October 19, 2011

Ethanol Industry vs Cattle Industry: Part III - Ethanol Production

I get asked the question "how does a person with a PhD in beef nutrition get a job at an ethanol plant?" almost weekly.   It was a situation of being in the right place at the right time and casually chatting with the right person.  I think that I look at the ethanol plant in a totally different way as most people.  I often refer to the plant as my stainless steel cow.  The way that ethanol and distillers is made is not much different in concept than how a steer turns the corn to beef and fertilizer.  There are more similarities between and ethanol plant and a cows digestive system than you think. 

Here are a few:
Cow                                            Ethanol Plant
Teeth                                          Hammer Mill
Rumen (fermentation)               Fermenters
pH sensitive                               pH sensitive
Hot/Cold sensitive                     Hot/Cold Sensitive
Can get infections                     Can get infections
Difficult to Control                     Can be as cantankerous
                                                       as a cow

The rumen in a cow is very sensitive to pH, changes in diet, temperature, changes in microorganism species and many other variables.  The yeast in the ethanol plant are sensitive to the same changes as a cow and use fermination to create desired substrates.  While a cows rumen microorganisms produce volatile fatty acids and other substrates that are useful to the cow the yeast in the fermentation tanks digest corn starch and produce ethanol and distillers grain.  Both systems require protein, energy, the right pH and the right temperature to perform efficiently. 

I included a schematic on the process of making ethanol and distillers.

Step1 - #2 yellow dent corn is the main cereal grain used in the ethanol industry, milo and wheat can also be used but the efficiency is different.  Corn is the more economical cereal grain in the US.  Historically it was thought that ethanol plants can use damaged or off spec corn and that they are the bottom feeders of all the corn users.  They can, but it comes at an efficiency cost and a risk of introducing bacteria to the process.  Once the corn is received into the ethanol plant it is ground into a flour like texture.
Step 2 - Mash Prep - Water, urea (nitrogen source for yeast), alpha amylase (catalyst to help chemical reactions happen) and heat is added to the ground corn.  There is a flash heat process that kills the bacteria that could enter the plant and cause harm to the plant.
Step 3 - Fermentation - Processes vary between plants (batch or continuous flow) but the end result is still the same.  The yeast get to live in the slurry that was created and work their magic turning the starch into ethanol.  The part of the plant take great care and attention to detail as the yeast are sensitive to changes in their environment.
Step 4 - Distillation - This is where the ethanol is pulled out of the slurry mixture.  Steam is used to float the ethanol to the top of a large column and everything else is sent on down the line to make distillers grain and recycled water
Step - 4b - Ethanol is blended with denatured alcohol to "poison" it to prevent human consumption.  It won't kill you if you drink the blended ethanol but it will make you sick. 
Step 5 - Centerfuge - The stillage (what is left after the ethanol is removed) is run through a centerfuge that separates the solids and liquids, the solids (wet cake) are sent down the line to get the syrup added.
Step 6 - Evaporation - The liquid portion of the stillage goes through a series of evaporators and condensed down to syrup and water.  The water is sent back to the front end of the plant to be reused and the syrup is added to the wet cake.
Step 7 - The now wet distillers grain (wet cake + syrup) can either be dried, partially dried, or left wet and sold as distillers grian.

Some plants will sell some of the syrup that is not blended with the wet cake.

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