TABLE I.2 Composition of Different Feedstocks (percentage)

 

Poplar Woodchips

Wheat Straw Dry

Dry Switchgrass

Dry Corn Stover

Miscanthus

Acetic acid

1.9

0.0

0.3

0.0

0.0

Ash

0.6

6.4

6.0

7.0

2.0

Cellulose

23.7

39.3

32.2

35.0

38.2

Extractives

1.9

4.2

13.6

5.0

6.9

Lignin

15.7

14.5

17.3

18.5

25.0

Water

48.0

5.0

0.0

2.5

3.6

Xylan

8.1

30.6

27.9

28.0

24.3

Glucose

0.0%

2.7%

4.0%

 

a wet-weight basis)—a 2 percent water content would reduce the price to ($70/ton)(0.98) = $68.60/ton. Another alternative would have been to augment every percentage composition proportionally so that the sum reached 100 percent. The two approaches have the same effect, but the former is more efficient.

ETHANOL-BIOREFINERY SIMULATION MODELS

Model for Corn-Grain-to-Ethanol Plants

The corn-grain-to-ethanol process is well developed and understood and is used by 130–150 ethanol plants in the United States alone; hence, it is a good starting point to evaluate the modeling method with SuperPro Designer. Because a previous study analyzed the corn-to-ethanol process with SuperPro Designer (Kwiatkowski et al., 2005), it was thought best to remodel the process with the panel’s simplification constraints (discussed in Chapter 3) and any price changes in costing and to compare the results with those of the prior study. The panel’s initial model would not only validate the approach but also verify that it calculated all the mass balances correctly and performed consistent energy-balance calculations for the process.

Figure I.1 shows a simple schematic of the corn-grain-to-ethanol manufacturing process, and Figure I.2 shows the corresponding schematic in SuperPro Designer. For adequate separation of concerns, the process was divided into three sections: preprocessing, production (fermentation), and recovery, including



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement