Agribusiness & Food

What goes into making a fan?

ABHR speaks to Victor Stiller, General Manager at Kotzur Bulk Solids Handling, about how the company designs and manufacturers its aeration equipment.

Aerating grain has four main purposes for silo operators. It prevents mould, impedes insect development, maintains seed viability, and reduces grain moisture.

The process typically uses centrifugal fans that blow air into and through perforated ducting. The air moves up through the grain and out of the silo roof through sealable roof vents.

The size of the silo, type and quality of grain stored (particularly moisture content) all lead into the calculation of total airflow and subsequently, the size and number of fans required for the silo to effectively store the grain.

The Kotzur Group, a family-owned business based in Walla Walla and Toowoomba, manufactures these components to support its customers in the grain handling sector.

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Victor Stiller, General Manager at Kotzur Bulk Solids Handling, says the company provides silos and other equipment such as screw conveyors, drag conveyors, fans and everything needed to support the product.

“The fans are something we make up here in Toowoomba. It can get fairly specific when it comes to the design, as the level or airflow and back pressure need to be correct for an aeration system to work properly,” he says.

The two most common types of fans are axial (propellor) fans and centrifugal fans. Centrifugal fans are better at handling back pressure than axial fans. The applications Kotzur uses fans for typically have higher back pressures, such as moving air through a grain column, and so all fans produced by Kotzur are centrifugal.

There are some variations in the impellors within the centrifugal range depending on the specific application.

One example is for grain aspirators, which are used for cleaning the dust and husks out of grain. Typically used in preparation of stock feed rations to clean the grain prior to wetting, these units enable continuous grain flow through the system to reduce downtime.

The fans are used to move the air at specific velocities through the controlled grain stream to pick up the lighter dust materials while leaving the whole grain. The dust is then removed from the air using a cyclone system. While not always the case, it is quite common to ‘pull’ the dust through the fan which can introduce high rates of wear to the fan impellor. To reduce this, abrasive resistant material is used to manufacture the impellor in this application.

Stiller says that due the available options, as well as the very specific requirements of given airflows at certain backpressures, it is essential that the fan designs are proven in a test environment prior to being put into service.

“The output of the testing is a fan curve, which graphs the performance of the fan for airflow and power requirement (current draw) at different back pressures. These fan curves can then be used to determine which model fan best suits the application and how many are required. We also perform the tests if there is a modification or revision to a fan for some reason to prove the fan curves are still valid,” he says.

The process for testing the fans is to bolt the fan onto a test rig which is essentially a long tube that has a mechanism on the output end that can vary the opening to adjust the back pressure in the tube. The fan is run at different backpressures and the current draw of the motor, air velocity within the tube and the tube pressure are measured and recorded. The velocity is used to calculate the airflow and results are plotted.

“The testing process gives us a very good feel for how much air is being circulated through the grain in a silo and confidence in what that can achieve with preventing mould, inhibiting insect development, maintaining seed viability and reducing grain moisture,” Stiller says.

Kotzur also employs an in-house engineering team, made up or structural, civil, and mechanical engineers, to help handle the complex design requirements of a bulk handling project. After a design is determined, the business can then fabricate it locally.

Most of the work is handled in-house, using Kotzur’s own manufacturing facilities. In addition, the company’s maintenance services division helps commission and maintain the equipment as well. 

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