LEC 8 Partech

Filtration

Filtration

It is a process of separating solids from a fluid by passing the mixture to a porous medium that retains the solids but allows the fluid to pass through

Slurry

It is a mixture of solids denser than water and its solution and is the feed to a filtration process. The solute inside the liquid (typically water) should be slightly soluble.

Filtrate

It is the fluid that passes through the filter medium

Filter Cake

The solid part that is trapped in the filter medium.

Physically or Mechanically

How are the suspended solid particles in a fluid of liquid or gas removed?

Septum (or porous filtering medium)

What is used to physically or mechanically remove the suspended solid particles?

A support with relatively large holes

What is used to hold the filter cloth which has small openings in the pores to block particle passage?

Yes, although resistance to flow also increases

Can the cake buildup act as a filter as well?

• Cake/Surface Filtration

• Clarifying/Depth Filtration

• Cross Filtration

What are the types of filtration?

Cake/Surface Filtration

Type of filtration where the filtrate passes through the medium and the cake builds up on the surface

Clarifying/Depth Filtration

Type of filtration that “captures” the particles and lets the filtrate pass through

Cross Filtration

Type of filtration wherein the flow is perpendicular, while the fluid flows horizontally, the particles are trapped vertically.

• Microfiltration

• Ultrafiltration

• Nanofiltration

• Reverse Osmosis

What are the different kinds of filtration depending on what they can capture?

• Gravity

• Vacuum

• Pressure

• Centrifugal

What are the other types of filtration systems?

• Bed filter

• Plate and Frame

• Leaf Filter

What are the types of filters?

Bed Filter

• type of filter used when relatively small amounts of solids are to be removed from large amounts of water

• bottom (coarse) to top (fine)

When the filtered particle clogs the fine sand layers and the flow rate of the drawn-out liquid drops

How to know if the filtration in bed filter is done?

Water is introduced in the reverse direction along the backwashing of the bed

How to regenerate the bed filter?

Plate and Frame

• this type of filter consists of plates and frames assembled alternatively with a filter cloth over each side of the plates

• slurry is pumped into the press and flows through the duct into each of the open frames so that the slurry fills the frames

The filtrate flows through the filter cloth then through the channels and the solids build up as a cake on the frame

How does filtration in plate and frame work?

When frames are completely filled with solids, plate and frame must be separable so that the cake can be removed; then reassembled for reuse.

How to know if the filtration in plate and frame is done?

Leaf Filter

• A type of filter where a number of leaves are hung in parallell in a closed tank. Each leaf is a hollow wire framework covered by a sack of filter cloth

A shell can be opened and air is blown in reverse to dislodge the cake from the leaf.

What is done in a leaf filter if the cake is wanted?

Water jets can be used to simply wash away the cakes without opening the filter.

What is done in a leaf filter if the cake is not wanted?

Rotary Drum Filter

• Type of filter where inside the drum consists of hollow circumferential sectors which is connected to a central valve which creates a vacuum sucking the slurry onto the surface of the drum

Scraper

What is used to remove the solid in a rotary drum filter?

• Cake resistance

• Filter medium resistance

What are the two resistance to flow present in filtration?

Filtration is operated at total operating pressure

What is done to overcome flow resistances?

Constant-pressure Filtration

The pressure drop is held constant while the flow rate allowed to fall with time

Constant-rate filtration

The filtration rate is held constant while the pressure drop progressively increases

Delta Pt = Delta Pc + Delta Pm

What is the formula for pressure drop?

Carman-Kozeny’s Equation

What equation is used for a laminar flow in a packed bed of particles to find the pressure drop of fluid through the filter cake?

4.17

What is the value of the constant k1 for random particles with definite size and shape in the carman-kozeny’s equation?

• gravitational

• centrifugal

• pressure

• electrical force field

• concentration

What are the driving forces of filtration?

Gravitational Force

What driving force is used in large sand-bed filters and in simple laboratory filtrations?

Centrifugal force

Centrifuges with a porous filter medium in which gravitational force is replaced by _____ many time greater than gravity

Pressure

It is a force that acts on the fluid above the filter or application of vacuum below te filter or by a combination of such forces

Electrical force field

It is a driving force used in electro-dialysis

Concentration

Dialysis is an example of a membrane separation process that uses this driving force.

• Filter Medium (Membrane)

• Compressor

• Support

• Rapper

What are the basic components of filtration?

Filter medium

Filter cloth, filter-screen, common lab filter paper, thicken masse barriers, sand beds, coke beds, porous ceramics, porous metal

Compressor

Used to push the particle-laden fluid through the filter medium

Support

It is a mechanical device that holds the filter medium

Rapper

Part of filter cake or other solid particles for washing

• Membrane charge

• Porosity

• Pore Size

What is the degree of separation based on?

Synthetic Polymers

What are membranes made of?

(10 to 0.1 micro m) small particles, large colloids, microbial cells

What are examples of materials separated by MF?

<0.1 micro m to 5 nm emulsions, colloids, macromolecules, proteins

What are the examples of materials separated by UF?

~ 1 nm dissolved salts and organics

What are the examples of materials separated by NF?

<1 nm dissolved salts and small organics

What are the examples of materials separated by RO or hyperfiltration

• Polyvinylidenefluoride (PVDF)

• Polyacrylonitrile (PAN)

• Polypropylene (PP)

What are some other materials used to build membranes?

Polyamide

What are RO membranes made of?

Polysulphones

What materials are used for UF and MF

Polysulphone, Polyimide, Ceramic materials

What materials are used to construct NF membranes?

below 2 bar

Operating Pressure of MF

between 1 to 10 bar

Operating Pressure of UF

between 5 and 35 bar

Operating Pressure of NF

10 to 70 bar

Operating Pressure of RO

Pervaporation Process

It is a membrane separation process for separating liquid mixtures, wherein the upstream of it is in contact with feed liquids and the downstream is kept at vacuum state or applied with sweeping gas or heat.

• Tubular

• Hollow Fiber Membrane

• Plate and Frame

• Ceramic and Polymeric Flat Sheet Membrane

• Spiral Wound

What are the different membrane configurations?

• Dead end Filtration

• Cross-flow Filtration

What are the two operational modes for membranes?

Dead end Filtration

All the feed applied to the membrane passes through it, obtaining a permeate. Since there is no concentrate stream, all the particles are retained in the membrane.

Cross-flow Filtration

The feed water is pumped with a cross-flow tangential to the membrane. This model implies that for a flow of feed0water across the membrane, only a function is converted to permeate products as recovery.

• Membrane permeability (k)

• Operational driving force per unit membrane area (Trans membrane pressure)

• Fouling and subsequent cleaning of the membrane surface

What are the key elements of any membrane process related to the influence of parameters on the overall permeate flux?

Pore Narrowing

Membrane fouling which consists of solid material that has been attached to the interior surface of the pores.

Pore Blocking

Membrane fouling that occurs when the particles of the feed-water become stuck in the pores of the membrane

Gel/Cake Layer Formation

Membrane Fouling where the solid matter in the feed is larger than the pore sizes of the membrane.

Scaling

Membrane fouling which concerns the formation of chemical precipitates

Biofouling / Colonization of the Membrane

Membrane fouling that takes place when microorganisms grow on the membrane surface.

TRUE

TRUE OR FALSE: For incompressible cake, specific cake resistance is independent of pressure drop and of position in the cake.

specific resistance of filter cake in m/kg

What is alpha?

Resistance of the filter medium in 1/m

What is Rm?

s/m^6

What is the unit of Kp?

s/m³

What is the unit of B?