Visbreaking and Coking

Like most separation processes in the refinery, the process water used in coker fractionators (as is also the case in other product fractionators) often comes in direct contact with oil and can have a high oil content (much of that oil can be recovered through wastewater oil recovery processes). Thus, the main constituents 

Particulate emissions from decoking can also be considerable. Coke-laden water from decoking operations in delayed cokers (hydrogen sulfide, ammonia, suspended solids) and coke dust (carbon particles and hydrocarbons) occur. 

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The gas oils from visbreaking and coking have better cetane numbers than LCO but they are unstable and need hydrotreatment before they can be used. 

Feedstocks for this very flexible process are usually vacuum distillates, deasphalted oils, residues (hydrotreated or not), as well as by-products from other processes such as extracts, paraffinic slack waxes, distillates from visbreaking and coking, residues from hydrocracking, converted in mixtures with the main feedstock. 

Thermal Cracking The most prevalent thermal processes are visbreaking and coking, both of which are applied to residium.(z> Visbreaking is a mild thermal cracking coking is a severe thermal cracking. 

Thermal cracking processes are commonly used to convert petroleum residua into distillable liquid products examples of thermal cracking processes currently in use are visbreaking and coking delayed coking. 

Treatment for crude oil residues is intended to minimize the adverse effects of the presence of asphaltenes during thermal processing. Generally, two types of treatment possibilities are available. There are physical and chemical treatments. The physical treatment essentially involves deasphalting whereas the chemical treatment includes thermal processes such as visbreaking and coking. 

There are a number of thermal processes, such a visbreaking and coking, that are directed at upgrading feedstock by the removal of asphaltenes. There is also the method of deasphalting with liquid hydrocarbons or gases such as propane, butane or iso-butane. This is very effective in the preparation of vacuum residues as cracking feedstock. 

Feed for thermal process units (visbreaking and coking) and catalytic units (fluid... 

The feedstocks in question are primary distillation streams and some conversion products from catalytic cracking, coking, visbreaking, and residue conversion units. 

Residuum Conversion This includes fluid coking, delayed coking, visbreaking, and residuum hydroprocessing. 

Catalytic cracking, coking, visbreaking, and other high-temperature refining processes can liberate sulfur from crude oil or from a process stream. Once free, sulfur can react to form low-molecular-weight compounds such as hydrogen sulfide, methyl mercaptan, carbon disulfide, and others. 

Carbon rejection processes, visbreaking, steam cracking, fluid catalytic cracking, and coking. 

Vacuum residium can be a fuel oil product after FCC cycle oil is added to reduce its viscosity. To feed the light cycle oil to the hydrocracker, the vacuum residium can be fed to a visbreaker for viscosity reduction. Alternatively, the vacuum residium may be fed to a coker for conversion to light products and coke. 

The GPC size data also were used to monitor the effect of various processes on the asphaltene molecular size distributions. Only the asphaltenes were studied in these experiments since they are the hardest to process, and they cause the most diffusion and coking problems. One of the processes studied was visbreaking, that is, noncatalytic thermal processing. Previous workers had examined the thermal decomposition of an Athabasca asphaltene... 

Although gas oils obtained from the atmospheric distillate still remain the main source of diesel fuels, in order to cope with the increased consumption of naphtha and middle distillates almost all refineries in Romania use conversion processes such as fluid catalytic cracking on vacuum distillates and coking or visbreaking on residue. These processes generate middle distillates with higher olefins, diolefins, sulphur, nitrogen and aromatics content compared to gas oil obtained from an atmospheric distillation unit... 

Unsaturated hydrocarbons can add to the deposit-forming cyclic structures with five or six C-atoms through Diels-Alder reactions. The successive dehydrogenations produce polycyclic aromatic structures. In the third reaction class, aromatic species add to macro-radicals of the surface. Note that these radicals are greatly stabilized by the aromatic resonance. Thus, the third reaction class is more important at lower temperatures, typically, in TLE, visbreaking and delayed coking units. 

This chapter presents the industrial applications and validations of certain detailed models which refer to the kinetics analysed earlier. The steam cracking process will be analysed first followed by visbreaking and delayed coking processes. Last of all, the method will be applied to the thermal degradation of plastic waste. 

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