Energía Fotovoltaica

Preliminary Design for Cellulosic Ethanol Production Facility
Capable of Producing 50 MMgal/yr
The goal of this project was to develop a complete preliminary design for a
cellulosic ethanol facility with a capacity of 50 MMgal/yr of ethanol.
The main components of the facility were first approximated by scaling
down the design prepared by the National Renewable Energy Laboratory for a 70MMgal/yr cellulosic ethanol facility [1]. While preparing the preliminary design for
this process a better understanding of the requirements for the facility was
developed, allowing for the enhancement of detail for the saccharification,
fermentation, and separations sections. Pre-treatment design was solely based
upon required residence times.
Corn stover was initially considered as the rawmaterial of choice, as
requested by the Client; although, attention was given to incorporating another
possible feedstock (wheat straw).

Central location of the plant to the raw

material, while balancing the factors involving product transportation, was to be
optimized. An analysis of the environmental impact of removing corn stover from
fields to use as a feedstock was also requested tobe included in the completed
design.
A final economic analysis of the cellulosic facility was to be based upon as
12% after-tax rate of return over 20 years, with 5-year MACRS depreciation.
Working capital was to be assumed to be 50% of the first-year cost of
manufacturing without depreciation (COMd), with zero salvage value.

Any

available subsidies offered by the government were also tobe included in the
economic analysis.

Cases including and not including the subsidies were

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requested to be presented in the final deliverable.
Results
A block flow diagram for the overall process is given in Figure 1. A brief
description of the important processes is given below.
Feed Handling: Figure 2
The corn stover or wheat straw is taken from storage, washed, and
shredded.The wash water is condensate from the separations section (Unit
A400). The used wash water is sent to a clarifier and the remaining solids are
disposed. A portion of the used wash water is sent back to a storage tank for
reuse.
Pretreatment and Conditioning: Figure 3
The feedstock is then steamed and reacted in the acid hydrolysis reactor
trains. Afterwards, the product is sent to theblowdown tank to remove the solids
and liquid components. The resulting slurry is then sent to solid/liquid separations
where the excess acid is neutralized and the gypsum is removed. The
hydrolyzate is then sent to saccharification and fermentation (Unit A300).
Saccharification and Fermentation: Figure 4
In this block, the hydrolyzate is reacted with bacteria grown in the seed
train reactors. Theresulting ethanol mixture is sent to separations for distillation
and the waste gas is sent to the scrubber in the same section.
Separations
In this section, the ethanol is distilled in the rectification section (Figure 5),
purified of excess water in the dehydration (Figure 6) and evaporation sections

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Figure 1: Cellulosic Ehtanol Process

3

3

Figure 2: Feed Handling

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Figure 3: Pretreatment and Conditioning

5

5

Figure 4: Saccharification & Co-fermentation

6

6

Figure 5: Rectification

7

7

Figure 6: Dehydration

8

8

Figure 7: Evaporation

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9

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(Figure 7), and sent to storage/blending (Unit A700). The solids are removed
from the slurry and sent to the boiler to be combusted and the waste gases are
sentthrough the scrubber. Excess condensate is sent to wastewater treatment
(Unit A600).
Storage
Here, the ethanol is blended with gasoline and stored. Some corn steep
liquor is fed into the process to aid in bacteria production. This is also the location
where purchased enzyme and sulfuric acid are stored and pumped to their
respective destinations.
Burner/Boiler Turbogenerator
Here, methane...