The gasification process is an endotherm reaction. To maintain the balance, heat must be applied. Therefore non-gasified carbon (charcoal) is transported by the rotating bed material (sand as heat transfer fluid) from the gasifier into the connected combustion chamber and burnt there. This exothermic reaction provides the energy for the gasification process by, in the combustion chamber, heated-up bed material being transported back into the gasifier where a thermal transfer from sand to biomass occurs. In addition to the product gas flow, a flue gas stream exists, which is similar to that of a conventional incinerator.