DDGS particle separation behind shipping cost troubles

March 30, 2010

WEST LAFAYETTE, Ind. - A Purdue University study solves a mystery that has long plagued ethanol producers and driven up shipping costs of a byproduct sold as cattle feed.

Distillers dried grains with solubles, or DDGS, is the grain product left after production of ethanol. However, when filled with DDGS, railcars register different weights – sometimes many tons different from each other – lowering shipping efficiency and raising costs.

The reason, according to Klein Ileleji, an assistant professor of agricultural and biological engineering, is that the cars aren't all holding the same-sized particles.

Previous studies show that when poured, like-sized DDGS particles congregate, with the smallest, called fines, accumulating in the center of the pile and the larger particles moving to the outside. Ileleji and doctoral student Clairmont Clementson hypothesized that this is what happens when DDGS is poured into railcar hoppers for transport.

To test the theory, Ileleji and Clementson created a scaled-down mechanism that mimicked the loading of railcar hoppers. When simulated, the first containers had mostly fines, with proceeding containers getting more of the larger particles. The containers with fines weighed more because they can be packed more densely.

"When we analyzed our data with what we would expect in theory, the weight pattern of our containers can be explained by particle segregation during filling of the hoppers, which is amplified during discharge, causing bulk density variation," said Ileleji, whose results were published in the early online edition of the journal Bioresource Technology.

The problem is exacerbated by the tendency of DDGS to discharge from hoppers in a funnel-like flow pattern in which the fines that have accumulated at the hopper's core are released first. Outside contents, which are primarily larger in size, are released last. Even mass-flow hoppers with steep sidewall angles designed to release their contents in layers caused weight irregularities because the DDGS continued to exhibit funnel-flow tendencies.

Ileleji suggests either finding a way to mix the contents better during loading or using a process he patented to create uniform-sized particles.

"The granules are larger, so they would not pack as well as fines. But granules are denser than the same amount of fines, so you get more in the same amount of space," Ileleji said. "This would ensure that railcars would weigh about the same amount and help control the cost of shipping DDGS."

Ileleji said the next step is to verify lab studies with field data and test loading methods in the field to reduce variability in DDGS bulk density during loading. An Anderson's Research Grant from Multistate Project NC-213 for Marketing and Delivery of Quality Grains and BioProcess Co-products and a Purdue Research Foundation fellowship funded the research as part of Clementson's doctoral work.

Writer: Brian Wallheimer, 765-496-2050, bwallhei@purdue.edu

Source: Klein Ileleji, 765-494-1198, ileleji@purdue.edu

Ag Communications: (765) 494-8415;
Steve Leer, sleer@purdue.edu
Agriculture News Page


Variability of Bulk Density Distillers Dried Grains With Solubles (DDGS)
During Gravity-Driven Discharge

C.L. Clementson and K. E. Ileleji

Loading railcars with consistent tonnage has immense cost implications for the shipping of distillers' dried grains with soluble (DDGS) product. Therefore, this study was designed to investigate the bulk density variability of DDGS during filling of railcar hoppers. An apparatus was developed similar to a spinning riffler sampler in order to simulate the filling of railcars at an ethanol plant. There was significant difference (P<0.05) between the initial and final measures of bulk density and particle size as the hoppers were emptied in both mass and funnel-flow patterns. Particle segregation that takes place during filling of hoppers contributed to the bulk density variation and was explained by particle size variation. This phenomenon is most likely the same throughout the industry and an appropriate sampling procedure should be adopted for measuring the bulk density of DDGS stored in silos or transported in railcar hoppers.