July 17, 2001

For several years Vincent Corporation has been testing various screw presses in ethanol plants.

In 1994 Pressing News #9 described a system that used corn stalk and a unique bacteria to produce ethanol. In 1995 Pressing News #26 described an NREL project where a Vincent press was used to extract cane juice, part of an effort to reclaim the lands left from phosphate strip mining. In 1997 Pressing News #54 reported a false start at producing ethanol from custard apples. More recently, in 1999, Pressing News #93 told how J. R. Simplot Company uses potato peel waste as a raw material for the production of ethanol.

All of this Vincent testing work has been aimed at penetrating the much larger market, ethanol production from corn and other grains. This ethanol is sold as an additive used in gasoline, producing gasahol. The leading firms in this government sponsored industry are ADM and Cargill, with a significant number of smaller firms, mostly farmer cooperatives, also operating facilities.

These ethanol plants share a common need to dewater the spent grain that remains at the end of the fermentation process. This fiber is dried and sold as animal feed. The industry would like to use screw presses for this dewatering. However limited success with Vetter, Stord, and even Vincent presses has led to the common use of centrifuges for dewatering spent grain. The high annual maintenance costs of centrifuges are cited as incentive to screw press designers.

In April 2001 a Vincent Twin Screw Press was tested in dewatering thin stillage. The results were better than achieved previously with our single screw Series VP, CP, and KP presses. However it was concluded that a press aid, such as cotton seed hulls, would have to be used in order to equal the performance achieved by centrifuges. In addition, a reversing starter, with an automatic timer, was required to keep the press screens operating at peak performance.

Press aids are commonly used by producers of apple and grape juice. For ethanol plants the roughage represented by the cotton seed hulls may improve the value of the feed and its drying characteristics. Yet clearly it remains to be seen if the industry will adapt to using these press aids.

Issue 119