Energy Consumption Analysis for a Single Screw Extruder - Intelligent Computing for Sustainable Energy and Environment - page 534

amounts to 380 million per annum. Thus, a reduction in electricity usage of 10% would
result in savings of £ 38 million per annum and a significant reduction in environmental
burden.
The extruder motor is obviously an energy intensive component which consumes
around 1/3 of the total energy. Its associated power factor is always an critical issues for
the plastic processing companies as lower power factor may lead to an undesired penalty
(or surcharge). The on-line monitoring of motor power consumption therefore becomes
necessary for the investigation of energy efficiency. Such energy monitoring can also
provide useful information on the melt stability and the quality of final product. The use
of power meter (e.g. HIOKI 3169-21) is of course the easiest way to monitor the motor
power consumption, including the apparent power, active power, reactive power and
the power factor. However, the installation of power meters for each extruder involves
a big cost and disruptions to the production line. Mathematical models based on the
process settings seems to be an affordable alternative for such purpose [2,3]. However,
the developed models highly depend on the geometry of the extruder and the materials
being processed. It is difficult to use the same model on a different machine without re-
training. Fortunately, most of the motor drive provides essential information which can
be used to theoretically calculate the power consumption. For a DC motor, these vari-
ables can be the rotational speed and armature current. In this paper, a simple method
will be first presented for on-line monitoring of the DC motor power consumption in a
single screw extruder.
Thermal heating is another big consumer of energy in polymer processing. The ma-
jority of thermal energy is used to keep the temperature of extruder barrel and die at a
specific level. Thus, real-time monitoring of thermal energy also plays a key role in en-
ergy efficiency optimization. Due to the same issue in motor power monitoring, power
meter and mathematical model are not suitable for this purpose. A more accurate and
reliable method based on temperature controller outputs will be given in this paper.
Based on the real-time monitoring of thermal energy and motor energy consumption,
the effects of operating settings on total energy efficiency in polymer extrusion can then
be carried out. It is well-known that the increase of screw speed leads to lower spe-
cific energy consumption (SEC) [4]. However, the material residence time is reduced
at higher screw speed, leading to possible poor melt quality. An optimal screw speed
therefore needs to be properly identified. According to literature research, the tempera-
ture settings of each heating zone have different effects on the total energy consumption.
However, the temperature of solid conveying zone near the feed area was found to have
the most significant influence [5]. Additionally, the temperature of water cooling not
only affects the extruder energy efficiency, but also determines the chiller power con-
sumption. In this paper, the aforementioned operation variables will be considered in
the analysis of extruder energy efficiency, the experimental results will provide use-
ful information for industry to incorporate the energy management system, and further
reduce energy cost in the plastic production line.

2 Fundamentals of Polymer Extrusion Process

Due to the poor heat conduction, polymer materials are usually processed through ex-
trusion. Single screw and twin screw extruder are the most common types being widely