Contents Issue 11 (2000)

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MEI Conference "Water Treatment and Chemistry, Chemistry Monitoring at Fossil and Nuclear Power Plants, and Fuel Utilization" MEI Conference "Water Treatment and Chemistry, Chemistry Monitoring at Fossil and Nuclear Power Plants, and Fuel Utilization"

This conference dedicated to the 70th anniversary of the Moscow Power Institute (Technical University) was held in Moscow, Russia on December 14-15, 2000. PowerPlant Chemistry presents short abstracts of all presented papers.

PowerPlant Chemistry 2000, 2(11)

R. Sonninen

Experiences from Oxygenated Water Treatment at Kymijarvi Power Station.

Since the commissioning of the Kymijarvi Power Station in 1976 up to 1995, all volatile treatment (AVT) has been used as the chemical control method in the plant. Due to the high total pressure drop across the high-pressure part of the steam boiler in the summer of 1995, caused by ripple oxide deposits on the evaporator tubes, the acid cleaning of the boiler evaporator was necessary. After the acid cleaning, AVT, used previously, was changed to oxygenated treatment (OT) in the fall of 1995. Since the OT conversion, the steam boiler has been operated using OT for five years. A comparison of data collected prior the conversion with the data collected following the conversion and with data 5 years later indicates the following advantages: reduction boiler pressure drop and boiler deposits and Improvement to the operating chemistry and the condensate polishing operation.
Few years after the OT conversion the gradually increasing turbine efficiency loss, caused by turbine deposits, was found. At present, the loss is about 2 %. The turbine has not been disassembled yet and due to this, the chemical composition and formation mechanism of turbine deposit is not known completely.

PowerPlant Chemistry 2000, 2(11)

M. de Martín Mas, M.S. Sáiz, E.R. Martín, and A.H. Gómez

Cycle Chemistry in Iberdrola's Velilla Power Plant (Unit 2)

Unit 2 of Iberdrola's Velilla power plant is a unit with a drum-type boiler and all-ferrous metallurgy in the feed train and copper-nickel and admiralty brass tubing in the condenser. This paper describes the steps performed at the Unit 2 in order to eliminate the use of oxygen scavenger. Currently, ammonia is the only chemical additive applied to the plant cycle.

PowerPlant Chemistry 2000, 2(11)

E. Liebig, R. Svoboda, H. Hehs, and H. Sandmann

Combined Cycle Plants: New Concepts - New Solutions

Inherent features of the water-/steam cycle in combined cycle power plants compared to conventional directly-fired steam power plants result in specific chemical conditions. E.g., modern plants are designed without feedwater preheating, resulting in the need to handle low feedwater temperatures and to rely on vacuum deaeration in the condenser. To date, combined cycle power plants have usually been equipped with unfired single-, dual- or triple-pressure drum-type boilers with or without reheat. Often two, in special cases three heat recovery steam generators (HRSG) are combined with one steam turbine. Depending on the pressure and the boiler type, different chemical requirements may lead to the parallel use of different types of boiler water treatment. Based on these special design features, an innovative HRSG concept is presented by a combination of a low-pressure drum-type boiler with a high-pressure once-through boiler and the appropriate water-/steam cycle. The water chemistry is based on the restrictive use of chemicals. First operating experience is given for novel techniques like water-/steam cycle treatment and the use of a high-pressure separator to remove impurities from the cycle.

PowerPlant Chemistry 2000, 2(11)

P. Ananthan and G. Venkateswaran

Influence of Carbon Steel and Other Structural Materials on the Dissolution of Hematite

The nature of the iron species formed during the dissolution of moderately sintered hematite in presence and absence of different base metals like carbon steel, stainless steel, Monel and Incoloy 800 has been investigated with a view to understand the mechanistic aspects of hematite dissolution in citric acid-EDTA-ascorbic acid (CEA) media. Amongst the various base metals employed in the present study, it was observed that carbon steel played an important role in increasing the dissolution rate as well as in increasing the Fe(II)/Fe(III) ratio in solution after the dissolution. The dissolution rate increased significantly with an increase of surface areas of carbon steel exposed. In the presence of carbon steel, formulation containing citric acid-EDTA (CE) was found to be as effective as CEA. A case study for applying CEA as decontaminating formulation in the regenerative modus in a stainless steel system such as reactor water clean-up system of a BWR is presented. This is based on the incorporation of a fresh carbon steel surface for the purpose of chemical decontamination of the RWCU system using CEA formulation by which the otherwise non-regenerative CEA process can become regenerative. No noticeable difference was observed in the iron species found between dissolution in simple CEA formulation and CEA formulation in presence of stainless steel or Monel 400 or Incoloy 800 as base metals.

PowerPlant Chemistry 2000, 2(11)

A.A.M. Prince, A.M. Remona, S. Velmurugan, S.V. Narasimhan, P.S. Raghavan, and R. Gopalan

Dissolution Behaviour of Mixed Ferrites and Chromites in Aqueous Solutions Containing Chelating Agents

Corrosion product oxide spinels that play host for the radioactive nuclides are formed in the coolant circuits of nuclear reactors at high temperatures. In the present study, model corrosion products were prepared by solid state methods using a-Fe₂O3 as starting material and at high temperatures. The dissolution experiments of the mixed ferrites were carried out in aqueous solution containing 2,6-pyridinedicarboxylic acid and other complexing agents. Special attention was given for the study of the dissolution behaviour of zinc ferrite and zinc chromite which are normally formed in systems that have adopted zinc ion passivation. The role of Fe(II) complex in aiding the dissolution of zinc ferrite has been investigated. The effect of citric acid on the dissolution of magnetite powder in various chelating media was studied. The dissolution studies carried out using magnetite coated carbon steel in citric acid an EDTA indicated that the dissolution behaviour of the magnetite film differs very much from that of magnetite powder. The difference in dissolution kinetics observed between light and heavy water medium is also outlined.
PowerPlant Chemistry 2000, 2(11)