Membranes for Gas Conditioning Hope Baumgarner Chelsea Ryden

How is natural gas currently processed?

Current Natural Gas Processing Sulfur Recovery Well & Condensate Removal Amine Unit Dehydration Problem needs to be more clear don’t start off with this much detail audience will be confused Nitrogen Rejection Natural Gas Liquid Fractionation Natural Gas Liquid Recovery Sale Gas

Amine Unit: CO2 and H2S Removal Sour Gas Treated Gas Wash Water CO2 Lean Amine Inlet Separator Cooler Filter Water Wash Drum Lean Amine Pump Cross Exchanger Stripper Amine Solution Tank Reboiler Pressurized Hot Water Water Condenser CO2 & H2S Removed Rich Amine Pump Amine Pump Water Wash Pump To Atmosphere Rich Amine Flash Drum Contactor

Current Natural Gas Processing Well & Condensate Removal Amine Unit Sulfur Recovery Dehydration Nitrogen Rejection Natural Gas Liquid Recovery Natural Gas Liquid Fractionation Sale Gas Problem needs to be more clear don’t start off with this much detail audience will be confused

Claus Unit: Sulfur Recovery Furnace Catalytic Section Liquid Sulfur Tail Gas 1000-1400°C Overall Reaction: 2H2S+O2 S2 + 2H2O Thermal Reaction: 2H2S +3O2 2SO2 + 2H2O Catalytic Reaction: Al2O3 2H2S+SO2 3S + 2H2O Problem needs to be more clear don’t start off with this much detail audience will be confused

Current Natural Gas Processing Sulfur Recovery Well & Condensate Removal Amine Unit Dehydration Problem needs to be more clear don’t start off with this much detail audience will be confused Nitrogen Rejection Natural Gas Liquid Fractionation Natural Gas Liquid Recovery Sale Gas

Glycol Dehydration Unit Rich Glycol Wet Gas Lean Glycol Glycol Contactor Filter Reboiler Flash Gas Water Vapor Problem needs to be more clear don’t start off with this much detail audience will be confused

Current Natural Gas Processing Sulfur Recovery Well & Condensate Removal Amine Unit Dehydration Problem needs to be more clear don’t start off with this much detail audience will be confused Nitrogen Rejection Natural Gas Liquid Fractionation Natural Gas Liquid Recovery Sale Gas

Nitrogen Rejection Nitrogen Vent Feed Gas Condenser Low Pressure Column High Pressure Column Reboiler Problem needs to be more clear don’t start off with this much detail audience will be confused

Current Natural Gas Processing Sulfur Recovery Well & Condensate Removal Amine Unit Dehydration Problem needs to be more clear don’t start off with this much detail audience will be confused Nitrogen Rejection Natural Gas Liquid Fractionation Natural Gas Liquid Recovery Sale Gas

Natural Gas Liquid Recovery Natural Gas Feed Refrigerant Turbo Expander Sale Gas Demethanizer Cold Reflux Compressor Cold Separator NGL Problem needs to be more clear don’t start off with this much detail audience will be confused

Current Natural Gas Processing Sulfur Recovery Well & Condensate Removal Amine Unit Dehydration Problem needs to be more clear don’t start off with this much detail audience will be confused Nitrogen Rejection Natural Gas Liquid Fractionation Natural Gas Liquid Recovery Sale Gas

Natural Gas Liquid Fractionation Deethanizer Depropanizer Debutanizer Recycle Vapor Propane Product Butane Product Reboiler Condenser Reflux Drum Problem needs to be more clear don’t start off with this much detail audience will be confused

Overview of Problem Overall Goal Explore the use of membrane networks in the separation of CO2, H2S, N2, & heavier hydrocarbons from natural gas Specific Goal Addressed in This presentation Separation of CO2 9 % CO2 89 % CH4 0.001% H2S 0.98 % C2H6 0.57 % C3H8 0.35 % C4H10 0.1 % N2 1.9 % CO2 97 % CH4 0.0001% H2S 0.68 % C2H6 0.25 % C3H8 0.09% C4H10 0.08 % N2 94% CO2 1.19 % CH4 0.03% H2S 2.14% C2H6 1.18% C3H8 0.86% C4H10 0.60% N2

Membranes Separates based on diffusion and solubility Overview of Problem Membranes Separates based on diffusion and solubility Membrane Network Simple case

Current Technology: Amine Absorption Overview of Problem Current Technology: Amine Absorption Sour Gas Treated Gas Wash Water CO2 Lean Amine Inlet Separator Cooler Filter Water Wash Drum Lean Amine Pump Cross Exchanger Stripper Amine Solution Tank Reboiler Pressurized Hot Water Water Condenser CO2 & H2S Removed Rich Amine Pump Amine Pump Water Wash Pump To Atmosphere Rich Amine Flash Drum Contactor

Existing cost comparison for membrane unit vs. amine unit Overview of Problem Existing cost comparison for membrane unit vs. amine unit

How do membranes work?

Membrane Theory Ideal membrane High permeance = High separation factor (selectivity) = A, B = components yi = mole fraction in permeate xi = mole fraction in retentate

Membrane Theory Fick’s Law describes mass transport Ni= molar flux species i Di= diffusivity component i lm= membrane thickness

Membrane Theory Assume thermodynamic equilibrium at interface Fick’s Law can be related to partial pressure by Henry’s Law Assume Hi independent of total pressure and same temperature at both interfaces

Membrane Theory Combining equations Neglecting external mass transfer resistances Substituting

Membrane Theory Where permeability depends on the solubility and the diffusivity High flux with thin membrane and high pressure on the feed side permeance

Membrane Designs

Common Membrane Modules Spiral wound <20% of membranes formed High permeances and flux More resistant to plasticization High production cost: $10-100/m2 Allow wide range of membrane materials

Common Membrane Modules Hollow Fiber Most common More membrane area per volume Low production cost: $2-5/m2 Low reliability due to fouling Careful and expensive treatment

Common Membrane Modules Spiral-Wound Hollow-Fiber Packing Density, m2/m3 200-800 500-9,000 Resistance to fouling Moderate Poor Ease of cleaning Fair Relative cost Low Main applications D, RO, GP, UF, MF D, RO, GP, UF D=Dialysis, RO=Reverse Osmosis, GP=Gas Permeation, PV=Pervaporation, UF=Ultrafiltration, MF=Microfiltration

Membrane Material Permeated Component Preferred Polymer Material Polymer used Selectivities over CH4 (%) CO2 Glassy Cellulose Acetate Polyimide Perfluoropolymer 10-20 H2S Rubbery Amide block co-polymer 20-30 N2 Silicone rubber 2-3 0.3 H2O Rubbery/Glassy several >200 C3+ 5-20 Table 1. Typical selectivities for high pressure natural gas (Baker & Lokhandwala)

Membrane Material Glassy Polymer Temperature below glass transition point Glassy Polymer Polymer chains fixed, rigid & tough Separate gases based on size

Membrane Material Rubbery Polymer Temperature above glass transition point Rubbery Polymer Motion of polymer chain material becomes elastic & rubbery Separate gases based on sorption

Membrane Material Non-reactive to most organic solvents Cellulose Acetate High CO2 / CH4 selectivity Lower H2S / CH4 selectivity High Permeability to water vapor BTEX: stands for Benzene, Toluene, Ethylbenzene, & Xylene Polyimide Rigid, bulky, non-planar structure Inhibited local motion of polymer chains

Membrane Advantages and Disadvantages

Membrane Advantages Lower capital cost Skid mounted Cost and time are minimal Lower installation cost Treat high concentration gas Membrane plant treating 5 mil scfd w/ 20% CO2 would be less than half the size of plant treating 20 mil scfd w/ 5% CO2

Membrane Advantages Operational simplicity Unattended for long periods (Single Stage) Start up, operation, and shutdown can be automated from a control room with minimal staffing (Multistage) Space efficiency Skid construction Offshore environments

Membrane Advantages Design efficiency Integrate operations Dehydration, CO2 & H2S removal, etc. Power generation Reduce electric power/fuel consumption Ecofriendly Permeate gases used as fuel or reinjected into well

Membrane Disadvantages Plasticization Membrane materials absorb 30-50 cm3 of CO2/cm3 polymer Absorbed CO2 swells and dilates the polymer Increases mobility of polymer chains Decreases selectivity Physical aging Glassy polymers are in nonequilibrium state Over time, polymer chains relax, resulting in lower permeability

Membrane Disadvantages High compressor cost Membranes only 10-25% of total cost Significant reductions in membrane cost might not markedly change total plant cost Compressor cost is 2-3 times the skid cost

Membrane Network

2 Membrane Network 3 Membrane Network Membranes, compressors, mixers, splitters, streams 2 Membrane Network 3 Membrane Network How do we find the membrane network? Superstructure

Superstructure allows for all possible network configurations

Superstructure For example:

Superstructure Resulting membrane network:

How do we build this superstructure?

Mathematical Model Mathematical programming model Assumptions: Countercurrent flow in hollow fiber module Uniform properties in each segment Steady-state No pressure drop across permeate or retentate side Constant permeabilities independent of concentration No diffusion in axial direction Deformation not considered

Hollow Fiber Mathematical Model Flux through membrane Shell side component balance Tube side component balance

Hollow Fiber Mathematical Model Mixer/Splitter Balances Feed balance

Hollow Fiber Mathematical Model Mixer/Splitter Balances Splitter balance 1 2

Hollow Fiber Mathematical Model Mixer/Splitter Balances CO2 composition rcomp=0.02

Hollow Fiber Mathematical Model Mixer/Splitter Balances Mixer Balance 1 2

Hollow Fiber Mathematical Model Permeate power 1 2

Hollow Fiber Mathematical Model Non-linear equations in model Non-linear equations discretized to give linear program

Annual Process Cost: minimized Objective Function Annual Process Cost: minimized Fcc: Capital Charge Fmr: Membrane Replacement Fmt: Membrane Maintenance Fut: Utility Cost Fpl: Cost of Product loss

Objective Function Fixed Capital Investment: fmh: Membrane Housing ($200/m2) fcp: Capital Cost of Gas Powered Compressor ($1000/kW) Wcp: Compressor Power (kW) ηcp: Compressor efficiency (70%)

fcc: Capital Charge (27%/yr) fwk: Working Capital (10% Ffc) Objective Function Capital Charge: fcc: Capital Charge (27%/yr) fwk: Working Capital (10% Ffc)

Objective Function Membrane Replacement: fmr: Membrane Replacement ($90/m2) tm: Membrane Life (3 yr)

Objective Function Membrane Maintenance: fmt: Membrane Maintenance (5% Ffc)

Objective Function Utility Cost: fsg: Utility and Sale Gas Price ($35/Km3) fhv: Sales Gas Gross Heating Value (43 MJ/ m3) twk: Working Time (350 days/yr)

Objective Function Product Loss: mp : total flow rate of methane in permeate

How is this implemented?

Set and Parameter Declaration Program Set and Parameter Declaration Variable Declaration

Program Equations

Program

Results

Results

2 Membrane Network at 79 lb-mol/hr 0.42 kW Objective function: $163,000 % CH4 lost: 11.20

3 Membrane Network at 79 lb-mol/hr Objective function: $130,000 %CH4 lost: 7.77

4 Membrane Network at 79 lb-mol/hr Objective function: $130,000 %CH4 lost: 7.77

Objective Function ($) Results: Comparison Objective Function ($) Area (m2) Wcp (KW) % CH4 Lost 2-Membrane Network 163,000 160 0.42 11.2 3-Membrane Network 130,000 435 80 7.77 4-Membrane Network Comparison between membrane models at 79 lb-mol/hr

3 Membrane Network at 127 lb-mol/hr Objective function: $230,000 %CH4 lost: 9.44

3 Membrane Network at 238 lb-mol/hr Objective function: $539,000 %CH4 lost: 10.90

Membrane Network Verification

Membrane Network Verification Compressor Model Work (kW) Pro-II Work (kW) C1 82.1 82.9 C2 39.1 39.5 C3 8.3 8.4 C4 93.6 94.7 C5 44.5 44.2 Work comparison for 238 lb-mol/hr

Results Total Annualized Cost vs. flow rate for an amine unit and 3 membrane network at 19% CO2 in the feed

Results: Cost Analysis Flow rate (MMscfd) FCI ($) Operating Cost ($/yr) TAC ($/yr) 15 yr. Membrane 90 30.6 M 13 M 15 M 180 61 M 26 M 30 M 270 92 M 39 M 45 M 365 123 M 52 M 60 M 455 153 M 65 M 75 M 550 184 M 77 M 90 M Amine 3 M 21 M 5.4 M 7.8 M 37 M 38 M 9.7 M 43 M 44 M 12 M 49 M 50 M 14 M 54 M 55 M Comparison between 3 membrane network and amine unit at 19 %CO2

Results Adjusted existing cost for membrane network

Results

Results Total Annualized Cost vs. flow rate for an amine unit and 3 membrane network at 9% CO2 in the feed

Results: Cost Analysis Flow rate (MMscfd) FCI ($) Operating Cost ($/yr) TAC ($/yr) 15 yr. Membrane 90 18M 9M 10M 180 36M 20M 270 55M 27M 31M 360 73M 41M 455 91M 45M 51M 550 109M 54M 61M Amine 5M 12M 6M 17M 7M 22M 8M 26M 29M 30M 11M 33M Comparison between 3 membrane network and amine unit at 9 %CO2

Recommendations Membrane networks have an overall lower total annualized cost and utility cost compared to an amine unit at flow rates less than 200 MMscfd Cost evaluation for membranes to replace other gas conditioning units CO2 concentrations other than 20% need to be investigated in more detail

Questions?

References Baker, Richard. “Future Directions of Membrane Gas Separation Technology.” Industrial & Engineering Chemistry Research. 2002. Sarkey’s Senior Lab. 7 Feb. 2009. <http://pubs.acs.org> Baker, Richard and Kaaeid Lokhandwala. “Natural Gas Processing with Membranes: An Overview.” Industrial & Engineering Chemistry Research. 2008. Sarkey’s Senior Lab. 4 Feb. 2009 <http://pubs.acs.org>. Kookos, I.K. “A targeting approach to the synthesis of membrane network for gas separations” Membrane Science, 208, 193-202, 2002. Mohammadi, T., Moghadam, Tavakol, and et al. “Acid Gas Permeation Behavior Through Poly(Ester Urethane Urea) Membrane.”Industrial & Engineering Chemistry Research. 2008. Sarkey’s Senior Lab. 4 Feb. 2009 <http://pubs.acs.org>. Natural Gas Supply Association. 2004. Sarkey’s Senior Lab. 7 Feb. 2009 <http://www.naturalgas.org/index.asp>. Perry, R.H.; Green, D.W. (1997). Perry’s Chemical Engineers’ Handbook (7th Edition). McGraw-Hill. Seader, J. D., and Henley, E. J. "Separation Process Principles.” New York: John Wiley & Sons, Inc., 1998.

APPENDIX

Membrane Simulation Results Figure 1. Molar compositions with varying membrane area. CO2 flow rate: 0.2 CH4 flow rate: 0.8

2 Membrane Network at 79 lb-mol/hr @ 19%CO2 0.42 kW

3 Membrane Network at 79 lb-mol/hr @ 19%CO2

Programming Output

Programming Output

Programming Output

Programming Output

3 Membrane Network at 127 lb-mol/hr @ 19%CO2

3 Membrane Network at 238 lb-mol/hr @ 19%CO2

3 Membrane Network at 79 lb-mol/hr @ 9% CO2

Hollow Fiber Mathematical Model Discrete Equations Lower bound component flow rate tube side : discrete variable : binary variable : total flow rate 1 0.25 0.75 0.50 1 2 3 4 segments binary variables

Hollow Fiber Mathematical Model Discrete Equations Upper bound component flow rate tube side : discrete variable : binary variable : total flow rate 1 0.25 0.75 0.50 1 2 3 4 segments binary variables

Amine Unit Simulation

Equipment & Utility Cost at 79 lb-mol/hr Columns Type No. of trays Operating pressure Cost 1 Absorber Valve trays 6 250 psia $15,334 2 Stripper 12 16 psia $32,736 Exchangers MOC Duty (MMBtu/hr) Area (ft2)   Rich amine / Lean amine Stainless Steel 16.45 241.73955 $4,772 Lean amine / water 10.96 37.191652 $2,651 3 6.098 28.193677 $2,439 Pump Power (HP) Pump lean amine solution 130 $1,803 Valve Diameter (m) Rich amine expansion valve 0.2 Flanged $8,484 MDEA initial amt cost $552 Total $68,771 Cooling water Flow(1000 kg/hr) Price ($ /m3) Cost ($ / yr) 17.53959549 0.29 $42,726 Natural gas as heating utility for reboiler Reboiler (MMBtu/hr) Price ( $ / MMBTU)   2.73 5 $114,516 Electricity Duty (kW) Price ($ / kWh) 4.42 0.062 $2,301.94 MDEA Recycle Flow (lb/hr) Price ($/lb) 0.11917 1.54 $1,541.58 Total $161,086

Equipment & Utility Cost at 127 lb-mol/hr Columns Type No. of trays Operating pressure Cost 1 Absorber Valve trays 6 250 psia $15,424 2 Stripper 12 16 psia $37,434 Exchangers MOC Duty (MMBtu/hr) Area (ft2)   Rich amine / Lean amine Stainless Steel 16.45 711.08872 $9,544 Lean amine / water 10.96 94.337643 $3,075 3 6.098 185.37014 $4,242 Pump Power (HP) Pump lean amine solution 130 $1,909 Valve Diameter (m) Rich amine expansion valve 0.2 Flanged $8,484 MDEA initial amt cost $701 Total $80,813 Cooling water Flow(1000 kg/hr) Price ($ /m3) Cost ($ / yr) 44.80690133 0.29 $109,150 Natural gas as heating utility for reboiler Reboiler (MMBtu/hr) Price ( $ / MMBTU)   6.96 5 $292,374 Electricity Duty (kW) Price ($ / kWh) 11.2611 0.062 $5,864.78 MDEA Recycle Flow (lb/hr) Price ($/lb) 0.11917 1.54 $1,541.58 Total $408,930

Equipment & Utility Cost at 238 lb-mol/hr Columns Type No. of trays Operating pressure Cost 1 Absorber Valve trays 6 250 psia $27,932 2 Stripper 12 16 psia $53,235 Exchangers MOC Duty (MMBtu/hr) Area (ft2)   Rich amine / Lean amine Stainless Steel 16.45 804.06735 $15,907 Lean amine / water 10.96 113.88082 $4,242 3 6.098 86.315086 $3,712 Pump Power (HP) Pump lean amine solution 130 $2,651 Valve Diameter (m) Rich amine expansion valve 0.2 Flanged $8,484 MDEA initial amt cost $871 Total $117,033 Cooling water Flow(1000 kg/hr) Price ($ /m3) Cost ($ / yr) 53.48166714 0.29 $130,281 Natural gas as heating utility for reboiler Reboiler (MMBtu/hr) Price ( $ / MMBTU)   8.311611536 5 $349,088 Electricity Duty (kW) Price ($ / kWh) 13.62 0.062 $7,093.30 MDEA Recycle Flow (lb/hr) Price ($/lb) 0.23834 1.54 $3,083.17 Total $489,545

Membrane Theory For binary gas mixture If PF>>PP

Membrane Theory Rearranging to get the Ideal Separation Factor Achieve large separation with large diffusivity or solubility ratio

Independent Verification

Comparison of GAMS and Excel Membrane Concentration Profile Figure 4. Excel simulation tube side 0.9 CH4 & 0.1 CO2 Figure 5. simulation tube side 0.9 CH4 & 0.1 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 6. Excel simulation shell side 0.9 CH4 & 0.1 CO2 Figure 7. GAMS simulation shell side 0.9 CH4 & 0.1 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 8. Excel simulation tube side 0.8 CH4 & 0.2 CO2 Figure 9. GAMS simulation tube side 0.8 CH4 & 0.2 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 10. Excel simulation shell side 0.8 CH4 & 0.2 CO2 Figure 11. GAMS simulation shell side 0.8 CH4 & 0.2 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 12. Excel simulation tube side 0.7 CH4 & 0.3 CO2 Figure 13. GAMS simulation tube side 0.7 CH4 & 0.3 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 14. Excel simulation shell side 0.7 CH4 & 0.3 CO2 Figure 15. GAMS simulation shell side 0.7 CH4 & 0.3 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 16. Excel simulation tube side 0.6 CH4 & 0.4 CO2 Figure 17. GAMS simulation tube side 0.6 CH4 & 0.4 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 18. Excel simulation shell side 0.6 CH4 & 0.4 CO2 Figure 19. GAMS simulation shell side 0.6 CH4 & 0.4 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 20. Excel simulation tube side 0.5 CH4 & 0.5 CO2 Figure 21. GAMS simulation tube side 0.5 CH4 & 0.5 CO2

Comparison of GAMS and Excel Membrane Concentration Profile Figure 22. Excel simulation shell side 0.5 CH4 & 0.5 CO2 Figure 23. GAMS simulation shell side 0.5 CH4 & 0.5 CO2