basics of petroleum refining
TRANSCRIPT
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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