Landfill Gas Treatment System: Contaminant Limits, Media Sizing, Equipment Selection

Methane runs 45–60% by volume and carbon dioxide 40–50%. Nitrogen and oxygen appear whenever wellfield vacuum pulls air through the cover, and the effect goes beyond dilution: ingress feeds aerobic zones, raises temperature in the waste mass and shifts the profile. The stream leaves the header at 90–120 °F, saturated, and composition drifts as the cell ages. Design against a twelve-month record covering seasonal swings.

Personal care products, defoamers, lubricants and cured silicone sealants put silicone-bearing material into the waste mass, where it breaks down into volatile cyclic D4 and D5 and linear L2–L5 species. Siloxanes and silicones in a landfill gas treatment system sit at different points in the chain: the silicones arrive as source material in the waste, and the siloxanes are what a sample of the stream measures. Published surveys report 1 to 136 mg/m³ of siloxanes, 5–15 mg/m³ typical at US sites. Combustion converts them to SiO₂ and microcrystalline quartz, which deposit in the combustion and exhaust stages as an abrasive white powder and drive wear and component failure. Engine builders answer by writing maximum siloxane figures into warranties.

Humidity targets are set per stage. Sorbent duties pull in opposite directions: carbons impregnated for H₂S generally rely on a water film to oxidize sulfide, while capacity for organic species including D4 falls as humidity rises. Take the inlet window from the data sheet for the grade.

Take a configuration that includes a wet stage. Sequence then follows the failure mode each step prevents, and the wet stage is what makes the order counterintuitive. Solids and free liquid come out first, on an element rated for line vacuum and liquid carryover; Torch-Air's cartridge collectors cover the site's atmospheric duties. Bulk sulfur removal comes next, since consumption in any polishing charge scales with the H₂S reaching it. A wet scrubber leaves the stream saturated again, so conditioning belongs after it: cool, separate the condensate, take carryover on a coalescer, then reheat away from the dew point. Organosilicon polishing sits last, and for pipeline RNG membrane or PSA upgrading follows with its own tail-stream control device.

Adsorbers and dry scrubbers hold a packed bed of granular sorbent and are the usual route to outlet concentrations of a few mg/m³ total siloxanes, though deep refrigeration and solvent absorption compete at some sites. Selection for siloxane compounds in a landfill gas treatment system follows the target species and site conditions.

Torch-Air's adsorber work is documented in tank-vent duty: the CO₂ breather units for water storage tanks ship with a mechanical clogging indicator and an optional analyzer fitting, and the fluosilicic acid units run lime-based sorbent. Vessel engineering, sorbent retention and change-out design carry across to fuel-gas service. Removal efficiency is a separate calculation: sorbent data gives equilibrium capacity, while the outlet concentration an operating charge holds also depends on contact time, mass transfer, geometry and loading, so confirm it by breakthrough calculation or pilot run.

Fix the reference state first: 1,200 Nm³/h at 0 °C and 101.325 kPa, inlet and outlet quoted on the same basis: 20 mg/Nm³ in, 5 mg/Nm³ as the engine target. The siloxane removal in a landfill gas treatment system duty is then 15 mg/Nm³ × 1,200 Nm³/h = 18 g/h, or 157.7 kg a year at 8,760 h. Assume 8% w/w working capacity as a figure for the worked example, and annual consumption is 1,971 kg, call it 2.0 t/y.

EBCT needs the actual volumetric flow inside the vessel. At 25 °C and 5 kPa gauge, 1,200 Nm³/h becomes 1,248 m³/h, or 0.347 m³/s. At 30 s EBCT the charge is 10.4 m³; at 3.0 m depth the cross-section is 3.47 m², a vessel 2.10 m in diameter, superficial velocity 0.10 m/s. At 450 kg/m³ bulk density the charge weighs about 4,680 kg.