The solubility of crystalline zincite (ZnO) has been re-evaluated in noncomplexing solutions over a wide range of pH to 350 °C at pressures ranging from slightly above saturation vapor pressure to significantly higher pressures in NaOH, NH3, F3CSO3H/F3CSO3Na (HTr/NaTr), CH3COOH/NaOH, and F3CSO3H/NH3 solutions using a hydrogen-electrode concentration cell and a flow-through cell with down-stream acid injection. Recent new results, coupled with our earlier data at 75-100 °C, indicate that the solubility of zinc oxide is higher in near neutral solutions than we reported previously [1], but substantially lower than previous estimates available in the scientific literature. The solubility of ZnO versus pH profile has a broad minimum in near neutral solutions. This is also the range of operation of the primary circuit of a PWR, where zinc injection is being carried out in some plants to mitigate stress corrosion cracking [2]. Therefore, a precise knowledge of the solubility in this pH region at all temperatures is required to permit significant doping with zinc(II) while not exceeding the solubility limits of ZnO.
PowerPlant Chemistry 2003, 5 (5)
Robert Svoboda, Hans-Dieter Pflug, and Thomas Warnecke
Investigations into the composition of the earky Condensate in Steam Turbines
This paper reports on investigations into concentration effects in the first condensate. The equipment and the analytical techniques used do not markedly differ from those applied in previous measuring campaigns. During these investigations, however, small amounts of various contaminants (e.g., NaCl) were injected into the cycle. In this way, the accuracy of the analytical techniques was improved. Care was taken to maintain the cation conductivity within the VGB guideline specifications. In comparison to the previous measurements, the extent of the analytical parameters measured was broadened.
Apart from inaccuracy in analytics and problems in sampling at very low steam moistures, the following conclusions could be drawn:
for strong electrolytes such as salts of sodium, potassium and calcium, the concentration is a reciprocal linear function of the steam moisture,
volatility of inorganic and organic acids affects the concentration dependence of the steam moisture,
for ammonia and carbon dioxide, any concentration dependence on steam moisture could not be found.
The experiment results may contribute to better assessing of possible steam turbine damage due to carbon dioxide and organic acids.
PowerPlant Chemistry 2003, 5 (5)
Vitaly A. Prisyazhniuk
Ways of Raising the Thermodynamic Efficiency of Steam Power Plants
An equation for estimating the thermodynamic efficiency of the Rankine cycle is proposed which includes the thermophysical characteristics of the working medium and the condensation completeness coefficient. Three alternative ways of raising the thermodynamic efficiency of the cycle are discussed:
by using, as a working medium, some chemical agent having "optimal" thermophysical characteristics,
by using a "composite" working medium, that is a solution with "optimal" thermophysical characteristics, and
by changing the thermophysical characteristics of a conventional liquid by way of restructuring the liquid with an active electrical or magnetic field, for instance, by employing the magneto-hydrodynamic (MHD) resonance method.
Some examples of actual cases of change in the thermophysical characteristics of a liquid by the MHD resonance method are given.
PowerPlant Chemistry 2003, 5 (5)
Hans-Günter Seipp
Corrosion as a Result of Unsatisfactory Attemperator Water Quality
In fossil power plants and particularly in industrial power plants, the superheated steam temperature is widely reduced via injection (attemperation) of water. Corrosion damage has been repeatedly observed in equipment downstream of the water injection point. For this reason, the technical codes of practice were checked for preventive explanations. Two case studies make the hardly surveyable coherences evident.
PowerPlant Chemistry 2003, 5 (5)
Stefan A. Huber
Sources and Behavior of Organics, in Particular Polysaccharides, in Boiler Feedwater Preparation and in Water-Steam Cycles
There are many different ways in which how organic matter (OM) may get into water-steam cycles. One important pathway is OM brought into the system via the makeup water under standard operation conditions. This is particularly true for sites where a surface water source is treated conventionally without reverse osmosis. Here, it has to be taken into account that high amounts of high-molecular weight organic matter, in particular polysaccharides, are brought into the water-steam cycle. Under hydrothermal conditions, polysaccharides are broken up into - among other things - to organic acids, in particular acetic acid. The different sources of polysaccharides in the different natural water systems are briefly discussed.
The results of a previously published and well-documented autoclave test are briefly discussed. The test supports another issue, the propensity of OM to mask halogens, in particular chlorine. Such organochlorine compounds are not necessarily amenable to trihalomethane or activated carbon organic-bound halogen analysis.
The impact of condensate polishers is briefly discussed.
Three case studies are described. At all sites, surface water was treated without reverse osmosis. In parallel, at all sites corrosion was observed in areas of the turbine or the boiler and organic acids were made responsible for this.
The paper finishes with some water treatment considerations: How can we remove polysaccharides effectively?
PowerPlant Chemistry 2003, 5 (5)
Hans-Günter Seipp
Schäden durch unzureichende Einspritzwasserqualität
In fossil befeuerten Kraftwerken und insbesondere in Industriekraftwerken wird die Frischdampftemperatur durch Einspritzung von Wasser herabgesetzt. Wiederholt wurden Korrosionsschäden an Anlagenteilen hinter der Einspritzstelle beobachtet. Aus diesem Grunde wurde in den technischen Regelwerken nach präventiven Hinweisen gesucht. Zwei Fallstudien machen die schwer überschaubaren Zusammenhänge deutlich.
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