) If true, then proceed with prototype experiments. What modelling tools available for viability screening purpose? Page 6

29 October 2021 “Analytical” Model of Kearns & Webley for Screening • Started with understanding Kearns & Webley’s analytical model of DR-PSA • Method of characteristics to reduce PDE to ODE’s • Analytical solution solved using numerical techniques Pros New Zealand - Insight into the process - Fast Solution - Search optimized parameters Cons - Idealized: assumes perfect separation - Can not be tested against experimental data The University of Auckland - Can’t be sure optimum found will actually achieve product specifications • Need a more realistic model to test optimum solution’s ability to achieve product specifications - Transfer function model – achieve goals faster and easier - Full numerical simulation of DR-PSA – still under development Page 7

29 October 2021 Transfer Function: Stripping • What is transfer function model? Lean Product Feed Stripping PSA The University of Auckland New Zealand (Transfer function) Waste Aspen Adsorption Page 8

29 October 2021 Transfer Function: Enriching Rich Product Feed Enriching PSA The University of Auckland New Zealand (Transfer function) Waste Aspen Adsorption Page 9

The University of Auckland New Zealand 29 October 2021 Transfer Function Model • Steady-state results from stripping & enriching PSA cycle simulations give half-cycle transfer functions (TFs) • Combine TFs & iteratively solve material balance • Test against Mc. Intyre et al. ’s experimental results 1 • Test optimized parameters from analytical model 1 J. A. Mc Intyre, C. E. Holland, and J. A. Ritter. Ind. Eng. Chem. Res. 2002, 41, 3499 -3504. 2 Lean Product Stripping Reflux PSA (Transfer function) 1 3 6 4 Feed 7 Enriching Reflux PSA (Transfer function) 5 Rich Product Page 10

2010 Scenario 1 Transfer (RS=0. 382, Function RE=72. 3) 1 Model Results Item Inputs Feed Rate (sccm) Lean Product Flow (sccm) Rich Product Flow (sccm) Total Cycle Flow (sccm) y. Feed Results The University of Auckland New Zealand 29 October 2021 Comparison with C 2 H 6/N 2 result of Mc. Intyre et al. y. Lean Product (ppm) y. Enriched Product N 2 Recovery C 2 H 6 Recovery 583. 6 573. 0 10. 63 733 1. 35% 2900 62. 6% 99. 2% 80. 8% 583. 3 573. 1 10. 30 723 1. 35% 2000 63. 9% 99. 4% 83. 2% 1 J. A. Mc. Intyre, Armin D. Ebner, and J. A. Ritter. Ind. Eng. Chem. Res. 49, 2010, 1848– 1858. Page 11

29 October 2021 Comparison with C 2 H 6/N 2 result of Mc. Intyre et al. Mean Deviations Item 2002 2010 Mean Scenario 1 Scenario 3 Scenario 1 Scenario 6 Deviation 0. 05% 0. 04% -0. 09% 0. 06% -2. 90% -4. 60% 1. 27% -5. 10% 3. 47% Rec. LP -1. 70% -0. 40% 0. 14% -0. 10% 0. 59% Rec. HP -5. 70% -4. 70% 2. 42% -5. 10% 4. 48% The University of Auckland New Zealand y. L (full %) y. E (full %) Page 12

29 October 2021 Apply TF model to Analytical Optimum Item Inputs Results The University of Auckland New Zealand Pressure Ratio Transfer Function Analytical Model using with Optimized Analytically Alternate Parameters Optimized Parameters 1. 9 3 5. 0 MMscfd 0. 85 MMscfd 0. 445 0. 5 Stripping Reflux Ratio 2. 7 10. 1 Enriching Reflux Ratio 199 8. 1 Lean Product 0% 2. 91% 0. 085% Rich Product 100% 10. 04% 5. 1% Methane Recovery Rate 100% 4. 42% 98. 8% Throughput Feed position Page 13

The University of Auckland New Zealand 29 October 2021 Conclusions and Future Work • Conclusions - Transfer Function Model were proposed - Showed close match with experimental data • Future work - Full DR-PSA model is available and under test - Proposed the first DR-PSA sizing tool and being extended - Conduct optimum search with transfer function model - Laboratory DR-PSA apparatus to test real CH 4/N 2 separation under construction Page 14

29 October 2021 Full Numerical Model of DR-PSA • Four column configuration with intermediate feed • Available for Feed to High Pressure New Zealand column • Unstable pressure-flow network observed • The University of Auckland • • Backflow at feed Switch to “ideal” compressor “Ideal” compressor Preliminary tests done (CH 4/N 2) • T, CH 4% in feed, axial feed position, cycle time “Real” compressor Page 15

29 October 2021 Preliminary Sizing Tool of DRPSA • First-order DR-PSA sizing tool • Enables rough estimation of DR-PSA column size & scale The University of Auckland New Zealand • Integrate stripping PSA with enriching PSA using idea of Transfer Function Model • • Estimate size of stripping part • Estimate size of enriching part Adding up and check output • Compromise in calculating gas residence time Page 16

The University of Auckland New Zealand 29 October 2021 Thank you Page 17

High pressure -> intermediate pressure Extract (N 2 enriched) 1 2 Pressure Equalization Low pressure desorption High pressure adsorption New Zealand 29 October 2021 Conventional PSA Cycles The University of Auckland 1 Feed Raffinate (C 1 enriched) Adsorption/Desorption Low pressure -> intermediate pressure 1 2 Depressurization/ Pressurization 2 1 Intermediate pressure > low pressure 2 Intermediate pressure -> high pressure Page 18

Transfer Function Model The University of Auckland New Zealand 29 October 2021 Pros and Cons Pros - Flexible source of TF (experiment or simulation) - Faster & more stable than full numerical model of DRPRSA - Reasonable match to Cons - CCS only - Operates as separate columns - Averaged flow between stripping & enriching PSA - Slower than analytic solution available experimental data Page 19

Research Motivation 29 October 2021 • Greater Gorgon LNG production: 1000 MMSCFD • N 2 contamination in raw gas New Zealand • Methane concentration in N 2 vent: ~3% • Substantial GHG emission and carbon tax! The University of Auckland (AU$23/ton) 435, 000 t CO 2 e -> 10 M AU$ for Gorgon • Objective Source: Finn et al. 2007 3%->100 ppm Page 20

The University of Auckland New Zealand 29 October 2021 DR-PSA Model Results Page 21

The University of Auckland New Zealand 29 October 2021 DR-PSA Model Results Page 22

The University of Auckland New Zealand 29 October 2021 DR-PSA Model Results Page 23

The University of Auckland New Zealand 29 October 2021 DR-PSA Model Results Page 24