Basic Operations

BASIC OPERATIONSBASIC OPERATIONSININ

REFINERYREFINERY

OUTLINE OF UNIT OPERATIONS

Unit Operation Schematic Representation Comments

1. Distillation (a) Batch

(b) Continuous fractionators

Used for intermittent operation and handling small volumes of feed and product

Used for high volume continuous separation of complex mixtures such as petroleum fractions

Connect these with appropriate pumps, reboilers, condensers and automatic controls

2. Drying of Solids

(a) Spray drier

Suitable for large capacity operation on liquid feed togive powdered, spherical, free – flowing product ; used in production of pigments, detergents, synthetic resins and misc. inorganic salts

Used to contact solvent and feed to give raffinate and extract ; widely adapted to removal of napthenes from lube oil fractions using solvents such as furfural

2. Extraction (a) Liquid - liquid

Unit Operation Schematic Representation Comments

Involves removal of a solute from a solid by means of a liquid solvent ; often used in ore treatment to recover metal values

Most widely used for liquid of all types ; simple in construction and maintenance

Generally used for higher pressure delivery ; may be used for metering or proportioning

(b)Solid – liquid (leaching)

3. Fluid Handling

(a) Centrifugal pump

(b) Reciprocating pump or compressor

Unit Operation Schematic Representation Comments

(c) Jet ejectorUse for low pressure operation or production of vacuum ; steam often used as motive fluid

Most widely used type of catalytic rector ; used with precious metal catalysts to minimize attrition losses ; catalyst usually in form of pellets

Unit Operation Schematic Representation Comments

4. Fluid – solid Contacting (a) Fixed bed

Unit Operation Schematic Representation Comments

(b) Fluid bedUsed to contact finely divided solids with reactant gases, e.g.; cracking catalyst with oil vapors and then with air ; also used in roasting of sulfide ores to give oxides and SO2

Combines virtues of fixed bed reactor with ability to regenerate catalyst by movement to separate regeneration zone

(c) Moving bed

Unit Operation Schematic Representation Comments

5. Fluid–solid Separation

(a) Centrifugation

Used to separate very finely divided solids from liquid or liquid from liquid emulsions

Simple device used to remove large particles from gas stream by simple settling in low- velocity zone

(b) Settling tank

Unit Operation Schematic Representation Comments

(c) Wet scrubberEffective means of removing suspended particles from gas stream by contact with liquid shower

Hot, nearly-saturated solutions are stirred and cooled to effect nucleation and crystal growth ; widely used with inorganic salts

(d) Crystallizer

Unit Operation Schematic Representation Comments

(e) Filter (rotary)Vacuum applied to interior of drum pulls filtrate out of cake ; used to separate minerals from slurries, pulp fibers from water, etc.

Simplest type of pressure filter ; widely used ; plates and fabric filter media may be made of a variety of corrosion - resistant materials

(f) Filter press

Unit Operation Schematic Representation Comments

(g) Cyclone separatorUsed to separate solid particles or liquid droplets from gases to permit product recovery or to cut down product loss and air pollution

Used to remove fine dusts or mists suspended in gases ; features high collection efficiency at wide variety of operating conditions

(h) Electrostatic precipitator

Unit Operation Schematic Representation Comments

(i) Bag filter

Batteries of tubular fabric bags are mounted so solids may be removed continuously by flow reversal and mechanical shaking

Used to separate slurry into sludges and clear liquid ; used widely in mineral industries and in sewage effluent clarification

(j) Thickener - classifier

Unit Operation Schematic Representation Comments

6. Fluid Storage (a) Gas holders

Used for low pressure storages of gases at constant pressure using liquid seal (usually water)

Widely used for storage of liquids of all types, usually at atmospheric pressure ; may have floating roof (Gas, oil, Diesel)

(b) Tanks

Unit Operation Schematic Representation Comments

(c) Pressurized spheres

Used for pressurized storage of liquefied gases or high vapor pressure liquids to permit safe storage with no vapor losses (LPG)

Used for large volume storage of liquids or of liquefied gases (Natural gas)

(d) Under ground caverns

Unit Operation Schematic Representation Comments

7. Gas – liquid Contacting(a) Absorption

Used for taking up a soluble gas in a solvent liquid and producing a solution plus a lean exit gas ; e.g., used in H2S removal from hydrocarbons (ATU)

Used for removing a soluble gas from solution by counter-current contact with an inert gas ; used to recover solute gas and regenerate solvent for subsequent absorption step.

(b) Stripping(Solution) (Solvent)

Unit Operation Schematic Representation Comments

8. Heat Exchange (a) Fired heater

Used to heat petroleum fractions to distillation or cracking temperatures in direct-fired tubes

Uses natural circulation to circulate fractionating tower bottom in heat exchange with steam, e.g., to provide necessary for fractionation

(b) Re boiler

Unit Operation Schematic Representation Comments

(c) Condenser Usually water-cooled tubular construction to provide reflux and overhead product from fractionating column

Common type of device for process heat exchange

(d) Shell and tube exchanger

Unit Operation Schematic Representation Comments

(e) Jacked kettle Common construction for reaction kettles ; water or brine may be used for cooling ; hot water, oil or Diathermy for heating

Features intimate contact of coolant fluid (e.g., water) quick quench, e.g., in hydrocarbon pyrolysis to acetylene

(f) Direct mixing (quenching)

Unit Operation Schematic Representation Comments

9. Membrane Separation (a) Dialysis

Used to separate mat’ls in sol’n having widely different mole wts., e.g., caustic from sugar or cellulose

Uses micro porous (e.g., Ni) barriers in multistage, operations to separate light (e.g., U235F6) from heavy (e.g., U238F6) components

(b) Gaseous diffusion U235F6

U235F6

U238F6

Unit Operation Schematic Representation Comments

10. Mixing

Agitation

May be used for liquid –liquid or solid – liquid mixing in single or multiple compartments ; widely used in process industries

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