Polyimide / CA / PSF · Baker 3e · GPSA 14e §17 · 40 CFR 80.1426 · LCFS slip CO₂e
Specific-area membrane sizing
Sizes a polymer hollow-fiber membrane unit (Evonik SEPURAN / Air Liquide MEDAL / Cynara / Permea-class) for upgrading raw biogas to pipeline-quality RNG (≥96% CH₄). Membrane area uses empirical specific-area model × permeance/selectivity/pressure correction factors. Methane slip CO₂e (CARB LCFS pathway-CI driver) accounts for off-gas combustion efficiency. Multi-stage with permeate recycle is standard above ~95% purity.
Feed Biogas
scfm
%
%
°C
psig
Membrane & Pressure
GPU
1 GPU = 1 × 10⁻⁶ cm³(STP)/(cm²·s·cmHg). Modern PI 80–150, Adv-PI 100–200, CA 50–80, PSF 5–15.
—
Industrial target 20–30; SEPURAN G5X up to 50.
psig
Industry typical 100–160 psig (~7–11 bar).
psia
Configuration & Recovery
%
Auto-set by config: single 90% / two-stage 97% / three-stage 99.3%.
%
%
Costs & Power
$/m²
CA $150 / PSF $100 / PI $250 / Adv-PI $350 (2024–26 mid-range).
years
%
%
$/kWh
—
Engineering Basis
Specific-area sizing: A = A_base × stage_factor × (100/permeance_GPU) × (30/α)^0.5 × (9 bar/P_feed). Empirical not rigorous module integration.
A_base for polyimide 100 GPU / α=30 / 9 bar: single 30 / two-stage 55 / three-stage 90 m²/(Nm³/h biogas).
Permeance defaults: CA 60 / PSF 8 / PI 100 / Adv-PI 130 GPU.