Powders transport

The properties of concern in this section are to do with behaviour of powders in an aerated state this is relevant in gas fluidization, powder transport and handling. Probably the most important tests in this category are those derived from fluidization and the results of such tests are not necessarily restricted to the area of gas fluidization. It should be emphasized that the following notes apply largely to fine powders (i.e. groups A and AC in Geldart s classification). 

Less tendency for deposit formation. Improved directional air flow. Improved powder transport control. Good bed emptying properties. Vibration normally not necessary. Particles are still sifting through holes. 

Further improvement in powder transport and movement control as gill openings can be... 

Monitoring of solid/gas flow is important to safe and efficient operation of pneumatic transport that is used in many industrial processes such as coal mining and powder transport. Commonly employed techniques to measure particle velocity are a radioactive tracer method (Somerscales, 1981), optical techniques (Lee Srinivasan, 1978), electromagnetic methods (Bobis et al., 1986) and conventional mechanical approaches (Soo, 1990). 

Powder transport lines can be considered as very lean fluidized beds. These are encountered in many industries for instance, conveying powder-laden gases to cyclone separators. Here, acoustic emission proves to be a sensitive indicator for the presence of powders or liquid droplets, the detection of blockages, and as a semiquantitative indicator of the particulate mass flow. 

In Chapter 8, we saw how a gas may be used to transport powders within a process. The efficient separation of the product from the gas at the end of the transport line plays an important part in the successful application of this method of powder transportation. In the combustion of solid fuels, fine particles of fuel ash become suspended in the combustion gases and must be removed before the gases can be discharged to the environment. 

Apphcations of ultrasound to electrochemistry have also seen substantial recent progress. Beneficial effects of ultrasound on electroplating and on organic synthetic apphcations of organic electrochemistry (71) have been known for quite some time. More recent studies have focused on the underlying physical theory of enhanced mass transport near electrode surfaces (72,73). Another important appHcation for sonoelectrochemistry has been developed by J. Reisse and co-workers for the electroreductive synthesis of submicrometer powders of transition metals (74). 

Polyacrylamide powders are typically shipped in moisture-resistant bags or fiber packs. Emulsion and solution polymers are sold in dmms, tote bins, tank tmcks, and tank cars. The transportation of dry and solution products is not regulated in the United States by the Department of Transportation, but emulsions require a DOT NA 1693 label. 

In pack cementation, the part to be coated is placed in a retort and surrounded with a powdered pack consisting of the coating component and an activator the latter reacts with the coating component to form the carrier vapor, usually a haHde or an inert diluent, to prevent the pack from sintering together and to permit vapor transport of the alloying component through the pack. 

Transportation and Disposal. Only highly alkaline forms of soluble sihcates are regulated by the U.S. Department of Transportation (DOT) as hazardous materials for transportation. When discarded, these ate classified as hazardous waste under the Resource Conservation and Recovery Act (RCRA). Typical members of this class are sodium sihcate solutions having sihca-to-alkah ratios of less than 1.6 and sodium sihcate powders with ratios of less than 1.0. In the recommended treatment and disposal method, the soluble sihcates are neutralized with aqueous acid (6 Af or equivalent), and the resulting sihca gel is disposed of according to local, state, and federal regulations. The neutral hquid, a salt solution, can be flushed iato sewer systems (86). 

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