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Jawaharlal Nehru Technological University Kakinada

Prof. K. V. RaoProgramme DirectorPetroleum CoursesJNTUKB. Tech. Petrochemical Engineering

Petroleum Refinery Engineering

Aviation Turbine FuelsUniversity College of Engineering (A) KakinadaDept. of Petroleum Engineering & Petrochemical EngineeringJet Engine

A jet engine is a reaction engine that discharges a fast moving jet which generates thrust by jet propulsion in accordance with Newton's laws of motion.2Turbine/Jet engines for Air Craft: Brief History

Jet propulsion can be traced back to the 1st century B.C. when an Egyptian, Hero, is credited with inventing a toy that used jets of steam to spin a sphere.

Sixteen centuries later, Leonardo da Vinci sketched a device that used a flux of hot gas to do mechanical work.

By the 17th century, inventors were beginning to develop simple turbine systems to operate machinery.

The development of a turbine engine for aircraft began independently in Germany and Britain in the 1930s.

3In Germany, Hans von Ohain designed the engine that powered the first jet flight in 1939.

Germany deployed the jet-powered Messerschmitt 262 late in World War II.

In Britain, Frank Whittle obtained a patent for a turbine engine in 1930.

An aircraft powered by an engine he designed first flew in 1941.

The first British jet fighter, the Gloster Meteor, also flew late in World War II.4Types of Fuel

Illuminating kerosine, produced for wick lamps, was used to fuel the first turbine engines.

Since the engines were thought to be relatively insensitive to fuel properties, kerosine was chosen mainly because of availability;

After World War II, the U.S. Air Force started using wide-cut fuel, which, essentially, is a hydrocarbon mixture spanning the gasoline and kerosine boiling ranges. 5Again, the choice was driven by considerations of availability: It was assumed that a wide-cut fuel would be available in larger volumes than either gasoline or kerosene alone;

However, compared to a kerosene-type fuel, wide-cut jet fuel was found to have operational disadvantages due to its higher volatility:

Greater losses due to evaporation at high altitudes.Greater risk of fire during handling on the ground.Crashes of planes fueled with wide-cut fuel were less survivable.

Kerosene-type jet fuel (including Jet A and Jet A-1) has a carbon number distribution between about 8 and 16 carbon numbers (carbon atoms per molecule);

wide-cut or naphtha-type jet fuel (including Jet B), between about 5 and 15 carbon numbers6Aviation Turbine Fuel

Jet fuel is a colorless, combustible, straight-run petroleum distillate liquid.

Its principal uses are as jet engine fuel. The most common jet fuel worldwide is a kerosene-based fuel classified as JET A-1.

The governing specifications in India are IS 1571: 2001 (7th Rev).

Indian Oil is India's first ISO-9002 certified oil company conforming to stringent global quality requirements of aviation fuel storage & handling.

Indian Oil Aviation also caters to the fuel requirements of the Indian Defence Services, besides refueling VVIP flights at all the airports and remote heli-pads/heli-bases across the Indian subcontinent.7Crude oil is fed to the distillation column where straight-run light and heavy gasoline, kerosine, and diesel are separated at atmospheric pressure.

The bottoms from the atmospheric column are vacuum distilled to obtain gas oils for FCC or hydrocracker feed.

The gas oils may be hydrotreated to reduce sulfur and nitrogen to levels that will improve the performance of the FCC process.

Previously, the vacuum resid might have been used as a low-value, high-sulfur fuel oil for onshore power generation or marine fuel.

But to remain competitive, refiners must wring as much high value product as possible from every barrel of crude.

As a result, the vacuum resid may be sent to a resid conversion unit, such as a resid cracker, solvent extraction unit, or coker.

These units produce additional transportation fuel or gas oils, leaving an irreducible minimum of resid or coke.8Blending

The jet fuel produced by a refinery may be all straight-run or hydroprocessed product, or it may be a blend of straight-run, hydroprocessed, and/or hydrocracked product.

Small amounts of heavy gasoline components also may be added.

Straight-run kerosene from low-sulfur crude oil may meet all the jet fuel specification properties.

But straight-run kerosene is normally upgraded by Merox treating, clay treating, or hydrotreating before it can be sold as jet fuel.9

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11Upgrading Processes

Sweetening processes remove a particular class of sulfur-containing compounds called mercaptans from jet fuel.

Mercaptans are undesirable because they are corrosive and also because of their offensive odor.

Several processes have been developed to remove mercaptans by converting them to disulfides.

These disulfides are not corrosive and their odors are not as strong as the mercaptans they replace.

Sodium plumbite and copper chloride have been used as catalysts for this conversion in the past.12In recent years, the Merox (mercaptan oxidation) process, which uses a cobalt-based catalyst, has almost completely replaced the older technologies.

Most of these chemical sweetening processes do not change the total sulfur content of the fuel; they merely convert sulfur from one chemical form to another.

Some versions of the Merox process extract the disulfides that are formed and thus lower the total sulfur content.

13Hydroprocessing

Hydroprocessing is a generic term for a range of processes that use hydrogen and an appropriate catalyst to remove undesired components from refinery streams.

The processes range from mild conditions that remove reactive compounds like olefins and some sulfur and nitrogen compounds, to more severe conditions that saturate aromatic rings and remove almost all sulfur and nitrogen compounds. Hydroprocessing breaks apart molecules containing sulfur and converts the sulfur to hydrogen sulfide, which is subsequently removed from the fuel.

14Clay Treating

Certain polar compounds can be removed from jet fuel by clay treating. In this relatively simple process, the fuel is allowed to pass through a bed of clay.

Certain classes of polar compounds, especially those that act as surfactants, adsorb onto the surface of the clay and thus are removed from the fuel.

In the Merox process discussed above, surfactants can be formed and it is usually necessary to clay treat the fuel after the Merox process to remove them.15Hydrocracking

The hydrocracking process yields a large percentage of product in the kerosine and diesel boiling range.16Aviation Turbine Fuel

Aviation turbine fuel is a mixture of many different hydrocarbons.

Modern analytical techniques are not powerful enough to separate all the individual molecular species present in jet fuel, so we dont know how many there are, but a good guess is a thousand or more.

Kerosene-type jet fuel has a carbon number distribution between about 8 and 16 carbon numbers; Wide-cut jet fuel, between about 5 and 15 carbon numbers.

Typical boiling curves of kerosene-type and wide-cut jet fuel are shown in Figure 4.1.17

Figure 4.1: Typical D86 DistillationCurves-Kerosene-Type and Wide-Cut Jet Fuels18

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20Figure 4.4 summarizes the relationships between hydrocarbon class and jet fuel properties.

Normal paraffins have poor volumetric energy contents and very poor low-temperature flow properties.

Aromatics have very good volumetric energy contents but poor combustion quality and low-temperature flow properties.

Isoparaffins and naphthenes are intermediate, with these properties falling between those of normal paraffins and aromatics. 21

22Figure 4.5 shows which of the important jet fuel properties are bulk properties, and which depend on the presence or absence of trace components.

The trace components may be present in the hydrocarbon base fuel as manufactured or come from another source, such as additives or contaminants.

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24Additives

Antioxidants

An approved antioxidant or mixture of antioxidants shall be added to a fuel (or a fuel component) which has been hydroprocessed (i.e. manufactured using a catalytic hydrogen process such as hydrotreating, hydrofining, hydrocracking, etc).

This shall be done immediately after hydroprocessing and prior to the product or component being passed into storage in order to prevent gum formation and peroxidation after manufacture. 25The total concentration of active material(s) in fuel or that proportion of the fuel blend that has been hydroprocessed shall not be less than 17.0 mg/l nor exceed 24.0 mg/l.

Where a finished fuel comprises a blend of hydroprocessed and non-hydro-processed components, the requirements for mandatory addition of antioxidant applies only to that portion of the blend which has been hydroprocessed.26Some of the approved antioxidants:

2,6-ditertiary-butyl-4-methyl-phenol; 2,4-dimethyl-6-tertiary-butyl-phenol; 2,6-ditertiary-butyl-phenol; A mixture consisting of 75 percent minimum of 2,6-ditertiary-butyl-phenol; and 25 percent maximum of tertiary and tritertiary butyl-phenols; A mixture consisting of 55 percent minimum of 2,4-dimethyl-6-tertiary-butyl-phenol; 15 percent minimum of 4-methyl-2-6-ditertiary-butyl-phenol; with the remainder, 30 percent maximum, a mixture of monomethyl and dimethyl-tertiary-butyl-phenols; A mixture consisting of 72 percent minimum of 2,4-dimethyl-6-tertiary-butyl-phenol and 28 percent maximum, mixture of tertiary-butyl-methyl-phenols and tertiary-butyl-dimethyl phenols. 27Metal Deactivator Additive (MDA)

An approved metal deactivator, N, N-disalicylidene 1, 2-propanediamine, may be added in amount not exceeding 2.0 mg/l on initial batching of the fuel at the refinery.

5.7 mg/l on cumulative addition when redoping the fuel to counteract the effects of metals known to be deleterious to thermal stability such as Cu, Cd, Co, Fe and Zn provided that the nature of the contamination is reported.28Static Dissipater Additive (SDA)

Stadis 450 Octel Starreon (USA) / The Associated Octel Company Ltd. (UK)

The concentration of SDA to be used in newly manufactured, or on first doping of fuel is 3.0mg/l maximum.

The cumulative concentration of SDA allowed when redoping fuel to maintain conductivity is 5.0mg/l maximum.29Lubricity Improver Additive (LIA)

Aircraft/engine fuel system components and fuel control units rely on the fuel to lubricate their moving parts.

The effectiveness of a jet fuel as a lubricant in such equipment is referred to as its lubricity.

Differences in component design and materials result in varying degrees of equipment sensitivity to fuel lubricity.

Similarly, jet fuels vary in their level of lubricity. A qualified LIA may be added to the fuel to impart improved lubricity to the fuel. 30The approved additives:

31Fuel System Icing Inhibitor (FSII)

A qualified FSII may be added to the fuel as agreed to between the purchasing authority and the supplier.

Concentrations less than 0.02% by volume can be considered negligible and do not require agreement/notification.

Diethylene Glycol Monomethyl Ether Not less than 0.1 percent and not more ( DIEGME ) 0.15 percent by volume32Handling and storage

For the safe handling and storage of the fuel the instructions given in IS 7667 shall be followed.33

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Thank You38