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A fluidized
bed heated by concentrated solar energy was characterized as a thermal
reactor for metallurgical applications. The bed uses typical foundry
sand, which is an inert, cheap material of easily controlled size. The
heat treatment rate depends on insolation and the amount of sand in the
bed, which is heated and fluidized by a double gas circuit. Fluidizing
air is preheated in a heat exchanger coil by solar-heated exhaust air. A
temperature of 1100 K is easily reached, making it suitable for many
metallurgical applications. Temperature stability remains good even
during changes in direct insolation for short periods of time due to
cloud transients or any other interruptions because the sand reactor
mass has a high thermal inertia. Fluidized beds are characterized by
temperature stability throughout the bed, so solid metal treatments at
specific required temperatures are possible. This characteristic is also
of great interest in gas-gas organic reactions or gas-solid organic
catalytic reactions.
During 2006 foaming of aluminum alloys and hardening of steel by heating
in the bed and quenching in water or oil were tested, demonstrating the
feasibility of a solar heated fluidized bed as a thermal reactor for
medium and high-temperature metallurgical applications.
Future applications to be tested during 2007 will include other thermal
treatments, such as nitriding, carburizing, etc., to coat metals in
reactive atmospheres, and cleaning soils contaminated by metallic zinc
and zinc chloride salts at galvanizing plants.
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