Control of Volatile Organic Compounds Emissions from Manufacturing

E.4.1 Catalytic Incinerator Design Procedure
The basic equipment components of a catalytic incinerator include
a blower, burner, mi xi ng chamber, catalyst bed, an optional heat
exchanger, stack, control s, instrumentation, and control panel s. The
burner is used to preheat the gas to catalyst temperature. There is
essentially no fume retention requirement. The preheat temperature is
determined by the VOC content of gas, the VOC destruction efficiency,
and the type and amount of catalyst required. A sufficient amount of
air must be available in the gas or be supplied to the preheater for
VOC combustion. (All the gas streams for which catalytic incinerator
control system costs were developed are dilute enough in air and
therefore require no additional combustion air.) The VOC components
contained in the gas streams include ethylene, n-hexane, and other
easily oxidizable components. These VOC components have catalytic
ignition temperatures below 315OC (600°F). The catalyst bed outlet
temperature is determined by gas VOC content. Catalysts can be operated
up to a temperature of 700°C (1,300°F). However, continuous use of
the catalyst at this high temperature may cause accelerated thermal
agi ng due to recrystal lization.
The catalyst bed size required depends upon the type of catalyst
used and the VOC destruction efficiency desired. About 1.5 ft3 of
catalyst for 1,000 scfm is required for 90 percent control efficiency
and 2.25 ft3 is required for 98 percent control efficiency.19 As
di scussed earlier many factors influence the catalyst 1 ife. Typical ly
the catalyst may loose its effectiveness gradual ly over a period of
2 to 10 years. In this report the catalyst is assumed to be replaced
every 3 years.
Heat exchanger requi rements are determi ned by gas inlet temperature
and preheater temperature. A minimum practical heat exchanger efficiency
is about 30 percent. Gas temperature, preheater temperature, gas dew
point temperature and gas VOC content determine the maximum feasible
heat exchanger efficiency. A maximum heat exchanger efficiency of
65 percent was assumed for this analysis. The procedure used to calculate
fuel requi rements is presented in Table E-8. Estimated fuel ' requi rements .
and costs are based on using natural gas, although either oil (No. 1
or 2) or gas can be used. Fuel requirements are drastically reduced