Transitions - Sustainable Design: The Science of Sustainability and Green Engineering - page 127

incomplete combustion with higher vapor pressures than those of the original
contaminants.
The disadvantages of hazardous waste incinerators include the following: (1)
the equipment is capital-intensive, particularly the refractory material lining the
inside walls of each combustion chamber, which must be replaced as cracks form
due to the contraction and expansion whenever a combustion system is cooled
and heated; (2) operation of the equipment requires very skilled operators and is
more costly when fuel must be added to the system; (3) ultimate disposal of the
ash is necessary and particularly troublesome and costly if heavy metals and/or
chlorinated compounds are found during the expensive monitoring activities;
and (4) air emissions may be hazardous and thus must be monitored for chemical
constituents and controlled.
Given these underlying principles of incineration, seven general guidelines
emerge:
1. Only purely organic liquid contaminants are true candidates for combustion.
2. Chlorine-containing organic materials deserve special consideration if in
fact they are to be incinerated at all; special materials used in the con-
struction of the incinerator, long (many seconds) of combustion time, high
temperatures ( > 1600 ◦ C), with continuous mixing if the contaminant is in
solid or sludge form.
3. Feedstock containing heavy metals generally should not be incinerated.
4. Sulfur-containing organic material will emit sulfur oxides, which must be
controlled.
5. The formation of nitrogen oxides can be minimized if the combustion
chamber is maintained above 1100 ◦ C.
6. Destruction depends on the interaction of a combustion chamber's temper-
ature, dwell time, and turbulence.
7. Off-gases and ash must be monitored for chemical constituents; each resid-
ual must be treated as appropriate so that the entire combustion system
operates within the requirements of local, state, and federal environmen-
tal regulators, and hazardous components of the off-gases, off-gas treat-
ment processes, and the ash must reach ultimate disposal in a permitted
facility.
Thus, the decision of whether to incinerate waste must be a green one. That
is, the designer should consider ways to eliminate the generation of any wastes at
the outset, and decide the most sustainable methods for any remaining wastes.