Expanded beds

Fig. 15. Zenz-Ducon expandable-bed granular filter. From Ref. 256,...

The fluidized-bed system (Fig. 3) uses finely sized coal particles and the bed exhibits Hquid-like characteristics when a gas flows upward through the bed. Gas flowing through the coal produces turbulent lifting and separation of particles and the result is an expanded bed having greater coal surface area to promote the chemical reaction. These systems, however, have only a limited abiUty to handle caking coals (see Fluidization). 

The reactor combinations for the two reactors in series consist of two fixed-beds for the Arco process an expanded bed followed by a catalytic distillation reactor for lEP a fixed-bed followed by a catalytic distillation reactor for CDTECH and two fixed-beds for Phillips. The Huls process uses an adiabatic reactor for the second reactor. 

FluidiZed-Bed Combustion. Fluidized-bed combustors are able to bum coal particles effectively in the range of 1.5 mm to 6 mm in size, which are floating in place in an expanded bed (40). Coal and limestone for SO2 capture can be fed to the combustion zone, and ash can be removed from it, by pneumatic transfer. Very Htfle precombustion processing is needed to prepare either the coal or the sorbent for entry into the furnace (41). 

Stable expanded-bed operations promise the ability to handle whole broths efficiently, all the while maintaining plug-flow characteristics. Magnetically stabihzed fluidized beds have been shown to work effectively for bioproduct separations, but are not yet used commercially. A commerci y available process uses well-designed beads of appropriate densities and sizes to enable bed fluidization and stable operation without appreciable recirculation. 

Aerobic systems including trickling filters and rotating biological contactors (RBC) are operated in a nonflooded mode to ensure adequate oxygen supply. Other aerobic, anoxic, and anaerobic systems employ flooded reactors. The most common systems are packed beds (anaerobic trickling filter) and fluidized or expanded bed systems. 

Carbon should be prewetted prior to being placed in the test columns. Backwashing the carbon at low rates (2.5 m/hr) does not remove the air. Rates that would expand the bed 50 percent or 15-30 m/hr, are required. The liquid used for prewetting can either be water, if it is compatible with the liquid to be treated, or a batch of the liquid to be treated which has been purified previously. There are three types of carbon systems (1) fixed beds, (2) pulse beds, and (3) fluidized beds, and these can be used singly, in parallel, or in combination. The majority of systems are either fixed or pulse beds. The two basic types of adsorbers which can be designed to operate under pressure or at atmospheric pressure are the moving or pulse bed and the fixed bed. Either can be operated as packed or expanded beds. 

The fraction q can be expressed in terms of the expanded bed height H and minimum fluidization height H , and terms may be substituted for U -... 

Another application shows the preparative purification and polishing of a therapeutic fusion protein with a humanized recombinant IgG protein. The fusion protein was expressed by the fermentation of baby hamster kidney cells. The filtered culture supernatant (155 liters) contained 2.2 g of IgG and 75.5 g of total protein. After the immunoglobulins were isolated by expanded bed adsorption and rebuffering, the IgG fraction was bound to Fractogel EMD SOj (M). This column achieved baseline separation of complete antibodies (fusion protein) from small amounts of antibodies lacking the fusion part. The resulting highly purified IgG fraction (110 ml) was diluted to 150 ml and... 

Fluidised beds have been used previously for the industrial-scale recovery of the antibiotics streptomycin and novobiocin.30 However, more recently, considerable interest has been shown in the use of fluidised beds for the direct extraction of proteins from whole fermentation broths.31 In a packed bed, the adsorbent particles are packed within the contactor. The voidage, that is, the inter-particle space, is minimal and thus feedstock clarification is mandatory to avoid clogging of the bed. In a fluidised/expanded bed, the adsorbent bed is allowed to expand by irrigation with feedstock. Bed voidage is increased, allowing the passage of particulates in the feed. The diameters of the adsorbent beads are exaggerated for illustrative clarity. 

To account for the difference in the dispersion characteristics of the classified, stable fluidised bed and the conventional, well-mixed fluidised bed, the term expanded bed has been used by several authors and the leading manufacture of chromatography media and equipment.38 In the work presented here, the term fluidised bed will be used synonymously with expanded bed to refer to adsorbents fluidised under conditions that seek to minimise particle mixing. 

Hydrodynamic Characterisation of Flow in Fluidised/Expanded Beds and Bed Yoidage... 

The degree of bed expansion contributes to the efficiency of fluidised bed/expanded bed adsorption as a composite function of liquid distribution, liquid and particle properties (size, shape and density) and process conditions. Besides being an important design feature, the degree of bed expansion may be used as a quick and simple measure of bed stability.48... 

The void fraction (s) is estimated from the measured height of the expanded bed (H) and is a function of superficial liquid velocity. Thus ... 

Flow direction during adsorption (expanded bed mode)... 

Bermejo, R. et al.. Preparative purification of B-phycoerythrin from the microalga Porphyridium cruentum by expanded-bed adsorption chromatography, J. Chromatogr. B, 790, 317, 2003. 

Bermejo, R. et ah. Expanded bed adsorption chromatography for recovery of phyco-cyanins from the microalga Spirulina platensis, Chromatographia, 63, 59, 2006. Thieghem, (van) R, Monascus, genre nouveau de I ordre des ascomycfetes. Bull. Soc. Bot. France, 31, 226, 1884. 

Expanded-bed adsorption (ERA) has gained popularity in bioprocessing since its commercial introduction in the 1990s because of its ability to handle a crude feedstock that contains cells or other particulates. ERA ehminates the need for a dedicated clarification step by combining sohd-hquid separation and adsorption into a single-unit operation [Hjorth et al., in Subramanian (ed.), op. cit., vol. 1, pp. 199-226 Mattiasson et al., in Ahuja (ed.), op. cit., pp. 417-451]. A... 

Clemmit, R.H. and Chase, H.A., Immobilized metal affinity chromatography of P-galactosidase from unclarified Escherichia coli homogenates using expanded bed adsorption, /. Chromatogr. A, 874, 27, 2000. 

Feuser, J., Halfar, M., Liitkemeyer, D., Ameskamp, N., Kula, M.-R., and Thommes, J., Interaction of mammalian cell culture broth with adsorbents in expanded bed adsorption of monoclonal antibodies, Process Biochem., 34,159,... 

Before the bed can become fluidized, however, the particles must dislodge from their packed state, which expands the bed. Thus, the porosity (s) in Eqs (14-5) and (14-9) is not the initial packed bed porosity but the expanded bed porosity at the point of minimum fluidization ( ml ), i.e., the minimum bed voidage in the bed just prior to fluidization. Actually, the values of C and C2 in Eq. (14-8) that give the best results for fluidized beds of uniform spherical particles have been found from empirical observations to be ... 

Figure 46. Expanded bed height model data compared to field data for multisolids fluidized bed for properly scaled steel pellets and mis-scaled gravel particles. (From Ake and Glicksman, 1989.)...

---