Pressing News #35 from November 1995 dealt with the subject of feather meal. This animal feed is an important by-product at rendering plants that handle waste material from poultry processing. Feathers are rich in protein content, but in their natural form they cannot be digested. Hydrolyzation, the process of cooking the feathers with steam, makes them digestible. Once these cooked feathers are dried, usually to around 8% moisture, they become a valuable animal feed additive.

The potential application for a Vincent screw press comes after the hydrolyzers and before the dryers. If moisture can be squeezed out of the meal prior to drying, there is a large impact on drying costs. During our testing in 1995, Vincent tried a Model VP-16 press on meal that left the hydrolyzers at 55-56% moisture. Our best results, obtained by reducing press speed by one half, were 49-50% moisture. Unfortunately, this does not compare favorably to sludge presses from some other manufacturers. These presses, with continuous screws and tapered (increasing diameter) shafts, have been known to reduce moisture content by 12-15 percentage points. In 2003, Vincent had another opportunity to test our equipment on feather meal.

While not our primary focus, excellent results were achieved with a Fiber Filter. A flow of 15 gpm of press liquor was fed to a Model FF-6 Fiber Filter. We were hoping to recover valuable meal that had been pressed through the screens of the screw press. With 43 micron sleeves installed, the FF-6 was just able to handle the full flow. Capture rate was excellent, and there was a very thick sludge discharge of over 2 gpm. The value of that recaptured meal over a year’s time is in the neighborhood of $25,000. Thus we uncovered a potentially lucrative market for the Fiber Filter.

Our primary focus in the testing was to evaluate two new technologies that had been developed since 1995. First, rather than a traditional Model VP-16 screw press, we conducted our testing using a Twin Screw Model TSP-12. With overlapping screws and two additional stages of compression, Twin Screw presses usually squeeze tighter than VP (single screw) presses. Second, we installed a vacuum pump on the press to draw additional moisture through the screens.

By reinforcing the press liquor collection pan, reinforcing and sealing the covers of the press, and installing a rotary air lock on the press liquor drain, we were able to maintain a vacuum of 20-22 inches of mercury around the screens. Keeping a high enough level in the feed hopper sealed the inlet, while the press cake sealed the discharge.

Surprisingly, test results were no better than those in 1995. We were still reducing moisture content by only four percentage points.

The press tended to trip out on overload because of the vacuum pump’s ability to draw more material into the press. The slower we ran the press, the less cone pressure we could apply without tripping out. Our best results were obtained at 30 Hz and 40 psi on the cone. A larger motor would have helped, but it was judged that, even under ideal conditions, we would not triple our moisture reduction. On this sad note the testing was discontinued.