Flowability Of Distillers Dried Grains With Solubles Research Articles

Heat Transfer During Cooling of Bulk Distillers Dried Grains with Solubles (DDGS)

Abstract. DDGS is often transported in railcars and trucks from the ethanol plants to the feed mills and animal farms. During unloading, flowability of DDGS is often reduced due to caking of DDGS bulk. Based on published research, the environmental relative humidity, DDGS glass transition temperature, syrup content, and duration of cooling of DDGS piles influence the caking behavior of DDGS. The objective of this study was to develop and validate a heat transfer model for predicting the cooling pattern of DDGS piles. A finite volume method approach was used to develop the heat transfer model. Ergun’s equation was used to implement airflow resistance in the porous media of the DDGS bulk. The heat transfer inside the pile was simulated for winter (6°C) and summer (24°C) ambient conditions. The model agreed well with the experimental temperature measurements from the three sets of experiments with two sizes of experimental piles. The overall predicted temperatures were 2.7°C and 0.7°C higher than the observed temperatures for small- and medium-size experimental piles, respectively. This heat transfer model could be used to predict the temperature variations in DDGS bulk during storage and as a measure to predict the caking behavior. Keywords: Caking, DDGS, Finite volume method, Heat transfer.

Measurement and Comparison of Glass Transition and Sticky Point Temperatures of Distillers Dried Grains with Solubles (DDGS) with Varying Condensed Distillers Solubles (CDS) and Drying Temperature Levels

ABSTRACTDistillers dried grains with solubles (DDGS) is the main coproduct of the U.S. fuel ethanol industry and has significantly impacted the livestock feed markets in recent years. Particle agglomeration and subsequent flowability problems during storage and transport are often a hindrance, a nuisance, and expensive. This paper aims at characterizing the glass transition (Tg) and sticky point (Ts) temperatures of DDGS samples prepared with varying condensed distillers solubles (CDS) levels (10, 15, and 20%, wb), drying temperatures (100, 200, and 300°C), and moisture contents (0, 10, and 20%, db), and it discusses implications on DDGS flowability behavior. Distillers wet grains were combined with specified levels of CDS and dried in a convection‐style laboratory oven to produce DDGS. Subsequently, predetermined amounts of water were added to the DDGS to achieve desired moisture content levels. To determine Tg (°C), a differential scanning calorimeter was used, whereas Ts (°C) was determined through a novel technique with a rheometer. Results indicated high correlations between observed Ts and observed Tg (R2 = 0.87) data for DDGS samples. Also, the empirical model for predicted Tg = f (drying temperature, CDS level, and moisture content) based on the Gordon–Taylor model showed favorable R2 (0.74). Stickiness of DDGS increased with an increase in moisture content, indicating flow problems resulting from moisture. It was found that drying temperatures and CDS levels each had significant effects on Tg and Ts as well.

Artificial Neural Network Modeling of Distillers Dried Grains with Solubles (DDGS) Flowability with Varying Process and Storage Parameters

ABSTRACTNeural network (NN) modeling techniques were used to predict flowability behavior of distillers dried grains with solubles (DDGS) prepared with varying levels of condensed distillers solubles (10, 15, and 20%, wb), drying temperatures (100, 200, and 300°C), cooling temperatures (–12, 25, and 35°C), and storage times (0 and 1 month). Response variables were selected based on our previous research results and included aerated bulk density, Hausner ratio, angle of repose, total flowability index, and Jenike flow index. Various NN models were developed using multiple input variables in order to predict single‐response and multiple‐response variables simultaneously. The NN models were compared based on R2, mean square error, and coefficient of variation obtained. In order to achieve results with higher R2 and lower error, the number of neurons in each hidden layer, the step size, the momentum learning rate, and the number of hidden layers were varied. Results indicate that for all the response variables, R2 > 0.83 was obtained from NN modeling. Compared with our previous studies, NN modeling provided better results than either partial least squares modeling or regression modeling, indicating greater robustness in the NN models. Surface plots based on the predicted values from the NN models yielded process and storage conditions for favorable versus cohesive flow behavior for DDGS. Modeling of DDGS flowability using NN has not been done before, so this work will be a step toward the application of intelligent modeling procedures to this industrial challenge.

Flowability Properties of Commercial Distillers Dried Grains with Solubles (DDGS)

ABSTRACTDistillers dried grains with solubles (DDGS), the major coproduct from the corn‐based fuel ethanol industry, is primarily used as livestock feed. Due to high protein, fiber, and energy contents, there is a high demand for DDGS. Flowability of DDGS is often hindered due the phenomenon of caking. Shipping and handling of DDGS has thus become a major issue due to bridge formation between the DDGS particles. The objective of this investigation was to measure flowability characteristics of DDGS samples from five ethanol plants in the north central region of the United States. Carr and Jenike tests were performed and the resulting data were mathematically compared with a previously developed empirical model. The largest particles had an average geometric mean diameter (GMD) of 1.19 mm, while the lowest particle size had an average GMD of 0.5 mm. Soluble solid levels were ≈10.5–14.8% (db). The effective angle of friction (δ) was 43.00–57.00°. Additionally, a few parameters exhibited fairly high linear correlations, including aerated and packed bulk densities (r = 0.97), geometric standard deviation and Carr compressibility (r = 0.71), geometric standard deviation and Hausner ratio (r = –0.70). Overall flowability assessment indicated that the commercial DDGS samples did have the potential for flow problems, although no samples exhibited complete bridging. Quantifying DDGS flowability is a necessary step toward overcoming this logistical challenge facing the fuel ethanol industry.

Effect of Flow Agent Addition on the Physical Properties of DDGS with Varying Moisture Content and Soluble Levels

Distillers Dried Grains with Solubles (DDGS) is widely recognized as a highly nutritious animal feed ingredient. With the exponential growth of the fuel ethanol industry in the past several years, significant quantities of distillers grains are now being produced. To effectively utilize these feeds in the domestic market, these coproduct streams have to be transported greater distances, and must be stored in various structures until final use. Unfortunately, DDGS flow is often problematic, as it frequently becomes restricted by caking and bridging during storage and transport. This issue may arise from a number of factors, including storage moisture, temperature, relative humidity, particle size, time, or temperature variations. The objective of this study was to examine the effect of various moisture content levels (10%, 15%, 20%, 25%, and 30% d.b.) and calcium carbonate (a common flow agent) levels (0%, 1%, and 2% w.b.) on the resulting physical and flow properties (Carr indices) of DDGS with varying soluble levels (10%, 15%, 20%, and 25% d.b.). The results showed that DDGS flowability declined with increased soluble and moisture content levels. Flow agent (CaCO3) addition did not have a significant effect in improving the flow properties of DDGS. This may have been due to no surface affinity between DDGS and the flow agent particles, or too little inclusion of the flow agent.

Physical and Flow Properties of Regular and Reduced Fat Distillers Dried Grains with Solubles (DDGS)

With the remarkable growth of the US fuel ethanol industry in the past decade, large quantities of corn-based distillers dried grains with solubles (DDGS) are now being produced. Flowability of DDGS has become a problem throughout the industry, as it is often restricted by caking and bridging during storage and transport. The objective of this study was to quantify physical and flow properties of commercially produced unmodified (9.3% db fat) and reduced fat (2.1% db) DDGS to determine if fat level affects flowability. The compressive modulus of reduced fat DDGS was 28.2% higher than unmodified DDGS, but shear stress resistance was the same (0.03 kg/m2). Carr testing indicated that reduced fat DDGS had an angle of repose 4.3% lower, and Carr compressibility 70% lower, than unmodified DDGS. However, in terms of uniformity and dispersibility, reduced fat DDGS was, respectively, 100 and 41.5% greater than regular DDGS. Jenike shear testing revealed that reduced fat DDGS had unconfined yield strength and Jenike compressibility values that were 15.7 and 40.0% lower, respectively, than unmodified DDGS, but had major consolidating stress and flowability index values that were 6.7 and 13.2% higher, respectively. For regular DDGS, the flow function curve was located closer to the shear stress axis, which indicated slightly worse flowability than the reduced fat DDGS. Overall, a reduction in the fat content did show slight improvement in some flow properties, especially compressibility. Both types of DDGS were ultimately classified as cohesive in nature. Exploration of the data using a previously developed assessment tool appeared to show that the reduced fat DDGS may have better flow. Continued research should be pursued, including an examination of the effects of other chemical constituents, as well as particle morphology.