Rotary filter comprising a screen drum and internal screw member

A rotary filter for filtering water out of raw material containing water comprising:

• a screen drum arranged rotatably about a longitudinal axis thereof and having first and second ends, said longitudinal axis being arranged substantially horizontally and said screen drum having an inner diameter;
• a screw means arranged rotatably about a longitudinal axis thereof within said screen drum, said screw means having an outer diameter smaller than said inner diameter of said screen drum, said longitudinal axis of said screw means being arranged substantially horizontally and being spaced from said longitudinal axis of said screen drum in a vertical direction such that a lower end of said screw means is brought into contact with a lower end of said screen drum for increasing resistance against transportation of said raw material by said screw means and providing increased water filtering efficiency;
• a raw material supplying means for introducing said raw material into a space formed between said screen drum and said screw means;
• said screw means further including a shaft formed of a hollow tube supporting a single spiral vane arranged about said hollow tube, a partition provided within said hollow tube adjacent said first end of said drum, and an opening provided in said hollow tube between said first end of said drum and said partition, and through said opening said raw material supply means communicates with said space formed between said screen drum and said screw means;
• a first driving means for rotating said screen drum in a first direction at a first rotating speed;
• and
• a second driving means for rotating said screw means in a second direction which is opposite to said first direction at a second rotating speed which is lower than said first rotating speed to transport said raw material introduced into said space from said first end to said second end of said screen drum,
• wherein said first and second driving means respectively and simultaneously rotate said drum and said screw means at said first and second rotating speeds and can be independently adjusted to respectively rotate said screen drum and said screw means at different speeds relative to each other.