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6

Condensation

Lawrence K. Wang, Clint Williford, and Wei-Yin Chen

CONTENTS
INTRODUCTION
PRETREATMENT, POSTTREATMENT, AND ENGINEERING CONSIDERATIONS
ENGINEERING DESIGN
MANAGEMENT
ENVIRONMENTAL APPLICATIONS
DESIGN EXAMPLES
NOMENCLATURE
REFERENCES
APPENDIX

1. INTRODUCTION
1.1. Process Description
Condensation is a separation process in which one or more volatile components of a
vapor mixture are separated from the remaining vapors through saturation followed by
a phase change (see Fig. 1). The phase change from gas to liquid can be accomplished in
two ways: (1) the system pressure may be increased at a given temperature or (2) the sys-
tem temperature may be reduced at a given pressure. Condensation occurs when the
vapor-phase partial pressure of a volatile component exceeds that of the component in
the liquid phase (or the vapor pressure for a pure liquid phase). Condensers are the unit
operations primarily used to remove volatile organic compounds (VOCs) from gas
streams prior to other controls such as incinerators or absorbers, but can sometimes be
used alone to reduce emissions from high-VOC-concentration gas streams.
Figure 1 illustrates a simple process flow diagram for condensation. A typical con-
densation system consists of the condenser, refrigeration system, storage tanks, and
pumps. Figure 2 further details an entire condensation and recovery process: (1) VOC
off-gas is compressed as it passes through a blower; (2) the exiting hot gas flows to an
aftercooler commonly constructed of copper tubes with external aluminum fins. Air is
passed over the fins to maximize the cooling effect. Some condensation occurs in the
aftercooler; (3) the gas stream cools further in an air-to-air heat exchanger; (4) the con-
denser cools the gas to below the condensing temperature in an air-to-refrigerant heat

From: Handbook of Environmental Engineering, Volume 1: Air Pollution Control Engineering
Edited by: L. K. Wang, N. C. Pereira, and Y.-T. Hung © Humana Press Inc., Totowa, NJ
307