Wall slip and rheological behavior of petroleum-coke sludge slurries flowing in pipelines

Experimental investigation was carried out on a bench-scale slurry transportation test facility to explore rheological properties and wall slip behavior for petroleum-coke water slurry (PCWS) and petroleum-coke sludge slurry (PCSS) flowing in pipelines with different diameters of 10 mm, 14 mm, 16 mm and 20 mm. A model combining the traditional Moony method for wall slip correction and numerical technique based on the Tikhonov regularization is used to determine the true rheological properties and wall slip behavior on the pipe wall. Results suggest that PCWS is dilatant fluid and sewage sludge can change its inherent rheological properties. When amount of the sewage sludge is 5 wt.% of petroleum coke in the PCSS, PCSS has similar rheological properties with Newtonian fluids approximately at higher shear rates, and turns into pseudo-plastic fluid when the sewage sludge amount ascends to 10 wt.% at higher shear rates, in spite of being dilatant fluid at lower shear rates. Besides, with the sewage sludge amount increase, the critical wall shear stress beyond which wall slip occurs decreases and wall slip velocity increases significantly, which is beneficial for pipe transportation with low energy consumption. The wall slip contribution defined as the extra slip flow rate over the entire duct area flow rate was found depending mainly on both of wall slip velocity and rheological behavior of bulk slurries which contains different amount of sewage sludge.

Graphical abstractWall slip velocity increases with wall shear stress. And wall slip velocity of CWS and CSS has the different trends with wall shear stress. Wall slip velocity of CWS presents the trends of accelerating growth. While the relationship between wall slip velocity of CSS and wall shear stress was a decelerating curve.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Sewage sludge alters slurry rheological from dilatants to pseudo plastic fluids. ► Sewage sludge promotes wall slip effects and reduces the critical shear stress. ► Contribution of wall slippage for coke water slurry increases with shear stress. ► Contribution of wall slippage for coke sludge slurry reduces with shear stress.