The peel is very wet, which limits its value as an animal feed.  Also the wet weight results in significant haulage costs.  By running it through a screw press its value is enhanced and trucking costs are reduced.

Normally the peel comes to the screw press with 86% to 93% moisture.  The lower figure may result from an existing screening device that drops out free water.  This device is best left in place as a pre-thickener for the screw press.

Dewatering potato peel is a tough application.  The best way to make it pressable is to react it with hydrated lime [calcium hydroxide, Ca(OH)₂].  Doing this allows the press to separate up to 70% of the flow as press liquor, and the rest is firm cake at 75% moisture content.  A short reaction time, with 2% lime by weight, is required.

When a press works without lime being used, typically the incoming flow of wet peel can be divided into a 50:50 split of press cake and press liquor.  Separation performance depends on the air pressure setting of the discharge cone.  Press cake moisture of 82% can be expected.

With a low cone pressure setting, the press liquor is relatively clear.  With high cone pressure a noticeable amount of “mashed potatoes”, or starch, will be forced through the screen and into the press liquor.  This may or may not be acceptable to the processor, depending on his wastewater treatment facility. 

The starch can be separated from the press liquor by directing it through a gravity decanter tank.  Alternatively, hydraclones and the Vincent Fiber Filter may be suitable.  When solids are screened from the press liquor, they are often added back to the flow of material going into the press. 

The less expensive Series KP presses, operating at very low speed, have found acceptance in this application.  These feature wedgewire screens with slot widths of 0.015″.  Auto-reversing VFD’s are provided where screen blinding problems occur. In addition to presses, Vincent maintains lime metering dosers and gravity screens in our rental fleet.  These are available for demonstrating peel dewatering techniques.