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Working Paper

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A fermentation plant was designed to ferment and process sugar cane juice into acetone, butanol, and ethanol (ABE) in Brazil. The plant was built to handle a feed of 40 tonnes of sugar per hour in 25% solution. The process runs continuously for 32 weeks out of the year, during the cane harvest, for 20 years.

The two main steps of the process are the fermentation and the separation of the ABE products into the desired 99.5% product purities. The fermentation section of the plant consists of nine 500,000 gallon fermenters that convert the bulk of the sugar cane into ABE products, as well as two 500,000 gallon fermenters that supply fresh cells to these fermenters and a series of smaller tanks that scale up cell concentrations from a test tube scale to the fermenter sizes used in this project. The separation section of the plant consists of a holding tank to store the ABE products, a gas stripper to remove most of the organics from water, a decanter to further separate the products into a butanol-rich phase and a water-rich phase, molecular sieves to remove the rest of the water from the butanol-rich phase, and two distillation columns to purify the products and prepare them for sale.

This design can be deemed a successful one with a 35.67% return on investment and a net present value $118,806,000. Also, the process as a whole was found to be significantly energy positive, with our combustible products having a fuel value of 3.36x108 BTU/hr and our utility inputs being only 2.14x106 BTU/hr. The main reason for our success on these two fronts was the use of a gas stripper and a molecular sieve, which allowed for most of the water in the separation step to be removed without needing to heat it.

Date Posted: 18 November 2010