In sewage treatment and sludge reduction projects, the decanter centrifuge has become the most commonly used mechanical dewatering equipment in the fields of municipal sewage, industrial wastewater, chemical waste sludge, etc. due to its advantages of continuous operation, high degree of automation, and stable separation efficiency. When the decanter centrifuge is in operation, one of its key internal parameters is the differential speed, that is, the speed difference between the drum and the screw conveyor.
The differential speed is the core variable for controlling the screw conveying speed and solid discharge efficiency. It directly determines the residence time of the sludge in the drum, the accumulation degree of the solid phase, the moisture content of the dry mud, the clarification degree of the clear liquid, and the operating load of the whole machine. Improper differential speed control may lead to high moisture content of the mud cake and low treatment efficiency, or even equipment blockage, overload, vibration, etc.Therefore, finding and mastering the “optimal differential speed” is not only one of the key technologies for the selection and operation commissioning of the decanter centrifuge, but also the technical core for achieving low energy consumption, high dehydration rate, and long-term stable operation.
Basic Concepts of Differential Speed in Horizontal Screw Centrifuge
1. Definition of Differential Speed
The core structure of the horizontal screw centrifuge consists of a high-speed rotating drum and a low-speed rotating screw conveyor. The high-speed rotation of the drum (such as 3000 rpm) forms a strong centrifugal force field, which throws the solids in the sludge to the drum wall; while the screw conveyor rotates synchronously at a relatively low speed (such as 2955 rpm), slowly pushing the solids deposited on the drum wall to the slag outlet. The speed difference between the two is the “differential speed”:
Differential speed = drum speed – screw speed
The differential speed is generally adjusted in the range of 0.5~50 rpm, depending on the equipment structure and material characteristics.
2. The role of differential speed
Control the solid pushing speed;
Adjust the residence time of solids in the drum;
Affect the dryness and compression ratio of dry mud;
Determine the equipment load and energy consumption level;
Affect the quality of clarified liquid and effluent SS.
How to determine the “optimal differential speed”?
1. Main factors affecting the optimal differential speed
Sludge type (municipal sludge/chemical sludge/papermaking sludge, etc.);
Sludge solid content (separation is difficult when <1%, and easy to spin dry when >3%);
Sludge particle distribution (coarse particles are easy to settle, and fine particles require longer residence time);
Mud stability (whether there are seasonal fluctuations);
Flocculation effect and reagent ratio;
Drum speed setting value;
Process parameters such as temperature and viscosity.
2. Differential speed adjustment method
The differential speed is controlled by the differential and is divided into the following two control modes:
Mechanical differential: fixed transmission ratio, suitable for stable working conditions;
Hydraulic differential/electronically controlled differential: adjustable differential to achieve intelligent operation under variable working conditions. Currently, mainstream high-end models basically adopt electronic control mode (such as VFD control).
3. Actual debugging method
Step method test: adjust the differential speed by 2~5 rpm each time, and observe the mud cake thickness and water quality;
Comparison method: test the processing capacity and energy consumption at different differential speeds at the same time;
Intelligent feedback method: automatically adjust the mud cake thickness through monitoring and load current feedback.
Recommendations for optimal differential speed range under different sludge types
| Sludge type | Solid content (%) | Recommended range (rpm) | Features |
| Municipal sludge | 0.8~2.5 | 12~20 | Easy to handle, suitable for medium differential speed operation |
| Chemical organic sludge | 2.0~4.0 | 8~15 | High viscosity, appropriately reduce the differential speed to avoid clogging |
| Petroleum mud | 5.0~10.0 | 5~10 | Contains oil, requires low-speed compression separation |
| Papermaking white mud | 1.5~3.5 | 15~25 | Stable composition, can push materials at high speed |
| Food waste sludge | 3.0~6.0 | 10~18 | High in oil, requires balanced dehydration and clarification |
Although differential speed is a simple parameter, it is related to multiple factors such as sludge characteristics, equipment structure, operating efficiency and comprehensive cost. For centrifuge manufacturers and users, the exploration of the optimal differential speed is not only a process of technical debugging, but also a key link to maximize value.
As a leading centrifuge manufacturer in China, we have always been committed to providing customers with a full set of technical services including intelligent control of differential speed, optimization of separation schemes, and operation data analysis. In the future, we will further promote the intelligent, adaptive and remote management of differential speed to create more efficient and intelligent sludge dewatering solutions for global users.
