Abstract: Heat exchange apparatus and process, particularly heat exchange primary reforming with the primary reformed gas being subjected to partial combustion (and optionally secondary reforming) and the resultant partially combusted gas being used as the heat exchange medium to supply heat required for the primary reforming. The apparatus includes process fluid inlet and outlet zones separated from the heat exchange zone by boundary means such as tube sheets or header pipes. A plurality of heat exchange tubes for a process fluid extending through a heat exchange zone from one of the boundary means and slideably engage at the other boundary means with seal tubes fastened to said other boundary means.