Prepare for Upcoming Flowability Challenges

Distillers grains flowablity is a complex problem, affected by factors an ethanol plant can control and some it cannot. Kurt Rosentrater writes that the most important step to improve flowablity is to minimize variability.
By Kurt Rosentrater | April 15, 2014

About 10 years ago, DDGS flowability became an issue as the industry began its exponential growth and ethanol plants began shipping coproducts.  Flowability has been a major challenge for transportation and logistics, not just because it does not always flow out of rail cars, but it also hangs up in trucks, storage bins, and even in on-farm storage structures.  Over the years, much effort has been expended into determining why flowability problems occur, and what can be done to eliminate, or at least reduce the occurrence.  Considerable progress has been made, and flowability problems have declined throughout the industry.  But, it seems that every summer the problem returns as temperatures and humidities increase.

So what have we learned?  Flowability (or lack of flow) is a complex phenomenon.  The most important factors are moisture content and syrup addition level (which the plant can control), and ambient temperature and relative humidity (which it cannot).  Other variables play a role, including dryer temperature and time, cooling temperature and time, cure time in flat storage, state of the residual sugars, fats and proteins after both fermentation and drying, the influence of yeast cell components, and fermentation products (such as glycerol, organic acids, acetic acid and lactic acid).  Also important are corn grind size (and thus DDGS particle size), as well as vibration and compaction during transport.
What about the reduced-oil distillers products that are now available?  It would stand to reason that by reducing fat content DDGS flowability should improve.  Unfortunately, this is not the case.  Experiments in our laboratory indicate some flow parameters do improve slightly, while others do not.  Similar to traditional DDGS, the most important factors are particle size, syrup level, temperature and humidity.

What can plants do to reduce flowability problems this summer?  First, and most importantly, minimize the variability in your DDGS.  The more consistent your production process, and more consistent your DDGS, the lower the probability of flow issues.  Second, don’t load railcars when the DDGS is still hot. The best practice is to allow the DDGS to cure/cool in flat storage until residual heat dissipates or, if stored in silos, to turn the material to break the bridges that may form between particles.  Third, if a batch of DDGS is likely be out of spec, the best choice is to send that to a well-equipped unloading  facility, if that is an option.

Even if your DDGS is in spec, it may still have issues. My research team has determined that the easiest way to predict flow problems is to conduct some simple tests, including measuring angle of repose, loose bulk density and tapped (compacted) bulk density.  The ratio of tapped-to-loose bulk densities is known as the Hausner ratio. By plotting Hausner ratio vs. angle of repose, we can estimate DDGS flow out of hopper bottoms  and estimate regions of good and poor flow. 

Production of ethanol is a biological process.  Biomolecules such as proteins and fats will always be present, as will products of fermentation, including glycerol and organic acids.  These all make DDGS a sticky product, especially in the summer when these molecules can melt and flow between particles.  Now is the time to start thinking about flowability issues and taking steps to reduce their impact.
If you have any questions or need any assistance with your DDGS, please feel free to contact us.  We look forward to working with you.

Author: Kurt A. Rosentrater
Executive Director, Distillers Grains Technology Council