Upgrading of Heavy Feeds Part 2 (Petroleum Refining)

Hydrovisbreaking Processing

1. hycar This is one type of noncatalytic process, based on visbreaking and involving treatment with hydrogen at mild conditions. This process is completed in three reactors:

• Visbreaking. This reactor carries out a moderate thermal cracking process in the presence of hydrogen. Hydrogen leads to more stable products than those obtained with straight visbreaking, which means that higher conversions can be achieved, producing a lower-viscosity product while no coke formation is induced.

• Hydrodemetallization. This reactor is to remove contaminants, particularly metals, prior to HCR. The product coming from the visbreaker is fed to the demetallization reactor in the presence of catalyst, which provides pore of sufficient size for diffusion and adsorption of high-molecular-weight constituents.

• Hydrocracking. In this reactor desulfurization and denitrogenation take place along with hydrocracking. Hydrocracking and hydrodemetalliza-tion reactors may employ inexpensive catalyst (CoMo) to remove metals and for cracking of complex molecules, respectively.

2. aquaconversion Another type of hydrovisbreaking technology is aqua-conversion, which is a catalytic process that uses catalyst-activated transfer of hydrogen from water added to the feedstock in slurry mode. The homogeneous catalyst is added in the presence of steam, which allows the hydrogen from the water to be transferred to the heavy oil when contacted in a coil-soaker system, normally used for the visbreaking process. Reactions that lead to coke formation are suppressed and there is no separation of asphaltene-type material.

The main characteristics of aquaconversion are:

• Hydrogen incorporation is much lower than that obtained when using a deep hydroconversion process under high hydrogen partial pressure.

• Hydrogen saturates the free radicals, formed within the thermal process, which would normally lead to coke formation.

• A higher conversion level can be reached, and thus higher API and viscosity improvements, while maintaining syncrude stability.

• It does not produce coke.

• It does not require a hydrogen source or high-pressure equipment.

• It can be implanted in the production area, thus eliminating the need for external diluent and its transport over large distances. Light distillates from the raw crude can be used as a diluent for both the production and desalting processes.

The presence of an oil-soluble catalyst and water prevents the coke formation and deposition of sediment that often occurs during visbreaking. In this process catalyst may be used as a support or mixed directly with the feedstock. The metals (metal salts) used for hydrovisbreaking are alkali metals such as potassium or sodium. The role of the catalyst is to enhance the dissociation of H2O to release hydrogen (H+) ions, which is subsequently consumed in hydroprocessing.

Fixed – Bed Hydroprocessing Hydroprocessing of residue in a fixed - bed reactor is well established and reported in the literature. The general characteristic of hydroprocessing is the simultaneous or sequential hydrogenation of hydrocarbon feed in the presence of sulfided catalyst by reacting with hydrogen. The main problem with fixed-bed catalyst is deactivation over time, which can be minimized by a guard-bed reactor in order to reduce metal deposition on the downstream reactors. Several combinations using two or three processing steps can be implemented in the refining. The catalyst in the guard-bed reactor is typically an HDM catalyst or large-pore catalyst with a high metal retention capacity.

Various improvements have been reported in the last decade to increase the efficiency of fixed-bed hydroprocessing, such as run length, conversion, and product quality. Some of these improvements have been focused on mechanical design, such as the use of a bunker, swing reactors, guard-bed reactors, feed distribution, and a coke and metal deactivation- resistant catalyst, including pore and particle grading and onstream catalyst replacement. Despite all disadvantages, mainly short catalyst life, up until now most residue hydroprocess-ing units have used fixed-bed reactors.

1. rds/vrds TheRDSprocessisusedforatmosphericresiduumhydrotreat-ing and the VRDS process for vacuum residuum desulfurization to remove sulfur and metallic constituents while part of the feedstock is converted to lower-boiling products. In both processes, AR or VR feedstocks contact with catalyst and hydrogen at moderate temperatures and pressures, consuming about 700 to 1300 standard cubic feet (SCF) H2/bbl of feed. The conversion increases with temperature, but due to the high coke deposition, the process is not appropriate for use at high temperature. The RDS and VRDS processes do not convert directly to transportation fuel, but this process is able to produce acceptable feedstock for RFCC or delayed coking units to achieve minimal production of residual products in a refinery. The basic process flow and catalyst are the same for RDS and VRDS.

A combination of RDS/VRDS and RFCC has gained wide acceptance due to the selective conversion of residue and smaller amount of by-products. The limitation for RFCC is deposited metals, since Ni deposition increases olefin yields through dehydrogenation, and as a result more coke formation is obtained, while deposition of V metal destroys the zeolite structure. Also, the combination of a desulfurization step and VRDS is often seen as an attractive alternative to the atmospheric residuum desulfurizer. In addition, either RDS or VRDS can be coupled with other processes (such as delayed coking and solvent deasphalting) to achieve the optimum refining performance.

2. hyvahl-f and hyvahl-s These processes are used to hydrotreat AR and VR feedstocks to convert them into more valuable products (naphtha and middle distillates). Hyvahl processes are designed primarily for feedstock containing high concentrations of asphaltene, maltenes, and metals, which strongly limit catalyst performance. The reactors can be used in the classical fixed – bed (Hyvahl F) or swing-mode system (Hyvahl S). Hyvahl-F uses fixed – bed reactors in which liquid and gas flow downstream co-currently in a trickle-flow regime. The first catalyst is resistant to fouling, coking, and plugging by asphal-tene constituents, has a high metals retention capacity, and is used for both hydrodemetallization and most of the conversion. So the highly active second catalyst is protected from metal poisons and deposition of cokelike products and can carry out its deep hydrodesulfurization and refining functions. Its main application is for processing distillate fractions and some atmospheric residua. For vacuum residua and heavy oils, it may require frequent catalyst replacements, which may be complex and uneconomical. Optimization of catalyst properties, space velocity, and maximum reaction temperature may extend the life of the catalyst, depending mainly on the metals content in the feed. Hyvahl-S, also called the Hyvahl- F- swing reactor, uses two guard reactors in a swing arrangement and switchable operation, which are fixed-bed reactors with simple internals. This configuration allows fast switching of the guard reactor in operation with a deactivated catalyst to the other guard reactor with fresh catalyst, without shutting down the plant. The major feature of this process is a fixed bed using the swing-mode reactor concept at high temperature, high hydrogen pressure, and low contact time. The switching of guard reactor and adjusting of conditions are fast and controlled by a conditioning package.

3. residue hydrocracking Thegrowingdemandformiddledistillateshas increased the need for HCR in terms of process flexibility as well as configuration and product composition. The catalysts used for HCR should have dual functionality [i.e., cracking and hydrogenation (HYD) functions]. The process scheme of a typical HCR fixed- bed system contains two reactors. The first reactor (first-stage HCR) contains an HDT catalyst of high activity for the removal of heteroatoms or metal, while the second reactor (second-stage HCR) contains the actual HCR catalyst. In general, the first – stage reactor contains NiMo catalyst, which removes S, N, metals, and hydrogenate aromat-ics, while the second reactor possesses an acidic support (zeolite, mixed oxides)-based catalyst that promotes hydrogenation as well as hydrocracking reaction.

In contrast to HDT, the support plays an active role in the conversion of the feed in HCR catalyst. The performance of HCR catalyst is determined by the ratio or balance between the hydrogenation metal (sulfide) site and the acid sites of support. When the number of hydrogenating sites is low compared with the number of acid sites, secondary cracking processes can take place, resulting in light products. Additionally, the hydrogenation function also prevents the oligomerization and coking over the acid sites. A deficient hydro-genation function will lead to enhanced deactivation of the catalyst. On the other hand, when a very strong hydrogenation function is used, cracking is suppressed in favor of isomerization. In the ideal HCR the catalyst requires a balance between metal and acid functions.

Several fixed-bed hydrocracking processes are used by refiners on the basis of their product selectivity:

• IFP hydrocracking. This process features a dual-catalyst system. The first catalyst is a promoted NiMo amorphous catalyst which acts to remove sulfur and nitrogen and hydrogenate aromatic rings, while the second catalyst is a zeolite which finishes the hydrogenation and promotes the hydrocracking reaction. There are two versions of this process:

• Single-stage process. The first reactor effluent is sent directly to the second reactor, followed by separation and fractionation steps. The fractionator bottoms are recycled to the second reactor or sold.

• Two-stage process. The feedstock and hydrogen are heated and sent to the first reaction stage, where conversion to products occurs. The reactor effluent phases are cooled and separated and the hydrogen-rich gas is compressed and recycled. The liquid leaving the separator is fractionated, the middle distillates and lower-boiling streams are sent to storage, and the high- boiling stream is transferred to the second reactor section and then recycled to the separator section.

• Isocracking. Depending on the feedstock properties, there are various process flow schemes: single – stage once – through liquid; single – stage partial recycle of heavy oil; single-stage extinction recycle of oil (100% conversion); and two-stage extinction recycle of oil. The isocracking process uses multibed reactors and a number of catalysts. The catalysts are dual function, being a mixture of hydrous oxides (for cracking) and heavy metal sulfides (for hydrogenation). The catalysts are used in a layered system to optimize the processing of the feedstock, which undergoes changes in its properties along the reaction pathway.

• Mild hydrocracking. This process uses operating conditions (and a flow scheme) similar to those of a vacuum gas oil desulfurizer to convert the feed into significant yields of lighter products. The conditions for mild hydrocracking are typical of many low-pressure desulfurization units, and the process is a simple form of hydrocracking.

• MRH. MRH is a hydrocracking process designed to upgrade heavy feedstocks containing large amounts of metals and asphaltene, such as VR and bitumen, and to produce mainly middle distillates. The reactor is designed to maintain a mixed three-phase slurry of feedstock, fine powder catalyst, and hydrogen, and to promote effective contact.

• Unicracking. There are various versions of this process:

• Basic unicracking. This is a fixed-bed catalytic process designed as a single-stage or two-stage system with provisions to recycle to extinction. The process operates satisfactorily for a variety of feedstocks. The catalysts, which induce desulfurization, denitrogenation, and hydrocracking, are based on both amorphous and molecular-sieve-containing supports.

• Advanced partial conversion unicracking (APCU). This is a recent advancement in the area of ultralow-sulfur diesel (ULSD) production and feedstock pretreatment for catalytic cracking units.

• HyCycle unicracking. This is designed to maximize diesel production for full – conversion applications.

Moving-Bed Hydroprocessing There are a few types of hydroprocessing reactors with moving catalyst beds in which the catalyst goes in downflow through the reactor by gravitational forces. In general, catalyst replacement is commonly a batch operation, which is done typically once or twice a week. The fresh catalyst enters at the top of the reactor and the deactivated catalyst leaves the reactor at the bottom, while the hydrocarbon goes either in counter-or co – current flow through the reactor. With this moving-bed system, the catalyst can be replaced either continuously or in batch operation. Catalyst transfer is the most critical section. The countercurrent mode of operation seems to be the best configuration since the spent catalyst contacts the fresh feed at the bottom of the moving-bed reactor while the fresh catalyst reacts with an almost already hydrodemetallized feed at the top of the moving-bed reactor, resulting in lower catalyst consumption.

1. hycon process The Hycon process is used to improve the quality of residual oils by removing sulfur, metals, and asphaltene constituents and is typically operated in fixed- bed mode, but with increasing metal content in the feedstock, one or more moving-bed "bunker" reactors are added as the leading reactors for HDM. The process is suitable for a wide range of the heavy feedstocks, particularly high in metals and asphaltene constituents. This process enables easy catalyst replacement (to remove or add portions of catalyst) without interrupting operation by means of valves of lock hoppers. The catalyst and heavy oil are fed in co-current flow; the fresh catalyst enters at the top of the reactor and deactivated catalyst is removed from the bottom. The catalyst is replaced at a rate that will ensure a total plant run time of at least a year, which depends on the metal contaminants in the feed. In this way, the bunker reactor technology combines the advantages of plug-i+ow fixed-bed reactor operation with easy catalyst replacement and provides extra process flexibility if it is used upstream from the desulfurization reactor, especially with reference to the processing of feedstocks with a high metal content. For feeds containing a large amount of metal, metal sulfide can be better accommodated on the catalyst in a bunker- flow reactor than on other reactor systems. Operating conditions and the catalyst addition and withdrawal rates can also be adjusted to ensure that the catalyst taken out is completely spent, while retaining an acceptable average activity in the reactor.

2. ocr process OCR (onstream catalyst replacement) is a moving-bed reactor for hydroprocessing of heavy oils and residua with a significant amount of metals operating in a countercurrent mode at high temperature and pressure. Fresh catalyst is added at the top of the reactor and the feed into the bottom, and both move through the reactor in a countercurrent flow, causing the feed with the highest content of impurities to contact the oldest catalyst first. The fresh catalyst can be added at the top of the reactor and the spent catalyst removed from the OCR reactor while the unit is onstream. An OCR moving-bed reactor can be incorporated in the processing scheme either before or after fixed-bed reactors, so that heavier feeds with higher levels of contaminants can be processed while maintaining constant the product quality and economical fixed-bed reactor run lengths.

3. hyvahl – m This process employs countercurrent moving-bed reactors and is recommended for feeds containing large amounts of metals and asphaltenes. It requires special equipment and procedures for safe and effective catalyst transfer into and out of the high-pressure unit, similar to the OCR reactor. Catalyst is taken at atmospheric pressure and transferred to a reactor operating under hydrogen pressure, and then the catalyst is taken from the reactor at high operating conditions and discharged to the atmosphere.

Ebullated – Bed Hydroprocessing In ebullated – bed hydroprocessing, the catalyst within the reactor is not fixed. In such a process, the hydrocarbon feed stream enters the bottom of the reactor and flows upward through the catalyst, which is kept in suspension by the pressure of the fluid feed. The hydrocarbon feed and hydrogen are fed upflow through the catalyst bed, expanding and backmixing the bed, and minimizing bed plugging and AP. The oil is separated from the catalyst at the top of the reactor and recirculated to the bottom of the bed to mix with the new feed. Alternatively, fresh catalyst is added to the top of the reactor and spent catalyst is withdrawn from the bottom of the reactor.

Ebullating- bed reactors are capable of converting the most problematic feeds, such as AR, VR, and all other heavy oil feedstocks, which have high contents of asphaltenes, metals, and sulfur. Ebullating-bed reactors can perform both HDT and HCR functions; thus, these reactors are referred as dual-purpose reactors. Ebullating-bed catalysts are made of pellets or grains that are less than 1-mm in size to facilitate suspension by the liquid phase in the reactor.

There are three main ebullated-bed processes, which are similar in concept but different in mechanical aspects.

1. H-Oil. The H-Oil ebullated-bed process uses a single-stage, two-stage, or three-stage ebullated-bed reactors and can operate over a wide range of conversion levels. It is particularly adapted to process heavy vacuum residues with high metals and Conradson carbon to convert them into distillate products as well as to desulfurize and demetallize feeds to coking units or residue fluid catalytic cracking units, for production of low-sulfur fuel oil or for production in asphalt blending. An H-Oil process maintains constant product properties during cycle length. Since an H-Oil reactor has the unique characteristic of stirred – reactor- type operation with a fluidized catalyst, it has the ability to handle exothermic reactions, solid- containing feedstock, and flexible operation while changing feedstocks or operating objectives.

2. T-Star. T/Star is an extension of the H/Oil process which can maintain global conversions in the range 20 to 60% and specifically, an HDS of 93 to 99%. This process can act as an FCC pretreater or vacuum gas oil (VGO) hydrocracker. H-Oil catalyst can be used in the T-Star process. A T-Star reactor can also be placed in-.ine with an H- Oil reactor to improve the quality of H-Oil distillate products. In mild hydrocracking mode, the T-Star process can reach conversions up to the 60%, with a catalyst not sensitive to sulfur and nitrogen levels in the feed and will provide constant conversion, product yields, and product quality. This consistency in output is due to the catalyst being replaced while the unit remains online.

3. LC-Fining. The LC-Fining ebullated-bed process is a hydrogenation process that can be operated for HDS, HDM, and HCR of atmospheric and vacuum residues. LC- Fining is well suited for extraheavy residue, bitumen, and vacuum residue feedstock HDT and has demonstrated long cycle lengths. The general advantages of LC-Fining are low investment, more light-end recovery, lower operating costs, and lower hydrogen losses. This process yields a full range of high-quality distillates; heavy residue can be used as fuel oil, synthetic crude, or feedstock for RFCC, coker, visbreaker, or SDA. The LC-Fining process can achieve conversions for HDS of 60 to 90%, HDM of 50 to 98%, and CCR reduction of 35 to 80%. The process parameters and reactor design are marginally different from the H-Oil process. The reaction section uses a commercially proven low-pressure hydrogen recovery system. An internal liquid recycle is provided with a pump to expand the catalyst bed continuously. As a result of an expanded bed operating mode, small pressure drops and isothermal operating conditions are accomplished. Small-diameter extruded catalyst particles as small as 0.8 mm (+2 in.) can be used in this reactor. Separating the reactor effluent and purifying the recycled hydrogen at low pressure results in lower capital cost and allows design at lower gas rates.

Slurry-Bed Hydroprocessing Slurry-bed reactor can also be used for hydro-processing of feeds with very high metals content to obtain lower-boiling products using a single reactor. SBR-based technologies combine the advantages of the carbon rejection technologies in terms of flexibility with the high performances peculiar to the hydrogen addition processes. SBR achieves a similar intimate contacting of oil and catalyst and may operate with a lower degree of backmixing than EBR. In contrast to FBR and EBR, in SBR a small amount of finely divided powder is used, which can be an additive or a catalyst (or catalyst precursors). The catalyst is mixed with the feed (heavy oil), and both are fed upward with hydrogen through an empty reactor vessel. Since the oil and catalyst flow co-currently, the mixture approaches plug-flow behavior. In an SBR the fresh catalyst is slurried with the heavy oil prior to entering the reactor, and when the reaction finishes, the spent catalyst leaves the SBR together with the heavy fraction and remains in the unconverted residue in a benign form.

1. canmet Canmet is a hydrocracking process for heavy oils, atmospheric residua, and vacuum residua which was developed to upgrade heavy oil and tar sand bitumen as well as residua. The process uses an additive to inhibit coke formation, thus allowing high conversion to lower-boiling products using a single reactor. The vertical reactor vessel is free of internal equipment and operates in a three-phase mode. The solid additive particles are suspended in the primary liquid hydrocarbon phase through which the hydrogen and product gases flow rapidly in bubble form. The spent additive leaves with the heavy fraction and remains in the unconverted vacuum residue. Typical operating conditions are a reactor temperature of 440 to 460°C and a pressure of 10 to 15MPa.

2. microcat-rc The Microcat-RC or M-Coke process is a catalytic ebullated-bed hydroconversion process which operates at relatively moderate pressures and temperatures. The catalyst particles are dispersed uniformly throughout the feed, which results in less distance between particles and less time for a reactant molecule or intermediate to find an active catalyst site. The hydrocarbon feed, microcatalyst, and hydrogen are fed to the reactor. The effluent is sent to a flash separation zone to recover hydrogen, gases, and liquid products. The residuum from the flash step is then fed to a vacuum distillation tower to obtain a 565°C- product oil and a 565°C+ bottoms fraction that contains unconverted feed, microcatalyst, and essentially all of the feed metals.

3. mrh The MRH process is a hydrocracking process designed to upgrade heavy feedstocks containing large amounts of metals and asphaltene, such as VR and bitumen, and to produce mainly middle distillates. The reactor is designed to maintain a mixed three- phase slurry of feedstock, fine powder catalyst, and hydrogen, and to promote effective contact. In the process, a slurry consisting of heavy feedstock and fine powder catalyst is preheated in a furnace and fed into the reactor vessel. From the lower section of the reactor, bottom slurry oil containing the catalyst, uncracked residuum, and a small amount of vacuum gas oil fraction are withdrawn. Vacuum gas oil is recovered in the slurry separation section, and the remaining catalyst and coke are fed to the regenerator.

4. vcc and hdh plus The Veba Combi Cracking (VCC) process is a hydro-cracking and hydrogenation process for converting residua and other heavy feedstocks. The VCC technology was transferred to HDH (hydrocracking distillation hydrotreating), which has been developed in parallel by Intevep since 1984. Only the HDH process survives. Recently, Intevep announced the implementation of HDH Plus technology in two refineries in Venezuela: Puerto La Cruz and El Palito. In the process, the heavy feedstock, slurried with a small amount of finely powdered additive and mixed with hydrogen and recycle gas, is hydrogenated (hydrocracked) using a commercial catalyst and liquid- phase hydrogenation reactor operating at 440 to 485°C and 2175 to 4350 psi pressure.

5. eni slurry technology ( est ) The EST process is based on the slurry hydrotreatment of heavy feedstock at relatively low temperature in the presence of hydrogen and a dispersed catalyst, which is recycled to the slurry reactor via solvent deasphalting together with the asphaltene recycle. EST has demonstrated residue conversion of 98 to 99%, HDS > 80%, HDM > 99% and CCR removal > 96% on a small pilot-plant scale. Part of the feedstock is converted directly to light and medium distillates, while the other products represent suitable feedstocks for FCC or hydrocracking. Some of the reported advantages of EST process are feedstock flexibility, optimal hydrogen utilization/consumption, and product slate flexibility.

Next post:

Previous post: