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# Tech Notes

Desilting basin research indicates larger size selection is preferable

To determine the optimum size and design of the underground desilting basin needed for the 5 MW Amethyst project, Sedicon AS in Norway employed a six-step methodology. Through this process, the company determined that the desilting basin for this project needed to be 50 percent larger than the size included in the original design. Because nearly all grain sizes can be abrasive, the optimum size depends more on the quantity of sediment rather than on the ability to exclude a certain grain size, the company found.

Amethyst is a run-of-river hydro project proposed for construction on the Amethyst River in New Zealand. Westpower is the company developing the project. Because of the large annual rainfall (up to 10 meters per year) and steep topography in the region, annual sediment loads in the water are substantial. The challenge with this project was to determine a desilting basin design that would balance the cost of removing sediment with the cost of sediment-induced wear to the turbines.

The method Sedicon applied was:

— Consider a range of desilting basin sizes (surface area of 99, 147, 215, 284, 400, and 500 m2);

— Use a sediment concentration-duration curve to estimate the annual sediment load and grain size distribution that would enter the plant intake;

— Use a two-dimensional numerical model to calculate trap efficiencies for the basin sizes for each grain size (assuming a flow of 2.2 m3/s);

— Calculate the amount of sediment trapped annually for each basin size, based on calculated inflow, grain size distribution, and trap efficiency;

— Determine the cost due to wear of the turbines (including efficiency losses, maintenance cost, replacement cost, and unit down-time) associated with each cubic meter of sediment that passes the desilting basin, depending on grain size distribution; and,

— Summarize the cost due to sediment wear and construction cost for each basin size.

Following these steps, the basin size with the least total sediment-induced cost would be the optimum size. Typical trap efficiency values for this kind of project are 98 percent of 0.3 mm particles. However, this approach led to a basin size that corresponds to a trapping efficiency of 98 percent of 0.2 mm particles.

This method also resulted in selection of a substantially larger desilting basin than was included in the initial design (100 m2). The present 150 m2 design provided the lowest sum total sediment cost of all six options. This indicates that desilting basin size may be underestimated during the hydro project design phase, particularly in rivers with high levels of sediment transport.

A key issue is efficient sediment removal from the basin. To allow continuous power production, Westpower intends to use the SediCon Sluicer sediment removal system, which can remove sediment without interrupting the water flow. This system has been applied at other projects, among them in the pressurized headrace tunnel at the 60 MW Khimti project in Nepal.

NACE opens office in Malaysia

NACE International (formerly the National Association of Corrosion Engineers) has opened an office in Kuala Lumpur, Malaysia.

This office was opened to meet the needs of the society's fast-growing membership in that part of the world, says Cliff Johnson, director of public affairs with NACE International.

The Kuala Lumpur office is headed by Astley Pung, a native of Malaysia who previously worked in business development for manufacturing firm Prestar Resources Berhad.

NACE International is based in Houston, Texas, USA. The association has more than 22,000 members in 110 countries and focuses on protecting people, assets, and the environment from the effects of corrosion.

HydroVision International announces call for abstracts

PennWell Corporation, organizer of the HydroVision International conference and exhibition, is accepting abstracts for the Technical Papers track. The conference will be held July 19-22, 2011, in Sacramento, California, USA.

Abstracts are requested on all topics of interest to technical professionals in the hydropower field. Preference will be given to abstracts that focus on innovative, practical, and proven technologies and methods.

Abstracts that describe the focus and content of proposed papers (maximum of 400 words) are due October 29, 2010. Submit abstracts through the Internet at: www.hydroevent.com.

All abstracts submitted will be reviewed by the conference Technical Committee. If accepted, authors will be invited to submit a paper by April 22, 2011, for inclusion in the official conference publication (in CD-Rom format) that will be distributed to all conference delegates.

In the past, in odd-numbered years, the conference and exhibition was called Waterpower; in even-numbered years, the event was called HydroVision. From 2011 on, the annual hydro industry event will be called HydroVision International.

UN endorses certification system for explosive areas

Through its United Nations Economic Commission for Europe, the United Nations (UN) has formally endorsed the use of the International Electrotechnical Commission (IEC) System for Certification to Standards Relating to Equipment for use in Explosive Atmospheres (IECEx).

The IECEx system covers equipment, systems, services, and competence of personnel in highly specialized industries where the risk of fire and/or explosions exists. This system verifies compliance with international safety standards related to the use of equipment in areas where flammable gases and liquids and combustible dusts may be present. This system is designed to provide assurance that equipment is manufactured to meet dedicated explosive safety standards and that services such as installation, repair, and overhaul also comply with IEC standards.

The IECEx system comprises three core certification schemes:

— IECEx Certified Equipment, which provides assurance that products listed on the IECEx certificate of conformity conform to the international standards;

— IECEx Certified Service Facilities, which assesses and certifies that organizations and workshops that provide repair and overhaul services to explosive industries do so respecting the requirements of IEC International Standard 60079-19, Explosive atmospheres – Part 19: Equipment repair, overhaul and reclamation; and,

— IECEx Certification of Personnel Competencies, which provides companies with independent proof that a person holding an IECEx certificate of personal competency has the qualifications, experience and competency necessary to implement the international explosive industries standards.

IEC's standards cover a range of technologies, including power generation, transmission, and distribution; office and medical equipment; public and private transportation; information technology; and more.

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