Multi-objective optimization of sugarcane bagasse utilization in an Indian sugar mill

Abstract

Sugarcane bagasse is a valuable lignocellulosic biomass resource in India. This work determines the optimal utilization strategy for bagasse considering economic and environmental objectives. An optimization model is formulated for an existing sugar mill and three potential products of bagasse processing, namely, electricity, ethanol, and pellets are considered. Additionally, options of selling bagasse and utilizing it in the boiler are also considered. Mass and energy balance equations for each of these options constitute the optimization constraints. The primary decision variables are the utilization patterns of bagasse and trash collected from farms. Three different objective functions, namely, NPV maximization, greenhouse gas (GHG) emission minimization, and water footprint minimization are considered. This results in the formulation of a mixed integer linear programming problem with three different objectives. The model was applied to a mill processing 181 Mg/hr of sugarcane in Kolhapur region of Maharashtra, India. The results recommended electricity production from bagasse and trash for optimizing NPV and GHG emissions. A strong trade-off was observed between water footprint and the other two objectives. Ethanol and pellet prices must increase by 77% and 122%, respectively, to become economically feasible. The model was extended to consider a set of 31 mills in the region and the possibility of transporting bagasse and trash between the mills. The regional integration increased the NPV of the sector by 37%. Moreover, the break-even selling prices of ethanol and pellets reduced by 30% and 35%, respectively, due to this regional integration. This provides a strong support for exploring industrial ecology approaches for the region.