Numerical Optimisation of Excess Air withRespect to Fibre-To-Shell Ratio duringIncineration Process

Abstract

The incineration of palm oil wastes mainly fibre and shell is currently mixed randomly whichmakes the amount of air required to be difficult to control or to maintain and consequently, thecontrol of flue gas emissions becomes the most difficult task. In this study, five different chemicalcompositions of fibre and shell were obtained from five different palm oil mills in Malaysia. With theexisting of powerful software STANJAN code, the emissions of flue gases were computed using all thedata from the five palm oil mills. The data output from those mills was analysed using analysis ofvariance (ANOVA) and the difference among the data output were found statically not significant,and thus, palm oil mill number three was selected as a base data. From the 24 chemical species, theoptimisation was done based on CO₂, CO, and O₂ emissions only, following the Ambient Air QualityMalaysian Standard (AAQMS). The required amounts of excess air for different ratios of fibre-to-shellwere computed, in addition, a mathematical model relating excess air to the percentage of fibre in theshell was developed. It was found that the percentage of excess air required for any ratio of fibre-to-shell in order to fulfil the requirement of AAQMS, varies from about 65% to 85%. The boiler operatorcan use more than 85% depending on the type of incinerator used, but the problem of increasing theheat loss and thus decreasing the thermal efficiency of the boiler is expected. Due to this reason aglobal optimisation is recommended, taking into account not only the CO emission but also the heatloss due to dry flue gas.