(7) to measure the mass of the sample in real time. Two additional
thermocouples were used to measure the surface and center temperatures
of the pellet during the reaction. N2 was applied as the
purging gas during sample insertion at the beginning of the process
and was also used to cool the residue char before removing it from
the furnace. A CCD camera was installed opposite to the glass window
(9) to record the entire process. ImageJ software was used to
determine the change in the size of the pellet particles via edge
detection of the pictures obtained from the CCD camera.
Selected images of the samples during pyrolysis were analyzed
using the ImageJ software. The swelling and shrinkage behaviors
were analyzed and calculated from the images based on the transient
diameter and height. The transient volumetric swelling and
shrinkage ratio is expressed as:
R ¼ ðVt V0Þ=V0 ð1Þ
where R is the volumetric swelling and shrinkage ratio, Vt is the
transient volume, and V0 is the initial volume.
3. Results and discussion
3.1. Heat transfer properties
The center temperature profiles of the pyrolysis stage under different
temperatures varied from 900 C to 500 C and are shown in
Fig. 2. Two phases were observed during heating to 900 C and appeared
to be more visible under lower temperatures. The first
phase lasted approximately 50 s at 700 C and ended at 105 s
and 195 s, respectively, at 600 C and 500 C. The primary phase
mainly involves the removal of volatile organic matter from the
pellets. This phase could be identified clearly from the change in
the shape of the curve between 350 C and 400 C. The primary
decomposition of most of the components in the center begins in