Enclosed Ground Flare

An enclosed ground flare is the right choice when noise, visibility of flame, and ground-level radiation must be minimized — typically near residential areas, sensitive ecosystems, or sites with strict community-impact requirements. The combustion happens inside a refractory-lined enclosure, hidden from view and acoustically dampened.

Choose enclosed ground when:

• Site is near residential, commercial, or environmentally sensitive areas
• Visible flame would create community or PR issues
• Noise limits are stringent (typically <60 dB at the property boundary)
• Steady or moderately variable gas flow allows for compact sizing
• Ground-level installation is preferred over an elevated stack

Open elevated flares remain the right choice for very high-flow emergency relief, where elevation is needed for safe heat dispersion.

Enclosed ground flares can be designed to achieve noise levels below 60 dB(A) at the property boundary and zero visible flame under normal operating conditions. The refractory-lined chamber contains the flame; the exhaust exits through a stack at the top, leaving no visible glow or flicker.

How it's achieved:

• Multi-burner staged combustion lowers individual burner intensity
• Refractory walls absorb radiated heat and dampen combustion noise
• Exhaust stack height and geometry control thermal plume dispersion
• Acoustic dampers on air inlets reduce intake noise from natural draft or forced air

Site-specific acoustic and dispersion modelling confirms compliance with local limits before fabrication.

CRA's enclosed ground flares deliver destruction efficiency above 98% for hydrocarbons, VOCs, and most waste gas streams, meeting API 537 and EPA 40 CFR 60.18 requirements. The enclosure improves DRE versus open flares by stabilizing combustion temperature and protecting the flame from wind disruption.

Performance characteristics:

• Combustion zone temperature 800–1,100°C, depending on gas composition
• Sufficient residence time for full oxidation of complex hydrocarbons
• Multi-burner design ensures stable flame across the full turndown range
• Refractory enclosure shields the flame from cross-wind and weather

For applications requiring >99% DRE (e.g., halogenated streams, sulphur-bearing gases), enclosed flares can be paired with downstream scrubbers or dedicated thermal oxidizers.

Enclosed ground flares handle a wide range of waste gas streams — biogas, landfill gas, refinery vents, petrochemical relief, sour gas, and low-BTU streams — at flow rates from a few kg/hr (small biogas plants) to several thousand kg/hr (refinery service). The enclosure is sized to the design relief flow.

Typical service:

• Biogas from anaerobic digestion (40–60% methane)
• Landfill gas with variable composition
• Acid and sour gas streams (with material upgrades)
• Tail gas and process vents from petrochemical plants
• Low-BTU gases that struggle to burn in open flares

Variable flow tolerance is a key strength: high turndown ratios (50:1 or higher) allow stable combustion from pilot flow up to peak relief.

Enclosed ground flares are designed to meet API 537 for flare design, EPA 40 CFR 60.18 for general control device requirements, and the EU Industrial Emissions Directive (IED) for European installations. Local environmental and noise regulations add site-specific requirements.

Typical compliance scope:

• Destruction efficiency demonstrated via stack testing or design verification
• Pilot flame monitoring and assured ignition
• Net heating value above the regulatory minimum at the combustion zone
• Continuous emissions monitoring where required (CO, NOx, SO₂)
• Noise survey at property boundary

Manufacturing follows ISO 9001, ASME, and CE requirements, with API certification and project-specific approvals added as needed.

In biogas and landfill applications, enclosed ground flares destroy methane and trace contaminants when the gas can't be productively used — during commissioning, maintenance, low-demand periods, or as a backup to upgrading or power generation systems. Methane destruction is critical for greenhouse gas reduction and odour control.

Typical biogas service:

• Backup destruction when CHP engines or upgrading units are offline
• Excess gas during high biogas production periods
• Commissioning of new digesters before downstream equipment is ready
• Odour control where venting is not permitted

Enclosed design is preferred at landfill and digester sites because they're frequently near communities, and methane destruction with no visible flame meets both compliance and community-acceptance requirements.

Footprint and installation timeline scale with design flow. A small biogas enclosed flare can occupy under 20 m² and install in 1–2 weeks; a refinery-scale unit can be 100+ m² with civil works requiring 8–16 weeks before commissioning.

Typical project phases:

• Design and engineering — 6–12 weeks (CFD modelling, vendor approvals, detailed drawings)
• Fabrication — 12–20 weeks (chamber, refractory, burners, controls)
• Site civil work — concrete pad, foundations, approach piping
• Mechanical erection — 1–3 weeks depending on size
• Commissioning and performance test — 1–2 weeks

Pre-fabricated, skid-mounted units shorten on-site time significantly when site constraints allow modular delivery.