Siloses

Localization of void sliding ducts in the concrete of a storage silo... 

Due to the outer circumference of the silo, about 25 meters, a non- or rarely destructive testing method was needed for the localization. Because the building was still in use, it was only accessable from the exterior side. We chose the ultrasonic pulse-echo-technique as an appropriate way of doing the testing. 

Industrial appHcations often require that bulk materials or Hquids be weighed in hoppers, silos, tanks, or reactor vessels, referred to collectively as vessels. Because they come in such a wide variety of si2es, shapes, and capacities, scales using these vessels as load receivers are not typically available as standard products. Vessels are usually custom-fabricated to suit a particular appHcation, then mounted on a scale. Some can be mounted on a standard scale such as a bench, portable, or floor scale. More typically, a number of weigh modules are used to support the vessel. This offers the scale designer great flexibiHty but certain precautions are necessary in order to constmct an accurate scale. Some of the more important factors associated with the design of vessel scales are discussed herein. 

Production, Storage, and Shipment. A plant of 50,000-t annual capacity could be considered viable for production of isophthahc acid, although no new plants have been constmcted since the early 1980s. Storage of isophthahc acid is in silos. Shipment is in 22.7- and 25-kg bags, 0.5-t and 1-t bags, or hopper tmcks. The far lower production quantity of isophthahc acid and its more varied apphcations vs terephthahc acid mean that high volume... 

With few exceptions, thermoplastics are marketed in the form of pellets. They are shipped in containers of various sizes, from 25-kg bags to railroad hopper cars. Resins are conveyed to silos for storage and from there to the processing equipment. Colored resins are available, but frequentiy it is more convenient and economical to buy uncolored resins and blend them with color concentrates. Using concentrates avoids handling dusty pigments and ensures uniform color distribution. 

Because mass flow bins have stable flow patterns that mimic the shape of the bin, permeabihty values can be used to calculate critical, steady-state discharge rates from mass flow hoppers. Permeabihty values can also be used to calculate the time required for fine powders to settle in bins and silos. In general, permeabihty is affected by particle size and shape, ie, permeabihty decreases as particle size decreases and the better the fit between individual particles, the lower the permeabihty moisture content, ie, as moisture content increases, many materials tend to agglomerate which increases permeabihty and temperature, ie, because the permeabihty factor, K, is inversely proportional to the viscosity of the air or gas in the void spaces, heating causes the gas to become more viscous, making the sohd less permeable. 

Structural Considerations. Sdos, bins, and hoppers fail, in one way or another, each year. The causes of silo failures are many and varied (9). Such failures can range from a complete and dramatic stmctural coUapse, to cracking in a concrete wall, or denting of a steel shell. This last is often a danger signal indicating that corrective measures are required. 

The other cause of constmction problems is the introduction of badly chosen, or even unauthorized, changes during constmction in order to expedite the work. Any changes in details, material specifications, or erection procedure must be given careful consideration by both the builder and silo designer. 

Wear owing to corrosion and/or erosion can be particularly dangerous. For example, as carbon steel corrodes, the reduced wall thickness can eventually lead to a stmctural failure. This problem can be compounded through erosive wear of the silo wall. 

R. T. Jenkyn and D. J. Goodwih, "Silo Failures Lessons to be Learned," Eng. Digest (Sept. 1987). 

J. W. Carson and R. T. Jenkyn, "Load Development and Stmctural Considerations in Silo Design," presented at Eeliable Flow of Particulate Solids II, Oslo, Norway, Aug. 1993. 

Several plants employ cooled-belt flakers. These consist of flexible steel belts, ca 1-m wide and up to 50-m long, that have short mbber skirting at the edges. Molten pitch flows from a thermostatically controlled tank over a weir to give a flat thin sheet on the belt, which is cooled from below by water sprays. At the end of the belt, the solid pitch is broken up by rotating tines. The pitch flakes are drained and transported to a covered storage silo by belt conveyor, during which time the surface moisture evaporates. 

For a coarse-grained (particle containing) graphite, the system depicted in Figure 1 is typical. The nin-of-kiln coke is brought in on railroad cars and emptied into pits where the coke is conveyed to an elevator. The elevator feeds a second conveyor that empties the coke into any one of a number of storage silos where the coke is kept dry. The manufacturer usually specifies a maximum moisture content in the incoming coke at about 0.1—0.2% to ensure that mix compositions are not altered by fluctuations in moisture content. 

A blending system provides the kiln with a homogeneous raw feed. In the wet process the mill slurry is blended in a series of continuously agitated tanks in which the composition, usually the CaO content, is adjusted as required. These tanks may also serve as kiln feed tanks, or the slurry after agitation is pumped to large kiln feed basins. Dry-process blending is usually accompHshed in a silo with compressed air. 

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