Distillers Dried Grains with Solubles (DDGS)
Currently corn grain is the primary biological material that can be economically converted into ethanol on an industrial scale. The corn-based fuel ethanol industry is poised to produce substantial quantities of biofuel during the coming century as this industry continues its rapid expansion. The number of corn ethanol plants, and their processing capacities, has been markedly increasing in recent years. For example, at the end of 2005, 97 manufacturing plants in the U.S. had an aggregate production capacity of nearly 16.3 billion L/y (4.3 billion gal/y), which represents a growth of 226% over the previous five year period. More information on the growth of this industry can be found in Lyons (2003), BBI (2006), and RFA (2006).
Bioethanol manufacturing from corn grain results in three main products: bioethanol, the primary end product; residual nonfermentable corn kernel components, which are typically marketed as “distillers grains” (Figure 1); and carbon dioxide. Anecdotally, the rule of thumb commonly used in industry states that for each 1 kg of corn processed, approximately 1/3 kg of each of these constituent product streams will be produced. The production process consists of several steps, including grinding, cooking, liquefying, saccharifying, fermenting, and distilling the corn grain.
The nonfermentable residues are removed from the process stream during the distillation stage in the form of whole stillage. They are centrifuged and dried, to ensure a substantial shelf life, and then sold as distillers grains (most commonly as DDGS – “dried distillers grains with solubles”) for feed rations to local livestock producers, or shipped via truck or rail for use by distant customers. The sale of distillers grains contributes substantially to the economic viability of bioethanol manufacturing, and is thus a vital component to each plant’s operations. Hence the nutritional content and quality of distillers grains is important to ethanol processors. Several studies have thoroughly examined chemical and nutritional properties of these byproduct feeds, including Belyea et al. (1998), Belyea et al., (2004), Shurson et al. (2004), and Spiehs et al. (2002). Rosentrater et al. (2005) comprehensively reviewed much of the available chemical and nutritional research.
To date, however, no studies have examined the physical properties of distillers grains. Property data are not only essential for livestock diet formulation, but also for the design and optimization of material handling systems, various unit operations, processing facilities, and storage structures. As this industry continues its rapid growth, it is imperative to establish baseline information from which engineers and scientists can work. Toward this end, it is the goal of this project to provide such information. The specific objective of this paper is to report initial findings for some of the physical properties of DDGS that have been determined to date, including moisture content, water activity, thermal properties, bulk density, angle of repose, and color.
|Moisture content (%, d.b.)||72||13.21||21.16||14.72||1.52||Rosentrater, 2006|
|Water activity (-)||72||0.527||0.634||0.552||0.021||Rosentrater, 2006|
|Thermal Conductivity (W / m °C)||72||0.06||0.08||0.07||0.01||Rosentrater, 2006|
|Resistivity (m °C / W)||72||13.10||15.60||14.00||0.52||Rosentrater, 2006|
|Diffusivity (mm2 / s)||72||0.13||0.15||0.13||0.01||Rosentrater, 2006|
|Bulk density (kg / m3)||72||389.28||501.46||483.27||24.12||Rosentrater, 2006|
|Angle of Repose (deg)||72||26.51||34.23||31.48||1.81||Rosentrater, 2006|
|Hunter L (-)||72||39.99||49.82||43.13||1.62||Rosentrater, 2006|
|Hunter a (-)||72||8.00||9.81||8.69||0.38||Rosentrater, 2006|
|Hunter b (-)||72||18.22||23.50||19.37||0.93||Rosentrater, 2006|
Table 2. Correlation coefficients (r) between physical properties of DDGS and (associated p values; significance level of 0.05).
Moisture Content Water Activity Conductivity Resistivity Diffusivity Bulk Density Angle L a b Moisture Content 1.000 --- Water Activity -0.053 1.000 (0.661) --- Conductivity 0.064 -0.443 1.000 (0.590) (0.000) --- Resistivity -0.091 0.679 -0.643 1.000 (0.447) (0.000) (0.000) --- Diffusivity 0.025 0.634 -0.414 0.828 1.000 (0.835) (0.000) (0.000) (0.000) --- Bulk Density 0.074 -0.932 0.414 -0.709 -0.671 1.000 (0.538) (0.000) (0.000) (0.000) (0.000) --- Angle -0.329 0.040 -0.097 0.049 -0.026 -0.097 1.000 (0.005) (0.739) (0.415) (0.684) (0.826) (0.418) --- L -0.253 0.729 -0.323 0.570 0.476 -0.784 0.198 1.000 (0.032) (0.000) (0.006) (0.000) (0.000) (0.000) (0.095) --- a 0.043 0.697 -0.243 0.393 0.473 -0.731 -0.075 0.435 1.000 (0.720) (0.000) (0.040) (0.001) (0.000) (0.000) (0.532) (0.000) --- b -0.247 0.832 -0.375 0.568 0.520 -0.886 0.236 0.917 0.640 1.000 (0.036) (0.000) (0.001) (0.000) (0.000) (0.000) (0.046) (0.000) (0.000) ---
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