Tanakorn Kittivech

Palm empty fruit bunches (EFB) is known as problematic biomass due to its high alkali content, i.e., more than half of inorganic matter is potassium (K). EFB when used as a fuel in fluidized beds with silica sand as bed material could form the sticky compound K₂O·nSiO₂ starting at around 750 °C and adhere bed particles together, resulting in bed agglomeration. Blending EFB with rubber wood sawdust (RWS) could improve the chemical properties and consequent ash composition of the blended fuel. In this study, RWS was blended with EFB at three ratios: RWS:EFB = 25:75, RWS:EFB = 50:50, and RWS:EFB = 75:25. Adding RWS to the fuel prolonged de-fluidization time. The high content of CaO in the RWS ash acted as an inhibitor to prevent the formation of K₂O·nSiO₂ and, instead, enhanced the formation of K₂CO₃, a higher melting point compound, which reduced bed agglomeration. During the experiment using RWS:EFB = 75:25, no bed agglomeration was found.

The high level of potassium compounds in Empty Fruit Bunch (EFB) induces ash-related problems, such as bed agglomeration, which is caused by the formation of a low-melting-point sticky compound: K₂On·SiO₂, especially in fluidised bed gasification using silica sand as bed material. Dolomite was found to be an effective alternative bed material for preventing bed agglomeration by the release of CaO via calcination processes during gasification. CaO acts as a catalyst to inhibit bed agglomeration by possibly enhancing the formation of K₂CO₃ instead of K₂O·nSiO₂. Alumina sand was also found to be a suitable alternative bed material to prevent bed agglomeration; however, due to the relatively high density of alumina sand, high gas velocity was needed to ensure good mixing and fluidisation. Using both dolomite and alumina sand as bed materials yielded a product gas having similar higher heating value (HHV) to that when using silica sand (i.e., 3.8–3.9 MJ/Nm³).