Energy Consumption Analysis for a Single Screw Extruder - Intelligent Computing for Sustainable Energy and Environment - page 537

Conventionally, the power consumption can be simply obtained through the pro-
duction of armature voltage and current. However, as PWM regulation is adopted, the
voltage and current change frequently at each PWM cycle. This change causes a phase
shift between the voltage and current, leading to a low power factor of this motor drive
system. An additional power meter attached to the motor drive power supply can ver-
ify such effect. As a result, the DC motor consumes more energy than it actually re-
quired to drive the screw. The recorded data also shows a clear relationship between the
power factor and screw speed. Thus, a full representation of the motor apparent power
consumption can be obtained. The resultant real-time monitoring of motor energy con-
sumption is then used for the investigation of optimal operating conditions discussed
later.

4 Effects of Process Settings on Thermal Energy Consumption

As thermal heating consumes nearly 2/3 of the total energy usage, it is desirable to
study the effects of operation settings on the thermal energy consumption. Basically,
the barrel and die heating temperatures, feed area water cooling temperature, and screw
speed are the main adjustable variables. The following will investigate their effects on
extrusion thermal energy consumption. All experiments (see table 1) were carried out
on the Killion KTS-100 sincle screw extruder, and the material been processed is low
density polyethylene (LDPE 2102TN00W, MFI 2.5 g/10min, density 921 kg/m 3 ) from
SABIC.

Ta b l e 1 . Experimental settings of each test on the single screw extruder

DOE Zone 1 Zone 2 Zone 3 Screw Speed Water Cooling
A 150 ◦ C 160 ◦ C 170 ◦ C 25 ◦ C 40

B 160 ◦ C 170 ◦ C 180 ◦ C 25 ◦ C 40

C 170 ◦ C 180 ◦ C 190 ◦ C 25 ◦ C

40

D 170 ◦ C 180 ◦ C 190 ◦ C 15 ◦ C 40

E 170 ◦ C 180 ◦ C 190 ◦ C 40 ◦ C

40

F 170 ◦ C 180 ◦ C 190 ◦ C 25 ◦ C 20

G 170 ◦ C 180 ◦ C 190 ◦ C 25 ◦ C 60

4.1 Heating Temperature Settings

The processing window of polymer melting temperature can be 50 ◦ C or even more for
some materials. Too low of the heating temperature would cause the plastic granules
not properly melted and more energy consumption from the motor. By contrast, higher
heating temperature increases the amount of energy lost to environment. Thus an opti-
mal heating temperature setting not only saves the energy, but also improves the melt
quality.
For numerical analysis, the experimental heating temperatures were then set at three
different levels: A (low), B (medium), and C (high) as shown in table 1. Each trial