Exergoeconomic analysis of lactic acid and power cogeneration from sugarcane residues through a biorefinery approach

The present survey was devoted to exergoeconomically investigating a lignocellulosic-based sugarcane biorefinery developed for cogeneration of lactic acid and power from sugarcane bagasse and harvesting residues, specifically brown leaves (trash). More specifically, this research was aimed at identifying the hotspots of the cost losses in the developed biorefinery. Exergoeconomic parameters including irreversibility-related cost rate, component-related cost rate, total cost rate, relative cost difference, and exergoeconomic factor were determined for all the nine subunits of the biorefinery. In addition, two new exergoeconomic variables called “economic impact ratio” and “economic modification requirement index” were introduced and elaborated throughout this study. After obtaining cost balances for all subunits of the biorefinery, product and fuel rules were considered according to Specific Exergy Costing (SPECO) approach for determining the unit exergoeconomic cost of all streams involved in the process. The unit exergoeconomic costs of lactic acid, power, steam, and liquid digestate were found to be 8.55, 15.61, 15.61, and 17.96 USD/GJ, respectively. The highest total cost rate was determined at 3715.86 USD/h for the steam generation unit, accounting for 43.73% of the total cost rate of the biorefinery. The lactic acid synthesis unit stood in the next rank, contributing to 20.49% of the total cost rate of the system. Overall, attempts to promote the exergoeconomic performance of the biorefinery must mainly focus on minimizing the irreversibility-related cost rate of the steam generation unit.