Abstract: A method of the exchange of heat between solids where the heated solids are passed through heat conducting tubes defining a first flow path or zone in the heat exchanger and the solids to be heated are passed through the interstitial space around the tubes, or through secondary tubes, in the heat exchanger, defining a second flow path or zone. The solids are physically separated by the walls of the tubes which act as a heat conducting barrier and the solids are flowed, under moving-bed conditions, in counter-current or concurrent directions to enable the heat transfer to be effected.