Hydrocarbon Processing - October 2021 - 79

Water Management
cal barrier on the metal surface. They do
not offer a panacea for poor chemistry
control; however, they do offer strong potential
for comprehensive steam generator
corrosion protection. The authors hope
to provide more details in the near future
with an article devoted to this technology.
With the wide variety of intermediate
and final products generated at industrial
plants, the possibilities for contaminant
leakage into condensate return are enormous.
Impurities may include complex
organics, strongly acidic or basic compounds,
mineral salts and many others.
One way to minimize impurity transport
to boilers is by equipping the condensate
return system with a dump line
so that an excursion shown by instrument
readings (e.g., specific conductivity) will
open a valve and allow the condensate
to be drained rather than returned to the
steam generators. Some plants employ
total organic carbon (TOC) analyzers to
monitor return condensate. If neutralizing
amines are utilized for pH adjustment, the
contributing TOC from the amine is taken
into consideration, and a target TOC
is selected for dumping. Dumping can
involve a large loss of water and may require
special makeup water system design
to handle periodic high makeup requirements.
An alternative idea-albeit one
that requires additional funding and staffing-is
to place a condensate polisher on
the return line to the boilers. The choice
of equipment and polishing process will
depend on the impurities to be removed
and mechanical conditions such as flowrate,
temperature and pressure, but a number
of options are available, including:
* Ion exchange resins, with
some flexibility of selection
for particular contaminants
* Particulate removal by fabric
or mechanical filters.
Ion exchange resins can be specifically
designed to remove a variety of dissolved
ions, ranging from primary cations
and anions to other trace constituents.
However, some resins may be limited by
temperature, as some anion resins begin
to break down at temperatures not much
higher than 100°F.
Direct filtration is a straightforward
technique, particularly if system corrosion
generates a significant amount of
iron oxide or other metal particulates. A
prime example comes from the power
industry, where air-cooled condensers
(ACC) are sometimes chosen as an alternative
to cooling towers and water-cooled
condensers for water conservation. ACC
units require a huge amount of carbon
steel piping to effectively cool turbine exhaust
steam, and even with the best chemical
treatment programs, the process still
introduces a large amount of iron oxide
particulates to the condensate.
Recommendations. Proper boiler protection
starts with reliable makeup water
system operation and good control over
corrosion and impurity ingress in condensate
return systems. Key principles include:
* Maintaining and controlling
makeup systems to provide
consistent effluent. Upsets can
send many scale-forming or
corrosive ions and compounds
to the boiler, including hardness,
aggressive anions and silica.
* Controlling chemistry consistently
for unit protection. While consistent
makeup water quality is important,
many impurities and corrosion
products can enter the condensate
return from leaking condensers
and process heat exchangers.
Condensate return dumping and
polishing methods are available
for mitigating these difficulties.
* Monitoring systems consistently.
The importance of monitoring
cannot be overstated. Upsets
have been known to cause boiler
tube failures within days, and
sometimes even hours. Continuous
online instruments are available
for complete steam generation
chemistry monitoring. Intelligent
water management software is also
available for tracking and analyzing
data and providing reports and
alarm notices to plant personnel.
This program is also well-suited
for monitoring other plant water
systems, including cooling water.
All systems are different. Like all
technologies, due diligence is necessary
to determine the feasibility for utilizing
these methods. Equipment manuals
and guides should always be consulted
before making changes to systems and
treatment processes.
LITERATURE CITED
1.
Sturla, P., Proc., Fifth National Feedwater Conference,
1973, Prague, Czechoslovakia.
FIG. 11. Severe calcium carbonate (CaCO3
)
scaling in a low-pressure boiler tube. This
is the same scale that appears in home hot
water systems.
FIG. 12. General illustration of filming amine
attachment to metal surfaces.2
2.
Stuart, D., " Mitigating flow-accelerated corrosion
with film-forming chemistry in HRSGs, " Power
Engineering, April 2021, online: www.power-eng.com
KURT KRAETSCH is a Technical
Staff Consultant with ChemTreat.
He has 20 yr of experience in the
specialty chemical industry, heavily
focused on boilers in the chemical,
refining, and petrochemical
industries. He also has an additional
10 yr of chemistry and steam plant operational
experience from the U.S. Navy while serving aboard
nuclear submarines. Mr. Kraetsch holds a BS degree
in nuclear engineering technology from Thomas
Edison State University in Trenton, New Jersey.
BRAD BUECKER is Senior Technical
Publicist with ChemTreat. He has
many years of experience in or
affiliated with the power industry,
much of it in steam generation
chemistry, water treatment, air
quality control, and results
engineering positions with City Water, Light & Power
(Springfield, Illinois) and Kansas City Power & Light
Co.'s (now Evergy) La Cygne, Kansas station. He also
spent 2 yr as acting water/wastewater supervisor at a
chemical plant. Mr. Buecker holds a BS degree in
chemistry from Iowa State University with additional
coursework in fluid mechanics, energy and materials
balances, and advanced inorganic chemistry. He is a
member of the ACS, AIChE, AIST, AMPP (NACE)
ASME, the IWC Advisory Council, the Electric Utility
Chemistry Workshop planning committee, and the
Power-Gen planning committee. Mr. Buecker has
authored many articles and three books on power
plant and water/steam chemistry.
Hydrocarbon Processing | OCTOBER 2021 79
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Hydrocarbon Processing - October 2021

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