Studies Toward Development of Unified Model for Solid Friction for Dense Phase Pneumatic Conveying of the Fine Powders

Abstract

The dense phase mode of flow is widely used to convey different materials in various industries such as power, chemical, pharmaceutical, alumina, limestone, refineries, owing to its advantages such as lesser particle degradation, higher efficiency, smaller gas-solid separator, increased pipeline life as compared to dilute phase. The solids friction factor is an important factor to be included in empirical models to calculate the pressure drop. The available empirical models (grouping of different dimensionless term) for solids friction factor of fluidized dense phase flow are material specific, that is the values of constants and exponents are different for different materials. Even for the same material these constants vary due to difference in their particle size distribution. Therefore in the present study an attempt has been made to develop a unified model for solids friction factor. First, the most reliable two layer models for ESP dust, two types of fly ash, cement for short straight horizontal pipeline have been used for the derivation of unified constants with the help of dimensionless terms such as Froude number of particles, density ratio and particle size distribution. In order to validate the accuracy and stability of the unified two layer model, concept of equivalent length (to compensate the bend and vertical length loss) has been utilized to predict the total pipeline pressure drop in different pipeline (69 mm I.D. × 169m, 105mm I.D. × 169m, 65mm I.D. × 254m) and have been compared with experimental data. The results thus obtained provided the accurate prediction of pressure drop at lower as well as higher mass flow rate. But this correlation is valid for very small range of ‘δ’. Due to this limitation, a new unified model was developed with three dimensionless terms by considering the wide range of data and then this model was validated with experimental data of Thapar University for grey and white cement which was conveyed in a 54mm I.D. × 70 m long pipeline. Also, the unified correlation has been defined to determine the pressure minimum curve with the inclusion of Stoke number and integral length scale of eddy for fine powders. This correlation has been validated with the experimental data of the given materials in different pipeline configurations. The correlation seems to predict the experimental data quite accurately.