Indirect Heating of Bubbling Fluidized Beds By Means of Liquid Metal Heat Pipes

Indirect heating of bubbling fluidized beds by means of liquid metal heat pipes enables highest heat fluxes into atmospheric or pressurized fluidized bed reactors. An application for such indirectly heated fluidized bed technologies is the Biomass Heatpipe Reformer. The technology was firstly presented during the Fluidization X conference in Bejing 2001.

Heat pipes are closed tubes partially filled with a working liquid. Evaporation and condensation inside the tube guarantee highest heat transfer coefficients at both ends of the tubes and provide extraordinary high heat fluxes along the tubes.

The heat pipes provide the heat-of-reaction for endothermic biomass gasification reactions from a bubbling fluidized bed combustion into a pressurized steam-blown fluidized bed reactor. The concept allows a complete separation of combustion chamber and gasification chamber and enables therefore the use of different fuels and pressures in combustor and gasifier. Temperatures of 900°C in the combustion chamber and above 800°C in the gasifier enable the production of a particularly hydrogen rich syngas. The syngas suites ideally for the synthesis of Substitute Natural Gas (SNG) from biomass. A total of three prototypes have been tested at Technical University of Munich between 2001 and 2007. The start-up agnion Inc. the commercialization of the technology in 2007. The presentation will present the experiences from agnion’s demonstration plants in the range from 500 kW and 1.3 MW. It will in particular discuss heat transfer and its impact on the reactor layout and dimensioning and long-term experiences with the heat pipes. Experimental observations have shown the essential impact of the fuel particles mixing on the syngas composition and quality.

An outlook will summarize further technical applications and recent developments for the application of liquid metal heat pipes in fluidized beds such as indirectly heated carbonate looping processes and pyrolysis applications.