Most cokings are delayed coking factors. It is a purely thermal (not catalyst) process in which heat is used to break down the heavy starting material into a number of lighter components as well as a significant amount of petroleum coke (solid carbon). The mixture of treated materials flows into large drums where the solid coke can settle and the lighter liquid/vapour is sucked in and introduced into a fractionator to separate the liquid products. When a drum fills with coke, the feed is replaced by another drum. The solid drum is cooled with water and then opened so that the solid coke can be pierced with high-pressure water jets. The flowchart and description of this section are based on a delayed coking plant with a single pair of coke drums and a raw material furnace. However, as mentioned above, larger units can have up to 4 pairs of barrels (8 barrels in total), as well as one oven for each pair of coke barrels. Hot product vapours and steam from the top of the drum are quenched by the feed entering the fractionator to prevent coking in the fractionator and to remove lighter components from the vacuum residue supply. The fractionator separates the coke products into gas, coke naphtha, light diesel and heavy coke gas. Lateral steam is used with the fractionator to ensure proper separation between naphtha coke and light diesel streams [2].
There are other petroleum refining processes for the production of petroleum coke, namely the fluid coking and flexicoking processes,[12][13] both of which were developed and licensed by ExxonMobil Research and Engineering. The first commercial unit entered service in 1955. Forty-three years later, starting in 1998, 18 of these units have been deployed worldwide,[14] including 6 in the United States. In the coking process in the refinery, the flow in the furnace is heated to the coking temperature, and then the in-line coking drum is fed. Large amounts of steam are injected after the furnace to delay the coking reaction until the flow enters the coke drum, where the heavy oil is cracked into lighter hydrocarbons and coke, which is mainly deposited in the drum to be removed during the regeneration cycle. The cracked hydrocarbons then go into the fractionation column to separate the different flows, returning the soils to the entrance for a subsequent passage through the coking. The operating variables of delayed coking include heating outlet temperature, pressure, recycling rate and cycle time. These variables are selected based on feed properties such as characterization factor, asphalt content and Conradson carbon residue (RCF) to ensure that coking in pipe heaters is minimized and that the efficiency of liquid products is maximized. The recycling rate, which is usually 3-5%, is used to control the end point of Coker heavy diesel. The coke yield can vary between 20% and 30% depending on the dietary properties and coking conditions. In the manual, you can find some suggested equations to predict coke and other product yields based on the CCR of the vacuum residue and estimates of the distribution of sulfur in the diet between coke products, suggesting that up to 30% by weight of the sulfur in the food ends up in the coke.
30 % by weight in the gas product and 20 % by weight in heavy gas oil coke. Delayed coking is a thermal cracking process as a tailings treatment process in which a heavy hydrocarbon raw material is converted into lighter, more valuable products and coke. The coke produced from a delayed coke has many commercial applications and applications, the greatest use is as fuel. Delayed coking is a type of coke whose process involves heating a residual oil inlet to its thermal cracking temperature in a furnace with several parallel passages. There are other similar coking processes, but they do not produce petroleum coke. For example, the Lurgi-VZK Flash Coker, which produces coke by pyrolysis of biomass. [15] A delayed coke oven is a type of coke whose process consists of heating a residual oil supply in an oven with several passages parallel to its thermal cracking temperature. As a result, the long-chain heavy hydrocarbon molecules of residual oil in coke gas oil and petroleum coke are cracked. [1] [2] [3] Coking is a process found in more complex refineries to convert residual or “residual” tar streams from vacuum and atmospheric distillation into value-added products and intermediates such as LPG, naphtha, diesel, light and heavy gas oils. Coking is often done via a delayed coking plant that includes an oven, two coke drums – one in-line and one in regeneration – and a fractional column. As shown in Figure 6.6, the tailings supply is introduced into the fractionator after being heated in the heat exchangers containing the coke diesel products. The floors of the fractionator, including the heavy ends of the vacuum residue supply with recycling of heavy coke diesel, are mixed with steam and fed by heating the pipe in the furnace to be heated to about 475 ° C at a pressure of 10-30 psi.
Steam is added to prevent coking in the heater and the heated supply is introduced from the bottom of one of the coke drums. Coking takes place in the insulated coke drum while the drum fills up for a period of 4 p.m. to 6 p.m. While drum A is filled, drum B is decoded with hydraulic cutters and drill shaft, and coke is removed from the bottom of the drum. When the coking in drum A is complete, drum B must be moved, sealed, heated and prepared for the change of power supply. The coking cycle is controlled so that the vacuum residue is continuously introduced into the unit (since the vacuum column operates day and night) and the liquid products are continuously recovered, while the coke is intermittently removed in a semi-continuous process scheme. Therefore, in each delayed coking plant, there are at least two barrels of coke, and some units have more than two barrels. All the heat needed for coking is provided in the heater, while coking takes place in the coke drum. Therefore, the process is called “delayed coking”.
Coke produced from delayed coke has many commercial applications. [7] [10] [11] The most used is the one used as fuel. Delayed coking is one of the unit processes used in many oil refineries. The photo opposite shows a delayed coking plant with 4 barrels. However, larger units have pairs of tandem drums, some with up to 8 drums, each of which can have diameters of up to 10 meters and total heights of up to 43 meters. [4] Variations in the delayed coking process are flexicoker and fluid coking. A Flexicoker contains a coke gasifier that continuously converts company coke into combustible gas, thus avoiding the need to accumulate coke in a drum and creating an important fuel source (low Btu) for the refinery. Fluid coking is a reduced flexicoker that gasses only enough coke to fuel the coke itself. Figure 6.6 shows an organizational chart of the delayed progression of coking and a photo of a delayed coking plant. The derricks above the barrels containing the drill pipes are used to drill coke out of the coke drums at the end of the coke cycle. The coke yield of the delayed coking process varies from about 18 to 30 percent by weight of the residual oil of the raw material, depending on the composition of the raw material and the operating size.
Many refineries around the world produce up to 2,000 to 3,000 tons of petroleum coke per day and some produce even more. [5] The table below illustrates the wide range of compositions for crude coke (called green coke[6]) produced in delayed coke and the corresponding compositions after the green coke has been calcined to 2375°F (1302°C): the residual oil from the vacuum distillation unit (sometimes including high boiling point oils from other sources in the refinery) is pumped into the bottom of the distillation column, which is called the main fractionator. From there, it is pumped into the fuel furnace with injected steam and heated to its thermal crack temperature of about 480 °C. Thermal cracking begins in the tube between the furnace and the first coke drums and ends in the running coke drum. The injected steam helps minimize the deposition of coke in the furnace pipes. Improves the efficiency and service life of the liquid-liquid coalesceur The main products of coke are mainly raw materials for other refinery processing units. These are: In the fractionator, the remaining coke refines and the initially injected steam leaves the process in the fractionated products in the form of contamination of particles and water. Depending on the product, the removal of excess particles and water is necessary to achieve the quality of the final product or to meet the raw material requirements for other unit operations, such as for kerosene or diesel streams that feed hydrotreatments. As cracking in the drum continues, diesel and lighter components form in the vapor phase and separately from liquid and solids.
The wastewater from the drum is only steam, with the exception of liquids or solids that are transported, and are routed to a fractionation column where they are separated into desired boiling point fractions.