Determination of processes suitable for cotton stalk carbonization and torrefaction by partial combustion using a metal kiln

• Cotton stalks carbonization and torrefaction by partial combustion was developed
• Carbonization cycle time of cotton stalks of two hours was achieved
• Mass and energy yields of cotton stalks carbonization are 29% and 47% respectively
• Cotton stalks charcoal suitable for cooking was obtained
• Shorter combustion time leads to torrefaction close to severe degree

In this work, the technical feasibility of cotton stalk carbonization and torrefaction was studied. A metallic homemade cylindrical furnace 60 cm in diameter and 90 cm in height was used for the experiments. A partial combustion process was used both for carbonization and torrefaction. Three carbonization methods were defined based on the amount of air supplied and cotton stalks introduced in the kiln. Torrefaction process was based on a shorter combustion time of 2 min during the partial combustion, in order to avoid cotton stalk carbonization. Mass and energy yield, proximate analysis and the unburnt cotton stalks proportion (ratio of non-carbonized cotton stalks over carbonized cotton stalks) for each process were determined. In order to avoid the burning of the loaded cotton stalk, and to optimize charcoal quality, an appropriate combustion time of 7 min was found for the carbonisation process. The anhydrous mass yield for the best carbonization process selected is about 28.4% while energy yield is 45.8%. The carbonized cotton stalk has 24.15% and 67.44% of volatile matter and fixed carbon content respectively. The carbonized cotton stalks are suitable for cooking purpose because their volatile matter content allows a rapid ignition. The torrefaction process has a mass and energy yields of 64.1% and 75.3% respectively. Torrefied cotton stalks are more appropriate for gasification compared to carbonized cotton stalks.