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Chapter 4a heavy_oil2

petroleum refining

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Chapter 4a heavy_oil2

  1. 1. HEAVY OIL PROCESSING
  2. 2. HEAVY CRUDE OIL • Heavy oil is plentiful around the globe and will become an increasingly important source of new crude supplies in the future. • It is found offshore and onshore; in liquid form as in ‘conventional’heavy oil or in solid form such as the bitumen in the Canadian oil sands. • Heavy oil is unlike conventional oil. Generally, heavy oil targets are known with depths identified and a general idea of the API gravity. • Most of the world’s oil resources are heavy, viscous HC that are difficult and costly to produce and refine, and with lower economic value. • Besides, heavy oil tends to have high concentration of metal and other elements which may also lead to high disposal of waste costing. • Heavy crude oil: 23.3º API or less. If 10º API or less  extra heavy, ultra heavy or super heavy.
  3. 3. LUBE COMPOSITION AND PROPERTIES n - Paraffins i - Paraffins mono - Naphthenes di & higher Naphthenes mono - Aromatics di - Aromatics tri & higher-Aromatics Molecular weight KV VI Pour PointVI
  4. 4. HEAVY CRUDE OIL • Why heavy oil demand increase? • Resource are abundant (30% or world’s total oil are conventional oil and the remainder in heavy oil, extraheavy oil or bitumen) • Heavy oil reservoirs can be exploited profitably.
  5. 5. BASE OIL GROUPS The American petroleum institute (API) classified several types of lubricant base oil: 1.Group I – saturates <90% and/or sulfur >0.03%, and society of automotive engineers (SAE) viscosity index (VI) of 80 to 120. Manufactured by:  Solvent extraction,  Solvent or catalytic dewaxing, and  Hydro-finishing processes. Common group I base oil are 150sn (solvent neutral), 500sn, and 150bs (brightstock) Remarks: Viscosity-measurement of internal resistance to flow.  Viscosity, thicker the oil and thicker the film of the oil clings to a surface.  Viscosity,  BP. Viscosity index (VI): the rate of change of viscosity with temperature of the oil.
  6. 6. 2. Group II – saturates over 90% and sulfur under 0.03%, and SAE viscosity index of 80 to 120. Manufactured by:  Hydrocracking and solvent or catalytic dewaxing processes. Group II base oil has superior anti-oxidation properties since virtually all hydrocarbon molecules are saturated. It has water-white color. 3. Group III – saturates > 90%, sulfur <0.03%, and SAE viscosity index over 120. Manufactured by :  Special processes such as isohydromerization.  From base oil or slack wax from dewaxing process. 4. Group IV – polyalphaolefins (PAO) 5. Group V – all others not included above such as naphthenics, PAG (polyalkylene glycol), esters.
  7. 7. COMMON ROUTE FOR BASE OIL PRODUCTIONDistillate/DAO Group I Group II Group II & III Group II Group II & III Group II & III
  8. 8. LUBE OIL PROCESSING • The heavier lube oil raw stocks are included in the vacuum fractionating tower bottoms with the asphaltenes, resins, and other undesirable materials. • The raw lube oil fractions from most crude oil contain components that have undesirable characteristic for finishing lubricating oils. • The undesirable characteristics include high pour points, large viscosity changes with temperature (low VI), poor oxygen stability, poor color, high cloud points, high organic acidity, and high carbon and sludge tendencies. • Processes used to change these characteristics are: • Solvent deasphalting • Solvent extraction and hydrocraking • Solvent dewaxing & selective hydrocracking • Hydrotreating and clay treating
  9. 9. Lube Processing
  10. 10. TREATING / REFINING FOR LUBE PROCESSING SOLVENT EXTRACTION SOLVENT EXTRACTION SOLVENT EXTRACTION SOLVENT EXTRACTION SOLVENT DEWAXING API GROUP I HYDRO-FINISHING HYDRO-FINISHING WAX CATALYTIC DEWAXING API GROUP I IHYDRO-FINISHING RAFF. HYDRO- TREATING HYDRO- ISOMERISATION HYDRO-FINISHING API GROUP II SOLVENT DEWAXING WAX ISOMERISATION API GROUP III
  11. 11. RESIDUAL UPGRADING • After vacuum distillation, there are still some valuable oils left in the vacuum-reduced crude. • Vacuum tower distillation bottoms and other residuum feeds can be upgraded to higher value products such as higher grade asphalt or feed to catalytic cracking processes. • Residual upgrading includes processes where asphalt components are separated from gas oil components by the use of a solvent. • It also includes processes where the asphalt value of the residuum is upgraded (e.g., by oxidation) prior to sale. Off-spec product and fines, as well as process sludges, are study residuals from this category. • Four types of residual upgrading processes: • Solvent deasphalting • Asphalt oxidation • Supercritical extraction • Asphalt emulsion
  12. 12. SOLVENT DEASPHALTING • Residuum from vacuum distillation is separated into asphalt components and gas oil components by solvent deasphalting. • The hydrocarbon solvent is compressed and contacted with the residuum feed. The extract contains the paraffinic fractions (deasphalted oil or DAO), and the raffinate contains the asphaltic components.
  13. 13. Vacuum residue contains paraffinic and naphthenic hydrocarbons as well as aromatic. Their mixture at this stage is called DAO. Meaning deasphalted oil, Products of this unit are oils and base asphalt.
  14. 14. SOLVENT DEASPHALTING (CONT’) • The extract and raffinate streams are sent to separate solvent recovery • Systems to reclaim the solvent. The DAO may be further refined or processed, used as catalytic cracking feed, sent to lube oil processing/blending, or sold as finished product. • The following types of solvents are typically used for the following residual upgrading processes: • Propane is the best choice for lube oil production due to its ability to extract only paraffinic hydrocarbons and to reject most of the carbon residue. • A mixture of propane & butane is valuable for preparing feedstocks for catalytic cracking processes due to its ability to remove metal-bearing components. • Pentane deasphalting, plus hydrodesulfurization, can produce more feed for catalytic cracking or low sulfur fuel oil. • One facility reported using propane and phenol solvents for deasphalting residuum. The DAO is sent to lube oil processing and the asphalt fraction is sent to delayed coking or fuel oil blending.
  15. 15. Propane Deasphalting • Coke-forming tendencies of heavier distillation products are reduced by removal of asphaltenic materials by solvent extraction. • Liquid propane is a good solvent (butane and pentane are also commonly used). • Deasphalting is based on solubility of hydrocarbons in propane. • Vacuum residue is fed to a countercurrent deasphalting tower. • Alkanes dissolve in propane whereas asphaltenic materials (aromatic compounds), ‘coke-precursors’do not. • Asphalt is sent for thermal processing.
  16. 16. PROPANE DEASPHALTING UNIT
  17. 17. LUBE REFINING PROCESSES • Chemical, solvent, and hydrogen refining processes have been developed and are used to remove aromatics and other undesirable constituents, and to improve the viscosity index and quality of lube base stocks. • Traditional chemical processes that use sulfuric acid and clay refining have been replaced by solvent extraction/refining and hydrotreating which are more effective, cost efficient, and environmentally more acceptable.
  18. 18. LUBE DEWAXING PROCESSES • Lube feedstocks typically contain increased wax content resulting from deasphalting and refining processes. • Waxes are normally solid at ambient temperatures and must be removed to manufacture lube oil products with the necessary low temperature properties. • Catalytic dewaxing and solvent dewaxing (the most prevalent) are processes currently in use; older technologies include cold settling, pressure filtration, and centrifuge dewaxing.
  19. 19. Solvent extraction and dewaxing • Solvent treating is a widely used method of refining lubricating oils as well as a host of other refinery stocks. • Since distillation (fractionation) separates petroleum products into groups only by their boiling-point ranges, impurities may remain. These include: 1. organic compounds containing sulfur, nitrogen, and oxygen 2. inorganic salts 3. dissolved metals 4. soluble salts that were present in the crude feedstock. • In addition, kerosene and distillates may have trace amounts of aromatics and naphthenes, and lubricating oil base-stocks may contain wax. • Solvent refining processes including solvent extraction and solvent dewaxing usually remove these undesirables at intermediate refining stages or just before sending the product to storage.
  20. 20. Solvent Extraction • The purpose of solvent extraction is to prevent corrosion, protect catalyst in subsequent processes, and improve finished products by removing unsaturated and aromatic hydrocarbons from lubricant and grease stocks. • The solvent extraction process separates aromatics, naphthenes, and impurities from the product stream by dissolving or precipitation. • The feedstock is first dried and then treated using a continuous countercurrent solvent treatment operation. • In one type of process, the feedstock is washed with a liquid in which the substances to be removed are more soluble than in the desired resultant product. • In another process, selected solvents are added to cause impurities to precipitate out of the product. • In the adsorption process, highly porous solid materials collect liquid molecules on their surfaces. 22
  21. 21. • The solvent is separated from the product stream by heating, evaporation, or fractionation, and residual trace amounts are subsequently removed from the raffinate by steam stripping or vacuum flashing. • The most widely used extraction solvents are phenol, furfural, and cresylic acid. • Other solvents less frequently used are liquid sulfur dioxide, nitrobenzene, and 2,2' dichloroethyl ether. • The selection of specific processes and chemical agents depends on the nature of the feedstock being treated, the contaminants present, and the finished product requirements.
  22. 22. AROMATIC SOLVENT EXTRACTION UNIT
  23. 23. SOLVENT DEWAXING • Solvent dewaxing is used to remove wax from either distillate or residual base stock at any stage in the refining process. There are several processes in use for solvent dewaxing, but all have the same general steps, which are: (1) mixing the feedstock with a solvent, (2) precipitating the wax from the mixture by chilling, and (3) recovering the solvent from the wax and dewaxed oil for recycling by distillation and steam stripping.
  24. 24. • Usually two solvents are used: toluene, which dissolves the oil and maintains fluidity at low temperatures, and methyl ethyl ketone (MEK), which dissolves little wax at low temperatures and acts as a wax precipitating agent. • Other solvents sometimes used include benzene, methyl isobutyl ketone,propane, petroleum naphtha, ethylene dichloride, methylene chloride, and sulfur dioxide. • In addition, there is a catalytic process used as an alternate to solvent dewaxing.
  25. 25. SOLVENT DEWAXING UNIT
  26. 26. SOLVENT DEWAXING UNIT (SDU) Good qualities of dewaxing solvent blends: High solvent power for oil & low solvent power for wax  Low visc. at operating temperature to get low pressure drop & to help in precipitation /crystallization  Good filterability Low freezing point & temperature effect of dewaxing High thermal/chemical stability Boiling point much lower than that of feed  Low latent heat/specific heat
  27. 27. LUBE HYDROFINISHING UNIT Feed stock : De-waxed oil (DWO) from solvent dewaxing unit (SDU). Catalyst : HR348 supplied by procatalyse. High purity alumina extrudates impregnated with nickel and molybdenum oxides Purpose: To improve color by removing Sulphur, oxygen & nitrogen in a reactor with cobalt / moly catalyst. Quality monitoring: Color, K.V at 100 oc, VI.
  28. 28. LUBE HYDROFINISHING UNIT • Major reactions : hydrodesulphurization, mild hydrodenitrogenation, olefins hydrogenation, mild aromatic hydrogenation, decomposition of heteromolecules. • Sulphur is usually present as mercaptan, sulphides, disulphide and thiophenic sulphur. Sulphur is removed as H2S. • Nitrogen is usually present as ammines and pyrrole, pyridine etc. More difficult reaction and ultimate product is hydrocarbon & ammonia. • Olefins are present in low quantity & most of them are saturated during hydro finishing. • Normally aromatics are not hydrogenated. Due to liberation of some aromatics rings towards the light compounds are stripped off to reach the required flash point. Thus results in slight viscosity index (VI) improvement also. • Oxygenated compounds are mostly removed in the solvent extraction step. If any remaining removed as water. • As a result, color & color stability improves, mild VI improvement occurs, product stabilization through saturation of poly nuclear aromatics.
  29. 29. HYDRO FINISHING UNIT Main operating variables : • Temperature: optimum to achieve desulphurization. Lower the temp, higher is the product viscosity & yields • Partial pressure of hydrogen : increase favors the reaction & reduces coke by avoiding polymerization reaction. Can be modified by change in total pressure and recycle ratio. Total pressure kept maximum compatible with the equipment • Space velocity : hourly volume flow rate of feed with respect to the catalyst volume. Lower is the space velocity higher the severity. (0.75-1.3 m3 of feed per m3 of catalyst) • Mole ratio of hydrogen/hydrocarbon: includes quantity needed for hydro finishing + quantity which increases the partial pressure of hydrogen • Feed quality: higher the impurities higher the severity

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