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234 Applied Process Design for Chemical and Petrochemical Plants

Finned Side Pressure Drop A. Plate and Frame Heat Exchangers

Brown 211 recommends: Figures 10-7, 10-7A, 10-7B, and 10-7C illustrate the gen-
eral arrangements of most manufacturers, although several
2
10.00043221f o 21G¿2 L variations of plate flow pattern designs are available to
P (10-253)
1D e 21Z>Z w 2 0.14 1 2 accomplish specific heat transfer fluids’ temperature
exchanges. Also, the gasket sealing varies, and some styles
Use Figure 10-156 to determine f o . are seal welded (usually laser) to prevent cross-contamina-
tion. Note that Figure 10-7C has no interplate gaskets and is
D e G totally accessible on both sides, yet easy to clean.
Re (10-254)
1Z212.422 The construction materials for the plates include most
corrosion-resistant metals, usually 304SS, 316SS, titanium,
®
®
where D e equivalent annulus diameter, ft; (see earlier Incoloy 825 , Hastelloy , and others, plus nonmetallic fused
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calculation) graphite, and fluoroplastic Diabon F . Typical gaskets
G flow, lb/(ft )(hr) 3,600 (G ) between the plates include nitrile rubber, butyl, and EPDM
2
2
G flow, lb/(ft )(sec) ® ®
elastromers, Hypalon and Viton , based on the various
Z viscosity, average, centipoise
manufacturers’ literature.
fluid density, lb/ft 3
A heat transfer comparison is made in Figure 10-157. The
L equivalent length of travel, including bend factor, ft
plate and frame designs are used in convection, condensing,
D tube I.D., ft.
and some evaporation/boiling applications.
This type of exchanger usually provides relatively high
After designing an approximate unit area requirement, it
heat transfer coefficients and does allow good cleaning by
is important to review the final design performance details
mechanically separating the plates, if back-flushing does not
with a qualified exchanger manufacturer. See Table 10-42.
provide the needed cleanup. An excellent discussion on the
performance and capabilities is presented by Carlson. 210 To
Miscellaneous Special Application Heat Transfer
obtain a proper design for a specific application, it is neces-
Equipment
sary to contact the several manufacturers to obtain their rec-
It is necessary to work with the manufacturer in sizing and ommendations, because the surface area of these units is
rating these special units, because sufficient public data/ proprietary to the manufacturer.
correlation of heat transfer does not exist to allow the design
B. Spiral Heat Exchangers
engineer to handle the final and detailed design with confi-
dence. 1. The spiral design heat exchangers, Figures 10-9A, 10-9B,
10-9C, and 10-9D are conveniently adaptable to many
process applications. The true spiral units (Figure 10-9A
and 10-9B) are usually large and suitable for higher flow
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rates, and the Heliflow -style, Figure 10-9C, can be fabri-
cated into small sizes, suitable for many “medium” (but
not limited) process and sample cooler applications.
The spiral units are used as cross-flow interchangers,
condensers, and reboilers. These units can often be con-
veniently located to reduce space requirements. They
are suitable for vacuum as low as 3mm Hg, because the
pressure drops can be quite low. Bailey 214 identifies tem-
perature limits of 30 to 1,500°F, pressure limits of 0
to 350 psia, maximum flow rate per shell of 3,000 gpm,
2
and a heat transfer area of 4,000 ft . Trom 213 discusses a
wide variety of process-related applications.
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2. The Heliflow is a tubular version of the spiral plate
heat exchanger, Figures 10-9C and 10-9D, and has a
high efficiency and counter-flow operation with a wide
Figure 10-156. Heat-transfer curve for annuli with longitudinal fins. range of applications while occupying a limited space.
(Adapted from DeLorenzo, B., and Anderson, E. D. Trans ASME, V. 67,
No. 697, ©1945. The American Society of Mechnical Engineers) (Used The applications include vent condensing, sample cool-
by permission: Kern, D. Q., and Kraus, A. D. Extended Surface Heat ers, instantaneous water heating, process heating and
Transfer, p. 464, ©1972. McGraw-Hill, Inc. All rights reserved.) cooling, reboilers and vaporizers, cryogenic coolers,