Ash and deposit characteristics from oil-palm empty-fruit-bunch (EFB) firing with kaolin additive in a pilot-scale grate-fired combustor

Abstract In the present work, we studied alkali-related problems arising from oil-palm empty-fruit-bunch (EFB) combustion and investigated countermeasures to overcome these problems by using kaolin as an additive. All of the experiments were conducted in a pilot-scale grate-fired combustor (150 kW th ). The composition and structure of the ash and deposit samples were investigated. In addition to pure EFB combustion, kaolin was co-fired with EFB by three different means. Kaolin was exploited at the stoichiometric amount required (8% of EFB on dry mass basis). Sintering profoundly influenced the process of the combination of Si and K to form K-silicates, which readily became molten under high-temperature combustion. Deposition intimately entailed a KCl-condensate, impeding the heat uptake by the heat transfer surfaces. Kaolin was found to be a very promising additive that could shift the equilibrium towards K–Al–silicate formation and hence remarkably discourage sintering and fouling. Complete pre-mixing of kaolin with EFB tended to be the most appropriate approach to counteract such problems. A sharp decrease in the deposit mass corresponded with a deposition flux of 4–12 g/m 2 h such that heat transfer to the air–water-cooled probe appeared to be unaffected.

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