Enclosed vs Open Flare Stacks: Which Does Your Mill Need?

If your mill is capturing biogas from POME treatment, you will eventually need to decide how to safely combust excess or off-spec gas. That decision usually comes down to two options: an open flare stack or an enclosed flare stack. Each has a different cost, footprint, and compliance profile, and the right choice depends heavily on your site's specific requirements.

What Each System Does

Both systems exist to safely combust biogas, converting methane into carbon dioxide and water vapour before it reaches the atmosphere. Since methane is a far more potent greenhouse gas than CO2, flaring — even in its simplest form — significantly reduces the environmental impact of untreated biogas release.

The difference lies in how the combustion is contained and controlled.

Open Flare Stacks

An open flare stack burns gas at an exposed tip at the top of an elevated stack, with the flame visible and open to the atmosphere. This is the more traditional and widely used design across Malaysian mills, particularly where budget and simplicity are priorities.

• Lower capital cost and simpler mechanical design
• Easier to maintain, with fewer components to service
• Flame is visible, which some sites use as a visual confirmation the system is operating
• Combustion efficiency and noise levels are harder to control precisely

Enclosed Flare Stacks

An enclosed flare stack combusts gas inside a refractory-lined chamber, with the flame hidden from view. Air and gas mixing is more tightly controlled, which generally produces more complete and consistent combustion.

• Higher combustion efficiency, often exceeding 99 percent destruction of methane
• Reduced visible flame and lower noise, useful for sites near residential areas or with strict community relations considerations
• Better suited to meeting stricter emissions monitoring requirements, since sampling ports can be built into the chamber
• Higher capital cost and a larger footprint than an equivalent open flare

Comparing the Two at a Glance

What to Consider for Your Site

In practice, the right choice depends on a few site-specific factors: your expected gas flow rate, proximity to residential areas, the emissions standards your mill is required to meet, and your budget for both capital and ongoing maintenance. Mills operating under stricter DOE monitoring conditions, or located closer to townships, generally benefit more from an enclosed system despite the higher upfront cost.

Some larger sites also install both — an open flare as a backup or emergency relief system, paired with an enclosed flare for routine combustion — giving redundancy without compromising on day-to-day compliance.

How THAGO Can Help

THAGO fabricates both open and enclosed flare stacks, sized to your site's gas flow rate and application, from 100 m³/hr systems up to 2400 m³/hr and beyond. We can assess your current setup and recommend whether an open, enclosed, or semi-enclosed system best fits your mill's requirements and budget.