Upflow packed-bed reactor

Mezohegyi G, Kolodkin A, Castro UI, Bengoa C et al (2007) Effective anaerobic decoloriza-tion of azo dye Acid Orange 7 in continuous upflow packed-bed reactor using biological activated carbon system. Ind Eng Chem Res 46 6788-6792... 

Partial anaerobic digestion of aerobic sludge Acid orange 7 Upflow packed bed reactor Batch and continuous... 

K.B. Van Gelder and K.R. Westerterp, Residence time distribution and hold-up in a cocurrent upflow packed bed reactor at elevated pressure, Chem. Eng. Technol. N°13, 27(1990). 

In general, when a fixed bed is selected, the issue whether to employ a concurrent upflow or downflow operation must be considered. Operating a randomly packed bed reactor in the countercurrent mode is usually not feasible because flooding occurs at gas velocities far below industrial relevance. In a concurrent upflow, complete catalyst wetting is obtained at the expense of much larger liquid holdup compared to a concurrent downflow. High liquid holdup... 

The upflow expanded-bed reactor operates in such a way that the catalyst remains loosely packed and is less susceptible to plugging and therefore more suitable for the heavier feedstocks as well as for feedstocks that may contain considerable amounts of suspended solid material. Because of the nature of the catalyst bed, such suspended material will pass through the bed without causing frequent plugging problems. Furthermore, the expanded state of motion of the catalyst allows frequent withdrawal from, or addition to, the catalyst bed during operation of the reactor without the necessity of shutdown of the unit for catalyst replacement. This property alone makes the ebullated reactor ideally suited for the high-metal feedstocks (i.e., residua and heavy oils) that rapidly poison a catalyst with the ever-present catalyst replacement issues. 

Upflow fixed bed reactors or submerged biofilters (SBF) have upward groundwater flow, the packing material is submerged under water and no bed expansion is obtained [45,94-97]. 

Type Upflow packed bed VbL- 1.21 Bed glass beads Met MTBE Con. 150 mg/1 HRT 1 day O2 14.5 mg/1 Recirc. non Rem. 70% Reactor seeded with petrochemical plant activated sludge dominant species are Micrococcus MTBE removal is comparatively low [67,68]... 

Table 4 Ranking of different reactor types suitable for MTBE biodegradation in terms of typical process characteristics. The reactors shown are the fluidized hed reactor (FBR), packed bed reactor (PBR), rotating biological contactor (RBC), membrane bioreactor and the aerobic upflow sludge bed reactor (AUSB)...

C Two-Phase Fixed Bed Catalytic Reactors with Cocurrent Upflow. "Upflow Packed Bubble Reactors"... 

Peixoto, G., Saavedra, N. K., Varesche, M. B. A., Zaiat, M. (2011). Hydrogen production from soft-drink wastewater in an upflow anaerobic packed-bed reactor. International Journal of Hydrogen Energy, 36(15), 8953—8966. 

Molga EJ, Westerterp KR. Gas-Uquid interfadal area and holdup in a cocurrent upflow packed bed bubble column reactor at elevated pressures. Ind. Eng. Chem. Res. 1997 36 622. 

Three phase packed bed reactors, filled with catalyst pellets with a size of a few mm. They are usually operated in one of the following ways with the liquid as a continuous phase (cocurrent upflow) or with the liquid running downward in a thin film (triclde flow, cocurrent downward). At high flow rates, pulsating two-phase flow can be obtained. Countercurrent flow is rarely used. 

Column reactors are the second most popular reactors in the fine chemistry sector. They are mainly dedicated reactors adjusted for a particular process although in many cases column reactors can easily be adapted for another process. Cocurrently operated bubble (possibly packed) columns with upflow of both phases and trickle-bed reactors with downflow are widely used. The diameter of column reactors varies from tens of centimetres to metres, while their height ranges from two metres up to twenty metres. Larger column reactors also have been designed and operated in bulk chemicals plants. The typical catalyst particle size ranges from 1.5 mm (in trickle-bed reactors) to 10 mm (in countercurrent columns) depending on the particular application. The temperature and pressure are limited only by the material of construction and corrosivity of the reaction mixture. 

The liquid hydrocarbon stream to be treated may be a crude oil, heavy crude oil, bitumen, or a refined fraction of the crude oil. The hydrogen gas stream is added to the mixture of the hydrocarbon stream with the organic solvent. The reactor, which is fed upflow, is a packed bed of biocatalyst dispersed on a support and is operated at about 74°C. Alternatively, the reactor can also be a batch reactor under stirring conditions. 

Industrial hazardous wastewater can be treated aerobically in suspended biomass stirred-tank bioreactors, plug-flow bioreactors, rotating-disc contactors, packed-bed fixed-biofilm reactors (or biofilters), fluidized bed reactors, diffused aeration tanks, airlift bioreactors, jet bioreactors, membrane bioreactors, and upflow bed reactors [28,30]. 

The analysis in this section is primarily dedicated to trickle-bed reactors. However, some basic aspects of packed bubble bed reactors will be presented as well. A bubble fixed-bed reactor is actually a tubular-flow reactor with concurrent upflow of gas and liquid. The catalyst bed is completely immersed in a continuous liquid flow, while gas rises as bubbles. 

Failing to identify the limiting reactant can lead to failure in the scale-up of trickle-bed reactors (Dudukovic, 1999). Gas-limited reactions occur when the gaseous reactant is slightly soluble in the liquid and at moderate operating pressures. For liquid-limited reactions, concurrent upflow is preferred (packed bubble columns) as it provides for complete catalyst wetting and thus enhances the mass transfer from the liquid phase to the catalyst. On the other hand, for gas reactions, concurrent downflow operation (trickle-bed reactors), especially at partially wetted conditions, is preferred as it facilitates the mass transfer from the gas phase to the catalyst. The differences between upflow and downflow conditions disappear by the addition of fines (see Section 3.7.3, Wetting efficiency in trickle-bed reactors). 

Most recently. Kirillov and Nasamanyan15 carried out a very interesting unsteady-state analysis of liquid-solid mass transfer for cocurrent upflow in a fixed-bed reactor. The analysis was compared and verified by the steady-state measurements of liquid-solid mass-transfer coefficients in a 10-cm x 10-cm square column with a height of 50 cm. Three types of packings, 30-mm and 8-mm... 

Intraparticle diffusion resistance may become important when the particles are larger than the powders used in slurry reactors, such as for catalytic packed beds operating in trickle flow mode (gas and liquid downflow), in upflow gas-liquid mode, or countercurrent gas-liquid mode. For these the effectiveness factor concept for intraparticle diffusion resistance has to be considered in addition to the other resistances present. See more details in Sec. 19. 

Fig. 5 Fixed-bed reactors with gas-liquid flow. (A) Trickle-bed reactor with cocurrent downflow (B) trickle-bed reactor with counter-current flow and (C) packed bubble-flow reactor with cocurrent upflow.

---