WASHING

1
WASHING DRYING PROCESSES FOR RECYCLED PLASTICS
Problem Statement 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.
Economic Analysis
Analysis
Layout 1 This layout is expected to clean light
contaminants, including dirt and light syrups.
The estimated cost is 750,000
Layout 1
Table 3. The cost analysis for Layout 1
Tables 3 and 4 show the necessary selling price
in order to justify the costs of the system after
20 years for each system with a throughput of
3,000 and 5,000 lbs/hr . This analysis is for
cold wash systems only.
Initial Cost () 750,000 750,000 750,000 750,000
Throughput (lbs/hr) 3,000 3,000 5,000 5,000
Annual Operating Cost (/year) 14,664 18,242 33,051 38,064
Price (/lb) 4.72 4.88 3.34 3.47
Layout 2 This layout is expected to clean heavy
contaminants, including dirt, labels, and heavy
syrups. The estimated cost is 1,500,000
Methods
Layout 2
Table 4. The cost analysis for Layout 2
The following flowchart illustrates the procedure
used for designing the plastic washing and drying
line.
Initial Cost () 1,500,000 1,500,000 1,500,000 1,500,000
Throughput (lbs/hr) 3,000 3,000 5,000 5,000
Annual Operating Cost (/year) 16,120 21,133 34,507 40,955
Price (/lb) 8.83 9.06 5.80 5.98
Table 1. Operating cost per pound of plastic
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.
Layout Throughput (lbs/hr) Unit Cost (/lb)
1 3000 0.292
1 5000 0.366
2 3000 0.339
2 5000 0.394
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.
If the contaminants include adhesives and
stickers, a hot water wash will be necessary to
clean the plastic. 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.
From the above procedure, the following four
methods were determined to be the best for each
process
Figure 3. Initial heating costs per 10 m3 of
water
Student Design Team Seunghee Han
Richard Pospiech Matthew Siero
William Smits
Project Sponsor Louis Padnos Iron
Metal Company Holland, MI Sponsor
Representatives Mr. Bob Herweyer
Mr. Martin Przekadzinski Faculty Advisor
Dr. Indrek Wichman
Table 2. The cost of running a hot water wash
system
Centrifugal Washer/Dryer
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.
Operating Temperature of Water (C) 3,000 lb/hr Throughput 3,000 lb/hr Throughput 5,000 lb/hr Throughput 5,000 lb/hr Throughput
Operating Temperature of Water (C) Cost (/lb) - Electric Heater Cost (/lb) - Gas Heater Cost (/lb) - Electric Heater Cost (/lb) - Gas Heater
22 lt 0.01 lt 0.01 lt 0.01 lt 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
Friction Washer
Sink/Float Tank
Thermal Dryer