Size Enlargement Flashcards
It is a particle that are set in motion by air and may be operate in batch and continuous mode.
Fluidized bed granulators
Fracture of a granule to form two or more pieces.
Fragmentation
Operates in continuous mode and able to deal with large through-puts.
Tumbling granulators
It occurs when there is a long period during which no increase in size occurs.
Induction Growth
It results in larger particles than those formed in spray dryers.
Prilling
The size distribution of particles in an agglomeration process; it is determined by the kinetics of the many processes occurring simultaneously.
Population balance
Increase in particle size but not in total mass of particles
Coalescence
Generating nuclei that re-enter the cycle again
Attrition
Particles are ‘tumbled’ in an open cylinder, roughened walls were subjected to a combination of gravitational and centrifugal forces.
Drum Agglomerators
Particularly used with large particles, the rapid circulation within the bed gives rise to a high level of inter-particle impacts.
Spouted beds
For solid particles, the propensity ________ with particle size because of the availability of a larger number of weaker microcracks. Hence, larger particles break more ________ than smaller particles.
increases ; frequently
Briquetting machines are used to create briquettes of material by compacting smaller pieces together. The following are the advantages of using briquetting machines except?
Rollers can wear down quickly
Like breakage frequency, the average number of daughter particles is dependent on _____________.
Particle Size
I. Pellet mills compact powder in a confined space via a process called pressure agglomeration.
II. The pressure is increased in the compression step, causing brittle particles to break and malleable particles to deform.
Both statements are True
This is the size distribution of daughter particles resulting from breakage of particles of a particular size.
Daughter distribution function
Disc granulators, or pelletizing discs as they are known in the ore industry, work based on the tumbling technique of agglomeration. ______, magnetic, and electrostatic forces bind the agglomerates together. The strongest force against agglomeration is the ______ of the solid.
Van der Waals ; weight
Aggregation efficiency is a function of size of both the aggregating particles in the pair and is denoted by______.
a(x, x′ )
The powder is chopped and mixed to produce a fine, free-flowing powder. Then a liquid binder is blended with the powder to produce granules.
Mixer Granulator
The ________ is usually a function of particle size and is denoted by Γ(x). The Γ(x) provides the fraction of particles that will break per unit ____
breakage frequency ; time
In __________, molten input is picked up by a rotating drum and moves toward the outer surface of the drum.
Thermal Agglomeration
It is a process by which smaller particles are put together to form larger masses in which the original particles can still be identified
Size Enlargement
Size enlargement is one of the single most important process steps involving ___________in the process industries.
Particulate Solids
Size enlargement is mainly associated with the
All of the above
Methods by which size enlargement is brought about include granulation, compaction (e.g. tabletting), extrusion, _______, spray drying and prilling.
Sintering
I: Agglomeration is the formation of agglomerates or aggregates by sticking together of larger particles and granulation is agglomeration by agitation methods
II: There are many reasons why we may wish to increase the mean size of a product or intermediate
Only statement II is true
These are specifically important to granulation processes
Liquid Bridge Forces
The rate processes are important to granulation and _____________ included in order to develop a ________ model for simulation for the granulation process.
Population Balance ; simple
There exist between all solids molecularly based attractive forces collectively known as
van der Waals forces
The energy of these forces is of the order of ____ eV and decreases with the _____ power of the distance between molecules.
0.1 ; 6th
The attractive force, Fvw, between a sphere and a plane surface as a result of van der Waals forces was derived by ____________
Hamaker (1937)
Granules formed by _________ are usually not the ______ product in a granulation process.
Liquid Bridges ; end
Solid bridges between particles may take three forms:
Crystalline Bridges, Liquid Binder Bridges, and Solid Binder Bridges
If the material of the particles is soluble in the liquid added to create granules, crystalline bridges may be formed ________________.
When the liquid evaporates
I: The process of evaporation reduces the proportion of liquid in the granules producing high strength pendular bridges after crystals form.
II: The liquid used initially to form the granules may contain a binder or glue which takes effect upon evaporation of solute.
Both Statements are false
This is a finely ground ______ which reacts with the ______ present to produce a solid _______ to hold the particles together.
Solid ; Liquid ; Cement
The relative importance of the forces varies with changes in _______ properties and with changes in the humidity of the surrounding _______.
Particle ; Atmosphere
There is considerable interaction between the _____________
Bonding Forces
In aqueous systems adsorbed moisture can considerably increase ___________.
Van der Waals Forces
I: Absorbed moisture can also reduce interparticle friction and potential for interlocking, making the powder more free-flowing.
II: Liquid Bridges Forces decay rapidly if the humidity of the surrounding air is increased.
Both statements are false
If humidity is further increased liquid bridge formation can result in a return to cohesive behaviour. This effect has been reported in powder mixing studies by _________
Coelho and Harnby (1978) and Karra and Fuerstenau (1977)
When the granules are very weak (Stdef > 0.2), they fall apart due to collisions and no granule growth occurs. This is the _______.
Crumb Regime
All collisions between wet granules will lead to coalescence and the rate of growth will be high. Stv < Stv*.
Non-inertial Regime
No collisions lead to coalescence. Granules grow very slowly by layering only. Stv > Stv*
Coating Regime
Some collisions will lead to coalescence. The rate of granule growth will be moderate and sensitive to formulation or process parameters that change Stv. Stv ≈ Stv*.
Inertial Regime
When two granules collide within the granulator, what will the collision lead to if Stv > Stv*.
Rebound
If the viscous Stoke number of two colliding granules is Stv < Stv* , what will happen?
Coalescence
In this growth behavior, granules quickly reach a minimum porosity and there is lots of deformation on collision.
Steady Growth
Where granules grow in size very quickly and any induction time is reduced to zero, this growth behavior occurs at very high liquid saturations.
Rapid Growth
A simulation process used by engineers that is the suitable approach for wet agglomeration processes when more mathematics or precision are required
Population Balance Modeling
A simulation process that is suitable for the compaction process because it uses a numerical method useful for computing stresses in solids under load and deformation.
Finite Element Analysis
The primary potential driving forces for sintering includes; (except)
A dense Solid
Low vacancy concentration; Concave Surface, High vacancy concentration; Convex Surface
Both Statements are false
In polycrystalline materials, the mass transport ways that are responsible for sintering are; (except)
plastic diffusion
Layering is the dominant growth mechanism in the coating regime and is therefore most important for beds of large granules and low binder viscosity e.g. ammonium nitrate granulation, urea prill fattening and coating applications. Consolidation has a strong effect on the final porosity of granules produced by coalescence.
Both statements are true
Low density, high velocity spout through which most of the air travels; and a low density, moving bed annular region through which air percolates at a low velocity.
Only statement I is true
Mixer granulators find wide application for;
Construction
Four major classes of particulate caking: (Except)
Physical Caking
Green agglomerates are formed from solid particles and binder. Green agglomerates are not cured
Only statement I is true
The mode of operation to achieve and control agglomeration is characterized by several consecutive steps; (except)
Cutting
Spray drying represents an attractive alternative to traditional granulation and feed preparation methods used. Atomization of the liquid feed and contacting the spray with air are the critical features of spray dryers
Both statements are true
