Earlier investigations have shown that low pH conditions caused by carbon dioxide enhance aqueous corrosion of steels.
The goal of the present investigation was the clarification of whether carbon dioxide in steam promotes stress corrosion cracking of turbine steels by a mechanism other than the pH effect. For this, sensitized turbine steel was subjected to a NaCl solution, with and without carbon dioxide, at constant pH conditions. The time to fracture and the morphology of the fracture surface were used as distinguishing criteria for assessing the influence of carbon dioxide. Although the sensitized turbine steel and NaCl solution may only be partly representative of the actual conditions in a steam turbine, the examination is nevertheless indicative of the influence of corrosion promoting factors.
The present investigation indicates that besides the pH effect, carbon dioxide does not specifically attack turbine steels. It is, however, unlikely that carbon dioxide causes low pH in the liquid film in steam turbines, provided that the cycle pH is controlled adequately.
These results indicate that under normal plant operating conditions carbon dioxide in steam is tolerable as long as a sufficient alkalization of the steam/water cycle is provided. Such tolerance would be consistent with Alstom's steam turbine performance history.
Organic acids, however, for example acetate, may not be so benign.
PowerPlant Chemistry 2003, 5 (10)
Second Announcement: 14th International Conference on the Properties of Water and Steam: Water, Steam and Aqueous Solutions for Electric Power – Advances in Science and Technology
The 14th ICPWS to be held from August 29 through September 3, 2004 in Kyoto, Japan, highlights the theme "Water, Steam and Aqueous Solutions for Electric Power – Advances in Science and Technology."
The Conference continues the series of International Conferences on the Properties of Water and Steam started in 1929 and is concerned with the physical and chemical properties of water, steam, and aqueous systems. It has traditionally provided the scientific foundation for the accurate thermophysical property and water chemistry data used by power generation and related industries, and is expanding into new areas of pure and applied research related to water and aqueous systems at extremes of temperature and pressure.
Relevant areas of basic science include spectroscopy, calorimetry, potentiometry, thermophysical property measurements and modelings, and molecular simulation studies of water and solvated species in high-temperature or supercooled water. Areas of application include power cycle chemistry, high-temperature aqueous technologies applicable to steam cycles and fuel cells, the use of high-temperature water and supercritical steam in chemical and metallurgical processes, supercritical destruction of toxic wastes, hydrothermal geochemistry and hydrometallurgy.
PowerPlant Chemistry 2003, 5 (10)
Masamichi Miyajima, Yasuhiro Nishino, Masayoshi Hirano, and Satoshi Itaba
Evaluation of the Oxygenated Feedwater Treatment at Chubu Electric Power's Plants
The Chubu Electric Power Company started research on the oxygen treatment method (combined water treatment, CWT) in 1992, about 10 years prior to other electric power companies in Japan. As a result, we have obtained good results, such as a suppressed increase in boiler differential pressure, reduced boiler feed pump power consumption and extended intervals between chemical cleanings of boilers; at the same time, we have detected no particular damage or negative influence on corrosion.
Based on these good results, CWT has been introduced to 14 units/10 400 MW, including Unit 1 at Chita Daini Power Station. In this paper we summarize these attempts and provide data on, among other things, the effects of small amounts of foreign matter on turbine materials and research on chemical cleaning criteria for boilers using CWT.
PowerPlant Chemistry 2003, 5 (10)
Albert Bursik
Selecting Cycle Chemistry – This Time in a Different Way
It is standard practice that when selecting cycle chemistry for a particular unit or a steam generating system, the type of boiler (once-through or circulation steam generator) and the cycle metallurgy are the two most decisive parameters. In this paper, many other factors affecting the selection are focused on.
These additional factors are important in particular for units (also combined cycle units) erected for and operated by inexperienced independent power producers and for all steam and power generating systems besides the classic fossil utility power plants (in the industry, e.g., chemical industry, refineries, sugar and paper mills, in municipal incinerators, and cogeneration units).
Dealing with the factors of influence shows that many "non-optimum" cycles have to be operated in the very right open end of the funnel of the continuum of treatments. The fact that alternative cycle chemistry treatments may probably represent a promising alternative for this area is dealt with in another conference paper.
PowerPlant Chemistry 2003, 5 (10)
Walter Guhl, Wolfgang Hater, and Thomas Hörtinger
The Environmental Behavior of Water Treatment Products in Cooling Water Systems (in German)
Water treatment products must be technically and economically effective; in addition, they have to be environmentally compatible, because they are generally discharged directly into the receiving water. Teamwork between product development, application technology and ecology from the beginning of the development of water treatment products leads to economically and ecologically optimized products, specially tailored for use in cooling systems. The ecological profile of a hardness stabilizer with long-term effects (P3-ferrofos 8444) shows that the product degrades slowly after use in the receiving water, but due to its nontoxicity to water organisms, the environment will not be affected. A hardness stabilizer for shock dosage (P3-ferrofos 8413-3) is nontoxic, too, but is additionally rapidly biodegradable. When using the biocide for shock dosage, the product is destroyed in the environment by hydrolysis within a few minutes to some hours, so that a negative influence on the environment can be excluded. To reduce the biocide quantity, a biocide activator and dispersant (P3-ferrofos 8460) with a very low toxicity to water organisms is used.
This product is eliminated slowly, but enrichment in the receiving water can be excluded. The product properties promised by the producer have been confirmed by use in a German power station for several years. The hardness stabilizing properties of the two products are determined by the threshold effect of the phosphonic acid composition and the polycarboxylic acid compounds, so that the concentration used is very low. In the same way that the products stabilize the hardness components to harmless aggregates, the mostly small organisms (bacteria, algae, protozoa) are stabilized, too, and eliminated with the effluent without any problems for the cooling system. It could be shown that the loss of product corresponds to the biological growth. Therefore, it is possible to reduce the application of biocide and biocide activator to one treatment per year. A peculiarity of this power station is the fish culture in by-passes of the cooling system. By a well-controlled dosing of the products, the fish are not impaired; any negative influence on the water conditioning, however, could be excluded by an optimization of the fish feeding. With this collaboration between producer, ecology, power station management and fish culture, we can speak of a symbiosis between technology and nature.
PowerPlant Chemistry 2003, 5 (10)
Walter Guhl, Wolfgang Hater und Thomas Hörtinger
Das Umweltverhalten von Wasserbehandlungsmitteln in Kühlkreisläufen
Wasserbehandlungsmittel müssen technisch und ökonomisch effektiv sein, zusätzlich müssen sie umweltverträglich sein, da sie üblicherweise nach Gebrauch direkt in den Vorfluter eingeleitet werden. Die Zusammenarbeit von Produktentwicklung, Anwendungstechnik und Ökologie von Beginn der Entwicklung von Wasserbehandlungsmitteln führt zu ökonomisch und ökologisch optimierten Produkten, die für ihren jeweiligen Einsatzzweck maßgeschneidert sind. Das ökologische Profil eines Härtestabilisators mit Langzeitwirkung (P3-ferrofos 8444) zeigt, dass er nach Gebrauch im Vorfluter zwar nur langsam abgebaut wird, aber aufgrund seiner Ungiftigkeit gegen Wasserorganismen die Umwelt nicht schädigt. Ein Härtestabilisator zur Stoßdosierung (P3-ferrofos 8413-3) ist ebenfalls ungiftig, wird aber zusätzlich biologisch sehr schnell abgebaut. Bei der Anwendung eines Biozids zur Stoßdosierung (P3-ferrocid 8580) zerfällt dieses in der Umwelt durch Hydrolyse innerhalb von einigen Minuten bis wenigen Stunden, so dass eine Umweltbeeinträchtigung ausgeschlossen werden kann. Der gleichzeitig zur Verminderung der Biozidmenge verwendete Biozidaktivator und Dispergator (P3-ferrofos 8460), der nahezu ungiftig gegen Wasserorganismen ist, wird zwar nur langsam eliminiert, eine Anreicherung im Vorfluter kann jedoch ausgeschlossen werden. Die vom Hersteller ausgelobten Produkteigenschaften werden durch den Einsatz der Produkte in einem deutschen Kraftwerk seit Jahren bestätigt: Die härtestabilisierenden Eigenschaften der beiden Produkte werden durch den Threshold-Effekt der Phosphonsäure-Kombination und der Polycarbonsäure-Komponenten bestimmt, so dass die Einsatzmenge sehr niedrig ist. Genauso wie die Produkte die gelösten Härtebildner in unschädliche Aggregate stabilisieren, werden auch die überwiegend kleinen Organismen (Bakterien, Algen, tierische Einzeller) stabilisiert und mit der Abflut aus dem Kühlsystem ausgetragen. Es konnte gezeigt werden, dass der Produktverlust im System abhängig vom biologische Wachstum ist. Deshalb ist es möglich, den Einsatz von Biozid und Biozidaktivator auf eine Behandlung pro Jahr zu reduzieren. Als Besonderheit werden in diesem Kraftwerk im Bypass des Kühlsystems Fische gezüchtet. Durch genau dosierte Produktzugabe werden die Fische nicht beeinträchtigt, andererseits konnte durch Optimierung der Fütterung ein negativer Einfluss auf die Wasserkonditionierung ausgeschlossen werden. Durch die Zusammenarbeit von Produkthersteller, Ökologie, Kraftwerksbetreiber und Fischwirtschaft kann man von einer Symbiose zwischen Technik und Natur sprechen.
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