How to Size a Biogas Flare Stack for Your Palm Oil Mill

Sizing a biogas flare stack correctly is one of the most consequential decisions in a palm oil mill's wastewater treatment plant. An undersized flare cannot safely combust peak gas flows and risks flame instability or blow-out; an oversized one wastes capital and can burn inefficiently at low loads. Getting the sizing right starts with understanding your mill's gas generation profile.

Start with Gas Generation Rate

The foundation of flare sizing is how much biogas your treatment plant produces, usually expressed in cubic metres per hour. This depends on the volume of palm oil mill effluent processed, the organic load, and the efficiency of the anaerobic digestion process. Because generation fluctuates with mill throughput, both average and peak flows matter — the flare must handle the peak, not just the average.

Key Sizing Factors

• Peak biogas flow rate, not just the average, so the flare can handle maximum generation
• Methane content, which determines the calorific value and flame characteristics
• Required combustion efficiency and any emissions limits that apply to the site
• Turndown ratio, the range between minimum and maximum flows the flare must burn stably
• Gas pressure available at the flare inlet

Diameter and Height

Flare diameter is driven by gas velocity: too small and the velocity is high enough to risk flame lift-off or blow-out; too large and low-load combustion becomes unstable. Height is influenced by radiation and dispersion requirements, ensuring heat and combustion products clear the working area safely. Both are calculated from the gas flow, composition, and site constraints rather than chosen from a catalogue.

Turndown Matters as Much as Peak

A mill's gas flow is rarely constant. A flare sized only for peak flow may burn poorly when generation drops, so the turndown ratio — the span between the lowest and highest flows it can handle stably — is a critical specification. A well-designed flare maintains stable, efficient combustion across the full operating range, not just at its design maximum.

Why Professional Sizing Pays Off

Because flare sizing depends on interacting variables — flow, composition, pressure, turndown, and site layout — it is best handled through proper engineering calculation rather than rules of thumb. The cost of correcting an incorrectly sized flare after installation far exceeds the cost of getting the design right at the outset.

How THAGO Can Help

THAGO designs, fabricates, and commissions flare stacks sized specifically for each mill's gas generation profile. Our in-house engineering team performs the process calculations to match flare capacity, diameter, and height to your site.