Top-entry agitation equipment may offer more predictable process results

By | May 01, 2002
Customer: U.S. Energy Partners, Russell, Kan.
Ethanol Plant

Date: May, 2002

Background: In early 2001, Dennis Vander Griend, design engineer for ICM, contacted Cleveland-Eastern Mixers regarding the need for agitation equipment for their ethanol project in Russell. While some ethanol producers have used circulating pump technology, ICM's standard plant designs utilize top-entry mixers. ICM believes top-entry agitation offers more predictable process results through better heat transfer and more uniform solid suspension. The result is a higher yield per tonnage processed.

Specifying the Equipment: In conjunction with Cleveland-Eastern's senior application engineer, Michael Reynolds, Vander Griend specified agitation equipment with the goal of achieving the best price-to-performance ratio. The mixers would be designed to offer a balance of long-term durability and lowest cost of acquisition and maintenance. One key design factor was the excessive height of the tanks, which required shaft designs capable of withstanding higher than average bending moment stresses. Another requirement was that the transmission be capable of torque loads higher than those demanded by other processes. Without equipment properly engineered for this rigorous service, U.S. Energy would be forced to process smaller batch sizes, impacting the operational efficiency of the plant.

A major design concern was to ensure uniform heat transfer throughout the batch. The goal was to have as low a temperature gradient as possible. In conjunction with heat transfer, solids suspension was another key concern. Without sufficient suspension, there is a risk of solids depositing in the heels of the tank, thereby restricting fermentation and heat transfer, and ultimately lowering the yield.

Agitation equipment is a very small portion of the overall plant construction costs, averaging less than 1% of the capital equipment budget. As such, specifying fail-safe equipment that ensures decades of trouble-free service does not negatively impact a plant's bottom line. Being such a critical part of the process, it is important to specify the best quality at inception.

Equipment Installed: Nine mixers total, all Cleveland's BHD series. The BHD series features helical/spiral bevel gearing, which is the most efficient for power transmission and speed reduction.

The drives are designed specifically for mixer service and are capable of withstanding the stresses of mixing applications while maintaining accurate component alignment. The BHD series features a no-leak drywell construction, unique because it isolates the low-speed output shaft from the oil sump to prevent lubricants from leaking and contaminating the process.

ICM could choose Cleveland-Eastern Mixers with confidence given the 60 years of application expertise offered. The BHD mixer series has a proven track record of over 20 years in the marketplace as well.

Process Data: While the mixers represent a small percentage of the total equipment purchased, they are indeed a key component of the process. The first step is to slurry the raw material with water. This is called the slurry tank. Next, the mash is continually stirred while being heated in the cook tube tank. This is where the starches are released and the mash is softened. The batch is then transferred to the liquefaction tanks where the chemistry is adjusted and the solids content altered to proper levels. From there, the mash is transferred to each of three large fermentation tanks. Here, the mixers agitate the material very slowly to promote the fermentation process and adequate heat transfer throughout the batch. Once the process is complete, the fermented batch is fed to the beer well tank which is close to one million gallons. The solids are then sent to the stillage tanks and are later converted into feed for livestock. If there should be any failure in the process, a syrup tank is on stand-by as a diversion area so that the entire process will not shut down.

Testimony: Ron Dunbar, plant manager at U.S. Energy Partners says "The BHD's are work horses. We installed them and were able to forget about them. We had a problem at installation and Cleveland-Eastern responded immediately with a short-term fix until the issue could be resolved. They really stand behind their products." n

For more information about this equipment, contact: Leslie Donkin, EMI, 860-669-1199