Pneumatic conveying lines

Constance, J.D. Calculating Pressure Drops in Pneumatic Conveying Lines, Chemical Engineering, Mar. 15, 1965, p. 200. 

Yang, W. C., Criteria for Choking in Vertical Pneumatic Conveying Lines, ... 

The pressure drop inside the draft tube is more complicated because it involves acceleration of solid particles from essentially zero vertical velocity. However, the model for calculating the pressure drop in vertical pneumatic conveying lines suggested by Yang (1977) can be applied. The acceleration length can be calculated from numerical integration of the following equation. 

Attrition in Fluidized Beds and Pneumatic Conveying Lines... 

Attrition of particulate materials occurs wherever solids are handled and processed. In contrast to the term comminution, which describes the intentional particle degradation, the term attrition condenses all phenomena of unwanted particle degradation which may lead to a lot of different problems. The present chapter focuses on two particular process types where attrition is of special relevance, namely fluidized beds and pneumatic conveying lines. The problems caused by attrition can be divided into two broad categories. On the one hand, there is the generation of fines. In the case of fluidized bed catalytic reactors, this will lead to a loss of valuable catalyst material. Moreover, attrition may cause dust problems like explosion hazards or additional burden on the filtration systems. On the other hand, attrition causes changes in physical properties of the material such as particle size distribution or surface area. This can result in a reduction of product quality or in difficulties with operation of the plant. 

In order to evaluate the extent of attrition and its impact on the particle size distribution, there is a need of a qualitative and quantitative characterization. This, however, is not as simple as it may seem at first. There are many different properties, parameters and effects that manifest themselves and could be measured. In addition, as will be shown, the choice of the assessment procedure is strongly connected with the definition of attrition which, on its part, depends on the degradation mechanism that is considered to be relevant to the process. Hence there are a lot of procedures and indices to characterize the process of particle attrition. Section 3 deals with those which are relevant to fluidized beds and pneumatic conveying lines. 

Test facilities are also used to investigate specific attrition phenomena of individual processes. Up to now only a few investigations have been carried out in full-scale equipment. Most results were obtained from very special devices which makes it difficult to compare the results of various research groups and to draw general conclusions. Despite of these difficulties, the specific attrition phenomena in fluidized beds and pneumatic conveying lines will be summarized in the Secs. 5 and 6, respectively. It will... 

Wall-Hardness. One can assume that the particle degradation increases with the hardness of the vessel wall. This effect will increase with increasing ratio of particle-to-tube diameter and will thus in practice be relevant in pneumatic conveying lines only. 

Detailed reviews of such test procedures are given by Bemrose and Bridgwater (1987) and the British Material Handling Board (1987). The present subsection is restricted to a short discussion of those tests that are relevant for fluidized beds or pneumatic conveying lines. 

Pneumatic Conveying Tests. In contrast to fluidized bed tests, no standard equipment exists that simulates the stress on particles in pneumatic conveying lines. There is no friability test quoted in the pertinent literature that is based on a specific pneumatic conveying system. 

Equipment for solids transport which is usually needed in fluidized bed processes will also add to the overall attrition rate. In screw feeders or rotary valves, the particles can be crushed or sheared between the vanes and the housing. The contribution of pneumatic conveying lines is discussed in Sec. 6. 

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