Packed beds packing structure

The application of CFD to packed bed reactor modeling has usually involved the replacement of the actual packing structure with an effective continuum (Kvamsdal et al., 1999 Pedernera et al., 2003). Transport processes are then represented by lumped parameters for dispersion and heat transfer (Jakobsen... 

All the spheres in a layer were supported by two spheres of the layer below and the column wall, creating a stable packing structure. As the tube-to-particle diameter ratio of the bed was only four, the entire packing structure was controlled by the influence of the wall. Nevertheless, the packing was divided into an immediate wall layer and a central section, but this should not be taken to imply that the central structure was not wall influenced. Although a three-sphere planar structure would almost fit within the nine-sphere wall layer, there was just not enough room at the same axial coordinate. When, however, the... 

When we want to look at the connection between the flow behavior and the amount of heat that is transferred into the fixed bed, the 3D temperature field is not the ideal tool. We can look at a contour map of the heat flux through the wall of the reactor tube. Fig. 19 actually displays a contour map of the global wall heat transfer coefficient, h0, which is defined by qw — h0(Tw-T0) where T0 is a global reference temperature. So, for constant wall temperature, qw and h0 are proportional, and their contour maps are similar. The map in Fig. 19 shows the local heat transfer coefficient at the tube wall and displays a level of detail that would be hard to obtain from experiment. The features found in the map are the result of the flow features in the bed and the packing structure of the particles. 

There are a few other kinds of industrial plants. An air-lift tower fermenter was developed by ICI for the production of single-cell protein from methanol which employs an external loop for heat removal. Trickle beds for the treatment of waste waters employ packing structures or packing elements of 4-6 cm dia and porosities above 50%. Microbial films are formed on the packing that react with the organic substrate and the air as the liquid flows down and the air up. 

Use of the ceramic honeycomb packing structure in the recuperator keeps fuel and air substantially isolated as they travel through the recuperator. Various ceramic materials such as cordierite, mullite, alumina and silicon carbide can be used to fabricate honeycomb beds. While metallic materials have the potential to be used in honeycomb bed, corrosion resistance is a major issue... 

Various reactor types have been used as the foundation for microreactor designs, including coated wall reactors, packed-bed reactors, structured catalyst reactors, and membrane reactors. 

When authors illustrate the subject of thermochemical conversion of solid fuels in the literature, the conversion zone in a packed bed is divided into different process zones (drying zone, pyrolysis zone, char combustion zone, and char gasification zone), one for each thermochemical conversion process. The spatial order of this process zones is herein referred to as the bed process structure or conversion process structure. The conversion process structure is a function of conversion concept. Even more important, the bed process structure can only exist in the diffusion controlled conversion regime when the conversion zone has a significant thickness. 

Columns, scrubbers, reactors, and similar process vessels, particularly those containing packed beds, either structured or random (or loose-fill), can be susceptible to internal fires when they are opened to the atmosphere for internal... 

A packed tower can successfully fractionate with a very small pressure drop, as compared to a tray. For a modern trayed tower, to produce one single theoretical tray worth of separation (that s like a single, 100 percent efficient tray), a pressure drop of about 6 in of liquid is needed. A bed of structured packing can do the same job, with one inch of liquid pressure drop, even when allowing for the vapor distributor. In low-pressure fractionators, especially vacuum towers used to make lubricating oils and waxes, this can be of critical importance. 

FIG. 14-51 Illustrative cutaway of a packed tower, depicting an upper bed of structured packing and a lower bed of random packing. (Courtesy of Sulzer Chemtech.)... 

The measured cross-sectionally averaged liquid holdup (i.e. measured liquid saturation times the bed voidage) are consistent with previously reported results [4], For a similar packing structure, Illiuta and Larachi [4] found liquid holdups, as calculated by their mechanistic model and compared with the reported experimental results, slightly lower than the values obtained in this study. However, there are some differences between the two studies this work was performed in a smaller diameter column ( 30 cm versus... 

In CEC, the EOF depends on the column packing structure and pore size of the packing material [51,111-116]. In a packed bed, there are many interconnected channels between particles, which leads to a porous packed structure. The porosity of the packed bed dictates the permeability through the column. The average channel size between particles in a CEC column can be estimated if the packed bed is assumed a... 

It is not uncommon to find bits of corroded structured packings at the bottom of the column. There have also been several instances where a bed of structured packings caught fire when air entered the column at shutdown. These fires were initiated by small amounts of flammable or pyrophoric materials adhered to packing surfaces. 

Figure 9 Close-up of packed-bed weir-SMEC using 20-pm-particle-sized polymeric support material. The homogenious packing structure of the packed bed can be seen on the left-hand side lining up close to the eight-channel microfluidic grid...

The A term of the van Deemter equation is independent of the mobile-phase linear velocity and describes the broadening that occurs due to the multiple flow paths present within the column. Since these paths are of different lengths, molecules will travel different distances depending on what flow paths they experience. For a column bed of randomly packed particles, the A term is proportional to the particle diameter, dp, and to a factor X related to the packing structure ... 

Simulations of an industrial scale column with structured packing have been reported by Taylor et al. (1992). They modeled a packed C4 splitter that had an internal diameter of about 2.5 m and five beds of structured packing with a total height of approximately 37 m as shown in Figure 14.33. The feed, which contains predominantly isobutane and n-butane... 

A catalytic MSR can be obtained simply by using the catalytically active phase in the form of a micropacked bed. Randomly packed beds and structured packed beds are discussed here, and typical examples are presented. 

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