Reactor vessel for performing a steam reforming reaction and a process to prepare synthesis gas

A reactor vessel for performing a steam reforming reaction comprising:

• a vessel inlet for natural gas and steam,
• a vessel inlet for a hot gaseous medium,
• a vessel outlet for a gaseous product comprising the steam reforming product;
• and
• a reactor space having a reactor space inlet and a reactor space outlet end, the reactor space comprising a plurality of reactor tubes filled with a bed of steam reforming catalyst, the reactor space inlet being fluidly connected to the inlet for natural gas and steam, and at the reactor space outlet end being fluidly connected with the outlet for the gaseous product;
• wherein inside each reactor tube a passageway running parallel to the axis of said reactor tube fluidly connects to the vessel inlet for the hot gaseous medium, the passageway being suitable for passage of hot gaseous mixture counter currently to a flow of reactants in the catalyst bed, and
• wherein each tube and passageway can be individually removed through the top of the vessel so that the catalyst can be replaced or refreshed.