Refining is a combination of physical and chemical processes through which the various components of crude oil are separated and transformed. To carry out this process, ENAP's refineries, Aconcagua, BioBío, and Gregorio, have a series of plants that play a role in it.
The Units of a refinery include:
Topping (Primary Fractionation)
The crude, free of water and other impurities, enters the refinery to begin the primary fractionation process. This process involves the initial separation of the hydrocarbons that make up crude oil by heating them to 370°C. These hydrocarbons are then separated in a distillation column called "Topping." The lighter or more volatile components are separated at lower temperatures and exit the distillation column from the top, while the heavier products are obtained in the lower sections. The output order of the products according to their volatility is as follows: liquified gas, gasoline, naphtha, kerosene, diesel, gas oil and reduced crude oil. The gas oil feeds the Catalytic Cracking and Hydrocracking units. The bottom product or reduced crude is sent to the vacuum plants. The Topping and Vacío units operate integrated to maximize heat exchange, thus reducing energy and cooling consumption.
Vacuum Plants (Vacuum Fractionation) Their function is to prepare a suitable feed for the Catalytic Cracking and Hydrocracking units by fractionating the reduced crude under vacuum to prevent the coking of these products. The reduced crude from the Topping plants is fractionated into gas oil and pitch in low-pressure distillation columns. The gas oil is sent for further processing in the Catalytic Cracking and Hydrocracking units. Part of the pitch is sent to the Visbreaker or Viscorreduction plants to obtain fuel oil, while another part of the pitch is sent to the Delayed Coking plants, where it is transformed into diesel and gasoline. The remaining pitch is asphaltene, which is used to produce asphalts for road construction.
Ethylene Plant (BioBío Refinery) A portion of the naphtha from the Topping unit is processed in this plant to produce light gases, liquified petroleum gas, ethylene, propylene, and high-octane gasoline. Ethylene is transported via a pipeline to the PetroDow plant, where it is polymerized into low-density polyethylene. The gasoline produced in this unit is used to prepare 93 and 97 octane special gasolines. Propylene is sent to the Petroquim plant, where it is polymerized into polypropylene.
Catalytics Reforming
This plant produces 97-octane gasoline, liquified gas and light gases from naphtha from the Topping columns. This unit is one of the main producers of hydrogen, an element that is used as a raw material in the processes of obtaining low-sulfur products.
Light ends recovery and treatment plant
It is designed to recover propane and butane from different sections of the refinery. The products of this plant are stabilized cracked gasoline, propane, butane and refinery gas that is burned in the furnaces.
Alkylation Plant (Aconcagua Refinery)
In petroleum technology, alkylation is the chemical combination of an isoparaffin (isobutane) and an olefin (butylene) to form isomeric hydrocarbons (isooctane) that distill in the range of gasoline which, due to its high-octane number, is used to prepare aviation gasoline.
Acid Plant (Aconcagua Refinery)
This unit's function is to regenerate the sulfuric acid (H2SO4) catalyst used in the Alkylation Plant so that it can be reused.
Diesel production unit
This unit consists of a moderate vacuum gas oil hydrocracking plant, an intermediate product of the refining process, which allows obtaining low sulfur diesel. The most important equipment of the unit is the reactor, where the vacuum gas oil feed, previously heated to high temperature and in the presence of catalyst, undergoes a combination of cracking and hydrogenation reactions. The reaction products are separated in a fractionation tower, cooled and sent to storage ponds as low-sulfur diesel.
Sulfur recovery unit
The Sulfur Recovery Unit works on the basis of the so-called "Claus Reaction," in which a mixture of sulfur gases in certain proportions reacts thermally at 1300 ºC and catalytically at a lower temperature to produce gaseous sulfur. This sulfur gas liquefies when cooled in two boilers, which produce useful steam for the refinery using recovered energy. The highly pure product is loaded in liquid form at 130°C, using an arm installed on a special tank truck loading island, for transportation to commercial distribution facilities.
Isomerization unit
This unit increases the octane rating of topping gasolines, allowing the production of high-octane gasolines to be increased.
Hydrocracking
The gas oil from all the units can also be sent to the hydrocracking unit, where gases (Fuel Gas), hydrocracking naphtha, high-quality, low-sulfur diesel, and unconverted gas oil are produced. This unit transforms the remaining vacuum gas oil, mainly into diesel and, to a lesser extent, into kerosene, naphtha, and light gases. The process involves the reaction of gas oil with hydrogen from the Hydrogen Plant. The diesel obtained in this process is of excellent quality with very low sulfur content. The hydrocracking process can also produce aviation kerosene.
Visbreaker
In this plant, the viscosity of the pitch from the Vacuum Unit is reduced to produce fuel oil. In addition, this unit produces a small amount of light gases, gasoline, and diesel.
Catalytic Cracking
This plant receives a portion of the gas oil from the vacuum columns to transform it into a base gasoline for preparing 93-octane gasoline. This plant also produces light gases used as fuel in the refining process, liquified gas, propylene, diesel, and some fuel oil. A catalytic cracking plant has two sections: the converter and the fractionator. The converter itself has two vessels that can be stacked or placed side by side. These are the reactor and the regenerator. Both pieces of equipment are interconnected and operate together.
Wet Gas Scrubber
This unit allows for the cleaning of gases generated in the Catalytic Cracking unit's combustion, reducing particulate emissions to the atmosphere.
Delayed Coking
The vacuum pitch can also be sent to a delayed coking plant or Coker, where it is converted into gases (Fuel Gas), coker naphtha, coker diesel, heavy coker gas oil, and petroleum coke. Delayed coking is a thermal cracking process where the heat required for the coking reactions is provided by a furnace. At the furnace's exit, there are two large and tall chambers or drums (8-9 meters in diameter by 25-30 meters in height), with one of them allowing the product to undergo coking for 24 hours. The other drum is isolated from the process to be unloaded of its coke load using water-cutting tools. Once freed of the coke, the drum returns to the production line, while the other follows the same unloading or decoking process.
Hydrodesulfurization or Hydrotreatment of Naphtha and Diesel
In the Hydrotreating (HDT) units, naphtha is treated with hydrogen to reduce the sulfur and nitrogen content of the Reforming unit's feed. Similarly, diesel is treated using a Hydrodesulfurization unit, reducing the sulfur content of this fuel to levels below 50 parts per million. The HDT unit processes the naphtha and diesel produced in the Coker, generating low-sulfur and low-nitrogen naphtha and diesel products.
DIPE Plant (Aconcagua Refinery)
This unit serves a triple purpose: it produces di-iso-propyl ether, a compound used in the production of high-quality reformulated gasoline; it reduces the emission of volatile components into the atmosphere, and it improves the combustion quality of gasolines.