Like any growing business operating in a competitive environment, ethanol producers must balance efforts that maximize investment in equipment, utilize processing methods that streamline operations for greater efficiency, and emphasize techniques that result in a quality product. The ethanol production process is evolving, and Cincinnati, Ohio-based Rotex Inc. is contributing to its progression by developing separation equipment that's making a significant contribution at two critical points in the ethanol production process.

When grain enters the production process, it often contains foreign material such as rocks and other debris that must be removed. Foreign material that has a considerably larger particle size than the grain itself is removed through a process referred to as "scalping." As an entry point in the process, Rotex Grain Cleaners separate those unwanted particles from the feedstock. Preventing impurities from entering the process assures quality and also protects downstream equipment. "Contaminants that are processed with the raw material will lower the quality of the final product and potentially damage equipment," says Dan Ferris, application engineering manager at Rotex. "Strategically placing Rotex Grain Cleaners at the beginning of the process will contribute to a higher- quality product, and reduce the maintenance costs and equipment failure that debris causes."

There is high competition for corn among ethanol plants and other users, and USDA Grade No. 2–sometimes called "Yellow No. 2"–corn has become the minimum quality grade for dry-grind corn-to-ethanol production. However, procuring top-quality grain alone is not enough to attain quality standards. The use of screening equipment to refine the material is necessary. Removal of oversized particles and fines from the corn will bring the material within the specifications required to meet these grades.

Not only do Rotex Screeners remove "off-size" particles and contaminants, but they also offer high throughput and excellent reliability. The machines are rugged and durable, built with heavy-duty features such as ceramic lining and wear-resistant urethanes to withstand the abrasive quality of grain, rocks, and grit. The equipment offers the highest loading per square foot of screen area in the industry. "We're proud of our leading reputation for performance, the lowest maintenance costs and highest uptime in the industry," says Steve Schmidt, senior application engineer ar Rotex.

As demand for ethanol increases, so will the call for higher production rates and more efficient processing. New processes are being developed that separate the corn into three fractions: fiber, germ (oil), and endosperm (starch). The primary benefit of the process is the elimination of the costly energy-consuming cooking process for the non-fermentable fractions of fiber and germ. Effectively addressing the issue requires more than simply increasing feed volume, but increasing yield through grading methods that target the starch necessary for ethanol. "Grading" is a separation, based on the size of material, through single or multiple screen surfaces into one or more grades of the material. Rotex separation equipment maximizes the recovery of desired fractions by making precise separations of ground corn. This increases yield by raising the amount of ethanol produced per bushel of corn.

Whether scalping or grading, there are many factors that affect screening performance with corn and other grains. These include material characteristics (e.g., particle size, bulk density, flowability, friability and surface moisture), screen selection, screen motion and configuration, and screening blinding.

--Particle shape: Certain particle shapes are prone to screen blinding, a situation where particles slightly larger than the screen opening become caught in the openings, effectively plugging the screen. Blinding can significantly affect screening performance and production rates.

--Bulk density: In general, the higher a material's bulk density, the higher the screening capacity. Gravity is the driving force in screening operations, so where there are higher mass or higher density materials, gravity simply applies a higher screening force, promoting particle separation.

--Flowability: The flowability of a material can affect screening performance. In materials that don't flow well, the particles don't spread over the screen surface and present themselves properly to the screen openings.

--Friability: This term refers to the tendency of a particle to crumble or break. Friability is a concern because the screening action itself can cause particle degradation and change the particle-size distribution.

--Moisture: Surface moisture can have a negative impact on screening performance. High levels of moisture can reduce screening accuracy by causing particle bridging, effectively blinding the screen opening and decreasing screening performance.

Selection of the screen media has a significant impact on screening performance. The most common screening media is woven wire cloth screen. Typically, production screens are specified by at least two of the following four parameters: mesh count, wire diameter, opening and percentage of open area.

While there are many methods of separation, vibratory and gyratory are the two most common types of screen motion used in production screening machines. Gyratory motion in a screener is characterized by a longer stroke and lower frequency motion than a vibratory screener, and is most suitable for applications involving finer separations or separation where accuracy is a priority. This motion has a more positive conveying characteristic, good for higher capacity applications such as corn and grain processing. The long stroke of gyratory machines spreads the material across the full width of the machine and stratifies the bed of material so the finer particles will work their way down to the screen surface. They also use a sifting motion that keeps the grain in contact with the screen surface, maximizing opportunities for fine particles to pass through the screen.

Screen blinding occurs when material obstructs the screen, reducing the open area of the screen surface. Blinding results in inconsistent screening performance due to loss of screening capacity. In screening applications where blinding is a concern, preventive measures must be used. The most common method of preventing blinding is to use bouncing balls that are trapped in pockets below the screen surface.

The performance of a screening machine can be significantly affected by the material feed rate. A screener has an ultimate volumetric capacity, which is a function of internal construction and material handling capabilities. However, its true capacity at which it will produce acceptable separation performance is typically a much lower feed rate. This balance between capacity and screening performance must be evaluated when selecting screening equipment.

All of these factors must be considered in determining what type of screener and features will provide the smart solution for ethanol plant grain processing. Rotex offers a comprehensive product line of screeners to meet the unique needs of any ethanol production facility, from a small, five- square-foot screener to a mighty, yet compact 350-square-foot model, as well as many other models in between. Whether your production requirements call for a capacity range from 50 bushels per hour or 50,000 bushels per hour, Rotex has the right solution.

Rotex Inc. is a pioneer and global leader in the development of screening equipment and technology for the process industries. John Y. Gerhardt is the company's marketing manager. Reach him at jygerhardt@rotex.com or (513) 591-5322.