Co-pelletization of Torrefied Cotton Stalk and Coffee Husk as an Alternative Energy Source for Cement Pyroprocessing

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Addis Ababa University


Cement manufacturing is an energy and emission intensive process. The use of alternative fuels to replace coal contributes to energy security and the total environmental footprint of the cement industry. This study investigated the suitability of co-pelletized torrefied coffee husk and cotton stalk as alternative energy mix for cement pyroprocessing. Process parameters which affect the calorific value such as particle size (100-125����, 125-250 ���� and, 250-500 ����), mixing ratio (0.33, 0.5 and 0.67) and torrefaction temperature (200℃, 250℃ and 300℃) were optimized via Box Behnken design (BBD). Characterization of raw coffee husk, cotton stalk and mixed torrefied pellet for proximate analysis, ultimate analysis, calorific value, bulk density, ash composition, Thermogravimetric analysis (TGA) and Fourier transmission infrared spectroscopy analysis (FTIR) were determined to understand the physiochemical and thermal property of the fuel. Based on the results, the optimal conditions were (particle size=100-125����, mixing ratio=0.62 and torrefaction temperature of 300℃), with a maximum calorific value of 5320.72kcal/kg. The optimum mixed torrefied pellet showed a decrease in moisture content (1.67%), volatile content (50.45%), hydrogen to carbon ratio (0.044) and oxygen to carbon (0.4239), while the fixed carbon (37.14%), elemental carbon (68.1195%) and calorific value (5322.31kcal/kg or 22.283 MJ/Kg) increased considerably. As shown in the FT-IR analysis, loss of -OH groups resulted in decreased hydrogen-bonding capacity which makes the mixed torrefied pellet more hydrophobic. Moreover, the TGA analysis showed that the lignin content at higher torrefaction temperature was higher which was responsible for the higher heating value of mixed torrefied pellet. In view of the results obtained in this study, the proposed mixed torrefied pellet has a potential to be used as a source of alternative energy for cement industries.



Torrefaction, Co-pelletization, Alternative energy, Cotton stalk, Coffee husk