Unit Operations Flashcards
Principal type of gas-solid separator employing centrifugal force
Cyclone
Evaporation is sometimes called ____
Water distillation
The total amount of evaporation an evaporator is capable of producing per unit time
Capacity
When the pressure of an evaporation chamber is decreased, the boiling point of the solution inside the chamber will _____
Decrease
The temperature driving force in an evaporator is determined as the difference between the condensing steam temperature and _____
Boiling point of the solution
In country where capital is scarce and energy cost is low, it is appropriate to install a ______ effect evaporator
Single
It is the deposition and growth on body walls, and especially on heating surfaces, of a material undergoing an irreversible chemical reaction in the evaporator
Scaling
It is the formation of deposits other than salt or scale and may be due to corrosion. It is caused by poor material of construction
Fouling
Slow cooling produces ____ crystals, and fast cooling produces ____ crystals
Large, small
The process by which crystalline bodies are created within a supersaturated fluid
Nucleation
The ability of a substance to crystallize into different crystalline forms
Polymorphism
Major stage of a crystallization process, and consists of the addition of new atoms, ions, or polymer strings into the characteristic arrangement of the crystalline lattice
Crystal growth
Technique widely employed to provide preformed templates on which new molecules can converge to form crystals
Seeding
When a solution is cooled to produce a supersaturated solution, the heat that must be removed is the sum of the ______ necessary to cool the solution and the heat of crystallization
Sensible heat content
During sensible cooling, relative humidity _____
Increases
Removal of all moisture from a wet solid requires _____
Perfectly dry air
Portion of water that cannot be removed by the air in its contact
Equilibrium moisture content
Moisture contained by a substance in excess of the equilibrium moisture
Free moisture
Drying method employed for heat sensitive materials such as pharmaceuticals and food stuff
Freeze drying or lyophilization
Detergent solution is dried to a powder in a _____
Spray dryer
Calcium ammonium nitrate fertilizer is dried using a _____
Rotary dryer
Feed characteristics for forward feed evaporation
Hot
Feed characteristics for backward feed evaporation
Heat sensitive, viscous
Feed characteristics for parallel feed evaporation
High feed rate
Advantage of parallel feed evaporation
Prevents salting or precipitation of solids
Suitable evaporator for concentration of foaming liquid
Long tube evaporator
Unit operation in which a soluble component is removed from an inert solid by a solvent which preferentially dissolves the soluble matter
Leaching
Unit operation by which soluble components of a liquid mixture are dissolved in a liquid immiscible with the insoluble component
Solvent extraction
Common leaching solvent in the vegetable oil industry
Hexane
In a counter-current extractor, extraction efficiency ____ with increasing axial mixing
Decreases
Extractor used for extraction of oil from oilseed
Bollman extractor
Extractor used in mineral processing to extract metals (e.g., Au and U) from their ores
Pachuca Tank
Extractor used to treat radioactive nuclear waste
Pulsed column extractor
Liquid-liquid extraction is based on the differences in _____
solubility
Single large washing is _____ effective than repeated small washing
Less
Why should the solvent used in liquid extraction not have a high latent heat of vaporization?
Recovery cost by distillation is high
Liquid-liquid extraction is preferred when extracting solvent is _____
cheap and abundantly available
TRUE or FALSE: In a counter-current liquid extractor, only one of the liquids may be pumped at any desired rate
True
It is comprised of a thin bed of substances with high porosity used in a mixer-settler liquid-liquid extraction column to increase the bubble size of the entering settler and to increase the settling rate of the bubbles.
Coalescer
Extraction equipment which best handles antibiotics
Podbielniak extractor
The relative volatility of most ideal binary solutions is _____ affected by temperature
greatly
Increasing the operating pressure of a distillation column makes separation ____
Difficult
Distillation technique used to avoid thermal decomposition of a component
Steam distillation
In steam distillation, the amount of steam required per unit quantity of distillate is reduced by ____ temperature, and ____ total pressure.
Increasing temperature, decreasing total pressure
Cooled liquid stream returned to the column to a cool plate or stage
Reflux
The pressure in a distilling column decreases from ____ to _____
Bottom to top
The temperature in a distilling column decreases from ____ to _____
Bottom to top
In a distillation column, the heat removed in the cooler ____ with increasing reflux ratio
Increases
Fenske equation is applicable when
Relative volatility is constant
Design calculation for multiple component distillation
Fenske-Underwood-Gilliland (tray-to-tray calculations)
Distillation technique wherein solvent is added to alter the relative volatility of the mixture
Extractive distillation
Distillation technique employed to separate a constant boiling mixture
Azeotropic distillation
Material passing one screening surface and retained on a subsequent surface
Intermediate material
Indicates the number of holes per linear inch
Mesh number
TRUE or FALSE: The Ponchon-Savarit method is more accurate than McCabe-Thiele method to determine the number of theoretical stages required for the separation of non-ideal binary systems by distillation
True
TRUE or FALSE: In Ponchon-Savarit method, the stripping and rectifying operating lines are vertical at total reflux
True
TRUE or FALSE: Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum
False
For an azeotropic mixture, the equilibrium liquid composition is ____ the vapor composition
Equal
Size measurement expression for coarse particles
cm, in, mm
Size measurement expression for ultrafine particles
surface area per unit mass
Size measurement expression for fine particles
mesh
Size measurement expression for very fine particles
microns
Property of a material to resist indentation or scratches
Hardness
Mohs Hardness Scale
Soft: talc, gypsum, calcite
Intermediate: fluorite, apatite, feldspar
Hard: quartz, topaz, corundum, diamond
Moisture content of coarse solids
< 3-4%
Moisture content of fine solids
> 50%
Reduction ratio (R = Df/Dp) for coarse solids
R = 5 to 7
Reduction ratio (R = Df/Dp) for fine solids
R ≈ 100
Measure of rate of grinding of materials in a particular mill
Grindability
Equipment for coarse size reduction
Hard: jaw crusher, gyratory crusher
Soft: squirrel cage disintegrator, hammer mill
Equipment for intermediate size reduction
Cone crusher, crushing rolls, roller crusher
Equipment for fine size reduction
Ball mill, tube mill, pebble mill, rod mill
Mechanism for coarse size reduction
Compression
Mechanism for fine size reduction
Impaction
Mechanism for very fine size reduction
Attrition
Mechanism for shaped size reduction
Cutting
Equipment for ultrafine size reduction
Fluid energy mill
The operating speed of a ball mill should be _____ than the critical speed
Less
The critical speed of a ball mill is dependent on
Radius of mill (D) and ball (d)
Operation by which solids are separated from liquids due to the difference in densities
Sedimentation
Forces acting on a particle settling in fluid
Gravitational or centrifugal, buoyant, and drag forces
Used to increase the porosity of the cake during filtration
Filter aid
Cake porosity is ____ at the filter medium
Minimum
In gas absorption, one solute is being absorbed while the rest of the components are assumed to be ____, and the liquid is _____
non-soluble, non-volatile
Ideal conditions in a gas absorber
low T, high P
Ideal conditions in a stripping column
high T, low P
The operating velocity in a packed tower is usually ____ the flooding velocity
Half
Types of membrane modules
Plate and frame
Tubular
Spiral-wound
Capillary
Hollow-fiber
Membrane configuration with low surface area per volume, used in flat and plate modules
Flat
Membrane configuration with high surface per volume; feed is preferably inside the membrane
Tubular
Fraction of stream that passes through a membrane
Permeate
Fraction retained in the membrane
Retentate
Usual flow arrangement for plate and frame module membranes
Perpendicular/cross flow
Selective flow by a fluid
Channeling
Instrument to prevent channeling in membrane separation
Stop disk
Advantages of plate and frame module
Easy to clean, easy to replace, high work pressure, for high viscosity liquids
Disadvantage of plate and frame module
Small area to volume ratio
Advantages of spiral-wound module
High packing density, easy and inexpensive
Disadvantages of spiral-wound module
Difficult to clean, high pressure drop, only for pure media
Advantages of tubular modules
Resistant to fouling, easy to clean
Disadvantages of tubular modules
Low packing density, expensive
Applications of tubular modules
Reverse osmosis, ultrafiltration
Type of module with the highest packing density (30,000 m²/m³)
Hollow-fiber module
Advantages of hollow-fiber module
High packing density, low cost
Disadvantages of hollow-fiber module
high fouling, high pressure drop
