Ethanol - Potato Waste

April 22, 1999

We recently visited an interesting ethanol plant in Idaho. It is one of two owned by the J. R. Simplot Company that uses potato peel waste as a raw material.

The potato peel is a zero value waste from nearby potato processing plants. These plants peel the potatoes as part of the production of french fries, instant potatoes and similar products. The resultant waste is hauled to the ethanol plant.

The first step at the ethanol plant is to shred the waste because it contains whole cull potatoes. The material contains a great deal of white starch that results from the peeling process. The material is processed with enzymes in order to liquify the starch and sugar. The flow, containing 12 to 15% total solids, is referred to as beer. It is pumped to a distillation tower. Alcohol is taken off the top of the tower, while stillage comes off the bottom.

The stillage consists of the remaining solids and water. The flow is 130 gpm with 5% solids. At the plant this is pumped to a Sharples centrifuge which separates the waste into filtrate and solids with 85% moisture content. Centrate is the name given to the filtered liquid; it is also called thin stillage. The solids from the centrifuge are trucked to nearby farms for use as a cattle feed.

The stillage is too thin to separate in a screw press. However, we feel that the Fiber Filter, feeding its sludge to a small KP-6 screw press, might achieve the same results as the centrifuge. Centrifuge maintenance costs are high, approaching the cost of a FF-12 Fiber Filter on an annual basis.

A more promising application is to use the FF-12 on the flow between the enzyme reactors and the distillation tower. This flow contains materials such as brown potato peel and stringy material referred to as vines or roots. They hinder the effectiveness of the distillation tower, so efforts have been made previously to filter them from the flow.

We hope to test a Fiber Filter at the plant later this year.

Issue 93