SAJJAD KHUDHUR ABBASCeo , Founder & Head of SHacademyChemical Engineering , Al-Muthanna University, IraqOil & Gas Safety and Health Professional – OSHACADEMYTrainer of Trainers (TOT) - Canadian Center of Human Development

Episode 45 : 4 Stages Of Solid 4 Stages Of Solid Liquid SeparationsLiquid Separations

Pretreatment- increase particle size &

reduce viscosity

Solids Concentration- To reduce the volume of

material to process

Solid Separation-To separate the solids from

the liquid- To form cakes of dry solids- To produce particulate free

liquid

Post Treatment- To remove soluble, remove

moisture or prepare material for down stream process

4 St

ages

Of S

olid

Liq

uid

Sepa

ratio

ns4

Stag

es O

f Sol

id L

iqui

d Se

para

tions

Chemical

Physical

Clarification

Thickening

Clarification

Filtration

Centrifugation

Physical

PretreatmentPretreatment• Cost of S/L relates directly to the volume of material• Pressurized equipment is more expensive to operate

than thickener• Other techniques are classified according to the

substances that act upon, namely the liquid, the solid particles, solids concentration and solid-liquid interaction

Filter

Thickener

Costs

Size

Act Upon Treatment Technique

Liquid HeatingDilution with solventDegassing by chemical additive

Solid particles Coagulation by chemical additivesFlocculation by shear forcesAgeing

Solids concentration Increase concentration with a thickenerClassify to eliminate fliesFilter aid body feed

Solid-liquid interaction Heat treatment/pressure cookingFreeze/thawUltrasonicsIonized radiationWetting agents

Treatment of LiquidTreatment of Liquid

• Treatment is to change its viscosity– Raise the temperature– Dilute with a less viscous liquid (drawbacks are

increase slurry volume and additional process)• Degassing

– Liquid passes through filter – decrease pressure– Bubbles form within the cake

o f General form of correlation

Treatment of Solid ParticlesTreatment of Solid Particles• Coagulation & Flocculation

– Coagulation: very fine particles of colloidal size adhere directly to each other as a consequence of Brownian motion

– Flocculation: formation of open aggregates formed by coagulations through bridging action of polymers between separate particles

• The technique is to agglomerate the particles to improve the separations by increasing the particle size

• Solutions can be classified into:– Lyophilic (hydropholic)– Lyophobic (hydrophobic)

• Formation of larger particle: small particles to come together

• All particles carry a residue charge• Attracting forces: Van der Waal’s and London forces• Reduce the charge, particles close approach is possible

+ - + + - - + -

- -

Repulsion between particles

Attraction between particles

Colloidal ModelColloidal Model• Most particles carry a residue charge on their solid

surface: negative (minerals and clay) and positive (sewage sludge)

• 3 postulate mechanisms:– Crystal lattice defects: thus excess of anions or cations exist at

the surface– Sparingly soluble ionic crystals: existence of equilibrium

determined from the Nernst equilibrium condition

– Adsorption of ions from solution: via hydrogen bonding, changing positive charges to negatively charged particles

lnoo

RT cvF c

- -- -

- + + - - + + -

- + + -- + + -

- -- -

Double layerDouble layer• Negative surface is

surrounded by a layer of attached positive ions

• Surrounded by a layer of loosely attached negative ions (hence “double layer)

• Zeta, , potential difference between the bulk fluid and the potential of the shear plane and is directly measurable

NegParticle

Distance

Zeta

Pot

entia

l

Ner

nst P

oten

tial

1 232 sinh

Boltzman constantvalencebulk concentration of the iondielectric constant of the liquid bulk phasedouble layer potetial at distance xelectronic charge

d nkT vedx kTkvn v

eN

Avogadro's numberIonic strengthI

Gouy-Chapman modelGouy-Chapman model

2 2

exp( )where is the Debeye-Huckel function

81000

For small colloid particles charge, and in presence of electrolyte, the thickness of the double layer, d, is approximately, 1 .For wate

o x

e N IRT

-9

r,

2.3 10d cmI

Rate of AggregationRate of Aggregation

• The rates depends upon the motion of the particle to collide:– Perikinetic Coagulation: coagulation due to

Brownian motion– Orthokinetic Coagulation: coagulation due to

stirring & agitation

Mix

ing

and

agita

tion

devi

ceM

ixin

g an

d ag

itatio

n de

vice

Paddles

Baffles

Pipes

Particles

PaddlesPaddles

PipePipe

Packed bedPacked bed

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