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Rectangular clarifiers
Sono dispositivi utilizzati nel trattamento delle acque reflue e industriali per rimuovere i solidi sospesi e altre particelle dal liquido.
Application
Municipal water and wastewater sedimentation
Industrial water and wastewater sedimentation
Steel rolling mill cooling water recycling
Scraping or suction type rectangular clarifiers
Models
EM50BB1
Hydraulic or mechanical scraping blade lifting clarifier
EM50 – SCRAPER WITH TRAVELLING BRIDGE FOR RECTANGULAR TANK
| Application | Clarifying of primary and secondary waste water |
| Tipi di macchine | Concrete runways Rails |
| Characteristics | The equipment consists of a rotating bridge with bottom and surface scrapers. |
| Operation | The waste water is clarified in a rectangular tank, the sedimentable solids settle on the tank bottom and are conveyed to a hopper by the bottom scrapers, while the floating material is conveyed into an oil removal pipe. |
| Materials | Hot dip galvanized carbon steel or Stainless steel |
| Installation | In a concrete tank |
| Tank diametre | From 4 to 25 m. |
| Tank length | From 2 to 100 m. |
| Optionals | Scum removal system |
PRINCIPLES OF SIZING
Hydraulic sizing (process) The sizing of the feeding zone is based on the following parametres: • influent flow rate • dimensions of the pipings The water flowing to the sedimentation zone must have a very low kinetic energy in order to guarantee a good separation and settling of the solids.
Mechanical Sizing The sizing of the bottom scraper is based on the type of sludge to be evacuated from the tank bottom. Normally the trolleys and the scrapers are designed to bear a stress of 20 Kg. per linear metre.
Checks The following checks regarding the movement of the machine components are very important for this kind of machine: • bridge: forward-backward movement • bottom scraper: lifting-lowering • surface scraper: lifting-lowering • electrical supply Our travelling bridges are always equipped with two limit switches for each movement (1 for operation and 1 for emergency) Buffer groups are also installed to limit the run of the moving units in case of failure the electrical limit switches and they are sized to bear the maximum stress.
Motorization We use a double motorization for bridges exceeding 6 m. of width and moving over a runway of more than 12 m. This solution allows to achieve a good alignment of the bridge, even if the two motorized wheels diametres are not exactly equal. In this case, a simple motorization through a central shaft may cause the side-slip of one of the two motorized wheels.
Characteristics Both the motorized hweels and the idle wheels must be perfectly parallel and at the same distance; for this purpose, after the installation of the bridge, the diagonals between the wheels must be carefully measured.
Contrast wheels and buffers The contrast wheels and the buffers must be designed and sized so that the bridge cannot skid laterally out of the runways, under no circumstances.
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EM50BB1 C04832
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EM50BB1 VYKSA-C05025-(2)
EM51
Suction system with air-lift or pump or siphon clarifier
EM51 – SUCTION TYPE SCRAPER WITH TRAVELLING BRIDGE FOR RECTANGULAR TANK
| Application | Clarifying of secondary waste water. |
| Type of sludge suction | Siphon Submersible pump Vertical pump Air lift |
| Characteristics | The equipment consists of a travelling bridge with bottom suction pipes and surface scrapers |
| Operation | The water is treated in a rectangular tank, the sedimentable solids settle on the tank bottom, are sucked by the suction pipes and conveyed to a channel while the floating material in conveyed into an oil removal pipe. |
| Materials | Hot dip galvanized carbon steel or Stainless steel |
| Installation | In a concrete tank |
| Tank diametre | From 4 to 25 m. |
| Tank length | From 20 to 100 m. |
| Optionals | Scum removal system |
PRINCIPLES OF SIZING
Sludge suction unit sizing For the project of the sludge suction unit we have to make sure that the sludge is quickly removed from the tank bottom because if it tends to settle or get too thick for staying in the tank for a too long time, it may happen that: • a part of the recycled sludge returns to the oxidation tank when it is no more fresh and this will affect the treatment efficiency • a shortage of dissolved oxygen may cause a leakage of sludge in the effluent
Mechanical Sizing Same principles as described for the Scraper with travelling bridge for rectangular tank mod. EM50.
OPERATION DESCRIPTION
The bottom of the suction scraper bridge tank is flat and the suction pipes, sized according to sludge recycle flow rate, are placed at a distance which does not exceed 3 m. The sludge is conveyed towards the suction pipe by V-shaped scrapers which make the flowing of the sludge towards the piping much easier. Each suction pipe is equipped with a telescopic valve to regulate the flow into the hopper. The quality and quantity of sludge sucked by each pipe can be checked from the bridge. The sludge flows into the hopper according to the principle of the communicating vessels. The sludge flow rate depends on the difference of level between the water surface and the sludge level in the hopper. The sludge sucked by all of the suction pipes is conveyed out of the tank by means of a self-regulating siphon. The triggering of the siphon can be made during the commissioning phase by means of a pump or ejector.
TECHNICAL AND DIMENSIONAL DATA NECESSARY TO MAKE A TECHNICAL PROPOSAL AND QUOTATION
| 1.1 | Flow rate to the sedimentation tank (total) | : m3/h |
| 1.2 | Flow rate coming from the sedimentation tank (at the overflow weir) | : m3/h |
| 1.3 | Flow rate of sludge coming from the sedimentation tank | : m3/h |
| 1.4 | Tank width | : m. |
| 1.5 | Tank length | : m. |
| 1.6 | Sludge level in the drain well | : +m. |
| 1.7 | Water level in the sedimentation tank | : +m. |
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EM51 BERNARDINELLO-C04996-2
Dredging chains clarifiers
Models
EM53
Bottom and or surface scraping clarifier
EM53 – SCRAPER WITH DREDGING CHAIN FOR RECTANGULAR TANK
| Application | Clarifying of primary and secondary waste water |
| Characteristics | The equipment consists of a dredging chain with bottom and surface scrapers. |
| Operation | The waste water is clarified in a rectangular tank, the sedimentable solids settle on the tank bottom and are conveyed to a hopper by the bottom scrapers, while the floating material is conveyed into an oil removal pipe. |
| Materials | Hot dip galvanized carbon steel or Stainless steel |
| Installation | In a concrete tank |
| Tank diametre | From 2 to 16 m. |
| Tank length | From 20 to 100 m. |
| Optionals | Scum removal system |
PRINCIPLES OF SIZING
Hydraulic sizing (process) The sizing of the feeding zone is based on the following parametres: • influent flow rate • dimensions of the pipings The water flowing to the sedimentation zone must have a very low kinetic energy in order to guarantee a good separation and settling of the solids.
Mechanical Sizing The sizing of the scrapers is based on the type of sludge to be evacuated from the tank bottom. Normally the scrapers, shafts and chains are designed to bear a stress of 20 Kg. per linear metre.
Torque limiting device (dynamometric cell) The dynamometric cell measures the torque transmitted by the drive unit. This value is evident directly on the instrument and allows to evaluate the stresses on the moving members during the rotation. The device is equipped with limit switches set at two different torque values, one for alarm and one for the machine shutdown.
Checks The movement of the chains must be carefully checked because it is very important for this type of machine. For this purpose, we use to apply some sensors to check the idle shafts rotation.
Accessories
Oil and grease collecting system with scraping blade
Oil collecting system with manual or automatic rotating pipe
Telescopic valve
Electronic alignment system
Ice protection on running path
Slipping alarm
OUTLINES OF THE SEDIMENTATION PROCESS
A good efficiency of the sedimentation process gives as a result a considerable reduction of BOD, COD, heavy metals, azote, phosphorus, etc. in the treated water. As the suspended substances in the waste water become larger, their sedimentation becomes easier.
Stokes’ law emphasizes the importance of the floc size for the speed of sedimentation.
V = speed of sedimentation in m/s ρ = density of solids in kg/m³ ρ0 = densità dell’acqua kg/m³ g = 9,81 m/s2 μ = viscosity of water in in Pa x s (at 15° C the viscosity of water is 1,06 x 10-3 Pa x s) D = diametre of the particle in m.
A good way to obtain large flocs in the clarifier feeding is the installation of baffles using the kinetic energy of water to agglomerate the flocs to each other
In the secondary clarifiers, the type of scraping blades and the sizing of the central drain well are very important.
Actually, given the enormous volume of “sludge” compared to the feed flow rate (50%), we can hypothize that the sludge characteristics are just a little different from the ones of the clarified water (under static conditions the clarified water and the sludge stratify with a horizontal separation surface) and that, consequently, due to the slight bottom slope (∼ 4%), it flows naturally towards the central well. However, we should not forget that the particles which touch the bottom, and the ones which stratify, adhere and loose the properties of “fluid”: so they must be actively moved and “pushed” towards the drain well before the layer becomes too thick and, above all, before the anoxic condition causes a strong de-nitrification with the production of floating plates. Therefore all of the sedimented sludge particles conveyed by the bottom scrapers to the central well from the tank periphery, must reach it quickly. This is achieved by giving a continuous profile with logarythmic shape to the blade; the relevant equation in polar coordinates is:
r=r0·emα
where r and α are the polar coordinates having the tank centre as a pole and ro is the radius of the drain well. Under these conditions, the scraper moves the sludge, makes it more “fluid” (by eliminating the adhesion) and conveys it by a perpendicular force to its surface (Pascal); this force has a radial centripetal component, not null and constant. The angle γ is determined by:
r=r0·emα
dove r e α sono le coordinate polari aventi per polo il centro della vasca ed ro è il raggio del pozzetto. In queste condizioni la pala smuove il fango ridandogli la caratteristica di “fluido” (annullando l’adesione) e lo spinge con una forza perpendicolare alla sua superficie (Pascal) che ha una componente radiale centripeta non nulla e costante. L’angolo γ è definito dalla:
