The Table Filter

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Disc Filter

 

Description

The Table Filters belong to the top feed group, introduced in the early 40's and were rather small and of a simple design. Their main limitation was at the discharge zone since the cake was contained in a fixed rim and special sealing arrangements had to be provided in order to avoid the spillage of brine at the table's circumference. Another problem was that the thin heel left between the scroll and the surface of the table was dislodged by applying a back blow but not removed from the surface of the passing cell. So, as it reached the feed zone it was mixed with the incoming slurry without the cloth being washed. This has caused progressive media blinding which effected filtration rate and required frequent stoppage of the operation for cloth washing.

 

As the demand for more area and higher throughputs has gone up in the 60's the Table Filters and Tilting Pan Filters were redesigned and upgraded since the rubber technology was unable to catch-up with the filtration area requirements of Horizontal Belt Filters.

A typical flowscheme for a counter-current washing may be seen on the left. The flowscheme consists of three washing stages and is a conventional design for phosphoric acid plants. The filter in the flowscheme is a table filter however the same diagram applies also to Tilting Pan Filters and Horizontal Belt Filters.

In the old design the rim that contained the cake was fixed to the main structure and had an opening just at the discharge point to allow cake removal. In this design a thin heel was left continuously on the filtering surface, could not be removed and caused loss of filtration rate due to  blinding. Likewise owing to the friction between the moving cake and the stationary rim the drive was subjected to high power consumption.

 

 

To solve the problems encountered with fixed rim a radically new engineering concept was developed in the late 60's. The new table filter features a rubber belt rim that rotates together with the cells but is removed from the table just after leaving the final wash and drying zone and before reaching the cake discharge hopper. The rim then moves away from the table, the cake discharges and the heel is removed by high impact jets to a cloth wash water to a separate chute. It then continuous to a cloth drying zone for such applications that the dilution of mother liquor is undesired and returns to the slurry feed section. 

Scroll Discharge End
 
Scroll
Scroll Drive
Cake Hopper
Fixed Rim
To view the components move mouse pointer over the menu Scroll cake discharge

Special rollers are diverting the rim at the cake discharge zone and a tension take-up roll ensures that the belt stays tight against the table and seals the circumference against leakages.

The filtration area of large Table Filters is more than 200 m2 and since there are few moving parts, contrary to Pan Filters, the table can rotate at a cycle time of 1 minutes.

 

These filters can handle thick cakes and may be operated at high vacuum levels. The major subassemblies of the Table Filter are:

To view the components move the mouse pointer over the menu

Feed+Cloudy Port Zone
Mother Filtrate Zone
1st Wash Filtrate Zone
2nd Wash Filtrate Zone
3rd Wash Filtrate + Drying Zone
Cake Discharge Zone
Cloth Washing Zone
Cloth Drying Zone
Cake Discharge Scroll
Cake Retaining Rubber Rim 

 Central Filtrate Valve

 

 

Selection Criteria

The criteria for selecting a Table Filter are:


Operational Sequence

The cycle of a Table Filter that includes three counter-current washing stages consists of the following zones:



Maintenance

When compared to Tilting Pan Filters the Table Filter has less moving parts so the major components to be checked as part of the preventive maintenance schedule are: