High compression shaft configuration and related method for screw press systems used in rendering applications

A method of rendering liquid fat from animal protein, the method comprising:

• heating the animal protein;
• after the heating step, feeding the heated animal protein into a rendering screw press machine having an internal shaft assembly, the shaft assembly comprising:
• a feed quill portion and a working portion, the working portion extending through a barrel cage of the rendering screw press machine, the working portion having:
• a length to diameter ratio of between about 4 to 1 and about 5 to 1;
• an overall compression ratio of greater than about 7 to 1;
• a first scroll flight section including one or more scroll flights, the first scroll flight section configured for decreasing cake thickness;
• a first high compression cone section adjacent and downstream of the first scroll flight section;
• a stepped decompression section adjacent and downstream of the first high compression cone section;
• a second scroll flight section adjacent and downstream of the stepped decompression section, the second scroll flight section configured for decreasing cake thickness;
• a second high compression cone section downstream of the second scroll flight section;
• and
• a straight collar section adjacent and downstream of the second high compression cone section and in part defining a choke opening for animal protein;
• rotating the shaft assembly to move the heated animal protein through the rendering screw press machine such that liquid fat passes out through the barrel cage and substantially dried animal protein cake is output from the choke opening, and the heated animal protein only undergoes one stepped decompression during such movement.

A shaft assembly for a rendering screw press machine, the shaft assembly comprising:

• a feed quill portion and a working portion, the working portion having:
• a length to diameter ratio of between about 4 to 1 and about 5 to 1;
• an overall compression ratio of greater than about 7 to 1;
• a first scroll flight section including one or more scroll flights, the first scroll flight section configured for decreasing cake thickness by between about 45% and about 55% over a length of between about 20 inches to about 30 inches with a compression ratio of between about 2.4 to 1 and about 2.5 to 1;
• a first high compression cone section adjacent and downstream of the first scroll flight section, the first high compression cone section defining a compression ratio of between about 1.2 to 1 and about 1.3 to 1 along a length of no more than about seven inches;
• a stepped decompression section adjacent and downstream of the first high compression cone section and defining a stepped decompression ratio of at least about 1.5 to 1;
• a second scroll flight section adjacent and downstream of the stepped decompression section, the second scroll flight section configured for decreasing cake thickness by between about 25% and about 35% with a compression ratio of between about 1.8 to 1 and about 1.9 to 1 over a length of between about 12 inches to about 18 inches;
• a second high compression cone section adjacent and downstream of the second scroll flight section, the second high compression cone section defining a compression ratio of between about 2.2 to 1 and about 2.6 to 1;
• and
• a straight collar section adjacent and downstream of the second high compression cone section.

A shaft assembly for a rendering screw press machine, the shaft assembly comprising:

• a feed quill portion and a working portion, the working portion having:
• a length to diameter ratio of between about 4 to 1 and about 5 to 1;
• an overall compression ratio of greater than 8 to 1;
• a first scroll flight section including one or more scroll flights, the first scroll flight section configured for decreasing cake thickness by between about 35% and about 40% with a compression ratio of between about 1.6 to 1 and about 1.7 to 1 over a length of between about 24 inches to about 34 inches;
• a first high compression cone section adjacent and downstream of the first scroll flight section, the first high compression cone section defining a compression ratio of between about 2.0 to 1 and about 2.5 to 1 along a length of no more than about ten inches;
• a stepped decompression section adjacent and downstream of the high compression cone section and defining a stepped decompression ratio of at least about 1.4 to 1;
• a second scroll flight section adjacent and downstream of the stepped decompression section, the second scroll flight section configured for decreasing cake thickness by between about 30% and about 40% with a compression ratio of between about 1.5 to 1 and about 1.6 to 1 over a length of between about 12 inches to about 18 inches;
• a second high compression cone section adjacent and downstream of the second scroll flight section, the second high compression cone section defining a compression ratio of between about 2.1 to 1 and about 2.4 to 1;
• and
• a straight collar section adjacent and downstream of the second high compression cone section.