The PellX pellet burner - how it works

PellX pelletsbrännare

A description of how it works

A pellet burner consists roughly of a so-called ignition element, a light sensor, a fan, a stainless steel tube, a temperature sensor and a control system. To the pellet burner, a tube is linked to feed the pellets. This feed device consists of a tube in which there is a spiral driven by an electric motor. The tube is mounted so that the opening is as far down the pellet store as possible, thus can transport as much pellets as possible before it's time for a refill.

There are, to my knowledge, two systems for the measurement functions: either it's an internal screw inside the pellet burner, in that case the system "buffers" a certain amount of pellets in the tube case (and a bit up in the hose) and portion it into brännarröret or it is portioned directly from the pellet store into brännarröret (by way of the tube and spiral of course); that's how PellX works. The disadvantage of the latter system is that it is quite difficult to get a steady, even supply and the advantage is that there are fewer parts that can malfunction.

The process begins with a starting dose from the store going down the first steel tube (that's how most/all pellet burners work). The starting dose can either be decided by weighing or by measuring its volume. I think you get a better result weighing it if we consider that different pellet brands can have different density.

When the starting dose is in place the ignition element heats up for a few seconds before the fan starts to run intermittently at low speed (starting, stopping, starting, stopping...), and when this has been going on for approximately half a minute the pellets starts to burn. It is now we can see if the starting dose is too high, in that case you get a gas explosion just in the moment of ignition, a so-called boiler boost, which may result in some of the smoke coming outside of the boiler instead of going up through the chimney.

Some of the pellet burner's components

When the light sensor registers the light from the flame it generates a weak electric voltage which is sent to the control system. The control system now know that there's a fire and enters the next phase where, for a moment, it will not feed the any pellets at all after which it will feed the pellets with a lower dose than in the operational phase, all this so the starting dose should have time to burn down to a moderate level.

It is now we can see if the starting dose is too low; the fire will simply burn out before the burner enters the operational phase. As the flames become smaller the electric voltage generated by the light sensor decreases and when it has fallen below a certain level the control system knows something is wrong and begin a new start.

This is where I think the system has a slight programming flaw, because it lets too much time pass before more pellets are fed, but this may have something to do with security so perhaps I should not be too judgemental.

When two restart attempts have been made the control system goes into idle mode and the fan runs for approximately four minutes letting any remaining pellets burn.

If the startup attempt is successful the control system goes into the operational phase after about five minutes and continue to feed more pellets intermittently, with a larger dose than during the start-up phase, until the temperature sensor registers that the boiler has reached the temperature where you have set the control system to stop feeding more pellets. When the temperature of the boiler has fallen to the starting temperature the process starts over again.

Pellet burner 3D View