Pneumatic conveying applications

However, this section pursues particle size measurement and evaluates its importance (as well as density) for the purpose of classifying the suitability of powders for long-distance pneumatic conveying applications. Initially, an appreciation of the fundamentals and the existing powder classification techniques is required. 

Consequently, more elaborate designs had to be tested and/or developed for this application of pneumatic conveying. The following two valves have been found useful in particular areas. Note that in each case it is imperative to ensure fast actuation time (e.g., 1 second for a 100 mm nominal bore NB valve and a few seconds for a 300 mm NB valve, if possible). Large-bore solenoid valves and quick-exhaust valves usually are required for this purpose. Also, note that each one of the following valves provides a full cross-sectional area of flow in the open position and a 100% seal in the closed position. One of the major problems of air-on-sleeve pinch valves is that they do not provide these important features for pneumatic conveying applications (e.g., a small hole in a closed sleeve quickly erodes due to the subsequent high velocities of air and solids). 

The use of the effective (aerodynamic) particle density is largely restricted to fluidization and pneumatic conveying applications at the moment. It is, however, potentially useful in other areas like particle size measurement by sedimentation or elutriation, or flow through packed beds where it has not yet been fully accepted. 

Cartaxo S.J.M. and Rocha S.C.S., Object-oriented simulation of pneumatic conveying— Application to a turbulent flow, Brazilian Journal of Chemical Engineering, 16(4), 329-337,1999. 

The separation step requires (1) application of a force that produces a differential motion of the particles relative to the gas, and (2) sufficient gas-retention time for the particles to migrate to the collecting surface. Most dust-collections systems are comprised of a pneumatic-conveying system and some device that separates suspended particulate matter from the conveyed air stream. The more common systems use either filter media (e.g., fabric bags) or cyclonic separators to separate the particulate matter from air. 

Fluidized Bed Tests. These tests have direct relevance to all applications where particles are subjected to conditions of fluidization. Some authors believe that these tests can also to some extent simulate the stress of pneumatic transport. Coppingeretal. (1992) found at least a good correlation with the attrition resistance in dense-phase pneumatic conveying when they tested various powders in a slugging fluidized bed. 

Pneumatic conveying systems and in particular dilute phase conveying systems are known to create a high stress on particulate solids leading to significant attrition. In contrast to fluidized beds, it is not the material loss which is the main problem. Depending on the application, problems may rather occur in a number of different areas. Attrition may, for example,... 

A significant number of developments have occurred over the past decade to address these important issues of pneumatic conveying (Wypych, 1995a). This chapter summarizes some of the major design considerations that have resulted from this work in relation to long-distance and pipe branching applications. 

Application to Long-Distance Pneumatic Conveying. From the above three classifications, there is sufficient evidence to suggest that powder classification (i.e., to select ultimately the most suitable mode of conveying for a given product and its behavioral properties) depends on the following properties ... 

The branching of pipes/ducts in pneumatic conveying has the following two main applications in industry. 

Timms, G., Pneumatic Conveying - a New Application for Larox Pinch Valves, Larox News, 14 8-11 (1992)... 

It is possible to operate a fluidized bed in either batch or continuous mode. Strictly, most batch applications are in tact operated in semibatch mode where the solids are treated as a batch but the fluidizing medium enters and leaves the bed continuously. In the case ot gas-solid beds used in termentation (see Chapter 6), the fluidizing gas is recirculated although reactants and products flow continuously. In true continuous operation the solids may be ted into a fluidized bed via screw conveyors, weigh teeders or pneumatic conveying lines and can be withdrawn trom the bed via standpipes or by flowing over weirs. 

The pumps of the DRYVAC family are the classic dry compressing claw vacuum pumps that are preferably used in the semiconductor industry, whereby the pumps need to meet a variety of special requirements. In semiconductor processes, as in many other vacuum applications, the formation of particles and dusts during the process and/or in the course of compressing the pumped substances to atmospheric pressure within the pump, is unavoidable. In the case of vacuum pumps operating on the claw principle it is possible to convey particles through the pump by means of so called pneumatic conveying". This prevents the deposition of particles and... 

P. Maijanovic, Determination of performance characteristics of dilute phase pneumatic conveying system, Proceedings of the 3rd Symposium of Process Industry Applications, Belgrade, Yugoslavia, 1988, pp. 215-223 (in Serbian). 

Pneumatic conveying. Direct type, continuous operation See comments under Slurries Can be used only if product is recirculated to make feed suitable for handling Usually requires recirculation of dry product to make suitable feed. Well suited to high capacities. Disintegration usually required Suitable for materials that are easily suspended in a gas stream and lose moisture readily. Well suited to high capacities Suitable for materials that are easily suspended in a gas streatm. Well suited to high capacities. Product may suffer physical degradation Not applicable Not applicable Not applicable... 

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