Energy optimization of bioethanol production via gasification of switchgrass

Abstract

Abstract.In this paper, we address the conceptual design of the bioethanol process from switchgrass via gasification. A superstructure is postulated for optimizing energy use that embeds direct or indirect gasification, followed by steam reforming or partial oxidation. Next, the gas composition is adjusted with membrane-PSA or water gas shift. Membrane separation, absorption with ethanol-amines and PSA are considered for the removal of sour gases. Finally, two synthetic paths are considered, high alcohols catalytic process with two possible distillation sequences, and syngas fermentation with distillation, corn grits, molecular sieves and pervaporation as alternative deshydration processes. The optimization of the superstructure is formulated as an MINLP problem using short-cut models, and solved through a special decomposition scheme that is followed by heat integration.The optimal process consists of direct gasification followed by steam reforming, removal of the excess of hydrogen and catalytic synthesis, yielding a potential operating cost of $0.41/gal

Energy and Water Optimization in Biofuel Plants

“…around half the lowest one shown in Table 1. An economic evaluation of this optimal solution yielded a production cost of 1.24USD/gal [44], which is a decrease of 20% with respect to the base case.…”

“…In terms of energy consumption and cooling needs, Fig. 7 summarizes the processes presented before including an optimized process in which ethanol is obtained from fermentation of syngas instead of catalytic synthesis [44] and the results from Philips et al [39]. As it can be seen, corn-based ethanol is together with the gasified-fermentation based process, the most energy intensive.…”

“…The process produces 18 MW of energy and requires 68 MW of cooling. The production cost of this design turned out to be 0.41 USD/gal due to the large contribution of hydrogen to the income as a byproduct [44].…”

“…In this section we apply the first in the methodology to optimize the energy use in flowsheets for the production of ethanol from corn and lignocellulosic switchgrass, which are reported in detail in [43] and [44].…”

“…The process described in [44] consists of four different parts: gasification (followed by gas cleanup), concentration adjustment, sour gases removal and synthesis. We The most profitable process uses high pressure gasification, followed by steam reforming, which increases the production of hydrogen.…”