How to Select a Decanter Centrifuge: Flow Rate, Bowl Diameter, G-Force

A decanter centrifuge (horizontal scroll centrifuge) performs continuous solid–liquid separation by centrifugal force: the conical–cylindrical bowl rotates at high speed to generate a large G-field, while the scroll (conveyor worm) rotates at a differential speed to push the solid cake toward the conical end; the clarified liquid phase overflows at the other end. The four parameters below collectively determine machine size and separation quality and must therefore be established together, not in isolation.

Flow rate is the starting point: you need to know the volume of fluid to be processed per hour (m³/h), along with the inlet solids content (SS or % dry solids). The higher the inlet flow rate or the greater the solids load, the larger the bowl diameter needed to provide adequate settling area and retention time — hence HAUS bowl sizes range from 200 to 800 mm. A larger bowl delivers higher throughput but also increases motor power, frame dimensions, and operating costs, so oversizing should be avoided.

A practical note: size based on peak flow rate rather than average, and allow margin for load fluctuations during peak seasons. For wastewater treatment plants, the sludge flow entering the decanter is typically only a small fraction of the raw water flow rate, so these two figures must be kept separate when sizing.

G-force (relative centrifugal acceleration) is the multiple of gravity generated by the bowl; the higher the G-field, the faster solid particles settle and the drier the cake. Together with the scroll differential speed (the difference in rotational speed between the bowl and the scroll), G-force determines the balance between cake dryness and liquid-phase clarity. A high differential speed discharges the cake quickly, reducing solids retention time and resulting in a wetter cake; a low differential speed retains solids longer for a drier cake but can carry fine solids into the liquid phase if taken too far.

In sludge dewatering, cake dryness also depends on the flocculant polymer dosage: polymer helps fine particles flocculate so that G-force can separate them more effectively. The three variables — G-force, differential speed, and polymer dosage — must therefore be optimized simultaneously during commissioning. On the HAUS range, the high-speed bowl and scroll are PLC-controlled, enabling real-time adjustment of the differential speed to track changing sludge characteristics.

Once the flow rate and separation quality requirements are established, the next step is to select the correct series based on the nature of the fluid. HAUS divides its decanter range into three application branches, all sharing the principle of a high-speed bowl combined with a scroll, but differing in hygiene configuration, contact materials, and accessories. Bowl and scroll materials are stainless steel AISI 304 or 316, depending on the corrosion level and hygiene requirements of the industry.

If the objective is fine liquid–liquid phase separation or processing of low-solids fluids (e.g., cream separation from milk, fruit juice clarification, vegetable oil separation), a disk-stack separator from the Separator D/I/F range is more appropriate than a decanter. Decanters handle high-solids fluids effectively thanks to the scroll that continuously conveys the cake out; separators use a disk stack to generate very high G-force for fine-phase separation.

A sound decanter selection process moves from inlet data to commissioning trials. The sequence below helps avoid oversizing on capacity or undersizing on G-force — two common errors that misalign capital and operating costs with actual requirements.