Ovivo Brackett Green - Double Entry Drum Screens
The in-to-out flow pattern of the Brackett Green double entry drum screen eliminates bypassing and carryover. It also allows for a downward load that eliminates the risk of the screen breaking free from its foundation. The patented mesh panels can handle high differential loading for fine screening, without failing. Our robust, custom-made screens are designed to meet the specific requirements of individual plants. Low maintenance costs, smooth operation and long equipment life is guaranteed!
- Flow capacities up to 35m3/sec
- Standard screening aperture size ranges from 1.5 mm to 10mm
- Robust design can sustain differentials up to 2.0m
- Diameter from 6m to 20m with effective widths up to 6.0m as standard
- Very low maintenance required
Brackett Green double entry drum screens are engineered to suit the particular operating conditions, water levels and design codes of any installation site. This may include seismic qualification or designs for nuclear safety-related cooling water duty. Other options include a fish recovery and return system, which recovers and returns captured fish unharmed to the water body, as well as adaptations for handling large volumes of jellyfish.
The drum screens have diameters of 6 to 20 meters with widths up to 6 meters. Ovivo can offer either the double entry (DE) flow pattern, used primarily for larger flows (typically ranging from 8 to 45m3/sec) or the single entry (SE) flow pattern, which provides all the advantages of the double entry drum screen but are suitable for flows of less than 10 m3/sec, depending on the specific application. Materials of construction range from coated carbon steel to 316 or duplex stainless steel, with a provision for either sacrificial anode or impressed current cathodic protection.
- Highly reliable with low maintenance requirements
- Robust, cost-effective design
- Effectively cleaned by low pressure backwashing, minimizing energy costs
High Efficiency, High Capacity and Low Energy requirements
The Brackett Green® double entry (DE) drum screen consists of a robustly constructed A-frame drum structure with a solid, horizontal center shaft that slowly revolves in heavy duty, self-aligning double roller bearings lubricated from deck level oil reservoirs.
A variable speed drive unit positioned at deck level drives the screen, and the drive’s polymer pinion engagement with a polymer gear ring on the outside of the drum is a more efficient setup than traditional drum screen drive arrangements. Positive sealing between the rotating drum screen structure and the concrete chamber wall is achieved when the pre-formed neoprene seal on the screen makes contact with a low friction sealing face attached to the chamber wall, resulting in zero bypass of screenings.
In the DE arrangement, water enters from both sides and flows radially from the inside to the outside of the drum, creating a screen that is balanced both hydraulically and mechanically. This flow pattern ensures that the water level inside the drum is higher than outside of it, with the loads pushing downwards onto the concrete foundation, thus eliminating the risk of the drum screen breaking free from its foundation and floating in the chamber, which can lead to lengthy plant downtime. The DE flow pattern produces an outlet flow that converges, which makes this flow pattern particularly suitable for close coupling to the inlet of the CW pump.
With the single entry (SE) arrangement, the screen main shaft is aligned with the direction of influent flow which enters the screen via a single inlet port, then passes radially out through the screening media and exits by two outlet ports located downstream in the civil works wall.
Although the initial capital cost of civil works, including one screen chamber and two inlet channels for each screen, may be higher than for a traveling band screen with the same capacity, the low maintenance requirement means that the extra costs can usually be recovered within 3-4 years, depending on the site conditions. When the intake flow exceeds about 22m3/sec, then the capital cost of one drum screen becomes cost effective compared with two traveling band screens.
- Brackett Green drum screens utilize a rack and pinion drive, eliminating chains, rollers, pins, bushings and seal fins commonly found in all band screens, thus reducing both energy use and the maintenance required for keeping equipment in service.
- Brackett Green’s proprietary, full-contact seals ensure zero bypassing and complete retention and removal of screenings greater than the screen aperture, guaranteeing the highest screenings capture ratio in the industry.
- Brackett Green drum screens utilize a proprietary and patented ProPaPanel® – 9.0mm thick panels with integrated tapered holes that are proven to eliminate hair pinning or stapling from stringy and fibrous debris, and to minimize potential plugging from wedged debris and kitchen grease.
- Screen panels of steel or other metallic mesh with slots, or plastic panels of lesser thickness may reduce but not eliminate hair pinning and often require brush cleaners, greater wash water pressures and water volume, with increased service and maintenance.
- The drum screen’s internal hopper receives screenings and wash water, which are flushed out by an end-pipe nozzle to external troughing, ensuring an unimpeded flow out of the screen for dewatering.
- All Brackett Green drum screens incorporate a substantial bearing assembly and a solid, high tensile steel shaft to support the screen for both durability and long term operation.
- Each drum’s A-frame construction provides a light, but rigid structure that is suitable when constructed in stainless steel that must be seismically qualified.