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Ebara Engineering Review No.220

Hydraulic Development of a Large-sized Volute Pump with Adjustable Guide Vanes

by Takaki SAKURAI, Atsushi KANEKO, Mitsutoshi HAGINO, & Takashi ENOMOTO

An impeller of a large-sized, adjustable vane volute pump was designed using the 3D inverse method and CFD (Computational Fluid Dynamics). CFD was applied for the entire calculation, from suction to volute casing, for optimizing the pitchwise location between guide and stay vanes. Experiments using a model pump were carried out under different guide vane adjustments to study factors such as pump performance, axial and radial thrusts, and the unbalanced torque of the adjustable guide vanes.

Keywords
Volute pump, Adjustable guide vane, Computational Fluid Dynamics (CFD), Inverse design, Unbalanced torque, Axial thrust, Radial thrust

A Coupled Vibration Analysis for Large-sized Vertical Pumps and a Pumping Station

by Michiko SUGIYAMA, & Shuji YAMASHITA

The Finite Element Method (FEM) was used to predict vibration of large-sized vertical pumps, as well as that of the pump station where they were to be installed. When such pumping stations have a structural foundation with low rigidity, vibratory problems such as vibratory reaction between pumps, and increases in vibration, due to resonance caused by pump excitation frequencies and natural frequencies of the foundation, tend to occur. The following discusses an actual case of coupled vibration analysis and the effective application of resulting data in reinforcing the pumping station and installing additional pumps. The vibration levels of the pumps were found to be well below the allowable limit and the resonance phenomena was prevented.

Keywords
Coupled vibration analysis, Evaluation of pump vibration, Finite Element Method (FEM), Foundation structure, Natural frequency, Resonance phenomena, Vertical pump, Pump station

Research on the Behavior of Phosphorus in an Anaerobic-Anoxic-Oxic Activated Sludge Process with an Ozonation System for Excess Sludge Reduction

by Kiyomi ARAKAWA, & Toshihiro TANAKA

Ozonation was added to an activated sludge process to study the possibility of reducing phosphorus in the effluent. Test results, comparing supernatants from an anaerobic tank and those from an ozone reactor, suggested that it was possible to achieve both biological nutrient removal, by the anaerobic-anoxic-oxic process, and phosphorus removal, by ozonation. The propagation of phosphorus accumulating organisms was also confirmed. It was determined that using the supernatant from the anaerobic tank as raw water for chemical phosphorus removal was reasonable, as there was sufficient discharge of phosphorus in the tank, also because the phosphorus concentration therein was high. An intermediate settling tank and a chemical phosphorus removal system were set downstream the anaerobic tank, resulting in reduced excess sludge and a lower phosphorus concentration in the effluent.

Keywords
Sludge reduction, Anaerobic-anoxic-oxic process, Ozonation, Phosphorus removal, Activated sludge teatment

Performance Report of a Sludge Dehydration System for Excess Sludge Recycling Plants

by Katsuko KUSUMOTO, & Masahiro WAKANA

A sludge dehydration system, namely the Ebara Value Sludge System, capable of outputting sludge with a moisture content of lower than 70% max., has been developed for recycling excess sludge, following the approval of combustion improver usage at sludge recycling plants. The system constitutes 3 main components: a shaft-sliding type screw-press dehydrator, a concentrator, and a flocculation reactor. The shaft-sliding mechanism of the dehydrator prevents excess sludge clogging in the dehydrator, a typical phenomenon which occurs during sudden drops in sludge moisture content in conventional screw-press dehydrators. This system is currently being used at 5 plants and excellent feedback is being reported.

Keywords
Combustion improver, Shaft sliding type screw-press dehydrator, Low sludge moisture, The resource recycling center of excess sludge, Human-waste treatment plant, Concentrator, Flocculation reactor

Lecture on Corrosion and Corrosion Protection of Seawater Pumps - Part 1 Basics of Corrosion and Seawater Corrosion Characteristics -

by Matsuho MIYASAKA

This is the first of 5 parts of a lecture on corrosion and corrosion protection of seawater pumps. Seawater corrosion characteristics, the mechanism of various types of seawater pump corrosion will be discussed, including an introduction of Ebara's R&D on corrosion resistant materials and corrosion engineering. Part 1 will feature basics of corrosion and seawater corrosion characteristics, Part 2 fluid dynamic effects on seawater corrosion, Part 3 galvanic corrosion and cathodic protection, Part 4 a numerical corrosion analysis technology, and Part 5 corrosion and corrosion protection of stainless steel and Ni-Resist cast iron. In the following Part 1, corrosion mechanism, seawater properties, and seawater corrosion characteristics are discussed. The relationship between seawater property characteristics and seawater corrosion will be explained, in which it is pointed out that seawater is a neutral aqueous solution which saturates dissolved oxygen, also that it includes a considerable amount of inorganic salt, mainly chlorides, and is therefore highly conductive.

Keywords
Corrosion, Seawater, Pump, Chloride ion, Dissolved oxygen, Potential, Crevice corrosion, Pitting corrosion, Galvanic corrosion, Cathodic protection