(best examples and good practices) on household organic waste ...

43
Two main types of fluidized beds are used in Europe for the combustion of
waste. In ‘bubbling’ beds, air velocity is maintained close to the maximum
above which bed material is carried away. In ‘circulating’ beds, air velocity is
high enough to entrain part of the bed material which is then captured <strong>and</strong>
returned to the bed. This second design allows more fuel to be burned in the
bed because more heat can be carried out of the bed by the recirculated
material. In terms of efficiency of energy recovery, fluidized bed combustors
have an advantage over grate furnaces because they can operate with only 30-
40% excess air. (Bontoux.,1999)
Fluidized beds (Figure 18.) can h<strong>and</strong>le liquids, solids, pastes <strong>and</strong> gases as long
as they can be injected through nozzles <strong>and</strong> they neither melt nor slag. This
bars the incineration of bulky items but has the advantage of maintaining a
more uniform temperature in the furnace. This is why they are mostly used for
refuse derived fuel (RDF) after significant pre-treatment. RDF is a material
proceeding from waste specially prepared so that it can be used as a fuel.
Figure 18.: HICB type fluidized bed type gasification furnace sketch
drawing
(Thermal methods of municipal waste treatment., 2009)