Producer Gas Flares

Possibly the first experience most researchers and consultants have with gasification,is to see the producer gas burning as a flare. This first exposure to making a combustible gas from biomass can be very deceptive, and the viewer lead to believe that this burning gas demonstrates it's capability to fuel, either engines, or process heat applications.

While producer gas can be so impressively combusted, hot straight out of the gasifier, contamination in the gas determines it's quality, and ultimately, the most appropriate end use application. This gas can contain water, char dust, carbon blacks, and ash, plus uncracked hydrocarbons, all of which have to be removed, if the gas is for engine powered electrical generation.

During Fluidyne projects, we have collected many photos of producer gas flares, and flu stack emissions, which combined with certified testing procedures, has provided considerable information on the behavior of producer gas from it's transition from hot to cold gas. The photos offered in the Fluidyne Archive,  are a selection of these test flares, and with some thought, can be used as a guide when observing combusting producer gas.

Observation is still one of the best free tools available, learn how to add this to your own knowledge.

August 2006.


This is a peep into a correctly functioning downdraft gasifier.

This flare is within 5 minutes of a cold start-up. Note how short and bushy, lots of red from fine char particles, and uncracked moisture from fuel wood. This gas has had only cyclone dust cleaning to approximately 10 micron.

Now flare exhibits white glare as hydrogen peaks, as the gasifier is now at normal operating temperature, and fuel moisture is cracked to hydrogen.

The glare is quite intense, but lots to observe during these test runs.

The fuel wood moisture has just about been depleted, and the flare now begins to revert back to predominantly CO, although hydrogen will continue to form at a lower output.

This is consistent behavior for batch fed gasifiers.


As the gas flow is closed down, the mixtures of gas can be observed in some cases to burn separately. This does depend on the type of burner nozzle phenomena, so care should be taken to ensure that test flares are provided with correct air ratios if emission tests are being conducted.


Slowed right down, the flare is seen to be a well organized flame with gases burning right up to the air inlet interface. This type of cyclomix burner nozzle was developed by Fluidyne, and the gas will not blow out, or off the nozzle with changing gas quality.


This flare is from cold filtered gas, and is the quality you need for engine application. It still contains water vapor, and carbon black, which will not burn in these flares. Water in the gas at this point is not desirable, and should be removed before the gas enters the engine.

On a larger scale, this Winter flare displays it's angry red caused by uncracked hydrocarbons, char particles, and water vapor. Only cyclone cleaning of the gas dust to 10 micron has been done for this test.

Flare inside the test flu stack during earlier testing, shows same angry red, and smoke in gas from uncracked hydrocarbons.

Now flare exhibits yellow colour as hydrogen levels increase, and uncracked hydrocarbons are tuned out of the gas making process.

This invisible emission would please most who see it, but it does not meet the EPA emission standards. Present are high levels of particulate formed from incorrect mixing of the gas and air. We have corrected this problem for our test programme, but do not be fooled by what appears to be the perfect combustion of producer gas.