The three-phase decanter process is an advanced wheat starch and vital wheat gluten separation technology developed in Germany. It derives its name from the core equipment adopted in the process — the three-phase decanter centrifuge.
1. Flour Preparation
Flour serves as the raw material for this process. Preference is given to flour similar to Grade 2 Special Flour, featuring a high flour yield, high gluten content, low ash content and low damaged starch rate.
2. Slurry Preparation
Weighed flour is conveyed into a mixer and blended with water to form a slurry, with the flour-to-water ratio controlled at approximately 1:(0.85–0.95). The mixer fully hydrates flour particles to produce a homogeneous slurry free of large agglomerates or uneven dough lumps, laying a solid foundation for the subsequent homogenization process.
3. Homogenization
The well-blended slurry is pumped into a homogenizer. The operating pressure is adjusted by changing the clearance of the homogenizing valve, with a maximum pressure of up to 100 bar.
When the slurry passes through the homogenizing valve, the pressure drops sharply from high pressure to atmospheric pressure. Combined with the shearing force generated by the valve, the slurry is gelatinized, and the protein network rapidly coagulates. The homogenizer used is a conventional model widely applied in the dairy industry.
4. Separation
The gelatinized slurry is delivered by an eccentric screw pump to the three-phase decanter centrifuge for component separation. Fresh process water may be added to dilute the slurry before feeding. This process consumes far less water than the Martin process and hydrocyclone process, with a water dosage of only 0.3 to 0.9 tons per ton of flour.
A decanter centrifuge is a horizontal centrifuge fitted with an internal screw conveyor. There is a slight rotational speed difference of around 60 r/min between the screw and the bowl, and its separation factor ranges from 2000 to 4000. Equipped with a dual-motor and dual-reducer system, the three-phase decanter allows stepless adjustment of the speed differential between the screw and the bowl. Different from ordinary decanter centrifuges, it is fitted with nozzles at the overflow outlet to separate out the intermediate phase, namely the third phase.
As the densest fraction in the feed, solid materials are conveyed forward by the screw conveyor and discharged as underflow. The overflow is discharged by a built-in centrifugal pump, which efficiently removes foamy materials and eliminates the need for an additional delivery pump.
The intermediate phase flow rate can be regulated by adjusting the number and position of the nozzles. Since pentosans have a low density, they are mainly concentrated in the overflow. Removing these viscous substances from gluten at the front end of the process cuts down water consumption and eliminates the adverse impact of pentosans on subsequent gluten separation and final product quality.
5. Gluten Separation
Gluten is mixed with water in a continuous kneader. Under combined axial compression and radial force, flour proteins are fully hydrated through thorough kneading, forming a toothpaste-like slurry for continuous discharge.
The slurry is then transferred to a maturation tank, where additional water is added for dilution and stirring. This step helps release part of the starch and aggregates gluten proteins into fine filamentous gluten clusters.
The matured slurry is pumped into a horizontal spiral decanter centrifuge with a separation factor of 3000 to 4000 for two-phase separation. Due to the difference in settling velocity between starch and gluten, high-density starch is discharged as the heavy phase via underflow, while low-density gluten mixed with fine starch particles is discharged as the light phase via overflow.
The mixture of gluten and fine starch is rinsed through round sieves to remove residual starch and obtain wet gluten. The wet gluten is then sent to the drying system to produce vital wheat gluten.
6. Starch Washing
The underflow from the three-phase decanter is diluted with process water and sent to centrifugal sieves to remove residual fiber. Afterwards, it enters a 12-stage hydrocyclone group for starch washing.
To achieve thorough separation of minor B-starch, pentosans and fine fiber contained in the underflow, a vertical high-speed three-phase disc nozzle centrifuge is installed upstream of the hydrocyclone group. The combined application of the two units ensures high-efficiency and thorough starch washing.
7. Gluten Recovery
The underflow and overflow from the three-phase decanter are treated with sieves to recover agglutinable gluten. The recovered gluten is returned to the production line and processed together with the intermediate phase. The resulting wet gluten undergoes dewatering and drying to make vital wheat gluten.
8. By-products
Pentosans contained in the overflow can be directly used as liquid feed. Alternatively, enzymatic treatment can be applied to separate solid fractions. The remaining liquid is concentrated together with process wastewater and then dried with fiber to produce compound feed.
9. Fiber Screening
The crude starch milk discharged from the decanter bottom contains trace fiber and protein impurities. Three sets of series-connected centrifugal sieves remove fiber, which is then dried to produce wheat bran.
10. Drying of Starch and Vital Wheat Gluten
Purified Grade A starch milk after classification and refining is dewatered by an automatic scraper centrifuge, followed by pneumatic drying to obtain finished Grade A wheat starch.
Low-concentration Grade B starch milk is concentrated by decanter centrifuges to collect starch from dilute suspensions.
Fine gluten separated by decanters is filtered to remove starch, dewatered by extrusion, and finally dried in a ring-type dryer to produce vital wheat gluten.
11. Process Characteristics
Adopting the three-phase decanter centrifuge to divide materials into three phases, this process removes pentosans at the early production stage, thereby reducing water consumption and guaranteeing product quality.
The combination of high-speed three-phase disc nozzle centrifuges and hydrocyclones for starch washing further improves starch purity.
Its main drawbacks include heavy reliance on imported equipment, complex process flow, demanding operation and high investment costs.
For more wheat starch processing information, please visit the official website of Beijing Meckey Engineering Co.