Integrated Decontamination & SSP Process Description
The RPET flakes from the washing line are homogenized in a blending silo to create a uniform feed distribution. The RPET flakes are transferred to the top of the SSP train and are then fed by gravity from the Feed Hopper (100) by a rotary valve into the BePET™ Flake Preheater (200).
The material is heated to reaction temperature in the Preheater (200) by conduction from the hot multiple disc rotor. The rotor also provides the required agitation and conveyance for efficient heat transfer and discharge.
A portion of the nitrogen gas leaving the Decontamination and SSP Reactor (300) sweeps the agitated bed surface and removes some dust, moisture and volatile organic chemicals released during preheating. The heated flakes are discharged through an overflow weir to the Reactor (300) through a rotary valve. The balance of the gas leaving the Reactor (300), along with the gas exiting the Preheater (200) is passed through a scrubber where the entrained fines and chemical contaminates are collected. The gas is then dehumidified before being returned back to the inlet of the Reactor (300).
The preheated RPET flakes are discharged from the Preheater (200) into the Reactor (300). The solids form a plug-flow, moving bed with sufficient residence time (4 or more hours) in order to remove the volatile contaminates within the RPET flakes and allow for the system to control the product’s intrinsic viscosity (IV) by the solid phase polymerization (SSP) reaction. Heated pure nitrogen with a low level of moisture and oxygen is fed through the bottom of the Reactor (300) forming a counter-current flow to the downward moving bed of RPET flakes. The nitrogen removes any volatile contaminates residing in the RPET flakes and by-products of the SSP reaction out to the gas purification system.
The Mechanical Discharge (310) in the bottom section of the Reactor (300) is designed to break up lumps and ensure uniform draw down of the bed material in plug-flow regime, and thereby minimize product variability. The gas distribution nozzles, also at the bottom, are designed to evenly distribute the clean hot nitrogen over the entire cross-section of the Reactor (300).
The hot and dry decontaminated and IV controlled RPET flakes from the Reactor (300) are transferred to the Hopper Cooler (400) through a rotary valve and elevating auger/ conveyor. A gas blower supplies cooled nitrogen to the bottom of the Hopper Cooler (400). The counter current flow of cold air cools the RPET flakes to temperatures that prevent color degradation and are acceptable for pack-out. The gas exhausted from the Hopper Cooler (400) is fed back into the blower after being de-dusted in a filter.