Effect of oxidative and non-oxidative torrefaction on the properties of Oil palm empty fruit bunches pellets

다국어 초록 (Multilingual Abstract)

Oil palm (Elaeis guineensis) empty fruit bunches (EFB) is solid wastes derived from palm oil production which has not been utilized optimally, hence it is considered as a low economic value resource. This biomass resource can be converted into bioenergy through torrefaction process. Torrefaction is a mild pyrolysis at temperatures ranging between 200 and 300°C and it is generally performed under inert (non-oxidative) atmosphere. The aim of this paper was to compare non-oxidative and oxidative torrefaction processes applying to EFB pellets. Non-oxidative torrefaction was conducted by using a pilot plant namely Counter-Flow Multi Baffle Dryer/Pyrolizer (COMB) with a capacity of 20 kg/h. COMB is a multi-station high moisture flow baffle plate dryer for drying, torrefaction, and pyrolysis. COMB has simple, flexible and movable baffles that could perform drying or torrefaction within a short residence time of up to 5 min, with low gas to solid ratio, and constant temperature difference along the column. Torrefaction with COMB was conducted at 280°C with a residence time of 4 min. Oxidative torrefaction was conducted under air atmosphere in an electric furnace at 280°C with a residence time of 20 min. The results showed a decrease in the equilibrium moisture content (EMC) with a lower EMC observed in samples treated with oxidative torrefaction. The results also showed that torrefaction caused an improvement of hygroscopic property that could make biomass more stable against chemical oxidation and microbial degradation, hence self-heating and auto-ignition during storage could be prevented. The heating value of biomass increased after torrefaction. Non-oxidative torrefaction with COMB reactor resulted in a heating value of 17.90 MJ/kg, which is comparable with the results of oxidative torrefaction (with longer residence time) of 18.28 MJ/kg. The results proposed that torrefaction using COMB reactor could provide a great improvement in the quality of the bioenergetic properties of biomass that make torrefied biomass particularly suitable for cofiring in power plants and as a feedstock for gasification.