Pneumatic conveying purpose

Pneumatic-Conveying Devices See Sec. 21 for descriptions, ratings, and design factors on these devices. Use is primarily for transport purposes, and heat transfer is a very secondary consideration. 

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). 

Flow diversion Flow diverting is a very common requirement with pneumatic conveying systems and can be achieved very easily. Many companies manufacture specific flow diverting valves for the purpose. Alternatively flow diversion can be achieved by using a set of isolating valves. The most common requirement is to divert the flow to one of two alternative routes, typically where material needs to be discharged into a number of alternative hoppers or silos. In this case the main delivery line would be provided with a diversion branch to each outlet in turn. 

For the purposes of design of a pneumatic conveying system, there is still no safe alternative to having some measurements of the flow characteristics of the bulk solid for which the system is to be designed, obtained from an actual pneumatic conveying pipeline. 

A comparison of the theoretical prediction of boundary B for low-velocity pneumatic conveying with the experimental results from the test rig described in this paper is shown in Fig, 7. The input data required for the model include the particle density (897 kg m ), the voidage of bulk solid (0.391), the coefficient of friction between the particles and wall (0.23), the coefficient of particle internal friction (0.5) and pipeline diameter (60 mm). The agreement between Ae modelling results and the experiments is quite good and the model can be used for design and optimisation purposes. Also, the model described in this paper is able to represent the mechanism of slug formation. 

When designing pneumatic conveying systems for light and free flowing granular materials, the unstable zone should be avoided. For such purpose, the accurate prediction of pressure drop caused by the long slugs in the unstable zone can provide some useftil information for the determination of the unstable zone boundaries. 

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