Pneumatic transport., example

Either a liquid or a gas can be used as the carrier fluid, depending on the size and properties of the particles, but there are important differences between hydraulic (liquid) and pneumatic (gas) transport. For example, in liquid (hydraulic) transport the fluid-particle and particle-particle interactions dominate over the particle-wall interactions, whereas in gas (pneumatic) transport the particle-particle and particle-wall interactions tend to dominate over the fluid-particle interactions. A typical practical approach, which gives reasonable results for a wide variety of flow conditions in both cases, is to determine the fluid only pressure drop and then apply a correction to account for the effect of the particles from the fluid-particle, particle-particle, and/or particle-wall interactions. A great number of publications have been devoted to this subject, and summaries of much of this work are given by Darby (1986), Govier and Aziz (1972), Klinzing et al. (1997), Molerus (1993), and Wasp et al. (1977). This approach will be addressed shortly. 

The physical transport of the reactor products may also need sufficient processing. Bulk polymerizations in high-pressure extruders may be followed by dicing the product into small pellets suitable for pneumatic transport. Emulsion and solution products are usually transported as obtained and frequently used in the same mode. The design of suitable containers and transportation protocols is very important to avoid harming the product during transportation and storage. For example, special containers may be required for air-sensitive materials, or to avoid solvent or water loss from solutions and emulsions, respectively. 

Bermti et al [13], for example, used the term CFB to generically describe systems like fast fluidized bed, riser reactor, entrained bed, transport bed, pneumatic transport reactor, recirculating solid riser, highly expanded fluid bed, dilute phase transported bed, transport line reactor and suspended catalyst bed in co-current gas flow. 

Pneumatic transportation of solids is important to many industrial processes, for example transporting coal and powder particles. To an operator of such a pneumatic conveyor, the mass flow rate of the solids is the primary process parameter to be measured accurately. A solid/gas flow is very difficult to control because it behaves quite differently from solid/liquid flows. A recent review (Yan, 1996) discussed several variables that may affect the performance of a flow instrument. The distribution of solids in a pneumatic pipeline can be highly inhomogeneous consequently, the particle velocity distribution over the pipe cross section can be widespread. Figure 6.28 shows examples in which the roping type flow is particularly difficult to understand and monitor. 

Unfortunately, to the best of our knowledge, there is no appropriate published experimental data on a 3D spray drying process for the pilot-scale spray chamber used here. However, the developed model of internal and external transport phenomena can be validated by experimental values available for a closely similar drying process, for example, pneumatic drying. For this purpose, the presented model, with slight modifications, has been utilized to perform steady-state numerical simulations of 3D pneumatic... 

The relative velocity for contact of particles with a surface may vary over wide limits. For example, if the particles are settling freely, this velocity will be no greater than 1 m/sec. In the movement of ground transport equipment, such as buses, the relative velocity of particle contact with the surface may be measured in tens of meters per second. In the movement of particles in the process of pneumatic transport, the relative velocity may be as great as hundreds of meters per second. 

In this chapter we deal with two examples of the transport of particulate solids in the presence of a gas. The first example is pneumatic transport (sometimes referred to as pneumatic conveying), which is the use of a gas to transport a particulate solid through a pipeline. The second example is the standpipe, which has been used for many years, particularly in the oil industry, for transferring solids downwards from a vessel at low pressure to a vessel at a higher pressure. 

In dilute transport the gas-to-wall friction is often assumed independent of the presence of the solids and so the friction factor for the gas may be used (e.g. Fanning friction factor - see worked example on dilute pneumatic transport). 

An example is using pneumatic transport rather than conveyors belts or other mechanical conveyors in transporting powders within the workplace. Also, use fully enclosed conveyor belts. 

The values of the HGI usually range from 15 to 140. The higher the HGI, the higher is the grindability of the material. The HGI has been found to correlate with the attrition characteristics of the particles in fluidized beds and in pneumatic transport lines (Davuluri and Knowlton, 1998). The HGI does not directly relate to hardness. For example, some materials such as plastics are difficult to grind. 

In order to increase the inadequate capacity of a pneumatic transport system, a number of actions can be taken. For example, consider modifying the air supply quantity ... 

One of the basic processes in technology occurs when a bed of particles is passed through by another phase. Examples of this process are fixed bed flow, fluidised bed flow, pneumatic transport etc., all of which are qualitatively similar, as the flow occurs around single particles in the presence of surrounding particles. The basic processes mentioned above also include the flooding of packed columns under certain operating conditions, i.e. in... 

Similar approaches have been proposed by others using different separation devices (e.g., Ban et al. 1996, 1997 Kim et al. 2000, 2001 Soong et al. 2001, 2002). One example is a device developed at the University of Kentucky Center for Applied Energy Research and is marketed by Solvera Controls, which utilizes plates and pneumatic ash transport. Ash particles are differentially charged as described previously, and deflected toward oppositely charged plates, thus achieving a carbon/ash separation. 

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