PHOTO: Herbold film washing line
HERBOLD Meckesheim GmbH in cooperation with Erema has designed a model plant for the production of film made from post-consumer waste for Poligroup in Bulgaria. The plant has been in operation since September 2013. High quality film is produced there, with thicknesses down to 30my made from plastic waste only.
The plastic waste is a mix of LDPE agricultural silage film waste, LLDPE film agricultural wrapping bale waste, and film from household waste.
Why this film mix? The principal material is agricultural LDPE that, to a large extent, forms a homogeneous material with an unchanging melt flow index (MFI). The LLDPE improves the physical properties of the film produced and films from household waste are well-priced.
Agricultural film is highly contaminated with up to 50% of the film, which means that as much contamination enters the film washing line as film. The main contaminants in agricultural film are sand and pebbles, as well as small screws. To separate this type of contamination from the film, Poligroup have installed a pre-washing unit, downstream from the main washing line.
Separation by hydro-cyclone
Film from household waste is a different issue as it is a mix of several different plastics. The real challenge here is the separation of unwanted plastics. To achieve this task Herbold is the only operator in the field of wet film recycling who opts for separation by means of a hydro-cyclone separation step. Plastics that are heavier than water will be separated from plastics that are lighter than water. This process ensures that heavier plastic components can be separated from the polyolefin.
A further advantage of hydro-cyclone separation is the high amount of water present in the water circuit, ensuring an excellent washing result. Deposits of organic substances, a frequent feature of film from household waste, are easily removed by washing. In contrast, films from supermarkets often have a high percentage of paper in the form of labels. It is a challenge to separate this paper from the film since the LLDPE films from supermarkets are ideal as a feeding material for recyclate used for the production of new film.
Quality of the end product depends on the washing process
The most important question is the one concerning the required quality of the end product. Economically speaking, only certain waste can be used for recycling. Operators increasingly turn to materials that are available on the market at a reasonable price. That is one of the reasons why plant manufacturers and operators should work hand in hand. The more precise the specification of the input material is, the more cost-efficient the design of the plant can be since unnecessary process steps or room for misinterpretation can be avoided. The operator of a washing plant will also have to find a solution for the collection of film waste.
The washing line at the Poligroup site transforms agricultural films and films from supermarkets into recycled material that is used to produce bin liners, protective sheeting and construction foils. No virgin plastic is used and the products are made of 100% recycled plastic material.
Economic operation of a washing plant
Many basic conditions for the economic operation of a washing plant for plastics waste are set by the market, such as the costs for the procurement and the transport of the input material, or the prices that can be charged for the finished product. With an optimal machine configuration, the operator will be able to process poor quality input material and obtain a high-quality end product. It is also extremely important to have well-trained personnel for the operation of the plant.
The overall cost effectiveness of a washing line for the recycling of film is determined by the recycling costs. The greatest cost is the energy cost. An economic, efficient plant design can reduce its energy costs.
The power demand of the film recycling plant installed for Poligroup is 0.8 to 1.0 MW per ton produced of end product which corresponds to 0.8 to 1.0 kW per kilo of end product. The system uses as little as 1 to 2m³ of fresh water per ton of input material.
The plant can cope with highly contaminated film as well as with extremely thin-walled film. The prewashing unit and hydro-cyclone separation step that are part of the washing line are the outstanding construction features of the plant.
The plant provides washed homogeneous high-quality film flakes that are ideal for further treatment in an Erema extrusion system.
With Poligroup, downstream of the Herbold washing line, the washed and recycled film flakes are then treated with the reliable plastics recycling technology from Erema. The Poligroup plant system consists of an Erema TVEplus® (throughput: 1,100 – 1,200 kg/h) with laser filter LF2/350 (fineness of filtration: 110 µm and the die-face granulating system HG 244.
The extrusion system with the patented TVEplus technology has been optimized for the treatment of materials that are difficult to process, such as washed mixed post-consumer film waste with a high percentage of residual humidity of 8 to 12% and a high degree of contamination. Poligroup GmbH is thus able to recycle the PE washed film flakes (from LLDPE stretch agricultural film and LDPE industrial waste) into high-quality granulates.
At the core of the plant on the multifunctional cutter compactor with patented air flush module, the material, still containing a small amount of residual humidity and contaminants, is optimally recycled. Cutting, homogenizing, heating, degassing, densifying, buffering and dosing – everything in one single step.
Melt filtration BEFORE degasification
The well-proven principle of the whole TVEplus system is the arrangement of the melt filtration BEFORE the degasification of the extruder with two important advantages: one is that the minimal shearing impact during the melting process prevents a further size reduction of the contaminants before the filtration and thus increases the efficiency of the filtering process. Another advantage is the fact that contaminants due to their early removal from the recycling system cannot prematurely outgas and thus additionally reduce the accumulation of odours to a minimum in the produced regranulate.
The optimized threefold degassing process of the TVEplus plant additionally ensures an efficient degasification of the filtered fusion.
A close cooperation of the two companies ensures the information exchange between plant operator and plant supplier, crucial for the further development of plant technology and paves the way for the successful conclusion of future joint projects.
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www.herbold.com