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380 Lawrence K. Wang et al.

In other words, check whether T falls in the interval 1000–1200ºF to ensure a high DE
co
without catalyst damage. Equation (2) can be used to calculate T . This equation
co
assumes a 50ºF temperature increase for every 1 Btu/scf of heat content
T = T + 50h (2)
co ci e
where h is the heat content of the emission stream (Btu/scf). In this expression, it is
e
assumed that the heat content of the emission stream and the combined gas stream is the
same. First, insert a value of 600ºF for T in Eq (2). Then, determine T if T is in the
ci co co
range of 1000–1200ºF. If this is true, then the initial value of T is satisfactory. If T is
ci co
less than 1000ºF, use Eq. (3) to determine an appropriate value for T (above 600ºF)
ci
and use this new value of T in the calculation
ci
T = 1,000 − 50h (3)
ci e
The value of T obtained from Eq. (3) is then used in Eq. (4) for the determination of
ci
the auxiliary requirement.
Emission streams with high heat contents will be diluted based on the requirements
discussed in Section 2.1. Therefore, values for T exceeding 1200ºF should not
co
occur.
For catalytic incinerators, a 50% efficient heat exchanger is assumed, whereas for
thermal incineration, a 70% efficient exchanger is assumed. A 70% efficient heat
exchanger for catalytic oxidation can result in excessive catalyst bed temperatures.
Therefore, a 50% efficient heat exchanger is assumed for purposes of this discussion,
although 70% efficient heat exchangers may be found on some streams.
To calculate supplementary heat requirements (based on natural gas as the fuel), the
following simplified equation can be used for dilute emission streams that require no
additional combustion air:
e[
DQ Cp (11. T − T − 01. T )]
he
Q = e air ci T − )] r (4)
f[
f
Dh − 11. Cp ( ci T r
air
f
where Q is the fuel gas flow rate (scfm), D is the density of the emission stream
f e
3
3
3
(lb/ft [typically 0.0739 lb/ft ]), D is the density of the fuel gas (0.0408 lb/ft for
f
methane at 77ºF), Q is the emission stream flow rate (scfm), Cp is the average spe-
e air
cific heat of air over a given temperature interval (Btu/lb-ºF) (see Table 5), T is the
ci
temperature of the combined gas stream entering the catalyst bed (ºF), T is the refer-
r
ence temperature (77ºF), T is the emission stream temperature after heat recovery (ºF),
he
and, h is the lower heating value of natural gas (21,600 Btu/lb).
f
Note that for the case of no heat recovery, T = T . The factor 1.1 is included in Eq.
he e
(4) to account for an estimated heat loss of 10% in the incinerator. The maximum emis-
sion flow rate should be used in Eq. (4) for determining supplementary heat requirements
and, hence, will lead to a conservative design. In contrast to thermal incineration, there
is no minimum supplementary heat requirement specified for catalytic incineration
because no fuel is needed for flame stabilization. Depending on the HAP concentration,