Impact of pre-treatment for coconut husk by water leaching on fuel and ash characteristics during combustion in a fluidized bed reactor

This study investigated the impact of water leaching of a coconut husk on improving fuel characteristics and preventing bed agglomeration in fluidized bed combustion. The leaching process was conducted in a laboratory-scale setup at water flow rates of 150 ml/min and 250 ml/min, and electrical conductivity (EC) was used to determine the optimum leaching duration. Potassium oxide decreased by up to 40%, chlorine by up to 82%, and ash content practically halved, reaching as low as 2.98% in the best case, as a result of the treatment. Importantly, the fuel’s heating value stayed around 20.5 MJ/kg. Physically, the leached husk exhibited a larger surface area and increased pore volume, corresponding to a rise in volatile matter from 65% to nearly 70%. During combustion tests at 800 °C, the treated coconut husk remained fluidized for much longer, up to 93 minutes, compared to just 32 minutes for the untreated fuel, indicating a strong reduction in bed agglomeration. The details of microscopic analysis revealed that leaching promoted the formation of compounds with higher melting points, thereby preventing the formation of low-melting-point potassium silicates that cause agglomeration. The FactSage program (version 8.2) was used for thermochemical modeling based on the ash composition, and the simulation results confirmed that the ash melting temperature increased from below 900 °C to above 1,300 °C after leaching. These results demonstrate that simple water leaching can effectively enhance the quality of coconut husk fuel and help prevent operational issues in fluidized bed combustors.