A reminder of how the twin-auger fuel feed of FACI pellet boilers works

Pellet boilers with a traditional single-auger system have a design flaw directly related to safety.

When the set temperature is reached, the boiler goes into standby mode: the air and fuel supply stops, and passive smouldering of the fuel in the burner begins.

Even with minimal oxygen access, combustion continues. If the downtime is long, the smouldering front can spread along the auger towards the fuel hopper.

This can lead to:

• pellets igniting in the hopper,
• heavy smoke in the room,
• a stoppage of the production process and damage to equipment and property.

The situation is made worse by emergency power cuts - in that case the auger does not work, and there is practically no barrier to the spread of smouldering

Limitations of fire valves

A common solution is to install a fire valve that supplies water when the temperature in the fuel feed rises.

However, this design has a number of significant drawbacks:

• a false alarm causes an emergency boiler shutdown;
• when water gets into the pellets, the fuel swells and then dries out into a dense mass that blocks the auger;
• cleaning the system after the valve has been triggered is very labour-intensive and almost always leads to equipment downtime.

Thus, a fire valve is only a partial solution and does not eliminate the root cause of the risk - the possibility of smouldering spreading along the fuel feed.

A feature of FACI pellet boilers: twin-auger fuel feed

FACI boilers use a fundamentally different design. All pellet and wood chip units are equipped with a twin-auger fuel feed system that provides mechanical and thermal separation between the hopper and the combustion chamber.

Main engineering advantages:

1. A permanent break in the fuel flow. There is always a free zone without fuel between the upper and lower augers. This "air gap" eliminates the possibility of smouldering passing into the hopper.
2. Reliability during power cuts. Even without power, the twin-auger design keeps working as a barrier: smouldering physically cannot pass through the gap.
3. Automatic response to overheating. The fuel feed temperature sensor installed in FACI boilers switches on the lower auger when it detects abnormal heating. The fuel is pushed into the combustion chamber and the source of smouldering is eliminated.
4. Independent auger control. The operating algorithm switches the augers off in sequence: first the upper one, then the lower one. This creates a larger gap and further reduces the risk of smouldering spreading back.

Using a twin-auger fuel feed in FACI pellet boilers makes it possible to:

• minimise the likelihood of a fire in the fuel hopper,
• improve equipment reliability,
• reduce unproductive downtime,
• comply with modern industrial safety requirements.

For companies and facilities with continuous or seasonal peak heat consumption, choosing boilers with a twin-auger system is the optimal solution, combining safety, efficiency and economic sense.