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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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