03.08.2015   Biotechnology. for Fuels and Chemicals

Variable Costs of Plant Operation

The estimated variable costs of operating a 40 million-gal ethanol plant excluding the cost of feedstock materials are shown in Table 3. These costs were compiled using data from the California Energy Commission (10), Pacific Gas and Electric (11), Yancey (9), and Northwestern Corpora­tion (12). The largest components of variable cost, excluding the feedstock, are the costs of natural gas and processing materials. The sum of all com­ponents is $0.479/gal of ethanol (Table 3). The estimated variable cost is $0.599/gal of ethanol if the DG is dried, when using corn as the feedstock.

Estimated Costs of Producing Ethanol from Selected Feedstocks for a 40 Million-Gal Facility ($/gal of ethanol)

Feedstock

Feedstock cost per unit of ethanol

Credit

for

coproducts

Net

feedstock

cost

Total

variable

cost a

Total

cost b

Culled oranges

3.92

NA c

3.92

4.40

4.51

Other tree fruit

1.42

NA c

1.42

1.90

2.01

Grapes

6.79

0.26

6.53

7.01

7.12

Raisins (high price)

3.36

0.06

3.30

3.78

3.89

Raisins (low price)

2.55

0.06

2.49

2.97

3.08

California corn

1.21

0.26

0.96

1.44 d

1.55 d

Midwestern corn

0.92

0.26

0.67

1.15 d

1.26 d

a Total variable cost includes the net feedstock cost plus the estimated variable cost of $0.479/gal of ethanol, from Table 3.

b Total cost includes the total variable cost plus the estimated fixed cost of $0.11/gal of ethanol.

c NA, not available.

d This estimate pertains to the case in which the DG is not dried. The total variable cost and the total cost will be higher by $0.12/gal if the DG is dried.

These estimates are somewhat higher than the estimated variable cost of $0.392/gal for a 40 million-gal dry-mill plant provided by Whims (13) and the average cash operating cost of $0.417/gal for dry mills reported in a survey of ethanol producers for 1998 (14). The difference is owing primarily to the higher cost of natural gas in California at the time we prepared our estimates. The prices of natural gas we use are explained in Table 3.

The estimated feedstock costs for the materials we examine range from $0.92/gal for Midwestern corn to $6.79/gal for grapes (Table 4). We adjust these costs for the value of coproducts generated when using grapes, rai­sins, or corn, and we express the adjustments on a per-gallon-of-ethanol basis. The coproduct values include $0.26/gal of ethanol for grape residue sold to the concentrate market, $0.06/gal of ethanol for raisin pomace, and $0.26/gal of ethanol for DDG [5]. The adjusted, net feedstock costs range from $0.67/gal of ethanol for Midwestern corn to $6.53/gal for grapes (Table 4). The total variable cost of ethanol production, which includes the net feedstock cost and the nonfeedstock variable costs, ranges from $1.15/ gal for Midwestern corn to $7.01/gal for grapes (Table 4). The total cost includes an additional $0.11/gal for all feedstocks. The costs shown for corn in Table 4 pertain to the case in which DG is not dried. An additional $0.12/gal of ethanol must be added to the total variable cost and total cost if the DG is dried.