Granular Media Filtration: Backwash Tab

Variable Definitions, Ranges and Default Values

The following table shows a brief description of the variables appearing in this tab. The table also displays their default values and their generally acceptable range:

Variable	Default Value	Range

○ Inlet Stream Indicates the input port that is connected to the backwash stream. If a stream is already present at the selected port, then the button next to the selection is active. Click on the button to bring up the attached stream’s simulation dialog in order to provide its composition.	<None>	Any Input Port
◙ Inlet Stream Amount Per Mass Filtered (wt/wt) The flow requirement of the backwash stream expressed as mass of washing solvent per mass of material withheld in the filter.	5.0	Positive
◙ Inlet Stream Amount Per Volume Washed (kg/m³) The flow requirement of the backwash stream expressed as mass of washing solvent per bed volume washed.	200.0	Positive
○ Fluidized Bed Void Fraction (%) The bed porosity at rest.	80.0	0 – 100
○ Fluidized Bed Expansion (%) The percent increase in bed volume upon fluidization with respect to the bed volume at rest.	50.0	0 – 100
○ Pump Efficiency (%) The efficiency of the backwash stream pump.	75.0	0 – 100
◙ Filtration Time (h) The actual duration of the filtration step (per cycle).	5.0	Positive
◙ Backwashing Time (h) The actual duration of the backwashing step (per cycle).	2.0	Positive
● Backwash Linear Velocity (m/min) The average axial velocity of backwash in the bed.	0.0	Positive
● Backwash Pressure Drop (kPa) The pressure drop of backwash in the bed.	0.0	Positive

Symbol Key: ○ User-specified value (always input); ● Calculated value (always output); ◙ Sometimes input, sometimes output

Specification Choices / Comments

The following list describes the available specification choices in this tab; for more details on how these are implemented, see Granular Media Filtration: Modeling Calculations.

•Backwash Requirement Options...

The backwash requirement can be the one available in the inlet stream or specified per mass of solids removed, per volume of liquid filtered, or calculated based on fluidization velocity. Further, backwashing can take place continuously or alternating with filtration.