Disc Vacuum Filters
The NFM Disc Vacuum Filter is a continuous filter for high production rates for thickening or solids concentrating requirements. It is used on low resistance filter cake applications. They are often high density, highly abrasive slurries.
Process slurry is fed into the vat along the full length of the vat for even distribution, while the overflow box runs the full length of the vat. The slurry is suspended by a high speed mixer commonly designed with heavy duty paddles. Homogenizing the solids ensures consistently thick cakes on all parallel discs, which directly results in high production and low cake moistures. All discs are attached to a single shaft through which vacuum is drawn. When the discs are submerged in the slurry, the cake forms on the individual disc sectors while filtrate passes through a filter fabric covering each sector, through the sector, into the staggered center barrel filtrate pipes.
The center barrel filtrate piping is welded to a pipe plate that mates with a rotary valve. From the valve, the filtrate flows to a vacuum receiver where the air and water separate to the vacuum pump and the self-priming centrifugal filtrate pump. Meanwhile, the filter cake dewaters as the disc rotates out of the vat level, until the vacuum is released and a quick snap-blowback of pressurized air discharges the filter cake over an adjustable doctor blade and down through a wide cake chute with hanging plastic liners.
Control points to achieve higher production rates and lower cake moistures are the vat level, the disc rotating speed, the timing of the form vacuum versus the dry vacuum, the snap-air pressure, and the position of the doctor discharge blades.
High hydraulic rates are achieved with the staggered discharge feature, different sector designs, heavy duty filter fabrics covering each sector, and the rotary filtrate valve positioning and timing.
The direct disc drive assembly and vat level control are automated to achieve the optimum cake thickness for maximum tonnage at the lowest cake moisture.
For example, NFM offers many different disc sector designs with different ways of replacing the filter fabric. For example, NFM offers various plastic grids, or metal designs with a wide variety of filter fabrics to maximize particle capture, cake release, reduce blinding, and good mechanical strength for long service life. We apply the same approach to other components such as rubber covered ferrules, the adjustable doctor scraper blades, rubber covers, filtrate pipe linings, floating stuffing box with Teflon lantern ring and rubber packing for the center barrel.
Ideally suited for fast filtering, rapidly settling abrasive slurries:
- High slurry densities > 1.9
- P80 Particle Size ranges greater than 75µm
- Cake Thickness ranges from 15mm to 100mm
- Cake Formation Time ranges from 5 seconds to 30 seconds
- No Cake Washing, the NFM Disc Vacuum Filter is for dewatering/concentrating only
- Producing solids greater than 150 dry pounds per hour per square foot
- Producing filtrate greater than 10 gallons per minute per square foot
- Ruggedly designed for abrasive conditions