Ebullated-bed reactors

EBRs exhibit many advantages for processing heavy oils. In general, EBRs are very flexible in operation, hydroconversion can be as high as 90 vol%, and the end products have low levels of sulfur, metals, and nitrogen. The ebullated-bed allows free movement of solids, which minimizes bed fouling and consequently pressure drop (Furimsky, 1998). Particle size is not restricted by pressure drop and therefore smaller particles can be employed. This reduces diffusional limitations significantly 

FIGURE 7.8 Examples of MBR, EBR, and SPR. (Adapted from Ancheyta, J., Reactors for hydroprocessing, in Hydroprocessing of Heavy Oils and Residua, Ancheyta, J., Speight, J.G., eds., CRC Press, Taylor Francis, Boca Raton, FL, 2007, p. 92.) 

One of the problans of EBRs is that they suffer from excessive catalyst consumption. The back-mixed character of EBRs is kinetically less favorable compared with plug-flow regime. The catalyst must have improved mechanical strength, because the conditions in an EBR promote serious attrition and erosion of the catalyst particles. EBRs require a larger volume with respect to EBRs due to their small ratio of catalyst per liquid volume. Sediment formation is a major concern as a result of the high conversion levels ( 50 vol%). Scale-up and design of EBRs are particularly more difficult due to the complex hydrodynamics. 

In general, slurry-phase hydroconversion can be advantageous for upgrading the heaviest feedstocks due to the remarkably high levels of conversion ( 90 vol%), the low costs associated to the catalyst stock, and the simple design of the reactor vessel. The slurry-phase is characterized by improved mass transfer and thermally is more stable. However, the main drawback is that the unconverted fraction is of extremely poor quality (very high contents of sulfur and metals). 

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Laboratory reactor for studying three-phase processes can be divided in reactors with mobile and immobile catalyst particles. Bubble (suspension) column reactors, mechanically stirred tank reactors, ebullated-bed reactors and gas-lift reactors belong the class of reactors with mobile catalyst particles. Fixed-bed reactors with cocurrent (trickle-bed reactor and bubble columns, see Figs. 5.4-7 and 5.4-8 in Section 5.4.1) or countercurrent (packed column, see Fig. 5.4-8) flow of phases are reactors with immobile catalyst particles. A mobile catalyst is usually of the form of finely powdered particles, while coarser catalysts are studied when placing them in a fixed place (possibly moving as in mechanically agitated basket-type reactors). 

Reported residue conversion is significantly high for the five types of included reactors and largest for the slurry type of reactor. Besides, the slurry reactor together with the ebullated bed reactor can handle heaviest feedstocks and highest metal contents. Resid conversion requires higher temperatures, and pressure drop is essentially zero in these two reactors. However, product quality is better for the fixed and moving bed processes. 

In normal operation of ebullated bed reactors, the reactor feed temperature is the control variable. The desired reactor feed temperature depends on both the feed rate and feed composition. The feed temperature is chosen such that the overall heat generation in the reactor is used to elevate the low temperature feed material to the bed temperature during... 

The H-Cocd Process, based on H-Oil technology, was developed by Hydrocarbon Research, Inc. (HRI). The heart of the process was a three-phase, ebullated-bed reactor in which catalyst pellets were fluidized by the upward flow of slurry and gas through the reactor. The reactor contained an internal tube for recirculating the reaction mixture to the bottom of the catalyst bed. Catalyst activity in the reactor was maintained by the withdrawal of small quantities of spent catalyst and the addition of fresh catalyst. The addition of a catalyst to the reactor is the main feature which distinguishes the H-Coal Process from the typical process. 

Reactors with moving solid phase Three-phase fluidized-bed (ebullated-bed) reactor Catalyst particles are fluidized by an upward liquid flow, whereas the gas phase rises in a dispersed bubble regime. A typical application of this reactor is the hydrogenation of residues. 

In ebullating bed reactor, such as the H-coal process, Ni-Mo or Co-Mo alumina catalysts have been used (96). The catalyst definitely improves the oil yields by accentuating aromatic hydrocracking, achieving conversions around 95% at catalyst make-up rates of 1 3%. 

A wide variety of process options can be used with the H-Oil process depending on the specific operation. In all cases, a catalytic ebullated-bed reactor system is used to provide an efficient hydroconversion. The system insures uniform distribution of liquid, hydrogen-rich gas, and catalyst across the reactor. The ebullated-bed system operates under essentially isothermal conditions, exhibiting... 

H-Oil process a catalytic process that is designed for hydrogenation of heavy feedstocks in an ebullated bed reactor. 

A large buildup of iron and titanium was found in a narrow band of the catalyst exterior of a spent catalyst. Improved catalyst aging is likely to occur by the use of an ebullated bed reactor, primarily by decreased interparticle coke formation as well as by mild abrasion of metal contaminants. 

FIG. 19-39 Gas-liquid-solid reactors, (a) Three-phase iluidized-bed reactor, b Ebullating bed reactor for hydroliquefaction of coal. (Kampiner in Winnacker-Keuchler, Chemische Technologie, vol. 3, Hanser, 1972, p 252.)... 

The H-Coal Process. The H-Coal process is an adaptation of the H-Oil process, which uses a catalytic ebullated bed reactor to... 

Figure 19.21 shows a schematic of the H-Coal process, which employs a single catalytic stage to produce a synthetic crude oil.37,38 Coal is crushed, dried, and mixed with recycle oil and hydrogen before being preheated to approximately 850°F (454°C). The preheater effluent is fed to the bottom of an ebullated bed reactor. During operation, fresh catalyst (a cobalt-molybdenum extrudate) is fed to the top of the reactor, while spent catalyst is removed from the bottom to maintain constant reactivity and inventory. The upward flow of the coal slurry and hydrogen causes... 

The H-Coal process produces approximately 3-3.5 barrels of liquid product for each ton of coal.42 Tests showed that the process is best suited for high-volatile bituminous coal the use of low-rank coals significantly reduced throughput and distillate yields. The successful performance of the ebullated bed reactor in the H-Coal process led to its later use in two-stage liquefaction systems. 

Catalysts for ebullating bed reactors are subjected to attrition. Those used for resid hydroprocessing and coal liquefaction must resist turbulence, from high gas velocities as well as erosion by the ash and impurities in the feedstocks. 

T-Star (2) A catalytic hydrocracking process using an ebullated bed reactor containing an extruded Ni/Mo-based catalyst. Developed by Axens North America, based on the H-Oil process. Planned to be used in a coal-to-liquids plant in Inner Mongolia from 2005. 

Slurry reactors and ebulating bed reactors typically contain 1 to 5% catalyst by weight. 

The whole oil and - -300°C fraction were desulfurized in bench-scale, fixed and ebullating bed reactor systems, and the product distributions obtained are shown in Figures 3 and 4. The data show that fuel oils... 

In many refineries thermal cracking processes are used to convert residues into lighter products. Low value petroleum coke is a product from the more severe cracking processes. The H-Oil process made it possible to convert the asphaltenic carbonizable portion of the residue to higher value liquid products rather than coke. In the H-Oil process an ebullated bed of catalyst is used to convert lower value heavy oil into upgraded higher value products in the presence of hydrogen. The ebullated bed reactor is an expanded bed of catalyst maintained in constant motion by the upward flow of liquid. The reactor behaves as a well mixed continuously stirred tank reactor. 

The H-Oil process is a catalytic hydrogenation technique that uses a one-, two-, or three-stage ebullated-bed reactor in which considerable hydrocracking takes place during the reaction. The process is used to upgrade heavy sulfur-containing crude oils, residual stocks, and low-sulfur distillates, thereby reducing fuel oil yield. 

A related reactor is that for coal liquefaction, which can be carried out in a three-phase slurry bubble column (see Fig. 5). Hydrogen can be supplied at the bottom of a column of downcoming product—oil. The solid coal reactant is blended with the product or carrier oil and fed at the top. The generic process depicted in Fig. 5 is a generalization of the liquefaction reactor in the Exxon Donor Solvent Process. As the gas flow rate increases, the bubbles change from uniformly small to chaotic. In the H-coal process, both the gas and a coal-oil slurry are fed from the bottom in an ebullating-bed reactor. Catalyst solids are fed from the top. This reactor operates as an expanded... 

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