Size a fuel gas filter separator: vessel dimensions, element count, and pressure drop.
Understand coalescence, filter element design, centrifugal separation, and two-stage filter separator principles
Key Characteristics:
Separation model:
Operating Limits:
Applications:
• Compressor fuel gas conditioning
• Gas turbine fuel preparation
• Burner fuel gas cleaning
• Instrument gas polishing
Outlet Quality:
• Compressor fuel: ≤0.1 gal/MMSCF
• Turbine fuel: ≤0.05 gal/MMSCF
• Instrument gas: ≤0.01 gal/MMSCF
Removal efficiency is not a fixed lookup. The centrifugal tuyere is modeled as an inertial separation stage: a cut size d50 is computed from a Stokes force balance in the swirl field using inlet velocity, gas viscosity, and the liquid-to-gas density difference. Grade efficiency at the target droplet size follows the Lapple relation η = 1/(1+(d50/dp)²). The coalescer element starts from a vendor grade rating and is derated for face velocity (re-entrainment) and inlet liquid loading, so efficiency varies with operating conditions.
Gas flow through fibrous coalescer media at these face velocities is in the viscous (Darcy) regime, so the clean element pressure drop scales linearly with face velocity and gas viscosity, not with the square root of gas density. The model uses ΔP = dpFactor × face velocity × (viscosity / reference viscosity) plus a small inertial term that grows with gas density at high pressure. Total clean ΔP also includes the tuyere velocity-head loss and vessel entry/exit losses.
Liquid loading is entered in gallons per MMSCF (gal/MMSCF), consistent with the input label, the report, and the server-side check. Fuel gas filter/separators are aerosol and mist devices, not slug catchers. Loadings above roughly 20 gal/MMSCF indicate bulk liquid that should be removed by an upstream scrubber or knockout drum first.
Elements are replaced when differential pressure reaches the change-out limit. The calculator estimates the dirty (change-out) pressure drop as about four times the clean value, consistent with GPSA Chapter 7 and vendor coalescer practice for compact fuel gas elements, and flags a warning if that dirty ΔP exceeds your specified maximum.
Operating pressure and temperature set the gas density and actual volumetric flow (ACFM), which drive vessel diameter and pressure drop. The target micron size strongly affects grade efficiency through the Lapple relation. Gas viscosity affects both the tuyere cut size and the element pressure drop. Liquid loading and element type derate the coalescer efficiency.