comparison of two different cooling methods for extrusion

6
COMPARISON OF TWO DIFFERENT COOLING METHODS FOR EXTRUSION PROCESSES Timothy W. Womer Walter S. Smith Richard P. Wheeler Xaloy Corporation, New Castle, PA Abstract This paper will compare the total power consumption of two different means of heating/cooling systems: air and water. For a single 90mm extruder, the total power consumption, output rate, and thermal control will be used to compare the two cooling means. Four different resins will be used. Introduction Heat can be added or removed from the extruder barrel with air or water cooling. Air cooling is ideal for processes that do not require high energy removal. It is less expensive for the hardware, easier to maintain, has lower operating costs, and requires less space compared to fluid cooling. Air cooling provides for slower changes in temperature compared to water cooling. Water cooling is best suited for processes that require high energy removal. Compared to air cooling, the equipment is more expensive, requires higher maintenance to prevent fouling, and requires more space and a water pump. Thermal instability can also occur if the cooling water flashes to steam. Large thermal gradients produced by water cooling can also contribute to excessive thermal strain and stress in the extruder. Equipment The extruder used for this study was a 90mm (3.5”) x 24:1 NRM Extruder with five temperature zone controllers. It is equipped with a 112 kW (150 Hp) DC motor. Max screw speed is 129 rpm. Figure 1 shows the extruder. The water cooled system consisted of five zones. It is a closed loop system. Each zone has a set of 3000 Watt heaters (6000 Watts per zone). Cooling of each zone is controlled by a solenoid that opens and closes a valve. Heat is pulled from the system through a heat exchanger and discarded. The solenoids and heat exchanger are both shown in Figure 2. A continuously running water pump is shown in Figure 3. This pump is a 1000 Watt. Figure 4 shows one zone of the air cooled setup. Each of the five zones contains a set of 3000 Watt heaters (6000 Watts per zone). Each heater is cast aluminum with cooling fins. The 205 Watt blower is to the right in Figure 4. Each blower is activated by the zone controllers. Each blower is rated at 7.5 cmm (265 cfm). Each zone is isolated by baffles. Figure 5 shows an overview of the air cooled system with all heaters, baffles and blowers installed. The top cover has been removed in Figure 5. The heated air exits in an air gap just under the top cover shown in Figure 6. Also shown in Figure 6 is the 711mm (28”) Flex-lip Sheet die and the Dynisco Screen Changer. The die was set to 2.5mm (.100”). The Screen Changer was loaded with a breaker plate and a 20/40/60/20 screen pack. A melt probe was inserted in the melt stream between the screen changer and die. A low shear barrier mixing screw was used for all testing. It was specifically designed for polypropylene with a long feed section. A Fluke Data Acquisition System was used to acquire data from the process. It will be referred to as NetDAQ. Resins Four resins were used for this study. ExxonMobil LDPE LD100BW, MFR of 2.0 g/10 min Novachemicals Novapol HD-2007-H HDPE, MFR of 8.5 g/10 min ExxonMobil PP 9852EI, MFR of 2.1 g/10 min Eastar EB062 PETG, IV of .75 dl/g Experimental Procedure Each of the four resins was extruded with water cooling and then with air cooling for a total of eight one-hour tests.

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This paper will compare the total power consumption of two different means of heating/cooling systems: air and water. For a single 90mm extruder, the total power consumption, output rate, and thermal control will be used to compare the two cooling means. Four different resins will be used.

TRANSCRIPT

Page 1: Comparison of two different cooling methods for extrusion

COMPARISON OF TWO DIFFERENT COOLING METHODS FOR EXTRUSION

PROCESSES

Timothy W. Womer

Walter S. Smith

Richard P. Wheeler

Xaloy Corporation, New Castle, PA

Abstract

This paper will compare the total power consumption of

two different means of heating/cooling systems: air and

water. For a single 90mm extruder, the total power

consumption, output rate, and thermal control will be used

to compare the two cooling means. Four different resins

will be used.

Introduction

Heat can be added or removed from the extruder barrel

with air or water cooling. Air cooling is ideal for

processes that do not require high energy removal. It is

less expensive for the hardware, easier to maintain, has

lower operating costs, and requires less space compared

to fluid cooling. Air cooling provides for slower changes

in temperature compared to water cooling.

Water cooling is best suited for processes that require

high energy removal. Compared to air cooling, the

equipment is more expensive, requires higher

maintenance to prevent fouling, and requires more space

and a water pump. Thermal instability can also occur if

the cooling water flashes to steam. Large thermal

gradients produced by water cooling can also contribute

to excessive thermal strain and stress in the extruder.

Equipment

The extruder used for this study was a 90mm (3.5”) x

24:1 NRM Extruder with five temperature zone

controllers. It is equipped with a 112 kW (150 Hp) DC

motor. Max screw speed is 129 rpm. Figure 1 shows the

extruder.

The water cooled system consisted of five zones. It is a

closed loop system. Each zone has a set of 3000 Watt

heaters (6000 Watts per zone). Cooling of each zone is

controlled by a solenoid that opens and closes a valve.

Heat is pulled from the system through a heat exchanger

and discarded. The solenoids and heat exchanger are both

shown in Figure 2. A continuously running water pump is

shown in Figure 3. This pump is a 1000 Watt.

Figure 4 shows one zone of the air cooled setup. Each of

the five zones contains a set of 3000 Watt heaters (6000

Watts per zone). Each heater is cast aluminum with cooling

fins. The 205 Watt blower is to the right in Figure 4. Each

blower is activated by the zone controllers. Each blower is

rated at 7.5 cmm (265 cfm). Each zone is isolated by

baffles. Figure 5 shows an overview of the air cooled

system with all heaters, baffles and blowers installed. The

top cover has been removed in Figure 5. The heated air

exits in an air gap just under the top cover shown in Figure

6.

Also shown in Figure 6 is the 711mm (28”) Flex-lip Sheet

die and the Dynisco Screen Changer. The die was set to

2.5mm (.100”). The Screen Changer was loaded with a

breaker plate and a 20/40/60/20 screen pack. A melt probe

was inserted in the melt stream between the screen changer

and die.

A low shear barrier mixing screw was used for all testing. It

was specifically designed for polypropylene with a long

feed section.

A Fluke Data Acquisition System was used to acquire data

from the process. It will be referred to as NetDAQ.

Resins

Four resins were used for this study.

• ExxonMobil LDPE LD100BW, MFR of 2.0 g/10

min

• Novachemicals Novapol HD-2007-H HDPE, MFR

of 8.5 g/10 min

• ExxonMobil PP 9852EI, MFR of 2.1 g/10 min

• Eastar EB062 PETG, IV of .75 dl/g

Experimental Procedure

Each of the four resins was extruded with water cooling and

then with air cooling for a total of eight one-hour tests.

Page 2: Comparison of two different cooling methods for extrusion

For each test, the barrel and screw were completely

cleaned. The die was pre-heated two hours prior to each

one hour test, and the barrel was pre-heated for one hour

before the testing started. Steady thermal conditions were

then assumed to prevail throughout each hour long test.

The four resins were run with the water-cooled system

first. Once the water-cooled trials were completed the

extruder was retrofitted for air-cooling. The same

controllers used for water-cooling were used with the air

cooling. Between switching of the systems the heater

amperage and voltage were checked on each zone.

For each one hour test, the extruder was started and set to

a speed of 75 rpm. The thermocouple temperatures, the

amount of time the heaters were on, motor amps, screw

speed, melt probe temperature, and the amount of time the

blowers ran (air cooling) were all monitored and recorded

every .02 seconds a NetDAQ. Melt temperature was

measured every ten minutes with an IR gun and a hand-

held melt probe. Output rates were measured and

recorded every twenty minutes.

The data were then extracted from the NetDAQ and

compiled with a spreadsheet program. The amount of

time the heaters and blowers were on was used in

conjunction with the heater amperage and voltage to

calculate the energy (kilowatt-hours) consumed by each

heater and blower during the hour long test. The same

was done for the drive motor energy. The energy added

to the polymer was calculated from the difference

between the polymer product melt temperature and the

feed temperature.

Presentation of Data and Results

The water-cooled system used slightly more energy than

the air-cooled system for all four polymers as shown in

figure 7.

There was little difference between the HDPE runs shown

in Figure 8. Power consumption for the drive was almost

equal. The main difference was power used between the

cooling systems. The water cooled used about 22% more

energy compared to the air cooled.

The same patterns are seen with the other tests. Please

reference Figures 9 and 10. LDPE tests had similar

values between the systems with the water using 7% more

energy. The PP runs had the lowest total power

consumptions with comparable values. The air cooled

used 20% less energy than the water cooled.

Figure 11 shows the highest power required for all the

runs. This came during the PET trials. The major

difference was the power usage for heating/cooling. The

water cooled used 80% more energy than the air cooled.

Output rates were higher for the water-cooled system on 2

out of the 4 resins. Please see Figure 12.

Temperature control varied according to resin. With respect

to only the heating/cooling system LDPE had the highest

power consumption for all resins mainly because of power

needed in zone 3. This zone was cooler during the whole

trial for both systems. Please see Figure 13. HDPE

exhibited a similar pattern of a cooler zone 3 for both

systems as well. Please see Figure 14. PP had no apparent

differences between the two systems. This is confirmed in

Figure 15. PET was the only resin that required extensive

cooling in Zone 1during the trials. The air system couldn’t

maintain the actual temperature to the set point. This is

illustrated in Figure 16.

Discussion of Data and Results

One of the major differences between the water and air

systems was the continuous running of the water pump.

This consumed 1kWhr for all water cooled tests. Since

water cooling is an abrupt mean of heat extraction energy is

removed quickly and many times resulting in excess energy

removal. So energy must be added back into the system to

keep the barrel at temperature. Air cooling is more gradual

and doesn’t over cool a barrel section as easily as water

cooling. So unless extensive cooling is needed then water

cooling can be avoided. Air cooling should be a sufficient

system for most properly designed extruders.

Water cooling would be useful when many different

polymers are to be processed by the same extruder. With a

given screw design, some polymers may require extensive

cooling or heating to produce the desired product

temperature. This may require the added heat capacity the

water provides. But it is versatility at the cost of thermal

stability and excessive energy consumption.

This can be seen by the high energy consumption values for

HDPE and LDPE. Zone 3 actual temperature values were

low during the whole test. This zone required constant

power for both resins and both cooling systems. A different

properly designed screw would alleviate this problem. The

screw was specifically designed for PP.

More cooling was required to run the PET resin on Zone 1.

The air cooling system could not control this zone. However

the water cooling could control this zone, but naturally used

more energy to do so. The PET output rates were 5% higher

for the air cooled. The water lowered the temperature of the

first zone which lowered the solids conveying to reduce the

output. So, output rate can also be affected by the cooling

means, especially as it affects solids conveying.

Page 3: Comparison of two different cooling methods for extrusion

Conclusions

1. Cooling of the extruder barrel should be

minimized. Excessive cooling will require more

motor power.

2. Heating of the extruder barrel should be

minimized. Excessive heating will produce large

thermal gradients in the melt and non-uniform

product melt temperature distribution.

3. Air cooling is recommended for an extruder

dedicated to a given product. However, the

screw must be properly designed to not require

excessive cooling or heating to maintain product

temperature.

4. Water cooling finds uses when a given extruder

is used to process multiple polymers and rates

with the same screw. Water cooling can provide

great energy transfer so that product temperature

can be maintained in spite of a screw that is not

optimized for a given polymer at a desired rate.

References

1. C. Rauwendaal, Polymer Extrusion, Hanser

Publishers, NY, 1986

2. E. Steward; W. A. Kramer, Air vs. Water Cooled

Single Screw Extruders, ANTEC 2003

3. J. Wortberg; T. Schroer, Novel Barrel Heating

with Natural Gas, ANTEC 2003

Figure 2-Water cooled system

Heat Exchanger and Solenoids

Figure 1-90mm x 24:1 NRM Extruder

with water cooled system

Heat Exchanger

Manifold

Solenoids

Page 4: Comparison of two different cooling methods for extrusion

`

Figure 3-Water cooled system-Water

Pump

Figure 4-Air cooled system-Single zone

Figure 5-Air cooled system-Overview

Water Pump

Flow Meters

Air Cooled Heater Blower

Baffle

Die

Screen Changer Air Gap

Figure 6-Die, Screen Changer and Air Gap

Page 5: Comparison of two different cooling methods for extrusion

Total Energy Consumed for Each System

70.49

52.2

41.87

87.75

69.33

50.05

39.64

86.54

0

10

20

30

40

50

60

70

80

90

100

HDPE LDPE PP PET

Resin Processed

En

erg

y C

on

su

me

d (

KW

h)

Water

Air

Comparison of Total Kilowatt-hours

for Processing HDPE

70.49 69.33

59.35 60.6

11.148.73

0

10

20

30

40

50

60

70

80

Water Air

Heating/Cooling System

Po

we

r A

ssu

mp

tio

n (

KW

h)

Total

Drive

Heat/Cooling

52.2

50.05

34.2133.25

17.9916.8

0

10

20

30

40

50

60

Water AirHeating/Cooling System

Po

wer

Co

nsu

mp

tio

n (

KW

h) Total

Drive

Heat/Cooling

Comparison of Total Kilowatt-hours

for Processing LDPE

Comparison of Total Kilowatt-hours

for Processing PP

41.87

39.64

30.27 30.28

11.6

9.36

0

5

10

15

20

25

30

35

40

45

Water Air

Heating/Cooling System

Po

wer

Co

ns

um

pti

on

(K

Wh

)

Total

Drive

Heat/Cooling

Comparison of Total Kilowatt-hours

for Processing PET

87.75 86.5484.07

85.85

3.680.69

0

10

20

30

40

50

60

70

80

90

100

Water Air

Heating/Cooling System

Po

wer

Co

ns

um

pti

on

(K

Wh

)

Total

Drive

Heat/Cooling

Throughput Rate for Each System

166 169

106

292

164171

97

307

0

50

100

150

200

250

300

350

HDPE LDPE PP PET

Resin Type

Th

rou

gh

pu

t R

ate

(kg

/hr)

Water kg

Air kg

Figure 7-Total Energy

Consumption for the 8 tests

Figure 8-Power Consumption for HDPE

for both systems

Figure 9-Power Consumption for LDPE

for both systems

Figure 10-Power Consumption for PP for

both systems

Figure 11-Power Consumption for PET

for both systems

Figure 12-Output Rates for all 8 Tests

Page 6: Comparison of two different cooling methods for extrusion

Temperature Control for LDPE of both systems versus

setpoint

180

190

200

210

220

230

240

250

260

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5

Te

mp

era

ture

C

Water

Air

Setpoint

Temperature Control for HDPE of both systems versus

setpoint

180

190

200

210

220

230

240

250

260

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5

Te

mp

era

ture

C

Water

Air

Setpoint

Temperature Control for PP of both systems versus setpoint

180

190

200

210

220

230

240

250

260

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5

Te

mp

era

ture

C

Water

Air

Setpoint

Temperature Control for PET of both systems versus setpoint

180

190

200

210

220

230

240

250

260

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5

Te

mp

era

ture

C

Water

Air

Setpoint

Figure 13-Temperature Control of LDPE

for both cooling systems

Figure 14-Temperature Control of HDPE

for both cooling systems

Figure 15-Temperature Control of PP for

both cooling systems

Figure 16-Temperature Control of PET

for both cooling systems