A novel concept of recovering heat from hot gases using countercurrently flowing vibrofluldized solids (that is, solids levitated solely by mechanical vibration) has been proposed and tested.

Based on a theoretical heat transfer model, the heat transfer coefficient between the air and the solids was calculated. A factorial design of experiments showed that a higher heat transfer coefficient was obtained with higher air flow rates and lower solid flow rates. The baffle height had an insignificant affect on the heat transfer. Tests with multiple baffles led to a maximum heat transfer coefficient (143 W/m²-K) when using four baffles. For all tests performed in this work, the solids were not truly vibrofluldized. Instead, they were merely vibro-conveyed (or vibro-shuffled) as a single mass. A new vibrating system will provide the sufficient energy for vibrofluidization, and enhanced heat transfer is expected.

This work demonstrated for the first time the solid impeding phenomenon in a fluidized-bed heat exchanger. Specifically, experimental tests showed that if a baffle was lowered past a limiting height at given air and solid flow rates, the increased air velocity past a baffle could prevent the solids from exiting the exchanger.

An economic evaluation showed that the vibrofluidized-bed heat-exchanger system would be economically feasible for the production of boiler feedwater using heat recovered from boiler combustion gases. The payback time for the system could be as little as 1.4 years.

The convective heat-transfer data from a supernatant gas to a flowing vibrofluidized bed of solids were the first of their kind, and they have led to a better understanding of the new vibrofluidized-bed heat-exchanger system. The successful completion of this project sheds encouraging light onto future heat-recovery operations with such a system.