Calculators›RNG / Biogas›Siloxane Removal Bed Sizing
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Siloxane Removal Bed Sizing
GAC / silica gel · Schweigkofler 2001 · Soreanu 2011 · ASTM D7833 / ISO 2613-2:2023
Silicon-basis sizing
Sizes a granular activated-carbon (or silica-gel) adsorption bed to remove cyclic (D3/D4/D5/D6) and linear (L2-L5) siloxanes from biogas to target downstream-equipment spec. Specification basis is mg Si/m³ (silicon). Critical pretreatment: chill/dehydrate biogas to ≤30% RH, and install H₂S scavenger upstream — both significantly affect GAC capacity.
Inlet Gas & Target
scfm
mg Si/m³
Landfill 5–50, WWTP 2–20, dairy <2, food-waste 5–30. To convert from mg total siloxane: multiply by ~0.37 (D-series).
mg Si/m³
mg Si/m³
Pretreatment State
%
≤30% RH: full capacity. 100% RH: ~50% of dry (Schweigkofler 2001). Chill biogas to ≤10°C if untreated.
°C
If unchecked: failure chip fires — H₂S beats siloxanes for adsorption sites on most GAC.
Adsorbent Media
kg Si/kg
Lab dry-N₂ can claim 0.20–0.65; real biogas typically 0.05–0.15 (Schweigkofler 2001).
kg/m³
%
Bed Geometry, Life, Costs
months
s
GAC for siloxane: 20–60 s typical (Soreanu 2011).
ft
$/kg
$/kg
Engineering Basis
Silicon basis: spec, inlet, outlet all in mg Si/m³ (since SiO₂ deposition is the failure mode and Si fraction varies by species).
RH penalty (Schweigkofler 2001): linear 30→100% RH gives 100→50% of dry capacity. Chill/dehydrate biogas to ≤30% RH for full capacity.
H₂S upstream required — H₂S beats siloxanes for adsorption sites on most GAC; impregnated GAC is an exception (H₂S co-removal).