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  • Writer's pictureDEMETO

A Microwaves Cavity design and optimisation for a homogeneous and faster drying process

Nowadays, the disposal and recycling of PET material is a real-world challenge. Current recycling processes allow the reuse of PET material only until it is too damaged to be employed in any manufacturing field. The DEM3TO project aims to recycle PET and bring it back to its main chemical components.

In order to produce the wished molecules, once the depolymerisation is finished, a filtration and drying system must be adopted. Filtration and drying process are critical operations in a variety of industrial processes, like DEM3TO, that require the separation of solid matter from liquid. Due to high temperature and use of dangerous substances, isolation, reduced product handling and environmental protection, the Agitated “Nutsche Filter” (ANF) filtration and drying technique is used.

The Institute of Applied Electronics was in charge of developing a new and innovative microwave-based evaporator model based on ANFD (“Agitated Nutsche Filter Dryer”) to speed up the depolymerisation of the initial polymer (PET) into its composing elements (glycol and terephtalic acid).

The major improvement of this innovative evaporator is the drying time reduction for homogeneous field distribution, using microwave technology combined with classical electric dissipation heating process.

The innovative microwave evaporator model is modelled taking in account the following criteria:

· accurate dielectric measurements

· mathematical regression models

· electromagnetic simulations

Through a deep analysis and characterisation of the mixed substances, it has been possible to create a mathematical model for an excellent estimation of the dielectric constant behaviour related to temperature and mixture concentration.

The EM parametrisation of the radiating cavity combined with the dielectric properties extrapolated from the mathematical regression models, gives the possibility to optimise the microwave absorption as a function of the geometrical parameters, temperature and reacted-mixture percentage.

The results shows that is possible to create an optimised evaporator model, where the efficiency of the dryer never drops below 80%, with an average efficiency around 90%.

Furthermore the model can be adapted for existing “Nutsche filter” geometries simulating the microwave field absorption efficiency, considering the microwave heating system as an add on component with minimal modifications of the usual electric dissipation systems.

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