Numerical evaluation of flow through a centrifugal slurry pump handling fly ash using CFD

Abstract

Centrifugal pumps are used for transportation of solids and liquids over short to medium distance through the pipelines. A centrifugal pump designed to handle the liquids is normally single stage, end suction type having radial or mixed flow configuration of blades. Centrifugal pump radial-flow type is the most common in slurry service. A conventional centrifugal pump is designed to handle clear liquids, bottom ash and fly ash slurry. The modifications incorporated in the pump include enlargement of flow passages to accommodate bigger solid particles, robust impeller with smaller number of vanes, special seals and proper material of construction to ensure longer life. These have to be operated with relatively wide clearance at impeller-casing contacts to minimize choking and localized wear. These modifications increase the hydraulic losses in the pump and deteriorate the pump performance. Computational fluid dynamics (CFD) is being increasingly applied in the design of the centrifugal pumps. 3-D numerical computational fluid dynamics tool can be used for simulation of the flow field characteristics inside the turbo machinery. Numerical simulation makes it possible to visualize the flow condition inside a centrifugal slurry pump, and provides the valuable hydraulic design information of the centrifugal slurry pumps. The present study is concerned with the evaluation of the performance characteristics of a centrifugal slurry pump when handling clear water and numerical simulation with different concentration namely 10%, 20%, 30%, 40% and 50% of bottom ash and fly ash slurry at different speeds namely 1000rpm, 1150rpm, 1300rpm and 1450rpm. The pump characteristics of centrifugal slurry pumps are influenced by various particle parameters such as concentration and flow velocity of slurries. Slurry flow through centrifugal slurry pump has been modeled using the Mixture approach with Multiphase model. A mixture property based k-ε turbulence model has been used using turbulence. A numerical model of an impeller and casing has been generated and the complex internal pressure and velocity distribution are investigated by using the CFX commercial computational code.