Transport of solids

Figure 22-8 shows the features of a horizontal center-fed column [Brodie, Au.st. Mech. Chem. Eng. Tran.s., 37 (May 1979)] which has been commercialized for continuous purification of naphthalene and p-dichlorobenzene. Liquid feed enters the column between the hot purifying section and the cold freezing or recovery zone. Ciystals are formed internally by indirect cooling of the melt through the walls of the refining and recovery zones. Residue liquid that has been depleted or product exits from the coldest section of the column. A spiral conveyor controls the transport of solids through the unit. 

Fluidized-bed adsorbers have several disadvantages. The continuous handling and transport of solids is expensive from an equipment standpoint fluidized-bed systems must be large to be economical. Solids handling also presents a potential for mechanical problems. Careful control is required to keep the adsorbent fluidized, while minimizing adsorbent loss with the gas-phase attrition of the adsorbent can be high, requiring substantial makeup. 

This subsection deals with the handling, storage, and transportation of solids, liquids, and gases. Each form is considered individually. 

In the hydraulic transport of solids through steel pipelines, inhibitors of the sodium-zinc-phosphate glass type have been shown" to be effective. In the case of coal slurries the polyphosphate type was rejected because the de-oxygenating action of the coal lowered the inhibitor effectiveness. Hexavalent chromium compounds at 20 p.p.m. were more effective". ... 

In production processes, raw material are converted into desired products using a series unit operations of unit operations. Such unit operations may be few in number and they are linked together in a logical sequence. Typical unit operations include such activities as the transport of solids and liquids, the transfer of heat, crysallisation, collection and drying. 

In a recent study of the transport of solids by liquid in a 38 mm diameter pipe. 30 the following variables were measured ... 

Chhabra. R. P. In Civil Engineering Practice, Volume 2, Cheremisinoff, P. N., Cheremisinoff, N. P. and Cheng, S. L. eds (Technomic Pub. Press PA, 1988). Hydraulic transport of solids in horizontal pipes. 

Durand, R. Ptoc. of the Minnesota Internationa] Hydraulic Convention (1953) 89. Basic relationships of transportation of solids in pipes — experimental research. 

Khan, A. R PIRIE, R. L. and Richardson, J. F. Chem. Eng. Sci. 42 (1987) 767. Hydraulic transport of solids in horizontal pipelines — predictive methods for pressure gradient. 

Fig. 9-3 Conceptual model to describe the interaction between chemical weathering of bedrock and down-slope transport of solid erosion products. It is assumed that chemical weathering is required to generate loose solid erosion products of the bedrock. Solid curve portrays a hypothetical relationship between soil thickness and rate of chemical weathering of bedrock. Dotted lines correspond to different potential transport capacities. Low potential transport capacity is expected on a flat terrain, whereas high transport is expected on steep terrain. For moderate capacity, C and F are equilibrium points. (Modified with permission from R. F. Stallard, River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco basins. In J. I. Drever, ed. (1985), "The Chemistry of Weathering," D. Reidel Publishing Co., Dordrecht, The Netherlands.)...

Belt conveyors are the most commonly used type of equipment for the continuous transport of solids. They can carry a wide range of materials economically over long and short distances both horizontally or at an appreciable angle, depending on the angle of repose of the solids. A belt conveyor consists of an endless belt of a flexible material, supported on rollers (idlers), and passing over larger rollers at each end, one of which is... 

This relation applies from the initial expansion of the bed until transport of solids takes place. There may be some discrepancy between the calculated and measured minimum velocities for fluidisation. This may be attributable to channelling, as a result of which the drag force acting on the bed is reduced, to the action of electrostatic forces in case of gaseous fluidisation—particularly important in the case of sands—to agglomeration which is often considerable with small particles, or to friction between the fluid and the walls of the containing vessel. This last factor is of greatest importance with beds of small diameters. Leva et al.<4 introduced a term, (GF — GE)/ GF, which is a fluidisation efficiency, in which GF is the minimum flowrate required to produce fluidisation and G / is the rate required to produce the initial expansion of the bed. 

A.G. Bain and S.T. Bonnington, The Hydraulic Transport of Solids by Pipeline, Pergamon, New York, 1970. 

Although the phenomena are not clearcut, partial settling out of solids from the gas stream and other instabilities may develop below certain linear velocities of the gas called choking velocities. Normal pneumatic transport of solids accordingly is conducted above such a calculated rate by a factor of 2 or more because the best correlations are not more accurate. Above choking velocities the process is called dilute phase transport and, below, dense phase transport. 

A.J. Stepanoff, Gravity Flow of Bulk Solids and Transport of Solids in Suspension, Wiley, New York, 1969. 

Pipelines to transport solids are called freight pipelines, of which three different types exist pneumatic pipelines, the use of which is known as pneumotransport or pneumatic conveying slurry pipelines, which may also be called hydrotransport or hydraulic conveying and capsule pipelines. When air or inert gas is used to move the solids in the pipeline, the system is called a pneumatic pipeline and often involves a wheeled vehicle inside the pipeline, propelled by air moving through the pipe (25). Slurry pipelines involve the transport of solid particles suspended in water or another inert liquid. Hydraulic capsule pipelines transport solid material within cylindrical containers, using water flow through the pipeline for propulsion. 

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