An Overview of Refinery Products and Processes
Considering the market drivers just reviewed along the small profit margins that are often usually associated with petroleum refinery products, refineries should carefully select the crude oil feedstock and configure the refinery processes such that they produce the desirable petroleum products at the lowest cost.
In the U.S. refineries, a principal focus is on the production of gasoline because of high demand. Diesel fuel is the principal refinery product in most other parts of the world. Figure 1.4 shows a typical distribution of products from a barrel of crude oil in a U.S. refinery. Distillation process separates the crude oil into boiling point fractions. The liquefied petroleum gas (LPG) constitutes the lowest boiling point (most volatile) product from a refinery and higher boiling fractions lead to most desirable distillate liquids, such as gasoline, jet fuel, diesel fuel, and fuel oil in the increasing order of boiling points, while asphalt is made from the residual fraction remaining after distillation.
The following animation shows a refinery flow chart indicating some of the major refinery processes and refinery products. Note that the distillation process (Fractionation Tower) separates crude oil into a number of distillate fractions that are sent as feedstocks to different processes, some of which are interconnected. It is also important to recognize that petroleum refining not only produces transportation fuels and fuels for space heating or industrial furnaces, but also produces materials needed for the operation of the combustion engines and paving the roads for vehicles to travel on.
Video: FSC 432 Refinery Flow Chart (4:12)
Figure 1.5 indicates that chemical constitution and physical properties of crude oils are important parameters that guide the refinery configurations. The refining processes can be divided into four groups, as indicated. While the separation processes involve just physical phenomena, the conversion, finishing, and support processes require chemical changes, i.e., breaking chemical bonds to modify the molecular structure of the feedstocks. These changes are necessary to produce the fuels and materials in accordance with industrial/commercial specifications.
Figure 1.6 (progressive image, 25 seconds) shows a more detailed refinery block diagram to show how different processes are integrated for producing the desired fuels and materials.
Separation processes, such as distillation, dewaxing, and deasphalting make use of the differences in the physical properties of crude oil components to separate groups of hydrocarbon compounds or inorganic impurities, whereas conversion processes cause chemical changes in the hydrocarbon composition of crude oils. For example, Fluid Catalytic Cracking process breaks chemical bonds in long-chain alkanes to produce shorter chain alkanes to produce gasoline from higher boiling gas oil fractions. Finishing processes involve hydrotreating to remove heteroatoms (S, N, and metals) and product blending to produce fuels and materials with desired specifications and in compliance with environmental and government regulations. Finally, supporting processes provide the recovery of the removed heteroatoms or heteroatom compounds, production of the hydrogen necessary for conversion and hydrotreating processes, and effluent water treatment systems.
Why is diesel fuel preferred over gasoline in many countries in the world?
ANSWER: Diesel fuel powers the engines in buses, locomotives, and ships used for public transport. Passenger vehicles fueled by gasoline are the most widely used means of transportation in the U.S.