Shapley-shubik index incorporated debottlenecking framework for sustainable food-energy-water nexus optimised palm oil-based complex

Abstract

Palm oil mill effluent (POME) elimination has been considered recently as the alternative to expensive biogas recovery to conquer environmental criticisms in the palm oil industry involving the release of biogas (i.e., a primary contributor towards climate change), during POME treatment. With POME elimination and mill-refinery integration considered, the integrated palm oil-based complex (POBC) serves as an appropriate system for sustainable food-energy-water (FEW) nexus evaluations. In this respect, multi-objective optimisation and debottlenecking of POBC has been suggested to address the economic and environmental trade-offs in palm oil mill (POM) for cleaner production. In this study, a stepwise debottlenecking framework was proposed to include previous fuzzy multi-objective optimisation approach and a new debottlenecking method to improve the fuzzy optimal POBC design and evaluate the impact of process on FEW nexus contributions. Each process creates distinctive impact or influence on the POBC performance. Shapley-Shubik Power Index (SSI) has been applied in the notion of power for yes-no voting systems. By evaluating the operate-fail possibilities of internal processes, SSI can be utilised to allocate the power of each process in achieving or failing the POBC performance target, prior to identifying the system bottleneck (SB) in terms of process stage. Therefore, a novel process-level debottlenecking approach with SSI incorporation for a sustainable FEW system was proposed. The SB of greatest impact on overall POBC performance within the fuzzy optimal flowsheet was identified based on SSI allocation and weightage assignment considering decision-maker's interest in multiple goals. Subsequently, the debottlenecked POBC flowsheet with improvement in SB process parameter was generated subjected to profit maximisation and environmental constraints. In this study, the nut/kernel separation and biomass cogeneration system was identified as the SB of fuzzy optimal POBC. The debottlenecked results show 0.8% and 51% of profit and net energy improvement upon 30% increment of boiler efficiency. The debottlenecked flowsheet is validated in the benefit-to-drawback ratio analysis with a feasible score of 3.9. The POME-eliminated POBC generated via the integrated multi-objective optimisation and debottlenecking framework is applicable for POM retrofit to secure 13%, 97% and 47% of improvements in terms of economic potential, greenhouse gas emissions and water footprint compared to the status quo biogas utilisation scenario. The results of the study could aid palm oil holders in real-life planning of budget distribution and maintenance schedule for process stages in the retrofitted POM.