IntroductionBasic Process FlowTypical FCCU ConfigurationsFeeds and ContaminantsChemistry and CatalystFluidization PrinciplesRegen and Reactor EquipmentControl SystemsDistillation FundamentalsMain FractionatorGas ConcentrationHeat and Pressure BalancesProcess Variable EffectsStartup Keys/ProceduresTroubleshooting

However, a barrel of crude oil will not always yield the desired ratio of hydrocarbons. For example, the market may be heavy for gasoline, but light for lubricating oil. Instead of discarding the lubricating oil, it is chemically cracked in an FCCU so that it can be turned into gasoline and other hydrocarbons with shorter changers. Hydrocarbons can be cracked in other ways, but chemical cracking in an FCCU is the most common and efficient.

The FCCU uses an extremely hot catalyst to crack the hydrocarbons into shorter chains. Zeolite, bauxite, silica-alumina, and aluminumhydrosilicate are all catalysts commonly used in an FCCU unit. Both the oil and catalyst in the FCCU are usually extremely hot, and the oil is often in a vapor form. The catalyst splits the long hydrocarbon chains into shorter units, and the mixture travels from the FCCU to another distillation column so that the cracked hydrocarbons can be extracted

Catalysts can be reused for additional cracking after the carbon which coats them after the process has been removed. In the 1930s, when the concept of an FCCU first began to be developed, a team of scientists designed an FCCU which would work in a continuous cycling mode, capable of processing 13,000 barrels of oil a day. A continuous FCCU has a primary reactor, a distillation column for separating out the cracked hydrocarbons, and a regeneration unit for cleaning the catalysts and preparing them for reuse.

OVERVIEW OF FLUID CATALYTIC CRACKING UNIT (FCC, FCCU)

FCC “heart” of a modern refineryo Nearly every major fuels refinery has an FCCU

One of the most important and sophisticated contributions to petroleum refining technology Capacity usually 35% to 40% of the crude distillation unit capacity Contributes the highest volume to the gasoline pool:

Processes gas oils using catalysts to crack carbon–carbon bonds

Cracking lowers the average molecular weight and produces higher yields of fuel

products

• Attractive feed characteristics

Small concentrations of contaminants (→ poison the catalyst)

Small concentrations of heavy aromatics (→ crack and deposit coke on catalyst)

• Products may be further processed

Hydrocracking

Alkylation: to improve gasoline anti-knock properties

Visbreaking

Visbreaking refers to the process of reducing the viscosity of a liquid through high temperatures. This is a type of thermal cracking that works by breaking the molecular bonds of the liquid. Big molecules that made up the liquid are "cracked" into smaller molecules. This enables the molecules to flow easier, reducing the liquid's viscosity. There are two general technologies used for inducing visbreak: coil and soaker.

The term visbreaking comes from the words "viscosity" and "breaking." It is a non-catalytic process, which means that a catalyst is not used to lower the temperature at which the cracking takes place. Pre-heated air is instead injected into the furnace to quickly increase the temperature.

A coil visbreaker uses a furnace tube called a coil to heat the feed stream. In the oil industry, feed or feed stream refers to crude oil. The temperature and speed of the furnace is mostly controlled through the feed stream and the flow of air in the furnace.

In soaker visbreaking, the feed needs a relatively low temperature but a long processing time for cracking. The heated feed soaks in the visbreaking unit, called a drum. It then transfers to a fractionator, which separates the feed into several byproducts. The lower temperature uses less energy and reduces the amount of residue in the process.

Some visbreaking units utilize the properties of both processes by combining them. The initial cracking takes place in the furnace tube where much of the feed is heated. The feed then passes through a quencher to reduce its temperature. After the feed is quenched, it soaks in a drum for further cracking.

Quenching the feed slows the production of coke, a low value product. A slow coke production leads to less decoking, which usually saves time and cost. The coke that accumulates in the drum is often recycled in the feed.

The oil industry developed visbreaking to produce petroleum products. When oils are first dug up, they are in an unrefined state. This is where the term "crude oil" originated. Oil refineries use the visbreaking process to convert this crude oil into several final products.

Products from the crude oil are commonly divided into three categories: gas distillates, middle distillates, and residues. Middle distillates are more valuable compared to other byproducts. Gas distillates and residues, while not as valuable, still have industrial uses.

A visbreaker unit typically aims to increase the amount of middle distillate. Gasoline and petroleum are two of the most valuable middle distillate byproducts made from crude oil. By increasing the amount of middle distillates in the feed stream, the oil refinery increases its profits.

Residues from the visbreaking process include tar and coke. They are used for different purposes like roofing and manufacture of dry cells. Gas distillates such as LPG are commonly sold as fuel for household use.

Catalytic reforming

Catalytic reforming is a petroleum refinery process in which low octane distillation products known as naphthas are chemically converted into high octane reformates. High octane reformation products produced from naphthas are used on their own in various industries or as additives in high octane products like gasoline. This catalytic reforming process involves restructuring hydrocarbon molecules in the naphthas in such a way that they form more complex chemical structures with higher octane ratings. The process of catalytic reforming has an added value in that it produces other desirable byproducts which are then used elsewhere in the refinery.

High octane petroleum products are complex hydrocarbon chemicals which do not occur naturally and are not produced by simple distillation of crude oil or coal tar. To synthesis these complex hydrocarbons, the low octane naphthas — i.e., flammable hydrocarbon mixtures such as kerosene which are products of crude oil and coal tar distillation — are subjected to a chemical process known as catalytic reforming. There are several different versions of this chemical process all of which produce different reformed products. These extremely complex processes rearrange the molecular structure of the naphtha elements, breaking several of the molecules down into smaller units in the process. The end result of this process is a far more complex hydrocarbon structure with elevated octane values.

Benzene is one of the distinct catalytic reformation products and is widely used in various industries as a solvent or a constituent of plastic, synthetic rubber, dye, and drug manufacture. Benzene is also used in addition to other catalytic reforming products such as toluene to boost the octane rating of gasoline, also known as petrol. Gasoline on its own is a low octane product of fractional petroleum distillation. Isopentane is another highly volatile reformate which is used in conjunction with liquid nitrogen to achieve extremely low fluid temperatures.

The basic variants of catalytic reforming include platforming, powerforming, ultraforming, and thermofor reformation. All these processes use noble metal catalysts such as platinum and rhenium in conjunction with high heat and pressure to achieve reformation of low octane naphthas. These catalysts are periodically regenerated, typically every six to 24 months, although newer plants regenerate their aged catalyst components continuously in-situ. The catalytic reforming process, which typically takes place at temperatures of between 923 to 968 degrees Fahrenheit (495 to 520 degrees Celsius) and pressures as high as 1,000 psi (69 bar), produces hydrogen, methane, ethane, propane, andbutane gas byproducts which are then utilized elsewhere.

Non-conventional oil Petroleum Sources