Pneumatic conveying pressure drop

One widely-used picture for illustrating the different types of flow in pneumatic conveying is the so-called state diagram, - in which the pressure drop is related to the air velocity. 

In this chapter the pressure drop for pneumatic conveying pipe flow is studied. The conventional calculation method is based on the use of an additional pressure loss coefficient of the solid particles. The advantage of this classical method is that in principle it can be applied to any type of pneumatic flow. On the other hand, its great disadvantage is that the additional pressure loss coefficient is a complicated function of the density and the velocity of the conveying gas. z lso, it is difficult to illustrate the additional pressure loss coefficient and this makes the theoretical study of it troublesome. 

Considerably more work has been carried out on horizontal as opposed to vertical pneumatic conveying. A useful review of relevant work and of correlations for the calculation of pressure drops has been given by Klinzing et a/.(68). Some consideration will now be given to horizontal conveying, with particular reference to dilute phase flow, and this is followed by a brief analysis of vertical flow. 

Figure 5.18. Pressure drop for flow of solids in pneumatic conveying...

Clark, R. IF, Charles, D. E., Richardson,. 1. F., and Newitt, D. M. Trans. Inst. Chem. Eng. 30 (1952) 209. Pneumatic conveying. Part 1. The pressure drop during horizontal conveyance. 

Mstlin. L. University of London. Ph.D. thesis (1954). A study of pneumatic conveying with special reference to solid velocity and pressure drop during transport. 

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

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. 

If the conveying velocity is a critical parameter, then the designer of a pneumatic conveying system should also consider the expansion effect caused by the pressure drop along the conveying line. The resulting increase of the gas velocity can be accounted for by increasing the pipe diameter. 

Knowlton, T., The Effect of the System Pressure/Pipe-Diameter/Mass Flux Interaction on Pressure Drop in Dilute Phase Pneumatic Conveying, Proc. of Pneumatic Conveying Workshop, Powder Technol. Forum, AIChE, Denver (1994)... 

Predict the pressure drop of large-throughput cement pneumatic conveying systems (Wypych, 1992)... 

Pan, R., and Wypych, P. W., Bend Pressure Drop in Pneumatic Conveying of Fly Ash, Powder Bulk Solids Conf., Reed Exhibition Companies, USA, Proc, pp. 349-360, Rosemont, Illinois, USA (1992b)... 

D. Mills, J.S. Mason, P. Marjanovic, A comparison of pressure drops in horizontal and vertical dense phase pneumatic conveying, Proceedings of the 3rd International Conference on Pneumatic Conveying, Pecs, Hungary, March 1985. 

R. Pan, P.W. Wypych, Pressure drop and slug velocity in low-velocity pneumatic conveying of bulk solids, Powder Technol. 94 (1997) 123-132. 

Blasco et al. [12] proposed two-dimensional mathematical model for the drying process of dense phase pneumatic conveying. However, heat and mass transfer were not considered and therefore their model may be used for dense phase pneumatic transport only. In their paper, both experimental and numerical predictions for axial and radial profiles for gas and solid velocity, axial profiles for solid concentration and pressure drop were presented. 

For transport of a gas-solid suspension, it is important to be able to evaluate the pressure drop in order to estimate the power consumption. In a pneumatic conveying system, particles are usually fed into the carrying gas and accelerated by the gas flow. The power consumption (or pressure drop per unit pipe length) for the acceleration of particles can be significant compared with that for a fully developed flow condition. Moreover, the pressure... 

Konrad, K., Harrison, D., Nedderman, R. M. and Davidson, J. F. (1980). Prediction of the Pressure Drop for Horizontal Dense-Phase Pneumatic Conveying of Particles. Pneumotransport, 5,225. 

Knowlton, T. M and Bachovchin, D. M. The determination of gas-solids pressure drop and choking velocity as a function of gas density in a vertical pneumatic conveying line, International Conference on Fluidization, Pacific Grove, June 15-20, p. 253 (1975). 

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