By investing in new, high performance screeners, United Harvest, LLC has been able to reach new 0.3 percent dockage standards and reduce ship loading time by 50 percent in the process.

United Harvest is a fully integrated company established in December 1999 by United Grain Corporation of Portland, Oregon and Cenex Harvest States, the largest farmers’ cooperative in the US, as an equally-owned joint venture.  United Harvest purchases grain directly through its own country elevator network and external country elevator businesses and markets it to overseas and domestic customers.

United Harvest operates two terminal grain elevators.  The Port of Vancouver Elevator is located on the Columbia River in Vancouver, Washington, 90 miles up river from the Pacific Ocean.  This elevator, constructed in 1935, is the second largest facility in the Columbia River District.  It receives grain by barge and rail and loads out to ocean going vessels.  The Port of Kalama Elevator, located on the Columbia River in Kalama, Washington, 75 miles up river from the Pacific Ocean, was built in 1962.

In 2000, the company upgraded its grain cleaning system with the installation of two MEGATEX™ M5350 Screeners and two ROTEX™ 722 Screeners from ROTEX Global, Cincinnati, Ohio.

“Prior to that, we had only two MEGATEX M4280 double deck Screeners and we were attempting to clean to 0.4 or 0.5 percent dockage,” said Jim Veltum, United Harvest Elevator Manager.  “In order to get to 0.3 percent standard, we had to install the additional equipment.”

The wheat cleaning process at United Harvest is a little different from the company’s competitors’ processes in that it’s more complex while still being cost effective.  “We’re attempting to minimize grain loss in the cleaning process, so we’ve added a few extra steps.  Essentially, we’re reprocessing part of the materials that shake through the screeners,” Veltum said.

High volume wheat cleaning at United Harvest consists of a primary and secondary screening operation.  The primary system uses MEGATEX Screeners to achieve a wheat yield of about 95 percent.  The secondary system consists of ROTEX Screeners which take the overage from the MEGATEX Screeners and re-screen it to optimize wheat recovery.  Approximately 75 percent of the wheat handled by United Harvest is screened.  Use of the two-stage ROTEX Wheat Cleaning System results in a yield of about 99.4 percent.

MEGATEX Screeners used in the primary system employ wide screening surfaces that allow a high volume of wheat to be separated by spreading it over the screen as thinly as possible, cleaning the bulk of the wheat to the required specification.  In any screening application, as the volume increases the depth of the material passing over the screen increases.  Increased bed depth diminishes the screener's ability to stratify material, which is essential to effective screening.  MEGATEX Screeners handle increased capacity and maintain screening accuracy by utilizing screen surfaces that are wider rather than longer.  This width serves to keep bed depths low so screening accuracy and efficiency are maintained at high capacity.

The MEGATEX M5350 Screeners at United Harvest have five screens of 70 sq. ft each, for a total screening area of 350 sq. ft., and are designed to handle very high volumes of material.  They use a unique design to evenly split and distribute the incoming flow of material to the five screens that are arranged in a stacked configuration to minimize the amount of floor space occupied by the machine.

Additional cleaning is performed using the secondary screening system.  In this system, ROTEX 722 Screeners use a combination of circular and reciprocating motion on near horizontal screen decks with little or no vertical component to further separate wheat from dockage.  This motion, at the head of the machine, spreads the wheat across the full width of the screen surface and eliminates the need for multiple feeders.  The horizontal, circular motion stratifies the wheat, causing wheat to sink down against the screen mesh and pass through.  Through the length of the machine, circular motion diminishes to a reciprocating movement.  The reduced action at the discharge end of the machine separates near-size wheat kernels from the oversize dockage floating off the top, providing high recovery of wheat, which is then combined with the cleaned wheat from the MEGATEX Screeners.

The long stroke, low frequency motion of the machine, up to 3 1/2” stroke @ 200 rpm controls the proper retention time and bed depth of the wheat on the screen surface.  This stratifies the flow of material so that coarse dockage can be floated off the top screen and fines can be quickly screened.

The combination of United Harvest’s proprietary processes and the added efficiency of the new screeners has helped the company improve its operational efficiency and significantly reduce its ship loading time, according to Veltum.

The MEGATEX and ROTEX Screeners at the United Harvest terminal grain elevators are installed using the cable suspension technique.  This installation technique isolates out-of-balance screening forces to minimize their effect on adjacent equipment, and at United Harvest, there was another important reason as well.

“We’re located in a Seismic Zone 3, an area of greatest anticipated damage if an earthquake should occur,” Veltum said.  “Cable suspension helped us meet some of the building code requirements for equipment installation in this area.”

Veltum said the United Harvest has found the MEGATEX and ROTEX Screeners reliable and easy to maintain.  “The ability to suspend them by cable was also a consideration when decided to install a new system,” he said.