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372 Lawrence K. Wang et al.

The following discussion will be based on fixed-bed catalytic incinerator system
with recuperative heat exchange (i.e., preheating the emission stream). Throughout this
chapter, it is assumed that adequate oxygen (i.e., O content greater than 20%) is present
2
in the emission stream so that combustion air is not required. The calculation procedure
will be illustrated using emission stream 2 described in Table 1.
1.2. Range of Effectiveness

Catalytic oxidation is a well-established method for controlling VOC emissions in waste
gases. The control efficiency (also referred to as destruction efficiency or DE) for catalyt-
ic oxidation is typically 90–95%. In some cases, the efficiency can be significantly lower,
particularly when the waste stream being controlled contains halogenated VOCs.
Factors that affect the performance of a catalytic oxidation system include the
following:
1. Operating temperature
2. Space velocity (the reciprocal of residence time)
3. VOC composition and concentration
4. Catalyst properties
5. Presence of poisons/inhibitors in the waste gas stream
6. Surface area of the catalyst
Poisons/inhibitors that can significantly degrade the catalyst activity include sulfur,
chlorine, chloride salts, heavy metals (e.g., lead, arsenic), and particulate matter. The pres-
ence of any of these species in the waste gas stream would make catalytic incineration
unfavorable.
If halogenated VOCs are present in the influent gas stream, then hydrochloric acid
(HCl) may be produced in the catalytic oxidizer. HCl emissions are regulated and off-gas
controls for HCl and other acid gases may be required.
Catalytic incineration can achieve overall hazardous air pollutant (HAP) destruction
−1
efficiencies of about 95% with SV in the range of 30,000–40,000 h using precious metal
catalysts, or 10,000–15,000 h −1 using base metal catalysts. However, greater catalyst vol-
ume and/or higher temperatures required for higher destruction efficiencies (i.e., 99%)
my make catalytic incineration uneconomical. In this chapter, discussions on catalytic
incineration design and operation will be based on HAP destruction efficiencies of 95%.
The influence of temperature and SV on the effectiveness of a catalytic oxidation
system is shown in Figs. 3 and 4, respectively. The data shown in these figures are for
a fluidized-bed catalytic oxidation system. The waste gas treated by this unit contained
10–200 ppmv (parts per million by volume) of mixed VOCs, including aliphatic, aro-
matic, and halogenated compounds. It can be clearly seen from Figs. 3 and 4 that DE is
a function of chemical composition of a stream under a given SV and temperature. As
the incineration temperature is increased with fixed SV, DEs increased linearly for most
mixtures. A decrease of DEs was observed as the SV was increased.
In designing a catalytic oxidation system, temperature and SV are not the only vari-
ables that must be considered. The emission stream composition and catalyst type
must be evaluated simultaneously because the type of catalyst chosen for a system
places practical limits on the types of compound that can be treated. For example,
waste gases containing chlorine and sulfur can deactivate noble metal catalysts such