The Flat Die Pellet Mill from AMANDUS KAHL as an Elementary Component of Chemical Plastics Recycling
Amandus Kahl GmbH & Co. KG from Reinbek, Germany, offers with its pellet mill the opportunity to convert large-volume plastic waste into compact, dosable pellets that can be fed into chemical recycling processes. In this way, the company makes a decisive contribution to a recycling economy in the plastics sector, which conserves fossil resources and has a positive effect in the fight against climate change.
Hardly any other topic has been discussed as much and as intensively in politics and society in recent years as climate change and the accompanying measures needed to curb global warming. Keywords such as "CO2", "greenhouse gases" and "fossil raw materials" come up again and again on this topic. To effectively combat climate change, a variety of measures are needed - both in the private and industrial sectors. The chemical or material recycling of plastics can make an important contribution in this regard, saving the use of crude oil and thus CO2 emissions.
Plastics such as polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET) and many others can be found today in almost every type of packaging, in a wide variety of clothing and even in various medical products. Their good technical properties, such as mouldability, hardness, elasticity, breaking strength, resistance to temperature, thermal deformation and chemicals, make them an ideal raw material for many applications. In 1950, the global production of plastics was only around 1.5 million tons; the threshold of 100 million tons was exceeded only 40 years later. Today, over 360 million tons of plastics are produced annually across the continent.
Crude oil is the most important raw material for almost all types of plastics. As for about 90 % of all chemical products manufactured in Germany, the fossil energy source crude oil is also needed for the production of plastics. For example, a 250 ml shampoo bottle made of PE contains about 1.1 litres of the "black gold", as crude oil or petroleum used to be called. But this designation has long been a thing of the past. It has long been known that the use of crude oil releases greenhouse gases that cause the earth's atmosphere to warm up and accelerate climate change.
A large part of plastics is often used only briefly and once. Examples are tubes and cannulas in medical technology, packaging for food or components of hygiene and care products. After their brief use, the various plastics are thrown into the rubbish and, in the worst case, end up in nature, where they often cause serious environmental damage - in addition to the CO2 emissions during production. But even with the current "recycling methods", plastic waste harms the environment. In the past, and still today, the majority of plastics are either thermally utilised in the form of substitute fuels - i.e. burnt to obtain energy from them - or used in landfill or stockpiled. Large amounts of CO2 are released during combustion and microplastics are released into the environment through land filling.
Rethinking Plastics Recycling
In recent years, however, there has been more and more rethinking in the field of plastics recycling. Plastic waste is no longer seen as just rubbish, but as a raw material. Instead of continuing to recycle plastic waste in environmentally harmful ways - which is more like "down-cycling" - the trend is now to recycle at least some of the plastics chemically or materially. Although the production of new plastics is still cheaper in some cases than recycling them completely, there is a clear upswing in the field of chemical plastics recycling. The reasons for this are, on the one hand, the rising oil prices, which have a direct influence on the manufacturing costs of plastics. On the other hand, the EU Commission under Ursula van der Leyen raised the legal quotas for chemical plastics recycling as part of the European Green Deal of 11 December 2019. Thus, the member states are obliged to chemically recycle one third of the plastic waste generated by 2030.
The chemical recycling of plastics takes place in several steps. First, the plastic waste is cleaned, pre-sorted and freed from foreign objects such as metals, stones and rubber components. Afterwards, the plastic parts, some of which are up to several square metres in size, are crushed to make them easier to handle. Due to the extremely low bulk density - in some cases only 10 kg/m³ - enormous volumes still result despite pre-crushing. With the AMANDUS KAHL flat die pellet mill, the pre-crushed plastics are processed into compact pellets that can be dosed. This reduces freight costs and facilitates handling. Above all, pelleting provides a basic material with which the actual chemical recycling process can be continuously and uniformly fed. After pelleting, the plastic is melted and homogenised by means of an extrusion process. The polymer chains are then broken down into the individual monomers in a thermochemical process. The monomers are subsequently separated from each other by type, stored and can then be marketed as "virgin material" for the manufacturing process of new plastics. In summary, the basic polymer structure of plastics is broken down into its monomeric building blocks during chemical recycling in order to be able to produce new plastics from them. This process allows the plastics to be fully recycled, creating a sustainable circular economy.
Pelleting with KAHL Flat Die Pellet Mill as an Important Process Step
The chemical recycling process consists of many individual process steps that must be precisely coordinated. In order to make the entire process as efficient and economical as possible, conditioning of the plastic waste is of particular importance. The flat die pellet mill from AMANDUS KAHL is an elementary component here. Due to the low bulk density of the plastic waste and the large quantities produced, there are enormous volumes to be processed. Pelleting allows the downstream processes, especially extrusion, to be fed continuously and uniformly. Even the throughput of these process steps can be significantly increased by the increase in bulk density resulting from pelleting. This is an important factor in ensuring economic efficiency of the chemical recycling process.
The product is fed into the pellet mill in free fall without any forced feeding or deflection, thus providing trouble-free product supply. This applies particularly to voluminous and inhomogeneous products. The dies of the AMANDUS KAHL flat die pellet mills have a diameter of up to 1500 mm. The diameter of the die perforation and the resulting diameter of the pellets can vary between 4 and 20 mm, depending on the requirements of the downstream processes. The large pelleting chamber of the flat die pellet mill ensures optimum feeding of the product to the rotating pan grinder rollers. Each pellet mill is equipped with an individual product dosing control system so that the optimum quantity of product is always fed into the machine. Due to the low speed of the pellet mill and the resulting low circumferential speed of the pan grinder rollers, the product can be optimally de-aerated during the pelleting process and pressed into the holes of the die. This also significantly increases the service life of the bearings, and the smooth, low-vibration pellet mill operation significantly reduces the noise emission of the pellet mill. The hydraulic system of the pellet mill with automatic roller gap monitoring and adjustment ensures optimum process control and product quality by automatically adapting the process pressure and the thickness of the product layer on the die to possible product fluctuations during operation. Intelligent lubrication of the roller bearings during operation contributes to a significant reduction in machine maintenance and an increase in machine availability. The robust design makes the pellet mills insensitive to the influence of impurities that can often be contained in inhomogeneous waste fractions. The simple machine construction and the good accessibility of the pelleting tools allow a quick change of pan grinder rollers and dies, which also benefits the availability of the plant. Pelleting with the AMANDUS KAHL flat die pellet mill can increase the bulk density of plastic fractions by up to 30 times, depending on the input product.
Many Years of Experience and the Combination with KAHL Belt Drying Units Ensure Stable, Safe and Energy-Efficient Pelleting
Plastic waste fractions from both the industrial and municipal sectors are among the most difficult materials to process. Particularly in the case of fractions from municipal waste, composition, size or initial moisture content change seasonally and regionally. Through years of experience, AMANDUS KAHL is up to the task and can deal with various requirements. Since the early 1980s, AMANDUS KAHL has been supplying flat die pellet mills for the processing of pre-sorted and pre-conditioned waste fractions with the aim of converting these wastes into different customer-specific qualities for downstream process steps.
Special attention must be paid to moisture when processing plastic waste. An excessively high and, above all, fluctuating moisture content leads to an unstable process and is particularly problematic for subsequent extrusion. By pre-drying the input product with a belt drier from AMANDUS KAHL, the moisture can be reduced and homogenised. The input product is uniformly distributed onto a belt that conveys the product through the drier at a controllable speed. Preheated air flows through the product. Thanks to the modular design, the drier can be executed precisely for the desired throughput and drying capacity and can be easily expanded if required.
The waste heat from the thermochemical reactor, which breaks down the polymer chains into their monomeric building blocks, can be used to pre-condition the drying air. Consequently, drying does not require any additional energy, which makes the entire recycling process much more efficient.
Close Cooperation with KraussMaffei Ensures a Holistic Solution for Pre-conditioning the Plastic Waste
In order to be able to offer the customer a holistic solution for preconditioning the waste fractions from the pre-sorting and cleaning of the plastics onwards, AMANDUS KAHL works together with the extrusion division of KraussMaffei in Hanover. Close cooperation means that both process steps, pelleting by AMANDUS KAHL and extrusion by KraussMaffei, are precisely coordinated. The increase in bulk density simplifies the handling of the plastics and increases the throughput rate as well as the process reliability in the extruder.
KraussMaffei is currently building the world's largest and most modern technology centre for plastics extrusion at its new plant in Hanover-Laatzen. AMANDUS KAHL provides a pellet mill for this purpose in order to test and further develop the combination of pellet mill and extruder and to be able to demonstrate it to the customer.
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