Hydrocarbon Processing - June 2021 - GP-30

HEAT EXCHANGE
and economic sustainability has led many
end-users to review the possibility of replacing
very large S&T exchangers with
more compact plate-type exchangers. In
this application for a gas-gas exchanger,
which includes high design pressure, the
printed circuit heat exchanger (PCHE)
and the PSHE are considered to be the
most appropriate alternatives (FIG. 3).
In the authors' opinion, the PSHE
appears to be the more attractive choice
from the economic and maintenance
points of view. The PSHE has larger channels
and easy access to the plate pack.
Feed gas entering the exchanger is usually
clean because of upstream separation and
filtration; however, fouling due to fine
sand carryover has been reported.
PSHE construction. The construction
of a PSHE is shown in FIG. 4. It essentially
consists of a cylindrical plate pack
within a round shell. The shell diameters
range from 360 mm-1,600 mm. The plate
pack is cylindrical, with circular plates of
0.8-mm thickness (depending on the design
pressure and temperature), pressed
with a pattern approximately 3 mm deep.
The resulting heat exchange area is approximately
300 m2
/m3
-more than
three times greater than an S&T type.
As the U-value for a plate-type heat exchanger
is more than twice that achieved
in an S&T exchanger, the physical size is
reduced by a factor of six or more.
The plate pack is held between cirFIG.
2. HTRI result for S&T exchanger design.
cular, thick-walled plates. The plates are
pressed from 316 grade stainless steel or
higher, with accurate spacing obtained by
the high points on adjacent ribbed plates.
Alternate plates are welded at the plateside
ports to create " shell-side " passages,
which are open to the annulus formed
between the plate pack and the shell.
The " plate-side " passages are connected
by inlet and outlet headers through holes
at the top and bottom of the plates, and
the shell side is sealed with a circumferential
weld around the rim. The diameter
of these connectors, and of the plate-side
connections on the front of the shell, are
geometrically limited to limit the loss
of the available plate area. The effective
plate area between these connections is
approximately two-thirds of the total circular
plate area.
Reliability and maintenance. Highquality
welding, plus accordion-like construction,
makes the PSHE suitable for the
larger temperature gradients experienced
in startup, shutdown and process upsets.
The plate packs also have been tested
FIG. 3. Channel-size PCHE (left) vs. PSHE (right).
30 MAY/JUNE 2021 | GasProcessingNews.com
for thermal transients, a common concern
with all heat exchangers during startup,
shutdown and process upsets. Thermal
cycling has been conducted between
ambient and -168°C, at 80 barg, where
an excess of 8,000 cycles was achieved
before failure occurred. Then, 36,000
cycles were performed between ambient
and 100°C, at which point the test was
stopped and a burst was performed. The
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Hydrocarbon Processing - June 2021

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