After the gas oil is cracked through contact with the catalyst, the resulting effluent is processed in fractionators, which separate the effluent based on various boiling points into several intermediate products, including butane and lighter hydrocarbons, gasoline, light gas oil, heavy gas oil, and clarified slurry oil. The butane and lighter hydrocarbons are processed further to separate them into fuel gas mostly methane and ethane , propane, propylene, butane, and butene for sale, or for further processing or use.
The FCC gasoline must be desulfurized and reformed before it can be blended into finished gasoline; the light gas oil is desulfurized before blending into finished heating oil or diesel; and the heavy gas oil is further cracked in either a hydrocracker using hydrogen and a catalyst or a coker.
The slurry oil can be blended with residual fuel oil or further processed in the coker. Carbon is deposited on the catalyst during the cracking process. Depending on the water source, there are many techniques for the chemical removal of these types of deposits that are effective, efficient and cost tolerant.
The air side of the fin-fan coolers will become fouled with a soot-like coating of ordinary dirt. This type of fouling can usually be removed by spray washing with a hot neutral detergent-based solution containing a suitable surfactant.
The boilers will become fouled with the same type of deposits that can be found in conventional boilers. Co and waste heat boilers are susceptible to fouling by operational deposits. These units must be periodically cleaned just like any other type of boiler. Lube and seal oil systems are very important in a cracking unit. In addition to the uses on pumps and boilers. There will be large systems for the air compressors and cyclone separators that are typically thousands of gallons in system volume.
While these systems do not require to be cleaned often, they are occasionally cleaned. Cleaning can be accomplished by the processes typical of preoperational cleaning techniques. Of interest, because of the extensive amount of temporary piping that is required to form a circulation loop, vapor phase cleaning with the appropriate chemical additives is a good candidate for the cleaning process. The fractionator and the associated equipment will contain fouling similar to that found in the crude plant distillation process.
The columns will require hazardous vapor removal for light-end hydrocarbons such as benzene and de-oiling. Additionally, since the catalytic reactions of the FCC unit result in the formation of unsaturated compounds alkenes , you also encounter low-molecular weight polymers and varnish that can deposit inside the fractionator and heat exchange equipment.
This vessel collects catalyst fines that have been suspended in slurry oil from the process. The separated slurry oil is decanted from the top of the vessel for re-use while the catalyst fines precipitate inside of the slurry tank forming a hard, concrete-like solid. The catalyst solids are impregnated with hydrocarbons that make the catalyst fines a hazardous waste that carries an EPE K hazardous waste code. This material is expensive to dispose.
Recent develops in extraction chemistry have resulted in a process and chemical products that are effective in removing low PPM-levels of the numerous constituents that comprise the K-code and allow for a non-hazardous disposal of the spent catalyst fines through conventional non-hazardous waste disposal facilities.
Imagine the savings to be gained in non-hazardous disposal. Through these conversations about refinery operations, we have tried to remove the sales pitch component, even though this is not completely possible. Our goal is to bring to your attention to new developments in the industry and the field of chemistry that will prove beneficial in your operations. Butane and ethene are produced. Cracking is important for two main reasons:.
The supply is how much of a fraction an oil refinery produces. The demand is how much of a fraction customers want to buy. Very often, fractional distillation of crude oil produces more of the larger hydrocarbons than can be sold, and less of the smaller hydrocarbons than customers want.
Smaller hydrocarbons are more useful as fuels than larger hydrocarbons. The hydrocarbon molecules are broken up in a fairly random way to produce mixtures of smaller hydrocarbons, some of which have carbon-carbon double bonds. One possible reaction involving the hydrocarbon C 15 H 32 might be:. This is only one way in which this particular molecule might break up.
The ethene and propene are important materials for making plastics or producing other organic chemicals. The octane is one of the molecules found in petrol gasoline. Modern cracking uses zeolites as the catalyst. These are complex aluminosilicates, and are large lattices of aluminium, silicon and oxygen atoms carrying a negative charge.
They are, of course, associated with positive ions such as sodium ions. You may have come across a zeolite if you know about ion exchange resins used in water softeners. The zeolites used in catalytic cracking are chosen to give high percentages of hydrocarbons with between 5 and 10 carbon atoms - particularly useful for petrol gasoline.
It also produces high proportions of branched alkanes and aromatic hydrocarbons like benzene. For UK A level and equivalent purposes, you aren't expected to know how the catalyst works, but you may be expected to know that it involves an ionic intermediate. Note: You should check your syllabus to find out exactly what you need to know.
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