COMPARING PHYSICAL AND THERMAL CHARACTERISTICS OF HANGU-ORAKZAI AND MAKHARWAL COAL AND CHAR IN AN INERT ATMOSPHERE

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