Pneumatic transport

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 this section we will look at the distinguishing characteristics of dense and dilute phase transport and the types of equipment and systems used with each. The design of dilute phase systems is dealt with in detail and the approach to design of dense phase systems is summarized. 

Introduction to Particle Technology, 2nd Edition Martin Rhodes 2008 John Wiley Sons Ltd. ISBN 978-0-470 -01427-1 

---

The hot reduced fines are pneumatically transported to an atmospheric pressure hoi ding dmm from which they are fed to the briquetting machines. The hot briquettes are separated, cooled on a circular grate, and deUvered to an outdoor storage pile. 

Hydrauhc transport is used in mines and for lifting coals to the surface in Russia, Poland, and France. Pneumatic transport of coal is used over short distances in power plants and steel mills. The longest (14.5 km) single flight conveyer belt in the world near Uniontown, Kentucky, has a capacity of 1360 t/h. 

A pneumatic-transport device designed primarily for heat-sensitive prodiicis is shown in Fig. 11-64. This was introduced into the United States after 5 years use in Europe [Chem. Eng., 76, 54 (June 16,... 

FIG. 11-64 A pneumatic-transport adaptation for heat-transfer duty. (Courtesy ofWerne [Pg.1097]

Pneumatic Transport Both low-pressure air-vacuum conduit transport systems have been used to transport sohd wastes. The most common application is the transport or wastes from high-density apartments or commercial activities to a central location for processing or for loading into transpoii vehicles. The largest pneumatic system in use in the United States is at the Walt Disney World amusement park in Orlando, Florida. 

Use pneumatic transport, enclosed conveyor belts, or self-closing conveyor belts, as well as wind barriers and other dust suppression measures, to reduce the formation of fugitive dust. 

An Empirid Approach for Calculating the Pressure Drop in Pneumatic Transport 1339... 

For calculating the pressure loss in pneumatic transport, the following simply modified version of Eq. (14.87) is often presented in the literature ... 

It is known from experience with vertical pneumatic transport that the influence of weight prevails at low velocities, but as the velocity increases friction gains importance. Therefore, in the calculation of the pressure loss one must find not only the weight of the solids, which could be set up theoretically, but also an empirical relationship for vertical transport from the measured data. A correlation of the pressure-loss coefficient for vertical pneumatic conveyance according to data measured by Flatow " has been developed by Weber, and the result is... 

A Theoretical Approach for Calculating the Pres re Drop in Pneumatic Transport... 

Praii, T. H., Static Electricity in Pneumatic Transport Systems, Process Safety Progress, V. 13, No. 3, 1994, p. 109. 

Gases carrying solid particles wholly or partly in suspension ( pneumatic transport ). 

KUMZING, G. E RuHATCU, N. D., ZalI ASH, A. and Myler, C. A. Powder Technol. 51 (1987) 135. Pneumatic transport — a review (Generalized phase diagram approach to pneumatic transport). 

Dust explosion possible if in powder or granular form, mixed with air. If dry, it can be charged electrostatically by swirling, pneumatic transport, pouring, etc. 

In the riser tube, the gas velocity of chlorine, is greater than both of the terminal velocities of the slag particle and the petrocoke particle, makes the particles to be at a pneumatic transport state. No agglomeration occurs in the riser tube. At the top of the riser tube, a... 

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. 

Molerus (1993) developed a state diagram that shows a correlation between these dimensionless groups based on an extremely wide range of data covering 25 < D < 315 mm, 12 < d < 5200/am, and 1270 < ps < 5250 kg/m3 for both hydraulic and pneumatic transport. This state diagram is shown in Fig. 15-3 in the form... 

One major difference between pneumatic transport and hydraulic transport is that the gas-solid interaction for pneumatic transport is generally much smaller than the particle-particle and particle-wall interaction. There are two primary modes of pneumatic transport dense phase and dilute phase. In the former, the transport occurs below the saltation velocity (which is roughly equivalent to the minimum deposit velocity) in plug flow, dune flow, or sliding bed flow. Dilute phase transport occurs above the saltation velocity in suspended flow. The saltation velocity is not the same as the entrainment or pickup velocity, however, which is approximately 50% greater than the saltation velocity. The pressure gradient-velocity relationship is similar to the one for hydraulic transport, as shown in... 

Fig. 15-4, except that transport is possible in the dense phase in which the pressure gradient, though quite large, is still usually not as large as for hydraulic transport. The entire curve shifts up and to the right as the solids mass flux increases. A comparison of typical operating conditions for dilute and dense phase pneumatic transport is shown in Table 15-1. 

Table 15-1 Dilute vs. Dense Phase Pneumatic Transport...

Figure 1. Recirculating fluidized bed concept—draft tube operated as a dilute phase pneumatic transport tube.

Draft Tube Operated As A Pneumatic Transport Tube... 

Most of the applications for the recirculating fluidized bed with a draft tube operate the draft tube as a dilute phase pneumatic transport tube. Hence we will discussed this system in more details. 

---