A Recipe for Optimum Mixing of Polymer Drag Reducers

Preparation of large-scale homogeneous solutions of drag reducing polymers requires an appropriate mixing procedure to ensure full disentanglement of the polymer chains without chain scission due to over-mixing. The latter is known as mechanical degradation and reduces the performance of drag reducing polymers. The dominant large-scale mixing parameters including time, impeller type, impeller speed, and impeller-to-tank diameter ratio are investigated to obtain a recipe for maximum mixing with minimum polymer degradation. Three water-based solutions of 100 ppm Superfloc A-110 (flexible structure), Magnafloc 5250 (flexible structure), and Xanthan Gum (XG) (rigid structure) are considered. The performance of the mixing parameters for each polymer is evaluated based on the solution viscosity in comparison with the highest viscosity (i.e., optimum mixing) obtained by 2 h of low-shear mixing of a small-scale polymer solution using a magnetic stirrer. The results demonstrate that optimum large-scale mixing is obtained at mean and maximum shear rates of ∼17 s⁻¹ and ∼930 s⁻¹, respectively, after 2–2.5 h of mixing for each of the polymers. This shear rate is obtained here using a three-blade marine impeller operating at 75 rpm and at impeller-to-tank diameter ratio of 0.5. The resulting polymer solution has the highest viscosity, which is an indication of minimal degradation while achieving complete mixing. It is also confirmed that chemical degradation due to contact with a stainless steel impeller is negligible.