Okara Washing Secondary Extraction Decanter Centrifuge Soy Protein Recovery

Single-stage separation always leaves protein behind. The okara that leaves a decanter still holds between two and four percent of the original soy solids, locked in the pulp structure, and in a plant running several hundred tonnes of soybeans a year that residual fraction is worth real money. A second washing stage, where fresh water is mixed with the discharged okara and the slurry is separated again, is the standard way to recover it. The problem is that this stage needs a machine that can handle a dilute, low-solids feed continuously and without dilution losses.

The LWS420 is configured exactly for that duty. A 420 mm bowl at 4,100 rpm produces 3,950 G, and the pond depth is set shallow so the machine is optimized for clarifying a weak slurry rather than for dewatering a heavy cake. Fresh water is added counter-current to the pulp flow, so the wash water meets the pulp that is closest to discharge, which is the most efficient arrangement. In field installations this second pass typically lifts overall protein recovery from around 85 percent to above 92 percent, with the recovered protein returning to the main stream as a clean, low-solids liquid.

• Counter-Current Washing: Water is introduced against the pulp direction so the freshest water contacts the most depleted pulp, achieving the highest extraction efficiency per litre of wash water used
• Dilute Feed Optimization: A shallow pond and a fine weir setting keep the clarification zone effective on feeds below three percent solids, where a standard dewatering configuration would lose protein to the overflow
• Continuous Two Stage Duty: The machine runs without batch interruption and is sized to match the discharge rate of the primary decanter, so the two stages operate as a single continuous train
• Protein-Friendly Shear Control: Low differential speed and a smooth scroll profile keep mechanical shear moderate, avoiding the foaming and denaturation that high-shear equipment causes on soy protein slurries
• Wash Water Ratio Control: A flow meter input and a PLC ratio block maintain a constant water-to-pulp ratio, so recovery stays stable when the upstream throughput varies
• Compact Skid Option: The washing stage can be supplied as a pre-piped skid with pump, mixer and flow control, which shortens installation and keeps the second stage footprint small

The LWS420 is installed downstream of a primary decanter in soy milk and tofu plants that want to raise yield without adding a third grinding stage. It is standard equipment in modern soy protein isolate and concentrate lines, where extraction efficiency directly determines the plant economics, and it is increasingly specified by producers who sell okara as a food ingredient and need the residual protein removed before drying.

The same configuration works for other dilute pulp washing duties in the food industry, including rice milk and oat base production, coconut milk second extraction, and nut milk processing where residual solids in the pulp still contain valuable protein and fat. Because the machine is optimized for weak slurries rather than heavy cakes, it complements a primary dewatering decanter instead of duplicating it.

Shipment is in a steel-framed export case with transport locks on the bowl, VCI film on machined surfaces and a separate crate for the skid-mounted pump and instrumentation when that option is selected. Documentation includes process and instrumentation diagrams for the two-stage train, utility requirements and a commissioning sequence.

Factory testing runs four hours on water and two hours on a soy pulp wash slurry, with records of throughput, overflow solids and calculated recovery. The bowl and rotating assembly carry a 24-month warranty, wear parts 12 months. Huading engineers assist with the first start-up and with tuning the wash water ratio to the plant's own material, and can review recovery data remotely after commissioning to confirm the target is being met.