EIRP sludge scraper for the primary radial-flow sedimentation tank

The EIRP sludge scraper design is shown in Figure 1

Figure 1. General view and basic design of the EIRP sludge scraper

1 - rotating bridge; 2 - drive cart; 3 - swing unit of the bridge and the scraper wing suspension frame; 4 - scraper wings; 5 - peripheral scrapers; 6 - pit scrapers; 7 - scraper wing suspension frame; 8 - submersible skimmer pipe; 9 - semisubmersible skimmer scraper; 10 - directing cylinder; 11 - semisubmersible board; 12 - edge cleaner (option); 13 - central annular power manifold; 14 - EIRP sludge exhauster control cabinet

One of the main elements of the sludge scraper is a rotary bridge, which is a three-dimensional truss. The truss rods have a curved profile shape. Such a constructive solution provided the bridge simultaneously with low sail and high strength.

The standard profile material is a deformable aluminum alloy AMg3M. The truss bridge made of the aluminum deformable alloy AMg3M, which is characterized by high strength and corrosion resistance, is assembled with rivets of 10 mm in diameter made of the same aluminum alloy - this allowed providing such a bridge with high strength with guaranteed corrosion resistance in comparison with the welded aluminum structure, and as a result, an extended service life.

Also, the bridge truss can be made entirely of stainless steel AISI 304 (optionally AISI 316). A stainless steel frame is assembled by welding with the subsequent etching of welded seams, however, this results in a heavier and more expensive bridge.

The flooring of the bridge is slotted, with an anti-slip surface, assembled from original unified elements made of modern polymeric material resistant to ultraviolet radiation and low temperatures. This ensures "dry" surface of the flooring in any weather conditions and improves its maintainability.

The rotating bridge rests with its peripheral part on the drive cart, and with the central part through the hinge on the scraper wing suspension frame, which in turn rests on the reinforced concrete central support of the radial-flow sedimentation tank through the swing device.

The swing device is designed on the basis of a thrust radial bearing of large diameter for hoisting mechanisms and is able to adjust its vertical and horizontal positions. Two scraper wings, rigidly connected to each other, are attached to the suspension frame with guy ropes and rotate together with it. Torque from the drive cart is transmitted to the suspension frame through the guy ropes. In addition, a guide cylinder is attached to the suspension frame on adjustable brackets, which, due to the flow restriction in the radial direction, ensures the subsurface intake of sewage into the sedimentation tank. Scraper wings have scrapers equipped with a rubber skirt for leveling the bottom of the sedimentation tank. When the scraper wings move, the scrapers rake the sludge on the bottom into the pit. To prevent deposition of sediments in the pit and its transportation to the discharge pipeline, a pair of pit scrapers is provided.

The load-bearing structure of the swing device, the scraper wings and all metal elements of the scraper wings are made of AISI 304 stainless steel (optionally AISI 316).

A two-wheel drive cart with direct drive from the gear motor to the rear wheel is shown in Figure 2a. The speed of the gear motor is regulated by a frequency converter. The choice of the rear wheel of the cart as a drive is determined by the vector of loads that arise during the operation of the sludge scraper due to its design features. A snowplow unit is installed on the cart and consists of a snow blower and a rotating brush with a drive and a positioning system, optionally – a snow blower.

The wheels of the cart are equipped with solid tires. The load-bearing structure of the cart is made of stainless steel.

Figure 2. EIRP sludge scraper

a) the outer end of the bridge with the cart; b) UVP skimming unit.

1 - transport cart with snowplow unit; 2 - semisubmersible skimmer scraper; 3 - semi-submersible UPV pipe ski; 4 - semisubmersible pipe; 5 - sliding support; 6 - flexible corrugated hose; 7 - supporting jamb; 8 - floats; 9 - pressure bracket with a roller; 10 - floating substance drain pipeline.

Floating substances are collected from the water surface by means of a skimmer - UPV, which is shown in Figure 2b. The UPV consists of a semisubmersible pipe, a sliding support, a flexible corrugated hose for the removal of collected floating substances and a supporting jamb.   

Such a design of the UPV ensures a uniform and simultaneous collection of floating substances radially through the entire water table of the sedimentation tank.

The operating principle of the UPV is as follows: the semi-submerged scraper suspended on the bridge during the rotation of the latter moves the floating substances to a semi-submerged pipe. The semi-submerged pipe has inlets for flushing the floating substances. In the initial position, the semisubmersible pipe is kept afloat with floats, the flush openings are above the water level in the sedimentation tank. When the bridge passes over the semi-submerged pipe, the skis fixed on the bridge submerse the pipe, so that its flush openings are below the water level and suck in the floating materials collected by the scraper. Further, through a special flexible corrugated hose, the flooded floating substances enter the regular drain pipe for floating substances. After the bridge passes over the semi-submerged pipe, it returns to its initial position. To support the semisubmersible pipe, during emptying the sedimentation tank and regulating its ascent, a supporting jamb with a corresponding adjustment unit is provided. To ensure uniform immersion of the pipe, its outer end is equipped with a sliding support, which limits the movement of the pipe only in the vertical plane. For reliable contact of semisubmersible pipe and skis, brackets with rollers are provided on the pipe.

Rollers and floats are made of polymer materials. The remaining parts and components of the UPV are made of AISI 304 stainless steel (optionally AISI 316).

The control cabinet with IP 66 housing and heating is located on the outer (peripheral) end of the bridge and provides operation of the equipment in automatic and manual mode. Power supply is fed to the equipment through the annular power manifold located on the bridge above the central support.

The sludge scrapers can be equipped with optional equipment:

• a device with rotating brushes for mechanical cleaning of spillways – an edge cleaner;
• an electric heating cable for sidewall flange heating;
• Infrared thermal radiator (installed between a snow blower and a rotating brush).