Environmental Engineering FOURTH EDITION

Reuse, Recycling, and Resource Recovery 287

0- Liohtfraction

Air classifier

Ferrous

.metals

Air a

Magnetic drum

To P@@”” I Glass

disposal

Figure 14-12. Diagram of a typical materials separation facility for refuse processing.

supplement coal or as the sole fuel in separate boilers. Fuel made from refuse is called
refuse-derived fuel, or RDF. Combustion of organic material is assumed to proceed by
the reaction

(HC), + 02 + xC02 + 5H2O +heat.

However, not all hydrocarbons are oxidized completely to carbon dioxide and water,
and other components of the fuel, like nitrogen and sulfur, are also oxidized, by the
reactions

2

N2 + 02 + 2N0

2NO + 02 + 2N02

s+02+s02

2s02 + 02 + 2so3.

As discussed in Chap. 19, NO2 is an important component in the formation of photo-
chemical smog. SO2 is damaging to health and vegetation, and the reaction product
SO3 forms “acid rain” by the reaction

so3 + H20 + H2S04.

Stoichiometric oxygen is the theoretical amount of oxygen required for combustion (in
terms of air, it is stoichiometric air) and is calculated from the chemical reaction, as
in the following example.