Filtration-MK

Filtration Overview

  • Filtration: separation of solids from fluids (liquids or gases) via a porous medium.

Filter Medium Resistance

Definition

  • Filter medium resistance (Rm) is defined by analogy with cake resistance.

Equation

  • Rm = Δp / (μ * v * A)

    • Δp: Pressure drop

    • μ: Viscosity

    • v: Linear velocity

    • A: Area.

Overall Pressure Drop

  • Overall pressure drop includes:

    • Cake resistance

    • Medium resistance.

Important Variables

  • V: Volume of filtrate collected.

  • C: Mass of particles deposited per unit volume of filtrate.

Constant Pressure Drop Filtration

  • At t=0, V=0, pressure drop is constant.

  • Rate of filtrate collection decreases with time.

  • Slope and intercept equations derived from integration between limits (0, 0) and (t,V).

Constant Rate Filtration

Characteristics

  • Flow of filtrate is constant, Δp varies to maintain constant rate.

  • Linear velocity (v) stays constant.

Specific Cake Resistance Equation

  • Adjusts for changes in pressure drop.

Continuous Filtration

Example: Rotary Drum Filter

  • Steps:

    • Element of filter cloth enters slurry pond.

    • Cake formation, washing, drying, discharging.

Cake Resistance

Empirical Equations

  • Specific cake resistance uses constants α0 and s.

  • Cake compressibility affects α; increases with Δp in compressible cakes.

Filter Designs

Plate and Frame Filter Press

  • Comprises square/circular plates and frames for solid collection.

  • Filters under 3 to 10 atm pressure.

Rotary Drum Filter

  • Submerged design allows continuous operation.

Hydrocyclones

  • Separates solids from liquids using centrifugal force.

Clarifying and Cleaning

Principles of Clarification

  • Removal of small solids from liquids/gases via mechanical or gravity methods.

Gas Cleaning Methodology

  • Uses disposable and reusable materials like cellulose or metal filters.

Dewatering

  • Separation of liquid from solids; processes vary based on solid size and density.

Settling Processes

  • Methods categorized into thickening and clarification, primarily utilizing gravity principles.

Centrifugal Separation

Advantages

  • Enhanced separation effectiveness and reduced size compared to gravity methods.

Types Include

  • Gas cyclones, hydrocyclones for separating solid and liquid phases.

Operational Principles

Cyclones

  • Utilize centrifugal force; efficiency depends on particle size and density.

  • Quick separation reduces the footprint needed for machinery.

Centrifugal Decanters

  • Separate immiscible liquids or solids; apply centrifugal force significantly greater than gravity.

Conclusion

  • Various filtration methods are optimized according to the material properties (density, size) ensuring effective separation in industrial applications.