Fluid Catalytic Cracking is widely used way to convert heavy feedstock into lighter, more valuable products to be used as fuel or as raw material for chemicals and plastics. Various feedstocks can be used, such as gas oils, vacuum gas oils or residual materials. Typical products are gasoline, light fuel oils and olefin-rich gases. Gasoline is typically the most desired product from a cat cracker, however the flexibility of the process allows for design and operating variables to be adjusted to maximize other products and change the type of feed processed. The three operation modes of an FCCU can be maximized towards gasoline production, maximum middle distillate production and or light olefin production. This process not only produces these valuable products, the continuous coke burning from catalyst creates heat that can be converted to power or used in steam production.
The FCC process may be divided into several major sections, including the converter, flue gas, main fractionator and vapor recovery units. The number of product streams, the degree of product fractionation, flue gas handling and other aspects of the process will vary from unit to unit, depending on the requirements of the application. Here’s a basic description of and FCCU process. Hot catalyst from the regenerator section flows in a fluidized state through the riser tube into the reactor. The incoming feed together with recycling slurry meet hot catalyst, start vaporizing and cracking in reactor. While the reactions take place, coke is formed on the catalyst. The spent catalyst is separated from cracked material and being regenerated through burning off the coke. After regeneration, the catalyst is sent back to the reactor with a lot of heat absorbed in regeneration phase. The cracked hydrocarbons enter a fractionating tower, where it is separated into gas, light cycle oil, heavy cycle oil and slurry. The gasoline product has good overall octane characteristics suitable to be used for gasoline blending.
Continuous catalyst regeneration makes it possible to manage the high catalyst coking rate. The constancy of the yields is achieved by catalyst cycling between reaction and regeneration, which ensures the reactor is continuously supplied with freshly regenerated catalyst, and product yields are maintained at fresh catalyst levels. It’s critical to control the regenerator temperature carefully to prevent catalyst deactivation by overheating and to provide the desired amount of coke burnoff.
Reference: R. A. Meyers, McGraw-Hill Handbooks, ‘Handbook of petroleum refining processes’, third edition.
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This blog post has been up-dated in July 2020, due to company name change to Neles.