Fluidized Bed Combustion of Industrial Wastes
M. JOHN RUHL, Project Engineer
Copeland Systems Incorporated
Oakbrook, Illinois 60521
INTRODUCTION
Recent technological advances in fluidized bed combustion have opened the doors for
many exciting new applications of fluidized processes. Some of the more important of these
are the disposal of industrial sludges and a variety of solid and liquid industrial wastes.
This paper briefly describes various processes now being used industrially and others
which have been proven on a pilot scale and which are available to industry. The processes
which are described include chemical recovery units as well as those used primarily for
volume reduction and destruction of objectionable materials. Many systems operate
without the use of auxiliary fuel, and several forms of heat recovery can be utilized, both of
which are becoming increasingly important facts as energy conservation continues to be the
focus of everyone's attention.
Two case histories are cited, one which has been in operation for nearly four years
burning a variety of solid wastes and clarifier sludges, and one which has been successfully
piloted and is now under construction which will burn sludge from the combined waste
streams of five different industries.
WHAT IS A FLUIDIZED BED?
Fluidization is a phenomenon in which fine solid particles are suspended by the
upward flow of a gas or liquid through the mass of solids. Take, for example, a vessel such as
a tin can which contains a few inches of sand. If we were to drill hundreds of tiny holes in the
bottom of the can and blow a small flow of air through the holes and upward through the
bed of sand, we would see movement of the sand particles because of the flow of the air
bubbles. As the flow rate of the air is increased we would begin to observe more and more
motion of the particles and a slight expansion of the bed until at some critical velocity, the
friction between the air and the surface of the sand particles becomes equal to the weight of
the particles and the sand is suspended in the air. The sand bed is then said to be fluidized,
because in this suspended state the mass of solids behaves very much like a liquid, obeying
most of the hydraulic laws. The motion of the bed even resembles that of boiling water. If
the vessel were to be tilted, the surface of the fluidized bed would remain horizontal, tapping
on the vessel would create waves on the surface of the bed, heavy objects would sink in the
bed while lighter ones float on the surface and the fluidized materials would flow like water
through a hole in the side of the  vessel. Figure I illustrates this last phenomenon.
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