Improving the Integrated Process of First- and Second-Generation Ethanol Production with Multiperiod Energy Integration

The growing demand and prices of fuel promote the development of technologies to improve the production process of biofuels. The energy integration in sugarcane biorefineries provides better use of utilities and cost reduction besides the possibility of increasing the amounts of ethanol or electricity produced. The latter is a result of the lower steam consumption in the plant, which allows diverting more bagasse to be processed into second-generation (2G) ethanol or electricity. This work assessed two case studies: case study 1 (CS1), which represents a biorefinery that produces first- and second-generation (1G/2G) ethanol and electricity, with disposal of the fraction of xylose, and case study 2 (CS2), where the pentose fraction is used to produce biogas. Differences in process operation conditions influence the design of a heat exchanger network (HEN). To handle this problem, concepts of synthesis of HEN with multiple operation periods were used. The multiperiod HEN synthesis problem is solved using a mixed integer nonlinear programming (MINLP) model. Each period has a different operating condition, and, for solving the MINLP problem, a hybrid meta-heuristic approach was used, which combines tabu search and particle swarm methods. For the cases studied in this work, energy integration can allow for surpluses of up to 8.8% of ethanol and 31.7% of electricity, as well as better use of environmental resources and energy security. The payback time of the HEN investment is a maximum of 5.2 years if the surplus bagasse is diverted to the 2G ethanol.