Fuel oil products


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Fuel oil products

  1. 1. Fuel oil products
  2. 2. Above: Typical modern oil refineryOil Refineries and the Production of Fuel OilAn oil refinery may be considered as a factory that converts crude oil into a range ofuseable products. It is designed to produce what the market requires in the mosteconomical and efficient manner. The first step in the manufacture of petroleum productsis the separation of crude oil into the main fractions by atmospheric distillation. Whencrude oil is heated, the lightest and most volatile hydrocarbons boil off as vapours firstand the heaviest and least volatile last. The vapours are then cooled and condensed backinto liquids. This distillation process is carried out in a fractionating column. The columnis divided into a series of chambers by perforated trays, which condense the vapours ateach stage and allow the liquids to flow into storage tanks. Pre-heating of the crude oil islimited to 350°C to prevent the oil being thermally cracked.Atmospheric DistillationThe residue from atmospheric distillation is sometimes referred to as long residue and torecover more distillate product, further distillation is carried out at a reduced pressure andhigh temperature. This vacuum distillation process is important in maximising theupgrading of crude oil. The residue from vacuum distillation, sometimes referred to asshort residue, is used as a feedstock for further upgrading or as a fuel component. Unlikethe fractionating column for atmospheric distillation, a system of packed beds instead oftrays is used for condensation of the low-pressure vapours. Refineries based just onatmospheric and vacuum distillation are said to be operating “the straight run” processand the fuel oil is basically either long or short run residue. The percentage of residuevaries depending on the composition of crude processed. For a typical “light” NorthAfrican crude the residue is 28%, whilst for a “heavy” Venezuelan crude it is as high as85%. The proportion of products produced does not always match the product demandand is primarily determined by the crude oil.Thermal Cracking
  3. 3. In order to meet the product demand, further refining processes were introduced. Today,a modern refinery, in addition to atmospheric and vacuum distillation, may also consist ofsecondary refining processes such as cracking, which may be thermal or with a catalyst.A typical modern refinery installation is shown below. Thermal cracking is the oldest andin principle the simplest refinery conversion process. It is carried out over a wide range oftemperatures, between 450-750°C and pressures from atmospheric to 70 bar. Thetemperature and pressure depends on the type of feedstock and the product requirement.At these elevated temperatures, the large hydrocarbon molecules become unstable andspontaneously break into smaller molecules. Another important factor in the process isthe residence time. The feedstock can be either the residue from the atmospheric orvacuum distillation units, or a mixture of the two. In modern refineries, there are threemajor applications of the thermal cracking process: visbreaking, a thermal gas oil unitand coking. Visbreaking is the most significant process with regard to the manufacture ofresidual fuel oil. It is a mild form of thermal cracking often used for reducing theviscosity of straight-run residual fuels. Normally such fuels are very viscous and, ifrequired for sale as heavy fuel oil, must be blended with a relatively high value distillateto meet the finished product specification. Visbreaking reduces the quantity of distillaterequired as diluent or “cutter stock” and this material can then be diverted to a moreprofitable product stream. The main aim of a thermal gas oil unit is to produce andrecover the maximum amount of gas oil. In extreme cases, the viscosity of the residuemay be higher than that of the feed stock. Coking is a relatively severe form of thermalcracking. It is designed to convert straight-run residues into more valuable products suchas naphtha and diesel oil. In addition, gas and coke are produced and thus this processdoes not feature in the manufacture of residual fuel oils.Catalytic CrackingCatalytic cracking has become the major process in the petroleum refining industry forthe conversion of heavy hydrocarbon fractions, mainly into high-quality gasoline and fueloil components. These are lighter, less viscous and more valuable than the feedstock.There are various different catalytic cracker designs however, in all cases the productoutput can finally be separated to: gases, gasoline blending components, catalyticallycracked cycle oils and cycle oil slurry. The cycle oils are very important with respect toresidual fuel oil since they are used as cutter stocks to reduce the viscosity of residues.Prior to use as a cutter stock, the cycle oil slurry has to be treated to remove particles ofcatalyst entrained in it. In a modern refinery, there is a wide range of residues and diluentavailable for the production of fuel oil. Usually the fuel will consist of visbroken residuediluted with cycle oils and smaller amounts of other distillates. The figure shows themain streams of feedstock, fuel oil diluent and fuel oil residues in a modern refinery.Clearly, if a refinery does not have a thermal cracking facility (visbreaker or thermal gasoil unit) then the fuel oil will be based on long or short residue. Additional to the mainresidual fuel streams in a modern refinery, it should be appreciated that otherdevelopments have taken place to further maximise the production of gasoline, keroseneand diesel from a barrel of oil. One of these is by residue hydroconversion where residualfractions are converted into feedstock, which in turn can be further processed inconventional crackers to yield lighter products. Maximisation of production for thelighter products is carried out at the expense of residual fuel oil. Below:
  4. 4. Below: Simplified diagram showing the straight run refinery process.Below:The main HFO refinery streams.Comment: Oil Refineries can include: Atmospheric Distillation Vacuum DistillationThermal/Catalytic Cracking. When used as a cutter stock, cycle oil slurry is also apotential source of catfines in residual fuel oil streams.Fuel SpecificationsIn 1982, the Working Group responsible for the development of the internationalstandard issued the Draft Proposal of what became ISO 8217 “Petroleum products - Fuels(class F) - Specifications of marine fuels”. Issued at the same time was the Draft Proposalof what became ISO 8216 “Petroleum products - Fuels (class F) - Classification Part 1 -Marine Fuels”. The first edition of the international standards was published in 1987. In1989, BS MA 100 was reissued and is identical to the International Standard. In 1996, the
  5. 5. second edition of ISO 8217 was issued and this is denominated as ISO 8217 : 1996 (E).The ISO 8217:2010 Standard represents a significant advance over the previous 2005version. The changes are designed to promote the safer use of marine residual anddistillate fuels, recognising the fact that the industry is entering into a new realm of multi-blend products driven by ever increasing environmental regulation. Furthermore, usersare provided with better protection against the supply of poor quality fuels. Additionally,the supporting Standard, ISO 8216, dealing with the classification of marine fuels, hassimilarly been updated to reflect the changes to ISO 8217.It should be noted that in some countries, gas oil and diesel oil are produced for the localland-based market to a national specification. Included in such a specification is usually aminimum flash point and this value may be below that required by internationallegislation for normal marine use.Summary of fuel specificationsNew parameters for both distillate and residual fuels are the inclusion of acid numberlimits as well as a limit on hydrogen sulphide. For distillate grades, oxidation stabilityand a lubricity requirement have been introduced. For residual marine fuels, CalculatedCarbon Aromaticity Index as an indictor of ignition delay, and a limit on sodium contenthave been introduced. As well as this, limits for ash and vanadium have been tightenedand there has been a significant reduction in limits for aluminium plus silicon, alsoknown as cat fines.Below: INTERNATIONAL STANDARD ISO 8217:2010 (F)Petroleum Products - Fuels (Class F) - Specifications of marine fuels. Requirements formarine distillate and residual fuels
  6. 6. Fuel Oil - Delivery & SamplingClick image to enlargeFuel Oil: ViscosityFuel oil, especially residual fuel grades, has historically been ordered by viscosity,although distillate fuels are often ordered by using other criteria.Whilst viscosity is an important characteristic, it does not give an indication of the othercharacteristics of the fuel. With viscosity as the sole criterion for ordering, engineoperators remain unaware of these other characteristics.Fuel Oil : CharacteristicsSimilarly, the designers of the machinery and fuel oil systems are not always informed ofthe fuel characteristics to which they should be designing. It is therefore necessary todefine the quality of the fuel over a range of parameters to which the engine plant issensitive. Specifications exist to assist this process.Fuel Oil DeliveryThis section deals with delivery of large volumes of fuel oil. It relies heavily on marinepractice but the methods and lessons have relevance to land-based applications wherecurrent procedures are often less strict, to the detriment of the fuel buyer. Associated withthe actual physical delivery of the bunkers is the accompanying paperwork. This can beconveniently sub-divided into two parts: • Pre-delivery documentation • Bunker Delivery Receipt (BDR)Pre-delivery Fuel Oil DocumentationThe purpose of the pre-delivery document is to record agreement on the operationaldetails of the transfer and to ensure safe transfer of the product. This document originatesfrom the seller’s representative and states the grade or grades with quantity which havebeen nominated. Ideally the grades will be expressed by reference to ISO 8217, whichdefines viscosity for residual fuel oil grades at 100°C. In reality, a residual grade may beexpressed as a maximum viscosity usually quoted at 50°C. Distillate grades, instead ofbeing referenced as DMA, DMB and DMC, may be referred to as marine gas oil, marinediesel or marine diesel blended.Having established what is to be transferred, agreement has to be reached on the pumpingrate acceptable to the receiving vessel to ensure safe transfer. The next aspect whichneeds to be considered is witnessing of tanks by sounding or ullage and the approach tothis is detailed later in this section. Agreement should be reached on the witnessing of arepresentative sample and this again is detailed later. Another aspect which should be
  7. 7. discussed and agreed is a spill prevention transfer procedure. The key to this iscommunication and a check list can be useful to ensure no points are missed.Bunker Delivery Receipt (BDR)The purpose of the Bunker Delivery Receipt (BDR) is to record what has beentransferred. Various factors are recorded including: • Location and time of transfer • Details of product delivered • Temperature of product delivered • Product density at standard reference temperature • Sample seal numbersCare should be taken before signing the BDR. For example, the bunkers should not besigned for in weight form, only for volume at observed temperature. The actual weightcan only be calculated after a representative sample of the delivery has been tested fordensity.MARPOL Annex VI requires you to retain the BDR for at least 3 years from thedate of issue.Letter of ProtestShould there be any dispute in the quantity of bunkers delivered, the purchaser or hisrepresentative should issue a letter of protest, which is properly signed and stamped byboth parties. An example of such a letter is shown below. The letter of protest system canbe used by both the barge or supplier as well as the ship owner or engine operator.Bunkering Check ListBunkering is often carried out when the engineering staff are under pressure in both timeand manpower. Key checks are often missed and only come to light when it is too late. Afew relevant points are detailed below:1. The purchaser should obtain specification acceptance from the supplier2. Purchaser needs to advise ship’s buyer what grade of fuel will be delivered and howtransferred3. Fuels from different deliveries should be segregated as far as practical4. All receiving tanks need to be gauged prior to taking fuel5. Don’t sign any documentation unless you have witnessed the actual event6. Always take up witness offers made by the supplier7. If the suppliers sampling method is unknown, then sign adding the words “for receiptonly - source unknown”8. Always take a fuel sample using a continuous drip method9. Take one sample per barge/ delivery10. Sign the BDR for volume only, if necessary adding the words “for volume only -weight to be determined after density tests”11. Ensure good records are kept throughout the bunkering12. Keep accurate engine logs in the event of any subsequent problems13. Keep fuel samples for at least 12 months
  8. 8. 14. Test all fuel on delivery for Viscosity, Density, Water,Stability, Pour Point and Salt(if water present)15. Use a laboratory to check results in the event of any discrepancies being indicated byon-site test equipmentThank youContactTINSEL CARGO & OIL COMPANYCOMMERCE HOUSE3RD FLOOR, SUITE 311,MOI AVENUE, NAIROBI.P.O. BOX 79456-00200 NAIROBI, KENYATELE FAX: +254-20-2229781,Cellphone: +254-722-761587,+254-734-939308Website: www.tinselcargo.comEMAIL: info@tinselcargo.com