Potential of Energy Saving for Bioethanol Plant by Polygeneration Integration

Economic competitiveness of bioethanol production strongly depends on the amount of heat and power consumed during the production process. Integration of different energy conversion processes by polygeneration is one of solutions to maximize the use of energy resources to best meet user’s the energy demands. In this study, biogas generation, fuel cell system and a greenhouse are integrated in the bioethanol plant to form a polygeneration system. Products of the polygeneration system include heat (steam), electric power and by-products (biogas, fertilizer, animal food, etc.). Simulation of the polygeneration system is carried out by Simulink, and the detailed energy flow and mass balances of the whole polygeneration plant were presented. Energy saving potential for the polygeneration plant is analyzed to find the optimum configuration by maximizing electricity production while producing sufficient heat from both the fuel cell system and pellets burning to satisfy the energy requirements of the whole plant. The result showed that for the studied polygeneration plant (84,000 ton/year bioethanol production), 65% of the stillage (60 ton/h) is used for biogas production; the rest is dried out and then burned to generate steam to cover the unsatisfied heat demand. After covering the energy demand of the whole plant, 3.6 MW of electricity can be sold to the grid. Additionally, some by-products can also be generated, such as forest fertilizer.