What’s the role of a crystallizer?

Demystifying the Role of Crystallizers in PET Processing

Crystallizer, a term that might sound complex and mysterious, plays a crucial role in the world of PET (Polyethylene Terephthalate) processing. If you’ve ever wondered what crystallizers are and what function they serve, this comprehensive guide will unravel the science behind them, their types, and their significance in PET material transformation.

The Role of a Crystallizer: Transforming PET

In simple terms, a crystallizer is a heating device designed to work its magic on virgin PET, post-process PET, or even scrap PET. Its mission? To convert these materials from an amorphous state into a semi-crystalline state. 

Now, let’s break down this mission step by step.

Amorphous to Semi-Crystalline Transformation: 

• PET, in its pure state, possesses a semi-crystalline structure. However, during processing, virgin PET is often transformed into an amorphous state. Unfortunately, amorphous PET cannot be reprocessed in high concentrations, posing a challenge for those who seek to reuse this material. This is where crystallizers come into play.

The Two Choices:

• For those handling substantial amounts of scrap or recycled PET material, the options are limited:
  1. Process a small percentage of amorphous PET regrind (typically 10% or less) alongside virgin PET.
  2. Utilize a crystallizer to “re-crystallize” the amorphous PET regrind back into a semi-crystalline form, akin to virgin PET.

Function of a Crystallizer: A Transformative Journey

A crystallizer’s role is akin to the superhero who transforms the ordinary into something extraordinary. It all starts with granulated amorphous PET, which is gently heated within the crystallizer. This process elevates the material’s temperature to just below its melting point while keeping it above the glass transition temperature.

As the heated PET reaches its “crystallization” temperature, a remarkable transformation occurs. The amorphous PET molecules swiftly shift states, developing and aligning crystalline structures within. This metamorphosis turns the material from an amorphous state to a semi-crystalline state, making it ready for subsequent drying (if needed) and further processing.

Without crystallization, amorphous materials tend to clump together during the drying process. 

These agglomerated masses can lead to various issues:

1. Disrupted material flow, causing some portions to have insufficient residence time in the drying hopper.
2. Difficulty in drying due to the large size of agglomerated clumps, which tend to retain excessive moisture.
3. Potential blockages or bridging in downstream processes, resulting in further material handling problems.

Different equipment and methods can carry out the process of crystallization, including continuous or batch processes. Typically, experts determine the size of crystallizers based on the hourly volume of material that can undergo crystallization.

Exploring the Types of Crystallizers:

There are two major types of crystallizers, each with its unique approach to achieving the same goal: transforming amorphous PET into semi-crystalline PET.

Hot-air Hopper Crystallizers-

These crystallizers share some similarities with dryers but have several distinctive features that set them apart. 

The process within a hot-air hopper crystallizer unfolds as follows:

• Ambient Air Usage: In an open-loop system, hot-air hopper crystallizers employ heated ambient air instead of dry or desiccated air found in closed-loop systems. While some drying may occur during the crystallization process, it does not provide the same precise control over moisture levels as dedicated drying. Therefore, if the recrystallized PET still contains moisture, it must undergo thorough drying before processing.
• Agitator Operation: Given that amorphous PET material can become tacky as it approaches its crystallization temperature, mechanical agitation is crucial within the hopper. This ensures that the material keeps moving, prevents clumping, and maintains smooth flow during and after crystallization.

Infrared Drum (IRD) Crystallizers-

IRD crystallizers offer an alternative approach to achieving crystallization, distinct from hot-air hopper crystallizers. 

Here’s how they differ:

• Infrared Heat Source: In the heart of an IRD crystallizer, an infrared emitter takes center stage. This emitter directly heats the material as it rotates within the drum, eliminating the need for the injection of heated air.
• Rotating Horizontal Drum: Unlike the vertical hoppers used in traditional crystallizers, IRD crystallizers employ a horizontal rotating drum. This slow, continuous rotation effectively reduces clumping, ensures thorough material mixing, and eliminates the need for an agitator, commonly found in hopper-type crystallizers.
• Simultaneous Crystallization and Drying: IRD crystallizers boast a powerful infrared source that heats pellets more rapidly, causing moisture to rise to the surface. This moisture is then carried away by a continuous stream of cool ambient air. While IRD crystallizers can remove 90% or more of moisture from the material, significantly more than hopper-type crystallizers, they may not achieve the precision moisture removal of a dedicated desiccant dryer. As a result, some secondary drying is often required.

The Crystallizer Supplier: Alaqua

Alaqua, a prominent player in the field of processing equipment, stands as a reliable crystallizer supplier in the USA. Alongside crystallizers, Alaqua offers a range of processing equipment, including evaporators and solvent recovery systems, catering to diverse industrial requirements. Their offerings extend to various sectors, including food processing, pharmaceuticals, and chemical industries. Should you seek more information or require their assistance, don’t hesitate to reach out to Alaqua today.

The WayForward:

In conclusion, crystallizers, while they may seem complex, serve a straightforward purpose in PET processing. They offer a means to reduce waste and reuse materials, making them an invaluable component in various industries. If you ever find yourself with questions about how crystallizers operate, their capabilities, or which type suits your specific process, consider seeking expert guidance. crystallizers supplier play a vital role in enhancing sustainability and resource efficiency, making them a key player in the world of materials transformation.

Frequently Asked Questions (FAQ) about Crystallizers

• What is a crystallizer, and what does it do?
  A crystallizer is a heating device that transforms amorphous PET into a semi-crystalline state, making it suitable for further processing.

• Why is a crystallizer essential in PET processing?
  Processing often turns virgin PET into an amorphous state, which can’t be reprocessed efficiently. A crystallizer reverts it to a semi-crystalline state, reducing waste and reusing material.

• How does a crystallizer work?
  It heats granulated amorphous PET to a specific temperature, causing rapid molecular changes from amorphous to semi-crystalline.

• Are there different types of crystallizers?
  Yes, two major types exist: hot-air hopper crystallizers and Infrared Drum (IRD) crystallizers, each with its unique approach.

• What is the role of a crystallizer supplier?
  A crystallizer supplier provides equipment and expertise, ensuring PET processors have access to efficient crystallization solutions.

Related Blogs Links:- https://www.alaquainc.com/crystallizer-and-its-types/