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HYDROCRACKING AND COKING
Publication date:2Q 2018
Hydrocracking and Coking
Hydrocracking (HC) is utilized in refineries to upgrade a variety of feeds that range from coker naphtha to various heavy gas oils and residual fractions into lighter molecules. The hydrocracking process has emerged as the primary diesel producer in many refinery configurations, and as environmental regulations on transportation fuels continue to tighten, the hydrocracker will be one of the tools available to refiners to meet new product specifications. Unlike FCCU processes, hydrocrackers can effectively yield ultra-low sulfur diesel (ULSD) streams whereas middle-distillate range FCC products (i.e. light cycle oil, LCO) will regularly require additional treating to meet product blending specifications.
Hydrocracking units can also offer improved flexibility to shift production modes between gasoline and diesel (or called gas oil) products based on process selection, operating conditions, and catalysts used. The severity (e.g., temperature, H2 partial pressure, LHSV, process configuration, catalyst type, etc.) of the unit is set based upon the composition and properties of the feedstock processed and the desired conversion level and/or product distribution. Certain feeds (e.g., paraffinic) may be difficult to crack and thus require a higher operating temperature, while others (e.g., aromatic feeds) may have a high tendency for coke formation and, thus, require special catalyst formulations. Hydrocracker operators have been looking to increase the profitability of the unit by processing heavier feedstreams, including heavy vacuum gas oil (HVGO), FCC LCO, coker gas oil, visbroken gas oil, deasphalted oil, and resid feeds, while minimizing the hydrogen consumption and boosting overall energy efficiency. Residual feeds present the problems of increased H2 consumption, lower product yields and quality, and reduction in cycle length. Technology developers have been searching for methods to allow for hydrocracking units to continue normal operation while processing these difficult-to-handle feeds. These optimized parameters include higher liquid-gas distribution and reactor volume efficiency. Along with optimized process parameters, catalyst companies are also developing novel formulations that aim to increase process performance while dealing with these challenging feeds. These novel catalysts may be paired with state-of-the-art reactor internals to maximize performance.
Typical yields for a full conversion hydrocracker using a flexible catalyst to swing between maximum diesel and naphtha modes are: 0.2-0.4 wt% dry gas, 6.0-13.0 vol% LPG, 28.0-48.0 vol% naphtha, and 54.0-85.0 vol% diesel and jet fuel combined. If the unit is designed to make maximum naphtha, the total naphtha yield could be as high as 115.0 vol%. Light naphtha from a hydrocracker often can be blended directly into gasoline pool. The heavy naphtha is typically sent to reforming unit for octane boost. The reformer generates hydrogen but a hydrogen plant is likely required to supplement the hydrogen requirement of the hydrocracker. The diesel and jet fuel require no further processing, as these often exceed the cetane and smoke point requirements, respectively.
Process designers and catalyst manufacturers are feverishly developing cost-effective and energy-efficient hydrocracking technology and revamp options to satisfy the refining industry around the world. Hydrocracking technology licensers are looking at new ways to remove heavy polynuclear aromatics (HPNAs) from the unit as the buildup of HPNAs can lead to increased catalyst deactivation and fouling. Multiple-phase hydroprocessing units have also been developed to minimize hydrogen consumption while also reducing unit severity. Finally, the utilization of hydrocracking technologies to upgrade resid and/or renewable feeds to produce additional supplies of high-quality liquid products has been covered extensively through commercial projects and R&D work over the past several years.
Additionally, the hydrocracking section features the latest trends and technology offerings, including:
The increased presence of heavy crudes on the market has led many refiners to focus on technology suitable for upgrading these discounted, heavy feedstocks. Coking is a major bottom-of-the-barrel upgrading process whose popularity has risen steadily in response to heavier crude supplies and the dwindling demand for residual fuel oils. This process converts heavy feedstocks such as vacuum residuals, heavy cracked gas oils, and decanted oils into gas, LPG, relatively low-boiling distillates, and solid coke. Furthermore, petroleum coke, a byproduct of coking, is finding use in a variety of markets throughout the industrial sector. Historically, strong gasoline markets and diverse outlets for petroleum coke made delayed coking the most prolific residue upgrading technique; however, some of these market factors are changing as diesel demand is outpacing gasoline and some outlets for petcoke have or will come under scrutiny with new SOX and CO2 regulations. Operational improvements and technical advances must be applied by refiners to support continued growth of coking technology as it is utilized in plants dealing with difficult feedstocks, tight production margins, demanding efficiency standards, and stringent environmental constraints.
As the worldwide crude slate shifts to heavy and extra-heavy refinery feeds, refiners will need to take advantage of various bottoms upgrading techniques to cut deeper into the crude barrel to yield valuable distillate products. Many of these technologies have been around since the 1950s or even earlier and have reached commercial maturity. Some of the more advanced processes have recently evolved as modifications of conventional processes to deal with the increased resid contents of incoming feeds. Finally, the development of highly integrated processing schemes has aided refiners in economically processing resid streams.
Due to the flexibility of the process, coking has emerged as the leading technology in residue upgrading both in the refinery and in upstream heavy oil upgrading plants. Several significant trends have emerged that can be identified by analyzing the recent research work related to coking processes. Delayed coking has received much of this focus, particularly with regards to innovations that increase product yields and quality as well as integrated processing options that incorporate delayed coking with other refining technologies such as hydroprocessing, solvent deasphalting, and catalytic cracking. Recent research work has resulted in the introduction of new furnace designs as well as other pieces of equipment and devices that can provide environmental, energy consumption, safety, reliability and economic benefits. Significant resources have also been invested in efforts to develop defoamers and anti-coking agents for use in the delayed coking process. And researchers have investigated drum cracking that occurs during coking operations and have utilized modeling for drum fatigue life prediction.
Additionally, the coking section features the latest trends and technology offerings, including:
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Keywords: hydrogen, hydrocracking, middle distillates, diesel, ULSD, heavy oil, tight oil, ebullated-bed, slurry-bed, fixed-bed, single-stage, two-stage, two-stage with recycle, jet fuel, kerosene, gasoil, gas oil, coker gas oil, coker naphtha, DAO, VGO, HVGO, LCO, mild hydrocracking, resid hydrocracking, renewable hydrocracking, renewable jet fuel, renewable diesel, biodiesel, dewaxing, cold flow properties, cloud point, pour point, cetane, platinum, palladium, NiMo, CoMo, NiW, heavy polynuclear aromatics, HPNAs, Fischer-Tropsch, F-T, thermal cracking, bottom of the barrel, heavy oil, upgrading, resid, opportunity crudes, residual fuels, residue conversion, bunker fuels, marine fuels, fuel oil, heavy oil upgrading, decoking, coke morphology, fluid coke, shot coke, unheading, coker gas oil , cogeneration, IGCC, petcoke gasification, integration, coke drum, anode grade coke, needle coke, coke drum foaming, coker additives