Control of Volatile Organic Compounds Emissions from Manufacturing

$0.335/scfm for units with no heat recovery (i e., fhr 4 in. Hz0 presLure
drop) and $0.838/scfm for units with heat recovery ( e . for 10 in. k20
pressure drop).
E.5 SURFACE CONDENSER DESIGN AND COST ESTIMATION PROCEDURE
This section presents the details of the procedire used for
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sizing and estimating the costs of condenser sysths applied to the
gaseo'us streams from the continuous process polystyrene model plant.
Two types of condensers are in use in the industry: surface condensers
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in which the coolant does not contact the gas or condensate; and
contact condensers in which coolant, gas, and condensate are intimatdly
mixed. 1
Surface condensers were evaluated for the fol loki Ag two streams ' I
from the polystyrene model plant: the styrene condens& vent and the
styrene recovery unit condenser vent. These streams consist of styrene
and steam, which are immiscible, or of styrene in air, a non-condensable.
The nature of components present in the gas stream determines the
method of condensation: isothermal or non-isothermal. The condensation
method for streams containing either a pure component or a mixture of
two immiscible components is isothermal. In the isothermal condensation
of two immiscible components,such as styrene and steah, the componetks
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condense at the saturation temperature and yieid "two immi scible 1 iqu~d
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condensates. The saturation temperature is reached when the vapor
pressure of the components equals the total pressure of the system.
The entire amount of vapors can be condensed by isothermal condensation.
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Once the condensation temperature is determined, the total heat load' is
calculated and the corresponding heat exchanger system size is estimated.
The condensation of styrene mixed with a non-condensable, such as air, -
can be considered isothermal if the temperature of one fluid is nearjy
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constant. The analysis shows that the condenser coolant tempearturel is
nearly constant for the combined material recovery vent stream from the
continuous polystyrene model plant. The condensation of styrene in '
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air, nevertheless, is accompl ished less readily, and thus more expensively,
than the condensation of styrene in steam.
The following procedures and assumptions were used in evaluating
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the isothermal condensation systems for the two streams containing
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