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Episode 44 : 4 Stages Of Solid Liquid Separations
The document discusses the four stages of solid-liquid separations: pretreatment, solid separation, post-treatment, and the costs associated with various techniques. It covers methods for improving particle agglomeration and separation through coagulation and flocculation, as well as treatment techniques affecting viscosity. Additionally, it explains the significance of particle charges and the mechanisms involved in aggregation rates.
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Episode 44 : 4 Stages Of Solid Liquid Separations
- 1. SAJJAD KHUDHUR ABBAS Ceo, Founder & Head of SHacademy Chemical Engineering , Al-Muthanna University, Iraq Oil & Gas Safety and Health Professional – OSHACADEMY Trainer of Trainers (TOT) - Canadian Center of Human Development Episode 44 : 4 Stages Of Solid4 Stages Of Solid Liquid SeparationsLiquid Separations
- 2. Pretreatment - increase particlesize & 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 4StagesOfSolidLiquidSeparations4StagesOfSolidLiquidSeparations Chemical Physical Clarification Thickening Clarification Filtration Centrifugation Physical
- 3. PretreatmentPretreatment • Cost ofS/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
- 4. Act Upon TreatmentTechnique Liquid Heating Dilution with solvent Degassing by chemical additive Solid particles Coagulation by chemical additives Flocculation by shear forces Ageing Solids concentration Increase concentration with a thickener Classify to eliminate flies Filter aid body feed Solid-liquid interaction Heat treatment/pressure cooking Freeze/thaw Ultrasonics Ionized radiation Wetting agents
- 5. Treatment of LiquidTreatmentof 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 fµ µ ε= General form of correlation
- 7. Treatment of SolidParticlesTreatment 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)
- 8. • Formation oflarger 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
- 9. 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 lno o RT c vF c ψ = ÷ ÷
- 10. - - - - -+ + - - + + - - + + - - + + - - - - - 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, ζ, potential difference between the bulk fluid and the potential of the shear plane and is directly measurable Neg Particle Distance ZetaPotential NernstPotential
- 12. 1 2 32 sinh Boltzman constant valence bulkconcentration of the ion dielectric constant of the liquid bulk phase double layer potetial at distance x electronic charge d nkT ve dx kT k v n v e N ψ π ψ ε ε ψ = − ÷ ÷ = = = = = = Avogadro's number Ionic strengthI = = Gouy-Chapman modelGouy-Chapman model 2 2 exp( ) where is the Debeye-Huckel function 8 1000 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 I RT ψ ψ χ χ π χ ε χ = − = -9 r, 2.3 10 d cm I × ≅ ∫
- 13. Rate of AggregationRateof 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
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