September 22, 2000 ISSUE M11
It is the goal of Vincent Corporation to have one basic press design that will work in all manure applications. We feel that it is reasonable to expect to separate all manure types with a single screw configuration, one screen selection, and one discharge plate mechanism. It is because of this goal that each production run of Series KP presses shows some improvement over its predecessors.
A wide variety of manure is being run through KP presses. The machines have proven themselves in four broad areas: cow, pig, biogas digester sludge, and slaughterhouse pauch manure. The varieties within these categories are surprising.
Cow manure general is split into scrape and flush barn systems. Obviously one has thicker solids than the other, and consistent agitation is required for consistent feed. However an equally important variable is the type of bedding that is in use. After all, the bedding can be a major component going into the pit. Straw and shredded paper make a great press aid and facilitate operation of the separator. Sawdust will press well, but it will draw more horsepower. (Of course, sawdust can range from sawdust to wood shavings or sanding dust; they behave differently in the press.) When manure is the only bedding used, we must count on the screen to pass the tiny digested solids into the press liquor flow; otherwise they tend to blind a screen.
Pig manure and sludge from a biogas manure digester have an important characteristic in common. Both have a high percentage of micron size particles that pass through the screen of the press. Thus, the solids capture rate is lower than when there is a preponderance of large particles of undigested food.
Definite variations exist in pig manure. For example, in Alberta, barley is fed to pigs. This is a coarse grain that puts fiber in the manure that facilitates press operation. On the other hand, in the States the feed is milled to 750 micron average particle size. This makes a manure whose tiny solids are hard to capture.
The absence of bedding in pig manure is normal, as is a lack of agitation. Flow starts with thick solids, material that has floated to the top. Then there is a prolonged flow of highly clarified water, followed by bottom sludge. To handle this range of conditions requires careful press design.