Determination of energy value and ash-sulfur content of clean fuel obtained from lignite carbonization at different heating rates

Abstract

Carbonization (low-temperature pyrolysis) is an economical and efficient method used to obtain solid products from lignite and improve calorific value. This research focused on the morphological and structural properties as well as the effect of pyrolysis heating rate on the solid product yield. Experiments were performed at 500°C, with a nitrogen gas flow of 200 mL/min, residence time of 60 min, and different heating rates (5, 10, 15, and 20°C/min). Proximate and ultimate analyses of the char products obtained from each experiment were performed. The changes in the char morphology and chemical structures were investigated via scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and the Brunauer-Emmett-Teller (BET) method. The effects of the different heating rates on the char structure were determined. The highest char yield (52.98%) and the highest C (49.45%) and the lowest S (2.51%) contents were determined in the char obtained from a heating rate of 15°C/min. The highest calorific value (5603 kcal/kg) was also calculated at this heating rate. These results showed that the chemical and physical properties of char at a heating rate of 15°C/min were better than those at other heating rates. As a result, a valuable solid fuel with high energy value could be obtained from low quality lignite.