Energy Optimization of Corn-Based Bio-Ethanol Plants
Special Symposium - EPIC-1: European Process Intensification Conference - 1
EPIC-1: New Concepts (NC)
Keywords: Bio-ethanol, MINLP, Superstructures, Heat Integration
In the past it was claimed that the use of “bio-ethanol” as a fuel for replacing or reducing the dependency on fossil fuels was not a sensible option since the energy balance for the production of ethanol from corn was negative as the process is very energy intensive. More recently, it has been countered that with recent improvements in the efficiency of the corn production as well as with the advances in the ethanol conversion, the sign of the energy balance has changed. Clearly, controversy continues about the long-term sustainability of ethanol production from corn.
In this work, we address the problem of synthesizing corn-based bio-ethanol plants through the use of mathematical optimization techniques to reduce the operating costs of the plant, minimize the energy usage and maximize the yields of the plant. With current high prices of gasoline making feasible the deployment of biorefineries, there is a significant incentive for improving the economics of these plants by their optimal design through systematic synthesis and optimization techniques, rather than using ad-hoc or empirical approaches for building such systems.
In the dry-grind process considered in this work, ethanol fuel is produced using corn-kernels as the feedstock. In order to design the bio-ethanol plant, we propose a superstructure optimization approach, where we first construct a flowsheet configuration embedding various process units involved in ethanol production. These units are interconnected to each other through network feed flows and other utility streams. Our objective is to optimize the structure determining the connections in the network and the flow in each stream in the network, such that we minimize the energy requirement of the overall plant while trying to maximize the yields. For this purpose, alternatives for heat integration of process streams, multi-effect distillation and water re-use are included. We also exploit different options for feedstock and processing technologies. The optimization of the system is formulated as a Mixed Integer Non-linear Programming problem, where the model that is optimized involves mass and energy balances for all the units in the system. We optimize the corn-based ethanol plant and present results for the optimal configuration where the energy usage in the system is minimized.
The results of this study show that with the optimal design of the process it is possible to reduce by more than half the steam consumption, which in turn translates in a 11% reduction in the manufacturing cost. Thus, the production of “bio-ethanol” along with other co-products and commodities in a bio-refinery using biomass as a sustainable source of fuels is significantly improved in terms of the economics and energy efficiency.
Presented Thursday 20, 16:20 to 16:40, in session EPIC-1: New Concepts (NC).
