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Petroleum Refinery Engineering Book

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PREFACE When first published () a main purpose of this book w fl» introduction of the principles of chemical engineering t refining industry. The situation is. Petroleum refinery engineering. Front Cover. Wilbur Lundine Nelson. McGraw- Hill, - Technology & Engineering - pages. 0 Reviews. Petroleum Refinery Engineering. Front Cover. Wilbur Lundine Nelson. McGraw- Hill, - Cracking process - pages. 0 Reviews.

An example case-study problem begins in Chapter 4 Crude Distillation and con- cludes in Chapter 18 Economic Evaluation. Valuable literature references are noted throughout the book.

Handbook of Petroleum Refining

Appreciation is expressed to the many people who contributed data and suggestions incorporated into this book. Corporations that have been very helpful include: The M. Robert W. Cheshire Jack S. Corlew Gary L. Ewy P. Geren Andy Goolsbee Jeff G.

Handwerk Jay M. Killen Viron D. Kliewer David R. Lohr 5. Preface v James R. Murphy Marvin A. Prosche Ed J. Smet Delbert F. Tolen Donald B. Trust William T. Gary, who helped greatly in improving the clarity of presentation. James H. Gary Glenn E. Handwerk 6. Contents ix 7. Gasoline Blending Economic Evaluation Light heating oils are not properly transporta- tion fuels but the hydrocarbon components are interchangeable with those of diesel and jet fuels, only the additives are different.

See also Photo 1, Appendix E. The processing equip- ment indicated is for processing crude oils of average gravities and sulfur con- tents. The quality of crude oils processed by U. The greater 1 Histori- cally this high-boiling material or residua has been used as heavy fuel oil but the demand for these heavy fuel oils has been decreasing because of stricter environmental requirements.

Sulfur restrictions on fuels coke and heavy fuel oils will affect bottom-of-the-barrel processing as well. The crude oil is heated in a furnace and charged to an atmospheric distilla- tion tower, where it is separated into butanes and lighter wet gas, unstabilized light naphtha, heavy naphtha, kerosine, atmospheric gas oil, and topped reduced crude ARC.

The topped crude is sent to the vacuum distillation tower and sepa- rated into vacuum gas oil stream and vacuum reduced crude bottoms residua, resid, or VRC.

The reduced crude bottoms VRC from the vacuum tower is then thermally cracked in a delayed coker to produce wet gas, coker gasoline, coker gas oil, and coke. Without a coker, this heavy resid would be sold for heavy fuel oil or if the crude oil is suitable asphalt. Historically, these heavy bottoms have sold for about 70 percent of the price of crude oil. These units crack the heavy molecules into lower molecular weight compounds boiling in the gaso- line and distillate fuel ranges.

The products from the hydrocracker are saturated. The unsaturated catalytic cracker products are saturated and improved in quality by hydrotreating or reforming. The heavy naphtha streams from the crude tower, coker, and cracking units are fed to the catalytic reformer to improve their octane numbers.

The products from the catalytic reformer are blended into regular and premium gasolines for sale. The unsaturated hydrocar- bons and isobutane are sent to the alkylation unit for processing. The product is called alkylate, and is a high-octane product blended into premium motor gasoline and aviation gasoline. The middle distillates from the crude unit, coker, and cracking units are blended into diesel and jet fuels and furnace oils. After re- moving the asphaltenes in a propane deasphalting unit, the reduced crude bottoms is processed in a blocked operation with the vacuum gas oils to produce lube- oil base stocks.

They are then treated with special clays or high-severity hydrotreating to improve their color and stability before being blended into lubricating oils. Table 2. Storage and waste dis- posal are expensive, and it is necessary to sell or use all of the items produced from crude oil even if some of the materials, such as high-sulfur heavy fuel oil and fuel-grade coke, must be sold at prices less than the cost of fuel oil.

Economic balances are required to determine whether certain crude oil fractions should be sold as is i. Usually the lowest value of a hydrocarbon product is its heating value or fuel oil equivalent FOE.

This value is always established by location, demand, availability, combustion characteristics, sulfur content, and prices of competing fuels. The petroleum industry uses a shorthand method of listing lower-boiling hydrocarbon compounds which characterize the materials by number of carbon atoms and unsaturated bonds in the molecule. The corresponding hydrogen atoms are assumed to be present unless otherwise indicated. This notation will be used throughout this book.

The physical properties of methane are given in Table 2. Boiling point rises with increase in molecular weight. Boiling point of a branched chain is lower than for a straight chain hydrocarbon of the same molecular weight. Melting point increases with molecular weight. Melting point of a branched chain is lower than for a straight-chain hydrocarbon of the same weight unless branching leads to symmetry.

Gravity increases with increase of molecular weight. In some locations, propylene is separated for sale to polypropylene manufacturers. Normal butane nC4 has a lower vapor pressure than isobutane iC4 , and is usually preferred for blending into gasoline to regulate its vapor pressure and promote better starting in cold weather.

Fundamentals of Petroleum Refining

Normal butane has a Reid vapor pressure On a volume basis, gasoline has a higher sales value than that of LPG, thus, it is desirable from an economic viewpoint to blend as much normal butane as possible into gasoline.

Normal butane is also used as a feedstock to isomerization units to form isobutane. Regulations promulgated by the Environmental Protection Agency EPA to reduce hydrocarbon emissions during refueling operations and evaporation from hot engines after ignition turn-off have greatly reduced the allowable Reid vapor pressure of gasolines during summer months.

This resulted in two major impacts on the industry. Isobutane not used for alkylation unit feed can be sold as LPG or used as a feedstock for propylene propene manufacture. Average properties of commercial propane and butane are given in Table 2.

The principal difference between the regular and premium fuels is the antiknock per- formance. In the posted method octane number PON of unleaded regular gasolines see Section 2. The non-leaded regular gasolines averaged about 88 PON.

For all gasolines, octane numbers average about two numbers lower for the higher elevations of the Rocky Mountain states.

Gruse and Stevens [5] give a very comprehensive account of properties of gasolines and the manner in which they are affected by the blending components. For the pur- poses of preliminary plant design, however, the components used in blending motor gasoline can be limited to light straight-run LSR gasoline or isomerate, catalytic reformate, catalytically cracked gasoline, hydrocracked gasoline, poly- mer gasoline, alkylate, n-butane, and such additives as MTBE methyl tertiary butyl ether , ETBE ethyl tertiary butyl ether , TAME tertiary amyl methyl ether and ethanol.

Other additives, for example, antioxidants, metal deactivators, and antistall agents, are not considered individually at this time, but are included with the cost of the antiknock chemicals added.

The quantity of antiknock agents added, and their costs, must be determined by making octane blending calcula- tions. As a result, it is processed separately from the heavier straight-run gasoline frac- tions and requires only caustic washing, light hydrotreating, or, if higher octanes are needed, isomerization to produce a gasoline blending stock.

Heavy straight-run HSR and coker gasolines are used as feed to the catalytic reformer, and when the octane needs require, FCC and hydrocracked gasolines of the same boiling range may also be processed by this unit to increase octane levels. The processing conditions of the catalytic reformer are controlled to give the desired product antiknock properties in the range of 90 to RON 85 to 98 PON clear lead-free.

The FCC and HC gasolines are generally used directly as gasoline blending stocks, but in some cases are separated into light and heavy fractions with the heavy fractions upgraded by catalytic reforming before being blended into motor gasoline.

This has been true since motor gasoline is unleaded and the clear gaso- line pool octane is now several octane numbers higher than when lead was permit- ted. It is usual for the heavy hydrocrackate to be sent to the reformer for octane improvement. Some aromatics have high rates of reaction with ozone to form visual pollutants in the air and some are claimed to be potentially carcino- Alkylate gasoline is the product of the reaction of isobutane with propylene, butylene, or pentylene to produce branched-chain hydrocarbons in the gasoline boiling range.

Normal butane is blended into gasoline to give the desired vapor pressure. The vapor pressure [expressed as the Reid vapor pressure RVP ] of gasoline is a compromise between a high RVP to improve economics and engine starting characteristics and a low RVP to prevent vapor lock and reduce evaporation losses.

As such, it changes with the season of the year and varies between 7. Isobu- tane can be used for this purpose but it is not as desirable because its higher vapor pressure permits a lesser amount to be incorporated into gasoline than n- butane. Concern over the effects of hydrocarbon fuels usage on the environment has caused changes in environmental regulations which impact gasoline and die- sel fuel compositions.

Here, main sources of items of concern are discussed along with relative impacts on the environment. Coker Gasoline 0. Field tests indicate that it is desirable to have gasoline sulfur contents of less than ppm 0. As shown in Table 2. The activities of these gasoline components are ex- pressed in terms of reactivity with OH radicals in the atmosphere.

The sources and reactivities of some of these gasoline components are shown in Tables 2. HC naphtha 2. The million tons of gasoline produced exceeded the output of steel, lumber, and other high-volume products [10]. Warm-up is expressed in terms of the distance operated to develop full power without excessive use of the choke. A two- to four-mile 3- to 7-km warm-up is considered satisfactory and the relationship between outside tempera- ture and percent distilled to give acceptable warm-up properties is: To keep crankcase dilution within acceptable limits, the volatility should be: In order to control vapor, the vapor pressure of the gasoline should not exceed the following limits: Altitude affects several properties of gasoline, the most important of which are losses by evaporation and octane requirement.

Khanna Publishers

Octane number requirement is greatly affected by altitude and, for a constant spark advance, is about three units lower for each ft m of elevation. In practice, however, the spark is advanced at higher elevations to improve engine performance and the net effect is to reduce the PON of the gasoline marketed by about two numbers for a ft m increase in elevation.

Octane requirements for the same model of engine will vary by 7 to 12 RON because of differences in tuneup, engine depos- its, and clearances. There are several types of octane numbers for spark ignition engines with the two determined by laboratory tests considered most common: Both methods use the same basic type of test engine but operate under different conditions. Obviously, the driver would like for the fuel to perform equally well both in the city and on the highway, therefore low sensitivity fuels are better.

Since the posting of octane numbers on the service station pump has been required in the United States, the posted octane number PON is the one most well-known by the typical driver. Increasingly severe environmental restrictions on fuel emissions have caused some users of heating oils to convert to natural gas and LPG. Expansion of air and truck travel has increased diesel and jet fuel demands.

Usu- ally jet fuels sell at higher prices than diesel fuels and No. Commercial jet fuel is a material in the kerosine boiling range and must be clean burning. Hydrocracking saturates many of the double ring aromatics in cracked products and raises the smoke point. Jet fuel is blended from low sulfur or desulfurized kerosine, hydrotreated The two basic types of jet fuels are naphtha and kerosine.

Naphtha jet fuel is produced primarily for the military and is a wide-boiling-range stock which extends through the gasoline and kerosine boiling ranges.

The naphtha-type jet fuel is more volatile and has more safety problems in handling, but in case of a national emergency, there would be a tremendous demand for jet fuels and to meet the requirements both naphtha and kerosine production would be needed. The military is studying alternatives and the JP-8 jet fuel is being phased in. The ignition properties of diesel fuels are expressed in terms of cetane number or cetane index. These are very similar to the octane number except the opposite and the cetane number expresses the volume percent of cetane C16H34, high-ignition quality in a mixture with alpha-methyl-naphthalene C11H10, low- ignition quality.

The number derived is called the cetane index and is calculated from the mid—boiling point and gravity of the sample. To improve air quality, more severe restrictions are placed on the sulfur and aromatic contents of diesel fuels. In recent years the proportional demand for heating oils has decreased as LPG usage has increased. The principal distillate fuel oils consist of No. It is composed of the heaviest parts of the crude and is generally the fractionating tower bottoms from vacuum distillation.

Currently only low- sulfur fuel oils can be burned in some areas and this trend will continue to expand. Heavy fuel oils with very low sulfur contents are much in demand and sell at prices near those of the crude oils from which they are derived.

NOTES 1. Bland and R. Davidson, Eds. Gruse and D. Stevens, Chemical Technology of Petroleum, 3rd Ed. NPRA Survey, Gas Processors Assoc. Reno, U. Bozzano, and W. Unzelman, Oil Gas J. Newsletter, Oil Gas J. The chemical compositions of crude oils are surprisingly uniform even though their physical characteristics vary widely. The elementary composition of crude oil usually falls within the following ranges. The U. The gravity of these two fractions is used to classify crude oils into types as shown below.

Each crude is compared with the other feed- stocks available and, based upon the operating cost and product realization, is assigned a value.

Product Details

The more useful properties are discussed. Crude oil gravity may range API gravi- ties are not linear and, therefore, cannot be averaged. The sulfur content is expressed as percent sulfur by weight and varies from less than 0. Crudes with greater than 0. There is no sharp dividing line between sour and sweet crudes, but 0.

The carbon residue is roughly related to the asphalt content of the crude and to the quantity of the lubricating oil fraction that can be recovered. In most cases the lower the carbon residue, the more valuable the crude. If the salt is not removed, severe corrosion problems may be encountered. If residua are processed catalytically, desalting is desirable at even lower salt contents of Crude oils show a narrower range of KW and vary from The correlation index is useful in evaluating individual fractions from crude oils.

Crudes containing nitrogen in amounts above 0. Distillation Range The boiling range of the crude gives an indication of the quantities of the various products present.

The most useful type of distillation is known as a true boiling The The TBP cut point for various fractions can be approximated by use of Figure 3. Metals Content, ppm The metals content of crude oils can vary from a few parts per million to more than ppm and, in spite of their relatively low concentrations, are of consider- able importance [4].

Minute quantities of some of these metals nickel, vanadium, and copper can severely affect the activities of catalysts and result in a lower- value product distribution. Vanadium concentrations above 2 ppm in fuel oils can lead to severe corrosion to turbine blades and deterioration of refractory fur- nace linings and stacks [2].

The metallic content may be reduced by solvent extraction with propane or similar solvents as the organometallic compounds are precipitated with the asphaltenes and resins. The composition of the total mixture, in terms of elementary composition, does not vary a great deal, but small differences in composition can greatly affect the physical properties and the processing required to produce salable products. Petroleum is essentially a mixture of hydrocarbons, and even the non-hydrocarbon elements are generally present as components of complex molecules predominantly hydrocarbon in char- acter, but containing small quantities of oxygen, sulfur, nitrogen, vanadium, When the number of carbon atoms in the molecule is greater than three, several hydrocarbons may exist which contain the same number of carbon and hydrogen atoms but have different structures.

Figure 3. The general formula is CnH2n. There are many types Figure 3. Some typical naphthenic compounds are shown in Figure 3. Aromatic hydrocarbons con- tain a benzene ring which is unsaturated but very stable and frequently behaves as a saturated compound.

Some cracking of hydrocarbons also occurs. The hot effluent from the reactor is cooled and sent to a high-pressure separator, where hydrogen flashes off and is recycled to the feed stream.

The liquid from the separator is sent to a fractionator, where hydrogen sulfide, ammonia and any low-boiling hydrocarbons are removed, and the remaining naphtha is distilled into fractions of the desired boiling range.

Hydrodesulfurization is applied to other process streams e. The isobutane is used as a feedstock for alkylation; isopentanes and isohexanes are of sufficiently high octane quality to be used directly as gasoline blending stocks.

The feedstock to the isomerization unit must be both dehydrated and desulfurized. Sweet, dry feedstock is mixed with hydrogen, heated to reaction temperature and catalytically hydrogenated to remove any benzene and olefins. It is then mixed with hydrogen chloride or organic chloride and passed over a fixed bed of chlorinated platinum-aluminium oxide isomerization catalyst, where straight-chain hydrocarbons are converted to isoparaffins.

The effluent product is cooled and passes into a high-pressure separator where recycled hydrogen flashes off. The liquid from the separator is sent to a stripper column where hydrogen chloride is removed.

The resulting isoparaffins are neutralized and sent to storage. In reforming, cycloparaffins are converted to aromatic compounds by a combination of dehydrogenation and dehydro-isomerization.

Some paraffins also form aromatic compounds by dehydrocyclization. Hydrogen is a net product of reforming, which can be used in the hydrotreating and hydrodesulfurization units of a refinery. The naphtha feedstock is mixed with hydrogen and heated by exchangers almost to reaction temperatures. The mixture then passes through a series of alternating furnaces and fixed-bed reactors usually three or four containing a platinum or platinum-rhenium on alumina catalyst.

The furnaces maintain the reaction temperatures between the catalyst beds. The reactor effluent is cooled by heat exchange and sent through a separator where hydrogen is flashed off. The liquid from the separator is taken to a stripping tower where light ends are removed.

The stabilized reformate is sent to storage or is further refractionated in a second tower. Since platinum catalysts are subject to poisoning by sulfur and nitrogen, reforming units require prior hydrodesulfurization of the naphtha feed or contain a pretreater containing a non-noble metal catalyst through which the feedstock and hydrogen pass before entering the main reaction vessels.

The operating conditions depend somewhat upon the boiling range of the feedstock and the activity of the catalyst. Although this is essentially a petrochemical operation, the facility is often integrated into larger refinery complexes.

Naphtha from steam cracking typically has very high concentrations of benzene see IARC, , b , and, since approximately the early s, benzene has normally been extracted from naphtha for its commercial value.

After mild hydrotreating to saturate olefins and polyolefins that cause instability and gum formation, naphtha from which the benzene has been removed may be blended with other streams to produce gasoline with the required performance specification.

Depending on the nature of the feedstock, the steam cracking process generates residual tars which may sometimes be blended in small quantities into residual heavy fuels. This is a frequent practice in refineries that utilize relatively low-sulfur crude oils. With such crude oils, it is more economical to eliminate the odour problem by chemical means than by removing the sulfur in a hydrodesulfurization unit.

In all sweetening processes, the stream to be treated is put into contact with an oxidizing agent, with or without a catalyst. Caustics or hypochlorites are commonly used, and a variety of processes can be used to treat mercaptans in virgin streams. Inhibitor and air—cresylate sweetening are frequently used in combination for catalytically cracked naphthas.

In inhibitor sweetening, mercaptans are oxidized in the presence of a phenylenediamine see IARC, , b inhibitor, trace amounts of caustic and olefin. The requirement that olefins be present makes the process well suited for the treating of catalytic naphthas; however, the reaction is relatively slow and the process is therefore usually used in combination with air-cresylate sweetening which uses the cresols present in catalytic naphthas as both solvents and oxidation catalysts.

Although still in use in many refineries, this process is gradually being replaced by Merox sweetening. It then passes to a settler where caustic and excess air are removed and the caustic is recirculated back to the mixer. Any caustic which remains dispersed in the treated product is removed in a sand coalescer.

The sour straight-run kerosene [5] feed is mixed with hydrogen, heated in a fired heater and then passed through a fixed-bed reactor containing a nickel- see IARC, , b or cobalt-molybdenum catalyst. Organic sulfur is removed as hydrogen sulfide. The reactor effluent is cooled, usually by heat exchange with the feed, and the excess hydrogen is separated and recycled.

It is then reheated and steam-stripped to remove dissolved hydrogen sulfide. Any olefins are also saturated. Some cracking into lighter components will occur. The feed to the hydrodesulfurization unit is a sour gas oil from the crude distillation tower. The feed is vaporized, mixed with a hydrogen-rich gas stream, heated to reaction temperature and passed through a fixed-bed reactor containing a non-noble metal catalyst, where nitrogen and sulfur are removed as ammonia and hydrogen sulfide.

The hot reactor effluent is cooled and condensed by heat exchange with the feed, and the liquid is sent to a high-pressure separator where the hydrogen flashes off and is recycled.

The liquid from the high-pressure separator then flows to a low-pressure separator where the hydrogen sulfide, ammonia and gaseous hydrocarbons are removed. The effluent product is a stabilized, hydrodesulfurized gas oil of improved colour and odour which is sent to storage for later blending or cracking.

Synthetic crude oil is a wide boiling-range material from which gaseous hydrocarbons, catalytically cracked naphthas [22, 23] and light and heavy catalytically cracked distillates [24, 26, respectively] are fractionated by distillation.

The feed to a fluid-bed catalytic cracker may be any hydrocarbon stock from straight-run kerosene [5] to heavy vacuum distillate [20] or solvent-deasphalted residual oil [32]. A fluid catalytic cracking unit consists of a catalyst section and a fractionating section which operate together as an integrated processing unit.

The catalyst section contains the reactor and regenerator, which, together with the standpipe and riser, form the catalyst circulation unit. The catalyst moves up the riser to the reactor, down through a stripper to the regenerator, across to the regenerator standpipe and back to the riser.

The catalyst is in the form of very small spherical particles which behave like a fluid when aerated with a vapour. Fresh feed and recycling gas oil enter the unit at the base of the riser, where they are vaporized and raised to reaction temperature by the hot catalyst.

The mixture of oil vapour and catalyst travels up the riser into the reactor. Cracking commences in the riser and continues until the oil vapours are disengaged from the catalyst in the reactor.

The cracked products travel through the reactor vapour line to the fractionator. The spent catalyst flows from the reactor to the regenerator where carbon deposits are burned off. In the fractionation section, the reactor effluent is separated from the catalyst and travels to the fractionation section, where it is separated by distillation into a recycling gas oil which is returned to the riser for further cracking into catalytically cracked clarified oil [27], light catalytically cracked distillate [24], catalytically cracked naphthas [22, 23] and wet gas.

Moving-bed catalytic crackers use the same type of catalyst as fluid units but in the form of extruded pellets about 0. They are usually smaller than fluid-bed crackers and generally consist of a catalyst section, contained in a single, tall vessel comprising the reactor and generator, and an associated fractionation section.

The catalyst is moved continuously to the top of the unit by bucket elevator or pneumatic lift pipes and flows downwards at a rate of about 4 ft [1. The reactor is isolated from the surge hopper and regenerator by steam seals. The products of cracking are separated by distillation into a recycling gas oil, catalytically cracked clarified oil [27], light catalytically cracked distillate [24], catalytically cracked naphthas [22, 23] and wet gas.

The feedstocks and operating conditions are essentially the same as those used for fluid-bed catalytic cracking. The process employs high pressure, high temperatures, a cobalt- or nickel-molybdenum catalyst and hydrogen. The reaction section is usually divided into two stages: the first is designed to remove sulfur and nitrogen compounds, while actual cracking takes place in the second stage in the presence of excess hydrogen.

The effluent from the second-stage reactor is fractionated by distillation into the desired products. The usual feed is a straight-run gas oil [7] or other distillate from the crude fractionator.

This separation sometimes referred to as decarbonizing produces an oil for use as a feed to catalytic cracking or for the manufacture of heavy lubricants, and as a raw bitumen see IARC, Deasphalting is usually accomplished by solvent extraction with propane.

The feed to a deasphalting unit is usually a vacuum residue [21], reduced crude oil[8] or any other heavy crude fraction containing bitumen. The feed and liquid propane are pumped to an extraction tower in a controlled ratio and at a controlled temperature. The extraction unit is often a rotating-disc contactor. A separation based on the differences in solubility is effected, producing a solution of deasphalted residual oil and one of bitumen. The effluents are processed by evaporation and steam stripping to recover the propane from the oil and the bitumen.

The charge to the unit, which is typically a waxy reduced crude oil [8], is heated and slightly cracked in the visbreaker furnace. The furnace effluent is quenched with a light gas oil and is fed to the lower or evaporator section of a fractionation tower where it is flashed.

A tar, thermally cracked residue [31], accumulates in the base of the tower, while in the upper part the vapours are fractionated into gas, thermally cracked naphthas [28, 29] and thermally cracked distillates [30]. The tower bottoms are withdrawn and vacuum-flashed in a stripping tower and the vacuum distillate returned to the fractionator.

There are two principal coking processes: the fluid coking process and the delayed coking process. Delayed coking is used most widely; in this process, the charge stock is fed to the bottom section of a fractionation tower where material lighter than the desired end-point of the heavy thermal distillate is removed.

The remaining material is pumped from the bottom of the fractionator to a coking heater, where its temperature is raised rapidly. The vaporized liquid leaving the coking heater enters a coke drum where coke is formed. The coke is recovered by cutting it out of the drum with a high-pressure water stream.

Reduced crude oil [8] is mixed with hydrogen, heated in a fired heater and then passed through a fixed bed of catalyst where the reactions occur. The active components of the catalyst are typically chromium see IARC, , b , molybdenum, iron, cobalt or nickel.

Organic sulfur and nitrogen compounds are converted to hydrogen sulfide and ammonia. The products from the reactor are cooled, usually by heat exchange with the feed, the excess hydrogen flashed off in a high-pressure separator and recycled, and the bulk of the ammonia and hydrogen sulfide removed in a low-pressure separator.

The products are then reheated and steam stripped to remove any residual hydrogen sulfide or ammonia. The desulfurized residue can be blended into fuel or be processed further to recover gas oil.

Worldwide distribution of petroleum refinery operations A general picture of the extent of petroleum refinery operations in various regions of the world can be obtained from data on refinery throughputs Table 3. Between and , the total petroleum throughput of refineries in the developed countries of the western world declined, while in other countries refinery throughput has generally increased. Table 3 Refinery throughputs thousands of barrels daily , — The importance of the various refinery process streams varies somewhat from region to region and even from season to season for individual refineries.

Although detailed data are not available to compare the throughput of various process streams in different geographic regions, regional consumption data for different product groups generally parallel local refinery product distribution, since, historically, refined products are mostly used in the same geographic region in which they are produced.

While there are many exceptions to this generalization e. Table 4 shows the consumption of gasolines, middle distillates, fuel oils and other petroleum products in several regions of the world from to The most notable trends are the worldwide decline in fuel oil production and consumption and the steady growth in production of all products except fuel oil in the lesser developed countries.

Consumption of petroleum products by geographical region millions of tonnes per year. Workers and working conditions It has been estimated that the world petroleum refining industry employs from to persons International Labour Office, in approximately refineries American Petroleum Institute, A wide range of potential occupational health hazards is present in petroleum refineries. Exposures result from skin contact and the inhalation of gases and vapours, mainly hydrocarbons either naturally present in crude oil and emitted during its refining or formed and emitted during one of the many transformations of the various process streams.

Gaseous sulfur compounds such as hydrogen sulfide, sulfur dioxide and mercaptans are emitted during removal and treatment of sulfur. Exposure to dusts and fumes results mostly from maintenance operations such as abrasive blasting, the use of catalysts and the handling of viscous or solid products such as bitumen and coke. In general, it is considered that exposures to hydrocarbons have not been subject to major reductions over the past two or three decades.

Nevertheless, useful reductions have resulted from the gradual introduction of controls over fugitive emissions, increased attention to the control of benzene exposures CONCAWE, and greater automation of refinery operations, including sampling and analysis of streams. Over the last 30 years or so, since a large conference in Page, created a much greater awareness of the potential skin hazards from some mineral oil streams, there has been a significant reduction in skin exposure as a result of more effective use of personal protective clothing, improved personal hygiene and safer operating procedures.

The petroleum industry has reached a stage of high automatization, with a concurrent reduction of the work force during the last two decades. It is not known whether such automatization has occurred in all countries to the same extent. Due to the intrinsic risks of fire and explosion from many refinery streams, operations take place in closed systems, and refinery operators spend most of their time in control rooms with little potential exposure to hazardous agents. Ubiquitous exposure exists mainly to hydrocarbon gases and vapours at usually very low levels resulting from constant and fugitive emissions from seals and valves in the complex network of pipes and columns; there is also potential dermal exposure during sampling Darby et al.

Heavier exposures may be encountered, however, during routine maintenance and turn-round operations Dynamac Corp. Outside contractors are often brought in for major turn-round operations. Other groups with potential heavy exposure to such hazards are those in bulk handling of final products and in laboratories Clayton Environmental Consultants, Inc.

A job code classification system for oil refineries has been developed American Petroleum Institute, in which workers can be classified using two standardized variables: process and task. This scheme was devised in order to allow better regroupment of workers who share a set of qualitatively common exposures.

Other exposure-based work category classifications have been devised for both epidemiological purposes Nelson et al. The main substances to which workers may be exposed in petroleum refineries are given in Table 5. The main occupational agents for which airborne exposure levels are available are presented in Tables 6—8. Aliphatic hydrocarbons Nearly all workers in petroleum refineries are exposed to aliphatic hydrocarbons. The principal individual aliphatic hydrocarbon compounds found in petroleum refinery air samples are butanes, pentanes and hexanes, which account for an overwhelming part of the total hydrocarbons measured.

Concentrations of up to hydrocarbons, mostly aliphatic, have been reported in gasoline vapour in gasoline manufacture and distribution operations in Europe CONCAWE, Average exposure levels to hydrocarbons for various categories of workers are summarized in Table 6.

A mean exposure level of 5. In general, gasoline loading operations represent the highest potential for exposure to hydrocarbons. Various short-term and 8-h time-weighted average TWA exposure levels for these operations are summarized in the monograph on gasoline. Data on exposure to 1,3-butadiene are given in the monograph on gasoline.

Aromatic hydrocarbons In petroleum refineries, exposure to aromatic hydrocarbons originates from their presence in crude oils and the conversion of naphthenes and paraffins during the catalytic reforming process. Exposure levels to benzene and toluene in various work situations are summarized in Table 7. Group average exposures of production and maintenance workers to benzene vary from about 0.

Petroleum Refinery Engineering

The highest values have been observed during gasoline drumming operations without good local exhaust ventilation. Various short-term and 8-h TWA exposure levels for these operations are summarized in the monograph on gasoline. The refinery under investigation included benzene petrochemical units Tsai et al.

Full-shift personal exposure measurements have also been obtained for 29 work categories in two French refineries, including work in catalytic cracking and reforming units.

At one US refinery, of 75 samples taken around a catalytic cracking unit, 61 contained less than 0. In , the American Petroleum Institute commissioned a study of exposure to benzene in petroleum companies over the period —84 Spear et al.

Personal exposure data submitted by nine refining companies were analysed in detail to characterize the distribution of exposures within work operations and job categories; the data covered location- and unit-specific job categories.

Most 8-h TWA exposures were reported to be below 1. Some short-term exposure data min TWA were also submitted; most showed levels below 1. These situations frequently involved loading and unloading of barges or tanker trucks. Several other mononuclear aromatic hydrocarbons were monitored in the CONCAWE study on gasoline and refineries, including toluene, the xylenes, the trimethyl-benzenes and isopropylbenzene cumene.Reaction Kinetics 7.

Thermodynamics of Hydrotreating 7. Coke deposition Due to the coke deposited on the active surface, the catalyst is required to be regenerated. Biological monitoring data on benzene exposure of gasoline-exposed workers are summarized in the monograph on gasoline. Catalog section from p. The middle distillates from the crude unit, coker, and cracking units are blended into diesel and jet fuels and furnace oils. Refinery Economic Evaluation Please see your emails regularly.

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