WASHING & DRYING PROCESSESFOR 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:

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

Layout #1

Layout #2

Initial Cost ($) 750,000

Throughput (lbs/hr)

3,000 5,000

Annual Operating Cost ($/year)

14,664 18,242 33,051 38,064

Price (¢/lb) 4.72 4.88 3.34 3.47

Initial Cost ($) 1,500,000

Throughput (lbs/hr)

3,000 5,000

Annual Operating Cost ($/year)

16,120 21,133 34,507 40,955

Price (¢/lb) 8.83 9.06 5.80 5.98

Analysis:

HDPE SHRED

Friction Washer

Sink/Float Tank

Centrifugal Washer/

Dryer

Water Circulation

Tank

HDPEGRANULES

GranulatorThermal Drying

Ferrous Metals Non-Ferrous Metals

Outside Water Source

Eddy-Current System

Magnet

Sink/Float Tank

Centrifugal Washer/

Dryer

Water Circulation

Tank

HDPE SHRED

Outside Water Source

HDPEGRANULES

GranulatorThermal Drying

Ferrous Metals

Eddy-Current System

Magnet

Non-FerrousMetals

Initial Heating Costs

0

10

20

30

40

50

60

70

0 20 40 60 80 100

Temperature of Water (°C)

US

Do

llars

Electric HeatingGas Heating

Layout #1

This layout is expected to clean light contaminants, including dirt and light syrups. The estimated cost is $750,000

Layout #2

This layout is expected to clean heavy contaminants, including dirt, labels, and heavy syrups. The estimated cost is $1,500,000

LayoutThroughput

(lbs/hr)Unit Cost

(¢/lb)

13000 0.292

5000 0.366

23000 0.339

5000 0.394

Table 3. The cost analysis for Layout #1

Methods:

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.

Figure 3. Initial heating costs per10 m3 of water

Table 2. The cost of running a hot water wash system

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.

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 4. The cost analysis for Layout #2

Conclusion:

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.

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.From the above procedure, the following four methods were

determined to be the best for each process

The following flowchart illustrates the procedure used for designing the plastic washing and drying line.

Fri

ctio

n W

ash

er

Problem Statement

Design Parameters

Researching Equipment

Decision Matrix

Initial Layouts

Vendor Interviews

Final Process Layouts

Operating Cost Analysis

Hot Wash Analysis

Economic Analysis

Final Recommendation

Metal Removal

Density Separation

Washing

Drying

Magnet

Electromagnet

Electrostatic Drum

Eddy-Current

Sink-Float Tank

Hydrocyclone

Centrifugal Drying

Friction Washer

Air Cleaning

Thermal Drying

Centrifugal Washing

Water Jet Washer

Steam Washing

Sin

k/F

loat

Tan

k

Cen

trifug

alW

asher/D

ryerT

herm

al Dryer

Operating Temperature of Water (°C)

3,000 lb/hr Throughput 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