Remember the 3Ds of Alkalizing Amines: Dissociation, Distribution, and Decomposition
Brad Buecker and Steve Shulder
Carbon steel corrosion control of condensate lines, feedwater piping, and boiler internals is
critically important in all steam generation applications. A key corrosion control aspect is
establishing and maintaining a mildly alkaline pH throughout these networks. Organicbased
alkalizing amines have a place in lower- and intermediate-pressure boilers,
industrial plant condensate-return systems, and nuclear power plant secondary cycles.
However, careful evaluation and research is needed when selecting a program. This
article examines the “3Ds” of alkalizing amines, dissociation, distribution, and
decomposition, and how these properties influence the selection of the compounds for
controlling condensate and feedwater chemistry. Dissociation and distribution are
equilibrium or reversible reactions while decomposition is irreversible. The article
examines these properties for high-pressure utility units and offers some
comparisons/contrasts for lower-pressure industrial systems, which often have extensive
steam and condensate-return networks.
A Low pH Excursion Exclusive to the IP Evaporator/Drum at a Combined Cycle Plant during a Start-up – Part I: Contamination Pathway
Emmanuel K. Quagraine, Philip Boutin, Jordan Rothwell, Cedric Huang, Nikki L. Wirtz, Jackie Sliva, Kellsey Hamel, Dwayne Selensky, Amy Tetlock, and Pratik Pansuriya
This is the first of a two-part article on the investigation of a low pH excursion which
occurred exclusively in the intermediate-pressure (IP) evaporator/drum of a combined
cycle plant at a start-up. The selective contamination occurred as glycol from closed-circuit
cooling water (CCCW). The proposed contamination route is via a boiler feed pump (BFP),
specifically O-ring seals separating the CCCW from the feedwater. The estimated leak rate
is 8.0–22.9 mL ⋅ h–1, which is sufficient to cause the pH excursion. At start-up, the BFP
would have charged the IP (and not the high-pressure (HP)) circuit line with water whilst in
recirculation mode; this was later used to fill the IP drum. The HP drum was filled an hour
later. Thus, accumulated glycol that leaked into the pump casing would have been
pumped more exclusively into the IP circuit, resulting in the selective contamination.
Through recirculation, glycol that potentially entered the low-pressure circuit, eventually
feeding the HP circuit, would have been sufficiently diluted to prevent such an excursion in
these two corresponding evaporators/drums.
Some Basics of Power Plant Chemistry – Corrosion and Deposition
Frank Udo Leidich
Undesired corrosion and deposition reduce the lifetime of a power plant or its specific
components. Even before a component in the water/steam cycle (WSC) is damaged or
destroyed, economic damage has already been caused in terms of a reduction in
efficiency, deterioration in availability, and increased maintenance and repair costs. In
order to limit corrosion and deposition to acceptable levels, monitoring and control of the
physico-chemical parameters of the working media is necessary. It is also necessary to
purify (treat) the working medium (water/steam) and add chemicals suitable for reducing
corrosion reactions and deposit formation on the components and parts of the WSC. This
paper gives an overview of the different types of corrosion, where they occur in the WSC,
and the potential hazards they pose. The most widespread deposits, their composition,
impact, and origin are also discussed.
Alkalisation and pH Stability in Water-Steam Cycles
Wolfgang Hater
The pH adjustment in the water-steam cycle is an important and widely applied measure to
maintain plant integrity. The impact of the most common alkalising agents on pH and
conductivity is discussed as well as the behaviour of mixtures. A methodology to calculate
pH and conductivity from base constant and equivalent conductivity including possible
intrusion of acid substances is presented.
With increasing basicity of the alkalising agent, the molar quantities needed to obtain the
desired pH value decreases, reaching the minimum value for sodium hydroxide. At the
same time, the impact of an ingress of an alkaline or acidic substance increases. Of the
alkalising agents discussed in this paper, ammonia shows the highest and sodium
hydroxide the lowest stability against pH excursions.
Mixtures of alkalising agents change their properties with regard to pH stability linearly as
a function of the composition. Their pH stability reflects the properties of the individual
components: a mixture of sodium hydroxide and ammonia has a lower resilience against
acid ingress compared to mixtures of trisodium orthophosphate and ammonia.
A high pH stability of the alkalising agent is an important measure to reduce the possible
impact of acidic substances entering the system by leakage or decomposition of organic
matter. Therefore, this has to be carefully considered when choosing the chemical for
alkalisation
Some Brief Comments on Microbiologically Influenced Corrosion (MIC) in Power
Plants
Reza Javaherdashti
This article deals with the most practical aspects of microbially influenced corrosion (MIC)
in power plants. The issues discussed here are mainly where to expect MIC in power
plants, the inaccurate nature of the term “biofilm” and the possibility of whether bacterial
adaptation to biocides can occur. These issues are particularly important from an
operation and maintenance point of view because they play an undeniably significant role
in reducing the useful service life by increasing the risk of MIC and the cost of its treatment
in power plants.
Oxidative Treatment of Waste Containing EDTA for its Safe Disposal – Choice of
Oxidant and Mode of Addition for Field Applications
Rajini P. Antony and A. L. Rufus
High amounts of ethylenediamine tetra acetic acid (EDTA) containing liquid waste along
with metal ions (predominantly iron) at pH ~ 8 are generated during the process of
chemical cleaning of steam generators in pressurized heavy water reactors and
pressurized water reactors. Hence, proper waste disposal involving complete or partial
decomposition of EDTA is indispensable. Three different oxidants, viz., air, H2O2, and
ozone, were explored for the decomposition of a test solution. Their efficacy was found to
be in the order: H2O2 > ozone > air. The lower rate of decomposition in the case of ozone
and air is due to their solubility limitations. Investigations on the mode of addition of H2O2
revealed that a bulk/one-time large addition of H2O2 and continuous addition of small
quantities at a controlled flow rate yield identical results. On weighing the practical
risks/hazards involved in bulk addition during field applications, continuous addition is
suggested as a better option.
Industrial Plants and Steam Purity for Turbine Operation – A Too Frequent and
Almost Classic Dilemma
Michael Rziha
Worldwide there are countless industrial installations using steam as a “byproduct” to drive
a steam turbine. The steam is generated by many different sources, such as quench
boilers and trans-line-exchangers, which are often found in refineries and petrochemical
plants. Waste heat boilers in refineries and petrochemical plants can be water tube boilers
and shell boilers. Fired flame tube boilers with low or medium pressure (5–50bar) are also
used in many installations.
Industrial steam generators often have special requirements regarding load gradients
(extremely fast load requirements and/or load reduction). Process steam extraction and
process steam condensate return are very common in these plants, and carry the
additional risk of the ingress of various contaminants from the different processes, finally
leading to a heavy impairment of the steam purity.
Guidelines which are applicable for the feed- and boiler water for the different boiler types
and operating pressures are misleadingly taken as “lead documents” although they do not
provide the special individual consideration needed for steam purity. It must be
emphasized that all such guidelines and standards are only valid for safe boiler operation,
and do not address the needs of steam turbines.
In consequence, low-pressure boilers are often operated with softened water. From the
perspective of boiler suppliers and boiler operators this might certainly be correct, as the
generated steam is used for heating only, where the requirements on steam purity may be
more relaxed.
However, and without exception, as soon as the steam is to be used to drive any kind of
steam turbine, the relevant standards and guidelines for steam need to be followed. As a
matter of principle this will always have an impact on the make-up water, feedwater, and
boiler water purity. For example, boilers with a low operating pressure are allowed to be
operated with softened or partially demineralized water. This is true and correct for the
boiler/steam generator, but it is definitely wrong for any steam turbine tied into this
process.
Steam turbine users should be aware of the risks associated with contaminants of the
steam, which may initiate, promote, or enhance stress corrosion cracking, corrosion
fatigue, general corrosion, erosion, and deposit buildup. Contaminants that are contained
in steam generally lead to deposits and corrosion in steam turbines and thus potentially
negatively affect their functioning and operational safety, as well as their lifetime. It must
also be emphasized that corrosion and/or deposit build-up and consequently damage
and/or impairment of performance or availability depend not on the size of the turbine, but
only on the impurity level and composition of the steam.
Especially when softened water is used, the concentration of sodium in the water is
significantly increased by the softening process! The thermal decomposition of sodium
carbonates and sodium bicarbonates (products due to softening) always leads to the
formation of caustic soda (NaOH), which strongly increases the risk of alkaline stress
corrosion cracking of the turbine material! Consequently, when softened water is used as
make-up water, a steam turbine operation is clearly excluded!
Report on the Power Cycle Instrumentation Seminar (PCIS) Austria 2022 in Linz,
Austria
Tapio Werder
For the first time in the history of these events, the Power Cycle Instrumentation Seminar
(PCIS) series stopped over in a German-speaking country. The PCIS Austria 2022 in Linz
was held under the patronage of PPCHEM AG, and SWAN Analytical Instruments
provided financial support.
Since 2012, PPCHEM AG and its precursor organization, Waesseri GmbH, have
organized more than 30 conferences and seminars around the world with the mission of
expanding the knowledge of cycle chemistry and the understanding of analytical
instruments. Over the past 10 years, different formats of events have been developed to fit
the different needs and interests within the power plant chemistry community.
This report summarizes the two days of the PCIS Austria 2022
