Volatile steam cracking

Almost any naphthenic or parallflnic hydrocarbon heavier then methane can he steam-cracked to yield elhylene. The preferred feedstock in the United Slates has been ethane and/or propane recovered from natural gas. or from the volatile fractions of petroleum. However, because of longterm uncertainties pertaining to natural gas, many producers have been turning to heavier petroleum fractions, such as gas oils, as feedstock. The consumption of ethylene throughout the free world is estimated to be about 40 x 10 pounds per year,... 

The first test with cellulose (Experiment 1.05) used no steam flow. Because the evolved volatile matter cracked on the vycor walls depositing an opaque, black material thereon, the wall temperature of the reactor rapidly climbed to temperatures above 1000°C. Gasification data is presented in Table 1 for the 0.54 g of cellulose fed into the reactor during the test. Subsequent, brief exposure of the reactor to the solar flux with steam (but no biomass) flow cleaned the reactor s walls nicely. 

Vacuum Distillation - Heavier fractions from the atmospheric distillation unit that cannot be distilled without cracking under its pressure and temperature conditions are vacuum distilled. Vacuum distillation is simply the distillation of petroleum fractions at a very low pressure (0.2 to 0.7 psia) to increase volatilization and separation. In most systems, the vacuum inside the fractionator is maintained with steam ejectors and vacuum pumps, barometric condensers, or surface condensers. 

Gas phase thermal cracking of the volatiles occurs, reducing the levels of tar. Char (fixed carbon) and ash are the pyrolysis byproducts that are not vaporized. In the second step, the char is gasified through reactions with oxygen, steam, and hydrogen. Some of the unbumed char may be combusted to release the heat needed for the endothermic pyrolysis reactions. 

The spent, i.e. coked, cracking catalyst and the SOx catalyst then move to the FCCU stripper. In the stripper, they are treated with steam to flush out the volatile hydrocarbons. The steam also hydrolyzes the metal sulfide on the surface of the SOx catalyst to give metal oxide and release H S in the stripper (Equation 6). 

In the process, a residuum is desulfurized and the nonvolatile fraction from the hydrodesulfurizer is charged to the residuum fluid catalytic cracking unit. The reaction system is an external vertical riser terminating in a closed cyclone system. Dispersion steam in amounts higher than that used for gas oils is used to assist in the vaporization of any volatile constituents of heavy feedstocks. 

Water and often fine sand and silt are held in various crude oils in permanent emulsions. Particularly crudes obtained by secondary methods and those from tar sands where water or steam are used contain water and mineral matter emulsified therein by the surface forces on small particles and drops. Azeotropic distillation removes the relatively small amount of water, using the solvent as an entrainer which dilutes the crude. This allows the mineral matter to be separated easily without using centrifuges with their substantial cost and wear, free of organic material, so it may be discarded with-out hazards of fire or odors the bitumen to be recovered for such use or cracked to give volatile fractions and coked to an ash-free coke the water to be obtained as distilled water for reuse. 

The present day FCC eatalyst eonsists typically of a USY zeolite in a siliea-alumina matrix. The matrix ean have a range of surface area and cracking activity (11). At the regenerator temperature, sodium has a solid state diffusion eoeffieient of lO to 10 em s" (12) and is expected to move easily within a eatalyst particle. The distribution of Na between zeolite and matrix and its effect on the stability of each component under these conditions is of interest. Furthermore, in the presence of steam, interparticle migration of volatile Na species is expected. The mechanism of this process has not been investigated. 

If V2O5 is not present on the catalyst how can it further react with steam to form the vanadic acidic entity We do not contest that finely divided bulk V2O5 may be hydrolyzed in the presence of steam to form this volatile acid as in the case of the key experiment of Wormsbecher. Rather we simply assert that formation of vanadic acid from vanadia species on a cracking catalyst does not occur at all. Instead it is... 

Each side-product liquid draw goes through a steam stripper, usually equipped with 5 or 10 trays, to prevent inclusion of more volatile hydrocarbons in the product. The side-product stripper may be reboiled for sharper separation. Optimum amounts of stripping steam will often be in the order of 2% or 3% w or more of each product rate. After stripping, the side products are cooled in the preheat train and cooled further in water or air coolers to safe storage temperatures. Heavy gas oil and residuum products often go to downstream cracking processes without cooling. 

In molten bath gasifiers, crushed coal, steam air, and/or oxygen are injected into a bath of molten salt, iron, or coal ash. The coal appears to dissolve in the melt where the volatiles crack and are converted into carbon monoxide and hydrogen. The fixed carbon reacts with oxygen and steam to produce carbon monoxide and hydrogen. Uiueacted carbon and ash float on the surface from which they are discharged. 

Use of a steam generator to separate the primary loop from the secondary loop largely confines the radioactive materials to a single building during normal power operation and eliminates the extensive turbine maintenance problems that would result from radio-actively contaminated steam. Radioactivity sources are the activation products from the small amount of corrosion that is present in the primary loop over the 12-18-month reactor cycle, as well as from the occasional (<1 in 10,000) fuel rod that develops a crack and releases a small portion of its volatile fission products. Uranium dioxide fuel is very resistant to erosion by the coolant, so the rod does not dump its entire fission product inventory into the RCS. 

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