A petroleum refinery is an industrial company that converts the raw material petroleum into fractions with a defined boiling range by purification and distillation under normal pressure and under vacuum . Further refinement takes place through processes such as extraction or chemical cleaning processes. In order 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 the products that either improve or suppress certain properties.
High-quality products such as petrol , diesel fuel , heating oil or kerosene are obtained. Raw materials such as liquid gas , naphtha and middle distillate are used for the chemical industry . Oil refineries are usually large industrial complexes, the image of which is characterized by extensive tank farms , rectification columns , pipeline systems and flare systems . Oil refineries are considered energy-intensive operations. The high (up to 50% of the costs) required energy input for production is partly obtained from the primary energy sources themselves, as well as being supplied as electrical and thermal energy.
The first refineries were built at the beginning of the mineral oil era in the middle of the 19th century. The first refinery was established in Ulaszowice (Poland) in 1856 by Ignacy Łukasiewicz , the inventor of the kerosene lamp . After this was destroyed by a fire, another, more modern refinery was built in Chorkówka. Very quickly began light oils derived from petroleum which until then from animal fats, especially whale oil to replace lamp fuels gained, including a first treatment of the crude oil was necessary by distillation.
The distillation of the extracted oil took place in a very simple way. About 750 liters of crude oil were brought to the boil in a copper kettle. The resulting vapors were passed through a cooling pipe system in which they condensed . In this way petroleum was extracted for lighting purposes. The tar-like residue remaining in the boiler was disposed of as waste.
The utilization of other products obtained from crude oil, and in particular the rapid spread of internal combustion engines after the First World War , not only required the construction of numerous new refineries, but also led to a rapid further development of the processes used in a refinery.
As in many other industries, the demands on a refinery, especially its products, have changed over the years. Basically, the adaptation of the product specifications that have changed due to the laws (environment and health) should be mentioned here. For example, the permitted sulfur content fell in most fuels and also in heating oil. Benzene and aromatic specs fell for carburetor fuels .
Petroleum consists of a mixture of hydrocarbons. The most common are linear or branched alkanes (paraffins), cycloalkanes (naphthenes) and aromatics. Every crude oil has a special chemical composition depending on where it was found, which also determines the physical properties such as color and viscosity . To a lesser extent, petroleum contains nitrogen, oxygen or sulfur-containing carbon compounds such as amines , porphyrins , mercaptans , thioethers , alcohols and quinones . There are also compounds of metals such as iron , copper , vanadium and nickel . The proportion of pure hydrocarbons varies considerably. The proportion ranges from 97% to only 51% 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 and 1.4%, 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 high quality, low sulfur, light crude oil from Cushing, Oklahoma . A European representative is the Brent Blend , a crude oil from the fuel system in the North Sea, which consists of 15 oil fields . The Dubai-Oman in the Middle East is promoted mainly for the Asia-Pacific market. The tapis from Malaysia is a light, Minas from Indonesia a heavy Far Eastern crude oil.
|Liquefied gases , e.g. B. propane , butane||~ 3%|
|Raw gasoline (naphtha, cycloalkanes)||~ 9%|
|Gasoline (Otto-fuel)||~ 24%|
|Aviation turbine fuel ( kerosene )||~ 4%|
|Diesel fuel, light heating oil (EL, L)||<21%|
|heavy fuel oil (M, S)||~ 11%|
|Bitumen , heavy fuel oil (ES)||~ 3.5%|
|Lubricants (e.g. spindle oil )||~ 1.5%|
|Other products, losses, etc.||~ 2%|
The finished products can be gaseous, liquid or solid. In percentage terms, the yield of a modern refinery is around 3% of liquid gases such as propane and butane . Around 9% are raw gasoline ( naphtha), 24% gasoline (Otto fuel). Higher boiling fuels such as aviation turbine fuel ( kerosene ) make up 4%, diesel fuel and light heating oil up to 21%, heavy heating oil around 11%. The highly viscous and solid components such as bitumen or heavy heating oil are 3.5%, lubricants 1.5%. Other products or losses account for around 2%. The refinery's own consumption is between 5 and 11% of the crude oil used, depending on the degree of further processing. The MiRO has, for example, 16 million tons of crude capacity, the 14.9 million tonnes of end products to be processed, that is, the own consumption is approximately 7%.
The proportions of finished products depend on the one hand on the types of crude oil used and on the other hand on the processing facilities in the refinery. "Light" crude oils contain relatively high proportions of light products, that is, those with a low density such as liquefied petroleum gas, kerosene, gasoline, diesel. Heavy crude oils contain larger proportions of heavy products such as heavy fuel oil and bitumen. In modern refineries, some of these heavy components can be converted to lighter ones, for example by cracking , so that such a refinery can process more heavy crude oil.
The crude oil extracted from the deposits is processed on site before being transported to the refinery, mainly by roughly separating undesirable components such as sediments and water. After these initial processing steps, the crude oil that is now produced is delivered to the refinery by ship or pipeline. Here the liquid mixture is separated into different fractions in further steps using a special distillation process and processed into salable products. The technology is so advanced today that none of the crude oil substances remain unused. Even the refinery gas, which occurs as an undesirable by-product, is used. It is either used directly in the process furnace as an energy source or used in chemical processing as a synthesis gas.
Petroleum purification / desalination
The oil / crude oil is already freed of sand and water at the deposit. To prevent corrosion in the systems, the crude oil is desalinated (to a salt content of <10 ppm) by creating a crude oil-water emulsion with the addition of water . The salt dissolves in the aqueous phase of this emulsion. The emulsion is then separated again in an electrostatic desalinator, whereby the salty water settles on the bottom and is fed to the appropriate processing systems and the desalinated crude oil is pumped further for distillation. The emulsion is broken at elevated temperatures of around 130 ° C in order to lower the viscosity of the crude oil and voltages of around 20 kV. Working at increased pressure prevents volatile components from evaporating during this process step. The oil-water emulsion can also be broken by adding suitable chemicals, so-called demulsifiers.
Primary processing (crude oil distillation)
After desalination, the crude oil is heated in two stages. Preheating takes place in heat exchangers by recovering heat from the draining product. The tip is preheated by ovens up to around 400 ° C. The heated oil is purified by rectification in an up to 50 m high column separated into its constituents. The crude oil enters the column in a two-phase flow (gas / liquid). The temperature profile drops towards the top. Since the temperature in the sump, i.e. at the bottom of the column, is highest and the light constituents cannot condense, they continue to rise in gaseous form. At the top of the column there is gas and light petrol, so-called naphtha, including kerosene, an intermediate product for fuels for turbine-powered aircraft (not to be confused with so-called "aviation petrol ", the AVGAS for aircraft petrol engines ), diesel fuel and light heating oil, below gas oil (Heating oil and diesel raw materials) and in the sump - at the foot of the column - the atmospheric residue (Long Residue). This first rectification takes place at atmospheric pressure and is therefore called atmospheric rectification.
The residue is distilled again in a further rectification column at low pressure (typically ~ 20 mbar) in order to split it into further products (see vacuum distillation ). A vacuum rectification is necessary because the chain length of the high-boiling hydrocarbons is greater and, at high temperatures from around 400 ° C, they tend to thermally crack rather than separate by distillation. The products of vacuum distillation are vacuum gas oil and the so-called vacuum residue (short residue).
Conversion process and blending
After primary processing, a number of refinement processes are used to remove pollutants (sulfur, nitrogen) and improve the quality of the intermediate products. The end products such as motor gasoline , Jet A-1 , diesel fuel or heating oils are then mixed together ( blended ) from various intermediate products / components that are produced in the manufacturing processes mentioned below.
The components obtained during fractional distillation (naphtha, middle distillates , vacuum gas oils ) are still rich in sulfur compounds. These would poison the catalysts during further processing (catalytic reforming, see below). Direct combustion of untreated products (heating oil) would produce environmentally harmful SO 2 . During hydrotreating, the components to be desulphurized are mixed with hydrogen and heated to around 350 ° C. The hot mixture enters a reactor filled with catalysts made of nickel, molybdenum or cobalt on aluminum oxide, and the hydrogen reacts with the sulfur, nitrogen and oxygen compounds to form hydrogen sulphide, ammonia and water.
Using the example of the implementation of mercaptans: ,
the implementation of alcohols:
and the reaction of amines: .
The aim of catalytic reforming is to increase the octane number of naphtha (boiling range ~ 70–1820 ° C) and to produce aromatic hydrocarbons. Furthermore, hydrogen is obtained as a product that is used in hydrotreating and hydrocracking processes. Reforming takes place at around 500 ° C and - depending on the type of process - 3.5–40 bar. Bifunctional catalysts (platinum-tin or platinum-rhenium, on chlorinated aluminum oxide or zeolites) are used.
Typical reactions to reforming are:
- Ring closure:
The hydrogenation / dehydrogenation reactions preferably take place at the metal centers of the catalyst, while the acid centers catalyze isomerization and ring closure reactions. An undesirable side reaction is coking of the catalyst as a result of polymerization and dehydrogenation reactions. The coking is removed by burning off the coke and subsequent oxychlorination of the catalyst.
In the isomerization , n -alkanes are converted into iso- alkanes with the aim of improving the octane number or changing the substitution pattern of aromatics. Thus, meta -xylene in o - and p -xylene isomerized as these for the preparation of phthalic anhydride or dimethyl terephthalate can be used. Similar catalysts are used as in catalytic reforming. The reaction is carried out at lower temperatures around 250 ° C. and - to prevent the catalyst from being deactivated by coking - at a moderate hydrogen partial pressure of about 15 bar. Due to the moderate process conditions compared to catalytic reforming, cracking and ring closure reactions are largely suppressed.
Other isomerization processes relate to the conversion of n -pentane to isopentane or of n -hexane to isohexane (octane number improvement, e.g. Hysomer process, PENEX process).
In the alkylation, iso-alkanes (isobutane) and alkenes ( n - and iso -) are converted to higher molecular weight, high-octane iso- alkanes (C 7 -C 12 ) with acid catalysis . This is how isobutene and isobutane react u. a. to 2,2,4-trimethylpentane ( isooctane ). The reactants in the liquid phase are reacted in excess alkane with concentrated sulfuric acid or anhydrous hydrofluoric acid. The typical residence time is around 10 to 15 minutes. The liquid phases are then separated by settling the phases. The iso- alkanes are separated off in the so-called iso-stripper and fed back into the process (recycled). The finished end product is called an alkylate. The process is ideal if the refinery has a steam or catcracker and can thus supply the feedstock for the alkylation.
There are three main groups in cracking: thermal, catalytic and hydrocracking .
When the thermal cracking no catalysts. This means that residues can also be fed into the petroleum distillation process which, due to their heavy metal and sulfur content, would damage the catalyst during catalytic cracking.
When visbreaking z. B. it is the cracking of heavy residual oils with moderate residence times and temperatures around 500 ° C with the aim of producing gas oil. The yield of gas oil (and lighter) with the Visbreaker is around 30%. The volatile fractions are separated off by subsequent distillation.
In delayed coking , petroleum coke is obtained by thermal cracking of residues from vacuum distillation. To do this, the residual oil is heated to around 500 ° C and sprayed into coking chambers, where it is converted into petroleum coke, liquid and gaseous hydrocarbons. After coking, the coke is separated mechanically and, if necessary, freed from volatile constituents in calcining ovens at temperatures of 1200 ° C.
However, naphtha, gas oil or even hydrogenated vacuum gas oils ( Hydrowax , Hydrocracker Bottoms) can also be thermally cracked by what is known as steam cracking , in order to produce ethene , propene and aromatics .
In catalytic cracking ( fluid catalytic cracking , FCC), acidic silicates serve as catalysts, the starting materials are heavy atmospheric gas oils or vacuum gas oil. Short-chain olefins and alkanes are the predominant products .
In hydrocracking , long-chain alkanes are converted into short-chain alkanes with the addition of hydrogen. At higher hydrogen partial pressures, even aromatics are hydrogenated and thus cycloalkanes are also produced. Vacuum gas oil is predominantly used as the starting material. Most of the sulfur and nitrogen compounds in the starting material are hydrogenated, so that considerable volumes of H 2 S and NH 3 are produced.
Hydrotreating processes, hydrocracking and possibly the production of synthesis gas from heavy oil produce not inconsiderable amounts of H 2 S, which cannot simply be "burned off". In the Claus process, the hydrogen sulphide produced is burned substoichiometrically with atmospheric oxygen in a reactor. The resulting SO 2 is proportioned with the remaining H 2 S to form elemental sulfur and water.
The initially incomplete reaction is driven to complete conversion over several catalytic stages at lower temperatures.
In another process ( WSA process , wet sulfuric acid ), sulfuric acid is produced directly from hydrogen sulfide.
Environmental protection, occupational safety and plant safety
The process engineering systems, the tank farm and the pipeline systems are the subject of extensive safety measures. The aim of plant safety and accident prevention is to prevent malfunctions and to limit the effects of malfunctions on people and the environment.
In Germany, plants for the production, storage and extraction of crude oil and its secondary products require a permit in accordance with the Federal Immission Control Act . This requires that the systems are built and operated according to the state of the art . Furthermore, the applicable technical rules must be followed. The requirements for handling water-polluting substances result from the Water Resources Act .
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- Ignacy Łukasiewicz, pioneer in the study of petroleum distillation
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