The caking behavior of Corn Distillers Dried Grains with Solubles (DDGS)
Abstract
Chemical, pharmaceutical, food and feed industries, around the globe, produce large volumes of bulk solids each year. Caking is a common problem in the bulk solids handling industries which alters the quality of the end product and incurs additional expenses to the industry. Corn Distillers Dried Grains with Solubles (DDGS) is a granular bulk co-product of dry-grind processing of corn grain into ethanol and is primarily used as a livestock feed ingredient. Handling is one of the major challenges associated with marketing of DDGS because DDGS is prone to caking during transportation and storage. Caking of DDGS in storage bins and railcar hoppers prevents easy loading and unloading of product, and thus increases handling cost. However, there is no understanding or quantification of the DDGS caking process or of environmental conditions favorable for caking. Direct and indirect methods were employed to investigate the effects of moisture content, relative humidity, temperature and storage time on the caking behavior of samples of DDGS having different chemical properties at particle and bulk level. The DDGS production process conditions (Wet Distillers Grains, WDG: Condensed Distillers Solubles, CDS mixing ratio) influenced the product chemical composition. Moisture sorption by DDGS decreased with the addition of less CDS. Also, the equilibrium moisture content (EMC) increased with temperature and ambient relative humidity. The effects of protein and fiber on moisture sorption were found to be greater than the effects of other constituents. Based on this result, a model was developed to predict the EMC of DDGS from its protein, glycerol, sugars, starch and fiber contents. Liquid bridging between the DDGS particles was observed above 60% relative humidity at a constant temperature. Dehumidification solidified the liquid bridge, demonstrating the irreversibility of the process of caking caused by humidity. The glass transition temperature of DDGS was highly influenced by both the chemical composition and moisture content. Glass transition behavior indicated that onset of caking in DDGS occurs in the temperature range of 20–30ºC depending on its chemical composition and moisture content. The bulk cohesiveness of DDGS depended on the moisture content, temperature and time of consolidation and as expected, there was greater cohesion between the particles as these variables increased. A continuum model based on the finite difference method was developed to predict the simultaneous heat and moisture transfer in DDGS bulk during handling and transportation. The coupled heat and moisture transfer model that was developed can be used to predict the temperature and moisture distribution within DDGS bulk as a prelude to caking. A mathematical model was developed, based on tensile strength and cohesion between particles, to predict the buildup of caking (unconfined yield strength) in DDGS. The acceptable percent error of predictions indicated that this model can be used to predict the caking of DDGS bulk due to change in environmental conditions during transportation and storage. The experimental results from this dissertation work and the prediction models will be helpful in development of quality control management systems for DDGS during production and transportation. In particular, the overall outcome of this study will help solve some of the logistical challenges due to caking. Additionally, the results from this study will contribute significantly to the science of caking of bulk solids.
Degree
Ph.D.
Advisors
Ileleji, Purdue University.
Subject Area
Food Science|Agricultural engineering
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