Optimisation of biomethane from palm oil mill effluent for offsite utilisation

Abstract

Palm oil mill effluent (POME) is a source that can be used for biogas generation that can be a substitute for fossil fuel. High content of biological oxygen demand and chemical oxygen demand of POME has the advantage to produce large amount of biogas through anaerobic digestion. The purpose of this research was to develop a mathematical model to determine the optimal process pathway of biogas, covering from the purification technology to the mode of transportation and utilisation by using a mixed integer programming model and general algebraic modeling system as the solver software. A case study based on PPNJ Kahang palm oil mill was conducted to run and test the model, in which different target locations with different utilisation modes were chosen. The model chose membrane scrubber as the purification technology and truck transportation to the targeted site, and electricity generation as the optimal pathway for biogas processing and utilisation. Total capital investment of 2,934,564 USD and yearly operational cost of USD 350,843 would give a payback period of 6 years for this optimal pathway. Sensitivity analysis on feed-in-tariff (FIT) determined that FIT should be increased to 0.116 USD/kWh to ensure that investment in biogas is worthwhile. Sensitivity analysis on compressed biomethane (CBM) was performed to determine the impact of product price on the biomethane process pathway selection. The sensitivity analysis revealed that the price of CBM has an impact on the model. Sensitivity analysis suggested that the CBM sales price should be at least 8.2 USD/MMBtu to be economically feasible and 12.9MMBtu to be profitable. In addition, a subsidy of 2.67 USD/MMBtu should be imposed for CBM project to ensure its economic viability and 7.37 USD/MMBtu to be a more economically attractive option than utilised as electricity.