2 replies to this topic

[Limilicious]

Taking corn as an example in fermentation processes. 1 bushel of corn produces about 2.7 gallons of ethanol, 18 pounds of DDGS and 18 pounds of carbon dioxide. Or somewhere around that.

So you have corn and you grind it up and throw in the water, enzymes, yeast and other things as needed. Then you have it in a tank for fermentation. During the fermentation process, the yeast eats up and produce carbon dioxide and it bubbles up into the tank and goes through the top vent that goes somewhere.

I really want to know is the carbon dioxide that didn't bubble out. How much exactly is left in the liquid? Is it a significant amount? I've researched on these fermentation processes that produces ethanol. The carbon dioxide just "disappears" and comes out at the end product being collected.

The stillage is split into thin stillage and animal feed. The animal feed will be dried so CO2 should evaporate out since its boiling point is like -50 something degrees C. The thin stillage is either returned back to the fermentation process so there would be less process water or processed. If the thin stillage is processed, corn oil can be removed from it and then turned into syrup or just turned to syrup. The syrup is then mixed back with the animal feed and then dried to become DDGS or the wet version.

So there are really two things I'm asking. Is there a significant amount of carbon dioxide in the stillage? And how would you remove it so it wouldn't be in the corn oil or syrup or DDGS? Well I think if its in the drying part of the DDGS, it can be collected through a vent or something. But I don't have an idea for corn oil or syrup.

[Art Montemayor]

Please define what the term “stillage” – as you employ it – means. This is a very specific and unique term used in the fermentation industry and it can mean various things to other people in other areas of industry.

Why are you looking to see if there is “significant” amount of carbon dioxide in the stillage? How much gas is left behind in the fermented liquids and residuum depends on the system’s pressure. Normally this is at atmospheric pressure and the amount of gas dissolved in the residual liquids and solids is not worth discussing. But is depends on what your process is. A process flow diagram or a P&ID would be of great value in communicating your query so that we can all see what it is that you are describing.

Do you regard parts per million as “significant”? Please define what that means.

[katmar]

You can estimate the amount of CO₂ left in the liquid from the Henry's law constant for CO₂ in water. The ethanol that is present may raise it a bit. The significance of the amount left behind depends on the application. In terms of the overall mass balance it would normally be neglected - so from this point of view I would call it insignificant.

However, it is usual to feed the fermented broth - usually termed "beer" - to an evaporator or a distillation train. Here a small amount of CO₂ can be significant because it would be an incondensible gas and could cause problems blanketing heat transfer surfaces in condensers. The first condenser would have a bleed to get rid of the CO₂ and many distilleries have a "degassing" section as the top portion of the first distillation column. This would get rid of the CO₂, plus some of the other nasties such as aldehydes and ketones which form in small quantities as by-products of fermentation.

I would disregard any CO₂ left behind in the animal feed. I suspect that next to the methane generated by the cattle, the CO₂ would have a minor effect on the digestion and "gas elimination" processes.