The Aegis® Underwater Torus Filter – Another Graver Improvement in System Performance
Torus pool maintenance is a must at most BWR reactor sites, and until now, it has been an expensive, time-consuming, inefficient process. Working with technical experts at one of the U.S. BWR nuclear generating plants, Graver Technologies developed a more efficient, cost-effective solution that delivers superior pool clarity: the Aegis® Torus Pool Underwater Element.
Time-Consuming Torus Pool Maintenance
Standard BWR reactors include a Torus containing over one million gallons of water that are available to the reactor for emergency cooling. During operation, the Torus accumulates both large and fine particle solids from blow off streams and post outage debris.
Because Torus water must maintain a high level of clarity to facilitate frequent visual inspections of the pool, cleaning the Torus pool is a regularly scheduled task. Typically, personnel employ vacuum systems that include a vacuum head, screening devices and multiple filter elements to capture the removed debris for disposal. Historically, the industry uses pleated cellulose filter elements contained within vacuum housing. These elements often cause operational difficulties including bursting upon solids loading and short run lengths that necessitate more personnel attention and exposure. Additionally, as certified divers must supervise the cleaning, costs are high and exposures must be monitored and limited.
The Aegis Solution
The inaugural generating plant installation asked Graver Technologies to develop an improved element for this Torus pool application. Graver developed the Aegis® Torus Pool Underwater Element – a high-solids-loading, inside-out flow element specifically for general vacuum system use in Torus pool cleanup during plant shut downs. The Torus filter boasts a number of innovative features:
- Removes solids and suspended solids from suppression pool water and is available in a variety of micron ratings that can be changed during the pool cleanup from coarse to fine as needed. (Often a cleaning operation initially uses the more porous rated element, progressing to the finest porosity to maximize pool clarity while minimizing cleaning time.)
- An inside-out flow pattern traps particles inside the filter after cleanup for safe and complete disposal of the element and entrapped solids.
Epoxy end seals and 3” Nylon CAM- Lock male fittings connect and disconnect securely and quickly.
- An extended removal handle with a protective cap secures the contents of the element for easy disposal.
- Proprietary filtration media features multiple media layers, high solids loading capacity and a wide variety of micron ratings.
- Integral epoxy end caps help the filter resist bursting even at high differential pressures. Unlike cellulose elements commonly in use, Graver’s design prevents tearing and bursting even under heavy solid loadings.
- A pleated design provides maximum surface area for long service life.
- A robust 27 square feet of surface area collects more solids.
- Easily endures temperatures up to 200º F.
New Standards of Clarity
The new Graver element delivers a number of welcome benefits: it improves overall filtration, reduces filtration time, reduces diver time and exposure, lowers costs and dramatically increases Torus pool visibility from 2-3 feet at cleaning start to 12-14 feet after cleaning. We look forward to discussing how the Torus filter can benefit your plant.
Powerline has a new feature: our experts address common precoat, powder, septa and condensate issues in Q&A format. Email questions to email@example.com. We’ll either answer them here, or if they concern issues specific only to your installation, we’ll contact you and answer them personally.
Q. Why is air surge so important in a septa or prefilter backwash?
A. An air surge/backwash is the most effective way to remove precoat and/or ferric oxides after the end of a run. A well-designed air surge removes more than 99% of the spent precoat and/or oxides from the surface of the septa. The backwash then carries away the spent precoat and/or oxides. Systems with poorly designed and operated air/water wash experience shorter run cycles and shortened septa life.
Q. What are the recommended precoat loadings when preparing a precoat solution?
A. The normal loading for condensate polishing running to ion exchange endpoints is 0.2 lbs of dry weight Powdex® (or Ecodex®) per square foot of septa area. For both Aegis® classic yarn septa and DualGuard® septa the precoat area is determined simply by calculating the circumferential surface area of the septa. The number of septa in each vessel can be determined by consulting the appropriate section of your Graver or other OEM service manual. The total surface area of the vessel can be determined by multiplying the number of elements by the surface area of the element. Multiplying the total septa surface area by the desired precoat dosage will give the required dry weight of precoat material needed for each precoat. See the example below for more guidance or contact your Graver rep for specific questions relating to your operation.
72" Powdex Vessel with 420, 2" diameter X 70" long polypropylene wound septa Precoat Dosage 0.2 dry lb per sq ft of Premix 22H (12 dry lbs/container)
1828 mm Powdex Vessel with 420, 51 mm X 1778 mm long polypropylene septa, Precoat Dosage 1kg/m² of Premix 22H (5 dry kg per bag)
Septa surface area = π X d(iameter) X h(eight)
Septa area = 3.14 X 2 X 70 = 440 sq in/144 = 3.06 sq ft
Septa area = 3.14 X 51 X 1778 / 1,000,000 = 0.285 m²
Surface Area for all Septa in Powdex Service vessel = Number of septa X Surface area per septa
Surface Area for all Septa in Powdex Surface vessel = 420 X 3.06 = 1285 sq ft
Surface Area for all Septa in Powdex Surface vessel = 420 X 0.285 = 120 m²*
Precoat material per precoat = Precoat Dosage X Vessel surface area
Precoat material per precoat = 0.2 dry lb per sq ft X 1285 sq ft = 257 dry lbs of precoat material
Precoat material per precoat = 1kg / m² X 120 m² = 120 kgs of precoat material*
Containers of Premix 22H = 257 dry lbs of precoat material/12 dry lbs of per container = 21.4 containers, rounded to 21 containers*
Bags of Premix 22H = 120 dry kg of precoat material / 5 dry kg per bag = 24 bags*
* Always round to and consume full containers due to resin exhaustion and drying from exposure to air.
Q. Does Graver provide system upgrades?
A. Depending on the type of upgrade, Graver Technologies or Graver Water personnel will perform system surveys and provide necessary upgrades including state of the art septa and attachment hardware, improved flow distribution, PLC controllers and more. System upgrades are not limited to only Graver-supplied systems; many can be applied to non-Graver systems as well. Many nuclear BWR plants have upgraded to the DualGuard septa and both top and bottom tube sheet prefilters have converted to the Graver Technologies’ Aegis® AFA pleated septa. Please contact our representatives for more information about how Graver can retrofit your OEM systems with proven Graver technology.
Robert Kunin (1919-2009): A True Ion Exchange Pioneer
World-renowned ion exchange expert Dr. Robert Kunin died in January of this year at age 90. Many at Graver Technologies were privileged to work alongside Dr. Kunin, who consulted for the company for more than 25 years. His unparalleled technical knowledge, insight and warm interpersonal skills left an indelible mark on many and a shining legacy of success at Graver. “He focused our efforts in many areas, implementing product and applications development starting more than 25 years ago that still constitute major business areas for us today,” says Al Tavares, Ion Exchange Technical/Product Manager, who says ion exchange and adsorbent products for condensate and other power generation waters, sugar treatment and pharmaceuticals are among these areas. “He also mentored others and advanced the field selflessly with a warm, personable style. A lab technician affectionately referred to him as the ‘Font of All Knowledge.’” Ion Exchange Development Group Leader Dr. Peter Yarnell also worked closely with Dr. Kunin. “Despite the fact that Dr. Kunin was the foremost authority on ion exchange, he always went out of his way to assist anyone interested in ion exchange technology,” Yarnell notes. “He was a valued mentor to me personally who offered many valuable insights and ideas. In addition, he was a true gentleman and scholar.”
After obtaining a doctorate from Rutgers University in 1939, Dr. Kunin worked at Rohm and Haas for 30 years in a variety of leadership positions. A pioneer in ion exchange technology, he authored several influential books, more than 350 articles and 40 patents. Many will remember what was perhaps his most popular publication: 185 issues of the Amber Hi-Lites technical information series that coincided with and advanced a dynamic period in ion exchange technology. During the last several decades, he continued to write seminal articles, shared his considerable knowledge at the industry’s leading conferences and consulted on cutting edge projects. His legacy lives on in our community and we’ll greatly miss his insight, enthusiasm and experience.
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