RotaScreen TrommelsPosted on December 6th, 2016 by vapro
The first Rotascreen Trommel was commissioned in 1975, and since that time a broad range of applications have been satisfied with the best machine features for each purpose. Rotascreens have been used in resource recovery to segregate solid waste in various forms including MSW (garbage), compost, incinerator ash and construction debris, or in mining and aggregate operations for scrubbing rock and sand, polish and remove fines from briquettes such as salt or potash. Roundness and concentricity are the hallmarks of quality in the RotaScreen construction. From ring forged riding rings to alloy steel trunnion wheels, the RotaScreen Trommel is built to last.
Form and Function
The Rotascreen Trommel is, at its simplest, a round rotating drum with holes in it. The screen surface may be either a wire mesh or punched plate; punched plate is used much more commonly. The feed advances through the drum by virtue of both the slope of the drum and the rotation of the drum. The rotation continually turns the material, ensuring that all of the feed is presented to the screen apertures.
The tumbling action of the trommel promotes passage of undersize particles through the screen. Continuously rolling over the material bed, the Rotascreen opens up the mass to constantly expose the undersize materials to the screen surface. The wide-open drum propels the large, bulky oversize materials found in moist waste streams out the oversize discharge.
Engineered without internal impediments, the clean design of the drum interior resists accumulations of sticks, wire, rags, fines or other materials. Screening drum diameters range from 2’ to 12’, and lengths from 4’ to 70’.
Supporting trunnions are basically wheels, machined from hardened steel castings mounted in spherical roller bearings that provide long wear and operation. On larger trommels, the supporting tires are one piece ring forgings machine finished and welded to the end shell of the drum. Thrust loads are carried by a hardened alloy steel thrust wheel, bearing against the vertical face of the discharge end tire.
Laser alignment of the drum during assembly assures good balance from centerline alignment, and concentricity. Drive options include both the direct chain and the trunnion friction drive. Chain drives use a large main sprocket attached to the drum, and a base mounted pinion that is driven through a gearbox by an electric motor. Friction drive trommels power the drum through the support trunnions.
For municipal solid waste recycling, the trommel may be fitted with one or two different sizes of screen aperture for removal of large oversize from fines and midsize. Fitted with bag opening spikes, the trommel opens the bags and screens dirt, rock, glass and other smaller incombustible materials that add to the ash content of the fuel. A second, mid-size fraction may also be screened from the refuse stream to provide a concentration of co-mingled recyclables, including aluminum cans. Fine materials are screened out for landfill or further processing.
Recent applications include:
- Screen 65 TPH of MSW (Opening 15,000 bags per hour)
- Screen up to 100 tph of compost waste through 1 ¼” openings
- Screen mixed msw at 40-50 tons per hour.
- Screen and scrub flash from potassium cyanide (KCN) and sodium cyanide (NaCN) pellets from briquetter at 12,000 pph, max. temp. 250 deg. F. Bulk density 50 PCF.
- Screen and breakup of flaked salt. 75 pcf.
- Screen calcined limestone through 2” round openings, then abrade oversize on 3/8” openings to remove approx. 20 wt. % high sulfur surface layers.
- Process mineral sand ore (post primary screen) at a design rate of 1200 tons/hour with a water slurry flow of 10,180 gallons per minute.
- Trommel rated at 22.0 metric tons of tire fluff & wood chips having a bulk density of 0.15 metric tons/ cubic meter
Tumbling of RotaScreen Trommel – Exterior
Tumbling of RotaScreen Trommel – Interior
Articles / Case Studies
This paper describes the applications of and specifications for trommels as used in various waste processing and resource recovery operations.