In-channel screening with a drum screen
In a water treatment system, which may be a wastewater treatment plant, a single-inlet drum screen is installed with its rotation axis perpendicular to the pattern of flow in a channel. Retrofitting of an existing screening system with a different form of screen, residing in an existing concrete channel is described.
1. A rotating drum screen installation for screening out debris from a flow of water in a channel, comprising:
a drum rotating on a horizontal axis, with a shaft supporting the drum for rotation, the shaft being supported on fixed structure of the channel, and a screen extending around the drum's circumference, forming the drum screen,
the axis of the drum screen being perpendicular to the channel flow direction such that the drum has a width that occupies part of a width of the channel, leaving a remaining width of the channel for water flow, the drum screen having a diameter not greater than about 10 feet, and being a single entry drum screen, with an open side facing said remaining width of the channel and positioned to receive a flow of water from said remaining width of the channel,
the channel having a flow direction from upstream to downstream, and said remaining width of the channel being blocked by a barrier adjacent to a downstream end of the drum screen,
a seal plate positioned in the channel alongside the open side of the drum screen, with a flexible contact seal between the seal plate and a circular side edge of the rotatable drum screen,
the seal plate having a water admitting opening to permit said flow of water into the drum screen from the open side,
a diverter plate in the channel, with a downstream end of the diverter plate connected to an upstream end of the seal plate, the diverter plate having an upstream end fixed to a wall of the channel and engaged against a floor of the channel, a main portion of the diverter plate being angled so as to form a parallel flow offset to direct all water and debris flowing in the channel into said remaining width of the channel prior to entering the drum screen through said water admitting opening, and
the drum screen installation including a debris hopper within the drum, fixed in position near a highest point of the drum, for catching debris from the screen as the drum screen rotates, and with a series of high-pressure water nozzles above the drum aimed at the hopper, to dislodge the debris from the screen into the hopper, and further including an exit trough positioned to carry away the debris and water from the hopper.
2. The rotatable drum screen installation of claim 1 , wherein the diverter plate and the seal plate are formed as a single unit.
3. The rotatable drum screen installation of claim 2 , wherein the diverter plate and seal plate are integrally formed from a single piece.
4. The rotatable drum screen installation of claim 2 , wherein the diverter plate and seal plate are secured together at said upstream end of the seal plate.
5. The rotatable drum screen installation of claim 1 , wherein the water admitting opening has a shape following the shape of a lower half of the drum screen, approximately an open half-circle.
6. The rotatable drum screen installation of claim 1 , wherein the high-pressure nozzles spray water at a minimum pressure of 45 psi.
7. The rotatable drum screen installation of claim 1 , wherein the drum screen has a width approximately half the width of the channel.
8. The rotatable drum screen installation of claim 7 , wherein the drum screen has a width of 45% to 55% the width of the channel.
9. The rotatable drum screen installation of claim 1 , wherein the contact seal is secured to said circular side edge of the drum screen.
10. The rotatable drum screen installation of claim 9 , wherein the contact seal is of elastomeric material and is deflected to a bending configuration by engagement against the seal plate, to exert a sealing force against the seal plate.
11. In a rotatable drum screen installation for screening out debris from a flow of water in a channel, including a drum rotatable on a horizontal axis, with a shaft supporting the drum for rotation, the shaft being supported on fixed structure of the channel, and a screen extending around the drum's circumference, forming the drum screen, the improvement comprising:
the axis of the drum screen being perpendicular to the channel flow direction such that the drum has a width that occupies part of a width of the channel, leaving a remaining width of the channel for water flow, the drum screen being a single entry drum screen with an open side facing said remaining width of the channel and positioned to receive a flow of water entering from said remaining width of the channel,
the channel having a flow direction from upstream to downstream, and said remaining width of the channel being blocked by a barrier near a downstream end of the drum screen,
a combination seal plate and diverter plate, the seal plate positioned in the channel alongside the open side of the drum screen, with a flexible contact seal between the seal plate and a circular side edge of the rotatable drum screen, and the seal plate having a water admitting opening to permit said flow of water into the drum screen from the open side, and the diverter plate having a downstream end connected to an upstream end of the seal plate, the diverter plate having an upstream end fixed to a wall of the channel and engaged against a floor of the channel, a main portion of the diverter plate being angled so as to form a parallel flow offset to direct all water and debris flowing in the channel into said remaining width of the channel prior to entering the drum screen through said water admitting opening, and
the drum screen installation including a debris hopper and means for collecting screened debris in the hopper and removing the debris from the drum screen installation.
12. The rotatable drum screen installation of claim 11 , wherein the diverter plate and seal plate are integrally formed from a single piece.
13. The rotatable drum screen installation of claim 11 , wherein the diverter plate and the seal plate are secured together at said upstream end of the seal plate.
14. The rotatable drum screen installation of claim 11 , wherein the drum screen has a width approximately half the width of the channel.
15. The rotatable drum screen installation of claim 14 , wherein the drum screen has a width of 45% to 55% the width of the channel.
16. The rotatable drum screen installation of claim 11 , wherein the contact seal is secured to said circular side edge of the drum screen.