Petroleum Refining

An Overview

• Mixture of organic carbon chain

molecules

• Impurities include sulfur and nitrogen

compounds

• Some metals and salts too

What is Crude Oil?

Components such as . . .

• Straight-Chain

Hydrocarbons

• Cyclic H/C

• Aromatics

(Benzene, toluene,

xylenes)

• Mercaptans

• Hydrogen Sulfide

(H2S)

• Greases

• Propane

• LPG

Refining Means. . .

1. To reduce to a pure state, to remove

impurities

2. To improve or perfect

Salable products are made from crude.

Refining is carried out in three main steps

Step 1 – Separation

Step 2 – Conversion

Step3 - Purification

Desalting and Dewatering • Crude oil is recovered from the reservoir mixed

with a variety of substances: gases water and dirt (minerals).

• Desalting is a water – washing operation performed at the production field and at the refinery site for additional crude oil cleanup.

• If the petroleum from the seperators contains water and dirt, water washing can remove much of the water – soluble minerals and entrained solids.

• Dewatering is the process of separating the wash water completely from the mixture. These two steps are essential before the crude is sent to a refinery.

Crude oil is a multicomponent mixture of

nearly hundred compounds.

Petroleum refining consists of the separation

and reactive processes to yield various

products and purify intermediate products.

Process of Refining

Refining deals with multicomponent feed

streams and multicomponent product

streams. Characterization of both crude,

intermediate product and final product

streams is very important to understand the

processing operations effectively

Primary refinery oil cuts include gases, light / heavy

naphtha, kerosene, light gas oil, heavy gas oil and

residue.

Intermediate refinery product streams give several

final product streams such as fuel gas, liquefied

petroleum gas (LPG), gasoline, jet fuel, kerosene,

auto diesel, lubricants, bunker oil, asphalt and coke.

Various feed properties are manipulated carefully

using both chemical and physical changes.

A process refinery has both physical and chemical

processes. The dominant physical process in a

refinery is the distillation process that enables the

removal of lighter components from the heavier

components. Other chemical processes such as

alkylation and isomerisation are equally important in

the refinery engineering as these processes enable

the reactive transformation of various occurring

functional groups to desired functional groups

in the product streams.

Both chemistry and physical properties characterize

petroleum process streams .

The chemistry characterizes the crude oil in terms of

the functional groups_ paraffins, naphthenes,

aromatics and resins.

The dominance of one or more of the functional

groups in various petroleum processing streams is

indicative of the desired product quality and

characteristics.

For instance, the lighter fractions of the

refinery consist of only cycloalkanes and

paraffins.

On the other hand, products such as petrol

should have high octane number which is a

characteristic feature of cycloalkane and

aromatic functional groups present in the

product stream.

Compounds to be removed

Crude oil consists of 84 – 87 wt % carbon, 11 –

14 % hydrogen, 0 – 3 wt % sulphur, 0 – 2 wt %

oxygen, 0 – 0.6 wt % nitrogen and metals ranging

from 0 – 100 ppm.

Understanding thoroughly the fundamentals of

crude chemistry is very important in various

refining processes.

Crude chemistry and Refining

The existence of compounds with various

functional groups and their dominance or

reduction in various refinery products is

what is essentially targeted in various

chemical and physical processes in the

refinery. Crudes have mostly paraffins,

naphthene and aromatics.

Oil Refining Production Process

• Desalting and Dewatering

• Distillation

• Reforming

• Cracking

• Alkylation

• Isomerisation

• Polymerisation

• Hydrotreating

Heat and Mass Transfer Operations

Fractionation (distillation) is

the separation of crude oil in

atmospheric and vacuum

distillation towers into groups of

hydrocarbon compounds of

differing boiling-point ranges

Petroleum Refining Products

• Refinery Gas, LPG

• Aviation Gasoline

• Motor Gasoline

• Kerosene

• Jet Fuel

• Gas Diesel Oil / (Distillate Fuel Oil)

• Heavy Fuel Oil Residual

• Naphtha

• Petroleum Coke

Products specific for users

• Spark Ignition & Compression Ignition

automobile engine.

• Aviation and Jet Engine

• Stationary Engine for Generator or Pump.

• Product for stoves and rural lighting

• Cooking gas for home use-LPG

• Lubricating oil and grease manufacture

• Chemicals from Petroleum fraction

Specification for final product

• A refinery makes products that are

specified by the user to meet his

application.

• If a crude has sulfur, and a product

should be free from it, refiner recovers

and makes sulfur a separate product.

• Products are thoroughly defined for

pollution free usage.

Examples of specifications of property

API gravity

• - Watson Characterization factor

• - Viscosity

• - Sulfur content

• - True boiling point (TBP) curve

• - Pour point

• - Flash and fire point

• - ASTM distillation curve

• - Octane number

Purification

Refinery Process Flow Chart

Dis

tilling

Flasher

Visbreaker

CCU

Alky

Sp

litter

Hydrotreating

Hydrotreating

Isom

Reformer

Gas Plant

Sulfur

Fuel Gas

Gasoline

Jet Fuel

Distillate Fuel

Residual

Fuel Leffler, 1985

TYPICAL REFINARY FLOW DIAGRAM

Major Refining Processes

Physical Separation

Dewatering

Desalting

Distillation

Solvent Extraction

Solvent De-asphalting

Solvent Dewaxing

Chemical Conversion

Catalytic: Reforming,

Hydro-treating, Hydro-

cracking, Alkylation,

Isomerization

Thermal: Cracking

Delayed Coking,

Visbreaking, Flexicoking

Cracking

• Cracking processes break down heavier

hydrocarbon molecules (high boiling point

oils) into lighter products such as petrol

and diesel. These processes include:

1. catalytic cracking

2. thermal cracking

3. hydrocracking

Catalytic Cracking

Fluid Catalytic cracking products (typical)

Catalytic Reforming

• Reforming is a process which uses heat,

pressure and a catalyst (usually containing

platinum) to bring about chemical reactions

which upgrade naphthas into high octane

petrol and petrochemical feedstock. It

involves cyclization and aromatization

reactions.

Forming aromatic compound in Catalytic Reforming

Naphthenes are "reformed" from paraffins and the

naphthenes into aromatics

Alkylation

• Alkylation refers to the chemical bonding of

these light molecules with isobutane to form

larger branched-chain molecules

(isoparaffins) that make high octane petrol.

Isomerisation

• Isomerisation refers to chemical

rearrangement of straight-chain

hydrocarbons (paraffins), so that they

contain branches attached to the main

chain (isoparaffins).

• Branched chain compounds have better

Octane Number and desirable in gasoline.

Polymerisation

• Under pressure and temperature, over an acidic

catalyst, light unsaturated hydrocarbon molecules

react and combine with each other to form larger

hydrocarbon molecules. Such process can be

used to react butenes (olefin molecules with four

carbon atoms) with iso-butane (branched paraffin

molecules, or isoparaffins, with four carbon

atoms) to obtain a high octane olefinic petrol

blending component called polymer gasoline.

Hydrotreating

• Hydrotreating is one way of removing many of the

contaminants from many of the intermediate or

final products. In the hydrotreating process, the

entering feedstock is mixed with hydrogen and

heated to 300 - 380oC. The oil combined with the

hydrogen then enters a reactor loaded with a

catalyst which promotes several reactions:

hydrogen combines with sulphur to form hydrogen

sulphide (H2S) .

Other Refinery Units • Steam Generation

• Hydrogen Generation

• Power Generation (e.g., cogen)

• Air Separation Plant

• Storage (high pressure hydrocarbon, crude oil, intermediates)

Floating-Roof Tanks - 150‘ diameter is common

Spherical Tanks - 50‘ are common

Horton Spheroid (refrigerated)

Steam-Heated Tanks for “Heavier” Products

• Self-Contained Firewater Supply

• Firewater Pumps, Waste water Treatment

Other Materials to be handled

• Sulfur

• Hydrofluoric Acid (HF)

• Sulfuric Acid (H2SO4)

• Ammonia (NH3)

• Sodium Hypochlorite

• Radioactive Materials

• Chlorine

• Amines

• MEK

• Sulfur Dioxide (SO2)

• Heavy Metal Catalysts

• Sour Water

• Caustic (fresh/spent)

• Alcohol

• Asbestos

Visualize All this Stuff, OK

What Goes on at a Refinery. . .?

• Separation of components by distillation, e.g.:

Atmospheric

Vacuum

Hydrotreating (uses excess hydrogen)

• Breaking apart molecules to make smaller ones, e.g.:

catalytic cracking

hydrocracking

• Joining molecules to make bigger ones, e.g.:

Reforming - alkylation that lengthens the hydrocarbon chain

Reforming - cyclic that generates hydrogen

Physical Hazards

• High Pressure/Temperature Steam

• Oil/Gas-Fired Furnaces

• Acoustic

• High Voltage (4160V, 480V, 13.2 kV)

• Falling Hazards

• Confined Space Hazards

• Cranes/Lifting Hazards

• Hot Work Hazards

• Acid Exposure

• Toxic Vapors

• Radiation

• Flammability Hazards

Common PPE Requirements

• Hardhat

• Hardsoled / Hardtoe Shoes

• Safety Glasses with Side

Protection

• Safety Goggles or Faceshield

• Fire-Resistant Clothing

Process Hazards

• Emergency Flare

• Atmospheric Pressure Relief

• High Temperature (up to 2000oF)

• Low Temperature (e.g., Brittle Fracture)

• High Pressure (up to 3000 psig)

• Low Pressure (e.g., vacuum)

Air

Preserving air quality around a refinery

involves controlling the following emissions:

sulphur oxides

hydrocarbon vapours

smoke

smells

Water

• The majority of the water discharged from

the refinery has been used for cooling the

various process streams. The cooling water

does not actually come into contact with the

process material and so has very little

contamination.

Rainwater falling on the refinery site must be

treated before discharge to ensure no oily

material washed off process equipment leaves

the refinery.

Process water has actually come into contact

with the process streams and so can contain

significant contamination.

Land

• The refinery safeguards the land environment by

ensuring the appropriate disposal of all wastes.

• Within the refinery, all hydrocarbon wastes are

recycled through the refinery slops system. This

system consists of a network of collection pipes

and a series of dewatering tanks. The recovered

hydrocarbon is reprocessed through the distillation

units.

References: Gary J.H., Handwerk G.E., Petroleum Refining: Technology and Economics, Taylor & Francis, 2005 Jones D.S.J., Elements of Petroleum Processing, John Wiley & Sons, 1995

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