Silo pressures

The chapter refers extensively to the provisions of the recently developed European standards for silo pressures (EN 1991-4 2007) and for metal silo structural design (EN 1993-4-1 2007), for which the author was the chief contributor and editor. Further useful information relating to the structural design of all silos may be found in Rotter (2001a). 

Although silos have been used to store solids (e.g. grains) for thousands of years, the earliest scientific studies of the pressures in silos were only undertaken at the end of the nineteenth century. Several researchers performed simple experiments and developed simple theories in this period (for a good description, see Ketchum 1907), but the most important of these was Janssen (1895) who both performed experiments on a tall square model silo and developed the theory which is almost universally used as the single reliable reference point in a sea of uncertainties concerning silo pressures. 

Janssen silo pressure theory for vertical walls... 

The most widely used switch theory for vertical walls was that of Jenike et al. (1973), which still underlies the flow pressure rules in the Australian Standard AS 3774 (1996), leading to a high ratio of design pressures for discharge to those after filling. This type of theory is still commonly expounded (Drescher 1991) as a formal part of silo pressure behaviour. 

This chapter has given a brief outline of the key aspects of silo pressure phenomena and their implications for potential damage to silo structures. It is evident that the subject is large and requires much more detailed treatment on many issues than is possible here. However, many references to other useful sources have been given. 

Our understanding of silo pressures and their consequences for storage structures is continually expanding, sometimes as a result of new catastrophes. As a result, current advice and standards are likely to be steadily improved, and better treatments should be available for many of the questions that were imperfectly answered here. The reader is invited to seek specialist advice when new problems are encountered. 

A powder s strength increases significantly with increasing previous compaction. The relationship between the unconfined yield stress/, or a powder s strength, and compaction pressure is described by the powder s flow function FE The flow function is the paramount characterization of powder strength and flow properties, and it is calculated from the yield loci determined from shear cell measurements. [Jenike, Storage and Flow of Solids, Univ. of Utah, Eng. Exp. Station Bulletin, no. 123, November (1964). See also Sec. 21 on storage bins, silos, and hoppers.]... 

Hopper Trucks These trucks are used to transport by highway a wide variety of materials. Vehicle types range from the open-dumping kind to the closed type. Most common is the type that unloads by pressure differential into its own pneumatic-conveying system, which is temporarily connected to a storage silo. On this type of truck, the unloading of 18,100 kg (40,000 lb) of produces takes about 1 h, sometimes less. 

Figure 7-8R. Low pressure bursting vents for explosion relief on storage silos, buildings, etc. Usually burst 1.0 to 8.0 psig depending on design. Round vents also available. By permission, Fike Metal Products DIv., Fike Corporation, Inc.

Low absolute pressure calculations, 129 Low pressure system, 129 American Petroleum Institute, 399 American Society of Mechanical Engineers, 399 API Codes, 399 API oil field separators, 239 API, heat absorbed from fire, 451-453 Babcock steam formula, 103, 107, 108 Back pressure, 404 Effect of, 407, 408 Baffles, lank mixing, 311 Diagrams, 330 Bag filters/separators, 270 Bag materials, 274 Cleaning, 272, 273 Heavy dust loads, 271 Specifications, 271 Temperature range, 271 Bins, silos, hoppers venting, 516 Blast pressure, 496 Blowdown, 404... 

Escoe, A. K. Mechanical Design of Process Equipment, Vol. 1. Piping and Pressure Vessels. Vol. 2. Shell-and-tube Heat Exchangers, Rotating Equipment, Bins, Silos and Stacks (Gulf, 1986). 

Figure 4-6 A combination vacuum-pressure system. A vacuum is used to withdraw material from a hopper car and positive pressure is used to transport it to storage silos.

The crew noticed fuel vapors escaping, and within 24 minutes, shortly after 8 P.M., the crew in the command control area had indications of fire in the silo and loss of fuel tank pressure. 

The polymer collected in the large-volume high-pressure separator is fed to a low-pressure separator for further degassing and is then pelletized in a melt-extruder by a die-face cutter. The pellets are dried and conveyed to silos. 

F. Hauert, A. Vogl, S. Radandt, Dust cloud characterization and its influence on the pressure-time-history in silos, Process Safety Progress 15 (1996) 178-184. 

It has been shown by Boruch et al.66 61 that solid starch changes its electrical conductivity on compression. At constant temperature and humidity there is a positive correlation between the tamping of starch layers in cylinders, containers, and silos and their electrical conductivity.67 Figure 10 shows how the electrical conductivity varies for potato starch as a function of the humidity and pressure applied. 

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