Tuke and Bell is one of the UK's leading manufacturers of sewage purification equipment with over 90 years experience in design and production.
Heavy investment in the most advanced technology and the latest computer aided design systems facilitate the production of the highest quality equipment, Through serving the needs of both the water industry and domestic customers to the highest possible standards we have achieved approval of our Quality Management System to ISO 9001 for Process Engineering, Design, Manufacture, Installation and Servicing of Water Purification Equipment.
Tuke and Bell offer a complete range of rotary scrapers for primary and secondary settling tanks, for sewage works and water treatment plants. The range is manufactured to standard designs but can be specially adapted to suit individual requirements.
The scraper has a rotating half-bridge with an open-mesh walkway, rigid scraper blade support arms and low-hinge-point scraper blades, vertical feed pipe and a fixed circular or multi-sided diffuser drum. The bridge can be constructed in steel or aluminium alloy, G.R.P. and plastic parts, where appropriate. Ancillary equipment such as automatic scum skimmers, side-wall scrapers, channel and weir-cleaning brushes can be fitted to make the machine suitable for use in primary or secondary settling tanks.
These are designed normally for the removal of thin final sludges from humus or activated sludge applications where the sludge must be removed from the sloping tank floor as quickly as possible. Hinged scraper blades operate from rigid depending arms or underwater booms attached to both sides of the bridge radii. The drive is by traction on the tank coping from one end of the bridge. The other end of the bridge has freewheeling polyurethane tyred wheels also running on the tank coping. For some special applications, twin synchronised drives can be fitted at each end of each bridge assembly.
This low-cost scraper is specifically designed for final settling tanks with sloping floors, greater than 20 degrees to the horizontal. One version has an access bridge while the other has a simple boom of circular or rectangular hollow section to connect the driving mechanism with the centre bearing. The rotating boom or bridge can be made of steel or aluminium.
Scraping of the tank floor is by a chain served by a swivel connection to a single depending arm suspended from the bridge, next to the tank wall. The chain is of sufficient length to form its own continuous spiral along the sloping floor and into the centre sludge zone of the tank.
In certain situations, heavy concentrations of settled sludge are present or rapid return of sludge is needed. In these cases extra scraping capability is necessary to avoid possible sludge build-up, particularly in the central tank area.
The simple solution is a standard rotating half-bridge extended a short distance beyond the centre pivot. Depending arms carry extra scraper blades to increase the scraping frequency in the centre tank area for extra concentration and subsequent draw-off.
These rugged machines are designed specifically for use in treatment plants where particularly heavy settled sludges may be a problem. The scraper assembly is mounted from the centre rotating tube assembly. Rotation is through a centre drive unit driving a full length vertical shaft, carried in a radial bearing on the tank floor, and a combined radial and thrust bearing assembly in the centre drive, mounted on the bridge. A lattice bridge structure is attached to the revolving shaft and carries a picket fence- type stirring mechanism as well as scraper blades arranged in echelon formation. Normally there is no diffuser drum or outlet weir; liquid is fed from the side and withdrawn as thickened sludge from the central collection hopper.
Many design variations of the machines are available for stirring and blending of sludge as pre-treatment to subsequent processing.
These can be provided with similar bridge structures and drives as rotary or fixed scraper units. However they are built more robustly to withstand the high loads created by the thickening and consolidation of the sludge. Machines are available for intermittent or continuous operation and can also be specially designed with additional ancillary equipment to suit individual requirements.
Normal application is when the sludge has high concentrations of solids. The bridge structure is supported by the tank walls and the drive operates from the centre of the tank, mounted on the bridge. The scrapers for this type of application are normally set in echelon formation to induce positive movement of the thickened sludge to the centre of the tank.
The bridge construction and drive are of similar construction to the half bridge scrapers. There is no diffuser drum or outlet weir. Influent enters directly from the side and is withdrawn as thickened sludge from the central collection hopper.
Scraper blades arranged in echelon formation are rigidly held by a structure attached to depending arms mounted from the bridge. Vertical mild-steel stirring tines are carried on the depending arms or booms and rotate with the bridge. Alternative designs employing mesh paddles, fixed rods, pump stirrers or diffused air blowers are also available.
There are a number of ways for supporting bridge scrapers at the tank centre.
For rotating bridge applications, a trunnion-mounted pivot bearing is used, which is usually mounted onto a fabricated steel tripod. The central feed pipe should terminate with a bellmouth inside the diffuser drum.
For secondary applications - free of screenings - the trunnion-mounted pivot bearing can be accommodated on the central feed pipe. In this arrangement the bottom of the feed pipe would be provided with additional supports for fixing onto the tank floor or rolled steel channels spanning the sludge collection hopper.
For fixed bridge applications, full diameter bridges support the drive unit and combined bearing assembly on the bridge with a radial bush bearing assembly mounted over the sludge hopper in which the centre drive shaft depends. With fixed half bridge units a rotating scraper boom support cage is mounted from a weatherproof cross roll bearing or ball bearing assembly which in turn is mounted on the centre feed/support column. The bearing attached to the cage is equipped with a spur gear meshing with the spur gear pinion on the output shaft of the drive unit. On extra deep tanks, guide pads are incorporated at the bottom of the support cage to ensure concentricity of rotation.
For rotating bridge applications, the electricity supply cable can be passed through a PVC conduit inside the feed pipe, or grouted into a chase along the tank floor, then alongside the vertical feed pipe, emerging in a centre pick-up unit mounted on the centre bearing support. When preferred, the cable can be arranged to run overhead, supported by catenary wire to the centre electrical pick-up unit. The pick-up unit is ready- wired to the motor and starter before delivery.
The drive arrangement, comprising a high efficiency motor, double reduction helical gear units, designed for 100,000 hours life and a torque limiter, is mounted on the end-carriage of the bridge. Two polyurethane-tyred wheels support the end-carriage; one of the wheels is driven by a drive arrangement on the leading edge of the end- carriage. On full-bridge machines, polyurethane-tyred wheels on the non- drive ends can take the weight and add balance for smooth running along the coping of the tank wall. The drive and trailing wheels are interchangeable. The pivot bearing on the bridge incorporates bushed trunnions to compensate for any slight rise-and-fall undulations in the tank coping.
A number of blades are arranged in a formation simulating scraping action equal in effect to a continuous helical blade. Hinged at the lowest point of a rigid depending arm or boom suspended from the bridge, each blade is free to hinge and ride at right angles to the tank floor and able to swivel at the pivot point to follow the contours of a tank floor.
These scraper blades are suitable for most types of sludges; the low hinge point and the dual action provide maximum clearing of the tank floor and ensure that there is only minimal wear to the renewable rubber blades.
Quite simply these blades operate sequentially in an echelon formation, and are ideally designed for heavy sludge concentrations.
Various arrangements of surface skimming blades and automatic scum collection mechanisms are available as required.
Problems of clinging sludge and algae growth can be avoided by automatic scraping, brushing or pressure spraying equipment. Cleaning gear can be supplied for outlet channels, weir channels, and tank walls.
A diffusion drum is incorporated to ensure that the influent feed velocity is stilled to such an extent that undue turbulence is reduced to a minimum within the settling tank.
Standard designs can be supplied, constructed in concrete or fabricated in steel, aluminium alloys, or plastic. The diffuser diameter is normally at least 1/6th of the tank diameter.
When a fabricated diffuser drum is supplied, it is normally mounted onto the central feed pipe or tripod. It may also be suspended from the bridge, depending on whether a revolving or fixed diffuser drum is used.
Tuke and Bell reserve the right to modify the design or amend the dimensions in respect of any equipment described on this brochure.
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2000 Tuke and Bell Ltd. All rights reserved. Last Updated : 17 March 2004 |