Slide 3 Membrane Unit (sometimes called Permeation Unit) Residue Permeate P i, res P i, perm A simple model to simulate components that can migrate selectively across a membrane. Composed of a bundle of hollow fibers. Flow passes from the high pressure feed/residue side to the low pressure permeate side of the fiber
Slide 4 Membrane Unit Assumptions Constant total pressure on both the permeate and feed/residue side The driving force is partial pressure as calculated by ideal gas law The permeate side gas is continually swept away from the membrane
Slide 5 Membrane Unit where: R i = Flowrate in std. vol/time K i = Permeation constant in vol/(time-area-pres) Area = Membrane area P i = Partial pressure of component i P i, res P i, surf P i, perm
Slide 6 Membrane Unit Solution technique Integrate on dArea Solution characteristics Based on partial pressure, not fugacity, therefore solutions do not change with change in thermo method Limiting case of small area: Flowrate can be calculated from product partial pressures Because permeate is continually carried away from the membrane, a membrane unit with 10 area units will have the exact same performance as ten 1 area unit membrane units in series.
Slide 7 Membrane Unit Oil Production with CO 2 Injection Oil/Gas Separator Oil Product Condensate Fuel Gas Membrane CO 2 Recovery Well Production CO 2 Injection CO 2 Makeup
Slide 9 Membrane Unit Flowsheet considerations The fuel gas is consumed on plant to drive process equipment. The fuel gas is targeted to 900 Btu/scf for proper equipment operation. The pressure of the permeate side of the membrane units is adjusted to achieve the heat content. The pressure drop across the residue side is negligible. Two membrane shells are included to allow intermediate condensate dropout. The temperature equilibrates between the permeate and the residue. The product streams have a lower temperature because of the Joule- Thomson effect of the pressure drop.
Slide 13 Membrane Unit Permeability Fitted to Arrhenious Form ComponentK i,o E i N20.188533958 H2S0.333721146 CO20.329621079 C10.198533809 C20.103733118 C30.030633375 IC40.006632125 NC40.009932125 IC50.000041162314.5 NC50.008132590 NC60.026840960 NC70.219453642 K i = K i,o exp[-E i /(RT)] R = 10.73159, ft3-psia/R-lb-mol
Slide 18 Membrane Unit Solution Technique Calculators are used to set permeation coefficients. It iteratively retrieves temperature from the membrane unit and recalculates the coefficients based on temperature. A controller is used to adjust the pressure of the permeate to achieve the heat content of the fuel gas.