книги / Переработка нефти и газа

Федеральное агентство по образованию

Государственное образовательное учреждение высшего профессионального образования «Пермский государственный технический университет»

В.Г. Рябов, Н.Н. Старкова, Л.Г. Тархов, А.В. Кудинов

V.G. Ryabov, N.N. Starkova,

L.G. Tarkhov, A.V. Kudinov

ПЕРЕРАБОТКА НЕФТИ И ГАЗА

OIL AND GAS REFINING

Утверждено Редакционно-издательским советом университета в качестве учебного пособия

Издательство Пермского государственного технического университета

2008

УДК 665.62/.63+665.65/.66](075.8)=111 ББК 35.514я73

П 271

Рецензенты:

канд. хим. наук, доцент С.Н. Пепеляев (Пермский государственный технический университет);

канд. хим. наук, главный специалист Н.П. Углев (ООО «ЛУКОЙЛ-Пермнефтеоргсинтез»)

Переработка нефти и газа: учеб. пособие / В.Г. Рябов, Н.Н. Старкова, П 271 Л.Г. Тархов, А.В. Кудинов. – Пермь: Изд-во Перм. гос. техн. ун-та,

2008. – (На англ. языке). – 103 с.

ISBN 978-5-88151-946-9

В пособии излагаются следующие темы: первичная переработка нефти, вторичная переработка нефти и очистка нефтяных фракций с целью получения товарных нефтепродуктов, вторичная переработка нефти с целью получения топлив, переработка газа. Кроме этого, приведены описания четырех практических занятий по определению состава и свойств нефти и нефтепродуктов.

Пособие рассчитано на специалистов Республики Ирак, обучающихся в Пермском государственном техническом университете по дополнительной образовательной программе профессиональной переподготовки специалистов «Руководитель нефтегазового производства».

Oil processing. Oil refining and oil cut treating commercial oil production. oil refining. Fuel production. Gas processing. Laboratory course on oil refining and oil cut treating commercial oil production

The textbook is destined for the Iraq Republic specialists studying on the extra educational program of professional retraining «Oil and gas production manager» at Perm State Technical University.

УДК 665.62/.63+665.65/.66](075.8)=111 ББК 35.514я73

Course of lectures on

OIL PROCESSING

INTRODUCTION

Oil processing is a sector of basic industry. It covers oil and gas condensate processing and high-quality oil product production, such as motor and power-generating fuels, lubricating and special oils, bitumen, oil coke, waxes, solvents, petrochemical industry raw materials and other products.

Industrial oil and gas condensate processing at modern oil refineries is a complex multi-staged physical and petrochemical processing in separate or integrated highcapacity process units and plants designed for producing various components or wide range of commercial oil products.

1. OIL REFINING SEGMENTS

Depending on the need for this or that oil product, physicochemical properties of oil, and the level of technology development, the produced oil or gas condensate are refined according to one segment of the following three: fuel, fuel and oil, or complex (petrochemical) segment.

The fuel segment means that oil and gas condensate are refined mainly to produce motor fuels and fuel oils. This segment can be non-deep and limited to withdrawing only the potential contents of motor fuels (not more than 55–60 mass %), or heavy (deep), which is characterized by a high yield of light oil products (initial boiling point 360°C) and a low yield of fuel oils. Deep refining ensures a maximum yield of high-quality motor fuels by engaging residues of distillation at the atmospheric pressure and under vacuum, as well as refinery gas in the production process. In this case, the depth of oil refining reaches 70–90 mass %.

In this connection, the number of the processe for producing additional light oil products from fuel oils (catalytic cracking, hydrocracking, coking, thermal cracking) or improving their qualitative characteristics (reforming, isomerization and hydrotreating), also grows. Non-deep refining is characterized by a small number of processing plants.

Under the fuel and oil segment, oil is refined to produce not only fuels, but also various mineral oils at the same time. Therefore, it becomes necessary to apply

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additional processes, which make it posssible to remove distillate and residual oil cuts from oil, to remove asphaltic-resinous components from them (solvent refining with phenol, furfurol, or N-methyl pyrrolidone, and deasphaltizing), to remove n-paraffins (dewaxing), and to perform advanced treatment of oil cuts and paraffins (bleaching earth treating and hydrotreating).

Under the petrochemical segment, oil yields not only fuels, oils, and other oil refinery products, but also raw materials for petrochemical industry and oil synthesis products. In this connection, refineries are additionally equipped with processing units for preparation of raw materials for synthesis (pyrolisis, dewaxing of oils and diesel fuels, precise fractionation, isomerization, reforming with a unit for extraction of aromatic hydrocarbons, production of the synthesis gas, etc.) and for synthesis (production of ethyl benzene and styrene, aldehydes and ketones, alcohols, acids, synthetic rubber and fibers, etc.).

Selection of specific line and, correspondingly, crude oil processing flows, range of oil products mainly depends on oil quality, its individual fuel and oil cuts, quality requirements for commercial oil, and the corresponding needs of the given economic region.

It is possible to estimate tentatively the potential of crude oil by considering the set of the indicators included in the technological classification of oil. However, such indicators are insufficient to determine the package of technological processes, oil product quality and range, and calculate the material balance of processing units, production, and refinery as a whole. To this effect, Reaserch and Development laboratories perform accurate studies to reveal all the indicators of the initial crude oil quiality required for project development, of its narrow cuts, fuel and oil components, intermediate stock for technological processes, etc.

2. METHODS OF PROCESSING OIL AND OIL CUTS

Oil recovered from the Earth interior is a complex mixture of hydrocarbons and heterocompounds (with intermediate structures). Along with that, oil includes many compounds with non-carbon structures (sulphur, nitrogen, oxygen compounds, etc.). Therefore, to produce oil products for different purposes, oil is processed at refineries using various methods. All the methods used for oil processing can be subdivided into two major groups: physical (mass-transfer) methods, which are not connected

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with chemical transformations of the compounds contained in oil (they are based on the differences in the physico-chemical properties of hydrocarbon and nonhydrocarbon oil components), and chemical methods connected with chemical transformation of oil compounds.

In terms of the mass transfer type, physical processes can be subdivided into the following categories:

–gravitational (electrical desalting plants, ELOU)

–fractionating (atmospheric (single-flash) pipe still – AT), atmospheric-vacuum (atmospheric-vacuum pipe still – AVT), gas-fractionation plant (GFU), etc.);

–extraction (deasphaltizing, solvent refining, crystallization dewaxing);

–absorption (absorption gas fractionation plant (AGFU), Н2S and СО2 removal).

In terms of activation of chemical reactions, the chemical processes used in modern refineries are subdivided into:

–catalytic, and

–thermal.

In terms of the type of proceeding chemical reactions, thermal processes can be subdivided into the following categories:

–thermal decomposition (thermal cracking, visbreaking, coking, pyrolysis, pitching, production of carbon black, etc.); and

–thermal-oxidative processes (production of bitumen, gasification of coak, coals, etc.).

The reactions proceeding in the thermal-decomposition processes are mainly the reactions of decomposition (cracking) of raw molecules into low-molecular compounds, and the condensation reactions resulting in formation of high-molecular products, e.g. pitch, etc.).

In terms of the type of catalysis, catalytic processes can be subdivided into the following categories:

–heterolytic, which proceed following the acid-catalysis mechanism (catalytic cracking, alkylation, polymerization, production of esters, etc.);

–homolytic, which proceed following the mechanism of the oxidation-reduction (electron) catalysis (production of hydrogen and synthesis of gases, methanol, elemental sulfur); and

–hydrocatalytic, which proceed following the mechanism of the bifunctional (complex) catalysis (hydrofining, hydraulic desulfurization, hydraulic cracking,

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catalytic reforming, isomerization, hydraulic dearomatization, selective hydraulic dewaxing, etc.).

Let us consider in more detail the physical processes of oil and gas condensate processing, especially: the processes of oil and oil cut (or gas condensate) treatment before processing and refining (or gas condensates) to closer cuts and individual hydrocarbons.

3.OIL TREATMENT BEFORE PROCESSING

3.1.Detrimental Impurities in Oils and Their Influence on Oil Transportation and Processing

Along with various hydrocarbons and heterocompounds, oil recovered from the Earth interior contains gaseous (under normal conditions) hydrocarbons dissolved in the liquid oil component, Н2S, CО2, nitrogen, helium, and other inorganic gases, particles of sands and clays, and other mechanical impurities, water and inorganic salts dissolved in it. Whereas light gaseous components leave oil mainly with hydrocarbon gases when oil is separated and do not affect oil processing further, mechanical impurities, water, and salts greatly affect oil processing and, primarily, straight distillation.

As a rule, the content of mechanical impurites in oil does not exceed 1.5 mass %, and they are not specially removed. They are separated simultaneously with the process of oil dehydration. On the contrary, the content of salts and water can vary in a very wide range. Especially, the content of salts can be 1800 mg/l and more, and the content of water can reach 98 mass %, especially when oil is recovered by using various types of productive formation flooding.

At the same time, refineries should receive oils containing not more than 0.2 mass % of water and not more than 100 mg/l of salts (group 1), not more than 300 mg/l of salts and more than 0.2 mass % of water (group 2), and not more than 1800 mg/l of salts and not more than 1 mass % of water (group 3). As a rule (in 90 % of cases), refineries receive oils of the first and second quality groups.

What is the detrimental effect of mechanical impurities, salts and water on oil processing?

Mechanical impurities cause corrosion of equipment and pipelines, deposting in equipment and, especially, on heat-exchanging surfaces, and enhance stability of oil- in-water emulsion.

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Salts, especially chlorides, undergo hydrolysis at higher temperatures (above 100°C), which lead to formation of hydrogen chloride, which, in its turn, intensifies equipment corrosion. Of the chlorides, one most susceptible to hydrolysis is МgCl2 (by 90 %). СаСl2 is hydrolyzed by 10 %, NaCl is almost unsusceptible to hydrolysis. Hydrolysis of chlorides proceeds as follows:

The corrosion is even stronger, if oil contains Н2S. Hydrogen sulfide is a very aggressive gas, and it reacts with equipment metal to form FeS which protects the metal from further corrosion. However, the presence of HCl destroys such protective film:

The formed FeCl2 is water-soluble and leaves the surface of metal. Naked metal reacts with Н2S again.

Water contained in oil, first, causes waste expenditures when water-cut oil is pumped from the field to a refinery. Second, it intensifies equipment corrosion and leads to foaming, which hampers the fractionating process during the straight oil distillation in atmospheric-vaccum pipe still processing units.

In terms of its parameters, oil received from the field at a refinery cannot be processed directly and is treated additionally under refinery conditions in electric desalting plant processing units. In accordance with modern requirements, oil received after electric desalting plant must contain not more than 3–5 mg/l and not more than 0.1 % of water (group 2) and less than 3 mg/l of salts and 0.1 % of water (group 1). The content of mechanical impurities must not exceed 0.02 %.

3.2. Oil Dehydration and Desalination.

Dehydration and Desalination Processes

As a rule, water recovered along with oil is dispersed in it, and we have to deal with oil emulsion when recovering, transporting, and treating oil. Such emulsions are formed due to turbulation of water-oil mixture as it flows along the borehole, through valves, chokes and pipelines.

Oil emulsions are dispersed systems consisting of two unsoluble fluids: water and oil. The most typical emulsion is water-in-oil (hydrophobic, or invert emulsion) emulsion. At the same time, oil-in-water (hydrophilic) emulsions can be found when developing

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old oil fields. Emulsions of such type are also dealt with when formation water is terated before injection.

The structure of oil-water emulsions can be schematically represented as follows: water globules have diameters from 0.1 to 1000 micrometers, and each of them is surrounded with solvate shell: a concentrate of high-molecular polar compounds contained in oil, i.e. emulsifiers. Substances with a high surface activity act as emulsifiers of oil emulsions. The latter are: asphaltenes, resins, high-melting paraffins, high-dispersive solids (mineral and carbonaceous suspensions). In this case, stability of emulsions depend not so much on the concentration of the said emulsifiers, as on the degree of their colloidicity. The availability of adsorption layer prevents merging of globules when they collide.

Formation of adsorption layers starts immediately at the moment when water splits into small globules and continues for the enitre life of emulsion. Due to that, the longer the emulsion exists, the greater is the thickness of the solvate shell, and the stronger is its protective effect.

The most important properties determining the destruction resistance of oil emulsions is its dispersion ability, i.e. the size of globules of the substance in the disperse phase. Dispersion ability is expressed either through the diameter of the particles, or through the specific surface of the disperse phase (the ratio of the total phase surface to its volume).

where dw is the average diameter of water globules.

Depending on the value of dw emulsions are subdivided into colloidal (dw < 0.1 µm), finely dispersed (dw = 0.1–20 µm), medium-dispersion (dw = 20–50 µm), and coarse (dw > 50 µm).

Oil emulsions after field treatment can be regarded as finely dispersed (dw = 0.1–20 µm). The smaller is the diameter of the globules, the slower will be the rate of the globule's subsidence, and the more stable the emulsion will be. The rate of globule subsidence under static conditions (low values of the factor Re, <1) can be expressed by the following equation:

where dw is the diameter of water globules, m; ρw and ρo is water density and oil density, kg/m3, and ηo is dynamic viscosity of oil, Pa sec.

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The strength of solvate shell of the globules in the disperse phase and, consequently, stability of the emulsion depends on pH factor of the medium. In this case, pH of the medium affects the strength of the solvate shell depending on its content. Especially, the strength of the shell formed by asphaltenes is higher in an acid medium and minimal, in the alkaline one. For resins, dependence is opposite: the strength is higher in alkaline media.

The stability of oil emulsions is also impacted by physicochemical properties of oil and chemical composition of water. For example, the higher the water density tr and the lower the oil density, the lower the oil viscosity, the higher the rate of globule subsidence, and vice versa.

Another factor of emulsion stability is temperature.

It affects both oil density and oil viscosity, especially, it reduces the corresponding values. As the temperature rises, the composition and thickness of the adsorption layer change, which also impacts the emulsion stability.

Oil Emulsion Destruction Methods

The methods used to destroy oil emulsions can be subdivided into three basic groups: mechanical, thermochemical, and electrothermochemical.

Mechanical methods of oil emulsion destruction are: gravitational segregation or settling, centrifugal separation, and filtration. We will consider each method in more detail.

Gravitational Segregation or Settling

Such method is used to remove the main water content from oil by settling it without heating, as a rule, in the presence of demulsifying agents. The rate of particle subsidence during settling obeys the Stokes law:

In its pure form, this method is used only to remove the main amount of water from the emulsion treated with a demulsifying agent. This is a mandatory element in all thermochemical and electrothermochemical processing units.

Centrifugal Separation

The efficiency of mechanical emulsion segregation can be improved significantly if one affects the emulsion with a centrifugal force, i.e. subjects it to centrifugal separation. In this case, water globules are affected by the centrifugal force equal to

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Fc = m r n2|900, where m is the mass of the globule, kg; r is the rotation radius, m; and n is the rotation frequency, rpm.

The rate of subsidence of a particle in a centrifugal machine, for particles with the same mass is by an order or two faster than the rate of gravitational segregation. Due to this fact, the efficiency of emulsion destruction in centrifugal machines is very high. However, due to the complexity of implementation and a low output of centrifugal machines, this method of oil emulsion destruction has not received recognition from industry.

Filtration

This method is based on selective wetting of the filter material by substance in the disperse phase. For invert emulsions (with water as the disperse phase), glass wool, sand, gravel, wooden and metal shavings, etc. are used as filtering materials.

Filtration is fairly efficient method for emulsion breaking. However, its industrial application for oil emulsion destruction is impeded by fast depositing of asphaltoresinous oil compounds on filter material.

Thermochemical methods

Such oil emulsion destruction methods combine the effect of chemical demulsifying agents and thermal energy. The use of demulsifying agents is based on the change in the strength of the adsorption layer on water globules due to a) displacement of molecules or emulsifying particles by a substance with a higher surface activity but lower strength of the newly formed adsorption layer; b) chemical interaction with emulsifying components and destruction of the adsorption layer; and c) formation of the emulsion of the opposite type (phase inversion).

As a result, the layer of emulsifying agents surrounding a water globule is destroyed, or its strength and protective properties are reduced. The globules coalesce and subside by gravity. The main requirements for demulsifying agents and their properties are as follows:

–they should not interact with the main substance of oil, and change oil properties;

–they should not cause equipment corrosion;

–they should have high demulsifying activity ensuring low consumption rates;

–they should be easily removable from waste waters;

–they should be non-aggressive; and

–they should be cheap and easily available.

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