Process Design and Economics for Ethanol from Corn Stover Via Dilute-Acid Hydrolysis: Development of a Base-Case Flowsheet for Parametric Analysis of Acid Hydrolysis Processes

摘要

This report presents a flow sheet for a cellulose-to-ethanol plant utilizing high-temperature dilute acid hydrolysis. The process can be divided into six sections: pretreatment, hydrolysis, fermentation, purification, carbon dioxide recovery, and heat generation and waste treatment. In the pretreatment section, the raw corn stover undergoes steam explosion, the lignin is extracted by ethanol extraction, and the amorphous five- and six-carbon sugars removed in prehydrolysis. The crystalline cellulose is hydrolyzed in the hydrolysis reactor. The sugar solution from the prehydrolysis and hydrolysis sections is neutralized and fermented to carbon dioxide and ethanol in a train of continuous fermenters. The ethanol is recovered by a distillation process, and the carbon dioxide is cleaned and liquified. The unreacted solids and various waste streams are either burned or sent to the waste pond. Capital and operating costs estimates are developed for the plant, and the total plant cost is estimated to be $236 million. The prime costs are heat generation, pretreatment, and hydrolysis. The ethanol produced costs $3.60/gal. Elimination of the lignin solvent extraction step and the prefermentation sugar concentration steps are recommended to reduce both the capital investment and energy usage of the plant. The system described in the report was not optimized. Instead it was configured to include a large number of processing steps, not all of which would be included in the same plant, in order to provide a basis for the coding of a simulation program. The ethanol costs reported are therefore much greater than would be achieved in an optimized system. (ERA citation 08:043453)