Notes petroleum-refining-1


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Refining has developed to give us fuels, lube oils and chemical feedstock from crude oil

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Notes petroleum-refining-1

  1. 1. PETROLEUM REFINERY ENGINEERING Petroleum is a combustible oily liquid of reddish brown to almost black colour, produced from oilwells. It is a complex mixture of hydrocarbons and their derivatives containing oxygen, sulphur,nitrogen and minor quantities of some other materials. The importance of petroleum crude oil and naturalgas has been realized with the development of its numerous applications as fuel and feedstock. Theinvention of the internal combustion engines in the last quarter of the nineteenth century gave animpetus to the development of petroleum processing. The most basic refining process is aimed atseparating the crude oil into its various components. Crude oil is heated and put into a still -- a distillationcolumn -- and different hydrocarbon components boil off and can be recovered as they condense atdifferent temperatures. Additional processing follows crude distillation, changing the molecular structureof the input with chemical reactions, some through variations in heat and pressure, and some in thepresence of a catalyst. The main constituents of petroleum _hydrocarbons _ may differ in the number of carbon andhydrogen atoms in the molecular structure. The hydrocarbons are present in the following groups orhomologous series: paraffins (saturated st. chain hydrocarbons, alkanes), naphthenes (cycloalkanes),and benzene hydrocarbons (aromatics). In most grades of petroleum, paraffins and naphthenes prevailmostly. Based on the chemical composition of the crude (1) Paraffin-Base Crude Oils These contain higher molecular weight paraffins which are solid atroom temperature, but little or no asphaltic (bituminous) matter. They can produce high-grade lubricatingoils. (2) Asphaltic-Base Crude Oils Contain large proportions of asphaltic matter, and little or noparaffin. Some are predominantly naphthenes so yield lubricating oil that is more sensitive to temperaturechanges than the paraffin-base crudes. (3) Mixed-Base Crude Oils The "gray area" between the two types above. Both paraffins andnaphthenes are present, as well as aromatic hydrocarbons. Most crude fit this category. CRUDE OIL PHYSICAL PROPERTIESThe physical properties of crude are as follows Specific Gravity: 0.669 to 0.99 API Gravity: 10 – 50 1
  2. 2. Viscosity: 1 – 4 centipoises The American Petroleum Institute (API) has developed the term DegreesAPI Gravity (°API) which is widely used as another general characterization ofthe density of crude oils. The relationship is as follows:°API = (141.5/Specific Gravity at 60 degrees Fahrenheit) - 131.5“ Specific Gravity at 60 degrees Fahrenheit” is the density of the crude oilmeasured at 60°F divided by the density of water at 60°F.Therefore, when comparing two crude oils, the higher density crude (i.e., the onewith the highest specific gravity) will have a correspondingly lower °API. Forexample, the 34.5°API West African crude oil Bonny Light is heavier than the40.4°API North Sea crude oil Forties.Chemical compositionOn an average crude oil is [ultimate analysis] made up of the following components:· Carbon - 84%· Hydrogen - 14%· Sulphur - 1 to 3% (hydrogen sulfide, sulfides, disulfides, elemental sulfur)· Nitrogen - less than 1% (basic compounds with amine groups)· Oxygen - less than 1% (found in organic compounds such as carbon dioxide, phenols, ketones, carboxylic acids)· Metals - less than 1% (nickel, iron, vanadium, copper, arsenic)· Salts - less than 1% (sodium chloride, magnesium chloride, calcium chloride)Crude oils are complex mixtures containing many different Hydrocarbons compounds that vary inappearance and composition from one oil field to another. Crude oils are generally classified asparaffinic, napthenic or aromatic based on the predominant proportion of similar Hydrocarbons. 2
  3. 3. Hydrocarbons found in crude may be of the following types 1. Paraffins (Alkanes) · General formula: CnH2n+2 (n is a whole number, usually from 1 to 20) · These compounds are saturated hydrocarbons with all carbon bonds satisfied, that is, the hydrocarbon chain carries the full complement of hydrogen atoms. · Consist of straight chain (normal)- or branched-chain ( isomers) atoms · The lighter straight chain molecules are found in gases and heavier in paraffin waxes. The branched chain (isomer) parrafins are usually found in heavier fractions of crude oil and have higher octane numbers than normal parrafins. · examples: methane, ethane, propane, butane, isobutane, pentane, hexane 2. Aromatics · General formula: C6H5 - Y (Y is a longer, straight molecule that connects to the benzene ring) · They are unsaturated ring type (cyclic) compounds which react because they have carbon atoms that are deficient in hydrogen. · ringed structures with one or more rings. They have at least one benzene ring. 3
  4. 4. rings contain six carbon atoms, with alternating double and single bonds between the carbons· typically liquids and are found in heavier fractions of crude oil.· examples: benzene, naphthalene3. Napthenes or Cycloalkanes· General formula: CnH2n (n is a whole number usually from 1 to 20)· ringed structures with closed rings (cyclic)Found in all fractions of crude except the very lightest.· rings contain only single bonds between the carbon atoms· typically liquids at room temperature· examples: cyclohexane, methyl cyclopentane 4
  5. 5. Nonhydrocarbons. 1. Sulfur Compounds. Sulfur may be present in crude oil as hydrogen sulfide (H 2S), ascompounds (e.g. mercaptans, sulfides, disulfides, thiophenes, etc.) or as elemental sulfur. Each crude oilhas different amounts and types of sulfur compounds, but as a rule the proportion, stability, andcomplexity of the compounds are greater in heavier crude-oil fractions. Hydrogen sulfide is a primarycontributor to corrosion in refinery processing units. Other corrosive substances are elemental sulfur andmercaptans. Moreover, the corrosive sulfur compounds have an obnoxious odor. 2. Oxygen Compounds. Oxygen compounds such as phenols, ketones, and carboxylic acidsoccur in crude oils in varying amounts. 3. Nitrogen Compounds. Nitrogen is found in lighter fractions of crude oil as basic compounds,and more often in heavier fractions of crude oil as non basic compounds that may also include tracemetals such as copper, vanadium, and/or nickel. Nitrogen oxides can form in process furnaces. Thedecomposition of nitrogen compounds in catalytic cracking and hydrocracking processes forms ammoniaand cyanides that can cause corrosion. 4. Trace Metals. Metals, including nickel, iron, and vanadium are often found in crude oils in smallquantities and are removed during the refining process. Burning heavy fuel oils in refineryfurnaces and boilers can leave deposits of vanadium oxide and nickel oxide in furnace boxes,ducts, and tubes. It is also desirable to remove trace amounts of arsenic, vanadium, and nickelprior to processing as they can poison certain catalysts. Fractionation Processes:Process name Action Method Purpose feedstocks productsAtmospheric separation thermal Separate Desalted Gas, Gas oil,distillation fractions Crude oil distillate, residueVacuum separation thermal Separate w/o Atm. tower Gas oil, lubedistillation cracking residue stock, residue 5
  6. 6. An oil refinery is an industrial process plant where crude oil is processed andrefined into more useful products. Oil refineries are quite large industrial complexes withextensive pipelines carrying streams of fluids between large chemical (thermal andcatalytic) processes. 6
  7. 7.  Temperature (Petroleum Gas)  increases  down the column  Petrol  Naphtha  Kerosene  Diesel  Lubricants  Bitumen 7
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  15. 15. Catalytic ReformingAlthough motor gasolines have numerous specifications that must besatisfied to provide the performance demanded by our high-performance motorvehicles, the most widely recognized gasoline specification is the octane number.Gasolines are typically retailed in grades of regular, mid-grade and premium,which are differentiated by the posted octane number.The Octane Number of a test fuel refers to the percentage by volume of 15
  16. 16. isooctane in a mixture of isooctane and heptane in a reference fuel that whentested in a laboratory engine, matches the antiknock quality, as measured by aknockmeter, of the fuel being tested under the same conditions. The octanenumber posted at the gasoline pump is actually the average of the ResearchOctane Number (RON) and Motor Octane Number (MON), commonly referred toas (R+M)/2. RON and MON are two different test methods that quantify theantiknock qualities of a fuel. Since the MON is a test under more severeconditions than the RON test, for any given fuel, the RON is always higher thanthe MON.Unfortunately, the desulfurized light and heavy naphtha fractions of crudeoils have very low octane numbers. The heavy naphtha fraction is roughly 50(R+M)/2. Catalytic Reforming is the refinery process that reforms the molecularstructure of the heavy naphtha to increase the percentage of high-octanecomponents while reducing the percentage of low-octane components.The hydrocarbon compounds that constitute heavy naphtha are classifiedinto four different categories: paraffins, olefins (a very low percentage of olefinsoccur in the heavy naphthas from crude), naphthenes and aromatics. In lieu of acomplete course in organic chemistry, simplistically the paraffins and olefins arecompounds with straight or branched carbon chains, whereas the naphthenesand aromatics are carbon rings. The paraffins and naphthenes are saturatedhydrocarbons. Saturated means that they have the maximum number ofhydrogen atoms attached to the carbon atoms. The olefins and aromatics,however, are unsaturated hydrocarbons because the compounds contain carbonatoms that are double bonded to other carbon atoms. The straight chain,saturated compounds exhibit very low octane numbers, the branched, saturatedcompounds exhibit progressively higher octane numbers, while the unsaturatedcompounds exhibit very high octane numbers.Catalytic Reforming uses a precious metal catalyst (platinum supported byan alumina base) in conjunction with very high temperatures to reform theparaffins and napthenes into high-octane components. Sulfur is a poison to theCatalytic Reforming catalyst, which requires that virtually all the sulfur must beremoved from the heavy naphtha through Hydrotreating prior to CatalyticReforming. Several different types of chemical reactions occur in the CatalyticReforming reactors.olefins are converted to paraffins, paraffins are isomerizedto branched chains and to a lesser extent to naphthenes, and naphthenes areconverted to aromatics. Aromatic compounds are essentially unchanged. Theresulting reformate product stream from Catalytic Reforming has a RON from 96-102 depending on the reactor severity and feedstock quality. Thedehydrogenation reactions which convert the saturated naphthenes intounsaturated aromatics produce hydrogen. This hydrogen is available for 16
  17. 17. distribution to other refinery processes which consume hydrogen.The Catalytic Reforming process consists of a series of several sphericalreactors which operate at temperatures of approximately 900°F. The reformingreactions are .endothermic. meaning that the reactions cool the hydrocarbons.The hydrocarbons are re-heated by direct-fired furnaces in between thesubsequent reforming reactors. As a result of the very high temperatures, thecatalyst becomes deactivated by the formation of .coke. (i.e., essentially purecarbon) on the catalyst which reduces the surface area available to contact withthe hydrocarbons. A simplified process flow for the Catalytic Reforming processis presented above. 17
  18. 18. Fluidized Catalytic CrackingThe Fluidized Catalytic Cracking (FCC) process unit is considered by many refiners to be the heart of thepetroleum refinery. This derives from the fact that the FCC is a key tool to correct the imbalance reflectedby the markets demand for predominantly lighter, lower boiling petroleum products, whereas fractionatedcrude oils typically provide an excess of heavy, high boiling range oils. The FCC process converts heavygas oils into lighter products which are then used as blend stocks for gasoline and diesel fuels. Theolefinic FCC catalytic naphtha product exhibits a very high-octane value for gasoline blending. The FCCprocess cracks the heavy gas oils by breaking carbon-to-carbon bonds in the large molecules comprisingthe gas oils and splitting them into multiple smaller molecules which boil at a much lower temperatures.The FCC may achieve conversions of 70-80% of the feed hydrocarbons boiling above the gasoline range(i.e., 430°F) to products boiling below 430°F. The lower density of the FCC products relative to the gas oilfeedstocks has the added benefit of producing a volume gain in which the combined volume of the liquidproduct streams is greater than the volume of the unit feed stream. Since most petroleum products arebought and sold on a volume basis, the volume gain aspect of the FCC process is a key aspect in how itenhances refinery profitability. The resulting FCC product hydrocarbons are highly olefinic (i.e.,unsaturated). Virgin is a term used to distinguish straight-run (i.e., crude distillation and possiblyhydrotreated only) hydrocarbons stocks from those that are products of conversion units such as theFCC.The FCC cracking reactions are catalytically promoted at very high temperatures of 950-1,020°F. At thesetemperatures, coke (i.e., essentially pure carbon) formation deactivates the catalyst by blocking catalystsurface area which prevents intimate contact between the catalyst and the hydrocarbons. To retaincatalyst activity, the FCC utilizes a very fine powdery, zeolite catalyst that behaves like a fluid (i.e., is ableto flow). The fluidized catalyst is continuously circulated in the FCC from the reactor to a regeneratorvessel and then returned to the reactor. Coke is removed from the catalyst in the regenerator vesselthrough the controlled incomplete combustion of the carbon with oxygen to form carbon monoxide andcarbon dioxide. 18
  19. 19. PETROLEUM REFINERY ENGINEERING Books for Reference:1. Petroleum Refinery Engineering, 4th Ed., 1958, W.L. Nelson, McGraw-Hill Book Company2. Handbook of Petroleum Processes, 3rd Edition, R. A. Meyers McGraw-Hill3. Fundamentals of Petroleum and Petrochemical Engineering. Uttam Ray Chaudhuri, CRC Press, 20104. Mcketta S. (Ed), “Petroleum Processing Hbk”, Marcell Dekker Inc. 1992.5. Gary J., Handework G., “Petroleum Refining Technology and Economics”, Marcell Dekker Inc. 1984.6. B. K. Bhaskara Rao, "Modern Petroleum Refining Processes",2nd Edn., Oxford and IBH Publishing Company, New Delhi, 1990.7. G. D. Hobson and W. Pohl., “Modern Petroleum Technology", Gulf Publishers, 2nd Ed., 19908. An Introduction to Industrial Organic Chemistry, 2nd ed., P. Wiseman, (1979), Applied Science Publishers, London. 19
  20. 20. About „Fundamentals of Petroleum and Petrochemical Engineering‟. BY Uttam Ray Chaudhuri, CRC Press, 2010: The supply of petroleum continues to dwindle at an alarming rate, yet it is the source of a range ofproducts - from gasoline and diesel to plastic, rubber, and synthetic fiber. Critical to the future of thiscommodity is that we learn to use it more judiciously and efficiently. Fundamentals of Petroleum and Petrochemical Engineering provides a holistic understanding ofpetroleum and petrochemical products manufacturing, presented in a step-by-step sequence of the entiresupply chain. Filled with crucial information relevant to a range of applications, the book covers topicssuch as:  The essential preliminaries for the exploration and production of crude petroleum oil and gas  Analysis of crude oil and its petroleum products  The processing of petroleum in refineries  The fundamentals of lubricating oil and grease Petrochemicals - their raw materials and end products, and  manufacturing principles of industrially important products  Theories and problems of unit operations and the processes involved in refineries and petrochemical plants  Automatic operations in plants Start up, shutdown, maintenance, fire, and safety operations Commercial and managerial activities are necessary for the ultimate success of a refining ormanufacturing business. Due to the advancement of technology, new petrochemicals are being inventedand will continue to be relevant to the petroleum industry in the near future. 20
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