Rotary vacuum filters are used widely in the chemical, biochemical, food, agricultural, and other industries. They feature a horizontal-axis drum covered on the cylindrical portion by filter medium over a grid support structure to allow drainage to manifolds. Sizes (in terms of filter area) range from 0.4 to 95 m2 (Perry et al, 1984). Most rotary vacuum filters are fed by operating the drum with about 35% of its circumference submerged in a slurry trough, although submergence can be set for any desired amount between zero and almost total. Common rotation speeds are in the range of 0.1 to 10 RPM. Variable-speed drives are usually provided to allow adjustment for changing cake-formation and drainage rates.
● Rotary Vacuum Filtration Procedure
The material balances for the filtration operation are based on the removal percentage of particulate components and the cake dryness. More specifically, the removal percentage of particulate components determines the amount of those components that is retained in the cake. The cake dryness expressed as Loss On Drying (LOD) % or Cake Porosity determines the amount of solvent and soluble components retained in the cake before washing. Alternatively, you have the option to specify the directly the solvent percentage that is retained by the cake. The amount of washing determines the displacement of solvent and soluble components in the cake with the wash solvent. It is assumed that the solvent and soluble components in the cake are displaced in an embolic (plug-flow) fashion. The wash volume is specified on an absolute (L per cycle) or relative basis (L of wash liquid per L of cake).
In design mode of calculation, the process (filtration) time (tp) is specified by the user and the filter area (A) is calculated using equation eq. (A.104).
In rating mode, the user specifies the filter area and the number of units and the program calculates either the average filtrate flux (when the filtration time is specified) or the filtration time (when the flux is specified).
If the operation is batch and the equipment is in design mode, then the user must set both the filtration time and the average filtrate flux. If the operation is batch and the equipment is in rating mode, the user has the option of setting either the filtration time or the average filtrate flux. If the filtration time is set, then the average filtrate flux is calculated from eq. (A.104). Alternatively, if the average filtrate flux is set, then the filtration time is calculated using the same equation. If the operation is continuous and the equipment is in design mode, the average filtrate flux is set by the user. If the operation is continuous but the equipment is in rating mode, the average filtrate flux is calculated by dividing the volumetric flow of slurry processed by the equipment by the filtration area.
1. R.H. Perry, D.W. Green, and J.O. Maloney (1984). Perry’s Chemical Engineers’ Handbook, 6th Edition, McGraw-Hill, New York, p. 19-78.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Rotary Vacuum Filtration: Oper. Conds Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab