Landfill gas (LFG) is an increasingly valuable energy source, but it arrives at the engine or turbine inlet carrying a cocktail of contaminants that can destroy expensive equipment within months. Siloxanes, moisture, hydrogen sulphide, and fine particulates are the primary culprits. Without robust landfill gas filtration, operators face unplanned shutdowns, costly overhauls, and shortened asset life. This guide explains what each contaminant does, how to remove it, and which R+F FilterElements products are engineered for the task.
Why Landfill Gas Is Harder to Handle Than Natural Gas
Unlike pipeline-quality natural gas, landfill gas is a raw, variable mixture. Typical LFG composition is 45–60 % methane and 35–45 % carbon dioxide, but the remaining fraction contains dozens of trace compounds that vary with waste type, landfill age, and seasonal temperature. The three contaminant families that cause the most damage to downstream plant are:
- Siloxanes — volatile organosilicon compounds that oxidise to hard silica (SiO₂) deposits on combustion surfaces
- Liquid water and condensed hydrocarbons — cause corrosion, compressor surge, and flame instability
- Particulates — dust, rust, and biofilm fragments that erode seals, valves, and injectors
Each contaminant requires a different removal mechanism, which is why effective landfill gas treatment almost always involves a multi-stage filtration train rather than a single vessel.
The Siloxane Problem: Small Molecules, Catastrophic Damage
Siloxanes are present in landfill gas because modern waste streams contain large quantities of personal care products, detergents, and silicone-based materials. As these decompose anaerobically, they release volatile methyl siloxanes — most commonly D4 (octamethylcyclotetrasiloxane), D5 (decamethylcyclopentasiloxane), L2, and L3 linear variants.
At combustion temperatures above approximately 300 °C, siloxanes oxidise to silicon dioxide. This fine, abrasive silica deposits on:
- Piston crowns and cylinder walls in reciprocating gas engines
- Turbine blades and nozzle guide vanes in micro-turbines
- Heat exchanger surfaces and catalytic oxidiser beds
- Spark plug electrodes, reducing ignition reliability
The deposits are extremely hard (Mohs hardness ~7, comparable to quartz) and act as an abrasive lapping compound. Engine manufacturers including Caterpillar, MWM, and Jenbacher publish maximum siloxane limits — typically 5–28 mg Si/m³ — and will void warranties if these are exceeded. In practice, raw LFG siloxane concentrations of 50–200 mg Si/m³ are common, meaning removal efficiencies of 90–99 % are required before the gas reaches the engine.
How Activated Carbon Removes Siloxanes
Activated carbon adsorption is the most widely deployed technology for LFG filter siloxane removal. Siloxane molecules are non-polar and relatively large; they adsorb strongly onto the hydrophobic surface of granular activated carbon (GAC) or impregnated carbon media. Key design parameters include:
- Empty bed contact time (EBCT) — typically 3–10 seconds for LFG siloxane removal
- Bed temperature — lower temperatures (5–20 °C) improve adsorption capacity; pre-cooling the gas before the carbon bed is beneficial
- Moisture content — liquid water competes with siloxanes for adsorption sites; the gas must be dried before the carbon stage
- Carbon type — coconut-shell-based GAC with high micropore volume typically outperforms coal-based carbon for siloxane removal
R+F FilterElements offers the RF-AC activated carbon adsorption element range, designed for use in standard RF-H series housings. The RF-AC elements achieve a residual oil and hydrocarbon carry-over of less than 0.003 mg/m³ and are available in all standard element sizes to suit flow rates from a few hundred to several thousand Nm³/h. For larger LFG installations, multiple elements can be deployed in parallel within a single housing or across a bank of housings.
The RF-DIA disposable inline adsorber is a compact alternative for smaller LFG generators or as a polishing stage downstream of a primary carbon vessel. Its activated carbon or molecular sieve fill can be specified to target siloxanes specifically, and the disposable cartridge format eliminates the need for carbon regeneration on site.
Moisture and Liquid Carryover: The Case for Coalescing Filtration
Landfill gas is typically saturated with water vapour at the point of extraction. As the gas cools in collection pipework, water condenses and can carry fine droplets of leachate, compressor oil (if a blower is used), and dissolved contaminants. Liquid water entering an activated carbon bed rapidly reduces its siloxane adsorption capacity — in some cases by 50 % or more — making upstream liquid removal essential.
Coalescing filtration is the correct technology for this duty. A coalescing filter element captures sub-micron liquid aerosols on borosilicate glass microfibre media, causing them to coalesce into larger droplets that drain by gravity to a sump. The R+F RF-C coalescing element achieves 99.99 % efficiency for liquid aerosols ≥ 0.1 µm at rated flow, making it highly effective against the fine mist that forms when saturated LFG cools in pipework.
For LFG applications, the coalescing stage is typically positioned immediately after any compression or blower duty, where liquid carryover is highest. The housing selection depends on operating pressure and flow rate. The RF-H-150 process gas housing (rated to 100 bar, 316L stainless steel) is suitable for pressurised LFG systems, while the RF-H series housings in the 310–395 range cover lower-pressure applications up to 17 bar.
Desired carbon bed service interval
Particulate Removal: Protecting Valves, Injectors, and Instrumentation
Even after coalescing and carbon adsorption, fine solid particulates remain a risk. Sources include:
- Rust and mill scale from carbon steel collection pipework
- Biofilm fragments and microbial debris from the landfill body
- Carbon fines migrating from upstream adsorption beds
- Dust ingress at wellhead connections
A final particulate filter stage — typically rated at 1–5 µm absolute — protects fuel gas control valves, engine injectors, and any downstream gas analysers. The R+F RF-P particulate element achieves 99.99 % efficiency for particles ≥ 0.3 µm and is available in the same housing sizes as the RF-C coalescing element, allowing a combined coalescing-plus-particulate train to be built from standard components.
For instrumentation protection — for example, where a gas chromatograph or calorimeter is used to monitor LFG quality — the RF-H-110 to RF-H-170 instrumentation filter range provides high-integrity filtration in 316L stainless steel housings rated to 700 bar. These are particularly relevant where sample conditioning systems are installed at the wellhead or engine inlet.
Recommended Filtration Train for Landfill Gas
A well-designed LFG filtration system typically follows this sequence:
| Stage | Function | Recommended R+F Product | Typical Rating |
|---|---|---|---|
| 1 — Bulk liquid knockout | Remove free water and large droplets | RF-H series housing with RF-P element (coarse) | 10–25 µm |
| 2 — Coalescing filtration | Remove sub-micron liquid aerosols and compressor oil | RF-C coalescing element in RF-H housing | 99.99 % ≥ 0.1 µm |
| 3 — Activated carbon adsorption | Remove siloxanes, H₂S, VOCs, odour | RF-AC element or RF-DIA inline adsorber | < 0.003 mg/m³ residual |
| 4 — Final particulate filter | Remove carbon fines and residual particulates | RF-P particulate element in RF-H housing | 99.99 % ≥ 0.3 µm |
| 5 — Instrumentation protection (optional) | Protect gas analysers and sample conditioning | RF-H-110 to RF-H-170 series | Up to 700 bar, 316L SS |
This staged approach ensures that each contaminant is addressed by the most appropriate technology, and that upstream stages protect the capacity and service life of downstream stages — particularly the activated carbon bed.
Use our free Engineering Tool to get a filtration recommendation for your specific application in under 2 minutes.
Sizing Considerations for LFG Filtration Systems
Correct sizing is critical. An undersized coalescing element will carry liquid over into the carbon bed; an oversized carbon vessel will have poor gas distribution and channelling. Key inputs for sizing include:
- Gas flow rate (Nm³/h or m³/h at actual conditions)
- Operating pressure and temperature
- Inlet siloxane concentration (mg Si/m³, measured by GC-MS or Tenax tube sampling)
- Target outlet siloxane concentration (per engine manufacturer specification)
- Moisture content and dew point
- Desired carbon bed service interval (typically 3–12 months depending on siloxane loading)
R+F FilterElements provides application engineering support for LFG projects. The online sizing wizard can be used for initial element and housing selection, and the technical team can assist with carbon bed sizing calculations and multi-stage train design. Contact R+F at the enquiry page or directly at [email protected] for project-specific support.
Seal and Material Selection for Landfill Gas Service
LFG contains hydrogen sulphide (H₂S), carbon dioxide, and trace halogenated compounds that can attack standard elastomers. Material selection for housings and seals must account for this aggressive chemistry:
- Housing material: 316L stainless steel is preferred for LFG service; aluminium housings are acceptable for low-H₂S applications
- Seal material: FKM/Viton seals (rated to 200 °C) offer good resistance to H₂S and hydrocarbons; EPDM is not recommended for LFG due to hydrocarbon swelling
- Element binder: For elevated-temperature applications (e.g., downstream of a compressor with high discharge temperature), RF-CS silica-bonded elements rated to 200 °C should be specified
R+F FilterElements supplies housings and elements with FKM seals as standard for biogas and landfill gas applications, and K-type elements with enhanced H₂S resistance are available on request for high-sulphur LFG streams.
Maintenance and Monitoring Best Practice
Even the best-designed filtration train will underperform if maintenance is neglected. Recommended practice for LFG filtration systems includes:
- Differential pressure monitoring across each filter stage — rising ΔP indicates element loading and approaching end-of-life
- Periodic siloxane sampling downstream of the carbon bed — breakthrough testing using Tenax tubes or online siloxane analysers confirms remaining carbon capacity
- Liquid level monitoring in coalescing filter sumps — automatic drain valves prevent liquid re-entrainment
- Scheduled element replacement based on operating hours and ΔP data, not calendar intervals alone
- Carbon bed regeneration or replacement — thermal regeneration is possible for some carbon types but requires careful temperature control; many operators prefer disposable cartridge formats such as the RF-DIA for simplicity
Keeping detailed maintenance records also supports warranty claims with engine manufacturers, who increasingly require documented evidence of gas quality compliance.
- Liquid water and condensed hydrocarbons
- Empty bed contact time (EBCT)
- Landfill gas is typically saturated with water vapour at the point of extraction.
- Even after coalescing and carbon adsorption, fine solid particulates remain a risk.
Conclusion: Protecting Your LFG Asset Investment
Landfill gas is a valuable renewable energy resource, but only if the engine or turbine converting it to power remains operational. Siloxane-induced silica deposits, liquid carryover, and particulate contamination are all preventable with the right landfill gas filtration strategy. A properly designed multi-stage train — coalescing, activated carbon adsorption, and final particulate filtration — using correctly specified R+F FilterElements products will protect your plant, extend service intervals, and maintain engine warranty compliance.
R+F FilterElements, based in Hildesheim, Germany, applies European engineering standards to every filtration solution. Whether you are commissioning a new LFG-to-power project or troubleshooting siloxane damage on an existing installation, the R+F technical team can assist with product selection, sizing, and system design.
