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Steam cracking

Steam cracking is a petrochemical process in which saturated hydrocarbons are broken down into smaller, often unsaturated, hydrocarbons. It is the principal industrial method for producing the lighter alkenes (or commonly olefins), including ethene (or ethylene) and propene (or propylene). Steam cracker units are facilities in which a feedstock such as naphtha, liquefied petroleum gas (LPG), ethane, propane or butane is thermally cracked through the use of steam in steam cracking furnaces to produce lighter hydrocarbons. The propane dehydrogenation process may be accomplished through different commercial technologies. The main differences between each of them concerns the catalyst employed, design of the reactor and strategies to achieve higher conversion rates.

Steamcracker II at the BASF site in Ludwigshafen/Germany

Olefins are useful precursors to myriad products. Steam cracking is the core technology that supports the largest scale chemical processes, i.e. ethylene and propylene.

Contents

General

In steam cracking, a gaseous or liquid hydrocarbon feed like naphtha, LPG, or ethane is diluted with steam and briefly heated in a furnace in the absence of oxygen. Typically, the reaction temperature is very high, at around 850 °C. The reaction occurs rapidly: the residence time is on the order of milliseconds. Flow rates approach the speed of sound. After the cracking temperature has been reached, the gas is quickly quenched to stop the reaction in a transfer line heat exchanger or inside a quenching header using quench oil.

The products produced in the reaction depend on the composition of the feed, the hydrocarbon-to-steam ratio, and on the cracking temperature and furnace residence time. Light hydrocarbon feeds such as ethane, LPGs, or light naphtha give mainly lighter alkenes, including ethylene, propylene, and butadiene. Heavier hydrocarbon (full range and heavy naphthas as well as other refinery products) feeds give some of these same products, but also those rich in aromatic hydrocarbons and hydrocarbons suitable for inclusion in gasoline or fuel oil.[citation needed]

A higher cracking temperature (also referred to as severity) favors the production of ethene and benzene, whereas lower severity produces higher amounts of propene, C4-hydrocarbons and liquid products. The process also results in the slow deposition of coke, a form of carbon, on the reactor walls. This degrades the efficiency of the reactor, so reaction conditions are designed to minimize this. Nonetheless, a steam cracking furnace can usually only run for a few months at a time between de-cokings. Decokes require the furnace to be isolated from the process and then a flow of steam or a steam/air mixture is passed through the furnace coils. This converts the hard solid carbon layer to carbon monoxide and carbon dioxide. Once this reaction is complete, the furnace can be returned to service.[citation needed]

Process details

The areas of an ethylene plant are:

  1. steam cracking furnaces:
  2. primary and secondary heat recovery with quench;
  3. a dilution steam recycle system between the furnaces and the quench system;
  4. primary compression of the cracked gas (3 stages of compression);
  5. hydrogen sulfide and carbon dioxide removal (acid gas removal);
  6. secondary compression (1 or 2 stages);
  7. drying of the cracked gas;
  8. cryogenic treatment;
  9. all of the cold cracked gas stream goes to the demethanizer tower. The overhead stream from the demethanizer tower consists of all the hydrogen and methane that was in the cracked gas stream. Cryogenically (−250 °F (−157 °C)) treating this overhead stream separates hydrogen from methane. Methane recovery is critical to the economical operation of an ethylene plant.
  10. the bottom stream from the demethanizer tower goes to the deethanizer tower. The overhead stream from the deethanizer tower consists of all the C2's that were in the cracked gas stream. The C2 stream contains acetylene, which is explosive above 200 kPa (29 psi). If the partial pressure of acetylene is expected to exceed these values, the C2 stream is partially hydrogenated. The C2's then proceed to a C2 splitter. The product ethylene is taken from the overhead of the tower and the ethane coming from the bottom of the splitter is recycled to the furnaces to be cracked again;
  11. the bottom stream from the de-ethanizer tower goes to the depropanizer tower. The overhead stream from the depropanizer tower consists of all the C3's that were in the cracked gas stream. Before feeding the C3's to the C3 splitter, the stream is hydrogenated to convert the methylacetylene and propadiene (allene) mix. This stream is then sent to the C3 splitter. The overhead stream from the C3 splitter is product propylene and the bottom stream is propane which is sent back to the furnaces for cracking or used as fuel.
  12. The bottom stream from the depropanizer tower is fed to the debutanizer tower. The overhead stream from the debutanizer is all of the C4's that were in the cracked gas stream. The bottom stream from the debutanizer (light pyrolysis gasoline) consists of everything in the cracked gas stream that is C5 or heavier.

Since ethylene production is energy intensive, much effort has been dedicated to recovering heat from the gas leaving the furnaces. Most of the energy recovered from the cracked gas is used to make high pressure (1200 psig (8300 kPa)) steam. This steam is in turn used to drive the turbines for compressing cracked gas, the propylene refrigeration compressor, and the ethylene refrigeration compressor. An ethylene plant, once running, does not need to import steam to drive its steam turbines. A typical world scale ethylene plant (about 1.5 billion pounds (680 KTA) of ethylene per year) uses a 45,000 horsepower (34,000 kW) cracked gas compressor, a 30,000 hp (22,000 kW) propylene compressor, and a 15,000 hp (11,000 kW) ethylene compressor.

Even though the thorough energy integration within a steam cracking plant, this process produces an unsurmountable amount of carbon dioxide. Per tonne of ethylene, 1 - 1.6 tonne of carbon dioxide (depending on the feedstock) is being produced. Resulting in a staggering amount of more than 300 million tonnes of carbon dioxide that is annually emitted into the atmosphere of which 70-90% is directly attributed to the combustion of fossil fuel. In the last few decades, several advances in steam cracking technology have been implemented in order to increase its energy efficiency. These changes include oxy-fuel combustion, new burner technology, and 3D reactor geometries. However, as is common within mature technologies these changes only led to marginal gains in energy efficiency. To drastically curb the greenhouse gas emission of steam cracking, electrification does offer a solution as renewable electricity can be directly transformed into heat by, for example, resistive and inductive heating. As a result, several petrochemical companies joined forces resulting in the development of several joint agreements in which they combine R&D efforts to investigate how naphtha or gas steam crackers could be operated using renewable electricity instead of fossil fuel combustion.

Several proprietary designs are available under a license that must be purchased from the design developer by any petroleum refining company desiring to construct and operate a Steam Cracking unit of a given design.

These are the major steam cracking furnaces designers and licensors:

  1. Giovanni Maggini (2013-04-17). "Technology Economics: Propylene via Propane Dehydrogenation, Part 3". Slideshare.net. Retrieved2013-11-12.
  2. Zimmermann, Heinz; Walzl, Roland (2009). Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a10_045.pub3.
  3. Amghizar, Ismaël; Vandewalle, Laurien A.; Van Geem, Kevin M.; Marin, Guy B. (2017). "New Trends in Olefin Production". Engineering. 3 (2): 171–178. doi:10.1016/J.ENG.2017.02.006.
  4. "Dream or Reality? Electrification of the Chemical Process Industries". www.aiche-cep.com. Retrieved2021-07-05.
  5. "BASF, SABIC and Linde join forces to realize the world's first electrically heated steam cracker furnace". www.basf.com/.
  6. "Petrochemical companies form Cracker of the Future Consortium and sign R&D agreement". www.borealisgroup.com/.
  7. "Pyrolysis/Steam Cracking | Lummus Technology". www.lummustechnology.com. Retrieved2020-07-16.
  8. "Ethylene - Technip Energies plc". www.technipenergies.com. Retrieved2021-10-27.
  9. "Cracking furnace technology". Linde Engineering. Retrieved2020-01-13.
  10. "Petrochemical Technologies | KBR". www.kbr.com. Retrieved2020-01-27.

Steam cracking
Steam cracking Language Watch Edit Steam cracking is a petrochemical process in which saturated hydrocarbons are broken down into smaller often unsaturated hydrocarbons It is the principal industrial method for producing the lighter alkenes or commonly olefins including ethene or ethylene and propene or propylene Steam cracker units are facilities in which a feedstock such as naphtha liquefied petroleum gas LPG ethane propane or butane is thermally cracked through the use of steam in steam cracking furnaces to produce lighter hydrocarbons The propane dehydrogenation process may be accomplished through different commercial technologies The main differences between each of them concerns the catalyst employed design of the reactor and strategies to achieve higher conversion rates 1 Steamcracker II at the BASF site in Ludwigshafen Germany Olefins are useful precursors to myriad products Steam cracking is the core technology that supports the largest scale chemical processes i e ethylene and propylene 2 Contents 1 Process description 1 1 General 1 2 Process details 2 Steam cracking furnaces licensors 3 See also 4 Notes and referencesProcess description EditGeneral Edit In steam cracking a gaseous or liquid hydrocarbon feed like naphtha LPG or ethane is diluted with steam and briefly heated in a furnace in the absence of oxygen 3 Typically the reaction temperature is very high at around 850 C The reaction occurs rapidly the residence time is on the order of milliseconds Flow rates approach the speed of sound After the cracking temperature has been reached the gas is quickly quenched to stop the reaction in a transfer line heat exchanger or inside a quenching header using quench oil 2 The products produced in the reaction depend on the composition of the feed the hydrocarbon to steam ratio and on the cracking temperature and furnace residence time Light hydrocarbon feeds such as ethane LPGs or light naphtha give mainly lighter alkenes including ethylene propylene and butadiene Heavier hydrocarbon full range and heavy naphthas as well as other refinery products feeds give some of these same products but also those rich in aromatic hydrocarbons and hydrocarbons suitable for inclusion in gasoline or fuel oil citation needed A higher cracking temperature also referred to as severity favors the production of ethene and benzene whereas lower severity produces higher amounts of propene C4 hydrocarbons and liquid products The process also results in the slow deposition of coke a form of carbon on the reactor walls This degrades the efficiency of the reactor so reaction conditions are designed to minimize this Nonetheless a steam cracking furnace can usually only run for a few months at a time between de cokings Decokes require the furnace to be isolated from the process and then a flow of steam or a steam air mixture is passed through the furnace coils This converts the hard solid carbon layer to carbon monoxide and carbon dioxide Once this reaction is complete the furnace can be returned to service citation needed Process details Edit The areas of an ethylene plant are steam cracking furnaces primary and secondary heat recovery with quench a dilution steam recycle system between the furnaces and the quench system primary compression of the cracked gas 3 stages of compression hydrogen sulfide and carbon dioxide removal acid gas removal secondary compression 1 or 2 stages drying of the cracked gas cryogenic treatment all of the cold cracked gas stream goes to the demethanizer tower The overhead stream from the demethanizer tower consists of all the hydrogen and methane that was in the cracked gas stream Cryogenically 250 F 157 C treating this overhead stream separates hydrogen from methane Methane recovery is critical to the economical operation of an ethylene plant the bottom stream from the demethanizer tower goes to the deethanizer tower The overhead stream from the deethanizer tower consists of all the C2 s that were in the cracked gas stream The C2 stream contains acetylene which is explosive above 200 kPa 29 psi If the partial pressure of acetylene is expected to exceed these values the C2 stream is partially hydrogenated The C2 s then proceed to a C2 splitter The product ethylene is taken from the overhead of the tower and the ethane coming from the bottom of the splitter is recycled to the furnaces to be cracked again the bottom stream from the de ethanizer tower goes to the depropanizer tower The overhead stream from the depropanizer tower consists of all the C3 s that were in the cracked gas stream Before feeding the C3 s to the C3 splitter the stream is hydrogenated to convert the methylacetylene and propadiene allene mix This stream is then sent to the C3 splitter The overhead stream from the C3 splitter is product propylene and the bottom stream is propane which is sent back to the furnaces for cracking or used as fuel The bottom stream from the depropanizer tower is fed to the debutanizer tower The overhead stream from the debutanizer is all of the C4 s that were in the cracked gas stream The bottom stream from the debutanizer light pyrolysis gasoline consists of everything in the cracked gas stream that is C5 or heavier Since ethylene production is energy intensive much effort has been dedicated to recovering heat from the gas leaving the furnaces Most of the energy recovered from the cracked gas is used to make high pressure 1200 psig 8300 kPa steam This steam is in turn used to drive the turbines for compressing cracked gas the propylene refrigeration compressor and the ethylene refrigeration compressor An ethylene plant once running does not need to import steam to drive its steam turbines A typical world scale ethylene plant about 1 5 billion pounds 680 KTA of ethylene per year uses a 45 000 horsepower 34 000 kW cracked gas compressor a 30 000 hp 22 000 kW propylene compressor and a 15 000 hp 11 000 kW ethylene compressor Even though the thorough energy integration within a steam cracking plant this process produces an unsurmountable amount of carbon dioxide Per tonne of ethylene 1 1 6 tonne of carbon dioxide depending on the feedstock is being produced 4 Resulting in a staggering amount of more than 300 million tonnes of carbon dioxide that is annually emitted into the atmosphere of which 70 90 is directly attributed to the combustion of fossil fuel In the last few decades several advances in steam cracking technology have been implemented in order to increase its energy efficiency These changes include oxy fuel combustion new burner technology and 3D reactor geometries 4 However as is common within mature technologies these changes only led to marginal gains in energy efficiency To drastically curb the greenhouse gas emission of steam cracking electrification does offer a solution as renewable electricity can be directly transformed into heat by for example resistive and inductive heating 4 As a result several petrochemical companies joined forces resulting in the development of several joint agreements in which they combine R amp D efforts to investigate how naphtha or gas steam crackers could be operated using renewable electricity instead of fossil fuel combustion 5 6 Steam cracking furnaces licensors EditSeveral proprietary designs are available under a license that must be purchased from the design developer by any petroleum refining company desiring to construct and operate a Steam Cracking unit of a given design These are the major steam cracking furnaces designers and licensors Lummus Technology 7 Technip Energies formerly TechnipFMC 8 Linde 9 KBR 10 See also EditPetroleum Petroleum refining processes Natural gas Cracking chemistry Notes and references Edit Giovanni Maggini 2013 04 17 Technology Economics Propylene via Propane Dehydrogenation Part 3 Slideshare net Retrieved 2013 11 12 a b Zimmermann Heinz Walzl Roland 2009 Ullmann s Encyclopedia of Industrial Chemistry Weinheim Wiley VCH doi 10 1002 14356007 a10 045 pub3 Amghizar Ismael Vandewalle Laurien A Van Geem Kevin M Marin Guy B 2017 New Trends in Olefin Production Engineering 3 2 171 178 doi 10 1016 J ENG 2017 02 006 a b c Dream or Reality Electrification of the Chemical Process Industries www aiche cep com Retrieved 2021 07 05 BASF SABIC and Linde join forces to realize the world s first electrically heated steam cracker furnace www basf com Petrochemical companies form Cracker of the Future Consortium and sign R amp D agreement www borealisgroup com Pyrolysis Steam Cracking Lummus Technology www lummustechnology com Retrieved 2020 07 16 Ethylene Technip Energies plc www technipenergies com Retrieved 2021 10 27 Cracking furnace technology Linde Engineering Retrieved 2020 01 13 Petrochemical Technologies KBR www kbr com Retrieved 2020 01 27 Retrieved from https en wikipedia org w index php title Steam cracking amp oldid 1052111610, wikipedia, wiki, book,

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