The use of PCR bottle flakes in polymer production / polymer condensation

Much has been written about the fast development of the worldwide polyester market, from the build up of huge capacities for virgin PET production to increased use of PCR bottle flakes.

The KREYENBORG Group, with almost 350 employees worldwide, made early recognition of this trend and has set the course to provide innovative and cost saving solutions for the industry. The development and industry-proven successful operation of the KREYENBORG POLY-filters, based on the KREYENBORG piston screen changer technology, the CrystallCut® pelletizing system from sister company BKG (Bruckmann & Kreyenborg Granuliertechnik GmbH), or the continuously advanced IRD Infrared Rotary Drum from KPT (KREYENBORG Plant Technology) for the simultaneous drying and crystallisation of PET in minutes rather than hours, are only a few examples of the leading position the KREYENBORG Group takes on the market.


The challenges of processing PCR bottle flakes - Melt filtration

The ability to process PCR material, especially PET bottle flakes, is now a major focus in our industry. Sustainability through manufacturing, “going green”, by using or recycling existing products, plays an important part, not just monetarily, in the awareness of producers and consumer opinion. For this reason, PET producers and processors are taking a leading role in defining and dictating rates of recycled material, for example in packaging. It is literally a competition of who can deliver the greenest PET bottle, or who has the highest rate of recycled material in their food packaging.

Since the development of the first backflush filter by KREYENBORG in 1988, KREYENBORG has continued to expand its leadership in melt filtration technology through many patent innovations and satisfied customers worldwide. This machine was designed to automatically clean the filter elements during the running production as well as filter out impurities like aluminium, adhesives, extrinsic plastics, etc. One particular innovation, the 4-channel-technology, has revolutionized the market during the last years. The advantages are quite clear: quick return on investment due to moderate purchase costs and very low operating costs, best backflush efficiency, and constant process pressure. Proudly “Made in Germany”, KREYENBORG plans, constructs, and produces its equipment at the headquarters in Münster (NRW). Managing director and owner Jan-Udo Kreyenborg knows that there is no substitute for quality. Sven Conrad, general sales manager, adds, “Saving money on investment can be quite expensive for a company.” What does he mean by that? He explains, “Often customers only see the initial purchase costs, which can lead to an ill-advised decision. There is a bigger picture to consider. What are my operating costs 2, 5, and 10 years down the road?” This is why KREYENBORG not only offers machines but also a broad technical and commercial consultation in order to develop a customized solution together with the client specifically for his/her application.

The processing of PCR bottle flakes garners very high requirements of the equipment with which the flakes are washed, melted and filtered. For many years KREYENBORG has maintained and improved its leading position in the melt filtration (backflush screen changers) of rPET lines for new food packing films, packing straps (a replacement for metal straps), and new bottle resin (so called bottle to bottle recycling). Now KREYENBORG has opened the door to a new area.


First commercial line for r-PET in polymer production

KREYENBORG has delivered and installed the first commercial line in which rPET flakes are fed into the main stream of the virgin material production to a customer in North America.

A direct integration of the PET recycling into the production process takes place giving the producer an enormous cost benefit. Because this is done with a maximum throughput of over 4 ton/hr, it demonstrates clearly that this is no small project, quite the opposite, in fact, an ambitious objective. A key component to this process is the KREYENBORG patented V-type backflush filter who’s cost-to-performance ratio is unmatched in the industry. Besides the common advantages of piston screen changers, the V-type backflush screen changer offers the best backflush efficiency on the market (lowest backflush losses) and a fully automated backflush which is carried out independent of the operating melt pressure. Contaminations which are caught in the screens at a particular pressure can be flushed out with the same or even a higher pressure, without having any negative influences on the downstream process thanks to an adjustable hydraulic backflush pressure. The filter operates process, pressure, and volume flow constantly and therefore can be used for extremely sensitive applications (e.g. direct spinning). KREYENBORG not only supplied the filter but also the complete discharge unit – another benefit for the customer thanks to less interfaces and only one responsibility for the whole package. Due to the highly contaminated material and a required filtration fineness of 40 µm, a tandem filtration method was executed. The key item in this line is the patented V-type backflush screen changer.


Structure and function of the discharge unit

The melted polyester from the extruder is first fed into the first melt filter. Here the main task is to remove coarse impurities and thus protect the downstream melt pump from possible damage. The booster pump type GPA which KREYENBORG has specifically designed for low-viscosity materials is necessary because of the material’s very low viscosity and the resulting lack of pressure building capacity of the extruder to run over the following V-type backflush screen changer and still have enough pressure to provide for the downstream components.

The V-type of size 280 performs the main task of filtration: the fine filtration at 40 µm.
There were three difficult conditions to be considered in developing a solution:

1.    extremely heavy contaminated raw material
2.    a requested very fine filtration of 40 µm
3.    almost no pressure behind the fine filter for a backflush
 
A solution for this task could only be delivered by the V-type.
The relatively large active filtration area, i.e. the filter units directly in the process – at normal production, all four screens are in use - ensures a high dirt holding capacity and a minimum initial differential pressure. Furthermore, it avoids that, different from other systems in the market, melt stays under temperature for long periods and thus thermally degrades and finally reaches the final process as degraded polymer.

Since during back-flushing and during a screen change as well, at least 75% of the active filter surface is in the process, pressure fluctuations can be that much reduced that they are irrelevant to the subsequent process.

This is realized by the integrated ACS control system which provides a fully automated backflushing and venting of the screen cavities after the screen change.
Due to the patented displacement piston principle and a sophisticated control system the production is carried out with minimal pressure fluctuations. These pressure limits of the system can even be changed and saved application oriented in the SPS.

This represents a novelty in melt filtration and makes this system so easily adaptable to various applications. Due to the very fast back-flushes of one of the four screens with the help of high process speed and the displacement pistons this plunger can also respond quickly to peaks in contamination without bringing the entire system to crash.

This customer, who already successfully uses two of the big KREYENBORG POLY type screen changers in the PET polycondensation, also trusts KREYENBORG’s expertise in PET Recycling filtration technology.