Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Suspended Beds

The operations considered in this paper may be classified under the headings of fixed-bed operations or suspended-bed operations, depending on the state of motion of the solid particles. [Pg.79]

In this group of operations, the solid particles are kept in a suspended state by momentum transfer from the liquid phase. Momentum may be transferred to the liquid phase by different means, and distinction will be made on this basis between three different types of operations. An upper limit exists for the particle size that can be used in suspended bed operations, and is of the order of in. [Pg.80]

However, the models represent only crude approximate descriptions of the complex physical systems involved. Probably the most important phenomenon excluded is that of heat transfer. Suspended-bed operations are characterized by a high effective thermal conductivity, and thus represent a good approximation to isothermal behavior, and the above models should provide an adequate description of these systems. Fixed-bed operations will probably in many cases depart significantly from isothermal conditions, and in such cases models should be constructed that take heat transfer into... [Pg.89]

Bubble-column slurry operation is the most widely used suspended-bed operation for large-scale continuous processes. It has been the subject of a considerable number of investigations, and it may be noted in particular that many studies of the overall reaction kinetics in such operations have been published. [Pg.108]

Date for mass transfer across the liquid-solid interface are virtually nonexistent for packed-bed gas-liquid-particle operations. The smaller particle size that may be employed in suspended-bed operations should be an advantage in this respect, but the packed-bed operations have, on the other hand, the advantage of having higher possible relative velocities between liquid and solid. [Pg.131]

The heat-transfer properties of the suspended-bed operations appear superior to those of the packed-bed operations. In particular, the former have a high effective thermal conductivity, and the development of uneven temperature distributions is therefore less likely. [Pg.131]

Three-phase reactors 2 can thus be divided into two main classes A. Suspended-bed reactors, and B. Fixed-bed reactors. [Pg.232]

A. Suspended-bed reactors. These may be further subdivided according to how the particles are maintained in suspension in the reactor. [Pg.232]

The individual mass transfer and reaction steps outlined in Fig. 4.15 will now be described quantitatively. The aim will be firstly to obtain an expression for the overall rate of transformation of the reactant, and then to examine each term in this expression to see whether any one step contributes a disproportionate resistance to the overall rate. For simplicity we shall consider the gas to consist of just a pure reactant A, typically hydrogen, and assume the reaction which takes place on the interior surface of the catalyst particles to be first order with respect to this reactant only, i.e. the reaction is pseudo first-order with rate constant A ,. In an agitated tank suspended-bed reactor, as shown in Fig. 4.20, the gas is dispersed as bubbles, and it will be assumed that the liquid phase is well-mixed , i.e. the concentration CAL of dissolved A is uniform throughout, except in the liquid films immediately surrounding the bubbles and the particles. (It will be assumed also that the particles are not so extremely small that some are present just beneath the surface of the liquid within the diffusion film and are thus able to catalyse the reaction before A reaches the bulk of the liquid.)... [Pg.235]

Fig. 4.20. Suspended-bed agitated-tank teactor Combination of mass transfer and reaction steps. Impeller used would typically be a pitched-blade turbine, pumping downwards as shown, serving both to suspend particles and to disperse gas... Fig. 4.20. Suspended-bed agitated-tank teactor Combination of mass transfer and reaction steps. Impeller used would typically be a pitched-blade turbine, pumping downwards as shown, serving both to suspend particles and to disperse gas...
Three-Phase Fluidised Suspended-Bed Reactor—Combination of Mass Transfer and Reaction Steps... [Pg.239]

Process Type Fixed or Moving Bed Fluidized Bed Suspended Bed... [Pg.122]

The combustion of coal in a fixed bed (e.g., stokers) is the oldest and most common method of coal combustion. In recent decades, however, the fixed beds have lost some of their popularity due to the increased use of fluidized bed and suspended bed combustors [2,7],... [Pg.122]

In a suspended bed or entrained flow reactor technology, the coal is crushed, dried, and then pulverized to fine powder in a crusher and mill. As Table 9.1 shows, the coal particles used in entrained flow reactors are very small. The pulverized coal is transported with air to the furnace (primary air), and secondary air is heated and fed into the combustor to ensure complete combustion. The residence time of the coal in the furnace is typically around 1-2 s, which usually suffices for complete combustion. However, not all coal burns completely, and fly ash will be generated (see Table 9.1). [Pg.122]

The heat is available at 1200 K, but there will be temperature differences in the heat exchanger, so more available work will be lost in the heat exchange process. What can we learn from this example If we examine the Carnot factor, the answer seems to be clear. If we increase the operating temperature of the combustor, we can increase the efficiency and lose less work in the process. For example, if we had chosen an operating temperature of 2000 K, as could be possible in the suspended bed, we would have obtained an efficiency of 0.79, which is quite considerable. However, any gain in efficiency could be offset by the increase in work necessary to pulverize the coal For the sake of simplicity, we have not included these in this analysis. From the point of view of efficiency of combustion,... [Pg.124]

Dilute-phase gas-solids contacting (a suspended bed or transport system) may be more suitable than fluidization, in other process situations. In such systems the contact time between a given particle and the gas is very short—no more than a few seconds—because of very high gas veloci-... [Pg.116]

Figure E5.8 is a hypothetical process used for demonstration by Diamond Shamrock Co. of their flowsheeting code PROVES. Makeup gas is compressed, combined with recycle gas, and fed, together with liquid raw material, into a three-phase, suspended bed catalytic reactor. The reactor is cooled by recirculating liquid through a heat reclamation steam generator. Reaction products are condensed and the pressure of the exit stream reduced in two stages. The gas from the first-stage separator is recirculated, whereas the liquid from the second-stage separator is fed into a distillation column. Pure product is withdrawn from the bottom of the column. The distillate is a by-product that is pumped to another plant. Figure E5.8 is a hypothetical process used for demonstration by Diamond Shamrock Co. of their flowsheeting code PROVES. Makeup gas is compressed, combined with recycle gas, and fed, together with liquid raw material, into a three-phase, suspended bed catalytic reactor. The reactor is cooled by recirculating liquid through a heat reclamation steam generator. Reaction products are condensed and the pressure of the exit stream reduced in two stages. The gas from the first-stage separator is recirculated, whereas the liquid from the second-stage separator is fed into a distillation column. Pure product is withdrawn from the bottom of the column. The distillate is a by-product that is pumped to another plant.
Suspended bed material load, which consists of coarser particles which are intermittently moved from the river bed into the flow profile. Typically concentrations vary logarithmically with depth, with mean concentration for a vertical profile being seen at 0.6 X depth, measured from the flow surface. Concentrations also vary across the river section, being highest in the centre, where flow velocity is highest, and lowest at the river banks. [Pg.247]

Clearly the measurement of these three transport modes requires different techniques. Wash load and suspended bed material load tend to be monitored together, either directly through sampling of water and sediment from the flow profile or indirectly through monitoring of turbidity. [Pg.247]

Development of Industrial Oxidative Acetoxylation Catalyst When a liquid phase reaction using a solid catalyst is implemented on an industrial scale, a fixed bed or a suspended bed can be considered as a reaction system. Due to the difficulty of the operation for the regeneration of deactivated catalyst and catalyst activation. [Pg.163]

In through circulation fixed bed dryers and in moving or suspended bed dryers (spouted beds, fluidized beds, rotary dryers, and so on), the actual interfacial area participating in heat and mass transfer is unknown. For such cases it is... [Pg.45]

Sarkits, V.B., Heat Tranterfrom Suspended Beds of Granular Materials to Heat Tranter Surfaces (Russian), Leningrad Technology Institute, Lensoviet, Russia, 1959. [Pg.186]

The important design parameters for a draft-tube agitated vessel are the diameters of the vessel and draft tube, the height of the draft tube and its position in the vessel, and the type and speed of the agitator. The liquid emerging from a down-flow draft tube under the action of the impeller has a radial component of velocity which may create an undesirable swirling motion in the annulus and induce a vortex at the free liquid surface. Vertical baffles located in the vessel wall can overcome this difficulty and produce a relatively stable suspended bed of particles. [Pg.453]

Mullin, J.W. and Giarside, J. (1970) Voidage-velocity relationships in the design of suspended-bed crystallizers. British Chemical Engineering, 15, 773-775. [Pg.560]

There are three main designs of combustion systems in which coal and air can be reacted as the start to power generation and they are (1) the fixed-bed combustor, (2) an entrained-bed combustor, also called a suspended-bed combustor, and (3) a fluidized-bed combustor. [Pg.478]


See other pages where Suspended Beds is mentioned: [Pg.22]    [Pg.71]    [Pg.80]    [Pg.411]    [Pg.294]    [Pg.259]    [Pg.390]    [Pg.274]    [Pg.22]    [Pg.235]    [Pg.240]    [Pg.245]    [Pg.122]    [Pg.375]    [Pg.116]    [Pg.240]    [Pg.302]    [Pg.365]    [Pg.282]    [Pg.267]    [Pg.249]    [Pg.164]   


SEARCH



Suspended bed reactors

Suspending

© 2024 chempedia.info