An enclosed and continuous filter press comprising:
- a pressure vessel;
- a filter zone within said pressure vessel partitioned by a filter into a filtrate chamber (A) and a chamber (B) for containing a slurry and a filter cake, said chamber (B) having a slurry feed inlet, said slurry feed inlet including a slurry feed inlet valve;
- a cake compressing zone disposed within said pressure vessel below and connected to said chamber (B) for compressing filter cake falling from the chamber (B);
- a cake discharging control valve connected to said cake compressing zone for discharging cake compressed in said zone;
- a rotatable hollow shaft, having an axis, passing through the filter zone and the cake compressing zone and having a compacting screw at a portion thereof positioned in the cake compressing zone;
- motor means for applying torque to said hollow shaft to rotate said hollow shaft about said axis;
- a means to feed a slurry to be filtered under pressure to said slurry feed inlet;
- said filter comprises (a) an outer cylindrical filter provided along an inner wall of said pressure vessel, (b) an inner cylindrical filter provided around said hollow shaft, and (c) a doughnut-shaped filter provided between said filters (a) and (b), these filters (a), (b) and (b) being arranged coaxially with said hollow shaft;
- said chamber (A) comprises a first filtrate collecting chamber which is a space between said inner wall of said pressure vessel and said filter (a), a second filtrate collecting chamber which is an internal space between said hollow shaft and said filter (b) and a third filtrate collecting chamber which is an internal space of said filter (c);
- a plurality of orifices formed in the portion of said hollow shaft positioned in said second filtrate collecting chamber for receiving filtrate flowing into said second filtrate collecting chamber and discharging said filtrate through an inner space of said hollow shaft;
- said first filtrate collecting chamber and said third filtrate collecting chamber being connected by a fluid passage, and filtrate collected in said first and third filtrate collecting chambers being dischargeable from said first filtrate collecting chamber,
- a fluid passage line, connected to a filtrate outlet valve and a backwashing liquid inlet valve, connected to said hollow shaft and said first filtrate collecting chamber;
- a means for feeding a backwashing liquid under pressure to said backwashing liquid inlet valve;
- said filter zone containing blades, rotatably mounted on said hollow shaft for rotation about said axis, said blades being independently driven for rotation about said axis by a drive mechanism in order to scrape off the cake accumulated on said filters (a), (b) and (c);
- a first detecting means for detecting the compression extent of the cake in said cake compressing zone by measuring torque variations of said hollow shaft and generating a first control signal in response thereto;
- a first control means for opening and closing said cake discharge control valve in response to said first control signal;
- a second detecting means for detecting the plug-up of said filters (a), (b) and (c) and generating a second control signal in response thereto;
- a second control means for closing said filtrate outlet valve and said slurry feed inlet valve and opening said backwashing liquid inlet valve in response to said second control signal to stop discharge of filtrate from the chamber (A) and feed a backwashing liquid under pressure to the chamber (A) for a predetermined period of time;
- and
- relief valve means responsive to said second control means for releasing a small amount of slurry from said chamber (b) during the feeding of the backwash liquid, whereby a pressure in chamber (B) is reduced and backwashing is performed.