Using the aggregated system exergoeconomic methodology as a comparative tool for the cost-effectiveness of the sugarcane biorefinery options

Abstract

The overall cost-effectiveness of integrated sugarcane biorefineries were assessed using the aggregated-system exergoeconomic methodology. Using A-molasses from the sugar mill as feedstock, five biorefinery scenarios were simulated in Aspen Plus® to produce (i) succinic acid (SA100); (ii) short-chain fructooligosaccharides powder (FOS (p)100); (iii) short-chain fructooligosaccharides syrup (FOS(s)100); (iv) a mixture of short-chain fructooligosaccharides syrup from 30% A-molasses and succinic acid from the remaining 70% of A-molasses (SA70-FOS(s)); and (v) a mixture of short-chain fructooligosaccharides syrup from 30% of A-molasses and succinic acid from a mixture of remaining 70% A-molasses and residual sugars from the short-chain fructooligosaccharides plant section (SA70I-FOS(s)). The results of exergoeconomics showed that A-molasses and chilled water were the most significant sources of input cost rates for all the scenarios. Scenario SA100 obtained the highest total cost rate and relative cost difference of 1690 US$/h and 0.38, versus 547 US$/h and 0.09 for scenario FOS(s)100, which were the lowest. Contrary to the requirement for optimal performance, all the scenarios have higher irreversibility cost rates than their respective investment cost rates except scenario FOS(p)100, with an exergoeconomic factor of 0.55, which is the closest value to 0.60 for an ideal cost-effective process. With relatively low total cost rate and relative cost difference of 1052 US$/h and 0.18, scenario FOS(p)100 emerged as the most cost-effective biorefinery for integration into the sugar mill. Sensitivity analysis demonstrated that scenario FOS(p)100 remained relatively optimal within ±20% changes in its capital investment and A-molasses prices. The cost-effectiveness of the other scenarios could be improved by employing more exergy efficient designs at the expense of capital cost.