Abstract: The specification describes a method and a fixed bed apparatus for producing olefinic hydrocarbons from a charge of saturated aliphatic hydrocarbons with 2 to 20 carbon atoms and hydrogen in a chamber 1 comprising a plurality of parallel tubes 3 filled with a catalyst and arranged in rows. A so-called reaction phase and a catalyst-regenerating phase are carried out in the tubes of the chamber. The tubes are heated by appropriate radiant heating means 6, arranged in layers substantially perpendicular to the tubes. These layers heat a first part of the tubes (at the feed side) with a heat flux greater than the mean heat flux of the chamber and a second, subsequent part with a mean flux no more than equal to the mean heat flux, so that the isothermicity of the catalyst is substantially maintained, using appropriate control means.

Abstract: A reaction chamber (E) comprises a calender reactor (5) comprising a device (4) for introducing a feedstock; a device (6) for carrying off the treated feedstock; at least two elementary reaction cells (52), not contiguous to one another, each one consisting of an individual feedstock distributor, an individual collector of the treated feedstock, and a catalytic bed, the cells being separated from one another by a channel (51); at least one device (V) for circulating a heat-carrying fluid in each channel (51); at least n partitions (S) for separating the flow of the heat-carrying fluid, n being an integer greater than or equal to 1; and at least n+1 means (T) for heating the heat-carrying fluid. The chamber can be used for performing the catalytic reforming of naphtha under low pressure.