Oil refinery

An oil refinery is an industrial company that produces high value products like gasoline, diesel fuel, fuel oil or kerosene from petroleum raw material through purification, distillation and conversion. Oil refineries are typically large industrial complexes whose image is characterized by extended storage tanks, distillation columns, piping and flare systems.

History

The first refineries already emerged at the beginning of the oil era, so the mid-19th century. The first refinery operation was set up in 1856 by Ignacy Łukasiewicz, the inventor of the kerosene lamp, in Ulaszowice (Poland). After it was destroyed by a fire, another, more modern refinery was built in Chorkówka. Very quickly began the petroleum-derived light oils to replace the hitherto from animal fats, especially whale oil, lamp derived fuels, what was necessary first of all a preparation of oil by distillation.

The distillation of the crude oil obtained was held in a very simple manner. For this purpose, a copper kettle was filled with about 750 liters of oil and put the kettle contents to boiling. The vapors were passed through a cooling pipe system in which they condensed. In this way Petroleum was, which served for lighting purposes in kerosene lamps, won. The tarry residue remained in the vessel was disposed of as waste.

The exploitation further from the petroleum-derived products and in particular the rapid spread of 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 methods used in a refinery.

As in many other industries, the requirements have changed to a refinery, in particular, on the products over the years. Basically, here is how to customize the product specification mentioned, which have changed in recent years due to the laws (environment and health). Thus, the allowable sulfur content decreased in most fuels and home heating oil. The motor gasoline fell benzene and the Aromatenspezifikationen.

Feedstocks

Oil consists of a mixture of hydrocarbons. Most frequently represented are linear or branched alkanes (paraffins ), cycloalkanes ( naphthenes ) and aromatics. Each oil has a specific location, depending on the chemical composition also determine the physical properties such as color and viscosity. Oil contains a lesser extent nitrogen-, oxygen-or sulfur-containing carbon compounds such as amines, porphyrins, mercaptans, thioethers, alcohols, and quinones. In addition, compounds of metals such as iron, copper, vanadium and nickel place. The proportion of pure hydrocarbons varies considerably. The proportion ranges from 97 % to only 50 % for heavy oil and bitumen. The carbon content is 83-87 %, the hydrogen content of 10-14 %. Other main group elements are between 0.1 and 1.5%, the content of metallic compounds is less than 1000 ppm.

Typical crude oils differ in the deposit. The "West Texas Intermediate " ( WTI) is a high quality, low sulfur and light crude oil from Cushing (Oklahoma). A European representative is the " Brent Blend", a crude oil from the consisting of 15 oil fields in the North Sea Brent system. The " Dubai - Oman " from the Middle East is promoted primarily for the Asia- Pacific market. The " Tapis " from Malaysia is a lightweight, " Minas " from Indonesia a heavy Far East oil.

Products

The finished products can be gaseous, liquid or solid. The yield percentage of a modern refinery in about 3 % of liquid gases such as propane and butane. About 9 % attributable to naphtha ( naphtha ), 24 % on petrol ( gasoline fuel ). Higher-boiling fuels such as jet fuel (kerosene ) make up 4%, diesel fuel and heating oil up to 21%, about 11% heavy fuel oil. The high viscosity and solid components such as bitumen or heavy fuel oil will be 3.5%, lubricants 1.5%. About 2% relates to other products or losses. The power consumption of the refinery, depending on the processing level between 5 and 10 % of the crude oil used. The MiRO for example, has 16 million tonnes of crude oil capacity, which are processed to 14.9 million t end products, ie, the power consumption is approximately 7%.

The proportions of finished products are dependent on the one hand on the used crude oils, on the other hand, from the present in the refinery processing plants. So "light" crude oils contain relatively high amounts of light products, ie those with low density such as LPG, kerosene, petrol and diesel. Heavy crude oils contain a higher proportion of heavy products such as heavy fuel oil and bitumen. In modern refineries, some of these heavy components are converted into lighter, for example, by cracking, so that such a refinery to process more heavy crude oil.

Refinery processes

The oil extracted from the deposits is processed prior to transport to the refinery site, mainly through a rough separation of undesirable constituents, such as sediment and water. After this initial processing, the resulting crude oil is now delivered by ship or pipeline to the refinery. Here, the liquid mixture is treated with a special distillation process separately in further steps in different fractions and processed into salable products. The technology is now so advanced that no substances of crude oil remain unused. Even obtained as unwanted by-product refinery gas is used. It is either used directly in the process furnaces as an energy source or used in the chemical processing as synthesis gas.

Oil purification / desalination

The oil / crude oil is already excluded in the deposit of sand and water. To prevent corrosion in the plants, the crude oil is desalted ( at salinities <10 ppm ) by a crude oil-water emulsion is prepared by adding water. The salt dissolves in the aqueous phase of this emulsion. The emulsion is then separated in an electrostatic desalter, where the salty water settles to the bottom and corresponding processing systems is supplied and the desalted crude oil is pumped to the distillation. The breaking of the emulsion is carried out at elevated temperatures of about 130 ° C to lower the viscosity of the crude oil and voltage of about 20 kV. By operating at elevated pressure prevents volatile components evaporate during this step. The oil -water emulsion can also be the addition of suitable chemicals, so-called Demulsifier broken.

Primary processing ( oil distillation)

After desalting, the crude oil is heated in two stages. Preheating occurs in heat exchangers using heat recovery of the running product. Spitzenvorheizung effected by the furnace to about 400 ° C. The heated oil is separated by rectification in an up to 50 m high column into its components. The crude oil occurs in a two-phase flow of a (gas / liquid ) in the column. The temperature profile falls upwards back. Since the temperature in the bottom, so the bottom of the column, is the highest and the light components thus can not condense, they rise gaseous further up. In the top of the column of gas and light fuel, so-called naphtha to, including kerosene, intermediate for fuels turbine -powered aircraft (not to be confused with the so-called " jet fuel ", the AVGAS for aircraft spark-ignition engines ), diesel fuel and light heating oil. Further down gas oil ( heating oil and diesel starting materials ) and in the bottom - the bottom of the column - the atmospheric residue (English: Long Residue ). This first rectification is carried out at atmospheric pressure and is therefore called atmospheric rectification.

The residue is distilled in a further rectification column under vacuum again to split it into other products (see the vacuum distillation). A vacuum rectification is necessary, as the chain length of the high-boiling hydrocarbons is greater and they tend at high temperatures around 400 ° C to thermally more likely to crack than to be separated by distillation. The products of the vacuum distillation are vacuum gas oil and the so-called vacuum residue (English: Short Residue ).

Conversion processes

After the primary processing a series of finishing processes is used to remove pollutants (sulfur, nitrogen) and to improve the quality of intermediate products - almost all petroleum products, which are leaving the refinery not just distilled / rectified from petroleum. Thus, motor gasoline, Jet A -1, diesel fuel, fuel oil extra light fuel oil and heavy mixed together from various intermediate products / components ( blinded ), which are produced at below manufacturing processes.

Hydrotreating

The obtained in the fractional distillation components ( naphtha, middle distillates, vacuum gas oils) are still rich in sulfur compounds. This would poison the catalysts in the processing ( catalytic reforming, see below). In direct combustion of untreated products ( fuel oil) would arise environmentally damaging SO2. Hydrotreating to desulfurize components are mixed with hydrogen and heated to about 350 ° C. The hot mixture passes into a container filled with catalysts of nickel, cobalt or molybdenum on alumina reactor, the hydrogen reacts with the sulfur, nitrogen and oxygen compounds to hydrogen sulfide, ammonia and water.

In the example, the reaction of mercaptans:

The reaction of alcohols:

The reaction of amines:

Catalytic reforming

Catalytic reforming has to generate the target to increase the octane number of the naphtha (boiling range 70-180 ° C, ~ ), and aromatic hydrocarbons. Further hydrogen is obtained as a product, which is used in the hydrotreating and in hydrocracking processes. Reforming runs at about 500 ° C, and depending on the process type - 3,5 to 40 bar from. Are being introduced bifunctional catalysts ( platinum-tin and platinum - rhenium on alumina or zeolites chlorinated ).

Typical reactions in reforming are:

• Ring closure:
• Dehydration:
• Isomerization:

Be running on the metal centers of the catalyst preferably the Hydrierungs-/Dehydrierungsreaktionen, while the acid sites catalyze isomerization and cyclization reactions. An undesired side reaction is the coking of the catalyst by polymerization and dehydrogenation reactions. The coking is removed by burning off the coke and subsequent oxychlorination catalyst.

Isomerization

In the isomerization of n- alkanes, iso -alkanes are converted to the target octane number improving or changing the substitution pattern on the aromatic. As meta-xylene is isomerized in the o- and p-xylene, as they are used for the production of phthalic anhydride or dimethyl terephthalate. There are similar catalysts such as catalytic reforming in use. The reaction is performed at lower temperatures around 250 ° C, and - bar performed at moderate pressure of hydrogen of about 15 - to prevent catalyst deactivation by coking. The moderate compared to the catalytic reforming process conditions cracking and ring closure reactions are largely suppressed. Further isomerization refer to the conversion of n -pentane to isopentane and n-hexane to iso-hexane ( octane improvement, eg Hysomer process, PENEX process).

Alkylation

In the alkylation of iso- alkanes ( iso-butane ) and olefins (n -and iso- ) is reacted under acid catalysis to form higher molecular weight high-octane iso -alkanes, (C7 - C12). To react isobutene and isobutane et al to 2,2,4 -trimethylpentane ( isooctane ). The reactants in the liquid phase will be implemented in the alkane surplus with concentrated sulfuric acid or anhydrous hydrofluoric acid. Typical residence time is about 10 to 15 minutes. Thereafter, the liquid phases are separated by settling of the phases. The so-called iso- stripper, the isoalkanes to be separated and recycled in the process ( recycled ). The finished product is called alkylate. The process is recommended when the refinery has a Steam or cat cracker and thus can provide the feedstocks for the alkylation.

Cracking

There are three main groups of cracking: thermal, catalytic and hydrocracking.

Thermal cracking, no catalysts are used. This also residues of petroleum distillation can be supplied that would harm because of their content of heavy metals and sulfur to the catalyst in the catalytic cracking. When visbreaking example is it about the cracking of heavy residual oils at moderate residence times and temperatures around 500 ° C with the target gas oil to produce. The yield of gas oil ( and lighter) is the Visbreaker at about 30%. By subsequent distillation, the volatile fractions are separated.

The delayed coking of petroleum coke is obtained by thermal cracking of vacuum distillation residue. To the residual oil is heated to about 500 ° C, and sprayed in the coke drums, where it is converted to coke, liquid and gaseous hydrocarbons. After coking, the coke is separated off mechanically and, where appropriate freed Calzinieröfen at temperatures of 1200 ° C of volatile constituents. But it can also be thermally cracked naphtha, gas oil, or even hydrogenated vacuum gas oils ( Hydrowax, hydrocracker bottoms ) through the so-called steam cracking to produce ethylene, propylene and aromatics.

In catalytic cracking ( engl. Fluid Catalytic Cracking FCC) are acidic silicates as catalysts, reactants are heavy atmospheric gas oils and vacuum gas oil. As products are produced predominantly short-chain olefins and alkanes.

Hydrocracking long-chain alkanes are converted under supply of hydrogen into short-chain alkanes. At higher hydrogen pressures are even hydrogenated aromatics and therefore also produces cycloalkanes. The reactant vacuum gas oil is used mainly. Most sulfur and nitrogen compounds of the starting material to be hydrogenated, so incurred considerable volumes of H2S and NH3.

Claus Process

Hydrotreating processes, hydrocracking and possibly the production of synthesis gas from heavy oil to produce considerable amounts of H2S, which can not simply be " burned off ". The Claus process, the resulting sulfide with oxygen in the reactor is burned substoichiometrically. This produces - besides sulfur - a gas mixture of H2S and SO2. In several subsequent catalytic stages, the mixture continues to react to sulfur, on balance: