Refinery Summary

8/3/2019 Refinery Summary

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Oil Refining- Summary

In the tank farm all the tanks have dikes (walls) built round them.

Where a lower voltage is needed step-down transformers are used to reduce the voltage towhat is required.

Kerosene hydrotreatment unit to improve the quality of Aviation Turbine Fuel (ATF). Thepurpose of the unit is to remove the sulfur from the kerosene. As part of this process hydrogen

must be added to the unsaturated hydrocarbon molecules to make them saturated. If this is

not done, the unsaturated molecules will attract sulfur to them and the sulfur will stay in

the kerosene. The catalyst used in the reactor vessel is nickel-tungsten base.

From the Kerosene HT unit a by-product called wild distillate is also produced in the unit.This is returned to the atmospheric crude oil distillation unit for further processing.

The vacuum residue can be used as heavy fuel oil (bunker oil) and for making asphalt (asused on road surfaces).

In hydrocracking unit, the catalyst used in the reactor vessels is known only by its trade nameof DHC-100.

In H2 plant, the hydrogenator reactor, which replaces sulfur atoms with hydrogen atoms, isused only if the feed gas contains more than a certain amount of impurities (10 ppm byvolume of carbonyl sulfide). The catalyst used is nickel on an alumina base.

The lead dioxide that produced during leaded gasoline burning. In the environment the leaddihalide undergoes oxidation-reduction by sunlight to elemental lead and halogen, both of

which are serious pollutants.

But lead coats the platinum and palladium and deactivates the converters, so unleaded gasmust be used.

These new gasoline do notsolve the pollution problem. They solve the lead pollutionproblem, but unleaded gasoline show larger emissions of other contaminants. Certain

unburned aromatic hydrocarbons and alkenes absorb sunlight readily and cause smog. When 10% ethyl alcohol is mixed with gasoline it is called gasohol

Thus MTBE, ethyl /-butyl ether (ETBE), ethanol, methanol, and other ethers and alcohols hadto be added at higher levels. This is called reformulated gasoline (RFG) and it may cut carbon

monoxide levels and may help alleviate ozone depletion.

But ethanol cannot be blended into gasoline at the refinery because it is hygroscopic and picksup traces of water in pipelines and storage tanks. Gasohol may increase air pollution because

gasoline containing ethanol evaporates more quickly. Studies and debate continue.

Boiling point of a branched chain is lower than for a straight chain hydrocarbon of the samemolecular weight.

The butanes present in crude oils and produced by refinery processes are used as components

of gasoline and in refinery processing as well as in LPG. Normal butane (nC4) has a lowervapor pressure than isobutane (iC4), and is usually preferred for blending into gasoline to

regulate its vapor pressure and promote better starting in cold weather.

Crankcase dilution is a phenomenon in engines where accumulation of unburned gasoline inthe crankcase, an excessively rich fuel mixture or poor combustion allows a certain amount of

gasoline to pass down between the pistons and cylinder walls and dilute the engine oil. When

a mixture of air and fuel enters the cylinder of an engine, it is entirely possible forcondensation of fuel to occur on the cooler parts of the cylinders. The condensate may wash


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the lubricating oil from the cylinder walls, travel past the piston rings and collect in the oil

pan, thus increasing wear and also diluting the lubricating oil. Since the less volatilecomponents of the fuel will have the greatest tendency to condense the degree of crankcase-

oil dilution is directly related to the end volatility temperatures of the mixture.

Altitude affects several properties of gasoline, the most important of which are losses by

evaporation and octane requirement. Distillate fuels can be divided into three types: jet or turbine fuels, diesel fuels, and heating oils.

The two basic types of jet fuels are naphtha and kerosene. Naphtha jet fuel is produced primarilyfor the military and is a wide-boiling-range stock which extends through the gasoline and

kerosene boiling ranges.

The chemical compositions of crude oils are surprisingly uniform even though their physicalcharacteristics vary widely.

API gravities are not linear and, therefore, cannot be averaged. But Specific gravities can beaveraged.

Crudes with greater than 0.5% sulfur generally require more extensive processing than those withlower sulfur content.

Carbon residue is determined by distillation to a coke residue in the absence of air. The carbonresidue is roughly related to the asphalt content of the crude and to the quantity of the lubricating

oil fraction that can be recovered.

If the salt content of the crude, when expressed as NaCl, is greater than 10 lb/1000 bbl, it isgenerally necessary to desalt the crude before processing.

Crudes containing nitrogen in amounts above 0.25% by weight require special processing toremove the nitrogen.

Vanadium concentrations above 2 ppm in fuel oils can lead to severe corrosion to turbine bladesand deterioration of refractory furnace linings and stacks.

The double bonds are reactive and the compounds are more easily oxidized and polymerized toform gums and varnishes.

In addition, some metals in inorganic compounds dissolved in water emulsified with the crudeoil, which can cause catalyst deactivation in catalytic processing units, are partially rejected in the

desalting process.

pH in desalting unit is important to control foaming and better separation of the oil-watermixture. The pH value is controlled by using another water source or by the addition of acid to

the inlet or recycled water.

In atmospheric distillation unit, 10 to 20% over-flash allows some fractionation to occur onthe trays just above the flash zone by providing internal reflux in excess of the sidestream

withdrawals.

To reduce the top diameter of the tower and even the liquid loading over the length of the tower,intermediate heat-removal streams are used to generate reflux below the sidestream removal

points.

The stripping steam reduces the partial pressure of the hydrocarbons and thus lowers the requiredvaporization temperature.

To eliminate essentially all volatile matter from petroleum coke it must be calcined atapproximately 1095 to 1260C.

Needle coke is preferred over sponge coke for use in electrode manufacture because of its lowerelectrical resistivity and lower coefficient of thermal expansion.


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Shot coke is undesirable because it does not have the high surface area of sponge coke nor theuseful properties, characteristic of needle coke, for electrode manufacture.

It is important to note that petroleum coke does not have sufficient strength to be used in blastfurnaces for the production of pig iron nor is it generally acceptable for use as foundry coke.

Usually furnace tubes have to be decoked every three to five months.

Long paraffinic side chains attached to aromatic rings are the primary cause of high pour pointsand viscosities for paraffinic base residua.

The oil fraction is soluble in propane the resin fraction is soluble (and the asphaltene fractioninsoluble) in either pentane, hexane, nheptane, or octane, depending upon the investigator.

The light gases produced by catalytic cracking contain more olefins than those produced bythermal cracking.

In catalytic cracking, The Thermafor catalytic cracking process (TCC) is representative of themoving-bed units and the fluid catalytic cracker (FCC) of the fluidized-bed units. Catalyst size 70micrometers (microns). Controlled reaction times (13 sec).

Two basic types of FCC unitso side-by-side type, where the reactorand regenerator are separate vessels adjacent

to each other, and theo Orthoflow, orstacked type, where the reactor is mounted on top of the

regenerator.

In FCC unit, it has been shown that catalyst activity loss due to metals is caused primarily byvanadium deposition, and increased coke and hydrogen formation is due to nickel deposited onthe catalyst. These metals come with the feed.

Crystalline synthetic silica-alumina catalysts called zeolites or molecular sieves.

Basic nitrogen compounds, iron, nickel, vanadium, and copper in the oil act as poisons tocracking catalysts. The nitrogen reacts with the acid centers on the catalyst and lowers thecatalyst activity. The metals deposit and accumulate on the catalyst and cause a reduction in

throughput by increasing coke formation and decreasing the amount of coke burn-off per unit of

air by catalyzing coke combustion to CO2 rather than to CO. Although the deposition of nickeland vanadium reduces catalyst activity by occupying active catalytic sites, the major effects are topromote the formation of gas and coke and reduce the gasoline yield at a given conversion level.

Over 95% of the sulfur in the gasoline blending pool is from the FCC naphtha.

Some of the advantages of hydrocracking are:

1. Better balance of gasoline and distillate production

2. Greater gasoline yield

3. Improved gasoline pool octane quality and sensitivity

4. Production of relatively high amounts of isobutane in the butane fraction

5. Supplementing of fluid catalytic cracking to upgrade heavy cracking stocks, aromatics,

cycle oils, and coker oils to gasoline, jet fuels, and light fuel oils

The catalytic cracker takes the more easily cracked paraffinic atmospheric and vacuum gas oils ascharge stocks, while the hydrocracker uses more aromatic cycle oils and coker distillates as feed.


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The cycle oils that result from cracking operations with zeolite catalysts tend to be highlyaromatic and therefore make satisfactory feedstocks for hydrocracking. Vacuum and coker gas

oils are also used as hydrocracker feed.

When the feed to the HCR unit contains large amounts of LCO, the major effects are increasedheat release and lower smoke point of the jet fuel product.

Hydrocracking operation is broken into two general types of processes;o those which operate on distilled feed (hydrocracking) ando Those which process residual materials (hydroprocessing).

The cracking reaction is endothermic and the hydrogenation reaction is exothermic. The overallreaction provides an excess of heat because the amount of heat released by the exothermic

hydrogenation reactions is much greater than the amount of heat consumed by the endothermiccracking reactions.

The volumetric yield of liquid products can be as high as 125% of the feed because thehydrogenated products have a higher API gravity than the feed.

Hydrocracking catalyst is susceptible to poisoning by metallic salts, oxygen, organic nitrogencompounds, and sulfur in the feedstocks.

The exothermic heats of the desulfurization and denitrogenation reactions are high Steam causes the crystalline structure of the catalyst to collapse and the dispersed rare-earth

atoms to agglomerate.

The HCR unit, GOFining process is a fixed-bed regenerative process employing a molecular-sieve catalyst impregnated with a rare-earth metal (platinum, palladium, tungsten, and nickel).The silica-alumina portion of the catalyst provides cracking activity while the rare-earth metals

promote hydrogenation.

The catalyst selectivity also changes with age and more gas is made and less naphtha producedas the catalyst temperature is raised

To maintain conversion.

Regeneration is accomplished by burning off the catalyst deposits, and catalyst activity is

restored to close to its original level. The catalyst can undergo several regenerations before it isnecessary to replace it.

If the feed has not been hydrotreated, there is a guard reactor before the first hydrocrackingreactor. The guard reactor usually has a modified hydrotreating catalyst such as cobalt-

molybdenum on silica-alumina to convert organic sulfur and nitrogen compounds to hydrogen

sulfide, ammonia, and hydrocarbons to protect the precious metals catalyst in the following

reactors.

In HC unit, the fractionator bottoms are used as feed to the second-stage reactor system. The unitcan be operated to produce all gasoline and lighter products or to maximize jet fuel or diesel fuel

products.

In HC unit, using different beds inside the reactor to allow for hydrogen injection andredistribute the flow.

The primary reaction variables are reactor temperature and pressure, space velocity, hydrogenconsumption, nitrogen content of feed, and hydrogen sulfide content of the gases.

At normal reactor conditions a 20F (10C) increase in temperature almost doubles the reactionrate, but does not affect the conversion level as much because a portion of the reaction involvesmaterial that has already been converted to materials boiling below the desired product end

point.


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The organic nitrogen content of the feed is of great importance as the hydrocracking catalyst isdeactivated by contact with organic nitrogen compounds.

At low concentrations the presence of hydrogen sulfide acts as a catalyst to inhibit the saturationof aromatic rings. However, hydrocracking in the presence of a small amount of hydrogen

sulfide normally produces a very low-smoke-point jet fuel.

Heavy polynuclear aromatics are formed in small amounts from hydrocracking reactions and,when the fractionator bottom is recycled, can build up to concentrations that cause fouling ofheat exchanger surfaces and equipment.

Nickel and vanadium in the resids act as catalysts for reactions creating carbon and light gaseoushydrocarbons. As a result, catalytic processes for converting resids usually use ARC for their

feedstocks, and VRC feedstocks are usually processed by noncatalytic processes.

Liquid propane is used to extract the oil fraction from vacuum tower bottoms, and liquid n-pentane, n-hexane, or n-heptane is then used to extract the resin fraction from the residue from

the propane extraction. The material insoluble in either the propane or the higher hydrocarbons is

termed the asphaltene fraction.

A significant feature of the asphaltene fraction is that 80 to 90% of the metals in the crude

(nickel and vanadium) are contained in this material. In hydroprocessing processes, feed conversion levels of 25 to 65% can be attained.

Typically the heavy naphtha fraction of the products will be catalytically reformed to improveoctanes, the atmospheric gas oil fraction hydrotreated to reduce aromatic content and improve

cetane number, the vacuum gas oil fraction used as conventional FCC unit feed, and the vacuumtower bottoms sent to a heavy oil cracker or coker.

In HP, typically each train will have a guard reactor to reduce the metals contents and carbonforming potential of the feed, followed by three to four hydroprocessing reactors in series. The

guard reactors catalyst is a large-pore-size (150200 A) silica-alumina catalyst with a low-levelloading of hydrogenation metals such as cobalt and molybdenum.

The terms ebullated bed and expanded bed are names given by HRI and C-E Lummus to a

fluidized-bed type operation which utilizes a mixture of liquids and gases to expand the catalystbed rather than just gases (definition of fluidized bed).

One of the main advantages of the ebullated-bed reactor process is the ability to add and removecatalyst during operation. This permits operators to regenerate catalyst while remaining on-

stream and to maintain catalyst activity by either regeneration or the addition of fresh catalyst.

The hydrocarbon solvent used is feedstock-dependent. As the molecular weight of the solventincreases (propane to pentane), the amount of solvent needed for a given amount of material

extracted decreases but the selectivity of the solvent also decreases.

As a result, the best decision for one refinery may be the worst for another refinery evenin the same company.

In hydrotreating units, In the presence of the metal-oxide catalyst, the hydrogen reacts with theoil to produce hydrogen sulfide, ammonia, saturated hydrocarbons, and free metals. The metalsremain on the surface of the catalyst and other products leave the reactor with the oil

hydrogen stream.

Catalysts developed for hydrotreating include cobalt and molybdenum oxides on alumina, nickeloxide, nickel thiomolybdate, tungsten and nickel sulfides, and vanadium oxide. The cobalt and

molybdenum oxides on alumina catalysts are in most general use today because they have

proven to be highly selective, easy to regenerate, and resistant to poisons.


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Nitrogen is usually more difficult to remove than sulfur from hydrocarbon streams, and anytreatment which reduces excess nitrogen concentration to a satisfactory level usually will

effectively remove excess sulfur.

Nickel-containing catalysts generally require activation by presulfiding with carbon disulfide,mercaptans, or dimethyl sulfide before bringing up to reaction temperature; however, some

refiners activate these cobaltmolybdenum catalysts by injecting the sulfiding chemical into theoil feed during startup. The sulfiding reaction is highly exothermic and care must be taken toprevent excessive temperatures during activation.

Cobaltmolybdenum catalysts are selective for sulfur removal and nickelmolybdenum catalystsare selective for nitrogen removal, although both catalysts will remove both sulfur and nitrogen

Catalytic reformate furnishes approximately 3040% of the U.S. gasoline requirements but, withthe implementation of restrictions on the aromatic contents of gasolines, can be expected to

decrease.

In catalytic reforming, the change in the boiling point of the stock passed through the unit isrelatively small as the hydrocarbon molecular structures are rearranged to form higher-octanearomatics with only a minor amount of cracking.

In CR unit, the paraffins and naphthenes undergo two types of reactions in being converted tohigher octane components: cyclization and isomerization

The light straight run LSR gasoline [C5- - -molecular-weight paraffins that tend to crack to butane and lighter fractions and it is noteconomical to process this stream in a catalytic reformer.

Aromatics have a higher liquid density than paraffins or naphthenes with the same number ofcarbon atoms, so 1 volume of paraffins produces only 0.77 volumes of aromatics, and 1 volume

of naphthenes about 0.87 volume.

In CR, The yield of aromatics is increased by:

1. High temperature (increases reaction rate but adversely affects chemical

equilibrium)2. Low pressure (shifts chemical equilibrium to the right)

3. Low space velocity (promotes approach to equilibrium)

4. Low hydrogen-to-hydrocarbon mole ratios (shifts chemical equilibrium to

the right, however, a sufficient hydrogen partial pressure must be maintained to avoid

excessive coke formation)

In CR these are fairly rapid reactions with small heat effects.

In CR, The hydrocracking reactions are exothermic and result in the production of lighter liquidand gas products. They are relatively slow reactions and therefore most of the hydrocracking

occurs in the last section of the reactor.

In CR, Low pressure reforming is generally used for aromatics production and the followinggeneralizations hold for feedstocks in the 155345F (68175C) TBP boiling range:

All of the reforming catalyst in general use today contains platinum supported on an aluminabase. Platinum is thought to serve as a catalytic site for hydrogenation and dehydrogenation

reactions and chlorinated alumina provides an acid site for isomerization, cyclization, andhydrocracking reactions

Catalyst activity is reduced during operation by coke deposition and chloride loss. The activity ofthe catalyst can be restored by high temperature oxidation of the carbon followed by chlorination.


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Metal parts exposed to the high temperature hydrogen atmosphere are constructed from steelcontaining at least 5% chromium and 0.5% molybdenum to resist hydrogen embrittlement.

n-pentane has an unleaded (clear) RON of 61.7 and isopentane has a rating of 92.3.

Equilibrium conversion to isomers is enhanced at the lower temperatures.

The available catalysts used for isomerization contain platinum on various bases. Some types of

catalysts require the continuous addition of very small amounts of organic chlorides to maintainhigh catalyst activities.

Separation of the normals from the isomers can be accomplished by fractionation or by vaporphase adsorption of the normals on a molecular sieve bed.

For refineries that do not have hydrocracking facilities to supply isobutane for alkylation unitfeed, the necessary isobutane can be made from n-butane by isomerization.

Characterization factor (Watsonfactor): A number which expresses the variations in physicalproperties with change in character of the paraffinic stock; ranges from 12.5 for paraffinic stocksto 10.0 for the highly aromatic stocks.

The addition of an alkyl group to any compound is an alkylation reaction but in petroleumrefining terminology the term alkylation is used for the reaction of low molecular weight olefins

with an isoparaffin to form higher molecular weight isoparaffins. Only isoparaffins with tertiarycarbon atoms, such as isobutane or isopentane, react with the olefins.

With sulfuric acid it is necessary to carry out the reactions at 40 to 70F (5 to 21C) or lower, tominimize oxidation reduction reactions which result in the formation of tars and the evolution of

sulfur dioxide. Contact times from 10 to 40 minutes are in general use. Low temperatures meanhigher quality.

In alkylation unit, in sulfuric acid alkylation, low temperatures cause the acid viscosity to becomeso great that good mixing of the reactants and subsequent separation of the emulsion is difficult.

At temperatures above 70F (21C), polymerization of the olefins becomes significant and yieldsare decreased.

Hydrocrackers and catalytic crackers produce a great deal of the isobutane used in alkylation but

it is also obtained from catalytic reformers, crude distillation, and natural gas processing. Olefins are more soluble in the acid phase and a slight amount of polymerization of the olefins is

desirable as the polymerization products dissolve in the acid and increase the solubility ofisobutane in the cid phase.

In portions of the process system where it is possible to have HFwater mixtures, the processequipment is fabricated from Monel metal or Monel-clad steel. The other parts of the system are

carbon steel.

The most desirable alkylation process for a given refinery is governed by economics.

In polymerization unit, The most widely used catalyst is phosphoric acid on an inert support.This can be in the form of phosphoric acid mixed with a natural clay or a film of liquid

phosphoric acid on crushed quartz. Sulfur in the feed poisons the catalyst and any basic materials

neutralize the acid.

If there is no sufficient isobutane available for alkylation unit then the remainder of propyleneand butylenes is directed to polymerization unit.

Naphthas can be blended into either gasoline or jet fuel, depending upon the product demand.

Geometric programming is preferred if sufficient data are available to define the equationsbecause components blend nonlinearly and values are functions of the quantities of thecomponents and their characteristics.


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Viscosity is not an additive property and it is necessary to use special techniques to estimate theviscosity of a mixture from the viscosities of its components. The method most commonly

accepted is the use of special charts developed by and obtainable from ASTM.

Gas oil additives can be selected to produce heating oil or diesel fuel.

Hydrogen requirement can be provided by one of two processes:

1. partial oxidation of heavy hydrocarbons such as fuel oil, or2. steam reforming of light ends such as methane

The catalyst at hydrogen steam reformer is 25 to 40% nickel oxide deposited on a low-silicarefractory base.

During hydrogen production, Shift conversion. More steam is added to convert the CO from step1 to an equivalent amount of hydrogen. Multiple catalyst beds in one reactor with external

cooling between beds are commonly employed to prevent the temperature from getting too high,

as this would adversely affect the equilibrium conversion. The catalyst used is a mixture of

chromium and iron oxide.

In hydrogen production unit,Methanation. In this step, the remaining small quantities of carbon

monoxide and carbon dioxide are converted to methane. The catalyst contains 10 to 20% nickelon a refractory base.

In hydrogen production by partial oxidation of fuel oils is accomplished by burning the fuel athigh pressures (800 to 1300 psig) with an amount of pure oxygen which is limited to that requiredto convert the fuel oil to carbon monoxide and hydrogen.

Enough water (steam) is added to shift the carbon monoxide to hydrogen in a catalytic in acatalytic conversion step.

Methyl-diethanolamine can be used to replace diethanolamine to reduce the absorption of carbondioxide and thereby produce an acid gas with a higher content of hydrogen sulfide. This providessome marginal improvement in Claus unit capacity or sulfur recovery efficiency

Any water which may be contaminated with oil is skimmed in large concrete sumps called API

separators. The skimmed oil is pumped to slop tanks and then reprocessed. Some water from theAPI separators is used in the desalters and the balance is purified by coagulation of impurities inflotation tanks. In this step a mixture of ferric hydroxide and aluminum hydroxide is used to

cause the impurities to form a froth or slurry which floats to the top of the water. The froth is

withdrawn and thickened or settled. The resulting sludge is then incinerated.

Water from the flotation tanks is oxygenated under pressure and then fed to digestion tanks whichmay also receive sanitary sewage from the refinery. A controlled flock of bacteria is maintained

in the digestion tanks to consume any remaining oils or phenolic compounds. A certain amount

of the bacteria is continuously withdrawn from the digestion tanks and incinerated. Water from

the digestion tanks may be given a final polish in sand filters and reused in the refinery oraerated to increase the oxygen content and subsequently discharged to natural drainage.

Tall stacks for incineration, often 200 feet or more in height, and at sufficient velocity so thatresulting ground level sulfur dioxide concentrations are well within safe values.

A related test is the cloud point, which reports the temperature at which wax or other solidmaterials begin to separate from solution.

The corrosion of bearing metals is largely due to acid attack on the oxides of the bearing metals.These organic acids are formed by the oxidation of lube oil hydrocarbons under engine operating

conditions and by acids produced as by-products of the combustion process which are introducedinto the crankcase by piston blow-by.


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Lube oil blending stocks from paraffinic crude oils have excellent thermal and oxidation stabilityand exhibit lower acidities than do oils from naphthenic crude oils.

For economic reasons, as well as process ones, the process sequence is usually in the order ofdeasphalting, solvent extraction, dewaxing, and finishing.

Propane has unusual solvent properties in that from 40 to 60C paraffins are very soluble in

propane, but the solubility decreases with an increase in temperature until at the criticaltemperature of propane 96.8C all hydrocarbons become insoluble. In the range of 40 to 96.8Cthe high molecular weight asphaltenes and resins are largely insoluble in propane.

Separation by distillation is generally by molecular weight of the components and solventextraction is by type of molecule. Propane deasphalting falls in between these categories because

separation is a function of both molecular weight and type of molecular structure.

The heavy oil product from vacuum residuum is called bright stock. It is a high-viscosityblending stock that, after further processing, is used in the formulation of heavy-duty lubricants

for truck, automobile, and aircraft services.

Organic nitrogen compounds seriously affect the color and color stability of oils, and theirremoval is a major requirement of the operation.

The boiling points of the C8 aromatics are so close together (Table 15.2) that separation bydistillation becomes more difficult and a combination of distillation and crystallization or

adsorption is used.

A lengthy distillation process (so many trays and high reflux rate) is applied to separateethylbenzene and p-xylene. This is because that the difference between boiling points ofethylbenzene and p-xylene is only about 3.9F (2C). This is a very energy-intensive operation

and, with todays energy costs, it is usually less costly to make ethylbenzene by alkylating

benzene with ethylene.

The primary source of benzene is from the refinery catalytic reforming unit, but substantialamounts of benzene are also produced by the hydrodealkylation of toluene.

A substantial amount of C3 and C4 olefins are produced by the fluid catalytic cracking unit in the

refinery and some C2 and C3 olefins by the cat cracker and coker, the steam-cracking of gas oilsand naphthas is the most important process for producing a wide range of unsaturatedhydrocarbons for petrochemical use.

Steam-cracking is the thermal cracking and reforming of hydrocarbons with steam at lowpressure, high temperature, and very short residence times (generally _1 second).

Bitumen That portion of petroleum, asphalt, and tar products which will dissolve completely incarbon disulfide (CS2). This property permits a complete separation from foreign products not

soluble in carbon disulfide.

Distillate Any stream that has been vaporized and then condensed to a liquid.

Slack wax: wax produced in the dewaxing of lube oil base stocks. This wax still contains someoil and must be de-oiled to produce a finished wax product.

Smoke point A test measuring the burning quality of jet fuels, kerosene, and illuminating oils. Itis defined as the height of the flame in millimetres beyond which smoking takes place.

Slurry oil The oil, from the bottoms of the FCC unit fractionating tower, containing aconcentration of FCC catalyst particles carried over from the reactor cyclones. The remainder of

the FCC bottoms is the decanted oil.

Sour crude: A crude which contains sulfur in amounts greater than 0.5 to 1.0 wt%, or whichcontains 0.05 ft

3or more of hydrogen sulfide (H2S) per 100 gal, except West Texas crude, which


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is always considered sour regardless of its hydrogen sulfide content. Arabian crudes are high-

sulfur. crudes which are not always considered sour because they do not contain highly activesulfur compounds.

Straight-run gasoline an uncracked gasoline fraction distilled from crude. Straight-run gasolinescontain primarily paraffinic hydrocarbons and have lower octane values than cracked gasolines

from the same crude feedstock. Wick char A test used as an indication of the burning quality of a kerosene or illuminating oil. It

is defined as the weight of deposits remaining on the wick after a specified quantity of sample is

burned.

Saponification number An indication of the fraction of fat or fatty oils in a given product. Thenumber of milligrams of potassium hydroxide required to saponify one gram of the sample.

Salt content Crude oil usually contains salts in solution in water that is emulsified with the crude.The salt content is expressed as sodium chloride equivalent in pounds per thousand barrels (PTB)

of crude oil. Typical values range from 1 to 20 PTB. Although there is no simple conversion from

PTB to parts per million by weight (ppm), 1 PTB is roughly equivalent to 3 ppm.

Reid vapor pressure (RVP) The vapor pressure at 100F of a product determined in a volume of

air four times the liquid volume. Reid vapor pressure is an indication of the ease of starting andvapor-lock tendency of a motor gasoline as well as explosion and evaporation hazards

Pipe still A heater or furnace containing tubes through which oil is pumped while being heated orvaporized.

Napthalene A double-ring aromatic compound in the jet fuel boiling range.

Naphthene A cycloparaffin compound which is paraffin with a ring structure.

MONC Motor octane number clear (unleaded).

Long resid The bottoms stream from the atmospheric distillation tower.

Short resid: The bottoms stream from the vacuum distillation tower.

Lamp sulfur The total amount of sulfur present per unit of liquid product. The analysis is madeby burning a sample so that the sulfur content will be converted to sulfur dioxide, which can be

quantitatively measured. Lamp sulfur is a critical specification of all motor, tractor, and burnerfuels;

Gas oil Any distillate stream having molecular weights and boiling points higher than heavynaphtha (_400F, or 205C). Frequently, any distillate stream heavier than kerosene. Originally

was added to manufactured or city gas to make it burn with a luminous flame. Hence, the name

gas oil.

Fuel oil equivalent (FOE) The heating value of a standard barrel of fuel oil, equal to 6.05 _ 106Btu (LHV). On a yield chart, dry gas and refinery fuel gas are usually expressed in FOE barrels.

Flux: Lighter petroleum used to fluidize heavier residual so that it can be pumped.

Raffinate The product resulting from a solvent extraction process and consisting mainly ofthose components that are least soluble in the solvents. The product recovered from an extraction

process is relatively free of aromatics, naphthenes, and other constituents that adversely affect

physical parameters.

Sulfuric acid treating A refining process in which unfinished petroleum products such asgasoline, kerosene, and lubricating oil stocks are treated with sulfuric acid to improve their color,

odor, and other characteristics.

Tail gas: The lightest hydrocarbon gas released from a refining process.

Vapour: The gaseous phase of a substance that is a liquid at normal temperature and pressure.


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In general crude oil and petroleum products with a flash point of


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withdrawn from the bottom of the reactor stack and sent to the regenerator. As the catalyst flows

down through the regenerator, the coke is burned away. Regenerated catalyst is lifted byhydrogen to the top of the reactor stack. Because the reactor and regenerator sections are separate,

each operates at its own optimum conditions.

Catalytic oligomerization also is called catalytic polymerization.

Refiners prepare lube base stocks from residual oils by removing asphaltenes, aromatics, andwaxes.

The Isodewaxing Process, commercialized in 1993 by ChevronTexaco, catalytically isomerizesn-paraffins into iso-paraffins. This decreases the wax content and increases the concentration

low-viscosity hydrocarbons, both of which are desirable.

Greases are made by blending salts of long-chained fatty acids into lubricating oils attemperatures of204 to 315C.

Treating improves the odor, color, and stability of straight-run liquids and conversion-unitproducts. Sulfuric acid treating removes olefins, sulfur, nitrogen, oxygen compounds, and other

contaminants. Clay/lime treating of acid-treated oil removes any residual traces of asphaltenes.Caustic washing with sodium (or potassium) hydroxide removes naphthenic acids, phenols,

mercaptans, and H2S. If the concentration of organic sulfur exceeds the capacity of a caustic or acid treater, the stream

must be sent to a hydrotreater.

In a spark-ignition engine, some compounds start to burn before they reach the spark plug. Thispremature ignition causes knocking,

In gasoline industry, the C stands for clear, which means that the fuel does not contain lead ormanganese additives.

Octane numbers do not blend linearly. For example, while the RON for pure 4-methyl-2-penteneis 99, its blended RON is 130.

It is easier to start a diesel engine when the cetane number of the fuel is high.

Cetane index, as defined by ASTM D976, is not a measurement, but the result of a calculation

based on density and mid-boiling point. Diesel index is a simpler calculation based on density and aniline point.

Volatile hydrocarbons react with NOx to make ozone.

Aniline point can be used to determine the quality of ignition in diesel cuts.

The carbon residue of a petroleum crude oil is proportional to the asphalt content.

Bromine Number is a measure of olefins in gasoline

Hydrocarbons are organic compounds composed entirely of carbon and hydrogen atoms.

Gasolines contain small amounts of compounds (less than 0.1 volume percent) with sulfur,nitrogen, and oxygen atoms in their structures, excluding added oxygenates. Even though thesecompounds are also composed primarily of carbon and hydrogen atoms, they are not classified

as hydrocarbons because of the presence of the other atoms. The straight-rungasoline (also called naphtha), Straight-run products are those isolated from

crude by simple distillation.

Polymerization is a less-favored process than alkylation because the products are also olefins,which may have to be converted to paraffins before they are blended into gasoline.

Regulations have prompted the commercialization of several non-hydrotreating processes forsulfur removal. One option is adsorption, in which an appropriate adsorbent removes selectedsulfur species directly from FCC gasoline.


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Etherification of Olefins High-octane oxygenates called ethersmay be produced during refiningby reacting suitable alcohols such as methanol and ethanol with branched olefins from the FCC,such as isobutene and isopentene.

FCC product must be sweetenedto convert reactive sulfur compounds (mercaptans) to moreinnocuous ones; otherwise, the gasoline blend will be odorous and unstable.

An emulsionis a stable mixture of two mutually insoluble materials.

Gasoline oxygenated with methanol corrodes fuel system metals and accelerates deteriorationof elastomers. Methanol, unlike ethanol, is toxic.

Denaturing of ethanol means adding of toxic material (denaturing) to make it unfit for humanconsumption.

Viscosityindex (VI):The effect of temperature change on viscosity. Paraffinic mineral oilsgenerally have a VI of 90100. High VI hydraulic oils are treated with VI improvers and have a VIof around 150.

Synthetic oils are beneficial for their higher thermal and oxidation stability

Hydrolyticstability:Ability of additives and certain synthetic lubricants to resist chemicaldecomposition in the presence of water

By convention, the power output of an engine is measured as brakepower. The adjective

brake indicates that it is the power developed at the engines drive shaft, which is less than thepower developed inside the engines cylinders.

A kilowatt-hour (kW-hr) or brakehorsepower-hour (bhp-hr) is a unit of work (energy); it is thework done when the engines shaft exerts one kilowatt (or brake horsepower) for one hour.

Methane is not included with all hydrocarbons because it is considered to have negligiblephotochemical reactivity in the atmosphere.

Because most exhaust aftertreatment devices (engines) are very sensitive to sulfur (somedevices can be permanently damaged by prolonged exposure to fuel sulfur levels as low as 50ppm), vehicles so equipped must use ultra-low sulfur diesel (ULSD) fuel.

While the densities of most petroleum products are less than one, the API gravity scale wasconstructed so that most values are between 10 and 70.

For compounds with the same carbon number, the order of increasing heating value by class is

aromatic, naphthene, and paraffin on a weight basis. However, the order is reversed for acomparison on a volume basis, with aromatic highest and paraffin lowest.

This same trend holds with fuels. Lighter (less dense) fuels, like gasoline, have higherheating values on a weight basis, whereas the heavier (more dense) fuels, like diesel, havehigher heating values on a volume basis.

Conductivity of a fuel is a measure of its ability to dissipate static electric charge. It is expressedin pS/m, picosiemensper-meter, also called a conductivity unit (CU). A siemen is the SI (metric)definition of reciprocal ohm, sometimes called mho.

Additives known as StaticDissipatorAdditives can be added to fuels to increase theconductivity, thus dissipating static charge.

Diesel engines need high compression ratios to generate the high temperatures required for fuelautoignition. Conversely, gasoline engines use lower compression ratios in order to avoid fuel

autoignition, which manifests itself as engine knock (often heard as a pinging sound). Antifoam Additives: Some diesel fuels tend to foam as they are pumped into vehicle tanks.

If the conductivity of the fuel is low, the fuel may act as an insulator allowing a significant amountof charge to accumulate. Static discharge may then occur posing a potential risk of fire hazard.Typically, the lower-sulfur diesel fuels have lower conductivity.

For fuel stability additive, Because of the complex chemistry involved, an additive that is effectivein one fuel may not work as well in another.


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Metal Deactivators: When trace amounts of certain metals, especially copper and iron, aredissolved in diesel fuel, they catalyze (accelerate) the reactions involved in fuel instability.

Microorganism (microbes) can produce acidic products.

Biocides: Because most microorganisms need free water to grow, biogrowth is usuallyconcentrated at the fuel-water interface, when one exists. Any water bottoms that containbiocides must be disposed of appropriately because biocides are toxic.

Demulsifiers are surfactants that break up emulsions and allow the fuel and water to separate.Pumping can stabilize the emulsion.

The additive package for diesel fuel may contain: A detergent/dispersant Lubricity improver One or more stabilizing additives A cetane number improver A low-temperature operability additive (flow improver or pour point reducer) A conductivity additive A biocide A corrosion inhibitor

In diesel fuel, Lubricity is a measure of the fuel's ability to prevent excessive wear when sliding

and rotating parts in fuel pumps and injectors come in contact.

ptb: pounds per thousand barrels


Floating tanks- crude, gasoline, kerosene f.p. 0.5 % S need extensive processing.

Crude >10 lb/1000 bbl (ptb)salts need extensive desalting. (1 ptb = 3ppm)

Zeolit (molecular sieve)- silica alumina catalyst.

Nitrogen reacts with the acid centers on the catalyst.

FCC feed (cracked paraffins and VGO)

HC feed (aromatic cycle oils (from vacuum units and cracking and coker gas oil) and cokerdistillate)

HCR catalyst- molecular sieve catalyst impregnated with vanadium, palladium, tungsten,nickel.

HCR catalyst poisoned by (metallic salts, O2, organic nitrogen compounds and sulfur)

Silica-alumina for cracking

Rare-earth metals- for hydrogenation.

In the feed to HCR is not desulfurized, then should be a guard reactor contain hydrotreatingcatalyst (Co-Mo on silica-alumina) to convert organic S and N to H2S and NH3 and hydrocarbonsto protect the precious metals catalyst in the following reactors.


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Organic nitrogen compounds deactivates HCR catalyst.

Co-Mo catalyst- selective, easy regeneration, resistant to poisoning.

Ni containing catalyst requires pre-sulfiding.

Co-Mo good for S removal.

Ni-Mo good for N removal.

In catalytic reforming minor amount of cracking.

Aromatics have higher liquid density than paraffins and naphthenes (1 paraffins = 0.77 aromaticsby volume, and 1 naphthenes = 0.87 aromatics)

Isobutane from HCR unit.

Hydrogen plant catalyst is Ni-oxides on silica refractory.

Isoparaffins have lower melting temperature than n-paraffins, this is why they are good forlubricants.

In solvent dewaxing, we remove n-paraffins not iso ones.

In HCR water is injected to reactor outlet to dissolve ammonia.

In HCR the first bed in the reactor is to hydrotreat the feed. But if the unit is designed formaximum production of diesel fuel all catalyst beds contain hydrocracking catalysts.

Volume swell 10-30% in HCR.

Injecting chloride will produce HCl on the catalyst. HCl promote catalyst acidity and helps tominimize catalyst coke.

Sulfuric acid treatment- removes olefins, S, N, O compounds and traces of asphaltenes.

Caustic washing- removes naphthenic acid, phenols. If the concentration of organic sulfur exceeds of the caustic or acid treater, the stream must by

sent to hydrotreater. Polyolefins in gasoline is unstable and can form gum, we allow monoolefins only in gasoline. But in aviation fuel, olefins are entirely unacceptable. S, N, O in oil come from living organism. Van Der Waals force- HC molecules together, larger molecules more van der Waals forces. Gasoline volatility depends on outdoor weather, we have to adjust average molecular size. unbranched paraffins ignite too easily (premature ignition).

RON - hard acceleration- low speed. MON- Zero acceleration- high speed. (RON+MON)/2 Normally RON > MON specially for alkenes and aromatics. The ideal diesel and jet fuel to be unbranched paraffins such as n-cetane (16). Long chains in lubricating oil unable to find the orderly arrangement to form crystals. Cycloparaffins and aromatics change their viscosity significantly with temperature. Two separate layers - immiscible (water- hydrogen bond too high but HC- van der Waals bonds-

weak one). Salts accumulate in water, they are electrically charged ions. In the desalter charged particles injected into the crude oil quickly attatch themselves to water

droplets and these electrically charged water droplets are pulled through the oil by electric field. thermal cracking above 360C will make small fragments these fragments may recombine to make

gum. Catalyst; -

speed up the reaction reduce the required energy selectivity.

In reforming, cycloparaffins are converted to aromatics. Thermal cracking and FCC increases H/C ratio by carbon rejection. In HCR:

paraffins chains are cracked.


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naphthenes rings are opened aromatic rings are dealkylated.

In catalytic reforming: Naphthenes to aromatics. Isomerization of naphthenes Dehydrogenation of paraffins to form aromatics Isomerization of paraffins.

Major refinery process: Separation Conversion Purification Formulation and Blending

657 refineries worldwide (85 MM bpd). There is no benefit of using high ocatne no. higher than the required one. Kuwait export oil API = 32 and 2.7% S At high temperature >120C MgCl2, CaCl2 hydrolyze to HCl. but NaCl is stable and doesnt

hydrolyze. HCl vapor is not corrosive at temperature above the dew point of water. Ammonia is injected to neutralize HCl to form NH4Cl, which is hygroscopic. Organic chloride are not removed in the desalter. In desalter chemical surfactants (demulsifier) are added to dissolve suspended solids. 50% operating cost for distillation. In vacuum distillation, large diameter to maintain comparable vapor velocity at reduced pressure. Asphaltene does not dissolve in propane. HCR can handle feed that can not be processed by FCC or CR. Specially with high polycyclic

aromatics or too high in S and N. In HCR- isobutane is produced, isomerisation for pour point control and smoke point control (jet

fuel). All metals in the poriodic table present in the crude oil with the major ones Ni & V. >500 HC in gasoline.

Heavy naphtha from the distillation column is sent to catalytic reforming. Kerosene from atmospheric distillation is more stable than that obtained from cracking process

(less olefins). sweet oil < 0.5% S and sour oil >2.5% S Static electricity- When electrical potential exists between two objects and there is no coductive

path. Then an electric spark will jump the gap between the two objects. Light hydrocarbons can generate static electricity. Prevented by bonding and earthing. Aniline point is defined as the temperature at which equal volumes of aniline(C6H5NH2)

and diesel oil are completely miscible. The value gives an indication of the aromatic content of diesel oil, since aniline is an aromatic

compound which is dissolved on heating by the aromatics in diesel oil. The greater the anilinepoint, the lower the aromatics in diesel oil. A higher aniline point also indicates a higher

proportion of paraffin. The diesel index is directly related to aniline point as:

Diesel index = ((aniline point(Deg F))(API gravity))/100 A higher aniline point (and therefore a lower aromatic content) in diesel oil is desirable, in order to

prevent autoignition in diesel engines. In cases where the Aromatic content in the oil is very high, in such cases "Mixed Aniline Point"

needs to me measured to determine the approximate content of aromatic in the oil. The TotalAcid Number(TAN) is the amount of potassium hydroxide in milligrams that is needed

to neutralize the acids in one gram of oil (mg KOH/g). It is an important quality measurement
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of crude oil. The TAN value indicates to the crude oil refinery the potential of corrosion problems.It is usually the naphthenic acids in the crude oil that causes corrosion problems.

In HCR, ammonia organic ammonia inhibits the hydrocracking catalyst activity, requiring higheroperating temperatures, but this generally results in somewhat better liquid yields than would bethe case if no ammonia were present.

Safetyvalve: (opens quickly at set pressure, immediate discharge and used for compressible

fluids (steam and gases)). Reliefvalve: (opens and closes slowly, immediate flow discharge not needed, and used for non-

compressible (water and oils)). Bullets drums = spherical tanks for economical shape. UOP Factor (Watson factor)(function of true boiling point and specific gravity) K = 12.5-13 for

highly paraffinic and 10.5-12.5 for cyclic (naphtenic) oils U.S. Bureau of Mines Correlation index (function of average boiling point and specific gravity)

is zero for normal paraffin series and is 100 for benzene. In Desalting/dehydration process metals and solid particles are also partially removed. In desalting process, if the crude oil is very heavy crude oil (API < 15) some gas oil may be added

as diluents. A secondary important function of the desalting process is the separation of suspended solids

from crude oil. Wetting agents are added to enhance separation of solid particles. Higher pHvalues enhance the formation of emulsions (mainly due to sodium naphthenate and sodiumsulfide)

In desalter, the wash water usually contains high concentration of phenols which must beseparated in wastewater treatment facility

The electrical field imposes an electrical charge on water droplets entrained in the oil stream,thus causing them to oscillate as they pass through the electrodes. During this oscillation thedroplets are stretched or elongated and then contracted during reversal of the imposing ACelectrical field. During this agitation the water droplets co-mingle and coalesce into droplets ofsufficient size to migrate, by gravity, back into the lower water phase of the vessel for disposal.

In distillation the overflash 10 20% bottom products vapor condenses in the first few traysabove the flash zone and enhance separation and also provide internal reflux.

In vacuum distillation addition of steam decreases the effective pressure to about 10 mm Hg. ifsteam injected into the heater it will increase the velocity and decrease coke formation.

Since lower pressure increases vaporization, the vacuum distillation towers are much larger indiameter compared to atmospheric distillation columns

Advantages of HCR:o facilitate product balance with the market demando Very high octane numberso production of large amount of isobutaneo Supplementing FCC to upgrade heavy stocks, aromatics and coker oils

Hydrocracking is capable of using aromatics and cycle oils and coker distillates as feed (thesecompounds resist FCC)

LCO = Light Cycle Oil (produced in FCC, High in aromatics and sulfur)

Isomerization is another type of reaction, which occurs in hydrocracking. In FCC unit, aromatics are not easily cracked. Aromatics are not preferred feedstock. They

produce excess gaseous products and have a low gasoline yield. In FCC, Light Cycle gas-Oil (LCO), widely used as a blending stock in heating oil and diesel fuel. Heavy coker gas-oil (HCO) is the heaviest product of FCC and used as a fuel in refineries. In the FCC regenerator, the ratio between CO2 and CO is related to temperature control of

regenerator. Coking is a preferred process for oil from tar sand. Fluid coking is a continuous process in which coking occur is a fluidized bed.
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Where a lower voltage is needed step-down transformers are used to reduce the voltage towhat is required.

Kerosene hydrotreatment unit to improve the quality of Aviation Turbine Fuel (ATF). Thepurpose of the unit is to remove the sulphur from the kerosene. As part of this processhydrogen must be added to the unsaturated hydrocarbon molecules to make them saturated.If this is not done, the unsaturated molecules will attract sulphur to them and thesulphur will stay in the kerosene. The catalyst used in the reactor vessel is nickel-tungstenbase.

From the Kerosene HT unit a by-product called wild distillate is also produced in the unit.This is returned to the atmospheric crude oil distillation unit for further processing.

The vacuum residue can be used as heavy fuel oil (bunker oil) and for making asphalt (asused on road surfaces).

In hydrocracking unit, the catalyst used in the reactor vessels is known only by its tradename of DHC-100.

In H2 plant, the hydrogenator reactor, which replaces sulphur atoms with hydrogen atoms, isused only if the feed gas contains more than a certain amount of impurities (10 ppm by

volume of carbonyl sulphide). The catalyst used is nickel on an alumina base. The lead dioxide that produced during leaded gasoline burning. In the environment the lead

dihalide undergoes oxidation-reduction by sunlight to elemental lead and halogen, both ofwhich are serious pollutants.

But lead coats the platinum and palladium and deactivates the converters, so unleaded gasmust be used.

These new gasolines do notsolve the pollution problem. They solve the lead pollutionproblem, but unleaded gasolines show larger emissions of other contaminants. Certainunburned aromatic hydrocarbons and alkenes absorb sunlight readily and cause smog.

When 10% ethyl alcohol is mixed with gasoline it is called gasohol

Thus MTBE, ethyl /-butyl ether (ETBE), ethanol, methanol, and other ethers and alcoholshad to be added at higher levels. This is called reformulated gasoline (RFG) and it may cut

carbon monoxide levels and may help alleviate ozone depletion. But ethanol cannot be blended into gasoline at the refinery because it is hygroscopic and

picks up traces of water in pipelines and storage tanks. Gasohol may increase air pollutionbecause gasoline containing ethanol evaporates more quickly. Studies and debate continue.

Boiling point of a branched chain is lower than for a straight chain hydrocarbon of the samemolecular weight.

The butanes present in crude oils and produced by refinery processes are used ascomponents of gasoline and in refinery processing as well as in LPG. Normal butane (nC4)has a lower vapor pressure than isobutane (iC4), and is usually preferred for blending intogasoline to regulate its vapor pressure and promote better starting in cold weather.

Crankcase dilution[1]is a phenomenon inengineswhere accumulation of unburnedgasolinein the crankcase, an excessively rich fuel mixture or poor combustion allows a

certain amount of gasoline to pass down between the pistons and cylinder walls and dilutetheengine oil. When a mixture of air and fuel enters the cylinder of an engine, it is entirelypossible for condensation of fuel to occur on the cooler parts of the cylinders. Thecondensate may wash thelubricating oilfrom the cylinder walls, travel past the piston ringsand collect in the oil pan, thus increasing wear and also diluting the lubricating oil. Since theless volatile components of the fuel will have the greatest tendency to condense the degreeof crankcase-oil dilution is directly related to the end volatility temperatures of the mixture.

Altitude affects several properties of gasoline, the most important of which are losses byevaporation and octane requirement.
http://www.answers.com/crankcase+dilution#cite_note-0http://www.answers.com/crankcase+dilution#cite_note-0http://www.answers.com/crankcase+dilution#cite_note-0http://www.answers.com/topic/enginehttp://www.answers.com/topic/enginehttp://www.answers.com/topic/enginehttp://www.answers.com/topic/gasolinehttp://www.answers.com/topic/gasolinehttp://www.answers.com/topic/motor-oil-2http://www.answers.com/topic/motor-oil-2http://www.answers.com/topic/motor-oil-2http://www.answers.com/topic/mineral-oil-2http://www.answers.com/topic/mineral-oil-2http://www.answers.com/topic/mineral-oil-2http://www.answers.com/topic/mineral-oil-2http://www.answers.com/topic/motor-oil-2http://www.answers.com/topic/gasolinehttp://www.answers.com/topic/enginehttp://www.answers.com/crankcase+dilution#cite_note-0


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Distillate fuels can be divided into three types: jet or turbine fuels, diesel fuels, and heating oils.

The two basic types of jet fuels are naphtha and kerosine. Naphtha jet fuel is produced primarilyfor the military and is a wide-boiling-range stock which extends through the gasoline andkerosine boiling ranges.

The chemical compositions of crude oils are surprisingly uniform even though their physicalcharacteristics vary widely.

API gravities are not linear and, therefore, cannot be averaged. But Specific gravities can beaveraged.

Crudes with greater than 0.5% sulfur generally require more extensive processing than thosewith lower sulfur content.

Carbon residue is determined by distillation to a coke residue in the absence of air. The carbonresidue is roughly related to the asphalt content of the crude and to the quantity of the lubricatingoil fraction that can be recovered.

If the salt content of the crude, when expressed as NaCl, is greater than 10 lb/1000 bbl, it isgenerally necessary to desalt the crude before processing.

Crudes containing nitrogen in amounts above 0.25% by weight require special processing toremove the nitrogen.

Vanadium concentrations above 2 ppm in fuel oils can lead to severe corrosion to turbine bladesand deterioration of refractory furnace linings and stacks.

The double bonds are reactive and the compounds are more easily oxidized and polymerized toform gums and varnishes.

In addition, some metals in inorganic compounds dissolved in water emulsified with the crude oil,which can cause catalyst deactivation in catalytic processing units, are partially rejected in thedesalting process.

pH in desalting unit is important to control foaming and better separation of the oil-water mixture.The pH value is controlled by using another water source or by the addition of acid to the inlet orrecycled water.

In atmospheric distillation unit, 10 to 20% over-flash allows some fractionation to occur on thetrays just above the flash zone by providing internal reflux in excess of the sidestream

withdrawals. To reduce the top diameter of the tower and even the liquid loading over the length of the tower,

intermediate heat-removal streams are used to generate reflux below the sidestream removalpoints.

The stripping steam reduces the partial pressure of the hydrocarbons and thus lowers therequired vaporization temperature.

To eliminate essentially all volatile matter from petroleum coke it must be calcined atapproximately 1095 to 1260C.

Needle coke is preferred over sponge coke for use in electrode manufacture because of its lowerelectrical resistivity and lower coefficient of thermal expansion.

Shot coke is undesirable because it does not have the high surface area of sponge coke nor theuseful properties, characteristic of needle coke, for electrode manufacture.

It is important to note that petroleum coke does not have sufficient strength to be used in blastfurnaces for the production of pig iron nor is it generally acceptable for use as foundry coke.Usually furnace tubes have to be decoked every three to five months.

Long paraffinic side chains attached to aromatic rings are the primary cause of high pour pointsand viscosities for paraffinic base residua.

The oil fraction is soluble in propane the resin fraction is soluble (and the asphaltene fractioninsoluble) in either pentane, hexane, heptane, or octane, depending upon the investigator.


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Conradson carbon (CCR) or Micro-Carbon Residue (MCR) is a measure of the ash left afterflame burning.

DAO: Deasphalted oil.


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Vacuum Distillation

There is no overhead distillate in vacuum distillation. Vacuum distillation is carried out with absolute pressures in the tower flash zone area of 25 to 40

mmHg Addition of steam (10 to 50 lb/bbl feed) to the furnace inlet increases the furnace tube velocity

and minimizes coke formation in the furnace as well as decreasing the total hydrocarbon partialpressure in the vacuum tower.

The effectivepressure (total absolute pressure partial pressure of the steam) at the flash zonedetermines the fraction of the feed vaporized for a given furnace outlet temperature.

A few millimeters decrease in pressure drop will save many dollars in operating costs. With the molecular weight of steam low at 18 the tower vapor traffic was extremely high in

velocity requiring a large tower diameter to accommodate it. The tower internals are usually expandedgrid (packing) type which offer low pressure drop. Dry vacuum unit where no steam is used in the distillation process itself. Most of the column usespacking materialfor the vapor-liquid contacting because such packing

has a lower pressure drop than distillation trays. Shortresidue: residue from vacuum distillation. Lately instead of using ejectors liquidringpumps are used. The heater transfer and flash zone temperatures are generally varied to meet the vacuum

bottoms specification, which is probably either a gravity (or viscosity) specification for fuel oil or apenetration specification for asphalt.

Quite often, when the level of the residuum rises, the column vacuum falls because of crackingdue to long residence time.

Volumes of vapor at reduced pressures are large, and pressure drop must be small to maintaincontrol, so vacuum columns are necessarily of large diameter.

If trays are used in vacuum columns, the diameter may be up to 14 m. The vapor rising above the flash zone will entrain some residuum that cannot be tolerated in

cracking units (carbon residue and metals contents). The vapor is generally washed with gas oilproduct sprayed into the slop wax section. The mixture of gas oil and entrained residuum is

known as slopwax. Slop wax can be recirculated through the heater to the flash zone and reflashed. But if the slop

contains volatilemetals it cannot be reflashed. The distillates from the vacuum column due to go to hydrotreatment/hydrocracking units do not

need to be metal free, but their Conradson carbon content and asphaltene content must be aslow as possible.

The Conradsoncarbon content of distillates sent to cracking is related to the asphaltene contentof the atmospheric residue vacuum distillation feed

Nickel and vanadium increases dehydrogentation and deactivate the catalyst. copper is alsodeactiveate the catalyst by neutralizing acidic sites.

The Conradson carbon content of distillates sent to cracking is related to the asphaltene contentwhich can deactivate the catalyst.

The atmospheric residue has to be stored at 150C if not sent directly to the vacuum tower. Vacuum distillation units have a system to create the vacuum that uses either ejectors or a

combination of ejectors and liquid ring pumps. But pumps are less reliable as not flexible duringstartup.

Likewise in atmospheric distillation, ammonia is often injected at the top of the tower (1 to 10 ppmof the feed) in order to lower the acidity of overhead water.
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Hydrocracking

Hydrocracking makes very good quality diesel fuels concerning the cetane number, coldbehavior, stability, and sulfur content. However this type of stock is only available in limitedquantities since the process is still not widely used owing essentially to its high cost.

Hydrocracking is ideal for obtaining middle distillate cuts that can be used in jet fuel

formulation. The treating reactions that will take place (if the respective contaminants are present) are the

following: sulfur removal, nitrogen removal, organo-metallic compound removal, olefinsaturation, oxygen removal, and halides removal.

The cracking reactions require bi-functional catalyst, which possess a dual function ofcracking, and hydrogenation.

However, the investment is clearly higher and is justified only when feedstoclcs are difficult toconvert and that their content in nitrogen is high.

The hydrocracking process is characterized by a very low gas production and a low LPGyield

Problems with heavy feeds which is the formation of polynuclear aromatics, and the solutionis partial residue purge.

Unconverted material from HDC unit which becomes feed stock for FCC units, ethyleneplants or lube oil units.

When using a pretreat and cracking catalyst configuration, the first catalyst (a hydrotreatingcatalyst) converts organic sulfur and nitrogen from hetero compounds in the feedstocktohydrogen sulfide and ammonia.

The poisonous effect of H2S and NH3 on hydrocracking catalysts is considerably less thanthat of the corresponding organic heterocompounds.

If we use two stages where the fractionator bottom only goes back to a second reactor, sothe feed to the second reactor will be without NH3 and H2S which allows the use of eithernoble metal or base metal sulfide hydrocracking catalysts.

In the hydrocracking reactions, these two functions are the acid function, which provide forthe cracking and isomerization and the metal function, which provide for the olefin formation

and hydrogenation. In hydrocracking, the products are highly isomerized, C1 and C3 formation is low, and single

rings are relatively stable. Polynuclear aromatics (PNA), sometimes called polycyclic aromatics (PCA), or polyaromatic

hydrocarbons (PAH) are compounds containing at least two benzene rings in the molecule. Heavypolynucleararomatics (HPNA) are up to seven benzene rings. They cause

downstream fouling, deposit on the catalyst and make coke. The cracking function is provided by an acidic support, whereas the hydrogenation function

is provided by metals. The acidic support consists of amorphousoxides (e.g., silica-alumina, a crystalline zeolite

(mostly modified Y zeolite)) plus binder (e.g., alumina), or a mixture of crystalline zeoliteand amorphous oxides.

Cracking and isomerization reactions take place on the acidic support. The metals providingthe hydrogenation function can be noble metals (palladium, platinum), or non-noble (alsocalled base) metal sulfides from group VIA (molybdenum, tungsten) and group VIIIA(cobalt, nickel). These metals catalyze the hydrogenation of the feedstock, making it morereactive for cracking and heteroatom removal, as well as reducing the coking rate. They alsoinitiate the cracking by forming a reactive olefin intermediate via dehydrogenation.

Four key performance criteria by which hydrocracking catalysts are measured:o Initialactivity,o Stability,


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o Productselectivity,o Productquality,

There are two methods of catalyst loading sock loading (canvas) and dense loading(mechanical).

Zeolites are crystalline aluminosilicates composed of Al2O3 and SiO2 tetrahedral units A metal, a metal oxide, a metal sulfide, or a combination of these compounds may supply the

metal function of the catalyst. The activation of HDC catalyst is called sulfiding, presulfiding, presulfurizing in addition to

activation. The noblemetal catalysts are activated by hydrogenreduction of the finished catalyst, in

which the metal is also in an oxide form. The metals on the greatest majority of catalysts are in an oxide form at the completion of the

manufacturing process. The non-noble (base metal) catalysts are activated by transforming the catalytically inactive

metal oxides into active metal sulfides. Ammonia injection is practiced during the sulfiding of high activity (high zeolite content)

catalysts to prevent premature catalyst deactivation. One example of a reversiblepoison is carbon monoxide, which can impair the

hydrogenation reactions by preferential adsorption on active sites. Deposition of metals is notreversible, even with catalyst regeneration. The metals may

come into the system via additives, such as silicon compounds used in coke drums to reducefoaming, or feedstock contaminants such as Pb, Fe, As, P, Na, Ca, Mg, or as organo-metalliccompounds in the feed primarily containing Ni and V.

The majority of commercial catalysts regeneration is performed ex-situ because ofenvironmental considerations as well as because it results in a better performing catalyst.

The thickness of the reactor walls can be as much as 1 ft (30 cm). To compensate for catalyst deactivation, the bed temperature should be increase in many

cases, it is very small, less than 2F/month (1C/month). Condensate is injected into the reactor effluent just upstream of effluent air cooler. The

function of the injection water is to remove ammonia and some H2S from the effluent.

Refinery Summary

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