Contents Issue 2(1999)

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Jan Stodola

Review of Conditions for Reliable Boiler Operation

This paper discusses the fundamentals of corrosion protection in boilers, different boiler water treatments used by the utility industry to achieve this objective as well as limitations boiler designs may impose on long term boiler performance.

It has been concluded that the most prevalent chemical treatment related cause of internal boiler corrosion has been eliminated by the replacement of Congruent Phosphate Treatment (CPT) with Equilibrium Phosphate Treatment (EPT). The root cause of the majority of the remaining internal boiler corrosion cases is now thought to be incorrect selection of boiler treatment for a particular boiler design.

This paper also questions the current industry guidelines whether they adequately address the impact of boiler design and the limitations of different commercial boiler water treatments on internal boiler corrosion. Both the ASME document for industrial boilers and the EPRI Guidelines for utility units are mainly designed to satisfy steam purity requirements, specified by turbine manufacturers, rather than to ensure protection of boilers against corrosion damage.

Internal boiler corrosion free performance is certainly possible, but chemical control strategies used need to take into account all risks of a particular boiler design / chemical treatment combination. To achieve consistently good results over the long term however, it is recommended that chemists implement chemistry control program based on ISO 9000 quality control principles.

PowerPlant Chemistry 1999, 1(2)

Karol Daucik

Water/Steam Cycle Chemistry of Ultra Supercritical Units

The development of ultra supercritical (USC) units is based on management of material problems at extremely high temperatures in last superheaters. A number of other chemical problems are connected to USC concept due to a general shift to higher temperatures in almost all power cycle components. The management of these problems on the first generation of USC units in Denmark is described.

The discussion includes the choice of materials, chemical treatment of water/steam cycle, design considerations of components, and operational procedures and control instrumentation to ensure a reliable operation of the units. The common denominator of these efforts is improvement of the purity of the cycle, thus ensuring an optimum operation with oxygenated treatment.

PowerPlant Chemistry 1999, 1(2)

Tamara I. Petrova

Effect of Demineralized Water Purity on Corrosion of Carbon Steel

Currently once-through units at power plants in Russia and abroad widely use oxidizing treatment with feed of oxygen into feedwater train; in some cases hydrogen peroxide is used as oxidant. A large operating experience of power plants with the oxidizing treatment has been gained; it shows significant advantages of this chemistry over others, e.g. all-volatile treatment. One of the requirements for operation with the oxidizing chemistry is high purity of feedwater. According to Russian guidelines, conductivity should not exceed 0.3 µS/cm; EPRI guidelines (USA) limit it below 0.15 µS/cm.

Recently, the problem on wide introduction of oxidizing treatment at drum units has been discussed. It is evident that purity of boiler water is much worse than that of feedwater. Therefore, the problem of effect of water purity on corrosion of construction materials, carbon steel in particular, arises. This problem is also important for low temperatures as regards to prediction of behavior of carbon steel with drastic deterioration of feedwater purity. The basic aim of this work was to study effect of water purity on carbon steel corrosion at high temperatures (approximately 285 °C) in presence of oxygen or hydrogen peroxide. Corrosion rate of carbon steel at low temperatures (25-98 °C) was studied simultaneously.

PowerPlant Chemistry 1999, 1(2)

Heinrich Maurer

On-line pH Measurement by Differential Cation and Specific Conductivity

Differential cation and specific conductivity is a reliable and trusted method for the detection of impurities in steam and condensate. This method is often used for the calculation of pH-values by means of tables and graphs. This paper covers some theoretical aspects, discusses the set-up and reports field experience with a new instrument designed to automate this application.

PowerPlant Chemistry 1999, 1(2)

René van der Wagt, Frank de Vos, Sergey Babichenko, and Larisa Poryvkina

On-line Analysis of Water Contamination by Organic Compounds

In many industrial and environmental applications decomposing the mixture of substances in the water into its various chemical components, for subsequent analysis, is a very complicated task. The most productive approach to on-line diagnostics is to treat the object as an integral spectroscopic sample, characterized by certain specific Spectral Fluorescent Signatures (SFS). Spectral parameters of SFS are defined by fluorescent characteristics of basic groups of organic substances in the water sample.

One of the possible examples of an organic substance is oil in the water. The fluorescent characteristics of oil products depend on the content of aromatic hydrocarbons. The SFS technique enables the Skalar Fluo Imager to specify and divide the oil products into separate classes based on the total fluorescent information about the group of aromatic hydrocarbons of the oil. High correlation was found between the oil concentrations determined by the Fluo Imager and standardized methods, infrared and gas chromatography, for the determination of oils in water, resulting in r2 values of 0.98 and 0.98 respectively. The Skalar Fluo Imager provides simultaneous detection, identification and quantification of different types of crude oil and fuel oil, technical lubricants, polyaromatic hydrocarbons and phenols and their derivatives, in waters down to sub-ppm levels. Values for DOC, COD, turbidity and suspended matter can also be derived using absorption, scattering and fluorescent techniques developed in the hardware and the software of the instrument. Used in fast screening mode, the Skalar Fluo Imager provides a powerful identification and quantification technique in the on-line monitoring and control of water quality in a variety of application fields. On-line screening for organic pollutants in industrial waste water effluents, cooling water of power plants and process waters are good examples of the versatility of the instrument.

PowerPlant Chemistry 1999, 1(2)

Eric V. Maughan

Why On-line Analytical Programmes Fail

The modern high-productivity plant requires optimum continuous on-line monitoring of the process, which includes the power industry. The need to optimise process and manpower requirements dictates the use of highly sophisticated monitoring equipment. Loss control due to chemical deposition and corrosion also requires on-line analysis of the plant cycle chemistry. However, many of these automated continuous monitoring systems suffer from failure. This paper identifies common causes for failure of on-line monitoring systems and proposes solutions.

PowerPlant Chemistry 1999, 1(2)

Malcolm Ball

Power Plant Chemistry -a Decade of Changes in Britain

Britain has experienced a decade of change in the electricity supply industry, brought about by privatisation and liberalisation of electricity generation and distribution. The release of natural gas for power generation has encouraged new generators to enter the market and the existing generators have seen their share of the market fall considerably. Some of the large coal and oil fired plants have been decommissioned or put into storage, whilst others have been required only to meet peak demand. Operation or storage of these plants has required special chemical considerations.

The new plants built have been combined cycle gas turbine plants. Some are linked to combined heat and power plants. The relatively low operating pressures of the early plants led the plant suppliers to adopt the cycle chemistries used for low-pressure industrial boilers. These usually involved phosphate and, sometimes, amines or other propriety chemicals. Changes to the chemistry during commissioning and early stages of operation of the plant were limited, due to contractual obligations. Many of the plants were equipped with very limited on-line chemical monitoring equipment.

The plants have compact multi-pressure boilers where complex chemical interactions can occur. Problems included phosphate hide out, erosion/corrosion at small radius bends and decomposition of organic impurities in the make water or added deliberately as conditioning chemicals, which depressed boiler water pH and increased steam turbine conductivity. These effects were compounded for increasing boiler pressures.

PowerPlant Chemistry 1999, 1(2)