DDGS storage and handling

by David McKee
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The rise of ethanol has given new prominence in the grain and feed industry to a commodity that has been around for centuries: distiller’s grains. Because of the need to store and transport huge quantities of the maize co-product, most ethanol plants mix in the solubles from the process and then dry it, resulting in Dried Distillers Grains and Solubles (DDGS).

Grain traders, animal nutritionists and feed millers are now adjusting to an unprecedented increase in production of this feed ingredient.

U.S. ethanol capacity in operation or under construction is 19.3 million tonnes (5.1 billion gallons) per year. The annual maize requirement of these plants at full capacity is 46 million tonnes (1.8 billion bushels), which is roughly 16% of current U.S. crop levels of nearly 280 million tonnes (11 billion bushels). Most estimates for U.S. ethanol production by the year 2010 call for at least a doubling of current capacity.

For every tonne of maize used for ethanol, about one-third remains in the form of DDGS. This means that DDGS volumes in North America could reach 30 million tonnes within a few years.

The official USDA data for the marketing year ending in September 2006 is 8.5 million tonnes of U.S. DDGS production, of which just 10% was exported. It should be noted that these figures include wet distillers grains converted to a dry basis for statistical purposes, but most new production is DDGS.

The traditional use of distiller’s grains is for cattle and other ruminants, but its availability and low cost have created the opportunity to include it in feed formulations for monogastric livestock. This process is well under way in North America, where extensive research is permitting DDGS to partially displace both maize, and to a much lesser extent, soybean meal in swine and poultry feed rations. However, according to Erick Erickson of the U.S. Grains Councils (USGC), “the inclusion rates are still quite limiting: around 15% for swine and 5% for poultry.” He added that “the limits in cattle feeding are 40% to 50%, so it is not a complete substitute for corn and soybeans.”

With fuel ethanol production taking off in both China and Europe, the same developments in feed are likely to occur. Also,  countries that are traditional markets for U.S. maize exports may find their supply reduced. To partially compensate, they may begin importing DDGS instead, once they understand its benefits.

The USGC has launched an ambitious program of DDGS education and promotion in countries that are the largest markets for U.S. maize. Promoting DDGS makes sense, since it offers almost all the energy of maize but includes 27% protein as well.

Mike Callahan, the USGC Director for Asia, notes that DDGS exports to his area are starting to take off, but so far all shipments have been containerized. Much needs to be done to improve supply logistics, he said, in order to move to more efficient bulk shipments. The minimum bulk quantity to fill one hold of a vessel is 8,000 tonnes, but he notes that “any one plant can’t put enough DDGS together. We need several plants, but there is variability in product quality.”

The solution, he says, is for “more plants to come on line to trade DDGS as a co-product and not a by-product. We must concentrate on quality.”


Another major logistical disadvantage of DDGS compared to maize is poor flow characteristics. Like oilseed meals, wheat midds and pelletized biomass materials of all sorts, DDGS is highly prone to caking and bridging. This complicates storage, handling and transport.

These bridging problems are due to a combination of factors: particle size, moisture and fat content, ambient temperatures, storage volumes and heights, and most important of all, days in storage.

When production and storage volumes were small and the product could be shipped on a daily basis, silos with steep hopper bottoms relying on gravity flow alone or a vibrator were feasible for DDGS. However, in an earlier phase of ethanol expansion in the late 1970s, DDGS volumes increased, storage times lengthened and bridging inevitably occurred, resulting in plant down time. This caused silos to fall out of favor for DDGS in the ethanol industry. There was a switch to flat storage in warehouses and the use of front end loaders.

Though it eliminates the bridging problem of silos, warehouse storage of DDGS has its own set of disadvantages. These include the high operating costs of front end loaders; employee safety and health issues in a very dusty and potentially toxic environment; poor hygiene of an animal feed ingredient due to infestations from birds, rodents and insects; difficulty in achieving first-in, first-out (FIFO) inventory management; inadequate cleanout and loss of product through degradation; segregation of particles (fines to the middle and larger particles to the outside of the pile), resulting in deliveries of inconsistent product and dockage fees; and, finally, the large land area covered by a warehouse.


It is not surprising then that, with the new application of proven silo reclaim technology to DDGS, the standard practice in the industry has changed once again. In North America, the majority of recently constructed plants are now incorporating round silo storage for their DDGS.

The technology underlying this change is an extremely powerful and heavy-duty auger-type, bottom reclaim system that can be switched on for automatic discharge even when a silo is full. Typical DDGS silos now measure 16.7 meters (55 feet) in diameter, with 34 meters (111 feet) of storage height, permitting storage of 3,000 tonnes of product. Discharge rates of 250 tonnes per hour into railcars and trucks are possible.

In today’s competitive environment, high storage volumes and fast load out are essential. Ethanol plants are relying more on unit trains of 75 to 100 cars, each with a load capacity of 90 tonnes, to move DDGS to customers in distant markets, whether they are cattle feedlots in Texas and Oklahoma, feed mills in Mexico and Canada, or river and ocean ports.

A leading supplier of such automated DDGS silo and reclaim systems in North America is Indiana-based Laidig Systems. Roger Laidig, vice-president of sales of Laidig, reports the company sold its first such equipment for DDGS just eight year ago, but now has systems installed or on order for 52 silos with capacity for more than 180,000 tonnes of DDGS storage at 35 ethanol plants in the U.S. and Canada.

Laidig first applied its reclaim systems to soybean and other meals in the late 1980s, after having concentrated on the wood products industry. In soybean meal, the largest installations are in silos up to 25 meters in diameter, holding 8,000 tonnes, but with designs for even bigger silos. Consequently, for DDGS the potential exists to go to much larger silos than what is common today.

With 20 to 30 million tonnes of U.S. DDGS production looming on the horizon, there is little question that storage infrastructure on a much bigger scale will be needed in the U.S. and other markets, perhaps sooner rather than later.

David McKee is a grain industry consultant who also represents Laidig Systems in Europe and Africa. He can be reached by e-mail at  davidmckee59@msn.com.