Abstract:
Physical, structural and thermal characteristics of Hangu-Orakzai and Makharwal
coal samples of Pakistan are investigated in this research by ultimate and
proximate analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD),
Scanning electron microscopy (SEM) and by Thermogravimetric analysis
(TGA). Coal sample were desulfurized by sodium hydroxide solutions of
different molarity. 1.5 molar sodium hydroxide solutions desulfurized 87 % of
the sulfur from Hangu-Orakzai coal while 60 % from Makharwal coal, more than
at any other tested molarities. Thermogravimetric analyses of both raw coal
samples were performed in an inert (nitrogen) and air (oxidizing) atmospheres at
a heating rate of 10 0C/min and atmospheric pressure of 10 L/min. Based on better
desulfurization and atmospheric comparison in TGA, and easy availability of air
oxidizing atmosphere in the industry rest of the thermogravimetric study was
continued with Hangu-Orakzai coal sample at different heating rates (10, 25, 40
0C/min) and air flow rates for combustion (3.5, 7 and 10 L/min). The research
also computes activation energy determination from the raw and sodium
hydroxide treated coal. The kinetic parameters for the coal combustion were
investigated by the Arrhenius equation using 1st order kinetics. Hangu-Orakzai
raw and treated coal sample have amorphous structure while Makharwal sample
has crystalline structure. SEM analysis of raw Hangu-Orakzai coal sample shows
that surfaces are generally covered with collotelinite, parallel laminated and
debris micrinite. Desulfurized coal sample have rod and spongy like structure
while Makharwal raw coal sample showed plate or rounded, collotelinite nonporous structure. Thermogravimetric results showed that higher activation energy
was required for combustion at low heating rate and higher air flow rate. Coal
desulfurization is not only essential for clean emissions to protect the
environment, but also aids coal degradation at lower activation energy
