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356 Lawrence K. Wang et al.

where HR is the heat recovery in the exchanger (%) and T is the temperature of the
e
emission stream (ºF). Assume that a value of 70% for HR if no other information is
available.
The factor 1.1 in Eq. (2) is to account for an estimated heat loss of 10% in the incin-
erator. Supplementary heat requirements are typically calculated based on maximum
emission stream flow rate, and, hence, will lead to a conservative design.

4. ENGINEERING DESIGN AND OPERATION

4.1. Flue Gas Flow Rate
Flue gas is generated as a result of the combustion process. Flue gas flow rate can be
calculated using the following equation:

Q = Q + Q + Q (4)
fg e f d
where Q is the flue gas flow rate (scfm), Q is the emission stream flow rate (scfm),
fg e
Q is the natural gas (fuel) flow rate (scfm), and Q is the dilutmon air requirement
f d
(scfm).
Because the flow rate auxiliary fuel is usually much lower than the flow rate of emis-
sion streams, the flue gas flow rate for dilute waste gases when auxiliary air is not
required is approximately equal to the waste gas flow rate. In cases where auxiliary air
is required, the flue gas flow rate is roughly equal to the sum of the waste gas flow rate
and the auxiliary airflow rate. The flue gas flow rate can be used in many correlations
to size the incinerator and estimate equipment costs.

4.2. Combustion Chamber Volume
The combustion chamber volume (V ) can be determined using the actual flue gas
c
flow rate and the desirable residence time (t ). The actual flue gas flow rate can be
r
calculated using
fg[
)
Q fg, a = Q ( T + 460 537 ] (5)
c
where Q is the actual flue gas flow rate (acfm), Q is the flue gas flow rate under stan-
fg,a fg
dard conditions [scfm calculated from Eq. (4)], and T is the combustion temperature (ºF).
c
The combustion chamber volume, V , is determined from the residence time t from
c r
Table 3 and Q obtained from Eq. (5):
fg,a
V = ( [ Q fg a 60 t ) r] × .05 (6)
1
,
c
The factor of 1.05 is used to account for minor fluctuations in the flow rate and follows
industry practice.
4.3. System Pressure Drop
The total pressure drop for an incinerator depends on the type of equipment used in
the system as well as other design considerations. The total pressure drop across an
incinerator system determines the waste gas fan size and horsepower requirements,
which, in turn, determine the fan capital cost and electricity consumption (12).