Biomasa a partir de maíz

Fuel Production from Corn Biomass
Ethanol Production

Introduction

The use of biomass for the production of alternative and renewable fuels is a global focus as the reserve of fossil fuels declines, energy demand increases, and concern for environmental changes increases. On the national front, we are looking for a way to increase our national security, which can include limiting ourdependence on foreign sources of oil. Biomass is material derived from plants or organisms that can be used in industrial process. A number of sources are being utilized for biomass, including corn, sugar beets, switch grasses, and soybeans and are being investigated as possible renewable sources for alternative fuels.

Ethanol produced from biomass is currently being integrated into the fuelingindustry. Ethanol and gasoline mixtures are currently being used as automotive fuel. The amount of carbon dioxide produced by the combustion of ethanol is significantly lower than gasoline (Figure 1).

[pic]
Figure 1: Production of carbon dioxide per gallon of gasoline equivalent.1

In 2006, 83% of the ethanol plants in the United States were using corn as the feedstock for the ethanolproduction; however, the amount of ethanol produced per acre of corn per year is less than that that of other feed stocks such as sugar beets or sugar cane. You are asked to optimize an ethanol plant that uses corn as the feedstock. A schematic for a sample corn plant is shown in Figure 2.
[pic]
Figure 2: Schematic of a corn ethanol production plant.2

The design should meet the followingcriteria:

• 1 million gallons of ethanol must be produced at a purity of 95%
• The conversion factor for sugar to ethanol will never reach above 50%
• The concentration of ethanol in the fermentation process must not exceed 10%, as not to kill the yeast

Background and Economic Data

Different feedstock materials require different processing in order to produce the required sugarfor fermentation by yeast into ethanol. The wet milling process is required for all feedstock material in order to extract the useful sugar or starch from the biomass. In the case of corn, the milling process releases starch. These extracted starches must undergo a hydrolysis process in order to convert the starch to a simple sugar, which can be used in the fermentation process. In thefermentation process, yeast feeds on the sugars and excretes carbon dioxide and ethanol. Both products have application in the area of alternative fuels; the carbon dioxide can aid in the production of biodiesel from algal oil, and the ethanol can be used directly as a fuel, which has a value of $2.54/gal.

As stated in the design criteria, the plant must produce 1 million gallons of ethanol per yearfrom corn, which is bought at $4/bushel of usable biomass. The production of ethanol occurs 24 hours a day for 350 days of the year. The interest rate for this plant will be 8.5% over 10 years. There are four components to the production of ethanol from biomass.

1) Conversion of feedstock to simple sugar
2) Cooling of the sugar slurry to the fermentation temperature
3) Fermentationof ethanol using yeast
4) Purification of ethanol from residual water of the slurry

Feedstock Conversion

The first step of converting feedstock to a simple sugar requires wet-milling, in which the feedstock is mixed with water to a concentration of 15 wt% and is processed into a slurry. The mill runs continuously, with a residence time in the mill of 12 minutes to achieve the requiredparticle size. The size of the mill, Vmill, is 20% larger than the volume of slurry, Vfeed, into the machine to allow for agitation (Equation 1)

[pic] (1)

The cost of this mill is based on its capacity. The cost equation is

[pic] (2)

The supply of water needed to create a slurry of the feedstock and starch is an annual utility cost, given in Equation 3.

[pic] (3)

where...