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IED Industrieanlagen und Engineering GmbH in Frechen, Germany
Our Scraper Systems
Scraper systems may differ depending on the customer’s requirements. They can be intended for round or rectangular basins. Or they can be created for bottom sludge or top scum scraping or for both of these tasks.
For rectangular basins, we prefer to use chain scraper systems. They run continuously and can treat both bottom sludge and top scum at the same time. Our chain scrapers consist of endless plastic chain conveyors running in parallel with the two longitudinal sides of the basin. To these chains, scraper beams are attached. These beams move the bottom sludge and top scums.
For circular basins, either movable rotary bridge scrapers or centrally driven rakes are used. The rotary bridge of the scraper is mounted on the centre support (pivot bearing). Depending on the basin diameter and sludge volume, either continuous full-size bridge scrapers (with two arms) or half-bridge scrapers are used. The bottom sludge is removed into a sludge hopper centrally. In some cases, suction scraper bridges are used, which continuously remove bottom sludge along the entire radius of the tank or basin.
In the case of rectangular tanks, longitudinal bridge scrapers (scraper trolleys) run back and forth and carry the bottom sludge into the hopper installed below the inlet opening. The top scum is carried into a scum trough via a slope. In this context, we call it a discontinuous scraping process, since the scraper only scrapes in a single direction (either back or forth). Discontinuous procedure is almost exclusively used in grit chambers or preliminary setting basins. Continuous sludge scraping is only done by the chain scrapers. Since no scraping trolley runs over the basin top, it is easy to attach a basin cover in this case. The basin covers are especially necessary for preliminary setting basins in the vicinity of residential buildings.
Central driven scrapers are mostly used as sludge thickening rakes or in the cases if the basin must be covered.
Chain Scrapers
Our DEWA® plastic chain scraper system is ideally suitable for continuous scraping of bottom sludge and top scum in rectangular sedimentation basins - both in municipal and industrial companies. Since the DEWA® system has both the ATEX and KTW approval (for plastics contacting drinking water), this system was implemented many times both in ATEX (API scrapers) and water treatment applications.
System design and thoroughly selected materials for the scraper individual components are important advantages of the DEWA® plastic chain scrapers. Load-bearing parts, e.g. shafts and guide rails, are made of stainless steel A2 or A4. Moving parts are manufactured from lightweight or glass-fibre reinforced plastics. This results in high stability, extreme durability, very low wear and tear and minimum maintenance and energy costs.
The DEWA® plastic chain scraper is used as a fat remover (skimmer) or as a pure bottom sludge scraper in grit chambers, as a bottom sludge and top scum scraper in preliminary and final setting basins and as a scum scraper in flotation plants. In waterworks for surface water treatment it is often used as a bottom sludge scraper under a lamella clarifier.
With our DEWA® chain scraper system, you can equip basins of widths from 0.6 to 12 m and lengths of up to 100 m. We are also going to offer equipment for basins of more than 12 m width. A very important factor for a smooth and low-maintenance operation over a long period of time is perfect planning and fault-free assembly of the system. Our best warranty for this is our experienced team of assembly experts and almost 500 successfully installed systems.
Longitudinal Scrapers
In rectangular tanks and basins, bridge scrapers are also used as longitudinal scrapers. In preliminary setting basins they are mostly used as blade sludge scrapers and in final setting basins as suction scrapers.
The sludge scrapers ensure that both the entire bottom sludge is moved from the basin into the provided sludge hopper and top scum is moved into the scum gutters provided for it. Prior to starting the bridge scrapers, the scraper blades are lowered to the bottom or into the water surface. In this context, we call it a discontinuous scraping process, since the scraper only scrapes in a single direction (either back or forth), unlike DEWA® chain scrapers that continuously remove bottom sludge and top scum.
Another method of a continuous sludge removal can be implemented with the aid of so-called suction scrapers. We offer them both as longitudinal and rotary scrapers. In this case, the function principle differs from the blade scrapers. Instead of the movable scraping blades, there are fixed guiding blades on the bottom that convey the sludge to several vertical suction pipes. These suction pipes lead up in a channel. The water level of this channel is below the water level of the basin.
So a suction process is established automatically: the bottom sludge is moved into the gutter. From the gutter, the sludge moves into a trough running near the basin according to the siphoning principle.
The major advantage of both scrapers is that all their driving components are above the water level. This facilitates maintenance. Spare parts can be easily replaced.
Both scraper types are offered either as scrapers without rails and driven by rubber wheels or as scrapers with rails and gear rack.
We recommend to use stainless steel 1.4301 (AISI 304) for components above the water level and 1.4571 (AISI 316TI) for components under the water surface.
Grit and Fat Collecting Scrapers
To discharge the sedimentary sand from a basin (grit chamber), you can use both scraper bridges with blades and suction scrapers with compressed air lifters or submersible pumps.
In the grit chamber the waste water should be made free both from grit particles (as the grit is abrasive and will disturb in further wastewater cleaning processes) and from fats and oil floating in the respective chamber.
The functional and well proved grit chamber blade scraper pushes the grit sedimenting at the bottom to the pump sump. In the sump the grit is removed by means of grit transfer pumps.
The suction scrapers continuously discharge the sedimenting grit from the bottom trough of the basin. This type of grit scrapers easily copes even with large grit quantities. The grit is released into a grit classifier or grit washer via a channel.
Both scraper types are offered either as scrapers without rails and equipped with driving and guiding wheels with rubber tyres or as bridge scrapers with forced drives, guiding rails and gear racks. We recommend to use stainless steel 1.4301 (AISI 304) for components above the water level and 1.4571 (AISI 316TI) for components under the water surface.
Our product range of grit and fat trapping includes:
- Grit-chamber bridge scrapers
- Grit-chamber chain scrapers
- Skimmers and fat trap scrapers
- Grit classifiers
- Grit washers
- Control systems
Rotary Scrapers
Rotary scrapers are used in round horizontal-flow sedimentation basins, mainly in preliminary and final setting basins.
Rotary bridge scrapers are used as blade scrapers for mechanic removal of bottom sludge and top scum in sewage tanks in non-stop operation. The walkway is equipped with safety grating according to the Regulations for Preventing of Accidents (UVV). The scum removing can be done in different ways. For example, scraping by means of a skim channel and paddle mechanism. But it can also be a blade scraper at which a floating matter scum box equipped with a ramp is installed at the outer edge of the rotary basin.
The complete electrical equipment and the control system is installed in a control cabinet. The scraper can run either at the automatic or manual mode.
Special Designs
Our scrapers can also be equipped with special units according to the customer’s individual requirements. Some examples of them are the following:
* • Scraper blades that can be lifted out
* • Suction scrapers
* • Trough or channel cleaners
* • Travel path cleaning and /or defrosting
* • Special versions of control cabinets
* • Special selection of materials
* • Basin internal fittings
Furthermore, additional basin fittings can be installed, for example:
* • Stirring ring
* • Clear water drainage channels, weirs, scum baffles
* • Special inlet flow fixtures, such as lamellas, baffles, etc.
Selection of Materials
We recommend to use stainless steel 1.4301 (AISI 304) for components above the water level and 1.4571 (AISI 316TI) for components under the water surface.
Rakes
Centrally driven scrapers (also called rakes) are used in municipal and industrial wastewater treatment plants for the static sludge thickening.
The bottom blades are arranged like sun blinds. They hang on two raking arms, which hang on a driven central shaft. So the bottom blades move the thickened sludge into a draw-off hopper in the middle.
You can optionally purchase additional build-in components, e.g. infeed cylinder, scum removal system and sludge liquor discharge unit. Materials are selected upon the customer’s request.
