Delayed coking unit

Delayed coking is a petroleum secondary processing technology. It uses hydrogen-depleted heavy oil as a raw material to conduct deep thermal cracking and condensation reactions at high temperatures (about 500°C) to produce rich gas, naphtha, diesel, and wax oil. And coke technology.

It is one of the main methods of deep processing of residual oil in the world, and its processing capacity accounts for one third of the residual oil processing capacity. The so-called delay means that the coking oil (feedstock oil and circulating oil) is heated by the heating furnace to rapidly increase the temperature to the coking reaction temperature. There is no coke in the reactor tube, but enters the coking tower to proceed the coking reaction, so there is a delay effect, which is called delay. Coking technology. Generally, there are one furnace (heating furnace) and two towers (coking tower) or two furnaces and four towers. The heating furnace is fed continuously and the coking tower is operated alternately, which is a semi-continuous process. The raw oil (vacuum residue or other heavy oils such as deoiled asphalt, clarified oil and even slop oil) is heated to 495~505℃ and enters the coke tower. The hot raw oil undergoes coking reaction in the coke tower to produce light products. From the top, it enters the fractionation tower, where rich gas, crude gasoline, diesel oil and heavy distillate oil are fractionally distilled. The heavy distillate oil can be sent for further processing (for example, as a feedstock for catalytic cracking and hydrocracking), or it can be fully or partially recycled back to the feedstock system. After the coke is gradually filled (leave a certain space), the raw material is improved into another coke drum, and the coke remaining in the coke drum is discharged by hydraulic decoking. After the coke tower is restored to the empty tower, the raw materials can be heated. The yield of coke in this process generally changes with the change of the raw material oil Conker Carbon Residue (CCR). The yield of rich gas is generally about 10% (mass) (gas yield%=7.8+0.144×CCR), and the rest is due to different circulation ratios. However, the diesel/steam ratio is greater than 1. The delayed coking feedstock can be heavy oil, residual oil, or even bitumen. Delayed coking products are divided into gas, gasoline, diesel, wax oil and coke. For domestic residual oil, the gas yield is 7.0~10%, the crude gasoline yield is 8.2~16.0%, the diesel yield is 22.0~28.66%, the wax oil yield is 23.0~33.0%, and the coke yield is 15.0~ 24.6%, the external oil rejection is 1~3.0%. Coking gasoline and coking diesel are the main products of delayed coking, but their quality is poor. The octane number of coking gasoline is very low, generally 51~64 (MON), and the cetane number of diesel is higher, generally 50~58. However, the two oils have high olefin content, high content of impurities such as sulfur, nitrogen, and oxygen, and poor stability. They can only be used as semi-finished or intermediate products. After being refined, they can be used as a blending component of gasoline and diesel. Coking wax oil is a poor quality wax oil for secondary processing due to its high content of sulfur, nitrogen compounds, gums, and carbon residues. As of 2014, it is usually blended into catalytic or hydrocracking as raw materials. Petroleum coke is one of the important products in the delayed coking process, and can be used as electrodes, metallurgy and fuels depending on the quality. After being desulfurized, the coking gas can be used as a raw material for hydrogen production or as a fuel in a fuel pipeline network.
Delayed coking process: Delayed coking is similar to thermal cracking, except that it is heated to the temperature required for the coking reaction in a short time, and the raw material is controlled to basically not crack in the furnace tube, but is delayed to the special coke tower for cracking reaction. “Delayed Coking” is also named for this. The delayed coking device is mainly composed of 8 parts: the folding coking part, the main equipment is a heating furnace and a coke tower. There are one furnace and two towers, two furnaces and four towers, and some are directly combined with other devices. In the folding fractionation part, the main equipment is a fractionation tower. In delayed coking, it is generally necessary to add chemicals such as defoamers/scorch inhibitors/liquid yield enhancers. Folding coking gas recovery and desulfurization. The main equipment is absorption tower, desorption tower, stabilization tower, reabsorption tower, etc. Fold the hydraulic decoking part. Taking into account the high hydrocarbon ratio of heavy residual oil, which is very easy to coke, the raw oil is quickly heated to a relatively high temperature (480~500℃), so that the heavy residual oil is too late to react in the tubular heating furnace. It is sent to a hollow container (called coke tower), where the heated oil undergoes cracking and condensation reaction. Heating and coking do not occur at the same time, so it is called delayed coking. The 415℃ high-temperature oil and gas generated by the cracking reaction in the coke tower escapes from the top of the coke tower into the feed section of the lower section of the main fractionation tower. After washing the coke particles carried by the washing plate (herringbone baffle), it rises from the evaporation section and enters the wax oil. Distillation and separation above the oil collection tank, fractional distillation of rich gas, gasoline, diesel and light and heavy wax oil fractions, while the coke formed by the condensation reaction in the coke tower remains in the coke tower, when the coke tower has reached a certain degree of coking, switch to another The coke drum continues to be coked into coke, while the original coke drum performs coke cleaning operations. Usually 2 to 4 coke towers are often used in a coking unit. The coke cleaning adopts the hydraulic decoking method. First, a hole is drilled in the center of the coke layer with a drill, from the top to the bottom, and then high-pressure water with a pressure of 12 to 30 MPa is introduced from the bottom to the top. The impact of the water is used to beat the coke. Come down and drain from the bottom. The high-pressure water delivered by the high-pressure water pump passes through the water line, hose, drill pipe to the nozzle of the hydraulic coke cutter, and the high-pressure water sprayed from the nozzle of the coke cutter forms a high-pressure jet, which uses the powerful impact of the high-pressure jet to remove the oil The coke is cut down. The drill rod is continuously raised and lowered and rotated until the coke is removed. Main hydraulic decoking equipment: (high pressure water pump), (decoking control valve), lubricating oil system, pneumatic valve, winch and pulley block, (new type decoking hose), (water turbine reducer), (automatic switching combined drilling and cutting Coke device), (tower top cover automatic loading and unloading machine), (tower bottom cover loading and unloading machine), (elevator), (drill pipe assembly) and (grab crane). Dehydration, storage and transportation of folded coke. Folding blowing and venting system. Folding steam generation part: The heat source for steam generation generally uses fractionation tower side line diesel, heavy wax oil, and bottom circulating oil. Fold the coke roasting section. The outlet temperature of the selected domestic furnace is 495~500℃, and the pressure at the top of the coke tower is 0.15~0.2 Mpa.

 

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