How to dry distillers’ grain?

Protein and fiber-rich, ethanol plants have turned distillers’ grain into a valuable by-product. What used to be waste is now considered highly nutritious and inexpensive animal feed. But while wetcake can be sold locally, its shelf life is too short for transport over long distances. Nor can it be stored for extended lengths of time. Drying opens a world of possibilities, but it has to be done properly. Read the pitfalls of DDGS drying and find out how to avoid them.

DDGS production

Grains , such as corn, rice, and wheat, are used in the production of alcoholic beverages. They are also the raw materials for ethanol production. Due to their nutritious composition, both brewers’ spent grain and ethanol waste turned out to be great animal feed. As can be seen in the image below, distillers’ grain contains large amounts of protein and is also high in vegetable oils, carbohydrates, and fiber. The feeding value, handling, and storage characteristics do vary among and within ethanol plants, but we will get to that in a moment. Over the years, the downstream processing of ethanol and brewers grain solids became an industry in its own right.

The rise of distillers’ grain

This is especially true in light of the dramatic increase in ethanol production that we have seen in the last fifteen years. Consequently, the production of distillers’ grain has peaked, too, and both wet distillers’ grain and distillers´ grains with solubles (DDGS) have gained significant market shares.

DDGS production is expected to stabilize at above 4 million tons in the European Union and above 35 million metric tons in the US.

The DDGS production process

So, what does the DDGS production process look like? It begins by grinding the grains into a coarse consistency. Hot water turns the starch in the grains into sugar, and yeast allows the mixture to ferment. The solids that remain after fermentation are called distillers’ grains. The next step in DDGS production is distillation: the distillers’ grains are heated to evaporate the ethanol, leaving behind whole stillage. Rich in vegetable oils, carbohydrates , fiber and protein, the whole stillage is centrifuged to separate the coarse solids and the liquid.

The coarse solids, also called wetcake or wet distillers´ grain (WDGs), are ready for sale to cattle farmers. The liquid, now called thin stillage, needs further evaporation to remove excessive moisture. After that process step, it too can be sold to cattle feeders as condensed distillers’ solubles.

Unfortunately, WDGs and condensed distillers’ solubles contain dry matter of 3% to 35% respectively. As a result, transport is economically valuable only within 200 km of the production facility. Moreover, they can be stored for merely 48 hours (WDG) or four to five days (condensed distillers solubles).

The solution: DDGS

With such short shelf lives, their use and subsequent profitability are severely limited. This is where drying comes in. WDGs, mixed with condensed distillers’ solubles, can be dried to produce dried distillers’ grains with solubles (DDGS). With a dry matter of approximately 88%, DDGS can be stored almost indefinitely and may be shipped to any market regardless of its proximity to an ethanol plant.

DDGS challenges

However, the physical properties of DDGS vary among and within ethanol plants, and much of this variation is caused by factors, such as:

• Raw material characteristics
• Hammermill settings
• Conditions, additives, and chemicals used during processing
• The proportion of condensed distillers´ solubles added to wet distillers´ grains before drying
• The drying time and temperature
• Cooling and conditioning of DDGS after drying
• Final moisture content

As a result, any of the following challenges may arise:

Flowability issues

First of all, several factors may synergistically interact, such as moisture content, particle size distribution, storage temperature, relative humidity and time. These interactions can lead to bridging or caking: the feed may interlock to build an arch above the outlet of a container. Flowability problems like these can become such that they limit the use of DDGS as animal feed.

Nutrient digestibility issues

Secondly, particle size affects nutrient digestibility and palatability, as well as mixing efficiency, pellet quality, bulk density, and the extent to which the ingredients are segregated during transport and handling. Therefore, particle size and particle size uniformity of feed ingredients are important considerations for livestock and poultry nutritionists who manufacture complete feeds or feed supplements. Unfortunately, DDGS product streams are notorious for their differences in particle size, posing challenges to the drying process.

Processing risks

A third challenge is posed by the explosion risks that come with drying DDGS. In high concentrations, dust can become explosive. Therefore, dust generation and dispersal in the air should be limited. Dust deposits should be cleaned, and non-sparking tools should be used at all times.

Reduced product quality

If DDGS is dried at excessive temperatures, it may impact nutrient content. Needless to say, in an industry that needs highly nutritious feed to grow cattle at optimal rates, nutrient contents should always be of first-class quality.

High energy consumption

Although drying distillers’ grain opens a wealth of commercial opportunities, it is also highly energy-consuming. Not only does this make it a costly process that impacts profit margins. More and more companies take issue with the environmental consequences of such energy use. So, how can these issues be solved?

How to dry distillers’ grain with a fluid bed dryer?

We believe that an optimized drying process greatly improves flowability, shelf-life stability, and product quality of DDGS animal feed. Let’s illustrate this with a Ventilex example.

Optimized flow-ability and nutrient digestibility

Our fluid bed drying process can be extended with a back mix-system. The wetcake from the filter press is mixed with condensed distiller’s solubles and dried to produce distillers’ dried grains with solubles. During the drying process, however, the feed product is blended with partially dried product. This back-mix flow enables better fluidization, and therefore, more optimal drying.

The biomass dryer is equipped with a state-of-the-art PLC control system. By controlling the powder layer in the back-mix fluid bed, we manage the residence time. By controlling the amount and temperature of the drying air, we manage the moisture content in the fluidized layer. And by controlling the granulation process, we manage particle size and color. As a result, the DDGS animal feed is dried evenly, and optimal flowability, as well as nutrient digestibility and shelf-life stability, are ensured.

Continuously high product quality

Secondly, our biomass dryer achieves high vapor extraction at relatively low temperatures. Combined with a gentle shaking motion, the quality of the DDGS is preserved, and energy, protein, and digestible phosphorus are maintained.

Safe production environment

We help to improve the safety of the production environment by equipping the biomass dryer with a fire detecting and extinguisher system . Moreover, in our test center, we design an explosion-safe operation, based on the physical properties of your DDGS product.

Highly energy-efficient

So how to dry distillers’ grain in an energy-efficient way? The beforementioned shaking bed mechanism enables the distillers’ grain to be dried at lower temperatures and with shorter residence times. This alone helps to reduce energy use. However, we also recirculate discharge air, thus further improving energy-efficiency. In this way, we allow you to save an average of 30% of energy costs, which is the lowest energy consumption among dryer beds.

Case study: drying distillers’ grain in India

Located in Kolkata, IFB Agro Industries is a large producer of vodka, amongst other business endeavors. The company has an ultra-modern grain distillery, producing 120,000 liters of alcohol a day from broken, non-edible rice. Ventilex: ‘Our client wanted to process the unutilised portion of the rice leftover into high-quality cattle feed. However, if this ‘wetcake’ is not dried, it needs to be used within 48 hours. This is not very practical with respect to storage, sales and transportation, which is why IFB Agro contacted us.’

Proven success
Dr. J.A. Gore: ‘We chose Ventilex because they built a similar installation for a whisky distillery in the USA. Lukas Veldmeijer came to India to discuss the details and we were soon convinced.’

Proteins remain intact
This system is equipped with a fluid bed dryer and a back mix-system. The latter ensures that the dryer feed at the right moisture content enters into the fluid bed dryer. Dr. Gore: ‘This is unique drying technology which dries the material at low temperatures and uses waste heat available at the plant to ensure optimum use of heat energy.

‘This type of dryer, unlike contact dryers, ensures that the protein in the dried product is not denatured. The high level of digestible protein in the DDGS means it can be turned into highly nutritious cattle feed. The dried product has a longer shelf life and is easy to pack and transport over long distances. All these factors help to boost sales in the Indian and overseas markets.’