Experimental research and influencing factors analysis on sand removal from sand‑containing xanthan gum solutions using a hydrocyclone

To improve the sand removal efficiency of thermally hydrolyzed sludge， this study proposed the use of a hydrocyclone for centrifugal desanding. In the experiments， a sand‑containing xanthan gum solution with similar non‑Newtonian fluid properties was used as a substitute for the sludge to evaluate the sand removal efficiency. The effects of xanthan gum concentration （0.2% to 0.4%）， sand particle size （50 to 214 μm）， and feed flow rate （4 to 6 m³/h） on sand removal efficiency and hydraulic loss were investigated. When the feed flow rate was fixed at 4 m³/h， increasing the xanthan gum concentration from 0.2% to 0.4% resulted in a decrease in the overall separation efficiency from 67.5% to 45.8%. Simultaneously， the underflow split ratio increased linearly from 72% to 76%. This indicated a negative correlation between solution concentration and sand removal efficiency， meaning that higher xanthan gum concentrations led to less efficient sand separation. For the 0.2% xanthan gum solution， the removal efficiency for particles smaller than 94 μm was below 50%， significantly lower than that for particles larger than 150 μm， which exceeded 65%. This demonstrated a positive correlation between particle size and removal efficiency， showing that larger particles are more easily separated. As the feed flow rate increased from 4 m³/h to 6 m³/h， the sand removal efficiency gradually improved. Specifically， the efficiency for sand particles in the size ranges of 50 to 94 μm， 94 to 150 μm， and 150 to 214 μm increased to 70%， 80%， and 95%， respectively. This indicated that increasing the feed flow rate enhanced the sand separation performance of the hydrocyclone， likely because higher flow rates result in stronger centrifugal forces， which in turn facilitate more effective separation. Moreover， hydraulic losses at both the inlet and outlet increased linearly with the flow rate. However， the pressure loss in the xanthan gum solution was consistently lower than that in the sand-water mixture. Furthermore， as the xanthan gum concentration increased， the pressure loss further decreased， suggesting that higher concentrations reduce hydraulic resistance. This study has clarified the primary factors affecting the sand removal efficiency of a hydrocyclone for non‑Newtonian fluids， providing valuable theoretical guidance for the pre‑treatment of thermally hydrolyzed sludge in industrial applications. Future research could explore the flow separation phenomena of different structures and real thermally hydrolyzed sludge within the hydrocyclone， potentially leading to an optimized design for the hydrocyclone's structure and operational parameters.