Steam Turbine Deposits – How They Occur, Their Effects and How They Can Be Eliminated
Frank Udo Leidich
During operation, impurities can enter the water-steam cycle (WSC) with the make-up water, through leaks or with the process condensate return and cause corrosion and deposits. Deposits can form at any point in the WSC, depending on the composition and local conditions (pressure, temperature, flow conditions). Deposits are formed from dissolved and suspended substances that are transported from the point of formation to the point of deposition in the WSC with the water or steam flow. The deposits formed on the turbine blades not only disrupt the flow around the blades, they also increase the pressure loss between the turbine inlet and outlet and thus reduce the efficiency of the overall process.
Three methods for removing turbine deposits have proven to be particularly effective, whereby each of the methods mentioned has specific advantages and disadvantages which will be discussed in this article.
Foam Cleaning of Gas Turbine Compressors – A Fast and Efficient Method to Reestablish Performance and Efficiency
Frank Udo Leidich
Especially in industrial environments, gas turbines (GTs) suffer from performance losses and efficiency losses due to compressor fouling. Compressor fouling is caused by soot, dust, salt spray and other airborne contaminants that are drawn into the compressor with the combustion air and are not fully retained by the air intake filters. Another cause of deposits on the compressor blades is the water used for fogging or high fogging if the water quality does not meet the purity requirements according to the original equipment manufacturer (OEM) specifications.
Depending on the pollutant load in the combustion air, GT compressors must be cleaned regularly to remove all deposits and restore the efficiency of the compressor. There are various methods for cleaning. These methods are discussed here.
A Brief Introduction to the International Association for the Properties of Water and Steam
Tapio Werder
This paper aims to offer a concise introduction to the International Association for the Properties of Water and Steam (IAPWS) in response to requests of PPCHEM readers. It briefly discusses the advancements in steam property research in the early 20th century and the establishment of international collaboration through the first international steam table conference held in London in 1929. Due to the limited space available, the article presents only a selection of the most important events and facts. It further outlines the organization’s activities, which encompass annual meetings, international conferences, working groups, and the creation of formulations, guidelines, releases, and certified research requirements.
Sodium Analyzers and Film-Forming Substances: Working Together?
Eric M. Etter and Harold Stansfield
The increasing application of film-forming substances (FFS) in power generation and
process steam applications as a corrosion mitigation strategy has raised concerns
regarding their impact on plant systems, particularly valves, piping, and instrumentation.
This study focuses on the adverse effects reported by users of film-forming amine (FFA)
products, including loss of instrumentation sensitivity, premature electrode failure, sensor
fouling, and overall accuracy and reliability issues.
Experiments aimed at replicating field conditions have revealed rapid sensor fouling
occurring well before standard maintenance cycles for electrode cleaning and
replacement. The observed accelerated fouling necessitates frequent mechanical
cleaning, posing risks of electrode damage, increased downtime, and additional labor for
maintenance. Because the fouling does not result in calibration failures, this creates a
situation where the analyzer appears to be functioning normally, but is no longer capable
of responding to adverse events such as a condenser leak. These highly dampened
responses will follow trends over time but are incapable of rapidly reflecting transient
spikes or changes in values.
Cooling Tower Operating and Water Treatment Fundamentals – Part 2
Brad Buecker
Cooling water systems are an integral component of many power plants and industrial
facilities of all types. Performance degradation from microbiological fouling, scale
formation, and corrosion can seriously impact plant operation and revenue. Severe cases
may force unit process or plant shutdowns. The remainder of this series examines the
most problematic fouling, scaling, and corrosion mechanisms, and it outlines modern
control methods for all of them. This installment focuses on microbiological fouling, with
much of the discussion extracted from Reference 1.
In steam and water analysis systems (SWAS), the sample cooler is one of the most
important components. The main function of the sample cooler is to reduce the
temperature of high-temperature samples from elevated temperatures to the temperature
required for analyser sensors. In the case of steam sampling, the steam samples are not
just cooled, but are condensed to water (phase change).
Additives from Natural Resources – The Way to the Future?!
Wolfgang Hater
Additives from natural resources have been known since the end of the 19th century and
have had a renaissance in recent years due to the demand to replace mineral-oil-based
chemistry with materials from nature. They are considered to be green and sustainable. In
spite of their positive image and a huge number of research papers, hardly any new
compounds from natural materials have successfully found their way onto the market.
The assumption that natural equals harmless, green, or sustainable is quite common but
does not always hold. While the criteria for green and sustainable are not well defined, the
European Community has developed a standardized risk-based approach for the
evaluation of whether a chemical can be safely applied.
This paper describes the major advantages and drawbacks related to natural material or
biobased material. On the one hand, the production process is generally more simple and
raw materials are cheap, especially if waste/recycled materials or residues are processed.
On the other hand, a serious obstacle is the high variability of their chemical composition
as well as the presence of components with no function.
Selected examples of studies and the application of additives from natural resources for
water treatment are briefly discussed which show the potential but also the roadblocks for
market success. It can be expected that they will play an increasing role in the future.
Legislation will also be a strong influencing factor.
Review vgbe Chemistry Conference 2023 October 24 to 26, 2023 in Ingolstadt
Around 170 participants attended the 59th vgbe Chemistry Conference from October 24 to 26, 2023. The wide-ranging lecture programme was once again rounded off by an accompanying trade exhibition with 20 exhibitors who presented their products and services relating to power plant chemistry.
The vgbe conference team would like to thank all speakers, exhibitors and sponsors as well as the interested participants for their support and looks forward to the next vgbe Chemistry Conference, which will take place in Potsdam from October 22 to 24, 2024.
The annual meeting of ABHUG held on the 14th–16th November 2023 in Brisbane, Australia was chaired by Barry Dooley of Structural Integrity Associates, UK and Bob Anderson, Competitive Power Resources, USA. This ABHUG conference included conventional fossil plant technology and issues closely related to those in HRSGs. ABHUG2023 attracted 100 participants from Australia, New Caledonia, New Zealand, Singapore, Switzerland, UK and USA. About 55 % of the participants were Users.
The next meeting of ABHUG will be in Brisbane around early December 2024.
A Specialty Ion Exchange Resin for Deoxygenation Treatment of Boiler Makeup Water
Zhendong Liu, Amy Peddie, and Juan Carlos Pinilla
Oxygen level control can be very important in the cycle chemistry of power plants.
Sometimes a higher oxygen level is desired for all-ferrous materials due to its creation of
the more corrosion-resistant ferric oxide hydrate layer in the natural magnetite. This is
practiced as either all-volatile treatment under oxidizing conditions (AVT(O)), or
oxygenated treatment (OT). However, for some alloy materials (e.g., copper alloys and
nickel alloys) used in the steam generation/recirculation systems, a reducing environment
and very low oxygen levels are favored to avoid corrosion. This paper reports on a
specialty ion exchange resin and its use in treating the makeup water for a pressurized
water reactor (PWR) nuclear power plant. The resin is coated with a precious metal as
catalyst for the oxygen-hydrogen reaction to generate water. It requires minimum
maintenance (only annual backwashes), and has fast reaction kinetics, a small footprint,
and a long operating life (> 20 years). The case study shows the resin can achieve
< 10 μg ⋅ L–1 oxygen consistently from a makeup water with 1–10 mg ⋅ L–1 oxygen at a
189–1 514 L ⋅ min–1 flow rate. The catalyst doping, reaction mechanism, and some
operational details are discussed.
Between September 3rd – 8th, 2023, 62 scientists, engineers and guests representing 20 countries converged in Turin, Italy at the Star Hotel Majestic for the annual meetings of the IAPWS Executive Committee and Working Groups. This continues a series of meetings
that began in 1929 in London, UK with the purpose to connect scientists and researchers
with the industry operators, engineers and managers who use their work. Collaboration
and engagement across these varied groups provides guidance to the researchers on
topical problems within industry and provides the engineers with the latest research results
for direct application in their facilities.
The main meetings included discussions around power cycle chemistry, high temperature
aqueous technologies applicable to steam cycles and hydrogen generation, oceanography
and global climate modelling, geothermal steam, electrode boilers, power cycles with CO2
capture and storage systems and combined heat and power systems.
The Role of Organics in Relation to Corrosion in Steam-Water Systems
Yu Xue, Karlien Dejaeger, Ben Bischoff Tulleken, Duygu Disci, Peter Janssen, Andrea M.Brunner, David Moed, Wolfgang Hater, Emile R. Cornelissen, and Marjolein Vanoppen
A sampling campaign was conducted in a film-forming amine product (FFAP) treated highpressure
steam-water system of an ammonia producing plant to optimize the cycle
chemistry. Cycle chemistry guidelines were assessed to be applicable with modifications
fitting the local situation according to the pH and conductivity. Methanol, a main organic
compound originating from the production process, entered the steam-water system with
the process condensate and was tested possible to degrade. Furthermore, organic
compounds from cation exchange resin were found in blowdown streams, suspected to
originate from resin carryover. No operational and corrosion issues were observed.
Lab-scale first condensate experiments confirmed that a lower pH was present in the first
condensate compared with the bulk steam, however, it was still partially buffered by
ammonia. Via corrosion tests it was observed that oleyl propylenediamine (OLDA), in
addition to ammonia, formed a smoother and more uniform magnetite layer. Moreover,
magnetite layers formed under OLDA added to ammonia were more resistant against
acidic conditions (pertinent to condensate return systems) than layers formed under the
ammonia only chemistry and blank chemistry (without a chemical additive), with less
reduction of the magnetite layer thickness.
These studies in combination with the plant experiences confirm that the steam-water
system can be safely run with the selected FFAP treatment concept even with organics
from the production process.
Cooling Tower Operating and Water Treatment Fundamentals – Part 1
Brad Buecker and Rich Aull
Process cooling is an important operational factor in many industrial plants and
commercial office buildings around the world. Most of these plants use cooling towers for
primary cooling. A large facility may have dozens of towers scattered throughout the
premises. Often, plant personnel are focused on process engineering and chemistry,
potentially neglecting cooling systems until a serious disruption occurs that threatens plant
production or, worse, jeopardizes employee safety.
This article forms the basis of a short series of articles dealing with the chemistry of
cooling systems. In this first part of the series, we examine the fundamentals of heat
transfer in the cooling tower and the methods that have been developed to improve heat
exchange in the tower. Subsequent parts discuss modern water treatment methods to
ensure reliable performance.
Cooling Tower Disinfection Switch to Chlorine Dioxide Reduces Boiler Chloride
Cycling: Why and How? – Part 2
Emmanuel K. Quagraine, Trever McNabb, Taneal Weiss, Gillian Bailey, Nikki Wirtz, Khrystyna Vasylkiv, and Daniel Schorr
This is the second half of a two-part article discussing the abatement of selective boiler
chloride cycling (SBCC) upon switching the recirculating cooling water (RCW) biocide from
NaOCl to ClO2. The use of ClO2 treatment significantly reduces SBCC, with only sporadic
spikes observed to a much lower extent. These spikes are found to be related to the
plant’s operation, coinciding with sudden load drops and increased air injector flows. It is
suggested that these spikes may be caused by small ClO2(g) residuals condensing at the
air injector condenser and entering the feedwater, eventually reducing to chloride ions
(Cl–) in the water/steam cycle. Unlike chlorination, ClO2 treatment prevents the formation
and persistence of volatile chlorine compounds (VCCs), including ClO2(g). The residual
ClO2 in the RCW that is responsible for the highest observed daily boiler chloride rise
during ClO2 treatment is estimated to be 4.05–9.74 ⋅ 10–5 mg ⋅ L–1. However, this
concentration range represents only 0.02–0.23 % of the highest to the least measured
residual concentrations, confirming the previous assertions that maintenance of substantial
residual ClO2 in RCW, especially when using treated municipal wastewater as make-up, is
unlikely. Overall, the operational data supports the switch from NaOCl to ClO2 as an
effective method for reducing SBCC in the water/steam cycle, with ClO2 treatment showing
superior performance and minimal VCC formation compared to NaOCl.
Safe and trouble-free operation of a steam turbine requires monitoring and control of the
operating medium “steam.” In particular, it is necessary to prevent impurities in steam from
causing corrosion attacks on turbine components, which, depending on the form of
corrosion, can lead to sudden, unpredictable component failure. This PPCHEM 101
describes typical damage and failures that will eventually occur if the quality of the water
and steam does not meet the requirements as stated in the operation manual of the steam
turbine manufacturer and/or global standards and technical guidance documents as
released by, for example, the International Association for the Properties of Water and
Steam (IAPWS).
Effect of Zinc Water Chemistry on the Corrosion and Stress Corrosion Cracking
Behavior of Structural Materials in Light Water Reactors – A Review
Xianglong Guo, Kai Chen, Hans-Peter Seifert, and Stefan Ritter
Zinc (Zn) injection into light water reactor coolants has attracted increasing attention since
the reporting of its positive effects on reducing the susceptibility to stress corrosion
cracking (SCC) of steam generator tubes made of Alloy 600. Revealing the corrosion and
SCC mechanisms of structural materials exposed to Zn water chemistry (ZWC) has gained
importance in quantifying potential benefits for the safe long-term operation of nuclear
reactors. This paper reviews the open literature on the current understanding of ZWC
effects on the (uniform) corrosion and SCC behavior of structural materials used in
western light water reactor plants. Some research with promising results has been
conducted, but more detailed and systematic work is still needed to draw meaningful
conclusions on the SCC mitigation capabilities of the ZWC.
Impurities in Water Supplies (Natural and Reclaim) and Modern Control Methods for Industrial Plant Makeup – Part 1
Brad Buecker
Makeup water for power and industrial plants typically contains numerous impurities. Many
come from natural processes, while others, often in slight but at times potentially
troublesome amounts, come from human activities. The contaminants can cause fouling,
scaling, and other problems in cooling, service, and high-purity makeup systems unless
treatment methods are employed to reduce impurity concentrations. This series examines
how impurities enter water supplies, and it provides an overview of modern treatment
methods.
Cooling Tower Disinfection Switch to Chlorine Dioxide Reduces Boiler Chloride
Cycling: Why and How? – Part 1
Emmanuel K. Quagraine, Trever McNabb, Taneal Weiss, Gillian Bailey, Nikki Wirtz, Khrystyna Vasylkiv, and Daniel Schorr
This is the first half of a two-part article which discusses the abatement of selective boiler
chloride cycling (SBCC), which has plagued the subject power plant, upon switching the
recirculating cooling water (RCW) biocide from NaOCl to ClO2. Evidence has been given
to attribute this mainly to gaseous ingress of volatile chlorinated compounds (VCCs)
through weak tube-to-tubesheet joints. Based on Henry’s constants in aqueous solutions,
ClO2 partitions more into the gaseous phase compared to chlorine species associated with
NaOCl, i.e., chloramines, Cl2, HOCl, and OCl–. The SBCC abatement hence seems
paradoxical. Based on literature and operational data, this is explained. Properties of ClO2
make keeping residual ClO2 in RCW difficult, if not impractical. At the cooling tower, major
losses occur physically and chemically and even when residual remains, its high solubility
in water at such low concentrations causes deviation from Henry’s law, i.e., a lower
tendency to form ClO2(g). In addition, inside the condenser, where ClO2(g) may occur, it
reacts quickly with oxidizable gases and (bio)organic compounds selectively yet
versatilely, where it is not only consumed but avoids formation of VCCs, thereby
preventing their ingress into the condensate side.
Connecting the Dots between Steam Generator Chemistry and Fundamental
Thermodynamics
Brad Buecker
Experience has shown the importance of the necessity of comprehending the
thermodynamics of steam generator heat transfer to better understand the chemistry
requirements. Besides the corrosion aspects of water- and steam-side impurity ingress,
efficiency losses can be expensive.
To minimize efficiency losses, condenser performance should be monitored diligently and
it must be ensured that cooling water chemical treatment programs are operating properly
and that air in-leakage has not become excessive. Reheating improves efficiency only by a
few percent, but basic thermodynamic calculations show that steam reheating and
introduction of the hot reheat to the intermediate-pressure turbine and crossover to the
low-pressure (LP) turbine keeps the steam significantly drier in the LP turbine, with final
moisture content usually below 10 % (and thereby minimizing water droplet erosion of the
last stage blades).
In this article, we make the connection between major steam generator design details (and
the thermodynamic principles behind them) and condensate/steam chemistry
fundamentals.
A Low pH Excursion Exclusively in the IP Evaporator/Drum at a Combined Cycle
Plant during a Start-up – Part II: Lessons Learned
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 second of a two-part article on a low pH excursion which occurred exclusively in
the intermediate-pressure (IP) evaporator/drum of a combined cycle plant, with the other
circuits (low-pressure (LP) and high-pressure (HP)) showing normal pH. This is an odd
situation, and the first half of the article explains how this was possible. Part II however
describes how this unexpected situation confounded interpretations of the plant’s on-line
instrumentation readings and the decision-making based on this data, which led to delays
and inadequate response to the low pH excursion. A lot of confusion and uncertainties
around pH readings were experienced and the causes have been identified. The plant also
experienced a protracted period to clear the contaminant and attain desired steam purity
for operation, the reasons for which are discussed. Lessons learnt and recommendations
are also given to ensure early leak detection, prevention, or proper response to such pH
excursions in the future.
Instead of a simple water exchange, another possible method to correct the water quality
in circulation systems is the method of bypass clean-up. To estimate the efficiency of a
bypass clean-up, one must consider the inner efficiency as well as the outer efficiency.
The inner efficiency is influenced exclusively by the method of cleaning being used, while
the outer efficiency is ultimately decisive for an efficient application of bypass clean-up
systems. The outer efficiency is determined by the relation between the different rate
constants of the various processes which contribute to the decrease (or increase) in the
concentration of the water constituents under consideration. Hence, one can find
applications where a bypass clean-up can have high efficiencies, but there are also cases
in which only low overall efficiencies may be achieved, despite high inner efficiencies.
Using the framework presented here, it should be possible to estimate the effects on a
theoretical basis.
IAPWS Film Forming Substances (FFS) Conference, FFS2023
Highlights and Press Release
The sixth IAPWS FFS International Conference was held on the 21st–23rd March 2023 in
Prato, Italy chaired by Barry Dooley of Structural Integrity Associates, UK and David
Addison of Thermal Chemistry, New Zealand. The FFS conferences are unique on a
narrow topic in cycle chemistry control of power plants and steam generating facilities. In
2023 the conference attracted 70 participants from 28 countries which included 20 plant
operators / users and representatives from 11 FFS chemical suppliers.
The FFS conferences are developed and supported by the International Association for
the Properties of Water and Steam (IAPWS), and FFS2023 was arranged in Prato by
Mecca Concepts, Australia and Combined Cycle Journal, USA. The sponsors of FFS2023
were Kurita Europe GmbH, Nalco Water an Ecolab Company and Termanox Water
Treatment Solutions.
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
Dechlorination Control and Optimization in Industrial Water Applications
Vadim Malkov and Gregory Fleck
The use of reverse osmosis (RO) membranes for water treatment has almost doubled in
the last five years [1]. The use is widespread across many industries, from municipal water
and wastewater treatment to ultrapure water production in various industrial applications.
For efficient RO membrane operation, it is important to accurately monitor and control the
residual chlorine concentration in the feedwater, which allows for minimizing of RO
membrane maintenance and extension of membrane life. Multiple studies demonstrate
that prolonged exposure of RO membranes to free chlorine exceeding 38 μg · L–1 (ppb)
(based on 1 000 mg · L–1-hours over three years [2]) is detrimental to the membrane
structure and integrity, while the absence of the disinfectant and/or excess of
dechlorinating agents promotes biofouling and causes loss of recovery. To maintain this
delicate balance, membrane operators must accurately monitor oxidant concentration and
addition of bisulfite, especially in the RO feedwater.
Causes and Effects of Insufficient Steam Purity and the Necessary Measures
Michael Rziha
As is well known, contamination in the steam very quickly leads to impairment of the steam
turbine, ranging from loss of efficiency to a massive reduction in service life, or even to
rapid destruction.
The causes and sources for the entry of contamination are very diverse, especially in
industrial plants. Plant-specific knowledge of the possible entry points and the types of
possible contamination is of crucial importance for the determination of a suitable
monitoring strategy for the most trouble-free and damage-free operation of the steam
turbine.
In addition, if such contamination occurs, suitable measures must be taken very quickly in
order to avoid long-term, undesirable and, above all, cost-intensive damage to the steam
turbine.
The most common sources and causes, their detection, and recommendations or
necessary avoidance strategies from the perspective of power plant chemistry are
presented.
Clean chemical conditions within the water-steam cycle and the steam generator systems
are of utmost importance for trouble-free operation and to maintain the required steam
purity for steam turbine operation. If the control of the chemical regime is not managed
correctly, the introduced contaminants will lead to the build-up of layers on the blading of
the turbine, reducing steam turbine efficiency and leading to corrosion processes which
can cause considerable damage in the water-steam cycle and steam generator systems.
In the worst case the steam generator or the turbine will be reduced to scrap metal.
To control these contaminants and to avoid an excessive concentration within the
evaporator, the blowdown of evaporator water is used to keep the concentration of the
contaminants within allowable limits.
However, this method of concentration limitation has the negative side-effect of
a loss of valuable enthalpy. It also increases the consumption of demineralized
water and chemicals.
Application of Chloramine as a Biocide for Cooling Tower Water Consumption
Reduction
Anderson José Beber
This paper shows the results of the application of a mild oxidizer on a large cooling tower
at a power plant in southern Brazil. This cooling tower utilizes grey water (tertiary treated
domestic sewage) as make-up. With the application of this technology, there was an
improvement in both microbiological control and corrosion rates. Additionally, the plant
was able to increase the concentration cycles from an average of 4.5 up to 6.5, resulting in
an annual savings of over 400 000 USD.
Sampling and Monitoring – The Daily Routine, Which Is Anything but Trivial or Simple
Michael Rziha
This article highlights some crucial and essential topics related to sampling and monitoring and how to obtain correct and representative samples and useful results.
Some classic mistakes; still experienced today in numerous plants; are highlighted as well.
Hints are given on how to avoid such mistakes and how to minimize the bias of samples. This article focuses on the most important basic rules for correct and representative sampling; but also draws attention to the most common mistakes being made.
It is our sad duty to inform you that Ken Galt passed away on May 1, 2022. He had been a member of the International Advisory Board (IAB) of the PPCHEM journal since the summer of 2020. Ken Galt was an outstanding scientist in the field of power plant chemistry, contributing a wealth of valuable research findings, notably studies on many topics.
For some applications in power plants; it is not a good option to wait until control loops reach the setpoint based solely on the reaction to the control deviation over time; as this may cause activation of warning signals or; in the worst case; may even trigger protection commands due to a delay in reaching the required setpoint. Some control loops are additionally susceptible to undesired oscillations. Hence; these affected control loops should be made smarter; so they behave more stably and react faster.
How this can be easily achieved is explained here with various examples.
Foundation of the German-Swiss Association for the Properties of Water and Steam (GSAPWS) on April 1, 2022, in Potsdam, Germany
On 1 April 2022; 13 delegates met in Potsdam; Germany; for the founding meeting of the German Swiss Association for the Properties of Water and Steam. This meeting was also the first in-person meeting of the German and the Swiss National Committees since the start of the Covid-19 pandemic.
Press Release: Last Regular Meeting of the VGB Working Group LWR-Chemistry at the NPP Emsland
Dr. Timo Stoll & Jörg Fandrich
On May 3–4; 2022; the last regular meeting of the VGB Working Group Light Water Reactor (LWR)-Chemistry took place at the nuclear power plant (NPP) Emsland; Germany. In addition to the technical experts of most of the German nuclear power plants; experts from all the Swiss nuclear power plants; the Netherlands; Spain and Belgium as well as from Framatome GmbH as consulting plant manufacturer participated.
