Abstract: A process and system for simultaneously cooling shale ash fines and flue gas produced during the combustion of spent shale. The flue gas and fine solids are introduced into a heat exchange zone for contact with conventional heat exchange tubes. Heat transfer particles are introduced into the heat exchange zone for mixing with the flue gas to provide increased heat transfer rates between the flue gas and heat exchange equipment. The heat transfer solids are also of a sufficient size to provide continual scrubbing of the heat exchanger surfaces to prevent the build up of an insulating layer of fine dust particles. A staged cooling system and process is also disclosed.