Chemical Engineering July 2022 - 38

FIGURE 3. In tube-and-fin air-cooled exchangers,
a motor-and-fan assembly forces ambient air over
a series of tubes, to cool or condense the process
fluids carried within. Tapered fins are typically
added to the tubes to extend the surface area and
maximize heat transfer
leaking through the gasket groove of
the plate and either contaminating
other fluids or escaping to the atmosphere.
Additionally, the replacement
of glued gaskets can be challenging.
Many plate-and-frame heat exchangers
are now offered with a
glueless gasket system. The plate
construction uses clips and studs
to secure gaskets to the plates. This
method eliminates irregularities in the
gasket groove and results in better
sealing of the plate pack.
The glueless system also cuts
service and maintenance costs,
since the plates can be cleaned or
regasketed without removing them
from the frame.
Double-wall plate exchangers.
Double-wall plate heat exchangers
offer even greater protection against
gasket failure. In traditional plateand-frame
exchangers, the process
fluids are contained by gaskets and
thin, metal plates. In double-wall exchangers,
two plates are welded together
at the port holes to form one
assembly, with an air space between
the plates. In the event that one of
the two plates should develop a hole
or perforation, the fluid will leak into
the space between the two plates
and then to the atmosphere, instead
of entering an adjacent fluid
passageway and contaminating the
other process stream.
Typical applications include:
* Domestic water heaters
* Hydraulic oil cooling
* Any service where cross contamination
of process fluids cannot be
tolerated
Welded-plate exchangers. In this design,
the field gasket that normally contains
the process fluid is replaced by
a welded joint, greatly minimizing the
amount of fluid exposed to the gasket
material and making this design suitable
for hazardous or aggressive fluids.
The welded plates form a closed
compartment or " cassette. " Similar
to gasketed designs, alternating
flow channels are created to divert
the flow of hot and cold fluids into
adjacent channels. Aggressive fluids
pass from one cassette to the next
through an elastomer or Teflon ring
gasket, while non-aggressive fluids
are contained by standard elastomer
gaskets. The use of welded joints
can reduce total gasket area by 90%
on the aggressive-fluid side.
Typical
applications
New Reactor Systems from Parr!
50 L & 100 L
Stirred
Reactors
* For scale-up
& pilot work
* 725 psi @
200 °C
Continuous Flow Tubular Reactors
* Compact footprint & easy setup
* Catalyst screening & testing
* 5000 psi @ 500 °C
Rotating Cylinder Electrode
* Compact footprint & easy setup
* Catalyst screening & testing
* 5000 psi @ 500 °C
include
exchangers
handling the following:
* Vaporizing and condensing
refrigerants
* Corrosive solvents
* Amine solutions
Wide-gap plate exchangers. Compared
with
traditional
plate-andframe
exchangers, this design relies
on a plate pattern with significantly
larger free channel spacing, which
provides improved resistance to
clogging. The plates are designed
with few, if any, contact points between
adjacent plates to allow fibers
or solids to pass. Some styles of this
exchanger use wide-gap plates on
the process side and conventional
chevron patterns on the coolant
side, to enhance heat transfer.
Typical
applications
* Slurries
Brazed-plate exchangers. In
this
design, the elastomer gaskets found
in most plate-and-frame exchangers
are replaced with a brazed joint,
which greatly reduces the possibility
of leakage. The corrugated
heat-transfer plates, which are typically
available in stainless steel, are
brazed together using either a copper
or nickel brazing material.
The brazed-plate exchangers
are typically rated to 435 psi, but
could be rated in excess of 2,000
psi. Temperature ratings vary from
450°F for copper brazing to 750°F
for nickel brazing. As with other
plate-and-frame exchangers, high
include
exchangers
handling the following:
* White water in pulp-and-paper
operations
Let us build one for you.
38
Parr Instrument Company
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Stand B77
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CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JULY 2022
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Chemical Engineering July 2022

Table of Contents for the Digital Edition of Chemical Engineering July 2022
