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General Information
"From Louisiana For Louisiana"
What A Barrel Of Crude Oil Makes?
Crude oils are complex mixtures containing many different hydrocarbon compounds that vary in appearance and composition from one oil field to another. Crude oils range in consistency from water to tar-like solids, and in color from clear to black. An "average" crude oil contains about 84% carbon, 14% hydrogen, 0.1%-3% sulfur, and less than 1% each of nitrogen, oxygen, metals, and salts. Crude oils are generally classified as paraffinic, naphthenic, or aromatic, based on the predominant proportion of similar hydrocarbon molecules. Mixed-base crudes have varying amounts of each type of hydrocarbon. Refinery crude base stocks usually consist of mixtures of two or more different crude oils.
Relatively simple crude oil assays are used to classify crude oils as paraffinic (West Texas crude, Brent), naphthenic (Louisiana crude, Nigerian Light), aromatic (Maya Crude), or mixed (Assam crude). One assay method (United States Bureau of Mines) is based on distillation, and another method (UOP "K" factor) is based on gravity and boiling points. More comprehensive crude assays determine the value of the crude (i.e., its yield and quality of useful products) and processing parameters. Crude oils are usually grouped according to yield structure.
Crude oils are also defined in terms of API (American Petroleum Institute) gravity. The higher the API gravity, the lighter the crude. For example, light crude oils have high API gravities and low specific gravities. Crude oils with low carbon, high hydrogen, and high API gravity are usually rich in paraffin’s and tend to yield greater proportions of gasoline and light petroleum products; those with high carbon, low hydrogen, and low API gravities are usually rich in aromatics. The price of a crude oil is usually based on its API gravity, with high gravity oils commanding higher prices.
Crude oils that contain appreciable quantities of hydrogen sulfide or other reactive sulfur compounds are called "sour." Those with less sulfur less than 0.5% are called "sweet." Some exceptions to this rule are West Texas crudes, which are always considered "sour" regardless of their H2S content, and Arabian high-sulfur crudes, which are not considered "sour" because their sulfur compounds are not highly reactive.
Hydrocarbon Groups :
The main constituents of petroleum can be grouped into four categories:
Paraffin: A series of saturated straight chain or branched hydrocarbons, the lowest members of which are methane, ethane and propane.
Olefins: Double-bonded hydrocarbons that are not normally present in crude oil but are formed during refinery processing and vehicle combustion of fuel. Olefins help improve the octane rating, but their use may lead to gum formation or deposits in engine intake systems.
Aromatic: Unsaturated cyclic hydrocarbons are known as aromatics. Aromatics occur naturally in crude oil and can also be produced in some refining processes. Aromatics common in petrol include benzene, toluene and xylene. Controlling the level of aromatics directly limits evaporative losses and exhaust emissions.
Naphthenic: Naphthalene’s are a class of compounds that are saturated hydrocarbons typified by cyclic hydrocarbon molecular structure. The general formula for cyclic hydrocarbons is CnH2n.
Why Weathering Test is performed?
95% of LPG sample under consideration should evaporate at a temperature of +2oc.
If the evaporation temperature exceeds +2oc then there is a probability that heavier hydrocarbons are present in LPG and if the evaporation temperature is less then +2oc then there is a probability that lighter fractions are more.
Significance: This test is intended to find out the presence of heavier hydrocarbons in LPG, which may not readily evaporate. This test is done specially for LPG.
What is Copper corrosion test?
This test serves as measure of corrosively of fuel with copper, brass, or bronze parts of a fuel system. The copper strip is polished smoothly and immersed in the sample and put into a bomb. This is placed into a water bath which is maintained at the specified temperature for the specified time. The strip is removed from the sample, washed with iso-octane or normal heptane, and examined for evidence of etching or discoloration. The color of the strip is compared with ASTM copper strip standards color code.
Significance: Copper corrosion limits provides assurance that difficulties will not be experienced in deterioration of the copper and copper alloy fittings and connections that are commonly used in many types of utilization, storage and transportation equipment. This test is required mainly for LPG, Naphtha, SKO, HSD, ATF and MS.
What is Flash Point?
The flash point of a fuel is the temperature to which the fuel must be heated to produce a vapour/air mixture above the liquid fuel that is ignitable when exposed to an open flame under specified test conditions. Flash point is important primarily from a fuel-handling standpoint. Too low a flash point will cause fuel to be a fire hazard, subject to flashing, and possible continued ignition and explosion. In addition, a low-flash point may indicate contamination by more volatile and explosive fuels, such as gasoline. A very important reason to maintain the flash point as high as possible is due to the electrostatic hazards in pumping distillate fuels. Flash point (BIS) requirements for some petroleum products are:
S.K.O. - 35 C
U.L.S.H.S.D. - 35 C
H.S.D. - 35 C
F.O. - 66 C
A.T.F. - 39 C
What is Fire Point?
Fire point is the lowest temperature, corrected to one atmosphere pressure (101.3 kPa), at which the application of a test flame to the oil sample surface causes the vapor of the oil to ignite and burn for at least five seconds. For ordinary commercial lubricating oils, the fire point usually runs about 30oC above the flash point. The test is carried out in open cup rather than in a close one. ASTM D 92 method offers the advantage of open flash point and fire point determination. Low fire point petroleum products are potential fire hazards.
What is Smoke point?
Smoke is an indication of clean burning quality of kerosene. Illumination depends upon the flame dimension although it is not related to flame height. Many paraffins may be gifted with better flame height but illumination may be poor. Smoke point is defined as the maximum height of flame in millimeters at which the given oil will burn without giving smoke. Different flame heights are obtained due to the presence of different components such as paraffins, naphthenes and aromatics. Aromatic contributes smoke, hence removal of aromatics increases the smoke point. Naphthenes with side chain one inevitably retained to give good illumination. In India, marketable kerosene should possess a smoke point of 18mm.
Why do you do Flame Height test?
This test is prescribed by Central Excise for distinguishing kerosene from Diesels for the purpose of charging duties. The test is similar to that of Smoke Point except in preconditioning the sample and wick
and also in the final reading. The flame height is read at the end of the 15th minute after the lamp is lighted.
What is the significance of Aniline Point?
Aniline point is defined as the minimum temperature at which equal volumes of anhydrous aniline and oil mix together. Aniline being an aromatic compound freely mixes with aromatic so a low aniline point indicates low diesel index (because of high percentage of aromatics).
Significance: High aniline point indicates that the fuel is highly paraffinic and hence has a high Diesel index and very good ignition quality. In case of aromatics the aniline point is low and the ignition quality is poor. This test is useful for calculating Diesel Index.
What is Diesel index?
Diesel index is a measure of ignition quality of fuel. Diesel engine works on the principle of compression ignition. During compression adiabatically the air temperature reaches around 600 c, when the fuel is finely atomized form is fed in, it instantaneously explodes. Self ignition temperature is low for paraffins while it is high for aromatics. Thus a fuel rich in aromatics burns later causing ignition delay and it gives rise to what is known as diesel knock. For this reason all diesel fuels are processed to have a diesel index in the range of 45 to 55.
Diesel Index = (Aniline Point in oF X oAPI)/ 100
Significance: High aniline point indicates that the fuel is highly paraffinic and hence a high Diesel Index and a very good ignition quality. In case of aromatics the aniline point is low and the ignition quality is poor.
What is Cetane Number ?
This is a measure of the tendency of diesel fuels to knock in a diesel engine. This is determined by CFR (Cooperative Fuels Research) engine having a single cylinder. The sample fuel is compared with that reference blend of known Cetane Number. The reference fuels used are Normal Cetane (100 cetane number) and Heptamethyl nonane (15 cetane number). Cetane number is a whole number which is indicative of the ignition quality of fuel. High Cetane Number fuels give good ignition and reduced roughness. The Cetane Number can also be calculated by the following formula.
Cetane Number =0.72* Diesel Index +10
Significance: Cetane number is the index of ignition quality of a fuel. High cetane number fuel will enhance easy starting of compression ignition engines and lessen engine roughness. This test is required mainly for HSD.
How do you measure Reid Vapor Pressure?
Vapor pressure is an important physical property of volatile liquids. It is the pressure that a vapor exerts on its surroundings. Its units are kilopascals, corrected to one atmosphere (101.3 kPa). For volatile petroleum products, vapor pressure is used as an indirect measure of evaporation rate. High vapor pressures and a low distillation temperature for 10% evaporated both help cold starting. Under hot-operating conditions, high vapor pressure also contributes to vapor lock and increases vapor formation in fuel tanks.
In cold weather, a gasoline that is not volatile enough may cause hard starting and poor warm-up. In the winter months, for example, your vehicle's engine is extremely cold before startup, and the gasoline must have a high enough volatility to be able to vaporize easily in a cold engine. Vapor pressure can be measured by a variety of methods including Reid, dynamic, static, vapor pressure balance, and gas saturation.
The most commonly used method for crude oils has been the Reid vapor pressure , as determined by ASTM D323 (American Society for Testing of Materials) method (Reid Method). This test method determines vapor pressure at 37.8 'C (100 'F) of petroleum products and crude oils with initial boiling point above 0 'C (32 'F). It is measured by saturating a known volume of oil in an air chamber of known volume and measuring the equilibrium pressure, which is then corrected to one atmosphere (101.3 kPa).
What is Octane Number?
Octane number is defined as percentage volume of Iso-octane (2,2,4-trimethyl pentane) in a mixture of Iso-octane and n-heptane that gives the same knocking characteristic as the fuel under consideration. Knocking in due to untimely burning of fuel in a spark ignition engine, which results in loss of power and sometimes it is powerful enough to cause damage to engine parts. With the advent of petrol engines of high compression ratios the tendency of knocking has also increased. Being a blend, gasoline responds in different ways, even in the same engine, depending on the components present. Iso-paraffins and aromatics have high octane number while n-paraffin’s have very low value, unsaturates do have high octane values but not preferred due to gum contribution.
Octane number is influenced by different factors like speed of engine, ambient weather conditions, altitude, combustion chamber deposits and coolant temperature. Knocking rating is tested by CFR engine for different purposes. Motor method gives the octane rating of high way driving (high speed), while research method gives for city driving (low speed) conditions and aviation method is for aviation gasoline. The rating can be done by either Research Method or Motor Method. If the fuel meets the minimum requirements in respect of Octane number it ensures trouble free operation. Apart from being a nuisance, the knocking in an engine may result in loss of energy and at times may cause severe damage to the engine.
What is anti-knocking index?
The AKI of a motor fuel is the average of the Research Octane Number (RON) and Motor Octane Number (MON) or (R+M)/2 and it remains the most important quality criteria for motorists. The Research Octane Number (RON) simulates fuel performance under low severity engine operation. The Motor Octane Number (MON) simulates more severe operation that might be incurred at high speed or high load. In practice the octane of a gasoline is reported as the average of RON and MON or R+M/2.
Significance: Today it is accepted that no one octane rating covers all use. The combination of vehicle and engine can result in specific requirements for octane that depend on the fuel. If the octane is distributed differently throughout the boiling range of a fuel, then engines can knock on one brand of 87 i.e (RON+MON)/2, but not on another brand. This "octane distribution" is especially important when sudden changes in load occur, such as high load, full throttle, and acceleration. Optimum performance and fuel economy is achieved when the AKI is adequate for the engine in which it is combusted. There is no advantage in using gasoline with a higher AKI than the engine requires to operate knock-free. In India Current BIS specification of AKI is 84 (unleaded regular) and 88 (unleaded premium).
What determines my car's octane requirements?
Your car's octane requirements are mainly determined by its basic design. In addition, variations in engines due to manufacturing tolerances can cause cars of the same model to require a different octane of several numbers. Also, as a new car is driven, its octane requirement can increase because of the buildup of combustion chamber deposits. This continues until a stable level is reached, typically after about 15,000 miles. The stabilized octane requirement may be 3-6 numbers higher than when the car was new
Other factors also influence your car's knocking characteristics:
Temperature: Generally, the hotter the ambient air and engine coolant, the greater the octane requirement.
Altitude: The higher the altitude above sea level, the lower the octane requirement. Modern computer-controlled engines adjust spark timing and air-fuel ratio to compensate for changes in barometric pressure, and thus the effect of altitude on octane requirement is smaller in these vehicles.
Humidity: The drier the air, the greater the octane requirement. The recommendations that vehicle manufacturers give are for normal- to low-humidity levels.
spark timing: The octane requirement increases as the spark timing is advanced. Both the basic setting of the spark timing and the operation of the automatic spark advance mechanisms are important in controlling knock
Method of driving: Rapid acceleration and heavy loading, such as pulling a trailer or climbing a hill, may result in a greater octane requirement. Stop-and-go driving and excessive idling can increase octane requirements by causing the buildup of combustion chamber deposits.
What is MTBE?
MTBE, or Methyl Tertiary Butyl Ether, is an ether compound in the same boiling range as gasoline. Ethers have an oxygen atom in each molecule and a characteristic smell. MTBE is made by combining isobutylene (from various refining and chemical processes) and methanol (usually made from natural gas). MTBE has been used as a gasoline-blending component since 1979. Originally, it was used to help raise the octane of gasoline. Now, it is also used to raise the oxygen content of gasoline. The oxygen atom in MTBE helps provide extra oxygen for complete combustion. Ideally, an oxygenate reduces the amount of unburned hydrocarbons and carbon monoxide in the exhaust. Chemical formula for MTBE is CH3OC (CH3)3.
What are Oxygenates?
Finished motor gasoline, having oxygen content of 2.7 percent or higher by weight is known as Oxygenated Gasoline. “Oxygenated gasoline" is a mixture of conventional gasoline and one or more combustible liquids which contain oxygen ("oxygenates"). At present, the most common oxygenates are ethanol and MTBE (Methyl Tertiary Butyl Ether). Oxygenated gasoline reduces fuel economy an average of 2%-3% because oxygenates contain less energy than non-oxygenated gasoline. Oxygenated gasoline helps engines run leaner, which helps engines, particularly older engines, produce less carbon monoxide.
Fuel Ethanol: Blends of up to 10 percent by volume anhydrous ethanol.
MTBE (Methyl Tertiary Butyl Ether): Blends of up to 15.0 percent by volume MTBE which must meet the ASTM D4814 specifications.
Other Oxygenates: Ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), Methanol and other oxygenates improve gasoline octane ratings and reduce carbon monoxide emissions.
What is Viscosity?
Viscosity is a measure of a fluid's resistance to flow; the lower the viscosity of a fluid, the more easily it flows. Like density, viscosity is affected by temperature. As temperature decreases, viscosity increases. The SI unit of dynamic viscosity is the millipascal-second (mPa . s). “Thin” liquids, like water or gasoline, have low viscosities; “thick” liquids, like Lubricating oils have higher viscosities.
Viscosity is an important characteristic of diesel. Fuels outside the required range may cause power loss or improper atomization of the fuel in a diesel engine. Lubrications assist in removing the frictional forces between two moving bodies. Absolute viscosity divided by fluid density equals kinematic viscosity. Absolute viscosity and kinematic viscosity are expressed in fundamental units. Commercial viscosity such as Saybolt viscosity is expressed in arbitrary units of time, usually seconds.
What Atmospheric Crude Oil Distillation?
The refining process of separating crude oil components at atmospheric pressure by heating to temperatures of about 600 oF to 750 oF (depending on the nature of the crude oil and desired products) and subsequent condensing of the fractions by cooling.
What is vacuum distillation?
A secondary refining process in which straight-run residue is distilled in a vacuum in order to separate more light hydrocarbons than through atmospheric distillation. The output of the process is vacuum gas oil, which can be used as feedstock for cracking units, and vacuum bottoms or residue, which are usually used as boiler fuel.
What is Viscosity?
Viscosity is a measure of a fluid's resistance to flow; the lower the viscosity of a fluid, the more easily it flows. Like density, viscosity is affected by temperature. As temperature decreases, viscosity increases. The SI unit of dynamic viscosity is the millipascal-second (mPa . s). “Thin” liquids, like water or gasoline, have low viscosities; “thick” liquids, like Lubricating oils have higher viscosities.
Viscosity is an important characteristic of diesel. Fuels outside the required range may cause power loss or improper atomization of the fuel in a diesel engine. Lubrications assist in removing the frictional forces between two moving bodies. Absolute viscosity divided by fluid density equals kinematic viscosity. Absolute viscosity and kinematic viscosity are expressed in fundamental units. Commercial viscosity such as Saybolt viscosity is expressed in arbitrary units of time, usually seconds.
What Atmospheric Crude Oil Distillation?
The refining process of separating crude oil components at atmospheric pressure by heating to temperatures of about 600 oF to 750 oF (depending on the nature of the crude oil and desired products) and subsequent condensing of the fractions by cooling.
What is vacuum distillation?
A secondary refining process in which straight-run residue is distilled in a vacuum in order to separate more light hydrocarbons than through atmospheric distillation. The output of the process is vacuum gas oil, which can be used as feedstock for cracking units, and vacuum bottoms or residue, which are usually used as boiler fuel.
What is Catalytic Cracking?
The refining process of breaking down the larger, heavier, and more complex hydrocarbon molecules into simpler and lighter molecules. Catalytic cracking is accomplished by the use of a catalytic agent and is an effective process for increasing the yield of gasoline from crude oil. Catalytic cracking processes fresh feeds and recycled feeds.
What Catalytic Hydrocracking?
A refining process that uses hydrogen and catalysts with relatively low temperatures and high pressures for converting middle boiling or residual material to high-octane gasoline, reformer charge stock, jet fuel, and/or high grade fuel oil. The process uses one or more catalysts, depending upon product output, and can handle high sulfur feed-stocks without prior desulphurization.
What is Catalytic Hydrotreating ?
A refining process for treating petroleum fractions from atmospheric or vacuum distillation units (e.g. naphtha, middle distillates, reformer feeds, residual fuel oil, and heavy gas oil) and other petroleum (e.g., cat cracked naphtha, coker naphtha, gas oil, etc.) in the presence of catalysts and substantial quantities of hydrogen. Hydrotreating includes desulphurization, removal of substances (e.g., nitrogen compounds) that deactivate catalysts, conversion of olefins to paraffins to reduce gum formation in gasoline, and other processes to upgrade the quality of the fractions.
What is Catalytic Reforming?
A refining process using controlled heat and pressure with catalysts to rearrange certain hydrocarbon molecules, thereby converting paraffinic and naphthenic type hydrocarbons (e.g., low-octane gasoline boiling range fractions) into petrochemical feedstocks and higher octane stocks suitable for blending into finished products.
What is Iso Sieve Process?
Another way of increasing octane number of gasoline is by removing altogether low octane hydrocarbon molecules specially straight run n-paraffin from the product (gasoline) by physical absorption process with the help of a specific catalyst which has the ability to trape n-paraffin molecules.
What is Delayed Coking ?
A process by which heavier crude oil fractions can be thermally decomposed under conditions of elevated temperatures and pressure to produce a mixture of lighter oils and petroleum coke. The light oils can be processed further in other refinery units to meet product specifications. The coke can be used either as a fuel or in other applications such as the manufacturing of steel or aluminum.
What is API gravity?
A measure of the weight of hydrocarbons according to a scale established by the American Petroleum Institute. Crude oils with higher values are lighter and tend to produce larger volumes of high-value lighter products in atmospheric distillation, which makes them relatively more valuable. Crude oil grades that are lower on the API scale tend conversely to be less highly valued because they produce smaller yields of lighter products.
API gravity = (141.5/Specific Gravity at 60 oF) - 131.5
What is Cloud Point?
Cloud point and pour point are measures of winter temperature behavior properties of distillate fuels. Cloud point is the temperature where paraffin first forms in fuel. In practice, cloud point helps to determine the temperature at which paraffin crystals will begin to block fuel filters and lines and cause starting and stalling problems for diesel engines.
What is Pour Point ?
The pour point of an oil is the lowest temperature at which the oil will just flow, under standard test conditions. The failure to flow at the pour point is usually attributed to the separation of waxes from the oil, but can also be due to the effect of viscosity in the case of very viscous oils. This test is required for HSD and FO. Pour point requirement is 6 deg C for Normal diesel and -12 deg C for winter grade diesel.
What is Distillation standard?
The "distillation" standard is one of several tests used to address gasoline's vaporization characteristics. Gasoline is metered in liquid form, through the fuel injectors (or carburetor), and mixed with air and atomized before entering the cylinders. Therefore, it is very important that a fuel's tendency to evaporate is controlled to certain standards. A fuel's ability to vaporize or change from liquid to vapor is referred to as its volatility.
In gasoline, the distillation characteristics, along with vapor pressure, define and control starting, warm-up, acceleration, vapor lock, crankcase oil dilution, and, in part, fuel economy and carburetion icing. The tendency of a fuel to vaporize is also characterized by determining a series of temperatures at which various percentages of the fuel have evaporated (boiling temperatures), as described in ASTM D86, Test Method for Distillation of Petroleum Products. The temperatures at which 10%, 50%, and 90% evaporation occurs are often used to characterize the volatility of gasoline. The 10% evaporated temperature is directly affected by the seasonal blending of the gasoline. This temperature must be low enough to provide easy cold starting, but high enough to minimize the vapor lock and hot weather drivability problems. Most cool weather drivability problems occur from the use of summer season gasoline in the winter months. This is especially true in premium grades, which normally have a high 10% evaporated temperature.
The 50% evaporated temperature must be low enough to provide good warm-up and cool weather drivability without being so low as to contribute to hot drivability and vapor locking problems. This portion of the gasoline greatly affects fuel economy on short trips.
The 90% and end-point evaporation temperatures must be low enough to minimize crankcase and combustion chamber deposits, as well as spark plug fouling and the dilution of engine oil. If the end-point temperature exceeds the ASTM maximum requirement, it is usually because of the presence of a distillate fuel. This contamination can be directly attributable to the delivery of diesel prior to the delivery of the gasoline. This problem is avoided if care is taken in handling the product.
What is Cold filter plugging (C.F.P.P.)?
The highest temperature at which the fuel, when cooled under the test conditions, either will not flow through the filter or requires more than 60 sec. for 10ml to pass through. For Diesel fuel in India specification is +6 Deg C in winter and +18 Deg C in summer.
What is Fluid catalytic cracking?
FCC uses a catalyst in the form of a very fine powder which flows like a liquid when agitated by steam, air or vapor. Feedstock entering the process immediately meets a stream of very hot catalyst and vaporizes. The resulting vapors keep the catalyst fluidized as it passes into the reactor, where the cracking takes place and where it is fluidized by the hydrocarbon vapor. The catalyst next passes to a steam stripping section where most of the volatile hydrocarbons are removed. It then passes to a regenerator vessel where it is fluidized by a mixture of air and the products of combustion which are produced as the coke on the catalyst is burnt off. The catalyst then flows back to the reactor. The catalyst thus undergoes a continuous circulation between the reactor, stripper and regenerator sections.
The catalyst is usually a mixture of aluminum oxide and silica. Most recently, the introduction of synthetic zeolite catalysts has allowed much shorter reaction times and improved yields and octane numbers of the cracked gasolines.
What is Isomerization?
Isomerization refers to chemical rearrangement of straight-chain hydrocarbons (paraffin’s), so that they contain branches attached to the main chain (isoparaffins). This is done for two reasons:
they create extra isobutane feed for alkylation they improve the octane of straight run pentanes and hexanes and hence make them into better petrol blending components.
Isomerization is achieved by mixing normal butane with a little hydrogen and chloride and allowed to react in the presence of a catalyst to form isobutane, plus a small amount of normal butane and some lighter gases. Products are separated in a fractionator. The lighter gases are used as refinery fuel and the butane recycled as feed.
Pentanes and hexanes are the lighter components of petrol. Isomerization can be used to improve petrol quality by converting these hydrocarbons to higher octane isomers. The process is the same as for butane isomerization.
What is Visbreaking?
Visbreaking, a mild form of thermal cracking, significantly lowers the viscosity of heavy crude-oil residue without affecting the boiling point range. Residual from the atmospheric distillation tower is heated (800°-950° F) at atmospheric pressure and mildly cracked in a heater. It is then quenched with cool gas oil to control overcracking, and flashed in a distillation tower. Visbreaking is used to reduce the pour point of waxy residues and reduce the viscosity of residues used for blending with lighter fuel oils. Middle distillates may also be produced, depending on product demand. The thermally cracked residue tar, which accumulates in the bottom of the fractionation tower, is vacuum flashed in a stripper and the distillate recycled.
What is Hydrofinishing Process?
A catalytic treating process carried out in the presence of hydrogen to improve the properties of low viscosity-index naphthenic and medium viscosity-index naphthenic oils. It is also applied to paraffin waxes and microcrystalline waxes for the removal of undesirable components. This process consumes hydrogen and is used in lieu of acid treating.
"Bringing New Ideas To Life!"
Crude oils are complex mixtures containing many different hydrocarbon compounds that vary in appearance and composition from one oil field to another. Crude oils range in consistency from water to tar-like solids, and in color from clear to black. An "average" crude oil contains about 84% carbon, 14% hydrogen, 0.1%-3% sulfur, and less than 1% each of nitrogen, oxygen, metals, and salts. Crude oils are generally classified as paraffinic, naphthenic, or aromatic, based on the predominant proportion of similar hydrocarbon molecules. Mixed-base crudes have varying amounts of each type of hydrocarbon. Refinery crude base stocks usually consist of mixtures of two or more different crude oils.
Relatively simple crude oil assays are used to classify crude oils as paraffinic (West Texas crude, Brent), naphthenic (Louisiana crude, Nigerian Light), aromatic (Maya Crude), or mixed (Assam crude). One assay method (United States Bureau of Mines) is based on distillation, and another method (UOP "K" factor) is based on gravity and boiling points. More comprehensive crude assays determine the value of the crude (i.e., its yield and quality of useful products) and processing parameters. Crude oils are usually grouped according to yield structure.
Crude oils are also defined in terms of API (American Petroleum Institute) gravity. The higher the API gravity, the lighter the crude. For example, light crude oils have high API gravities and low specific gravities. Crude oils with low carbon, high hydrogen, and high API gravity are usually rich in paraffin’s and tend to yield greater proportions of gasoline and light petroleum products; those with high carbon, low hydrogen, and low API gravities are usually rich in aromatics. The price of a crude oil is usually based on its API gravity, with high gravity oils commanding higher prices.
Crude oils that contain appreciable quantities of hydrogen sulfide or other reactive sulfur compounds are called "sour." Those with less sulfur less than 0.5% are called "sweet." Some exceptions to this rule are West Texas crudes, which are always considered "sour" regardless of their H2S content, and Arabian high-sulfur crudes, which are not considered "sour" because their sulfur compounds are not highly reactive.
Hydrocarbon Groups :
The main constituents of petroleum can be grouped into four categories:
Paraffin: A series of saturated straight chain or branched hydrocarbons, the lowest members of which are methane, ethane and propane.
Olefins: Double-bonded hydrocarbons that are not normally present in crude oil but are formed during refinery processing and vehicle combustion of fuel. Olefins help improve the octane rating, but their use may lead to gum formation or deposits in engine intake systems.
Aromatic: Unsaturated cyclic hydrocarbons are known as aromatics. Aromatics occur naturally in crude oil and can also be produced in some refining processes. Aromatics common in petrol include benzene, toluene and xylene. Controlling the level of aromatics directly limits evaporative losses and exhaust emissions.
Naphthenic: Naphthalene’s are a class of compounds that are saturated hydrocarbons typified by cyclic hydrocarbon molecular structure. The general formula for cyclic hydrocarbons is CnH2n.
Why Weathering Test is performed?
95% of LPG sample under consideration should evaporate at a temperature of +2oc.
If the evaporation temperature exceeds +2oc then there is a probability that heavier hydrocarbons are present in LPG and if the evaporation temperature is less then +2oc then there is a probability that lighter fractions are more.
Significance: This test is intended to find out the presence of heavier hydrocarbons in LPG, which may not readily evaporate. This test is done specially for LPG.
What is Copper corrosion test?
This test serves as measure of corrosively of fuel with copper, brass, or bronze parts of a fuel system. The copper strip is polished smoothly and immersed in the sample and put into a bomb. This is placed into a water bath which is maintained at the specified temperature for the specified time. The strip is removed from the sample, washed with iso-octane or normal heptane, and examined for evidence of etching or discoloration. The color of the strip is compared with ASTM copper strip standards color code.
Significance: Copper corrosion limits provides assurance that difficulties will not be experienced in deterioration of the copper and copper alloy fittings and connections that are commonly used in many types of utilization, storage and transportation equipment. This test is required mainly for LPG, Naphtha, SKO, HSD, ATF and MS.
What is Flash Point?
The flash point of a fuel is the temperature to which the fuel must be heated to produce a vapour/air mixture above the liquid fuel that is ignitable when exposed to an open flame under specified test conditions. Flash point is important primarily from a fuel-handling standpoint. Too low a flash point will cause fuel to be a fire hazard, subject to flashing, and possible continued ignition and explosion. In addition, a low-flash point may indicate contamination by more volatile and explosive fuels, such as gasoline. A very important reason to maintain the flash point as high as possible is due to the electrostatic hazards in pumping distillate fuels. Flash point (BIS) requirements for some petroleum products are:
S.K.O. - 35 C
U.L.S.H.S.D. - 35 C
H.S.D. - 35 C
F.O. - 66 C
A.T.F. - 39 C
What is Fire Point?
Fire point is the lowest temperature, corrected to one atmosphere pressure (101.3 kPa), at which the application of a test flame to the oil sample surface causes the vapor of the oil to ignite and burn for at least five seconds. For ordinary commercial lubricating oils, the fire point usually runs about 30oC above the flash point. The test is carried out in open cup rather than in a close one. ASTM D 92 method offers the advantage of open flash point and fire point determination. Low fire point petroleum products are potential fire hazards.
What is Smoke point?
Smoke is an indication of clean burning quality of kerosene. Illumination depends upon the flame dimension although it is not related to flame height. Many paraffins may be gifted with better flame height but illumination may be poor. Smoke point is defined as the maximum height of flame in millimeters at which the given oil will burn without giving smoke. Different flame heights are obtained due to the presence of different components such as paraffins, naphthenes and aromatics. Aromatic contributes smoke, hence removal of aromatics increases the smoke point. Naphthenes with side chain one inevitably retained to give good illumination. In India, marketable kerosene should possess a smoke point of 18mm.
Why do you do Flame Height test?
This test is prescribed by Central Excise for distinguishing kerosene from Diesels for the purpose of charging duties. The test is similar to that of Smoke Point except in preconditioning the sample and wick
and also in the final reading. The flame height is read at the end of the 15th minute after the lamp is lighted.
What is the significance of Aniline Point?
Aniline point is defined as the minimum temperature at which equal volumes of anhydrous aniline and oil mix together. Aniline being an aromatic compound freely mixes with aromatic so a low aniline point indicates low diesel index (because of high percentage of aromatics).
Significance: High aniline point indicates that the fuel is highly paraffinic and hence has a high Diesel index and very good ignition quality. In case of aromatics the aniline point is low and the ignition quality is poor. This test is useful for calculating Diesel Index.
What is Diesel index?
Diesel index is a measure of ignition quality of fuel. Diesel engine works on the principle of compression ignition. During compression adiabatically the air temperature reaches around 600 c, when the fuel is finely atomized form is fed in, it instantaneously explodes. Self ignition temperature is low for paraffins while it is high for aromatics. Thus a fuel rich in aromatics burns later causing ignition delay and it gives rise to what is known as diesel knock. For this reason all diesel fuels are processed to have a diesel index in the range of 45 to 55.
Diesel Index = (Aniline Point in oF X oAPI)/ 100
Significance: High aniline point indicates that the fuel is highly paraffinic and hence a high Diesel Index and a very good ignition quality. In case of aromatics the aniline point is low and the ignition quality is poor.
What is Cetane Number ?
This is a measure of the tendency of diesel fuels to knock in a diesel engine. This is determined by CFR (Cooperative Fuels Research) engine having a single cylinder. The sample fuel is compared with that reference blend of known Cetane Number. The reference fuels used are Normal Cetane (100 cetane number) and Heptamethyl nonane (15 cetane number). Cetane number is a whole number which is indicative of the ignition quality of fuel. High Cetane Number fuels give good ignition and reduced roughness. The Cetane Number can also be calculated by the following formula.
Cetane Number =0.72* Diesel Index +10
Significance: Cetane number is the index of ignition quality of a fuel. High cetane number fuel will enhance easy starting of compression ignition engines and lessen engine roughness. This test is required mainly for HSD.
How do you measure Reid Vapor Pressure?
Vapor pressure is an important physical property of volatile liquids. It is the pressure that a vapor exerts on its surroundings. Its units are kilopascals, corrected to one atmosphere (101.3 kPa). For volatile petroleum products, vapor pressure is used as an indirect measure of evaporation rate. High vapor pressures and a low distillation temperature for 10% evaporated both help cold starting. Under hot-operating conditions, high vapor pressure also contributes to vapor lock and increases vapor formation in fuel tanks.
In cold weather, a gasoline that is not volatile enough may cause hard starting and poor warm-up. In the winter months, for example, your vehicle's engine is extremely cold before startup, and the gasoline must have a high enough volatility to be able to vaporize easily in a cold engine. Vapor pressure can be measured by a variety of methods including Reid, dynamic, static, vapor pressure balance, and gas saturation.
The most commonly used method for crude oils has been the Reid vapor pressure , as determined by ASTM D323 (American Society for Testing of Materials) method (Reid Method). This test method determines vapor pressure at 37.8 'C (100 'F) of petroleum products and crude oils with initial boiling point above 0 'C (32 'F). It is measured by saturating a known volume of oil in an air chamber of known volume and measuring the equilibrium pressure, which is then corrected to one atmosphere (101.3 kPa).
What is Octane Number?
Octane number is defined as percentage volume of Iso-octane (2,2,4-trimethyl pentane) in a mixture of Iso-octane and n-heptane that gives the same knocking characteristic as the fuel under consideration. Knocking in due to untimely burning of fuel in a spark ignition engine, which results in loss of power and sometimes it is powerful enough to cause damage to engine parts. With the advent of petrol engines of high compression ratios the tendency of knocking has also increased. Being a blend, gasoline responds in different ways, even in the same engine, depending on the components present. Iso-paraffins and aromatics have high octane number while n-paraffin’s have very low value, unsaturates do have high octane values but not preferred due to gum contribution.
Octane number is influenced by different factors like speed of engine, ambient weather conditions, altitude, combustion chamber deposits and coolant temperature. Knocking rating is tested by CFR engine for different purposes. Motor method gives the octane rating of high way driving (high speed), while research method gives for city driving (low speed) conditions and aviation method is for aviation gasoline. The rating can be done by either Research Method or Motor Method. If the fuel meets the minimum requirements in respect of Octane number it ensures trouble free operation. Apart from being a nuisance, the knocking in an engine may result in loss of energy and at times may cause severe damage to the engine.
What is anti-knocking index?
The AKI of a motor fuel is the average of the Research Octane Number (RON) and Motor Octane Number (MON) or (R+M)/2 and it remains the most important quality criteria for motorists. The Research Octane Number (RON) simulates fuel performance under low severity engine operation. The Motor Octane Number (MON) simulates more severe operation that might be incurred at high speed or high load. In practice the octane of a gasoline is reported as the average of RON and MON or R+M/2.
Significance: Today it is accepted that no one octane rating covers all use. The combination of vehicle and engine can result in specific requirements for octane that depend on the fuel. If the octane is distributed differently throughout the boiling range of a fuel, then engines can knock on one brand of 87 i.e (RON+MON)/2, but not on another brand. This "octane distribution" is especially important when sudden changes in load occur, such as high load, full throttle, and acceleration. Optimum performance and fuel economy is achieved when the AKI is adequate for the engine in which it is combusted. There is no advantage in using gasoline with a higher AKI than the engine requires to operate knock-free. In India Current BIS specification of AKI is 84 (unleaded regular) and 88 (unleaded premium).
What determines my car's octane requirements?
Your car's octane requirements are mainly determined by its basic design. In addition, variations in engines due to manufacturing tolerances can cause cars of the same model to require a different octane of several numbers. Also, as a new car is driven, its octane requirement can increase because of the buildup of combustion chamber deposits. This continues until a stable level is reached, typically after about 15,000 miles. The stabilized octane requirement may be 3-6 numbers higher than when the car was new
Other factors also influence your car's knocking characteristics:
Temperature: Generally, the hotter the ambient air and engine coolant, the greater the octane requirement.
Altitude: The higher the altitude above sea level, the lower the octane requirement. Modern computer-controlled engines adjust spark timing and air-fuel ratio to compensate for changes in barometric pressure, and thus the effect of altitude on octane requirement is smaller in these vehicles.
Humidity: The drier the air, the greater the octane requirement. The recommendations that vehicle manufacturers give are for normal- to low-humidity levels.
spark timing: The octane requirement increases as the spark timing is advanced. Both the basic setting of the spark timing and the operation of the automatic spark advance mechanisms are important in controlling knock
Method of driving: Rapid acceleration and heavy loading, such as pulling a trailer or climbing a hill, may result in a greater octane requirement. Stop-and-go driving and excessive idling can increase octane requirements by causing the buildup of combustion chamber deposits.
What is MTBE?
MTBE, or Methyl Tertiary Butyl Ether, is an ether compound in the same boiling range as gasoline. Ethers have an oxygen atom in each molecule and a characteristic smell. MTBE is made by combining isobutylene (from various refining and chemical processes) and methanol (usually made from natural gas). MTBE has been used as a gasoline-blending component since 1979. Originally, it was used to help raise the octane of gasoline. Now, it is also used to raise the oxygen content of gasoline. The oxygen atom in MTBE helps provide extra oxygen for complete combustion. Ideally, an oxygenate reduces the amount of unburned hydrocarbons and carbon monoxide in the exhaust. Chemical formula for MTBE is CH3OC (CH3)3.
What are Oxygenates?
Finished motor gasoline, having oxygen content of 2.7 percent or higher by weight is known as Oxygenated Gasoline. “Oxygenated gasoline" is a mixture of conventional gasoline and one or more combustible liquids which contain oxygen ("oxygenates"). At present, the most common oxygenates are ethanol and MTBE (Methyl Tertiary Butyl Ether). Oxygenated gasoline reduces fuel economy an average of 2%-3% because oxygenates contain less energy than non-oxygenated gasoline. Oxygenated gasoline helps engines run leaner, which helps engines, particularly older engines, produce less carbon monoxide.
Fuel Ethanol: Blends of up to 10 percent by volume anhydrous ethanol.
MTBE (Methyl Tertiary Butyl Ether): Blends of up to 15.0 percent by volume MTBE which must meet the ASTM D4814 specifications.
Other Oxygenates: Ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), Methanol and other oxygenates improve gasoline octane ratings and reduce carbon monoxide emissions.
What is Viscosity?
Viscosity is a measure of a fluid's resistance to flow; the lower the viscosity of a fluid, the more easily it flows. Like density, viscosity is affected by temperature. As temperature decreases, viscosity increases. The SI unit of dynamic viscosity is the millipascal-second (mPa . s). “Thin” liquids, like water or gasoline, have low viscosities; “thick” liquids, like Lubricating oils have higher viscosities.
Viscosity is an important characteristic of diesel. Fuels outside the required range may cause power loss or improper atomization of the fuel in a diesel engine. Lubrications assist in removing the frictional forces between two moving bodies. Absolute viscosity divided by fluid density equals kinematic viscosity. Absolute viscosity and kinematic viscosity are expressed in fundamental units. Commercial viscosity such as Saybolt viscosity is expressed in arbitrary units of time, usually seconds.
What Atmospheric Crude Oil Distillation?
The refining process of separating crude oil components at atmospheric pressure by heating to temperatures of about 600 oF to 750 oF (depending on the nature of the crude oil and desired products) and subsequent condensing of the fractions by cooling.
What is vacuum distillation?
A secondary refining process in which straight-run residue is distilled in a vacuum in order to separate more light hydrocarbons than through atmospheric distillation. The output of the process is vacuum gas oil, which can be used as feedstock for cracking units, and vacuum bottoms or residue, which are usually used as boiler fuel.
What is Viscosity?
Viscosity is a measure of a fluid's resistance to flow; the lower the viscosity of a fluid, the more easily it flows. Like density, viscosity is affected by temperature. As temperature decreases, viscosity increases. The SI unit of dynamic viscosity is the millipascal-second (mPa . s). “Thin” liquids, like water or gasoline, have low viscosities; “thick” liquids, like Lubricating oils have higher viscosities.
Viscosity is an important characteristic of diesel. Fuels outside the required range may cause power loss or improper atomization of the fuel in a diesel engine. Lubrications assist in removing the frictional forces between two moving bodies. Absolute viscosity divided by fluid density equals kinematic viscosity. Absolute viscosity and kinematic viscosity are expressed in fundamental units. Commercial viscosity such as Saybolt viscosity is expressed in arbitrary units of time, usually seconds.
What Atmospheric Crude Oil Distillation?
The refining process of separating crude oil components at atmospheric pressure by heating to temperatures of about 600 oF to 750 oF (depending on the nature of the crude oil and desired products) and subsequent condensing of the fractions by cooling.
What is vacuum distillation?
A secondary refining process in which straight-run residue is distilled in a vacuum in order to separate more light hydrocarbons than through atmospheric distillation. The output of the process is vacuum gas oil, which can be used as feedstock for cracking units, and vacuum bottoms or residue, which are usually used as boiler fuel.
What is Catalytic Cracking?
The refining process of breaking down the larger, heavier, and more complex hydrocarbon molecules into simpler and lighter molecules. Catalytic cracking is accomplished by the use of a catalytic agent and is an effective process for increasing the yield of gasoline from crude oil. Catalytic cracking processes fresh feeds and recycled feeds.
What Catalytic Hydrocracking?
A refining process that uses hydrogen and catalysts with relatively low temperatures and high pressures for converting middle boiling or residual material to high-octane gasoline, reformer charge stock, jet fuel, and/or high grade fuel oil. The process uses one or more catalysts, depending upon product output, and can handle high sulfur feed-stocks without prior desulphurization.
What is Catalytic Hydrotreating ?
A refining process for treating petroleum fractions from atmospheric or vacuum distillation units (e.g. naphtha, middle distillates, reformer feeds, residual fuel oil, and heavy gas oil) and other petroleum (e.g., cat cracked naphtha, coker naphtha, gas oil, etc.) in the presence of catalysts and substantial quantities of hydrogen. Hydrotreating includes desulphurization, removal of substances (e.g., nitrogen compounds) that deactivate catalysts, conversion of olefins to paraffins to reduce gum formation in gasoline, and other processes to upgrade the quality of the fractions.
What is Catalytic Reforming?
A refining process using controlled heat and pressure with catalysts to rearrange certain hydrocarbon molecules, thereby converting paraffinic and naphthenic type hydrocarbons (e.g., low-octane gasoline boiling range fractions) into petrochemical feedstocks and higher octane stocks suitable for blending into finished products.
What is Iso Sieve Process?
Another way of increasing octane number of gasoline is by removing altogether low octane hydrocarbon molecules specially straight run n-paraffin from the product (gasoline) by physical absorption process with the help of a specific catalyst which has the ability to trape n-paraffin molecules.
What is Delayed Coking ?
A process by which heavier crude oil fractions can be thermally decomposed under conditions of elevated temperatures and pressure to produce a mixture of lighter oils and petroleum coke. The light oils can be processed further in other refinery units to meet product specifications. The coke can be used either as a fuel or in other applications such as the manufacturing of steel or aluminum.
What is API gravity?
A measure of the weight of hydrocarbons according to a scale established by the American Petroleum Institute. Crude oils with higher values are lighter and tend to produce larger volumes of high-value lighter products in atmospheric distillation, which makes them relatively more valuable. Crude oil grades that are lower on the API scale tend conversely to be less highly valued because they produce smaller yields of lighter products.
API gravity = (141.5/Specific Gravity at 60 oF) - 131.5
What is Cloud Point?
Cloud point and pour point are measures of winter temperature behavior properties of distillate fuels. Cloud point is the temperature where paraffin first forms in fuel. In practice, cloud point helps to determine the temperature at which paraffin crystals will begin to block fuel filters and lines and cause starting and stalling problems for diesel engines.
What is Pour Point ?
The pour point of an oil is the lowest temperature at which the oil will just flow, under standard test conditions. The failure to flow at the pour point is usually attributed to the separation of waxes from the oil, but can also be due to the effect of viscosity in the case of very viscous oils. This test is required for HSD and FO. Pour point requirement is 6 deg C for Normal diesel and -12 deg C for winter grade diesel.
What is Distillation standard?
The "distillation" standard is one of several tests used to address gasoline's vaporization characteristics. Gasoline is metered in liquid form, through the fuel injectors (or carburetor), and mixed with air and atomized before entering the cylinders. Therefore, it is very important that a fuel's tendency to evaporate is controlled to certain standards. A fuel's ability to vaporize or change from liquid to vapor is referred to as its volatility.
In gasoline, the distillation characteristics, along with vapor pressure, define and control starting, warm-up, acceleration, vapor lock, crankcase oil dilution, and, in part, fuel economy and carburetion icing. The tendency of a fuel to vaporize is also characterized by determining a series of temperatures at which various percentages of the fuel have evaporated (boiling temperatures), as described in ASTM D86, Test Method for Distillation of Petroleum Products. The temperatures at which 10%, 50%, and 90% evaporation occurs are often used to characterize the volatility of gasoline. The 10% evaporated temperature is directly affected by the seasonal blending of the gasoline. This temperature must be low enough to provide easy cold starting, but high enough to minimize the vapor lock and hot weather drivability problems. Most cool weather drivability problems occur from the use of summer season gasoline in the winter months. This is especially true in premium grades, which normally have a high 10% evaporated temperature.
The 50% evaporated temperature must be low enough to provide good warm-up and cool weather drivability without being so low as to contribute to hot drivability and vapor locking problems. This portion of the gasoline greatly affects fuel economy on short trips.
The 90% and end-point evaporation temperatures must be low enough to minimize crankcase and combustion chamber deposits, as well as spark plug fouling and the dilution of engine oil. If the end-point temperature exceeds the ASTM maximum requirement, it is usually because of the presence of a distillate fuel. This contamination can be directly attributable to the delivery of diesel prior to the delivery of the gasoline. This problem is avoided if care is taken in handling the product.
What is Cold filter plugging (C.F.P.P.)?
The highest temperature at which the fuel, when cooled under the test conditions, either will not flow through the filter or requires more than 60 sec. for 10ml to pass through. For Diesel fuel in India specification is +6 Deg C in winter and +18 Deg C in summer.
What is Fluid catalytic cracking?
FCC uses a catalyst in the form of a very fine powder which flows like a liquid when agitated by steam, air or vapor. Feedstock entering the process immediately meets a stream of very hot catalyst and vaporizes. The resulting vapors keep the catalyst fluidized as it passes into the reactor, where the cracking takes place and where it is fluidized by the hydrocarbon vapor. The catalyst next passes to a steam stripping section where most of the volatile hydrocarbons are removed. It then passes to a regenerator vessel where it is fluidized by a mixture of air and the products of combustion which are produced as the coke on the catalyst is burnt off. The catalyst then flows back to the reactor. The catalyst thus undergoes a continuous circulation between the reactor, stripper and regenerator sections.
The catalyst is usually a mixture of aluminum oxide and silica. Most recently, the introduction of synthetic zeolite catalysts has allowed much shorter reaction times and improved yields and octane numbers of the cracked gasolines.
What is Isomerization?
Isomerization refers to chemical rearrangement of straight-chain hydrocarbons (paraffin’s), so that they contain branches attached to the main chain (isoparaffins). This is done for two reasons:
they create extra isobutane feed for alkylation they improve the octane of straight run pentanes and hexanes and hence make them into better petrol blending components.
Isomerization is achieved by mixing normal butane with a little hydrogen and chloride and allowed to react in the presence of a catalyst to form isobutane, plus a small amount of normal butane and some lighter gases. Products are separated in a fractionator. The lighter gases are used as refinery fuel and the butane recycled as feed.
Pentanes and hexanes are the lighter components of petrol. Isomerization can be used to improve petrol quality by converting these hydrocarbons to higher octane isomers. The process is the same as for butane isomerization.
What is Visbreaking?
Visbreaking, a mild form of thermal cracking, significantly lowers the viscosity of heavy crude-oil residue without affecting the boiling point range. Residual from the atmospheric distillation tower is heated (800°-950° F) at atmospheric pressure and mildly cracked in a heater. It is then quenched with cool gas oil to control overcracking, and flashed in a distillation tower. Visbreaking is used to reduce the pour point of waxy residues and reduce the viscosity of residues used for blending with lighter fuel oils. Middle distillates may also be produced, depending on product demand. The thermally cracked residue tar, which accumulates in the bottom of the fractionation tower, is vacuum flashed in a stripper and the distillate recycled.
What is Hydrofinishing Process?
A catalytic treating process carried out in the presence of hydrogen to improve the properties of low viscosity-index naphthenic and medium viscosity-index naphthenic oils. It is also applied to paraffin waxes and microcrystalline waxes for the removal of undesirable components. This process consumes hydrogen and is used in lieu of acid treating.
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