Xylem Heat Exchangers - Manual (Page 5)

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In all installations there should be no pul-
sation of fluids, since this causes vibration
and will result in reduced operating life.
10
Under no circumstances is the heat
exchanger to be operated at a flowrate
greater than that shown on the design
specifications. Excessive flows can cause
vibration and severely damage the heat
exchanger tube bundle.
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Heat exchangers that are out of service
for extended periods of time should be
protected against corrosion as described
in the storage requirements for new heat
exchangers.
Heat exchangers that are out of service
for short periods and use water as the
flowing medium should be thoroughly
drained and blown dry with warm air,
if possible. If this is not practical, the
water should be circulated through the
heat exchanger on a daily basis to pre-
vent stagnant water conditions that can
ultimately precipitate corrosion.
recoMMended Start-uP and SHut-doWn ProcedureS
cautIon: Every effort should be made to avoid subjecting the unit to thermal shock, overpressure, and/or hydraulic hammer, since these conditions
may impose stresses that exceed the mechanical strength of the unit or the system in which it is installed which may result in leaks and/or other damage
to the unit and/or system.
fluid location & relative temp.
Start-up
Procedure
Shut-down
Procedure
Shell Side tube Side
type of
fluid
rel.
temp.
type of
fluid
rel.
temp.
Start both fluids gradually Shut down both fluids gradually
at the same time. at the same time.
Start hot fluid first, then slowly Shut down cold fluid first, then
start cold fluid. Avoid temperature hot fluid.
shock. (1)
Start cold fluid first, then hot fluid. Shut down cold fluid gradually,
then hot fluid.
Start both flows gradually at the Shut down both fluids gradually
same time. at the same time.
Start cold fluid first, then hot fluid. Shut down hot fluid first, then
cold fluid.
Start cold fluid first, then start Shut down hot fluid first, then
hot fluid gradually. cold fluid.
Start cold fluid first, then start Shut down cold fluid first, then
hot fluid gradually. shut down hot fluid gradually.
Start cold fluid first, then start Shut down hot fluid first, then
hot fluid gradually. cold fluid.
Start cold fluid first, then start Shut down hot fluid first, then
hot fluid gradually. cold fluid.
Start cold fluid first, then start Shut down hot fluid first, then
hot fluid gradually. cold fluid.
General comments:
1.) In all start-up and shut-down operations, fluid flows should be regulated so as to avoid thermal shocking
the unit regardless of whether the unit is of either a removable or non-removable type construction.
2.) For fixed tubesheet (non-removable bundle) type units where the tube side fluid cannot be shut down, it is recommended that:
a) A bypass arrangement be incorporated in the system; and, b) the tube side fluid be bypassed before the shell side fluid is shut down.
3.) Extreme caution should be taken on insulated units where fluid flows are terminated and then restarted.
Since the metal parts could remain at high temperatures for an extended period, severe thermal shock could occur.
Fixed Tubesheet
(Non-Removable
Bundle)
U-Tube
Packed Floating
Head
Packed Floating
Tubesheet
Internal Floating
Head
(All these types have
Removable Bundles)
TABLE 1
Heat exchanger
type of
construction
Liquid Hot Liquid Cold
Condensing Liquid
Gas Hot or Cold
(e.g., steam) Gas
Gas Hot Liquid Cold
Liquid Cold Liquid Hot
Liquid Cold Gas Hot
Liquid Hot Liquid Cold
Condensing Liquid
Gas Hot or Cold
(e.g., steam) Gas
Gas Hot Liquid Cold
Liquid Cold Liquid Hot
Liquid Cold Gas Hot
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