Flowing solids

Vibrating-conveyor dryers are suitable for free-flowing solids containing mainly surface moisture. Retention is limited by conveying speeds which range from 0.02 to 0.12 m/s. Bed depth rarely exceeds 7 cm, although units are fabricated to carry 30- to 46-cm-deep beds these also employ plate and pipe coils suspended in the bed to provide additional heat-transfer area. Vibrating dryers are not suit le for fibrous materials which mat or for sticky sohds which may ball or adhere to the deck. 

FIG. 17-2 Schematic phase diagram in the region of upward gas flow. W = mass flow solids, lh/(h fr) E = fraction voids Pp = particle density, Ih/ft Py= fluid density, Ih/ft Cd = drag coefficient Re = modified Reynolds uum-her. (Zenz and Othmei Fluidization and Fluid Particle Systems, Reinhold, New York, 1960. )... 

FIG. 21-28 Sloping striker plate in the belt of an apron feeder ensures the flow of non-free-flowing solids, Couitesif of Chemical Engineering,)... 

Two types of continuous flow solid oxide cell reactors are typically used in electrochemical promotion experiments. The single chamber reactor depicted in Fig. B.l is made of a quartz tube closed at one end. The open end of the tube is mounted on a stainless steel cap, which has provisions for the introduction of reactants and removal of products as well as for the insertion of a thermocouple and connecting wires to the electrodes of the cell. A solid electrolyte disk, with three porous electrodes deposited on it, is appropriately clamped inside the reactor. Au wires are normally used to connect the catalyst-working electrode as well as the two Au auxiliary electrodes with the external circuit. These wires are mechanically pressed onto the corresponding electrodes, using an appropriate ceramic holder. A thermocouple, inserted in a closed-end quartz tube is used to measure the temperature of the solid electrolyte pellet. 

CONFINED SPACE A spacc which is substantially, although not always entirely, enclosed and where there is a reasonably foreseeable risk of serious injury from hazardous substances or conditions within the space or nearby. The risks may include flammable substances oxygen deficiency or enrichment toxic gases, fume or vapour ingress or presence of liquids free-flowing solids presence of excessive heat. For the purpose of the Confined Spaces Regulations 1997 a confined space means any place, including any chamber, tank, vat, silo, pit, trench, pipe, sewer, flue, well or other similar space in which, by virtue of its enclosed nature, there arises a reasonably foreseeable specified risk. 

Kilns. Reactions involving free-flowing solid, paste and slurry materials can be carried out in kilns. In a rotary kiln, a cylindrical shell is mounted with its axis making a small angle to the horizontal and rotated slowly. The solid material to be reacted is fed to the elevated end of the kiln and it tumbles down the kiln as a result of the rotation. 

A steady jet without bubbling can be maintained in a sand bed between the jet nozzle and the draft tube inlet with high jet velocities of the order of 60 m/s and without downcomer aeration. Once the downcomer is aerated, the solids circulation rate increases dramatically and the steady jet becomes a bubbling jet. Apparently, the inward-flowing solids have enough momentum to shear the gas jet periodically into bubbles. 

Although most of the experimental data reported here were obtained with large particles, Geldart Class B and D powders, it is believed that the concept can equally be applied for any fine aeratable and lfee-flowing solids, Geldart s Class A powders. 

Figure 2. DRIFT spectra measured in the vOH and v( region in He flow (solid lines) and in 6.1% hexane/He flow (dashed lines) at 553 K, i.e., under reaction conditions.

Once filling is complete, filtration begins [Fig. 22.3(b)]. Treated brine is pumped into the vessel at the desired flow rate through an automatic control valve. The flow of brine is from the outside to inside of the filter candles. Filtrate clarity is achieved immediately no recycling of flow is required. As the filtration proceeds at constant flow, solids accumulate as a filter cake on the outside surface of the filter socks. While... 

E Atherton, E Brown, RC Sheppard. A physically supported gel polymer for low pressure, continuous flow solid phase reactions. Applications to solid phase peptide synthesis. J Chem Soc Chem Commun 1151, 1981. 

BW Bycroft, WC Chan, SR Chhabra, ND Hone. A novel lysine-protecting procedure for continous flow solid phase synthesis of branched peptides. (Dde group) J Chem Soc Chem Commun 778, 1993. 

A Di Fenza, M Tacredi, C Galoppini, P Rovero. Racemization studies of Fmoc-Ser(tBu)-OH during stepwise continuous-flow solid-phase peptide synthesis. Tetrahedron Lett 39, 8529, 1998. 

JD Wade, J Bedford, RC Sheppard, GW Tregear. DBU as an V -deprotecting reagent for the fluorenylmethoxycarbonyl group in continuous flow solid-phase peptide synthesis. Pept Res 4, 194, 1991. 

Because of the ease of experimentation batch-solids devices are much preferred however, they can only be used when deactivation is slow enough (in the order of minutes or longer) so that sufficient data on the changing fluid composition can be obtained before exhaustion of the catalyst. When deactivation is very rapid (in the order of seconds or less) then a flowing-solids system must be used. Cracking catalysts whose activity half-lives can be as short as 0.1 second fall into this class. 

In the following sections we treat the batch-solids devices in some detail, and then briefly consider the flowing-solids system. 

Another area that is lacking is the chemistry of solids. In pharmaceuticals, an active drug is often made into a tablet or some other solid. Unknowns remain in the areas of solids flow, solids compressibihty, and compaction. The physical incompatibility of various inert ingredients also remains a mystery. The engineering community has a great opportunity to help in this area. 

Macro-coating is used mainly to stabilise fragrances or transform them from liquid to free-flowing solid powder. Microencapsulation or nanoencapsulation is the process of enclosing a substance inside a miniature capsule. These capsules are referred to as microcapsules or nanocapsules. The substance inside the capsule can be a gas, liquid or solid. The capsule wall can consist of various materials, such a wax, plastic or biopolymers like proteins or polysaccharides. 

Spray-drying is an economical effective method widely used for flavour encapsulation [22-27]. The technology has been used in the food industry since the late 1950s to provide protection of aroma chemicals against oxidation or degradation and to convert liquids into free-flowing solids. The main limitations... 

Most of the relief sizing equations given in Chapters 6-8 yield the two-phase required relief rate, W. The two-phase mass flow capacity per unit area, G, is then needed in order to obtain the required relief area. Chapter 9 contains important background information about two-phase flow, and calculation methods for G. Some system types are special cases involving highly viscous (laminar) flow, solids and/or... 

Sodium Carbonate Peroxyhydrate. Sodium carbonate peroxyhydrate [15630-89-4], which contains about 14 wt % of active oxygen, has the composition 2Na C(% 3H202. A white, free-flowing solid, it generally can be used in all applications where perborate is used. Despite the fact that sodium carbonate peroxyhydrate has a greater rate of dissolution than sodium perborate tetrahydrate, the latter is usually favored for its good storage stability and better compatibility with the various materials used in formulations (79). 

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