Control of Volatile Organic Compounds Emissions from Manufacturing

and, in some cases, reused in the process. Condensers are widely used
for recoveri ng organics from both conti nuous and intermittent rich
by-product streams in polystyrene manufacturing processes. The VOC is
mainly styrene which is easily condensed because of its relatively high
condensation temperature. The ease of styrene recovery and the abi 1 ity
of a condenser to handle an intermittent stream makes it a desirable
control technology for all process VOC emissions in the polystyrene
industry. Condensers may a1 so be used in series with other air pol lu-
tion control systems. A condenser located upstream of an incinerator,
adsorber, or absorber will reduce the VOC load entering the downstream
control device. The downstream device will abate most of the VOC that
passes through the condenser.
Adsorbers are used on gas streams which contain relatively low VOC
concentrations. Concentrations are usual ly we1 1 be1 ow the 1ower expl osi ve
limit in order to guard against overheating of the adsorbent bed.
Adsorbers are often neither suitable nor the most efficient means of
control for the higher VOC concentration streams characteristic of the
polymers and resi ns industry .
Absorbers, which use low volatil ity 1 iquids as absorbents, are
another control option. Thei r use is general ly limited to applications
in which the spent absorbent can be used directly in a process, since
desorption of the VOC from the absorbent is often prohibitively expensive.
Recovery techniques either condense the organic or contact the
VOC-containing gas stream with an appropriate liquid or solid. Gases
containing only one or two organic gases are easier to process by recovery
techniques than multi-component mixtures. The presence of inert or
immi scible components in the waste gas mixture compl icates recovery
techniques.
3.2.1 Condensers
Condensation devices transfer Chermal energy from a hot vapor to a
cooling medium, causing the vapor to condense. Condenser design thus
typically requires knowledge of both heat and mass transfer processes.
Heat may be transferred by any combination of three modes: conduction,
convection, or radi ation.
The design of a condenser is significantly affected by the number
and nature of components present in the vapor stream. The entering