Method for changing heat transfer bed depth in packed bed heat exchangers

A preheating apparatus for particulate material comprising:

• a containment vessel;
• a floor to said containment vessel having a material outlet for discharging preheated particulate material out of the apparatus;
• a vertically oriented outer annular preheating section which circles the material outlet;
• a feed pipe having a material entry and material exit, said feed pipe extending vertically downward into the preheating section to deliver particulate material into the annular preheating section to form a material pile in the preheating section extending above the floor, said feed pipe being adaptable to be extended or retracted within the preheating section to thereby lower or raise the material pile;
• means to deliver hot gas into the annular preheating section;
• and
• means to discharge said gas from the annular preheating section after the gas has passed through the particulate material in the section.