ducts namely a first duct 27 opening tangentially into the combustion chamber 20 a second duct 28 opening through a voluted casing 29 into the said chamber 20 at the level of a burner 30 fitting this chamber and a third duct 3 1 opening into the duct 24 connecting the reaction chamber 22 to the cyclone 25 it should be pointed here that the first duct 27 and the voluted casing 29 are imparting to the hot air the same direction of rotation within the combustion chamber 20 the hot air flow issuing from the third duct 31 and as shown by arrows is making with the smokes issuing from the reaction chamber 22 and as physically shown by the arrow i an angle greater than 60 u00b0 this angle should advantageously lie between 140 u00b0 and 160 u00b0 at 32 is shown a set of valves for adjusting the hot air flow rate reaching on the one hand via the first duct 27 the combustion chamber 20 arrow j and on the other hand the second and third ducts 28 31 in each one of these ducts 28 31 is arranged an adjusting valve 33 referring now to fig3 there is seen that the burner 30 mounted at the top portion of the combustion chamber 20 in coaxial relation to the voluted casing 29 essentially comprises three coaxial envelopes or shells which are defining from the inside towards the outside a central passage way 34 for a make up fuel which may be heavy fuel oil or recovered solvents a passage way 35 providing for the injection of air under pressure.