Hydrocyclone separation and sludge thickening for granulation process water

Challenge

Unilin Industries in Wielsbeke produces laminate flooring. For the manufacturing of the laminate underlayer, lime and PVC granules are used, which are also produced on-site. During production, the lime and PVC powder are granulated in hot RO water (70–90°C) and subsequently separated using a centrifuge. Due to the sensitive nature of the produced granules, fine particles were released during the separation process. These fine particles caused regular clogging, product fall-outs, and increased maintenance interventions.

Trevi was asked to develop a solution to address this issue.

Solution

After intensive preliminary investigation, it was proposed to apply hydrocyclone separation combined with sludge thickening. Key boundary conditions for this choice included the available space, the high water temperature, and the particle size distribution of the solids to be removed. Process water from the granulation process is led to a process tank, from where it is pumped to a hydrocyclone at a flow rate of approximately 50 m³/h under constant pressure.

The hydrocyclone separates the granulates in the wastewater based on particle size. All particles larger than 25 μm are removed (>99%) via the underflow. Smaller particles are discharged with the overflow. The sludge stream (underflow) is directed over a thickening table (mesh 150 μm). The sludge is thickened, and the filtrate returns by gravity to the process tank.

Result

Since the underflow already consists of a light slurry forming a filter cake on the thickening table, a significant portion of the finest particles (25–150 μm) is retained by the cake rather than by the filter mesh itself. The dewatered sludge reaches a dry solids content of 7%. The treated water (overflow) is sent to a second process tank, from where it is returned to the initial granulation process.