Plastic Waste Separation via Sink-Float and Air Classification
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Solution Overview
Problem
Current methods for recycling mixed plastic waste, such as beverage cartons, fail to achieve high selectivity and purity, leading to significant energy loss and contamination, with existing processes like the Corenso process and plasma jet treatment being inefficient and unsustainable.
Innovation Solution
A method and system that separates individual recyclable materials from shredded plastic waste using air classification, sink-float separation, and selective dissolution processes, allowing for the recovery of high-purity plastic fractions with minimal energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional recycling methods (mechanical crushing, sink-float separation, near-infrared separation) are used for mixed plastic waste, then processing can be performed with simple equipment, but high selectivity and purity cannot be achieved
Solution Approach 1:
The separation process is divided into multiple sequential stages: pre-separation to remove large impurities, sink-float separation to divide plastics by density, and near-infrared separation to sort by polymer type. Each stage handles specific separation tasks, achieving high overall purity through cumulative refinement rather than attempting single-step separation of all components.
Solution Approach 2:
A flotation medium with specific density is introduced as an intermediary substance to enable separation of plastic fractions based on their density differences. This mediator allows lightweight plastics to float while heavier materials sink, creating distinct separable streams that can be further processed for high purity recovery.
2Loss of energy
If mixed plastic waste is used for energy recovery in cement furnaces, then energy can be utilized, but 78% of cumulative energy content is lost
Solution Approach 1:
Valuable plastic materials are extracted and separated from the mixed waste stream before energy recovery processes. By isolating pure plastic fractions, the system enables these materials to be reused in manufacturing, thereby retaining their energy content and avoiding the 78% energy loss that occurs when mixed plastics are combusted for energy recovery.
Solution Approach 2:
Instead of discarding mixed plastic waste to energy recovery, the system recovers individual plastic materials through multi-stage separation. The recovered pure plastic fractions are then discarded into appropriate recycling streams for manufacturing new products, maximizing energy retention and material value.
3Reliability
If pyrolysis is used to gasify polyethylene at temperatures above 400°C, then aluminum remains in solid form for separation, but the process has not been installed again worldwide despite 10 years of operation
Solution Approach 1:
The process operates at moderate temperatures that preserve the solid form of aluminum while avoiding the extreme conditions of pyrolysis. By changing the temperature parameter to a milder range, the system achieves reliable separation without the technical and economic problems that made the Corenso process unsustainable.
4Manufacturing precision
If plasma jet heating to over 1100°C is used to decompose plastics, then aluminum can be recovered as usable ingots, but very large proportion of cumulative energy is lost due to high energy consumption
Solution Approach 1:
Plastics are separated and removed from the waste stream before aluminum recovery processes. This preliminary separation action prevents the need for extreme heating to decompose plastics, thereby avoiding the massive energy consumption associated with plasma jet heating while still achieving pure aluminum recovery through less energy-intensive methods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves recovery of plastic fractions with purities over 97% and retains 70% of the cumulative energy content, enabling the production of high-quality recyclable materials that can replace new goods in markets with reduced energy loss.
Implementation Method 1
the plastic waste is separated into foils and composite foils on the one hand and hard plastics on the other by means of air classification
Implementation Method 2
at least one separating step comprises a swim-sink separation
Data Source
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AI summary
The invention relates to a method and to an installation for separating individual valuable materials from mixed, in particular milled, plastic waste, comprising film parts, laminated film parts and hard plastic parts, plus optionally impurities. Any impurities are separated from the plastic waste. Next the plastic waste is separated into hard plastics and films as well as laminates, and the hard plastics are separated from the films, and finally the hard plastics are separated into the different types of plastic. At least one separation step comprises a sink-or-float separation.