A landfill-gas-to-RNG plant concentrates everything hazardous about landfill gas into enclosed spaces: blower buildings moving thousands of SCFM of 50% methane, compressor enclosures, gas upgrading equipment, condensate handling, and tail-gas systems. Fixed gas detection in these buildings is what stands between a small leak and a reportable event — and it’s increasingly a requirement of insurers, AHJs, and corporate safety standards, not just good practice. Getting the system right comes down to detecting the right gases, with the right sensor technologies, in the right locations.
The hazard set
Methane is the headline hazard — flammable from roughly 5% to 15% by volume in air, and present at pipeline concentration on the product side of an upgrading plant. Hydrogen sulfide rides along in raw landfill gas at concentrations that vary site to site; it is toxic at low ppm levels and notorious for deadening the sense of smell exactly when concentrations become dangerous. Carbon dioxide, roughly half of raw LFG and the primary reject stream of the upgrading process, is an asphyxiant that displaces oxygen in enclosed and low-lying spaces. A complete design typically addresses combustible gas (LEL), H2S, and — in enclosed spaces where CO2 can accumulate — CO2 or oxygen-deficiency monitoring.
Choosing sensor technology
For methane/combustible detection in this service, infrared (IR) sensors have largely displaced catalytic bead as the preferred technology, for reasons specific to landfill gas: IR sensors are immune to the catalyst poisons (notably siloxanes and sulfur compounds) that quietly degrade catalytic sensors in LFG atmospheres; they fail-to-alarm rather than failing silently; they function in high-gas, low-oxygen conditions where catalytic beads cannot; and they hold calibration longer, cutting maintenance trips. Catalytic bead retains a place where budgets are tight and gas is clean — which raw LFG is not. For H2S, electrochemical sensors are the standard, sized for a low-ppm measuring range with alarm points aligned to occupational exposure limits.
Placement: think like the gas
Methane is lighter than air — mount combustible detectors high, above the leak sources, near roof peaks and ventilation dead zones in blower and compressor buildings. H2S is heavier than air and dangerous at breathing height — mount H2S sensors low to mid-level, in the breathing zone and near floor-level accumulation points, particularly around condensate sumps and drains. CO2 pools low — oxygen-deficiency or CO2 sensors belong in low and confined spaces. Put detection at the equipment most likely to leak (compressor seals, valve clusters, flange-dense piping runs) and at the air-handling points where a leak would be carried. Outdoor flare and wellfield areas are generally addressed by area classification and hot-work practice rather than fixed detection, but enclosed analyzer shelters and electrical buildings adjacent to gas processes deserve coverage.
System architecture
Detectors should report to a controller that drives local alarm beacons and horns, executes voting logic where appropriate, and integrates with the plant: typical actions include alarm annunciation to SCADA, ventilation activation at low alarm, and equipment shutdown or ESD initiation at high alarm. Specify sensors with appropriate hazardous-area approvals for their mounting location (blower and processing buildings are commonly classified areas), plan calibration access at mounting height, and establish a bump-test and calibration program from day one — a detection system nobody tests is a liability dressed up as a safety system.
Specification checklist
Gases and ranges (CH4 %LEL; H2S ppm; CO2/O2 where enclosed); sensor technology (IR for combustibles in LFG service); area classification of each mounting location; alarm setpoints and actions (ventilate, shut down, notify); controller capacity and SCADA integration (4-20mA, Modbus); environmental rating for washdown/outdoor sensors; and calibration gas and access provisions.
Local application support
George Grant Co. represents GDS Corp fixed gas detection — IR and catalytic combustible sensors, electrochemical toxic sensors, controllers, and complete monitoring systems — across Tennessee, Georgia, Alabama, and the Florida Panhandle. We support RNG developers, landfill operators, and their engineers with detector selection, placement review, and system layout for new plants and retrofits.