The document provides an overview of petroleum refinery processes, highlighting the various refining units such as distillation, hydrocracking, and desulfurization. It discusses the types of impurities in crude oil that require removal, their impact on refining efficiency, and the test methods for determining corrosive properties. The document also details quality assessments for petroleum products including octane and cetane numbers, which are essential for evaluating fuel performance.

1. Petroleum Products: Refinery
Basics
Quality Controls and Market Standards
By-
Aniruddha Sanyal
Assistant Professor
Department of Chemical Engineering
National Institute of Technology Calicut
Kozhikode 673601, Kerala, India.

2. Refinery Basics
• A small refinery will take in 2k to 10k tons of crude oil/day.
• A large refinery will take 20k to 40k tons of crude oil/day, and there
are few refineries which can reach up to 60k tons of crude oil/ day.
• Refineries vary in complexity; i.e. in the variety of processes operated
and of products that are send out.
• Simple refinery may make only gasoline, diesel fuel and heavy fuel. In
such cases units like distilling unit, sweeteners and reformers will be
present.
• The complex refineries have desulfurizers in addition.

3. Objectives in Refining

4. Typical Petroleum
Refinery Flow Diagram

5. Main Processing Units
• Crude Oil Distillation unit:
Distills the incoming crude oil into various fractions for further processing in
other units.
• Vacuum distillation unit:
Further distills the residue oil from the bottom of the crude oil distillation
unit. The vacuum distillation is performed at a pressure well below
atmospheric pressure.
• Naphtha hydrotreater unit:
Uses hydrogen to desulfurize the naphtha fraction from the crude oil
distillation or other units within the refinery.
• Catalytic reforming unit:
Converts the desulfurized naphtha molecules into higher-octane molecules
to produce reformate, which is a component of the end-product gasoline or
petrol.

6. Main Processing Units
• Alkylation unit:
Converts isobutane and butylenes into alkylate, which is a very high-
octane component of the end-product gasoline or petrol.
• Isomerization unit:
Converts linear molecules such as normal pentane into higher-octane
branched molecules for blending into the end-product gasoline. Also
used to convert linear normal butane into isobutane for use in the
alkylation unit.
• Distillate hydrotreater unit:
Uses hydrogen to desulfurize some of the other distilled fractions from
the crude oil distillation unit (such as diesel oil).
• Merox (mercaptan oxidizer) or similar units:
Desulfurize LPG, kerosene or jet fuel by oxidizing
undesired mercaptans to organic di-sulfides.

7. Main Processing Units
• Amine gas treater, Claus unit, and tail gas treatment:
For converting hydrogen sulfide gas from the hydrotreaters into end-
product elemental sulfur. The large majority of the 64,000,000 metric
tons of sulfur produced worldwide in 2005 was byproduct sulfur from
petroleum refining and natural gas processing plants.
• Fluid catalytic cracking (FCC) unit:
Upgrades the heavier, higher-boiling fractions from the crude oil
distillation by converting them into lighter and lower boiling, more
valuable products.
• Hydrocracker unit:
Uses hydrogen to upgrade heavier fractions from the crude oil
distillation and the vacuum distillation units into lighter, more valuable
products.

8. Main Processing Units
• Visbreaker unit:
It upgrades heavy residual oils from the vacuum distillation unit by
thermally cracking them into lighter, more valuable reduced viscosity
products.
• Delayed coking and fluid coker units:
Convert very heavy residual oils into end-product petroleum coke as
well as naphtha and petrol oil by-products.

9. Auxiliary Processing Units: Pretreatments
• Steam reforming unit: Converts natural gas into hydrogen for the
hydrotreaters and/or the hydrocracker.
• Sour water stripper unit: Uses steam to remove hydrogen sulfide gas
from various wastewater streams for subsequent conversion into end-
product sulfur in the Claus unit.
• Utility units such as cooling towers for furnishing circulating cooling
water, steam generators, instrument air systems for pneumatically
operated control valves and an electrical substation.
• Desalting: Typically contains 10 – 200 PTB (pounds per thousand
barrels of oil), which are removed using settling with/without
electrical means. The crude may still contain 2-4 PTB salts.

10. Pretreatments- contd.
• Wastewater collection and treating systems consisting of API
separators, dissolved air flotation (DAF) units and some type of
further treatment (such as an activated sludge bio treater) to make
the wastewaters suitable for reuse or for disposal.
• Liquified gas (LPG) storage vessels for propane and similar gaseous
fuels at a pressure sufficient to maintain them in liquid form. These
are usually spherical vessels or bullets (horizontal vessels with
rounded ends).
• Storage tanks for crude oil and finished products, usually vertical,
cylindrical vessels with some sort of vapour emission control and
surrounded by an earthen berm to contain liquid spills.

11. Types of Impurities in Crude Oil:
which needs to be removed
• Oleophobic
❖Salts- mainly chlorides and sulphates of Na, Ca, Mg
❖Sediments- such as silt, sand, drilling mud, iron oxide, iron sulphide
❖Water – presents as soluble, emulsified and/or finely dispersed water
• Oleophilic
❖Sulphur compounds
❖Organometallic compounds containing Ni, V, Fe, As.
❖Naphthenic acids
❖Nitrogen compounds

12. Problems that may be caused by the impurities:
• Corrosion in the atmospheric distillation overhead system caused by HCl,
which is liberated due to hydrolysis/dissociation of chloride salts
• Increased consumption of ammonia to neutralize the HCl
• Erosion of crude oil pumps, pipelines and valves by suspended matter
through abrasive action
• Plugging of equipment and fouling of heat-transfer surfaces
• Product degradation, like high ash content in fuel oil
• Trace metals in distillates, which act as catalyst poisons

13. Test methods for determination of corrosive
properties in crude oil
• Total Sulphur
Inorganic Sulphur creates corrosion, and hence a refiners needs to
know its initial composition.
(Lamp method for volatile petroleum products or Bomb Method IS
1448:1991 for heavy petroleum products).
Sulphur in the sample is oxidized by combustion, and it is estimated
volumetrically after absorption in hydrogen peroxide or by gravimetric
methods after converting into barium sulphate.

14. Test methods for determination of corrosive
properties in crude oil
• Acidity and Alkalinity
New and used petroleum products may contain acidic constituents
present as additives or as degradation products, such as oxidation
products, formed during service.
Total acidity is the sum of organic and inorganic acidity.
Acids in the sample are extracted using neutral alcohol and then
titrated against KOH under hot conditions.
Inorganic acidity accounts for mineral acid present in the sample.

15. Test methods for determination of corrosive
properties in crude oil
• Copper-strip Corrosion Test
This test serves as a measure of
possible difficulties with Cu, Brass, or
Bronze parts of the fuel systems.
A clean and smoothly polished Cu strip
is immersed in the sample at specific
temperature for a certain time. The
strip is then removed, washed with
aromatic and Sulphur-free petroleum
spirit; and examined for corrosion
standard color code.
Indicates presence of
Sulphur compounds

16. Flash Point and Fire Point
Flash point is the lowest temperature at which application of test flame
causes the vapour above the oil to ignite.
Fire point is the lowest temperature at which the oil ignites and
continues to burn for 5 second.
• Abel Apparatus
• Pensky-Martens Apparatus (19 ℃ -49℃)
• Cleveland Apparatus (> 79℃)

17. Octane Number
• It checks the anti-knocking quality of the gasoline (petrol or motor spirit).
• The knocking of motor fuels is compared with the blends of reference fuels.
• It is the volume percentage of iso-octane in a blend with n-heptane which is
equal to the test fuel in knock intensity under standardized and closely controlled
conditions of test in a “single-cylinder, variable compression ratio” engines.
• Two octane tests can be performed for gasoline.
• The motor octane number (MON) indicates engine performance at highway
conditions with high speeds (900rpm). On the other hand, the research octane
number (RON) is indicative of low-speed city driving (600rpm).
• Pure n –heptane is assigned a value of zero octane while isooctane is assigned
100 octane. Hence, an 80vol% isooctane mixture has an octane number of 80.

18. Ignition quality of Diesel/Kerosene
• Cetane Number
• Diesel Index
• Aniline Point

19. Properties of Different Crude Oil Fractions