Fuel enters the pyrolysis chamber where the fuel particles are pyrolysed at approximately 650°C upon contact with sand and ash particles. The pyrolysis chamber is a Circulating Fluid Bed gasifier. The low pyrolysis temperature and residence time results in the formation of only light tars.
The residual char and the pyrolysis gasses are blown upwards to the 1st cyclone.This cyclone separates the sand and char particles to a char reactor wherefrom mainly the sand and ash is recirculated to the pyrolysis chamber.
The char reactor is a bubbling bed reactor where the char is gasified at approximately 730°C using mainly air. Efficient char gasification at this low temperature is possible due to a high char retention time which is facilitated by recirculating mainly sand and ash particles from the bottom of the char reaction chamber to the pyrolysis chamber. The mentioned stream of mainly sand and ash carry heat from the char reaction chamber to the pyrolysis chamber. Hence, no internal heat transfer surfaces is necessary to provide the heat necessary for pyrolysing the added fuel.
From the 1st cyclone the pyrolysis gasses continue to the 2nd cyclone. This cyclone is more efficient than the 1st cyclone and therefore most of the finest ash particles are separated out here. In this way it is possible to retain 95% of the ash.