The characteristics of low temperature carbonization for producing active carbon and solid fuel char were investigated by using a thermogravimetric analyzer (TGA) and a kiln type reactor.
The effects of carbonization temperature (350-900℃), caking property in terms of free swelling index (0-7), residence time (50-85min), heating rate (10-900℃/min) and the composition of seven different parent coals on the reactivity of carbonization and the physical properties of char have been determined. The experimental results from TGA showes that heating rate has a slight effect on the weight loss, but the carbonization temperatures (450-650℃) produce a significant effect on the weight loss.
The temperature-time programming of carbonization in a kiln type reactor was established based on the softening, fluidity and solidification temperature of coal.
The weight loss in the kiln type reactor reached to 28% at 650℃ and the amounts of gases and tar increased proportionally with the volatile content of the parent coal.
Depending upon the plastic property and volatile matter content of different coals, the weight loss of coal was reached the values of 1.7-9.2% under the isothermal reaction at fluidity temperature. The variation of residence time at a same carbonization temperature exhibits the different weight loss of each coal, but each coal finally approached to the limiting values.
The form of produced ball shape-char in the kiln type reactor was different from that of char in the fixed bed reactor. The size of ball char formed from different coals increased with increasing fluidity (Dial Division Per Minute), especially over 3000.
An elemental analysis of the remaining char indicated that the relative amount of H/C decreased significantly with increasing temperature. The decomposition rate of sulfur was faster than that of coal itself thus, the sulfur content of char could be lower than that of the parent coal about 30%. On the other hand, nitrogen evolution was negligible within this experimental temperature ranges.
Pore structure showed that maximum micro and macropore volumes occured around 600℃ but a partial collapse of pore structure over 750℃ was observed owing to repolymerization.
From the experimental results of hardness and surface area of char it is regarded that the optimum temperature range for producing active carbon and solid fuel should be in the 500-700℃. However higher reactivity of char-$O_2$ reaction by TGA were detected in the ranges of 600-650℃.
