An oil refinery is an industrial plant, of the oil raw material by purification and distillation under normal pressure and under vacuum in fractions with a defined boiling range transferred. The additional refinement of the boiling cuts is done by methods such as extraction or chemical cleaning methods. To increase the quality of products, such as their octane number, conversion processes such as isomerization or catalytic reforming are used. In addition, additives are added to products that improve or suppress certain properties.
Higher value products are obtained, such as gasoline, diesel, diesel or kerosene. For the chemical industry, raw materials such as liquefied petroleum gas, naphtha and middle distillate are produced. Oil refineries are usually large industrial complexes whose image is made up of extensive tank parks, rectification columns, pipe systems and flare systems. Oil refineries are considered energy intensive businesses. The high energy input required (up to 50% of costs) for production is obtained in part from the primary energy carriers themselves, and is supplied as electrical energy and thermal energy.
History of refineries
The first oil refineries were already built at the beginning of the era of mineral oil, that is, in the middle of the 19th century. The first refinery was established in 1856 by Ignacy Łukasiewicz, the inventor of the kerosene lamp, in Ulaszowice (Poland). After it was destroyed by fire, another more modern refinery was built in Chorkówka. Very quickly, the luminescent oils derived from petroleum began to replace the fuels for lamps that until now had been obtained from animal fats, in particular Waltran, for which first a treatment of crude oil by distillation was necessary.
The distillation of the recovered oil was carried out very simply. For this purpose, a copper kettle was filled with approximately 750 liters of oil and the contents of the kettle were boiled. The resulting vapors were passed through a system of cooling tubes where they condensed. In this way, oil, which was used for lighting in kerosene lamps, won. The tar residue left in the boiler was removed as waste.
The exploitation of other petroleum products, and in particular the rapid spread of internal combustion engines after the First World War, not only required the construction of many new refineries, but also led to a rapid development of the process of refinery.
As in many other industries, the requirements for a refinery, and in particular for products, have changed over the years. Basically, here is the adaptation of the product specification to the call, which has changed due to the laws (environment and health). For example, the sulfur content allowed in most fuels and also heating oil decreased.
Raw materials: oil
The oil consists of a mixture of hydrocarbons. The most frequently represented are linear or branched alkanes (paraffins), cycloalkanes (naphthenes) and aromatics. Each oil has a specific chemical composition, depending on the location, which also determines physical properties such as color and viscosity.
Oil contains, to a lesser extent, carbon compounds that contain nitrogen, oxygen or sulfur, such as amines, porphyrins, mercaptans, thioethers, alcohols and quinones. In addition, there are metal compounds such as iron, copper, vanadium and nickel. The proportion of pure hydrocarbons varies considerably. The proportion varies from 97% to only 50% for heavy oils and bitumen. The carbon content is between 83 and 87%, the hydrogen content between 10 and 14%. Other elements of the main group are between 0.1 and 1.5%, the content of metal compounds is less than 1000 ppm.
Typical crude oils differ according to the deposit. The West Texas Intermediate (WTI) is a light, low-sulfur, and high-quality light crude from Cushing, Oklahoma. A European representative is Brent Blend, a crude oil from the 15 existing Brentsystem oil fields in the North Sea. The Dubai and Oman in the Middle East is mainly promoted for the Asia-Pacific market. The Tapis of Malaysia is light, Mines of Indonesia is a heavy crude of the Far East.
The finished products can be gaseous, liquid or solid. Percentage, the performance of a modern refinery is approximately 3% of liquefied gases, such as propane and butane. Around 9% are derived from petroleum (naphtha) and 24% from gasoline ( gasoline). Higher-boiling fuels, such as jet fuel (kerosene), account for 4%, diesel fuel and light fuel up to 21%, heavy fuel 11%.
Solid and high viscosity components, such as bitumen or fuel oil, are weighed at 3.5%, lubricants at 1.5%. Around 2% is accounted for by other products or losses. Depending on the degree of additional processing, the own consumption of the refinery is between 5 and 10% of the crude oil used. The MiRO, for example, has 16 million tons of crude capacity, which is processed in 14.9 million tons of final products, which means that self-consumption is around 7%.
The quantities of finished products depend, on the one hand, on the types of crude oil used and, on the other, on the processing plants available at the refinery. Therefore, "light" crude oils contain relatively high levels of light products, that is, low density, such as LPG, kerosene, gasoline, diesel. Heavy crudes contain large amounts of heavy products, such as heavy fuel oil and bitumen.
In modern refineries, some of these heavy components can be converted into lighter ones, such as cracking, so that a refinery of this type can process more heavy crude.
The oil extracted from the tanks is treated in the place before transport to the refinery, essentially by thick separation of undesirable components, such as sediments and water. After these initial processing steps, the crude oil that is produced is now delivered to the refinery by ship or pipeline. Here, the liquid mixture is separated in additional steps with a special distillation process in different fractions and processed into salable products. Technology is so advanced today that no substance of crude oil remains unused. Even the refinery gas produced is used as an undesirable by-product. It is used directly in process ovens as an energy carrier or used in chemical processing as synthesis gas.
Petroleum purification / desalination
Oil / crude oil is already released in the sand and water tank. To avoid corrosion in the equipment, the crude oil is desalinated (up to a salinity <10 ppm), adding water, an emulsion of crude oil and water is produced. The salt dissolves in the aqueous phase of this emulsion. Then, the emulsion is re-separated in an electrostatic desalter, the saline water is deposited on the bOttom and fed to the appropriate treatment plants, and the desalted crude oil is pumped for distillation.
The refraction of the emulsion occurs at elevated temperatures of approximately 130 ° C to decrease the viscosity of the crude and voltages of approximately 20 kV. Working at high pressure prevents the volatiles from evaporating during this process step. The oil and water emulsion can also be broken by adding suitable chemicals, called demulsifiers.
Primary processing (distillation of crude oil)
After desalting, the crude is heated in two stages. The preheating is carried out in heat exchangers by recovering the heat of the expired product. The maximum preheating is carried out by ovens up to approximately 400 ° C. The heated oil is purified by rectification in a column up to 50 m high. Separated in its components. Crude enters the column in a two-phase flow (gaseous / liquid).
The temperature profile drops towards the top. Since the temperature in the sump, that is, in the lower part of the column, is higher and the light components can not condense, they continue to increase in gaseous form.
At the top of the column, gas and light gasoline, called naphtha, including, kerosene, intermediate for turbine-propelled aircraft (not to be confused with the so-called "airplane fuel", the AVGAS for ottmotorenen aircraft), fuel Diesel and light fuel (Gas oil and diesel heating - Stock) and in the lower part - the lower part of the column - the atmospheric waste (in English: Long waste). This first rectification takes place at atmospheric pressure and, therefore, is referred to as atmospheric rectification.
The residue is redistilled in another low pressure rectification column (usually ~ 20 mbar) to decompose it in other products (see vacuum distillation). Vacuum rectification is necessary because the chain length of the high-boiling hydrocarbons is higher and, at high temperatures, above 400 ° C, they tend to break thermally instead of separating by distillation. The products of vacuum distillation are vacuum gas oil and the so-called "short residue".
Conversion and mixing method
After primary processing, a variety of finishing processes are used to remove contaminants (sulfur, nitrogen) and improve the quality of the intermediates. Subsequently, the final products, such as motor gasoline, Jet A-1, diesel fuel or fuels of various intermediate compounds / components mixed together (lattices), which are produced in the manufacturing processes mentioned below.
The components of fractional distillation (naphtha, middle distillates, vacuum gas oils) are still rich in sulfur compounds. These could poison the catalysts during further processing (catalytic reforming, see below). Direct burning of untreated products (heating oil) would produce environmentally damaging SO 2. In hydrotreating, the components to be desulfurized are mixed with hydrogen and heated to about 350 ° C. The hot mixture enters a reactor filled with nickel, molybdenum or cobalt catalysts on alumina that reacts hydrogen with the sulfur, nitrogen and oxygen compounds to produce hydrogen sulphide, ammonia and water.
The catalytic reforming aims to increase the octane rating of naphtha (boiling range ~ 70-180 ° C) and produce aromatic hydrocarbons. In addition, hydrogen is obtained as a product that is used in hydrotreating and hydrocracking processes. The reforming is carried out at approximately 500 ° C and, depending on the type of process, from 3.5 to 40 bar. Bifunctional catalysts (platinum-tin or platinum-rhenium, on chlorinated aluminum oxide or zeolites) are used.
In the metal centers of the catalyst, the hydrogenation / dehydrogenation reactions are preferably carried out, while the acid sites catalyze the isomerization and ring closure reactions. An undesirable secondary reaction is the coking of the catalyst by polymerization and dehydrogenation reactions. The coke is removed by burning the coke and then oxychlorinating the catalyst.
In the isomerization are n -alkanes in iso -alkanes converted with the goal of improving octane or changing the substitution pattern in the aromatic. Therefore, meta-xylene in o- and p isomeriza-xylene, since these for the preparation of phthalic anhydride or dimethylose terephthalate used. There are catalysts similar to those of the catalytic reform in use. The reaction is carried out at lower temperatures, around 250 ° C and, to prevent deactivation of the catalyst by coking, at a moderate partial pressure of hydrogen of about 15 bar. Due to the moderate conditions compared to the catalytic reforming process, cracking and ring closure reactions are largely suppressed.
Other isomerization processes refer to the conversion of n-pentane to isopentane or n-hexane to isohexane (improvement of the octane number, for example, Hysomer process, PENEX process).
In alkylation are iso-alkanes (isobutane) and alkenes (n - and iso -) under acid catalysis to form higher molecular weight high octane iso -alkanes (C 7 -C 12) implemented. This is how isobutene and isobutane react. to. to 2,2,4-trimethylpentane (isooctane). The reactants are reacted in the liquid phase in an excess of alkane with concentrated sulfuric acid or anhydrous hydrofluoric acid.
The typical residence time is about 10 to 15 minutes. From then on, the liquid phases are separated by the sedimentation of the phases. In the so-called iso-stripper, the iso-Alcan is separated and returned to the process (recycled). The finished final product is known as alkylate. The process is suitable if the refinery has steam or catcracker and, therefore, can supply the starting materials for alkylation.
There are three main cracking groups: thermal, catalytic and hydrocracking.
When thermal cracking there are no catalysts. As a result, residues from petroleum distillation can be supplied, which would damage the catalyst during catalytic cracking due to its heavy metal and sulfur content.
When visbreaking z. B. is the cracking of heavy residual oils in moderate residence times and temperatures around 500 ° C in order to produce diesel. The diesel (and lighter) performance is around 30% for the icebreaker. The subsequent distillation separates the volatile fractions.
In delayed coking, petroleum coke is recovered by thermal cracking of the vacuum distillation residues. For this purpose, the residual oil is heated to approximately 500 ° C and pulverized in coking chambers, where it is converted into petroleum coke, liquid and gaseous hydrocarbons. After coking, the coke is mechanically separated and, if necessary, released from volatile compounds in calcination furnaces at temperatures of 1200 ° C.
However, naphtha, diesel or even hydrogenated gas oils under vacuum (Hydrowax, Hydrocracker BOttoms) can also be thermally cracked by the so-called steam cracking of ethene, propene and aromatics. to produce
During catalytic cracking are acid silicates as catalysts, the starting materials are atmospheric heavy oil gas oil or vacuum gas. The products are predominantly short-chain olefins and alkanes.
When hydrocracking long chain alkanes they become the hydrogen feed in short chain alkanes. At higher partial pressures of hydrogen, even the aromatics are hydrogenated and, therefore, cycloalkanes are generated. The educt used is predominantly vacuum gas oil. Most of the sulfur and nitrogen compounds of the reactant to be hydrogenated, so that substantial volumes of H 2 S and NH 3 are incurred.
The hydrotreating, hydrocracking and the necessary production of synthesis gas from heavy oil produce considerable quantities of H 2 S, which can not simply be "burned". In the Claus process, the resulting hydrogen sulfide is burned in a substoichiometric manner with atmospheric oxygen in a reactor. The resulting SO 2 is decomposed with residual H 2 S in elemental sulfur and water.
Initially incomplete reaction is conducted through several catalytic stages at lower temperatures to complete the conversion.
In another process (WSA process, wet sulfuric acid), sulfuric acid is produced directly from hydrogen sulfide.
Protection of the environment, occupational safety and plant safety
Process equipment, tank tanks and piping systems are subject to extensive safety measures. The objective of plant safety and accident prevention is to prevent disturbances and limit the effects of disturbances that still occur on people and the environment.
Facilities for the production, storage and extraction of crude oil and its derivatives require a permit in Germany in accordance with the Federal Law of Control of Immission. This requires that the plants be constructed and operated in accordance with the state of the art. In addition, the applicable technical standards must be followed. Requirements for the management of water polluting substances arise from the Water Resources Law.