Vacuum/Atmospheric Distillation Unit

Chevron’s Pascagoula Refinery processes 330,000 barrels (thirteen.9 million gallons) of crude oil a day – an amount equal to the size of a football field coated to a depth of forty feet.

Operators management the refining processes utilizing hi-tech computers situated in management centers situated all through the refinery.

Hello-Tech Course of Control

Using the most recent digital technology to monitor and control the plants, operators run the process units 24 hours a day, 7 days every week. From control rooms located in every Operations area, operators use a pc-driven course of management system with console screens that show shade interactive graphics of the plants and actual-time data on the status of the plants. The process control system permits operators to “fine-tune the processes and respond immediately to course of modifications. With redundancy designed into the management system, safe operations are assured in the occasion of plant upset.

Refining’s Primary Steps

Most refineries, no matter complexity, perform a few primary steps within the refining course of: DISTILLATION, CRACKING, TREATING and REFORMING. These processes happen in our fundamental working areas – Crude/Aromatics, Cracking I, RDS/Coker, Cracking II, and on the Sulfur Recovery Unit.

1. Distillation

Modern distillation involves pumping oil by means of pipes in scorching furnaces and separating light hydrocarbon molecules from heavy ones in downstream distillation towers – the tall, slender columns that give refineries their distinctive skylines.

The Pascagoula Refinery’s refining course of begins when crude oil is distilled in two large Crude Models that have three distillation columns, one that operates at near atmospheric pressure, and two others that function at less than atmospheric strain, i.e., a vacuum.

Click on the picture for
Distillation Column Diagram

Throughout this process, the lightest materials, like propane and butane, vaporize and rise to the top of the primary atmospheric column. Medium weight materials, together with gasoline, jet and diesel fuels, condense in the center. Heavy materials, known as gasoline oils, condense in the lower portion of the atmospheric column. The heaviest tar-like materials, called residuum, is referred to because the “bottom of the barrel as a result of it by no means really rises.

This distillation course of is repeated in lots of other plants as the oil is further refined to make varied merchandise.

In some cases, distillation columns are operated at less than atmospheric pressure (vacuum) to lower the temperature at which a hydrocarbon mixture boils. This “vacuum distillation (VDU) reduces the chance of thermal decomposition (cracking) resulting from over heating the mixture.

As a part of the 2003 Clean Fuels Project, the Pascagoula Refinery added a brand new low-strain vacuum column to the Crude I Unit and converted the RDS/Coker’s VDU into a second vacuum column for the Crude II Unit. These and different distillation upgrades improved gas oil restoration and decreased residuum volume.

Utilizing the most recent computer control programs, refinery operators exactly control the temperatures in the distillation columns which are designed with pipes to withdraw the assorted types of products where they condense. Merchandise from the top, middle and bottom of the column travel by means of these pipes to different plants for additional refining.

2. Cracking

Since the market establishes product value, our competitive edge is determined by how efficiently we can convert middle distillate, gas oil and residuum into the highest worth merchandise.

At the Pascagoula Refinery, we convert middle distillate, gas oil and residuum into primarily gasoline, jet and diesel fuels through the use of a series of processing plants that literally “crack giant, heavy molecules into smaller, lighter ones.

Heat and catalysts are used to convert the heavier oils to lighter products using three “cracking methods: fluid catalytic cracking (FCC), hydrocracking (Isomax), and coking (or thermal-cracking).

The Fluid Catalytic Cracker (FCC) uses high temperature and catalyst to crack 86,000 barrels (3.6 million gallons) each day of heavy gasoline oil principally into gasoline. Hydrocracking uses catalysts to react fuel oil and hydrogen below excessive strain and high temperature to make both jet fuel and gasoline.

Additionally, about 58,000 barrels (2.4 million gallons) of lighter gas oil is converted daily in two Isomax Items, utilizing this hydrocracking process.

We blend most of the products from the FCC and the Isomaxes instantly into transportation fuels, i.e., gasoline, diesel and jet gas. We burn the lightest molecules as gasoline for the refinery’s furnaces, thus conserving pure gasoline and minimizing waste.

In the Delayed Coking Unit (Coker), 98,000 barrels a day of low-worth residuum is converted (using the coking, or thermal-cracking process) to high-worth gentle products, producing petroleum coke as a by-product. The large residuum molecules are cracked into smaller molecules when the residuum is held in a coke drum at a excessive temperature for a time period. Solely solid coke stays and must be drilled from the coke drums.

Modifications to the refinery during its 2003 Clear Fuels Challenge elevated residuum quantity going to the Coker Unit. The venture elevated coke dealing with capability and replaced the one hundred fifty metric-ton coke drums with new 300 metric-ton drums to handle the elevated residuum quantity.

The Coker usually produces more than 6,000 tons a day of petroleum coke, which is bought to be used as fuel or in cement manufacturing.


Whereas the cracking processes break many of the fuel oil into gasoline and jet fuel, in addition they break off some pieces which are lighter than gasoline. Since Pascagoula Refinery’s main focus is on making transportation fuels, we recombine 14,800 barrels (622,000 gallons) every day of lighter components in two Alkylation Items. This process takes the small molecules and recombines them within the presence of sulfuric acid catalyst to convert them into excessive octane gasoline.

Three. Treating (Eradicating Impurities)

The products from the Crude Units and the feeds to other items comprise some pure impurities, akin to sulfur and nitrogen. Using a course of known as hydrotreating (a milder model of hydrocracking), these impurities are removed to scale back air pollution when our fuels are used.

As a result of about 80 percent of the crude oil processed by the Pascagoula Refinery is heavier oils which are excessive in sulfur and nitrogen, numerous treating models all through the refinery work to remove these impurities.

Within the RDS Unit’s six 1,000-ton reactors, sulfur and nitrogen are removed from FCC feed stream. The sulfur is transformed to hydrogen sulfide and despatched to the Sulfur Unit the place it’s transformed into elemental sulfur. Nitrogen is remodeled into ammonia which is faraway from the process by water-washing. Later, the water is treated to recover the ammonia as a pure product to be used in the production of fertilizer.

The RDS’s Unit main product, low sulfur vacuum fuel oil, is fed to the FCC (fluid catalytic cracker) Unit which then cracks it into high worth products akin to gasoline and diesel.

4. Reforming

Octane rating is a key measurement of how effectively a gasoline performs in an car engine. Much of the gasoline that comes from the Crude Models or from the Cracking Models doesn’t have sufficient octane to burn effectively in cars.

The gasoline course of streams within the refinery which have a fairly low octane rating are despatched to a Reforming Unit the place their octane levels are boosted. These reforming items make use of treasured-metal catalysts – platinum and rhenium – and thereby get the name “rheniformers. Within the reforming process, hydrocarbon molecules are “reformed into excessive octane gasoline components. For example, methyl cyclohexane is reformed into toluene.

The reforming course of really removes hydrogen from low-octane gasoline. The hydrogen is used throughout the refinery in varied cracking (hydrocracking) and treating (hydrotreating) items.

Our refinery operates three catalytic reformers, where we rearrange and change 71,000 barrels (about three million gallons) of gasoline per day to present it the high octane vehicles need.

Product testing


A closing and demanding step is the mixing of our products. Gasoline, for example, is blended from handled elements made in several processing items. Blending and Transport Space operators exactly mix these to ensure that the blend has the appropriate octane level, vapor strain ranking and different important specifications. All merchandise are blended in the same vogue.

Quality Control

In the refinery’s modernly-equipped Laboratory, chemists and technicians conduct high quality assurance tests on all finished merchandise, including checking gasoline for proper octane rating. Techron® Chevron’s patented efficiency booster, is added to gasoline at the company’s advertising terminals, one in every of which is located on the Pascagoula Refinery.