To provide a steam reformer for a hydrocarbonaceous raw material where the degradation problem of a reforming catalyst at a reforming catalyst portion in the steam reformer is solved and which can be stably operated for a long term.

In the steam reformer where the reforming catalyst portion is located in a space between double cylinders consisting of an outer tube and an inner tube, the mixed gas of the hydrocarbonaceous raw material and steam is introduced from the upstream part of the reforming catalyst portion and a hydrogen-rich reformed gas is exhausted from its downstream part, a reforming guard catalyst portion in which the reforming catalyst is filled is located to be connected to the upstream end of the reforming catalyst portion. The amount of the reforming catalyst filled in the reforming guard catalyst portion is 7% or more of the total amount of the reforming catalyst in the reforming catalyst portion and the reforming guard catalyst portion. The mixed gas of the hydrocarbonaceous raw material and steam flows to the reforming guard catalyst portion and the reforming catalyst portion and the hydrogen-rich reformed gas is exhausted from the downstream part.

COPYRIGHT: (C)2007,JPO&INPIT