Category: Year 2022

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

PPCHEM® 2022, 24(5,6), 196–206

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.

PPCHEM® 2022, 24(5,6), 208–213

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.

PPCHEM® 2022, 24(5,6), 214–223

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!

PPCHEM® 2022, 24(5,6), 224–229

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

PPCHEM® 2022, 24(5,6), 238–240

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.

PPCHEM® 2022, 24(4), 136–159

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.

PPCHEM® 2022, 24(4), 164–169

HINTS FROM THE EXPERTS

Saving Money with Clever Blowdown Management

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.

PPCHEM® 2022, 24(4), 170–173

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.

PPCHEM® 2022, 24(4), 174–182

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.

PPCHEM® 2022, 24(3), 96–103

Tribute to Ken Galt

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.

PPCHEM® 2022, 24(3), 108

HINTS FROM THE EXPERTS

Making Control Loops Smarter

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.

PPCHEM® 2022, 24(3), 118–119

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.

PPCHEM® 2022, 24(3), 120–121

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.

PPCHEM® 2022, 24(3), 122–123

Conductivity Limits for Direct Water-Cooled Generators

Robert Svoboda and Wolf-Dietrich Blecken

For normal operation, a conductivity limit of ≤ 0.2 μS · cm^–1 is an indirect indicator of correct pH and restricts undue corrosion. With protective additives, e.g., NaOH for alkaline treatment, a higher limit corresponding to the objective of the treatment is appropriate.

With too high conductivity the water inside the insulating hoses of high-voltage stator windings will warm up and if it boils there is a risk of electric flashover inside the insulating hose with damaging consequences. Therefore, a short-term action limit in the order of 10 μS · cm^–1 has been set by the industry in the past.

With correct water flow, conductivity inside the insulating hoses at these values does not warm up the water significantly and there are no restrictions regarding the duration of such an event.

However, when cooling water flow is lost, the water inside the insulating hoses will warm up exponentially with time. The time until boiling has a strong (square) dependence on the rated generator voltage, as well as on the insulating hose length, and has a linear dependence on water resistivity. The spatial position of insulating hoses (hoses are mounted vertically, horizontally, or bent) is also of importance. In addition, the stationary cooling water inside the stator bars, as well as the entire stator winding, is subjected to critical temperatures, especially at high load conditions. Therefore, appropriate action must be taken prior to reaching the water boiling level. To avoid a costly stator winding breakdown, the cooling water flow must be restored at once. Otherwise, the generator has to be shut down completely as soon as possible.

PPCHEM^® 2022, 24(2), 52–63

Avoidance of Common Mistakes during Failure Analyses and Misinterpretation of Lab Results – Part 2: Lab Analyses / Sample Handling, Preparation, and Analytical Procedures

Frank Udo Leidich

For a proper failure analysis or root cause analysis (RCA), a great deal of data and evidence-based information is needed. Within this context, various types of samples from different locations need to be taken for chemical and/or metallurgical examination. In addition to proper and correct sampling without alteration of the composition or contamination of the samples, which is described in the first article of this short series [1], it is of utmost importance to use the right analytical methods and execute sample preparation carefully. This includes being aware of the basic principles of the methods applied and of course knowing their limits. This article discusses the analytical part of an RCA and is the second part in a short series of ongoing articles.

PPCHEM^® 2022, 24(2), 70–75

HINTS FROM THE EXPERTS

Considerations for the Control of the Dosing of Trisodium Phosphate (Na₃PO₄) in Boiler Water

In the recent past, various organizations have been trying to establish a more or less full automatization of the dosing control for the phosphate boiler water treatment (typically called PT), similar to the well-established and well-functioning automatic dosing control of ammonia. Although this may sound easy, as nowadays very reliable instruments and sampling systems are available, it is relatively difficult to implement, especially for PT, as the entire phosphate chemistry is very complex compared to that of ammonia. Therefore a safe and reliable automatic control of PT involves a lot of traps and risks which must be considered. The most common and challenging issues in this respect are described here. Although this list may not be complete, it could be used to reconsider the idea of fully automated control of phosphate dosing.

PPCHEM^® 2022, 24(2), 76–81

Deviation in Turbidity Readings at a Low Range

Irene Rüegg

Various factors contribute to deviations encountered in low turbidity readings by different analyzers. Turbidity measurement is instrument-dependent; different instruments calibrated with formazine according to the standard methods only show identical readings on a sample if the instruments incorporate the deviation factors. This article examines the interferences that affect a “zero” measurement and demonstrates how the concept of the Swan AMI Turbiwell turbidity analyzer reduces these inaccuracies.

PPCHEM^® 2022, 24(1), 4–8

Cleaning of Newly Erected Steam Boiler Plants and Associated Pipework

Wolfgang Rost

Experience gained over the years has shown that the strict adherence to prudent industry practice regarding the clean assembly of steam generator and water/steam cycle systems is the key to quickly establishing normal and trouble-free steam turbine operation of newly built power plants. It is therefore most valuable to understand what kinds of contamination can occur in what production step, what adverse consequences they imply, and how to generally avoid them by setting up very simple guidelines to start with. In addition, it is very helpful to know what sort of remedies exist as effective corrective measures if things go wrong in the first place. The knowledge of what state-of-the-art cleaning procedures exist and how they are conducted properly is also a very important key to success. If all the aforementioned points are adhered to, a reduction in execution time and money expenditure will be the result at the end of the day.

PPCHEM^® 2022, 24(1), 10–23

Review – vgbe Chemistry Conference 2021

Andreas Wecker and Sabine Kuhlmann

The 57th vgbe Chemistry Conference took place again as an attendance event. As usual, this chemistry conference was also accompanied by a trade exhibition with 21 national and international exhibitors. The approximately 160 participants were offered an interesting lecture programme.

PPCHEM^® 2022, 24(1), 28–29

HINTS FROM THE EXPERTS

How IAPWS-IF97 can be used to optimize the so-called “Cleaning Force Ratio” during the steam cleaning of power plants

Throughout the entire process of the fabrication and construction of newly erected power plants, contaminants are introduced into the systems of the steam generator and the water/steam cycle due to the nature of the work. Some of these contaminants may not be removed successfully during chemical cleaning. Thus, due to the cleanliness requirements regarding the absence of particles, steam systems of power plants must undergo steam-blow operation prior to commencing the first steam admission to the turbine.
Therefore, all steam pipes routed to the steam turbine must be steam-blown by using enough “force” to remove solid contaminants effectively. The so-called “Cleaning Force Ratio” (CFR) is used to determine whether this required “force” is achieved during steam cleaning.

PPCHEM^® 2022, 24(1), 30–31

2021’s Scientific and Technical Contributions

PPCHEM^® 2022, 24(1), 32–40