An oil refinery is an industrial plant, from the oil raw material by purification and distillation under normal pressure and under vacuum into fractions with a defined boiling range transferred. Further refinement of boiling cuts is done by methods such as extraction or chemical cleaning methods. To increase the quality of the 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, gas oil or kerosene. For the chemical industry, raw materials such as liquefied petroleum gas, naphtha and middle distillate are produced. Oil refineries are often large industrial complexes whose image is made up of extensive tank farms, rectification columns, piping systems and flare systems. Oil refineries are considered energy intensive businesses. The high energy input necessary (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.
What is the raw material of a refinery?
The raw material for refineries is oil. Petroleum 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.
Petroleum contains, to a lesser extent, carbon compounds containing 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 main group elements are between 0.1-1.5%, the content of metal compounds is less than 1000ppm.
Typical crude oils differ depending on the deposit. West Texas Intermediate (WTI) is a high-quality, light, low-sulfur 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. Tapis from Malaysia is light, Minas from Indonesia is a heavy crude from the Far East.
What products are obtained in a refinery?
The finished products can be gaseous, liquid or solid. Percentage, the yield of a modern refinery is about 3% of liquefied gases, such as propane and butane. About 9% are derived from petroleum (naphtha) and 24% from gasoline (gasoline). Higher boiling point 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 heavy at 3.5%, lubricants at 1.5%. About 2% is accounted for by other products or losses. Depending on the degree of further processing, the refinery's own consumption is between 5 and 10% of the crude oil used. The MiRO, for example, has 16 million tons of crude oil capacity, which is processed into 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 hand, 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 crude oils contain large amounts of heavy products, such as heavy fuel oil and bitumen.
In modern refineries, some of these heavy components can be converted to lighter ones, such as cracking, so that such a refinery can process more heavy crude.
How does an oil refinery work?
The oil extracted from the tanks is treated on site before transport to the refinery, essentially by coarse separation of undesirable components, such as sediment 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 into different fractions and processed into salable products. Technology is so advanced today that no substance in crude oil remains unused. Even refinery gas produced is used as an undesirable by-product. It is used directly in process furnaces as an energy carrier or used in chemical processing as synthesis gas.
Oil purification / desalination
The oil/crude oil is already released into the sand and water reservoir. To prevent corrosion in the equipment, the crude oil is desalted (to <10 ppm salinity), by adding water, an emulsion of crude oil and water is produced. The salt dissolves in the aqueous phase of this emulsion. The emulsion is then re-separated in an electrostatic desalter, the saline water settles to the bottom and is fed to appropriate treatment plants, and the desalted crude oil is pumped for distillation.
Emulsion refraction occurs at elevated temperatures of approximately 130°C to decrease the viscosity of the crude oil and voltages of approximately 20 kV. Working at high pressure prevents volatiles from evaporating during this process step. The oil and water emulsion can also be broken by adding suitable chemicals, called demulsifiers.
Primary processing (crude oil distillation)
After desalting, the crude oil is heated in two stages. Preheating is done in heat exchangers by recovering heat from expired product. The maximum preheating is done by ovens up to about 400 ° C. The heated oil is purified by rectification in a column up to 50 m high. Separated into its components. The crude oil enters the column in a two-phase flow (gas / liquid).
The temperature profile descends towards the top. Since the temperature at the bottom, i.e. at the bottom of the column, is higher and the light components cannot condense, they continue to rise in gaseous form.
At the top of the column, gas and light gasoline, called naphtha, including, kerosene, intermediate for turbine-powered aircraft (not to be confused with the so-called "jet fuel", the AVGAS for ottmotorenen aircraft), diesel fuel and light fuel (Oil and diesel heating. -Stock) and at the bottom - the bottom of the column - the atmospheric residue (in English: Long residue). This first rectification takes place at atmospheric pressure and is therefore called atmospheric rectification.
The residue is redistilled in another rectification column at low pressure (usually ~20 mbar) to break it down into other products (see vacuum distillation). Vacuum rectification is necessary because the chain length of high-boiling hydrocarbons is longer, and at high temperatures, above 400 °C, they tend to break down thermally rather than distill out. 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 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.
Hydrotreatment
Fractional distillation components (naphtha, middle distillates, vacuum gas oils) are still rich in sulfur compounds. These could poison the catalysts during downstream processing (catalytic reforming, see below). Direct burning of untreated products (heating oil) would produce environmentally harmful 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 on alumina catalysts that react hydrogen with sulfur, nitrogen, and oxygen compounds to produce hydrogen sulfide, ammonia, and water.
catalytic reforming
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. Reforming takes place 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.
At the metal centers of the catalyst, hydrogenation/dehydrogenation reactions are preferentially carried out, while the acid sites catalyze isomerization and ring closure reactions. An undesirable side reaction is coking of the catalyst through polymerization and dehydrogenation reactions. The coke is removed by burning the coke and then oxychlorinating the catalyst.
isomerization
In isomerization n-alkanes are converted to iso-alkanes with the goal of octane enhancement or changing the substitution pattern on the aromatic. Therefore, meta-xylene into o- and p-xylene isomerizes, since these are used for the preparation of phthalic anhydride or dimethyl terephthalate There are catalysts similar to those of catalytic reforming in use. The reaction is carried out at lower temperatures, around 250 °C and, to prevent catalyst deactivation by coking, at a moderate hydrogen partial pressure of about 15 bar. Due to the mild conditions compared to the catalytic reforming process, cracking and ring closure reactions are largely suppressed.
Other isomerization processes relate to the conversion of n-pentane to isopentane or n-hexane to isohexane (octane number upgrading, eg Hysomer process, PENEX process).
alkylation
In the 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 reagents are reacted in the liquid phase in an excess of alkane with concentrated sulfuric acid or anhydrous hydrofluoric acid.
Typical residence time is about 10 to 15 minutes. Thereafter, the liquid phases are separated by sedimentation of the phases. In the so-called iso-stripper, the iso-Alkane is separated and returned to the process (recycled). The finished end product is known as the alkylate. The process is suitable if the refinery has steam or catcracker and can therefore supply the starting materials for alkylation.
cracking
There are three main groups of crackers: thermal, catalytic, and hydrocracking.
When thermal cracking there are no catalysts. As a result, oil distillation residues 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 with the aim of producing gas oil. The yield of diesel (and lighter) is around 30% for the icebreaker. Subsequent distillation separates the volatile fractions.
In delayed coking, petroleum coke is recovered by thermal cracking of 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 coke, the coke is mechanically separated and, if necessary, freed from volatile compounds in calcination furnaces at temperatures of 1200 ° C.
However, naphtha, gas oil or even vacuum hydrogenated gas oils (Hydrowax, Hydrocracker BOttoms) can also be thermally cracked by so-called steam cracking of ethene, propene and aromatics. to produce
During catalytic cracking are acid silicates as catalysts, the starting materials are heavy atmospheric oil gas or vacuum gas. The products are predominantly short chain olefins and alkanes.
When I hydrocrack long chain alkanes they are converted on the hydrogen feed to short chain alkanes. At higher partial pressures of hydrogen, even aromatics are hydrogenated and thus cycloalkanes are generated. The educt used is predominantly vacuum gas oil. Most of the sulfur and nitrogen compounds in the reactant will hydrogenate, so substantial volumes of H 2 S and NH 3 are incurred.
claus method
The processes of hydrotreating, hydrocracking and the necessary production of synthesis gas from heavy oil produce considerable amounts of H 2 S, which cannot be simply "burned". In the Claus process, the resulting hydrogen sulfide is burned substoichiometrically with atmospheric oxygen in a reactor. The resulting SO 2 decomposes with residual H 2 S to elemental sulfur and water.
The initially incomplete reaction is conducted through several catalytic steps at lower temperatures to complete the conversion.
In another process (WSA process, wet sulfuric acid), sulfuric acid is produced directly from hydrogen sulfide.
Environmental protection, work safety and plant safety
Process equipment, tank tanks and piping systems are subject to extensive security measures. The goal of plant safety and accident prevention is to prevent disturbances and limit the effects of still-occurring disturbances 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 Immission Control Act. This requires that the plants be built and operated according to the state of the art. In addition, the applicable technical standards must be followed. The requirements for the management of polluting substances in water arise from the Water Resources Law.
history of refineries
The first oil refineries were already built at the beginning of the mineral oil era, 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, luminescent oils derived from petroleum began to replace fuels for lamps that had hitherto been obtained from animal fats, particularly Waltran, for which a treatment of the crude oil by distillation was first necessary.
The distillation of the recovered oil was carried out in a very simple way. 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 cooling tube system where they condensed. In this way, oil, which was used for lighting in kerosene lamps, won. The tar residue remaining in the boiler was disposed of as waste.
The exploitation of other petroleum products, and in particular the rapid spread of internal combustion engines after World War I, not only required the construction of many new refineries, but also led to a rapid development of the refinery process. .
As in many other industries, the requirements for a refinery, and in particular for the products, have changed over the years. Basically, here is the adaptation of the product specification to the call, which has changed due to laws (environment and health). For example, the permitted sulfur content in most fuels and also in heating oil decreased.