Contents Issue 12 (2000)

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PowerPlant Chemistry Contents 1999-2000 (Volume 1 and 2)

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PowerPlant Chemistry 2000, 2, (12)

Hong Xu

Improvement of Flushing Procedure in Chemical Cleaning

Each conventional flushing sequence after the acid cleaning of a utility boiler requires a vast amount of demineralized water and should be followed by a rinsing process. We have developed a novel flushing procedure which can be performed mainly by using deoxygenated service water, and, after which the rinsing process can be omitted. For deoxygenating, an erythorbate formulation based on sodium erythorbate (sodium isoascorbate) is used.

PowerPlant Chemistry 2000, 2, (12)

Jürgen Koppe, Dietmar Mielke, and Dietmar Polster

The Catalytic Disinfection of Cooling Water in Cooling Tower Systems

The catalytic disinfection of cooling water in cooling tower systems applying the GEA-MOLCLEAN procedure is based on the combined effect of hydrogen peroxide, solid metal catalysts and microorganisms present in the cooling water. In contrast to many other disinfection treatments, no toxic or environmentally problematic substances are required. Hydrogen peroxide decomposes to oxygen and hydrogen after the disinfection reaction. For the last 18 months, this treatment has been successfully applied in the cooling system of AUSIMONT Deutschland GmbH, Bitterfeld, among other sites. The treatment employment in existing systems is, as a rule, simple and does not require particular protective measures or maintenance. The biocide and algaecide effect is limited only to the treated cooling system.

PowerPlant Chemistry 2000, 2, (12)

Wolfgang Hater, Bernd Mayer, and Matthias Schweinsberg

Development of Environmentally Benign Scale Inhibitors for Industrial Applications

The formation of scale, i.e., from calcium carbonate and calcium sulfate, on technical surfaces in contact with flowing water systems is a major challenge throughout a wide variety of industrial processes. Consequently, special water treatment chemicals are used in all processes in which the prevention of scaling is critical, ranging from industrial cooling water circuits to mining facilities. Traditionally, scale inhibitor formulations are based on phosphonic acids and polycarboxylates, which effect an excellent performance at very low concentrations.

However, an increasing need for phosphorus-free and biodegradable systems has arisen due to legislative constraints on the use of poorly biodegradable materials in systems with free discharge of process waters into the environment. Several new organic scale inhibitors based on carboxylic acids with excellent environmental compatibility i.e. with improved biodegradability, have recently been developed at Henkel. The development process of these new systems and their performance compared to classical non-biodegradable compounds is presented from the physical characterization and laboratory screening of raw materials to actual field tests of complete formulations.

PowerPlant Chemistry 2000, 2, (12)

Manfried Lasch, Udo Krumpholz, Gerhard Klessen, and Christian J. Scheuerer

The Application of Ozone for the Clarification of Water in Nuclear Power Plants

Visibility conditions in reactor wells and fuel pools of boiling water reactors do not normally cause any problems in German units. In particular cases, visibility and filter problems may occur during decommissioning or occasionally in units with pressurized water reactors. In the KRB Unit A, unexpected visibility trouble has appeared under decommissioning conditions. Turbidity has been the reason for the poor visibility and has caused a delay in decommissioning work. A report on attempts to solve this problem is presented. In the end, ozone has proven to be the best remedy.

PowerPlant Chemistry 2000, 2, (12)

Barry Dooley and Warren P. McNaughton

Recent Developments in Understanding of the Phase Transition Zone in the Low Pressure Steam Turbine

The local steam environment is the key to whether corrosion related damage mechanisms (pitting, corrosion fatigue and stress corrosion cracking) will occur on blade and disc surfaces. The phase transition zone (PTZ) in the LP turbine, where the expansion and cooling of the steam leads to condensation, is particularly important. A number of processes that take place in this zone, such as precipitation of chemical compounds from superheated steam, deposition, evaporation, and drying of liquid films on hot surfaces, lead to the formation of potentially corrosive surface deposits. Understanding the processes of transport, nucleation of droplets, formation of liquid films on blade surfaces, and concentration of impurities is vital in understanding how to prevent the damage mechanisms that result, and to improving unit efficiency/capacity.

The increase in knowledge of all aspects associated with the PTZ has positioned us on the brink of possibly two significant advances in the LP turbine: (i) understanding and reduction of the two major corrosion processes in the PTZ (SCC and CF), and (ii) producing significant unit performance and capacity increases. Both relate to the electrostatic effects of charged droplets and liquid films, and to how these can be modified.

PowerPlant Chemistry 2000, 2, (12)