High pressure dewatering rolls: Effect of process variables on cake solids concentration and throughput

The High Pressure Dewatering Rolls (HPDR) is a novel solid–liquid separation technology that combines compression, vacuum, and shear to enhance dewatering of fine mineral suspensions without requiring filter cloths. This study explores how roller speed, shear, feed concentration, flocculation, particle size distribution, and minimum roller gap affect HPDR performance using well-characterised calcium carbonate suspensions. Increasing roller speed reduced cake solids concentration due to shorter dewatering times, but increased solids throughput up to an optimal speed near 4 rpm. At 7 rpm, throughput decreased due to material floating on top of the rollers and not passing through the nip effectively. Introducing shims to maintain a minimum roller gap eliminated floating and improved throughput by allowing more cake to pass through the nip. For the coarser suspension, moderate speed difference (5%) slightly improved both performance measures: the highest cake solids concentration of 84.3 wt% was achieved at 0.5 rpm, while the maximum throughput of 445 kg/m 2 .hr occurred at 4 rpm. Flocculation reduced solids passing through the filter and reporting to the filtrate, while adding 20% ultrafine calcium carbonate improved cake packing, reaching 87.9 wt% solids at low speed. These results highlight the trade-offs between roller speed, shear, gap size, and feed properties in HPDR operation. Optimising these variables is essential to achieve both high throughput and cake solids, supporting the potential of HPDR as an effective dewatering solution for fine and compressible suspensions. • HPDR combines compression, vacuum, and shear for dewatering fine suspensions. • Increasing roller speed raises throughput but decreases cake solids concentration. • Moderate shear improves cake solids concentration. • Flocculation reduces solids passing through the wedge wire. • Shims prevent material floating, stabilising nip entry and increasing throughput.