WASHING & DRYING PROCESSES
FOR RECYCLED PLASTICS
Problem Statement:
Economic Analysis:
Analysis:
To determine a method of cleaning and drying a continuous
stream of shredded high density polyethylene before it proceeds
to granulation in the recycling line of Louis Padnos Iron & Metal
Company. The process should involve removing all foreign
materials, some of which may need to be collected for alternate
processing.
Layout #1
Layout #1
This layout is expected
to clean light
contaminants, including
dirt and light syrups.
The estimated cost is
$750,000
Layout #2
HDPE SHRED
Eddy-Current
System
Magnet
Ferrous Metals
Centrifugal
Washer/
Dryer
Sink/Float
Tank
Thermal
Drying
Granulator
HDPE
GRANULES
Water
Circulation
Tank
Non-Ferrous
Metals
Outside Water
Source
Layout #2
Methods:
HDPE SHRED
The following flowchart illustrates the procedure used for
designing the plastic washing and drying line.
Problem Statement
Metal Removal
Magnet
Electrostatic Drum
Researching Equipment
Eddy-Current
Density Separation
Initial Layouts
Vendor Interviews
Ferrous Metals
Sink-Float Tank
Hydrocyclone
Washing
Thermal
Drying
Granulator
HDPE
GRANULES
Water
Circulation
Tank
Non-Ferrous
Metals
Outside Water
Source
Table 1. Operating cost per
pound of plastic
Throughput
Layout
(lbs/hr)
1
Centrifugal Washing
Friction Washer
Centrifugal
Washer/
Dryer
Sink/Float
Tank
Friction
Washer
Electromagnet
Design Parameters
Decision Matrix
Eddy-Current
System
Magnet
2
Table 1 shows the operating cost of running
each layout with two different throughputs.
The cost is shown as a unit price per pound of
plastic for a cold wash system, assuming 8
hour work days.
Unit Cost
(¢/lb)
3000
0.292
5000
0.366
3000
0.339
5000
0.394
This layout is expected to
clean heavy contaminants,
including dirt, labels, and
heavy syrups. The
estimated cost is
$1,500,000
Final Process Layouts
Air Cleaning
Water Jet Washer
Hot Wash Analysis
Economic Analysis
Final Recommendation
Steam Washing
Drying
Thermal Drying
Centrifugal Drying
Centrifugal
Washer/Dryer
Thermal Dryer
Sink/Float Tank Friction Washer
From the above procedure, the following four methods were
determined to be the best for each process
Figure 3 shows the cost of heating 10 m3 of
water from 10° C to various temperatures.
The blue line shows the cost using an
electric heater, while the pink line shows
the costs of heating with a gas heater.
Initial Heating Costs
70
60
US Dollars
Operating Cost Analysis
If the contaminants include adhesives and
stickers, a hot water wash will be
necessary to clean the plastic.
Electric Heating
Gas Heating
50
40
30
20
10
0
0
20
40
Operating
Temperature
of Water (°C)
80
100
Temperature of Water (°C)
Figure 3. Initial heating costs per
10 m3 of water
Table 2. The cost of running a hot water wash system
3,000 lb/hr Throughput
60
5,000 lb/hr Throughput
Cost ($/lb) Electric
Heater
Cost ($/lb) Gas Heater
Cost ($/lb) Electric Heater
Cost ($/lb) Gas Heater
22
< 0.01
< 0.01
< 0.01
< 0.01
32
0.03
0.01
0.02
0.01
42
0.05
0.02
0.03
0.01
52
0.07
0.04
0.04
0.02
62
0.09
0.05
0.06
0.03
72
0.11
0.06
0.07
0.03
82
0.14
0.07
0.08
0.04
92
0.16
0.08
0.09
0.05
Table 2 shows the
cost per pound of
plastic if a hot
water wash system
is used. The prices
are shown for two
different heater
types and
throughputs.
Table 3. The cost analysis for Layout #1
Tables 3 and 4 show
the necessary selling
Throughput
3,000
5,000
(lbs/hr)
price in order to
Annual
justify the costs of
Operating
14,664 18,242 33,051 38,064
Cost ($/year)
the system after 20
Price (¢/lb)
4.72
4.88
3.34
3.47
years for each
Table 4. The cost analysis for Layout #2 system with a
Initial Cost ($)
1,500,000
throughput of 3,000
Throughput
and 5,000 lbs/hr .
3,000
5,000
(lbs/hr)
This analysis is for
Annual
Operating
16,120 21,133 34,507 40,955
cold wash systems
Cost ($/year)
only.
Price (¢/lb)
8.83
9.06
5.80
5.98
Initial Cost ($)
750,000
Conclusion:
Due to the uncertainty of possible contaminants, two
final processes are recommended to clean and dry the
HDPE shred. Layout #1 can remove all contaminants
effectively, except heavy syrup, stickers, and adhesives.
Layout #2 will be suitable for removing tougher
contaminants, such as thick syrups and labels. For a
system capable of removing stickers and adhesives, a
warm water wash must be used; however, will be
expensive to operate and is not recommended. Both
Layouts are capable of a throughput of 3,000 lbs/hr and
5,000 lbs/hr, depending on the specific machinery
selected.
Project Sponsor:
Louis Padnos Iron &
Metal Company
Holland, MI
Student Design Team:
Seunghee Han
Richard Pospiech
Matthew Siero
Sponsor Representatives:
Mr. Bob Herweyer
Mr. Martin Przekadzinski
Faculty Advisor
Dr. Indrek Wichman
William Smits