IR Batch, more than just a perfect crystallizer

At NPE 2012, KREYENBORG Plant Technology, Muenster, Germany will display its latest addition to their well known IRD technology, the IR Batch, which uses very efficient short wave Infrared radiation instead of hot air as a heat source.

For several years now, Infrared-Drum Dryers have proven themselves as superior technology in many PET applications. The success story has been justified through clear advantages in comparison to other drying methods and processes. These proven advantages include energy efficiency, short residence time, and flexibility through its ability to handle various material forms and properties. Last but not least, ease of operation and reliability of crystallization and drying are advantages reported most often by IRD customers.

IRDs are often used in PET applications such as cast film, thermoforming sheet, strapping, and recycling production.

Continuous KREYENBORG IRDs are also successfully installed as crystallizers of color masterbatch. Normally, companies using continuous IRDs in PET masterbatch are running rather large quantities and do not change the color very often. The smaller model IRD-A is also used as a crystallizer for quantities up to 150 kg/hr. Frequent color changes required adaptations to enable proper and sufficient cleaning as well as quick start up times.

Often, color masterbatch companies are asked to deliver hundreds of different colors and sometimes very small lots. Thus, conventional, agitated mixing crystallizers were not reliable, as the start-up of such systems with amorphous material is a definite challenge. These conventional systems were originally built for semi-continuous silo-type FiFo principal working crystallizing jobs in the injection molding industry. In these semi-continuous processes, the start-up of the system is not an issue, as crystallized material for the start-up process is usually available.

When these systems are started with amorphous MB, the material tends to clump in the cone due to poor agitation in this area which often results in broken or jammed mixing elements.

conventional crystallizer with limited agitation in the lower cone

As a result, the system has to be completely disassembled, cleaned, and fixed, and in these cases the small lot of MB material is negatively affected, unable to be sold at a higher price.

These issues do not exist when IRDs are used for crystallization.

Most color masterbatch companies are interested in a system for crystallization of color masterbatch off-line. The market mainly asks for small quantities and throughputs. Different colors, different loads of color, and the final converting application for the masterbatch requires different processing conditions for the crystallizer. Due to their reaction to heat, IR radiation in particular, some colors can be heated quickly over the glass transition point while others require a very gentle and rather long heating process in this part of the processing window.

A small IRD-A type for small throughputs offer little options to adjust the process according to various MB types. It offers only one temperature zone and a limited drum rotation speed adjustment.

Even larger machines of an IRD-B type offer a maximum of three different temperature zones for running a temperature profile but only a small process window for the drum rotation speed as well. Therefore, the amount of mechanical mixing energy cannot be varied through the length of the drum.

Materials which are difficult to heat up can really challenge the processing limits of such continuous IRDs. Such difficult materials may include specific colors and/or PET CoPolymer types for special applications. The IRD may not offer enough residence time or mechanical mixing energy to produce perfectly crystallized granules, for example “twins” of granules which were melted together can exist.

Example of a continuous working IRD with 2 temperature zones

These really challenging applications can be perfectly crystallized in the IR Batch. As opposed to the continuous working IRD types, the IR Batch operates in a discontinuous or batch principle. A defined Batch size (i.e. 30 lbs of PET pellets) is fed into the drum and then heated up by a preset temperature profile to the crystallization temperature while the drum is rotating. After finishing the crystallization, the material is discharged out of the machine by a counter-rotational movement of the drum. Once emptied, the machine is ready for the next crystallization cycle and can be fed with new material again.

Processing sequence of the IR Batch System

The discontinuous process has some important advantages for materials which are difficult to crystallize. As it is not directly linked to an inline process, the drum rotational speed can be increased as high as possible to achieve an excellent mixing of the pellets during the critical crystallization phase.

The typical sequence is a fast heating of the PET Masterbatch in the beginning. Therefore the drum rotation is relatively slow and the IR radiator power of the system is at a higher level. In this first phase, the only target is to heat up the material to a predetermined temperature, for example 200 °F. Once the material gets to the critical crystallization temperature in between 220 °F and 275 °F, the speed of the drum is increased to a much higher rotational speed to avoid any clumping of the material and assure a very good cross mixing of the material. After the material is through this critical section, the radiator power or heat can be increased again to finish the crystallization process, meanwhile the drum rotation can be slowed down again. Typically this crystallization process is finished after 15 – 20 min, depending on the material.

After finishing the process, the IR Batch will automatically discharge the drum and begin the sequence again by refilling the drum. A pneumatic slide gate will open the dosing hopper and new material will be loaded into the drum. While the crystallization/heating process starts again, the machine will meanwhile refill the dosing hopper for the next cycle. With the operation of the IR Batch running automatically and in a closed loop, the throughput rate (i.e. for 30lbs / 15 min) will result in a total average throughput of 120 lbs/hr.

The automatic refilling as well as all relevant parameters for the different temperature ramps is fully integrated in the state-of-the-art Touch Screen control. Once parameters and temperature profiles are found for a specific material, theses settings can be saved as recipes in the control system.

A common side-effect of highly-filled masterbatches is the electrostatic loading of the pellets. In order to avoid sticking from electrostatic effects, KREYENBORG Plant Technology developed a special Masterbatch Package for the IR Batch which includes an ionization unit to neutralize electrostatic loadings within the material.

Besides the critical behavior of highly-filled or modified PET masterbatches, the cleaning of processing equipment can be one of the most important and time consuming details. Therefore the IR Batch can be opened completely, and the Infrared module slides out on a separate frame. The drum with the simple mixing elements has no hidden spots and can be cleaned easily with a vacuum cleaner or compressed air. This enables the operator to have a very quick change from one material to another.

Fast, efficient and flexible – with the development of the IR Batch system, KREYENBORG Plant Technology takes another innovative step forward by using Infrared Technology tailor-made for the special requirements of the masterbatch Industry.