Reactors for hydroprocessing

Most HDT and HCR commercial units employ FBRs. Historically, FBRs were meant for processing naphtha, kerosene, and gas oil, but they were gradually modified to handle tougher feeds such as VGO and AR/VR. They are the preferred choice of refiners due to their relative simplicity, flexibility, and ease of operation. 

One of the main advantages of TBRs is that Uquid flow nearly approaches to plug flow, and therefore, TBRs exceed in performance other three-phase reactors such as EBRs or SPRs. They also exhibit a higher ratio of catalyst loading capacity per Uquid volume. In practical terms, TBRs are very simple in construction, require low investment, and are the most flexible with respect to the demanded throughput and reaction severity for different conversion levels. 

The drawbacks of TBRs include the presence of diffusional limitations inside the catalyst due to the particle size. This is because in commercial practice, the reactor must be loaded with relatively large catalyst particles to avoid an excessive pressure drop. However, the main disadvantage of this type of reactor is certainly the loss of catalyst activity over time. In addition, TBRs are exposed to fouling-related problems because of the presence of solids in the feedstock (iron scale, salts, coke fines, etc.) and reaction products (coke plugs and metal deposits) [64]. This means that the operation must be interrupted after a certain period of time for replacing the catalyst, which procedure takes around 1 month and requires 

Reactor internals. One vital aspect for FBR performance is the internal hardware design [65]. Reactor internals are responsible for efficient catalyst utilization and process operation by means of uniform volumetric and thermal reactant distribution across the catalyst bed and for quenching performance and fouling protection [67]. Inappropriate reactor internal designs cause poor catalyst utilization due to maldistribution of reactants and deficient quenching performance. 

In terms of catalyst utilization, the most relevant reactor hardware is the distributor tray as it is responsible for the liquid distribution across the catalyst bed. In general, traditional distributor designs such as sieve trays, chimney trays, and bubble cap trays are known for their poor performance, whereas state-of-the-art distributors facilitate complete irrigation of the catalyst bed (e.g.. Sheiks HD tray, Topsoe Vapor-Lift tray, Exxon s Spider Vortex technologies, Akzo Nobel s Duplex tray, and Fluor s Swirl Cap tray) [65]. 

---

Furimsky E. Selection of catalysts and reactors for hydroprocessing. Appl. Catal. A Gen. 1998 171 177-206. 

Ancheyta J. Reactors for hydroprocessing. In Ancheyta J, Speight JG, editors. Hydroprocessing of heavy oils and residua. 1st ed. Boca Raton, FL CRC Press/Taylor Francis 2007. p 71-120. 

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.)... 

The catalysts applied in hydroprocessing operations are typically sulfided CoO—Mo03—A1203 or NiO—M0O3—A1203. The results of relevant studies281 and the application in refinery processes of these and other transition-metal sulfide catalysts were reviewed.282 Selection of catalysts and reactors for particular feeds and products is also an important issue.257,280,283,284... 

Fig. 14. Schematic flow diagram showing multiple fixed-bed reactor residuum hydroprocessing coupled with distillation equipment for high-severity RDS (Paraskos et al., 1974).

In pilot-scale hydroprocessing trickle-bed reactors, low liquid flow rates make the catalyst effectiveness dependent upon the liquid flow rate. Henry and Gilbert15 proposed that this may be due to insufficient liquid holdup in the reactor. For the first-order reaction, they modified Eq. (4-1) as... 

Figure 19-39 shows examples of gas-liquid-solid fluidized-bed reactors. Figure 19-39a illustrates a conventional gas-liquid-solid fluidized bed reactor. Figure 19-39h shows an ebuUating bed reactor for the hydroprocessing of heavy crude oil. A stable fluidized bed is maintained by recirculation of the mixed fluid through the bed and a draft tube. Reactor temperatures may range from 350 to 600°C (662 to 1112°F) and 200 atm (2940 psi). An external pump sometimes is used instead of the built-in impeller shown. Such units were developed for the liquefaction of coal. 

The study of the Vanadium deposition profiles in spent catalyst particles from resid hydroprocessing confirms that HDM is a sequential reaction. Furthermore, it is shown that the distribution parameter for the deposited Vanadium Qv is constant through the reactor for each catalyst type and that Qv is proportional to the efficiency of the Vanadium removal reaction. 

Step Cooling This is a testing procedure only to evaluate the long term effects of temper embrittlement. The test was developed by GE originally for turbine blades and since adopted by the refining industry for hydroprocessing reactors. This test of temper embrittlement is used for 2-1/4 Cr materials only. The heat treatment takes about 12 days before testing of the coupon can occur. 

Figure 5.6 Liquid and gas loads in typical trickle-bed reactors for gas oil hydroprocessing.

Compared with the reactor model developed in Chapter 6 for hydrotreating of heavy-oil-derived gas oil, the reactor model for hydroprocessing of heavy oil must account for other phenomena that are implicit with the heaviness of the feed, such as... 

Chapter 8 is dedicated to the modeling of heavy oil upgrading via hydroprocessing. Experimental studies for generation of kinetic data, catalyst deactivation, and long-term stability test are explained. Mass and heat balance equations are provided for the reactor modeling for steady-state and dynamic behavior. Simulations of bench-scale reactor and commercial reactor for different situations are also reported. 

---