the present invention relates to an installation intended for the pyrolysis of solids , comprising a rotary furnace inside which pyrolysis is achieved , and a means for heating the rotary furnace . the installation according to the invention further comprises a means for preheating the solids , located upstream from said furnace , said means comprises at least two zones in which the solids are preheated at different temperatures and a gas extraction device into which the pyrolysis gases are led after passing through at least one of said preheating zones .