Matlink Digester (Continued)
MAY 28, 2002, Revised September 2010 ISSUE #M23
Three months ago we wrote about an extremely smooth start-up that had taken place at the Matlink Farm in Clymer, New York. This involved a manure digester system designed by RCM of Berkeley, California, 510-658-4466.
The Vincent screw press worked very well dewatering the digester sludge. However this only lasted for a few months during which sawdust was used as bedding. When the farm switched over to using composted press cake, troubles were encountered. The gpm capacity of the press went down by about 50%.
A worse problem was that the press would occasionally go into a purge condition. This condition is commonly referred to as having the press "blow the plug" at the cake discharge. At this time unpressed manure flows through the press without any dewatering, flooding the area where press cake normally forms a pile.
It was observed that the purge condition occurred when firm, solid press cake held open one side of the discharge door. This reduced the pressure against the cake on the other side of the door. The cake would become more and more moist, eventually reaching a condition where it flowed, without being pressed, past the door.
After two visits and testing a number of experimental doors, a very satisfactory solution was developed. The shaft of the screw was extended an additional 14". This makes the screw extend well past the cake discharge of the press. A door with a hole in the center, to allow for the extended screw length, was required. The result was absolute: there is no longer sufficient door area for cake to hold the door open. The purging characteristic has been totally eliminated.
Retrofit kits are being produced to modify manure presses that have had problems with purging. The kit consists of an extension that is welded to the end of the screw shaft along with a new door and yoke style actuator arms. The kits can be installed without the need to disassemble the machine.
At the same time a screw design has been developed that drastically increases the capacity of the press on digester sludge. This design, operating at Matlink, includes double flighting in the inlet portion of the press where the manure is thin. This design has also been found to significantly improve screw press capacity on flush barn systems where press cake is used for bedding.
TEN YEARS LATER
The farm entered bankruptcy and the digester is no longer being operated. The Vincent press was purchased by Noblehurst Farms. Today we would eliminate the purging problem by using half pitch (not double pitch) flighting and the rotating cone feature.