As we all know crude oil extracted from the earth is not suitable for direct consumption, it needs to be refined further to create value-added products. The refining process also helps to remove the impurities in the crude oil which could cause emissions during combustion of the fuel products. This makes refining is an integral part of the oil and gas value chain that helps supply of value-added products to the consumers.
Basic phases in refining process
There are three basic phases in refining process that transform crude oil into desirable products. The first step is the distillation process where only heat and temperature are used to split crude oil into basic products and intermediate products such as straight run gases, naphtha and gas oils. These are termed as intermediate products as they need to be processed further in order to make them consumable again.
These intermediate gas oils are taken to the next phase of refining to make more value-added products. This phase is called conversion process. This is where FCCU (Fluid Catalytic Cracking Unit) plays a key role in producing more valued products. In this phase, a number of different refinery process technologies are utilized including processes to remove impurities such as sulfur. The difference in this step is that in addition to heat and pressure, catalysts are used to invoke chemical reactions that actually modify the molecular structure. This is the key to transforming the undesirable products into desirable ones. The magic is possible because the processes change the products at the molecular level. The flow of intermediate products between these units can be a very complex path. FCCU provides absolute flexibility in refining process both from the perspective of processing wide range of feedstock and also in the operating range of the conversion units. This unlimited operational flexibility helps to produce different ranges of gasoline in the FCCU process.
The third phase is called blending, where outputs from conversion process are blended to make more customized, valued-added products as per market requirements.
Evolution of FCCU
FCCU is the resultant technological upgrade from the basic catalytic process which was first developed during 1920s by Eugene Houdry for upgrade of residue. This process was commercialized later in the 1930s and it was based on cyclic fixed bed. FCCU feed stock is normally light gas oil from vacuum distillation column. Catalytic cracking cracks low value high molecular weight hydrocarbons to more value-added products (low molecular weight) like gasoline, LPG, diesel along with important petrochemical feedstock like propylene, and C4 gases like isobutylene, Isobutane, butane, etc.
Full-fledged commercialization of FCCU came into existence as from 1942. Since then more than 400 refineries have FCCU units today, which are also called secondary processing units. FCCU provides about 50% of the transportation fuel and 30% of total gasoline pool.
FCCU the most profitable unit in a refinery
FCCU has been and still remains one of the most important and most profitable processes in a refinery operation. This is mainly due to the process which converts the low value feedstock into a wide range of much more valuable products. These include yields of about 60% of high-octane gasoline product, about 20% of a diesel-boiling-range product, and significant amounts of lighter gases, some of which become feedstock for other downstream processes, as well as a major contribution to the refinery fuel gas system.
Another interesting feature of the FCCU is that it helps refineries to gain in terms of the product volumes, i.e., the total volume of products represents an actual overall increase over the volume of feedstock. This is due to the addition of catalyst in the process which increases the volumes of output substantially during the process. The process also has great flexibility to handle a wide range of feedstock and operating conditions can be manipulated to satisfy divergent product requirements. Thus, optimizing FCCU operation has a very significant bearing on overall refinery profitability.
Optimizing FCCU is the key
As stated above, FCCU has great flexibility but not without complexity. Hence, because of this nature of the unit, it is possible to vary operating conditions for processing variety of components for better product mix and profitability. However, to achieve this maximum economic opportunities with FCCU, one needs to get the design aspects right. The unit has to be designed perfectly and the modern FCCUs are having the capability to maximize value-added products through what is known as short contact time cracking.
Nowadays, most refineries use riser cracking compared to dense bed cracking which was followed during the 1960s and 70s. Technology has improved vastly and some of these risers deploy short contact time cracking reactors in which the feed backed up by high velocity is injected to engage with the catalyst to speed up contact cracking time of the feed. This helps to realize improved product mix while minimizing thermal cracking possibilities. However, due to higher velocity of injection, the reactor is hard on the catalyst and has an adverse impact on the catalyst power for cracking. Since catalysts are high-cost and capital intensive components, a lot of care needs to be taken while designing the unit to optimally use catalysts. Hence, robust design has to be put in place for effective catalyst stripping and regeneration.
Most of the refineries in the world today survive mainly because of the secondary processing facilities as they provide much needed economics in their operations. This is mainly through the value-added products produced in FCC units especially the gasoline range of products with high octane number. Also, FCC units through their capability to process multiple feedstocks can provide a value-added olefins and aromatics rich stream for extracting benzene, toluene and xylenes, by processing C3/C4 components. Indeed, these petrochemicals are high value products and are used by variety of industries such as chemicals, perfumes, fertilizers, paints, and tire manufacturers.
To conclude, FCCU plays a crucial techno-commercial role in a refinery. It is a very comprehensive unit that provides great flexibility in refinery operations through its capability to process variety of feedstocks. Also at a macroeconomic level, it helps to balance the demand supply scenario of gasoline range of products.