Designing a tank for sorting and separation of waste plastics for recycling using
3D CAD
Evbade Alfred, Liu Runbo, Masao Yukumoto(Department of Mechanical Engineering, Graduate school of Engineering, Chubu University)
Abstract: This paper presents the design of a tank for plastic separation and sorting by sink float method.
This write up includes technologies that are commercially available and those that are still in the researchphase. Using a water tank, different conditions like flow rates and tank shape was taken into consideration.
With the use of a 3D CAD for simulation analysis, the velocity distribution in the tank was calculated.
Plastics that were used in this experiment are light plastics such as PP and PE; and heavy plastics such as PS,
PVC and PET. The plastics is feed through the inlet and collected from the outlet.
Key Words: plastics; sorting; sink-float separation; simulation analysis; tank

Introduction
Plastic recycling can be classified basically intomechanical recycling, feedstock recycling and energy
recovery. Mechanical recycling is a method by whichwaste materials are recycled into new (secondary) raw
materials without changing the basic structure of thematerial. It is also known as material recycling.
Feedstock recycling also known as chemical recycling
involves changing the chemical structure of wastematerial and recycling the chemical constituents intomaterials other than the original material of the waste.
Liquefaction is an example of chemical recycling.
Energy recovery is a process by which solid waste isconverted into renewable energy. Some examples ofenergy recovery are usually in solid fuels like RDF(refuse derived fuel) and RPF (refuse paper and fuel) [3].
This research discuss about plastic separation andsorting in mechanical recycling. Companies that buy
recycled products want characteristics as same as thevirgin pellets. Otherwise, it is not necessary to use
recycled materials. Recently, the plastic industries,
colleges and homes have been faced with the problemsof sorting and separation of plastics in recycling. There
are many studies concerning the separation of mixed
plastics for recycling [1].

one another. For example the separation of PVC andPET is very difficult. And the reaction between PVC
and PET could give hydrochloric acid [2]; that is if it isnot properly separated the recycled products can beharmful. The table 1 above shows the relative density
range of plastics materials.
Materials and methods
A water tank was designed for this experiment.
The experimental set up is shown in the figure1 below.
The rectangular tank has a volume of 0.0145m 3 an inletof 15mm diameter, and an outlet of 10mm at the bottom
and 30mm×10mm at the top as shown in figure 1. From
figure 1 we can see the water inlet from the top of thetank, and then the light plastic pellets goes out fromthe top and the heavy plastic pellets goes out from thebottom of the tank. Simulation analysis of the watertank using 3D CAD software was carried out under
different condition. The flow velocity of water wasadjusted to 0.95m/s 2. Then the hose was placed at about
90 degree at the inlet. Thereafter the separation andsorting of PVC, PET, PS, PP and PE was then carriedout in this setup.

Table 1Polymer relative density range
Polypropylene (PP)0.916-0.925

Polyethylene (PE)0.936-0.955

Polystyrene (PS)

1.050-1.220

Polyvinyl chloride(PVC)

1.303-1.336

Polyethylene
terephthalate (PET)

1.330-1.400This paper is focused primarily on designing andtesting a variety of shapes for sorting of waste plastics
mixtures. The designed shape of the tank will beintroduced later. For a sink float separation to work
properly, the relative density must differ greatly from

Figure 1 (shape of tank)water inlet

Figure 3 simulation analysis results
Figure 1 (schematic diagrams)
Results and discussion
The results of the simulation analysis of the tank isshown in the figure below. We can see that the water
goes in through the inlet and the goes out through theoutlet.
After putting the various plastics in the water, it wasobserved that plastics with relative densities less thanwater, that is PP and PE floats and goes through thetop outlet of the tank. While plastics with relative
densities greater than water, for example PET and PVC
sinks and goes through the bottom of the tank.
When the hose was at 90 degrees to the tank, it wasobserved that for the heavy plastics (PVC), it took about
4s to sink to the bottom. Which implies the timedepends on the height of the tank and the velocity offlow. When the water goes through the inlet, it wasobserved that the plastics moves round and round andfinally goes through to the outlet. The velocity of flow,
size of the inlet and shape of the tank is a key factor.

During the simulation analysis, the velocity of flow
was examined. As we can see from the results of theanalysis, the flow velocity is highest at about 0.95m/s
and lowest at about 0.1m/s. when the hose was placedat about 90 degree time taken for the plastic to reachthe bottom was about 4s. But at an angle to the tank,the flow rate was a little slower. The flow distribution
in the pipe also varies. It was observed that the resultsof the flow simulation analysis, matches closely withthe experiment.
Conclusion
We can conclude that to successfully separate plastic
for recycling, different conditions should be considered.
For example the shape of the tank, flow rates of fluid
and the angle of the hose to the tank. Since the resultsof the flow simulation analysis matches closely withexperimental results, simulation software (3D CAD)
can be used to design a system for sink float separationof mixed plastics.
References[1]. G. Dodbida, J. Sadaki, A. shibayama, T. Fujita “sortingTechniques for Plastics Recycling”, The Chinese Journal ofProcess Engineering. 6(2006) 186-189[2]. E. A. Bruno “Automated Sorting of Plastics for Recycling
http://infohouse.p2ric.org/ref/09/08620.pdf[3]. 松藤敏彦: プラスチック入門、p15-18

Figure 2 ( Result of flow simulation analysis)