Control of Volatile Organic Compounds Emissions from Manufacturing

other dryers may have higher or lower emissions. The combi ned stream
characteri sti cs were cal cul ated based on the indi vidual stream character-
istics and compositions given in Table 2-6 and an assumed composition
of 0.7 percent isobutane in air (thus requiring no further dilution to
reduce the lower heating value to below 25 percent of the lower explosive
limit in order to prevent an explosion hazard). Because of the substantial
VOC content of the combined waste gas stream, quench air is required to
reduce the combustion temperature of the incinerator and no auxiliary
natural gas is required for flaring,
Table 5-10 summarizes the results of the cost analysis for the
high-densi ty polyethylene model plant. Breakdowns of capital and operating
costs are presented for both thermal incinerators and flare systems.
The total installed capital cost estimated for RAC T is $557,400 for a
thermal incinerator system and $54,500 for a flare system. The annualized
RACT cost estimates are $166,000 for a thermal incinerator and $47,400
for a flare system. As was done for the polypropy lene model plant,
two additional cost analyses were undertaken, The results of these two
analyses are summarized in Table 5-11.
5.2.3 Polystyrene (PS)
Costs of ach ievi ng RACT for polystyrene continuous processes were
estimated based on further condensation of JOC emitted from the two
vents from the system recovering unreacted styrene monomer: the styrene
condenser vent and the styrene recovery unit condenser vent. The extruder
quench vent, the other stream within the scope of this CTG, contains
only a trace of styrene in steam and was not considered for control
under RACT. The styrene emissions from the two streams were combined
and cooled to reduce gaseous emissions to 0.12 kg VOC/1000 kg of product.
Current industry control is in a transitional period in which vacuum
pumps are replacing steam eductors to produce the required vacuum. This
transition is taking place because of cost incentives to recover styrene
as vacuum pumps' result in lower emissions of styrene to the atmosphere.
Both an "uncontrolled" emission level of 3.09 kg VOC/1000 kg of product
and an already relatively well-control led emission level of 0.20 kg
VOC/1000 kg of product were examined in the cost basis, The higher level
is based on one plant that is already in the process of reducing emissions to