Gas generating system for a fuel cell system and process for operation of a gas generating system

A start up assembly for a fuel cell (3) has a gas generator with a hydrocarbon reformer (1) unit and one or more selective oxidation stages (2) for the removal of carbon monoxide from re-formed substances. The system also has one or more catalytic fuel burners (5). During the warm-up phase one or more of the burners is operated to evaporate fuel and water, and to heat a supplementary partial re-forming unit or a partial oxidation stage (7). During re-forming or partial oxidation, a flow of hydrogen gas is delivered to the fuel cell (3) which then operates at limited power during the warm-up phase. During the warm-up phase, the catalytic burner (5) is pre-heated by electrical power and receives a feed of hydrocarbon fuel or hydrogen from a reservoir. Also claimed is a commensurate process.