Chemical Engineering March 2023 - 36

Feature Report
Part 2
Precoat Filter Demineralizers
in Steam Loops
By minimizing, or even eliminating, the need for blowdowns in steam systems, precoat
filter demineralizer systems can greatly contribute to water-conservation efforts
John Yen
Marmon Industrial
Water LLC
IN BRIEF
CONDENSATE
CONTAMINATION
THE HIGH COST OF
BLOWDOWNS
RECOVER CONDENSATE
WATER CONSERVATION
ENHANCED STARTUP
AND EFFICIENCY
S
team is essential in any chemical
process plant, primarily for generating
heat and power. Power
generation (the largest consumer
of industrial water) and water-dependent
thermal plants generate more than 81%
of the world's electricity using steam to rotate
an electric generator. The steam can
be generated in various ways, which include:
by coal-fired boilers; waste heat from gas- or
oil-fired turbine generators; and by direct or
secondary generation in a nuclear reactor.
Because demand for electricity also drives
demand for water, in a time when water as
a resource is becoming less predictable
and more stressed, power outages caused
by water shortages are becoming a realistic
threat. To help themselves out of this
quandary, power plants, and other industrial
plants that generate steam, stand to benefit
from investment in technologies that conserve
and make the greatest use of water.
Condensate contamination
The condensate water that results from
steam-turbine operation is one area where
water conservation can be realized. For both
boilers and heat-recovery steam generators
(HRSGs), condensed water collects in the
system and can be reused. However, this
fact is complicated by
the fact that, over time,
the condensate in the
steam loop becomes
increasingly
contaminated,
which will cause
damage to plant components.
This includes
boilers, steam generators,
reactors and
turbines. Untreated
condensate can damage
the steam turbine
by erosion through the
impingement of abrasive
particulate matter
transported with the
36
steam, or by deposition of soluble material,
such as silica and copper, on the turbine
blades. Other damage caused by contamination
can include tube pitting, tube rupture
and drum pitting (Figure 1). Contamination of
boiler feedwater and condensate occur from
four principal sources, as follows:
Makeup-water system leakage. Dissolved
and colloidal solids that pass through
the makeup water system can often
cause contamination.
Condenser leakage. Mainly dissolved, including
some suspended, solids can leak from
the condenser. The amount of such solids is
dependent on the condenser design, level of
maintenance and the quality of cooling water
present on the tubeside. In the case of seawater-cooled
systems, the smallest leak can become
a significant problem for high-pressure
boiler systems.
Metallic corrosion. Metal-oxide-based suspended
solids are created within the boiler
steam cycle as byproducts of corrosion.
These metal oxides are usually forms of iron
oxide, but oxides of copper, chromium and
nickel can also contribute.
Startup contaminants. Silica is a notorious
contaminant due to its frequent presence
during initial boiler startup, typically as residue
from the system manufacture and assembly.
FIGURE 1. Contaminated condensate can lead to several types of costly damage
Marmon Industrial Water
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
MARCH 2023
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Chemical Engineering March 2023

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