TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: Before stage (a), the product (P) is stored in the form of solid with a particle size of 10-1000 (preferably 100-300) microns, at a relative humidity of 1-12 (preferably 5-10) %. Pyrolysis gas is taken off from the last part of the reactor (20) (with regard to the direction of circulation of (P)) and kept at the same temperature until it reaches the condenser (30), where it is then cooled rapidly by passing between tubes (34) carrying refrigerant fluid circulating at about 0 degrees C, preferably between a set of vertical tubes (34) which are cleaned by the trickling condensate. Uncondensable fractions of the pyrolysis gas are taken off from the top of the condenser (30) (preferably by forced extraction via an oil droplet trap (39)), for rapid combustion in a furnace (36) or for recycling in a hot-air dryer (61) used for preconditioning the product (P). The process also includes the extraction of residual coke from the bottom of the reactor (20), for cooling in the absence of oxygen in a sealed cooler (40), preferably by progressive cooling to not above 50 degrees C. Preferred Installation: The preconditioner (10) comprises a channel with a double jacket (11) (through which hot fluid passes) and a conveyor screw (12) mounted in the channel so as to turn at a constant and controlled speed; on top of the channel there is an upstream feed hopper (15) and an outlet (17) for vapour. Alternatively, the preconditioner (60) comprises a hot-air drier (61) fitted with a strip belt (62) with hot air passing over it. The reactor (20) comprises a closed chamber (21) with walls of refractory material, which is connected, via gate valves (23, 42), to the preconditioner (10) (at the top) and to a sealed coke cooler (40) (at the bottom). The reactor chamber (21) has a pipe (29) at the top for injecting reaction gas or neutral gas. The two ends of the conveyor screw (22) heated by the Joule effect are mounted outside the chamber (21) and cooled before being connected to the electricity supply. The outlet tap (31) in the reactor (20) is connected to the condenser (30) by a pipe (32) which is equipped, over its entire length, with electrical or fluidic means (33) of maintaining the temperature. The condenser (30) contains a set (34) of vertical tubes with circulating fluid refrigerant inside them; it has an outlet (37) at the top for the non-condensable pyrolysis fractions, connected by a pipe (38) to a combustion chamber (36); this pipe (38) includes an extractor fan (38.1) working in suction mode to maintain a reduced pressure in the reactor (20); there is also a trap for oil droplets (39) in this pipe (38) upstream from the fan (38.1).