Hydrocarbon Processing - November 2022 - 42

Maintenance and Reliability
CDLs are unnecessary. FIG. 12 shows a
result in systems that are not adequately
trapped. Water hammer from a slug of
condensate moved a 400-ft. section of
this 24-in., 220-psig superheated line a
distance of 7 ft. When the drain valves
were later opened, condensate drained
continuously for 3 d.5
The moral of this
case history is that superheated mains
can carry a lot of condensate and require
well-maintained CDLs.
Turbine drainage. After utility lines are
confirmed to have best-practice trapping
and moisture separator installations, it
is useful to examine at least seven areas
on a turbine installation, starting with
the inlet separator and continuing with
multiple important stages through the
turbine and its exhaust (FIG. 13).6
The CDL before the separator is intended
to remove condensate that has
already been disentrained. Each stage
of the turbine installation can pool
condensate and appropriate CDLs can
mitigate issues.
FIG. 14 provides additional detail on
the inlet side of a turbine installation.
The trap on the separator is commonly
larger than a standard utility main drip
trap or the trap at the inlet of the control
valve due to anticipated wetness to be
removed, while the inlet to the control
valve steam trap is typically a smaller size.
It is common to see inadequate drainage
at the steam chest, trip and throttle
valve, and even the casing drains. Often,
these drains are plugged, which can lead
to condensate buildup that causes damage.
For these reasons, those connections
are recommended for steam trap drainage
(FIG. 15).
The supply steam quality and work
efficiency of the turbine determine the
amount of condensate on the exhaust
side. Often, the trap for the turbine exhaust
is larger than a simple utility main
drip trap due to the potential for wet exhaust
flow (FIG. 16).
Another misconception about steam
FIG. 13. Installing effective CDL at these seven drainage points can be crucial to improving
turbine reliability.
trapping on turbines is that any type of
trap can be used. However, many types
of traps, such as inverted bucket, bimetal
or expansion or balanced pressure thermostatics,
and thermodynamic, have
cyclical discharge characteristics, meaning
they can back up condensate into
the turbine, which is undesirable. Some
traps, such as bimetal or expansion designs,
can have large temperature suppression,
draining condensate on cold
startup but not draining effectively during
normal operation. For this reason, it
is preferred to use immediate response
float trap designs (FIG. 17).6,7
Steam trap condition health is sometimes
not carefully managed, and this
can have a significant effect on turbines
and other equipment, such as ejectors
on air exhauster systems (reviewed later
in this article). A blocked trap causes
condensate backup into the separator it
needs to drain and can render it useless,
which highlights the need for effective,
sustainable trap testing and maintenance
(FIG. 18).8
FIG. 14. The turbine inlet piping is the last defense to provide high-quality drive steam
to the turbine.
42 NOVEMBER 2022 | HydrocarbonProcessing.com
Condensing turbines. Some turbines
are designed to have their steam fully
condensed by a surface condenser to
create a vacuum or to generate optimum
power. One such example is a condens

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