STF Maschinen und Anlagenbau GmbH
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LDPE/HDPE - recycling plants

Material feeding

The foil bales are put onto a lifting platform which lifts them to the sorting belt. The sorting personnel can then drag the foils onto the sorting belt and sort out foreign materials. The sorting belt is mounted onto a stage frame and is designed for four manual sorting places. The detection coil built into the belt identifies metals and stops the belt. The sorting personnel can remove the metals and can then restart the belt. The material then falls on an elevating belt and is transported to the feeding funnel of the cutting mill.


  Cutting and pre-cleaning

The cutting mill is designed as a wet-shredding mill and possesses the necessary connection points for the circulating water.

Two hose lines lead in water at the funnel area which produces cleaning effects and keeps temperature low during the cutting process.

The cutting rotor has a 40 mm punched sieve at the lower area.

Through the sieve punching, the cut foils get into a collection funnel. It is continuously filled with circulating water, through which the small parts get washed into the following friction cleaner.

In the friction cleaner unit, the washing water including removed dirt is separated from the material and pumped to the fibre separator of the respective circulatory container. The material is blown to the washing stage.

  Washing stage

The material is introduced via cyclone, which separates the cut LDPE parts from the material stream and transports them into the turbo washer. Inside the turbo washer, the material is intensively washed by the high turbulences produced by a stirrer. The mixture consisting of water and LDPE is pumped into the following friction cleaner, where the washing water including dirt is separated. The dried foil is then transported into a second turbo washer, which uses the same principle as the first one. Another pump brings the material to the first friction cleaner of the separating stage.

  Separating stage

A friction cleaner removes the dirty water and introduces the material into the stirring container of the separating stage.

The plastics are blended into the water, which serves as a separating medium, with the help of a stirring mechanism. The homogenous mixture is then pumped into a separation container entirely filled with water, where due to a laminar flow the material is separated into a stream that sinks to the bottom and one that moves to the top of the flow. The principle behind this separation is the different density of the plastic materials and water. Since LDPE has a lower density than water, it moves to the top and gets into a two-stage friction cleaner through a pipe. Foreign materials with a density higher than water sink to the bottom and are pumped into the collection container of the two-stage friction cleaner. Inside, the foil is dried and then blown to the silo. The separation of the LDPE from the air stream is done through a cyclone.

The friction cleaner separates the material from the water. The washing water containing the removed dirt is pumped to the fibre separator of the respective circulatory container.

  Drying

The drainage press reduces the water content of the foil from 40% to less than 10%.

The material that comes from the push floor silo is transported to the drainage press with the help of a blower. The dried material is then blown to the next station.

  Decanter with water collecting tray (Optional)

The circulatory pumps bring the cleaned water from the circulatory containers to the corresponding plant component (see layout).

The dirty water that has been removed by the friction cleaners is pumped to the corresponding fibre separator, which removes foreign materials (fibres, fluffs, dirt etc.). It then flows into the corresponding circulatory container. The removed dirt falls into a collecting screw and is brought to a waste press which dries the materials.

With the help of a controlled gate operation and a rotary pump, a defined amount of water that contains sediments (approx. 1.5 - 2.5 m³/h) is extracted from the underflows of the storage containers. It is then treated in a decanter that is available optionally or in a water treatment system. According to the quality reached after the treatment, the water can be piped back into the plant. In order to obtain an optimal quality of the end product, a feeding with fresh water (2-3 m³/h) is explicitly recommended.

  Dosing station

The dosing station consists of several dosing pumps (membrane pumps) which feed the chemicals that are necessary for the washing process into the plant.

  Electrical installations

The plant control is installed in the main control box, including all important gauges (power consumption, flow-through, temperatures etc.) and warning indicators. For repair or manual mode, all plant components can be controlled separately via the control software.