Process Units

STORAGE

Gases
Low pressure, gas holders
Liquid-sealed type storage
If high pressure needed - liquefy by pressure/ refrigeration

Liquids
In bulk in vertical cylindrical steel tanks
Fixed/floating-roof tanks
Horizontal cylindrical/ rectangular tanks for small quantities

Solids
Piles in open air - long-term storage
Overhead bunkers (bins/ hoppers) used for short-term storage - material easily withdrawn at steady rate

PUMPS

Liquids only (gases fans)
Energy required - depends on height, required pressure, pipe dimensions, flow rate, fluid viscosity & density, power supply
Pump selection - depends on quantity, head, nature of liquid, nature of power supply

Positive displacement
Mechanical parts directly push liquid
Can generate v/ high temps
Volume of liquid delivered directly related to displacement of piston
Reciprocating piston pumps & rotary gear pumps - near constant delivery required

Piston/reciprocating, rotary gear, mono, peristaltic — high pressures, near-constant delivery

Centrifugal
High KE imparted to liquid > converted into pressure energy
Spinning disc-like impeller produces liquid flow
Liquid is accelerated to same speed as impeller > forces the liquid to collecting area around periphery of impeller and to pump outlet
Curved vanes allow control over direction of liquid reducing losses

Cavitation
Air present in pump
Can result in mechanical damage when air bubbles collapse
Accentuated by any sudden change in magnitude or direction of the velocity of the liquid in pump
(Marked increase in noise, vibration, & loss of pump head)
Pump priming - removing air from pump & suction line (pump filled with liquid, air forced out)

MIXING
Homogeneity or for heat/ mass transfer

Single-phase liquid mixing
Immiscible liquid-liquid - emulsion
Gas-liquid (high interfacial area e.g. bubbles)
Liquid-solid (suspend particles in low-viscosity liquid)
Solids-solid (particulate solids)

CRUSHING & GRINDING EQUIPMENT

Fine crushers - compressive & shear forces
Ball mill - rotating hollow cylinder partially filled with balls

SEPARATION

Solid-solid - mesh size/ opening size
Liquid-solid - gravity (thickeners & clarifiers)/ centrifugal hydrocyclones(4-500microns)/ filtration
Drying - tray (batch), conveyor (bed with open structure), rotary (free-flowing granular), fluidised (high heat transfer, granular and crystalline materials1 to 3 mm), spray (liquids/ slurries, heat sensitive)
Dissolved solids - evaporation (e.g. long-tube falling-film) concentrate solutions; crystallisers produce, purify and recover solids
Liquid-liquid - decanters (density difference, three zones) and sedimentation centrifuges (small density differences as low as 100 kg/m³, and can handle high throughputs, up to around 100 m³/h)
Gas-solid (cleaning of gas streams to prevent contamination of catalysts or products & avoid damage to equipment) - cyclones (reverse-flow, centrifugal) and fabric/bag filters
Reactor classification - mode (batch vs continuous), phases (homogeneous vs heterogeneous), geometry (stirred tank, tubular, packed bed, fluidised bed)
Reactor type - tubular/PFR (gas reactions, minimal back-mixing), CSTR (well-mixed, outlet = tank composition), packed bed (solid catalyst/reactant, gas/ gas-liquid reactions), fluidized bed (suspended solids, high heat/mass transfer)
Heat exchangers - shell-and-tube exchanger - large area in small volume, wide material range, easily cleaned; baffles direct flow and support tube bundle

SEPARATION OPERATIONS (ESA/MSA)

Separating agents - ESA (heat/work e.g. partial condensation, flash) versus MSA (added phase e.g. solvent, absorbent, stripping vapour)
Partial condensation/ flash vaporisation - phases created by removing heat (condensation) or reducing pressure (flash); vapour enriches in the more volatile species
Distillation - counter-current vapour/liquid contacting on stages/trays, exploiting volatility differences; uses reflux (condenser) and boilup (reboiler)
Absorption/ stripping (MSA) - absorption dissolves feed-vapour species into a liquid absorbent; stripping is the inverse, using a vapour stripping agent
Extraction (MSA) - liquid–liquid extraction (temp sensitive, selective liquid solvent) and liquid–solid extraction/ leaching (solute diffuses from solid into solvent)
Drying & evaporation - drying removes liquid from a solid using gas/heat (vp>pp); evaporation transfers volatile components of liquid into gas by heat transfer
Crystallisation - a purification step forming solids by cooling and/or solvent evaporation (solution) or partial freezing (melt)
Membrane separations (natural fibres, synthetic polymers, ceramics, metals) - exploit differences in permeability; includes osmosis & reverse osmosis (pressure > osmotic pressure)
Adsorption & ion exchange - adsorption binds solute to a solid surface (must be regenerated); ion exchange similar but involves chemical exchange reaction (e.g. water softening)