Crude Oil Refining Process

Crude oil refining process are the processes (chemical and other facilities) used in oil refineries to transform crude oil into useful petroleum products. Each refinery has its own unique arrangement and combination of refining processes largely determined by the refinery location, desired products and economic considerations. There are most probably no two refineries that are identical in every respect but each refinery maintain basic processing units. Hence in studying crude oil refining process, we will be looking at the processing units used in crude oil refineries and basic process of each unit.

Here are basic crude oil refining processing units and processes employed by each unit:

Crude Oil Distillation Unit (CDU)

In crude oil refining process, the distillation unit in crude oil refinery distill and separate valuable distillates (naphtha, kerosene, diesel) and atmospheric gas oil (AGO) from the crude feedstock.

Processes

• Desalt and dehydrate the crude using electrostatic enhanced liquid/liquid separator (Desalter).
• Heat the crude to the desired temperature using fired heaters.
• Flash the crude in the atmospheric distillation column.
• Utilize pumparound cooling loops to create internal liquid reflux.
• Product draws are on the top, sides, and bottom

Vacuum Distillation Unit (VDU)

The next step in crude oil refining process involves the vacuum distillation unit of the refinery. The objective of this unit is to recover valuable gas oil from reduced crude via vacuum distillation.

Processes

• Heat the reduced crude to the desired temperature using fired heaters
• Flash the reduced crude in the vacuum distillation column
• Utilize pumparound cooling loops to create internal liquid reflux
• Product draws are top, sides, and bottom

Delayed Coking Process

                              

The next step in crude oil refining process is the delayed coking process. The objective is to convert low value residue to valuable products such as naphtha and diesel.

Processes

• Preheat residue feed and provide primary condensing of coke drum vapors by introducing the feed to the bottom of the main fractionators
• Heat the coke drum feed by fired heaters
• Flash superheated feed in a large coke drum where the coke remains and vapors leave the top and goes back to the fractionator
• Off-line coke drum is drilled and the petroleum coke is removed via Hydrojetting

Fluidic Coking Process

Another step in crude oil refining process is fluidic coking process. The objective of this process is to convert low value residue to valuable products like naphtha, diesel and coker gas oil.

Process

• Preheat residue feed, scrub coke particles, and provide primary condensing of reactor vapors by introducing the feed to the scrubber
• Residue is atomized into a fluid coke bed and thermocracking occurs on the particle surface
• Coke particles leaving the reactor are steam stripped to remove remaining liquid hydrocarbons
• Substoichiometric air is introduced to burner to burn some of the coke and provide the necessary heat for the reactor
• Reactor vapors leave the scrubber and go to the fractionators

Fluid Catalytic Cracking (FCC) Unit

                    

Another crude oil refinery process is carried out in the fluid catalytic unit with the objective to convert low value gas oils to valuable products like naphtha, diesel and slurry oil.

Process

• Gas oil feed is dispersed into the bottom of the riser using steam
• Thermal cracking occurs on the surface of the catalyst
• Disengaging drum separates spent catalyst from product vapors
• Steam strips residue hydrocarbons from spent catalyst
• Air burns away the carbon film from the catalyst in either a “partial-burn” or “full-burn” mode of operation
• Regenerated catalyst enters bottom of riser-reactor

HF Alkylation Process

Another important crude oil refinery process is the HF Alkylation process. Its objective is to combine light olefins like propylene and butylenes with isobutene to form a high octane gasoline (alkylate).

Process

• Olefins from FCC are combined with IsoButane and fed to the HF Reactor where alkylation occurs
• Acid settler separates the free HF from the hydrocarbons and recycles the acid back to the reactor
• A portion of the HF is regenerated to remove acid oils formed by feed contaminants or hydrocarbon polymerization
• Hydrocarbons from settler go to the DeIsobutanizer for fractionating the propane and isobutane from the n-butane and alkylate
• Propane is then fractionated from the isobutane; propane as a product and the isobutane to be recycled to the reactor
• N-Butane and alkylate are deflourinated in a bed of solid adsorbent and fractionated as separate products

Hydrotreating Process

Another crude oil refining process is the hydrotreating process. The objective is to remove contaminants like sulfur, nitrogen, metals and saturate olefins and aromatics to produce a clean product for further processing or finished product sales.

Process

• Feed is preheated using the reactor effluent
• Hydrogen is combined with the feed and heated to the desired hydrotreating temperature using a fired heater
• Feed and hydrogen pass downward in a hydrogenation reactor packed with various types of catalyst depending upon reactions desired
• Reactor effluent is cooled and enters the high pressure separator which separates the liquid hydrocarbon from the hydrogen/hydrogen sulfide/ammonia gas
• Acid gases are absorbed from the hydrogen in the amine absorber
• Hydrogen, minus purges, is recycled with make-up hydrogen
• Further separation of LPG gases occurs in the low pressure separator prior tosending the hydrocarbon liquids to fractionation

Hydrocracking Process

Hydrocracking process is crude oil refining process aimed to remove feed contaminants like nitrogen, sulfur, metals and to convert low value gas oils to valuable products like naphtha, middle distillates, and ultra-clean lube base stocks.

Process

• Preheated feed is mixed with hot hydrogen and passes through a multi-bed reactor with interstage hydrogen quenches for hydrotreating
• Hydrotreated feed is mixed with additional hot hydrogen and passes through a multi-bed reactor with quenches for first pass hydrocracking
• Reactor effluents are combined and pass through high and low pressure separators and are fed to the fractionator where valuable products are drawn from the top, sides, and bottom
• Fractionator bottoms may be recycled to a second pass hydrocracker for additional conversion all the way up to full conversion

Catalytic Reforming Process

Another crude oil refining process is the catalytic reforming process with an objective to convert low-octane naphtha into a high-octane reformate for gasoline blending and/or to provide aromatics like benzene, toluene, and xylene for petrochemical plants. Reforming also produces high purity hydrogen for hydrotreating processes.

Process

• Naphtha feed and recycle hydrogen are mixed, heated and sent through successive reactor beds
• Each pass requires heat input to drive the reactions
• Final pass effluent is separated with the hydrogen being recycled or purged for hydrotreating
• Reformate product can be further processed to separate aromatic components or be used for gasoline blending

Isomerization Process

Isomerization process is another crude oil refining process used to convert low-octane n-paraffins to high-octane iso-paraffins.

Process

• Desulfurized feed and hydrogen are dried in fixed beds of solid dessicant prior to mixing together
• The mixed feed is heated and passes through a hydrogenation reactor to saturate olefins to paraffins and saturate benzene
• The hydrogenation effluent is cooled and passes through a isomerization reactor
• The final effluent is cooled and separated as hydrogen and LPGs which typically go to fuel gas, and isomerate product for gasoline blending