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Feedstock Chemistry in the Refinery
Published in James G. Speight, Refinery Feedstocks, 2020
Two extremes of the thermal cracking in terms of product range are represented by high-temperature processes: (i) steam cracking or (ii) pyrolysis. Steam cracking is a process in which feedstock is decomposed into lower-molecular-weight (often unsaturated) products and saturated hydrocarbon derivatives. In the process, a gaseous or liquid hydrocarbon feed like such as ethane or naphtha is diluted with steam and briefly heated in a furnace (at approximately 850°C, 1,560°F) in the absence of oxygen at a short residence time (often on the order of milliseconds). After the cracking temperature has been reached, the products are rapidly quenched in a heat exchanger. The products produced in the reaction depend on the composition of the feedstock, the feedstock/steam ratio, the cracking temperature, and the residence time. Pyrolysis processes require temperatures on the order of 750°C–900°C (1,380°F–1,650°F) to produce high yields of low-molecular-weight products, such as ethylene, for petrochemical use. Delayed coking, which uses temperature on the order of 500°C (930°F) is used to produce distillates from viscous feedstocks as well as coke for fuel and other uses – such as the production of electrodes for the steel and aluminum industries.
Feedstock Preparation
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Two extremes of the thermal cracking in terms of product range are represented by high-temperature processes: (i) steam cracking or (ii) pyrolysis. Steam cracking is a process in which feedstock is decomposed into lower molecular weight (often unsaturated) products saturated hydrocarbon derivatives. Steam cracking is the key process in the petrochemical industry, producing ethylene (CH2=CH2), propylene (CH3CH=CH2), butylene [CH3CH2CH=CH2 and/or CH3CH=CHCH3 and/or (CH3)2C=CH2], benzene (C6H6), toluene (C6H5CH3), ethylbenzene (C6H5CH2CH3), and the xylene isomers (1,2-CH3C6H4CH3, 1,3-CH3C6H4CH3, and 1,4-CH3C6H4CH3). These intermediates are converted into a variety of polymers (plastics), solvents, resins, fibers, detergents, ammonia, and other synthetic organic compounds.
Production of Bio-Oil
Published in M.R. Riazi, David Chiaramonti, Biofuels Production and Processing Technology, 2017
Kevin M. Van Geem, Ismaël Amghizar, Florence Vermeire, Ruben De Bruycker, M.R. Riazi, David Chiaramonti
Steam cracking is a noncatalytic process where hydrocarbons are pyrolyzed in the presence of steam. Steam cracking is performed in tubular reactors suspended in a furnace. Heat is supplied by burners in the furnace floor and side walls. In the reactor, the temperature of the gas increases from 500°C to 650°C at the inlet, also known as coil inlet temperature, to approximately 750°C–875°C at the outlet, also known as coil outlet temperature (COT). The residence time is below 0.5 s. The hydrocarbon feedstock fragments into alkenes such as ethene, propene, and 1,3-butadiene and aromatics such as benzene and toluene through a free-radical mechanism (Dente et al. 2007). The outlet gas is rapidly quenched to avoid reaction of valuable products.
Fouling in a Steam Cracker Convection Section Part 2: Coupled Tube Bank Simulation using an Improved Hybrid CFD-1D Model
Published in Heat Transfer Engineering, 2020
Shekhar R. Kulkarni, Pieter Verhees, Abdul R. Akhras, Kevin M. Van Geem, Geraldine J. Heynderickx
One such downstream application is steam cracking. In steam cracking, that is thermal cracking of a hydrocarbon feedstock diluted with steam to produce ethylene, propylene, and additional valuable coproducts, the cost of the feedstock amounts to 40% to 70% of the total production costs. Replacing a conventional feedstock, e.g., naphtha, by a heavy hydrocarbon feedstock, e.g., a gas condensate, a heavy vacuum gas oil or crude oil [16], provides a significant economic advantage due to the reduced cost of feedstock. The shift to heavier hydrocarbon feedstock is, however, accompanied by an increase in tube fouling [17–19]. Additional fouling is mainly observed in some of the heat exchanger tubes in the steam cracker convection section. In these heat exchanger tubes, the feed is evaporated and superheated to the required reactor inlet temperature by heat exchange with the hot flue gas leaving the radiation section. The tail of a heavy feed requires higher temperatures for complete evaporation as compared to conventional feeds. A small part of the heavy tail is possibly not evaporated before it percolates in the heat exchanger tubes with a high tube wall temperature. Fouling of the high temperature tube walls due to the precipitation of asphaltenes is observed [20]. Remark that, even on clean tubes fouling can be observed, due to the flow profiles present therein. The 1D model takes into account the axial variation in wetting of the perimeter, due to which the predictions of ‘local’ hot spots is possible.