NOVELTY - Plant for slow pyrolysis of organic matrix material, comprises a reaction chamber divided into a pre-heating portion and a pyrolysis portion downstream of the pre-heating portion; and a combustion chamber that is co-axial with and external to the reaction chamber, the combustion chamber being divided into a pre-heating portion, surrounding the pre-heating portion of the combustion chamber, and in a heating portion surrounding the pyrolysis portion of the reaction chamber, the heating portion of the combustion chamber housing burners.    USE - The plant or process is useful for slow pyrolysis of organic matrix material (claimed), preferably for pyrolysis of carbonious or at least partially carbonious material, such as one originating from biomasses or from organic and mixed waste of various origins.    ADVANTAGE - The pyrolytic method is based on the combination of three process parameters, i.e., low reaction speed, adjustment of the water content and presence of catalysis, allowing converting the starting organic matrix material, whether it is composed of woody or agricultural wastes or biomasses, into synthesis gases with a very high yield.    DETAILED DESCRIPTION - Plant for slow pyrolysis of organic matrix material, comprises a reaction chamber divided into a pre-heating portion and a pyrolysis portion downstream of the pre-heating portion; and a combustion chamber that is co-axial with and external to the reaction chamber, the combustion chamber being divided into a pre-heating portion, surrounding the pre-heating portion of the combustion chamber, and in a heating portion surrounding the pyrolysis portion of the reaction chamber, the heating portion of the combustion chamber housing burners, where the reaction chamber rotates along a horizontal axis within the combustion chamber, and the outer surface of the pre-heating portion of the reaction chamber comprises a helicoidal tongue creating a spiral path for the combustion gases generated by the burners. An INDEPENDENT CLAIM is included for an organic matrix material slow pyrolysis process, involving: (a) providing the plant; (b) adding a cracking reaction catalyst, preferably selected from nickel-, iron-, or chrome-based catalysts, to the organic matrix material; (c) pre-heating the organic matrix material and adjusting the water content to about 30 wt.%; (d) carrying out a slow pyrolysis of the organic matrix material, and collecting the pyrolytic gases comprising hydrogen and carbon monoxide; (e) quickly cooling the pyrolytic gases; and (f) washing the cooled pyrolytic gases.