Chemical Engineering May 2020 - 47

crease the amount of heat that flows
into certain processes, so it is key
to minimize pressure drop through
separators to maintain the highest
temperature that can drive heat into
a process.
The importance of separators
Once systems have condensate
properly drained through steam
traps, the use of separators can have
a profoundly positive impact on various
equipment.
Turbines. Turbines may be single or
multi-stage (Figure 7). Regardless of
the number of stages, it is important
to use steam that is free from water
slugs or droplets. Often, the steam
quality driving turbines is less than
ideal, with the result that plant operations
may open bypasses or bleed
valves, creating a fog zone (Figure
8). Even when such measures are
implemented, turbines can experience
issues with the trip and throttle
valves,
plating,
erosion, or severe
damage to the blades.
Problems caused by condensate
generally fall into the following two
cause classifications:
1. The condensate in the steam line
feeding the turbine was not properly
drained through properly functioning
steam traps [8, 9]. This can be
mitigated by implementing procedures
to maintain the traps on the
distribution line supplying steam to
the turbine, and checking the overall
drainage design to make sure that
locations in which pool water before,
at, or after the turbine have steam
traps installed that function well.
2. The supply steam has significant
amounts of entrained moisture. Not
only does water striking a blade at
high velocity create erosion, but
there is also the dynamic that the
blade spins at high speed. As steam
is slung outward, the acceleration
creates a drop in localized static
pressure - causing entrained water
droplets to vaporize. This action creates
" moisture loss " (negative work
[10]), adds to erosion, and any precipitate
in the condensate will drop
out of the steam and can deposit
on the blades. Mechanical separation
offers an excellent means to
reduce or remove entrained mois93rd
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ture in the steam supply. Turbines
experiencing frequent washdowns
should have the steam trapping and
steam separation systems checked
for good design and operation to
mitigate the frequency.
Furthermore, " The results of many
tests indicate that the efficiency of a
[turbine] stage is reduced by about
1% for each 1% of moisture present
in the steam " [10].
This does not imply an energy
efficiency benefit, as the same
amount of energy must still be created
at the boiler. However, moisture
droplets that can cause interruptions
from drag or flashing are
removed, allowing the turbine to
operate at optimal efficiency.
When the steam distribution
line feeding the turbine is properly
drained, and when steam is pulled
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Chemical Engineering May 2020

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