Torrefaction is a well-known method to thermally treats biomass at lower temperature range (200 to 300 Celcius) under inert atmosphere. However, the continuous supply of pure inert gas on large scale resist the commercialisation of this process. To investigate the effect of combustion gas (flue gas) on torrefaction performance of oil palm fronds leaves (OPFL) and stems (OPFS), both samples were torrefied at 200 Celcius for 30 min in a vertical tubular reactor under the atmosphere of combustion gas produced from wood pellets and nitrogen (inert) gas. The major components of combustion gas were nitrogen and carbon dioxide (total 76 vol% to 83 vol%) and the rest of the mixture contained oxygen, carbon monoxide and hydrogen. The effects of combustion gas atmosphere on the torrefaction performance of OPFL and OPFS including solid yield, calorific value, energy yield, proximate and ultimate compositions were investigated and compared with those of nitrogen atmosphere torrefaction. The combustion gas torrefaction resulted in lower solid yield and energy yield but with higher energy density (calorific value, carbon content) as compared to nitrogen torrefaction. Under combustion gas atmosphere, torrefaction of OPF stems gave higher solid yield (84.66 wt%) than OPF leaves (80.85 wt%) while solid yield of both samples under nitrogen atmosphere was almost same (88.02 wt% and 88.54 wt%). The increase in solid conversion under combustion atmosphere was caused by the partial oxidation took place in the presence of oxygen. Non-condensable gases at the outlet of the torrefaction reactor contained carbon dioxide and carbon monoxide.

---

Torrefaction experiments of OPF leaves and OPF stems were conducted by using experimental setup. The setup contained two vertical tubular chambers made of stainless steel, one chamber for generating combustion gas (with internal diameter 10 cm and height 20 cm) and another chamber (with internal diameter 12 cm and height 15 cm) for conducting torrefaction experiment, both equipped with electric heater, respectively. Four thermocouples at different heights of the torrefaction reactor were used to measure the temperature at different depths of the biomass bed and one thermocouple was installed in the combustion chamber. For the torrefaction under combustion gas atmosphere, first, 700 g to 800 g of biomass wood pellets were placed in the combustion chamber and were ignited manually. During burning of wood pellets, air was supplied from the bottom of chamber.The duration of combustion with flame took place for approximately one hour. Once the flame went off and red glowing phase (stable combustion phase) appeared, the combustion chamber was closed tightly and thermocouple was inserted into the chamber and then combustion gas was directed into the torrefaction reactor, in which prescribed quantity of OPF leaves (100 g) or OPF stems (200 g) were kept and its temperature increased from room temperature to 200 Celcius with the heating rate of 4 Celcius /min, then kept at 200 Celcius for 30 minutes of process time. The combustion gas was continuously flowing during heating, processing and cooling phases. Throughout the experiment (from heating to cooling phase) the air was continuously supplied to the combustion chamber from the cylinder at 5 L/min which was controlled by mass flow controller. Temperature readings were recorded every 5 minutes during heating, processing and cooling phase. Combustion gas was sampled at 15 and 30 minutes of the processing and torrefaction gas was sampled at 10, 20 and 30 minutes of the processing time. After the process, torrefied samples were collected manually from the reactor, weighed and transferred into airtight containers until characterization. Liquid product was collected from two condensers fitted at the bottom of the reactor.Torrefaction under nitrogen (inert) atmosphere was also performed by following the same procedure mentioned above except that, the pure nitrogen was supplied into the reactor instead of combustion gas, with the flow rate of 5 L/min

---

Solid and Energy Yield: The torrefaction process under combustion gas resulted in lower solid yield and energy yield compared to nitrogen torrefaction. This could impact the overall efficiency and productivity of the torrefaction process when using combustion gas.

Energy Density:Despite lower energy and solid yield, combustion gas torrefaction resulted in higher energy density, indicated by higher calorific value and carbon content. This suggests that the combustion gas atmosphere leads to a more concentrated and potentially more valuable energy product.

Understanding Process Dynamics: Understanding the effects of different atmospheres (combustion gas vs. nitrogen) on torrefaction performance, providing valuable insights for optimizing the process and making it more practical for large-scale implementation.

Energy Density Improvement:The combustion gas torrefaction process, despite lower overall yield, provides a benefit in terms of higher energy density. This is particularly important for applications where a more concentrated energy product is desirable.

---

Increased Calorific Value under Combustion Atmosphere:The torrefied biomass under combustion atmosphere showed higher calorific value, carbon contents, and fixed carbon. This suggests that the torrefaction process can enhance the energy content of the biomass, making it potentially attractive for energy applications.

Effect of Torrefaction Atmosphere:The text mentions that the torrefaction atmosphere has an impact on performance. Understanding these effects is crucial for tailoring the torrefaction process to specific applications.

Utilization of Flue Gases:The conclusion suggests that flue gases from industrial boilers can be utilized in the torrefaction reactor instead of pure nitrogen gas, making the process economically feasible. This could potentially lead to cost savings and increased efficiency.

Economic Feasibility and Commercialization:The suggestion of using industrial flue gases instead of pure nitrogen gas implies a consideration for economic feasibility. If the process becomes more economically viable, it could lead to commercialization opportunities.

---