1. Membranes for Gas Conditioning
Hope Baumgarner
Chelsea Ryden

2. How is natural gas currently processed?

3. 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

4. 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

5. 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

6. Claus Unit: Sulfur Recovery
Furnace
Catalytic Section
Liquid Sulfur
Tail Gas °C
Overall Reaction:
2H2S+O S2 + 2H2O
Thermal Reaction:
2H2S +3O SO2 + 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

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

17. 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

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

19. How do membranes work?

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

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

22. 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

23. Membrane Theory Combining equations
Neglecting external mass transfer resistances
Substituting

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

25. Membrane Designs

26. 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

27. 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

28. Common Membrane Modules
Spiral-Wound
Hollow-Fiber
Packing Density, m2/m3
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

29. 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)

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

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

32. 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

33. Membrane Advantages and Disadvantages

34. 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

35. 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

36. 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

37. Membrane Disadvantages
Plasticization
Membrane materials absorb 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

38. 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

39. Membrane Network

40. 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

41. Superstructure allows for all possible network configurations

42. Superstructure
For example:

43. Superstructure
Resulting membrane network:

44. How do we build this superstructure?

45. 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

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

47. Hollow Fiber Mathematical Model
Mixer/Splitter Balances
Feed balance

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

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

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

51. Hollow Fiber Mathematical Model
Permeate power 1 2

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

53. 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

54. 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%)

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

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

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

58. 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)

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

60. How is this implemented?

61. Set and Parameter Declaration
Program
Set and Parameter Declaration
Variable Declaration

62. Program
Equations

63. Program

64. Results

65. Results

66. 2 Membrane Network at 79 lb-mol/hr
0.42 kW
Objective function: $163,000
% CH4 lost: 11.20

67. 3 Membrane Network at 79 lb-mol/hr
Objective function: $130,000
%CH4 lost: 7.77

68. 4 Membrane Network at 79 lb-mol/hr
Objective function: $130,000
%CH4 lost: 7.77

69. 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

70. 3 Membrane Network at 127 lb-mol/hr
Objective function: $230,000
%CH4 lost: 9.44

71. 3 Membrane Network at 238 lb-mol/hr
Objective function: $539,000
%CH4 lost: 10.90

72. Membrane Network Verification

73. 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

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

75. 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

76. Results
Adjusted existing cost for membrane network

77. Results

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

79. 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

80. 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

81. Questions?

82. References
Baker, Richard. “Future Directions of Membrane Gas Separation Technology.” Industrial & Engineering Chemistry Research Sarkey’s Senior Lab. 7 Feb <
Baker, Richard and Kaaeid Lokhandwala. “Natural Gas Processing with Membranes: An Overview.” Industrial & Engineering Chemistry Research Sarkey’s Senior Lab. 4 Feb <
Kookos, I.K. “A targeting approach to the synthesis of membrane network for gas separations” Membrane Science, 208, , 2002.
Mohammadi, T., Moghadam, Tavakol, and et al. “Acid Gas Permeation Behavior Through Poly(Ester Urethane Urea) Membrane.”Industrial & Engineering Chemistry Research Sarkey’s Senior Lab. 4 Feb <
Natural Gas Supply Association Sarkey’s Senior Lab. 7 Feb <
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.

83. APPENDIX

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

85. 2 Membrane Network at 79 lb-mol/hr @ 19%CO2
0.42 kW

86. 3 Membrane Network at 79 lb-mol/hr @ 19%CO2

87. Programming Output

88. Programming Output

89. Programming Output

90. Programming Output

91. 3 Membrane Network at 127 lb-mol/hr @ 19%CO2

92. 3 Membrane Network at 238 lb-mol/hr @ 19%CO2

93. 3 Membrane Network at 79 lb-mol/hr @ 9% CO2

94. 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

95. 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

96. Amine Unit Simulation

97. 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
$4,772
Lean amine / water
10.96
$2,651 3
6.098
$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)
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)
1.54
$1,541.58
Total
$161,086

98. 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
$9,544
Lean amine / water
10.96
$3,075 3
6.098
$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)
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)
0.062
$5,864.78
MDEA Recycle
Flow (lb/hr)
Price ($/lb)
1.54
$1,541.58
Total
$408,930

99. 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
$15,907
Lean amine / water
10.96
$4,242 3
6.098
$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)
0.29
$130,281
Natural gas as heating utility for reboiler
Reboiler (MMBtu/hr)
Price ( $ / MMBTU) 5
$349,088
Electricity
Duty (kW)
Price ($ / kWh)
13.62
0.062
$7,093.30
MDEA Recycle
Flow (lb/hr)
Price ($/lb)
1.54
$3,083.17
Total
$489,545

100. Membrane Theory
For binary gas mixture
If PF>>PP

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

102. Independent Verification

103. 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

104. 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

105. 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

106. 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

107. 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

108. 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

109. 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

110. 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

111. 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

112. 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