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Video: FSC 432 Lesson 3 (2:16)
In lesson three, we will take a quick walk through a refinery, and go through some different kinds of processes. There are four types of processes at a petroleum refinery. They are separation processes, which are essentially physical processes. No chemical change takes place in these processes, just physical separation.
The second category is conversion processes, where there's a lot of chemistry that's involved. We are breaking and making new chemical bonds, so that we could produce the fuels in quantities that we want, in the yields that we want.
The third kind of process is the finishing process, which is really to make sure that any product leaving the refinery is compliant with performance specifications as well as environmental regulations.
And the fourth kind of process is supporting process, and these are essential processes to make sure that whole refinery functions, and all these processes actually do perform their function, in essence, or their objectives.
Now, as we go through this refinery, we will see that there are certain areas of focus. Most recently, the refineries have focused on upgrading heavy oil. When we say heavy, we really refer to the density-- high-density crude oil.
High-density crude oil typically has a high aromatic hydrocarbon content, and these crudes are difficult to process, more expensive to process. So we will talk about some basic strategies-- how one could upgrade these heavy, highly aromatic crude oils into the desirable products, which tend to be lighter. That means lower density, such as gasoline, diesel, and jet fuel.
Overview
Selected properties of crude oil provide information on its quality and the conditions for the optimum operation of a petroleum refinery for processing the crude oil to produce the desired fuels. Readily measurable physical properties of crude oil (such as density, boiling point, and viscosity) not only help in predicting the physical behavior of crude oil during refinery but also give insight into the chemical composition of the oil. Therefore, physical properties can be used in developing characterization factors that relate to the chemical behavior of crude oil and the characteristics of the resulting refinery products. In addition to using characterization factors, crude oils are classified using ternary diagrams reflecting the hydrocarbon composition in terms of paraffins, naphthenes, and aromatics.
As introduced in Lesson 1, petroleum refining integrates four types of processes: separation, conversion, finishing, and supporting processes. This lesson involves a quick walk through a simple refinery in the U.S. to see what happens to a barrel of crude oil, and to provide more detail on how different processes are sequenced for optimum operation. The simple animation below shows a simplified diagram of processing network to maximize gasoline yield and produce the other distillate fuels (jet fuel, diesel fuel, and fuel oil) in high yield.
The first sequence of processes in a refinery makes use of physical separation to wash the salt out and to fractionate the desalted crude into different boiling ranges in a distillation column. Following the distillation, these fractions are subjected to further separation processes, such as those in Light Ends Unit (LEU) dewaxing and deasphalting units; to finishing processes, such as hydrotreatment; and to conversion processes, such as catalytic cracking, hydrocracking, visbreaking, and delayed coking. As shown in the animation below, the final products from these processes include Liquefied Petroleum Gas (LPG), lubricating oil base stock, asphalt, jet fuel and diesel fuel, gasoline, fuel oil, and petroleum coke. Some fractions from LEU are sent to finishing processes (blending and hydrotreatment) and further to a conversion process (reforming) to produce additional gasoline. Light products from catalytic cracking are subjected to further conversion in the alkylation process to produce more gasoline. Finally, supporting processes, hydrogen production and sulfur recovery, help remove the major heteroatom contaminant, sulfur, from the petroleum fuels through hydrotreatment [1].
This refinery scheme is typical in U.S. refineries where the premium product is gasoline, as one could tell from the number of processes that lead to gasoline as the major product. The gasoline streams from different processes are blended in sophisticated linear and non-linear programming schemes to produce the three grades of gasoline sold in the U.S., regular, intermediate, and premium grades defined in reference to octane number. Elsewhere in the world, there is more emphasis on producing diesel fuel rather than gasoline, since the transportation systems are not as heavily dependent on gasoline-powered passenger vehicles. Diesel fuel is preferred for mass transport options (e.g., buses and trains), as diesel engines (with compression-ignition) can deliver more power than spark-ignition gasoline engines.
In the following sections, each major process group in a refinery network will be introduced in sequence. We will discuss how they fit in the “industrial ecology” of petroleum refining for the overall economic goal of maximizing profit in the prevailing markets for crude oil and the refined petroleum products. The video below presents a flow diagram integrating the four types of processes in a petroleum refinery.
Video: FSC 432 Simple Refinery Flow (4:36)
PRESENTER: Here we will go over a very simple refinery flow. This is a much simpler scheme than we have included in lesson one for different types of refinery processes, separation, finishing, convergence, and support. Here what we would like to do is to connect crude oil feed to these major refinery products starting with LPG, the lightest, gasoline, jet fuel, fuel oil, asphalt, and coke.
One point to make, look at the number of arrows that go to gasoline, which really shows the significance of this product as the major product in US refineries, the gasoline. Quite a few different processes produce gasoline. Of course jet fuel and diesel also are important refinery products.
So let's look at the processes that we can use to connect crude oil to these major products. Here again crude oil goes through desalting and distillation. And through the light ends unit separations we produce the first product, LPG, or liquefied petroleum gas. That is essentially propane and butane.
The light straight-run naphtha coming from the light ends unit go through blending to the gasoline pool. And from the atmospheric distillation unit, kerosene and light gas oil go through hydrotreatment treatment to produce jet fuel and diesel. So you can see here that using just separation and finishing processes we could produce LPG straight from gasoline, which would be low octane number, and jet fuel and diesel without any convergent process.
We bring in two additional separation processes, dewaxing and deasphalting. You would remember dewaxing would produce the lubricating oil base stock and the wax byproduct. And deasphalting, treating the vacuum distillation resid would separate out asphalt and produce deasphalted oil for further conversion.
So we have pretty much exhausted our separation process. You can see there are still quite a few arrows pointing nowhere. So we need to go to our conversion processes to connect to our final products.
Here are our conversion processes in color purple. Starting from the left, hydrocracking treats the heavy vacuum gas oil to make additional jet fuel and diesel. Visbreaking takes the VDR from the vacuum distillation process and produces fuel oil.
Moving to the right, catalytic cracking takes the feed from the distillation unit-- could be a light gas oil or a heavy gas oil-- to produce gasoline. This is the major gasoline production path. And the byproducts from cat cracking goes through alkylation to make additional gasoline, high octane number gasoline.
And the heavy naphtha, straight heavy naphtha coming from the light ends unit through hydrotreatment goes through reforming to make another high octane gasoline stream. And finally the VDR from the vacuum distillation could go through coking to make additional gasoline, as well as the byproduct coke.
Finally, we will use the two major supporting processes, hydrogen production and sulfur recovery, to connect all the arrows. You know that hydrogen is used to remove sulfur in the crude oil fractions as hydrogen sulfide. And hydrogen sulfide is converted to elemental sulfur in the sulfur recovery unit. And elemental sulfur is sold as a refinery product. So that completes our simple refinery flow.
Learning Outcomes
By the end of this lesson, you should be able to:
- illustrate the refinery processes with examples for each category of processes;
- distinguish and evaluate the functions of different refinery processes to control refinery product yield and composition;
- evaluate the principles behind the major refinery processes and examine the products from each process from Distillation to Hydrocracking;
- formulate strategies for upgrading heavy oil.
What is due for Lesson 3?
This lesson will take us one week to complete. Please refer to the Course Syllabus for specific time frames and due dates. Specific directions for the assignments below can be found on the Assignments page within this lesson.
| Readings: | J. H. Gary, G. E. Handwerk, & Mark J. Kaiser, Chapter 1, pp. 32-36; Chapter 2, pp. 41-55 and the course material from this site |
|---|---|
| Assignments: | Exercise 2: Using ternary classification to characterize crude oil blends |
Questions?
If you have any questions, please post them to our Help Discussion (not email), located in Canvas. I will check that discussion forum daily to respond. While you are there, feel free to post your own responses if you, too, are able to help out a classmate.