MAS updates its DRD 'waterless' cleaning system for plastic

In the background are two DRD-26 certrifuge chambers in combination with the electrical and control cabinets, while a buffer tank for material feeding stands in the foreground.

The Austrian plastics machinery manufacturer MAS Maschinen-und Anlagenbau Schulz GmbH has upgraded its DRD (Double Rotor Disc) “waterless” drying and cleaning systems for plastic film, flakes and fibers. These improvements offer significantly higher throughput rates without affecting the systems’ low energy consumption rates, according to Pineville, North Carolina-based eFactor3 LLC, the North American distributor for the company.

The standard DRD single-stage system can be used as a dryer for already washed film scrap, as well as to clean contaminated dry scrap. The two-stage DRD-DS systems are designed to handle the combined cleaning and drying of wet and dirty scrap in two steps for superior contamination removal, e-Factor3 says. The single and double DRD systems are designed to handle the most difficult scrap, including agricultural films, flakes and fibers, the company adds.

MAS Maschinen-und Anlagenbau Schulz and its affiliated company EKUMA began developing the DRD 10 years ago. It is based on a vacuum cleaner principle and works without water. In a news release, EFactor3 says, “Many customers have been looking for a solution for their costly water treatment and the associated regulatory requirements and have quickly found our DRD to be the solution to that burdensome issue.” The company says the DRD system has lower operating costs than systems that use water in addition to consuming less energy.

The most noticeable change in the next generation of the DRD, according to eFactor3, is the “significant” increase in throughput with only a moderate increase in power consumption. MAS also has improved serviceability by making the screens, rotors and drive elements more accessible.

The DRD is intended to be used to dry plastic scrap after it has been washed or to clean and dry mineral-contaminated plastic scrap, which is found primarily in agricultural products and in some postindustrial and postconsumer products.

The central component of the MAS dry cleaning unit is a double rotor system in a centrifuge housing. The lower rotor sucks the material supplied by a shredder and spreads it uniformly, according to eFactor3. During the cleaning process, larger and heavier impurities, such as metal parts and stones, are separated by gravity and discharged periodically from the bottom of the centrifuge chamber via a pneumatic flap. Simultaneously, the upper rotor creates a vortex of air, forcing the prepurified material into a turbulent cycle. To absorb the moisture during the cleaning process, hot air is generated by a central heater register. The particle separation occurs in the vortex using the friction between the plastic flakes, film or fibers in combination with declining moisture content to assist the liberation of residual dirt particles. These particles are removed by the centrifugal force on the lateral screens by dust collectors. After the purifying process, the plastic flakes are discharged and fed into a material-silo at the plant.

When combined in a recycling process that uses a pelletizing unit, the DRD system can use the waste heat from the pelletizer.

According to eFactor3, the DRD can produce flake with a residual contamination level of less than 0.5 percent and with a residual moisture content of approximately 2 percent.

The process is automated using a PLC (programmable logic controller). Power consumption and residence time of the plastic in the dryer/cleaner can be individually adjusted to the moisture content and the rate of contamination, eFactor3 says.

With the most recent upgrade to the DRD process, the previous DRD systems 18 and 24 containing a centrifugal diameter of 1,800 or 2,400 millimeters (72 or 96 inches) have been replaced by the DRD 21 and 26 with 2,100 and 2,600 millimeter (84 or 104 inch) diameters. By doubling the number of rotor blades, increasing the rotor speeds and drive power, the material throughput per batch could be doubled using almost the same volume of process air, eFactor3 says. In practice, the batch volume can be increased from 12 to 25 kilograms (26 to 55 pounds) for the smaller unit and from 20 to 25 kilograms (44 to 55 pounds) to 40 to 50 kilograms (88 to 110 pounds) with the larger unit. A batch time for "normal" contaminated feedstock with 15 percent moisture content is about 2 minutes, the company says. Accordingly, the hourly output has increased from 750 to 900 kilograms (1,650 to 1,980 pounds) to 1,200 to 1,500 kilograms (2,640 to 3,300 pounds).

Material that has more than 25 percent moisture may need a predewatering process in a centrifuge to keep the throughput and operation of the DRD more economical, the company adds.

The MAS dry cleaning plants are available as a two-stage stand-alone system, as well as a single-stage-system in combination with a “wet system.” When used prior to a wet cleaning process, heavily soiled sheets can be cleaned more efficiently, since most of the solids can be separated beforehand, avoiding overconsumption of process water, eFactor3 says. When applied after wet cleaning of purified material, the DRD can be an efficient dryer and additional cleaner.

DRD cleaning and drying systems are modular and also suitable for combining with recycling systems from other manufacturers as well as those from MAS.

EFactor3 offers a variety of preshredding, shredding and granulating equipment, along with conveying and separation equipment, systems integration and installation.