What is the role of a crystallizer?

What is the role of a crystallizer?

A crystallizer is heating equipment that transforms amorphous PET into a semicrystalline state from virgin, post-process, or scrap PET.

Processors who produce or use considerable amounts of scrap or recycled PET material need crystallizers. Because processing converts virgin PET to amorphous PET, which cannot be reprocessed in high concentrations, those who must re-use this material have only two choices:

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Process a small percentage of amorphous PET regrind (10% or less) with virgin PET, or blend a small percentage of amorphous PET regrind (10% or less) with virgin PET before processing.

Using a crystallizer, “re-crystallize” the amorphous PET regrind to a semicrystalline form (similar to virgin PET).

What is the function of a crystallizer?

A crystallizer raises the temperature of granulated amorphous PET to slightly below its melting point, but above its glass transition temperature. When heated PET reaches its "crystallization" temperature, the amorphous PET molecules rapidly change state: Crystalline structures develop and align inside the molecules and the material transitions from an amorphous to a semi-crystalline state.

When the transformation is complete, the “crystallized” PET is ready for drying (if necessary) and processing in the same way that virgin PET is. When amorphous materials are heated during drying, they tend to clump together since they haven't crystallized. Several issues arise from agglomerated materials: 1) They cause insufficient residence time for some materials by disrupting smooth mass flow through a drying hopper.

2) Agglomerated clumps are difficult to dry because of their huge size, and they are more prone to retain moisture than is desirable.

3) Agglomerated clumps can become caught or bridged in downstream processes, resulting in a slew of other material handling problems.

Depending on the capabilities of your crystallizer equipment, crystallization can be done in a continuous or batch process. Crystallizers are typically sized according to the amount of material that can be crystallized in an hour.

What are the types of crystallizers?

Majorly the crystallizers are of two types mentioned below:  

Hot-air hopper Crystallizers Infrared Drum (IRD) Crystallizers

Hot-air hopper Crystallizers The crystallizers are similar to dryers in many ways: Material is fed into a hopper, heated to a precise temperature with warmed air, and then discharged into a downstream process.

A hopper-type crystallizer and a dryer, on the other hand, have numerous key functional differences:

Crystallizers use ambient air: In an open loop crystallizer, heated ambient air is used, rather than dry/desiccated air in a closed loop system (however, closed loop systems are available). While some drying may occur as a result of the heating and crystallisation process, crystallisation does not provide the same level of moisture control as drying. If the recrystallized PET is still damp, it must be thoroughly dried before use.

Crystallizer hoppers use an agitator: Mechanical agitation is required within the hopper to keep amorphous PET material moving, break up clumps, and ensure that it flows easily before and after the crystallization process because it can become sticky as it is heated to its crystallization temperature.

Infrared Drum (IRD) Crystallizers Infrared Drum (IRD) crystallizers are distinguished from hopper-type crystallizers in a number of ways: Infrared Heat Source: An infrared emitter, located in the drum's middle, heats material directly as it rotates in the drum, eliminating the need to inject heated air.

Rotating Horizontal Drum: Instead of a vertical hopper, the IRD employs a horizontal rotating drum. Slow, continuous rotation reduces clumping, ensures complete material mixing, and removes the need for the agitator found in traditional vertical crystallizer hoppers.

Can Simultaneously Crystallize and Dry: The powerful infrared source heats pellets more quickly, causing moisture to rise to the top and be transported away by a steady stream of cool, ambient air.

While IRD crystallizers can remove 90% or more of the moisture from a material, which is a far larger percentage than hopper-type crystallizers, they can't give the precision moisture removal that a specialized desiccant dryer can.

Alaqua is the best crystallizer supplier in USA along with other processing equipment such as the evaporator, solvent recovery, and other equipment to serve various industrial requirements. Alaqua supplies processing equipment such as crystallizers made in USA worldwide for various food processing, pharmaceutical and various chemical industries. To know more contact us today!

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