Method and apparatus for heating air containing solids

A system for heating air containing solids, the system comprising a vertical tubular heat exchanger for heating air containing solids, the heat exchanger a tube side and a shell side and comprising:

• a shell,
• an upper tube sheet,
• a lower tube sheet,
• a plurality of straight tubes,
• an upper head
• a lower head, and
• one or more intermediate tube sheet(s) which divide(s) the shell side of the heat exchanger into two or more separate shell side chambers,
• wherein:
• the shell side has connections for steam inlet condensate outlet and inert gas outlet,
• the system comprises a first steam source connected to the steam inlet of a chamber located closer to the upper head, and wherein
• the system comprises a second steam source connected to the steam inlet of a chamber located closer to the lower head,
• wherein:
• the connections for steam inlet and condensate outlet are located in the lower part of the shell side chambers and the connection for inert gas outlet is located at the upper part of the shell side chambers,
• the tubes extend continuously between the upper tube sheet and the lower tube sheet, and in that
• the first steam source is configured to provide a steam with a lower condensing temperature than the second steam source, wherein the upper tube sheet is in contact with the steam with the lower condensing temperature.