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.
Figure 1.4: A typical distribution of products made from crude oil in a U.S. refinery.
Click here for text description of Figure 1.4
Products Made from a Barrel of Crude Oil
23% Diesel Fuel & Heating Oil
18% Other Products
10% Jet Fuel
4% Liquefied Petroleum
Source: U.S. Department of Energy
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)
A refinery flow chart for converting crude oil to fuels and materials.
Click here for transcript of FSC Refinery Flow Chart.
Here, we will build a simple refinery flow chart. On the left, you see the crude oil feed to the refinery. On the right hand side, the major refinery products going from the lightest to the heaviest. Starting with gasoline, jet fuel and kerosene, heating and diesel fuels, industrial fuel oil, waxes, lubricating oils, greases, asphalt, and petroleum coke would be the heaviest product, which will be a solid obtained from a refinery.
The crude oil is fed to the fractionating tower that we call the distillation calm. We separates the crude oil into various boiling fractions. And these fractions are fed to the processes, the downstream, which are vapor recovery unit, also forming alkylation, catalytic cracking, extraction, coking, dewaxing, grease manufacturing, treating and blending, among others and there's additional processing there as well. So, we essentially will connect to crude oil through these processes to the final product.
Now, please note that some of the refinery units are connected. If you look at vapor recovery unit connected to catalytic cracking, that is also connected to coking. And at the top is ultraforming. Now, these processes all produce gasoline and light to hydrocarbons, like LPG, from different bonding fractions of crude oil coming from the distillation columns. That's why they're linked on this diagram.
Let's follow what happens to different distillation fractions coming from the distillation column. First, the vapor product from the top is sent to the vapor recovery unit, and separates into a gasoline and LPG-- that's liquified petroleum gas. You can see the ultraforming we call now the process Catalytic Reforming is involved to make a high-octane gasoline.
You can see that additional processing is also needed to remove sulfur out from these products. LPG as well as gasoline. We should note that catalytic cracking can also produce jet fuel. As you can see the arrow from cat cracking touching the jet fuel point. And catalytic cracking also produces feed stocks for the alkylation unit to produce additional high octane gasoline.
As we go down to the distillation column, we are now into the vacuum distillation territory, and the product from vacuum distillation would go through extraction, dewaxing, and various treating and blending to produce lubricating oils as well as waxes and greases.
We are now at the bottom of the vacuum distillation column, the vacuum distillation residue can do various things with this fraction versus coking. It's a very severe thermal cracking process, which leads to petroleum coke as a byproduct. Refineries use coking to produce more jet fuel gasoline and then LPG. Petroleum coke is just a byproduct.
The vacuum distillation residue could be treated in a deasphalting process to produce asphalt. So, again, as a byproduct, the principal product from the deasphalting called the deasphalted oil could be used to making a lighter, hydrocarbons, fuels, and chemicals from this fraction.
And this pretty much completes building off a very simple refinery flow chart.
Source: 1995 Amoco Corp.
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 1.5. Classification of refining processes and types of refinery products.
Source: Dr. Semih Eser
Figure 1.6 shows a more detailed refinery block diagram to show how different processes are integrated for producing the desired fuels and materials.
Figure 1.6. A flow diagram integrating the four types of processes in a petroleum refinery.
Source: Dr. Semih Eser
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.
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