Fluidized bed

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Fluid Bed

Early work on fluid bed were reported in the beginning of the eighties by the University of Waterloo in Canada. In 1990, a 200 kg/hr demonstration plant was built by Union Fenosa, a utility company in Spain for generation, transmission and distribution of electricity. This plant is dismantled. Another 200 kg/hr fluid bed system was developed and constructed by Enco Enterprises Inc. on a standard trailer in the late 1980’s and early 90’s of the last century, with the intention to convert peat moss into liquid fuel. After extensive testing it became clear that scale up could be limited, and this project was abandoned. The Canadian Dynamotive Corporation, however, commercialized the fluid bed technology of the University of Waterloo. A patent dates back to 1998 (Piskorz et al., 1998). Design and development of the first commercial plant at West Lorne started in 2002. The plant started operations early 2005 with a design capacity of 100 tons per day of waste sawdust but never reached the designed bio-oil production capacity, presumably due to design and construction problems. Nevertheless, a second plant was built in 2006 with an even larger design capacity of 200 tons per day. Operational performances for both plants cannot be found in the open literature, and both units are out of operation now. Gulephs has been dismantled completely and information on the status of the Dynamotive plants is not provided since then, though the focus seem to have changed towards the upgrading of the pyrolysis oils to motor fuels, in a cooperation with IFP Energies Nouvelles and Axens (Dynamotive 2012).

Scale up of fluid bed pyrolysis is limited in case the heat is indirectly transferred, especially if submersed coils are applied. Application of a twin fluid bed with solids exchange (and separation of biomass pyrolysis and char-gas combustion) could solve this problem, and an example of such a system is proposed by Wellman Process Engineering. The fluid bed was surrounded by the char combustor, with heat transfer through the separating wall and by exchange of solids. Construction of a pilot plant was completed early 1999, but never started, reportedly due to permit problems, and is not reported to be used since then. Although fluid bed operation is reportedly a pretty well understood technology for pyrolysis, experimental experiences in fluid bed pyrolysis still indicate a number of serious technical problems to overcome. Amongst other these include the fact that the inert gas used for fluidization of the reactor bed must be the non-condensable part of the pyrolysis gas. This gas needs to be reheated and compressed, which requires careful cleaning to avoid blockage of heat exchangers, blowers, etc.