Polypropylene Polyethylene Recovery Hammer Mill Screening
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for recovering polypropylene and polyethylene from grinding residues are expensive due to the need for precise density adjustments and cleaning of fragments, making them inefficient and costly.
Innovation Solution
A method involving a hammer mill to break fragments while sparing polypropylene and polyethylene, followed by screening and subsequent separation steps using flotation and ventilation to isolate these materials without requiring precise density adjustments or cleaning, leveraging their mechanical properties to separate them effectively from other materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If density-based flotation separation is used to recover polypropylene and polyethylene, then separation can be achieved, but the process becomes expensive due to requirements for precise density adjustment and cleaning of fragments
Solution Approach 1:
The invention applies preliminary action by performing size-based screening separation before density-based flotation. The fragments are first screened to remove small particles, retaining only larger fragments (greater than 0.5mm) that contain the polypropylene and polyethylene. This preliminary size separation simplifies subsequent processing by reducing the complexity of density adjustment and cleaning requirements, as the retained fragments are already pre-concentrated and require less intensive treatment.
Solution Approach 2:
The invention applies segmentation by dividing the recovery process into two distinct stages: (1) size-based screening separation to isolate larger fragments, and (2) density-based flotation for final separation. This segmentation allows each stage to focus on a specific separation criterion, making the overall process more manageable and less complex than attempting single-stage density separation of all fragment sizes.
2Reliability
If traditional flotation methods are used, then polypropylene and polyethylene can be separated, but cleaning of fragments is required to improve wettability and remove dirt, increasing cost
Solution Approach 1:
The screening step serves as a preliminary action that pre-concentrates the polypropylene and polyethylene in the retained fraction (larger fragments). By removing small fragments beforehand, the subsequent flotation process works with a pre-prepared feed that requires minimal cleaning, as the target materials are already concentrated and less contaminated with fine dirt particles.
Solution Approach 2:
The invention extracts the small fragments (less than 0.5mm) from the mixture through screening before the flotation process. This extraction removes the majority of fine contaminants and dirt that would otherwise require extensive cleaning to improve wettability, allowing the flotation step to focus primarily on separating the polypropylene and polyethylene from each other rather than from various contaminants.
3Measurement precision
If precise density adjustment is implemented for flotation separation, then accurate separation of polypropylene and polyethylene is achieved, but the equipment and operational complexity increases
Solution Approach 1:
The screening step performs a preliminary concentration of polypropylene and polyethylene in the retained fraction, creating a feed stream with higher content of target materials. This preliminary action reduces the burden on the flotation system, allowing it to operate with less stringent density control requirements, as it is processing a pre-concentrated rather than a dilute mixture.
Solution Approach 2:
The two-stage approach segments the separation task: the first stage (screening) handles size-based separation with simple mechanical equipment, while the second stage (flotation) handles density-based separation of the pre-concentrated material. This segmentation allows the flotation equipment to be simpler and less precise than it would need to be for processing the entire original mixture directly.
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
This process allows for efficient and cost-effective recovery of polypropylene and polyethylene, reducing the complexity and expense associated with traditional methods by utilizing mechanical properties to maintain the integrity of these polymers during processing.
Implementation Method 1
a first stage of grinding the fragments of the mixture carried out by means of a hammer mill, this hammer mill being arranged in such a way as to cause the fragments of the mixture to break into grains while essentially sparing the fragments of polyethylene and of polypropylene
Implementation Method 2
a second screening separation step to extract the fragments having dimensions greater than the predetermined threshold
Implementation Method 3
separating by density with flotation, the various fragments of materials, by gradually increasing or decreasing the density of the liquid medium in which the mixture of materials is immersed
Data Source
Figure 1
Figure 2
AI summary
This process is intended to recover polypropylene and polyethylene that are not filled or that are less than 20% filled in a mixture (12) of fragments (14) of materials obtained directly by shear milling of articles. It comprises a first step of milling the fragments of the mixture (12) by means of a hammer mill (16) equipped so as to cause the fragments of the mixture (12), mainly consisting of polyethylene and polypropylene fragments, to break into grains, so that they retain dimensions above a predetermined threshold and a second step of separation by screening to extract the fragments having dimensions above the predetermined threshold.