Contents Issue 3 (2000)

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Digby D. Macdonald, Jing Pang, and Peter J. Millett

The Hydrolysis of Metal Salt Solutions at Elevated Temperatures

The hydrolysis of NiSO4 (0.01 - 1.0 m), ZnSO4 (0.01 - 1.0 m), and FeSO4 (0.01 - 5 m) solutions have been explored by measuring the pH at temperatures from 200°C to 325°C using yttria-stabilized zirconia (YSZ) and tungsten/tungsten oxide (W/WO3) pH sensors. After correcting for water activity and isothermal liquid junction potential effects, the pH values are compared with the corresponding values calculated directly from a code (MULTEQ) that is used extensively for modeling water chemistry problems in the thermal power industry. Good agreement is obtained over the entire concentration/temperature field except for NiSO4 at the highest temperature (325°C). In this case, it appears that the hydrolysis constant data for Ni2+ are seriously in error.

Finally, a comparison has been made between the pH responses of the YSZ and W/WO3 pH sensors. We found that the W/WO3 sensor is Nernstian (i.e. the dependence of potential on pH is 2.303RT/F) and reproducible. At low pH and at the highest temperature, the data suggest that the potential determining reaction may be different from that at higher pH values and lower temperatures.

PowerPlant Chemistry 2000, 2(3)

Anwer Puthawala and Norbert Henzel

Hydrogenation of Reactor Water in BWR Plants by On-Line Membrane Electrolyzers

Conventional hydrogen water chemistry technology for hydrogenation of BWR reactor water and simultaneous injection of oxygen to the offgas system requires provision on the power plant site of either large-volume gas storage tanks or an aqueous potassium hydroxide (KOH) electrolysis device with compressor. In both cases, complex valve and control stations as well as long gas piping systems are necessary. The innovative Siemens technology for generation of hydrogen and oxygen in stoichiometric ratios for direct injection into the relevant plant systems using a H2/O2 generator equipped with membrane electrolyzers installed on-line in the condensate system piping eliminates the need for expensive gas storage systems and prevents the risk of ingress into the steam, condensate and feedwater cycle of foreign substances with high conductivity characteristics such as KOH.

PowerPlant Chemistry 2000, 2(3)

Elton W. Floyd, J. C. Carpenter, Robert Svoboda, and Ronnie Jones

On-Line Chemical Cleaning of a Water Cooled Generator Stator

TU Electric's Valley 2, water cooled generator stator experienced progressive plugging due to deposits of copper oxide. The stator bar cooling water thermocouples indicated excessive temperature resulting in limiting the generating capacity of the unit. The classical methods of cleaning the stator required an extended outage. Since this was undesirable during the peak load season, a global flush was attempted with minimal success. Based on experience reported in an EPRI conference on generator water chemistry, we contacted ABB to discuss the possibility of utilizing their process of applying Na2EDTA to chelate the copper oxide and permit removal from the water system. This report is to discuss the generator's history, the chelating process and the results obtained by the cleaning.

PowerPlant Chemistry 2000, 2(3)

Hiroshi Takaku

Plant Cycles with Heat Recovery Steam Generators: Water Quality Guidelines (Japan)

Examples of water quality guidelines for plant cycles with heat recovery steam generators for both normal operation and startup were compiled. Drum-type and once-through steam generators as well as double and triple pressure drum boiler systems are covered in this compilation.

Publishing of this information was possible through the generous support of the Japanese industry experts working in this field (Nobuyuki Funabashi, Tokyo Electric Power Co. Limited; Masamichi Miyajima, Chubu Electric Power Co. Limited; Yasuyuki Yagi, Kansai Electric Power Co. Limited; Genroku Nakao, Babcock-Hitachi Co. Limited, Kure Research Laboratory; Takashi Morimoto, Mitsubishi Heavy Industry Co. Limited, Nagasaki Research Lab. Shuichci Inagaki, Toshiba Corporation Limited, R&D Center; Keiichi Miwa, Ishikawajima-Harima Heavy Industry Co. Limited; Yukiitada Tsunematsu, Kawasaki Heavy Industry Co. Limited; Ichiroo Myougan, Fuji Electric Co. Limited.).

PowerPlant Chemistry 2000, 2(3)

Albert Bursik

Cycle Chemistry Monitoring in Combined Cycle Units and in Units with Heat Recovery Steam Generators

The issue of adequate monitoring equipment or of its extent is as old as power generation itself. With the implementation of combined cycles with heat recovery steam generators, this topic has become increasingly important. Experience in the design and operation of standard power cycles is not completely transferable to the relatively new cycle design. This is true for the chemistry monitoring equipment, too. The recommendations of EPRI and VGB with respect to the monitoring extent are discussed and commented on. The significance of the individual monitoring parameters (cation conductivity, specific conductivity, pH, oxygen, oxidizing-reducing potential, hydrazine sodium, phosphate, silica, dissolved organic carbon, and corrosion products) and the right sampling points for those parameters are the subject of this paper.