Application of Horizontal Decanter Centrifuge in Chemical Wastewater Treatment (1)

1. Introduction

The sludge drying section of a wastewater treatment facility was originally designed for batch sludge discharge. Biochemical sludge generated by phosphorus removal equipment accumulates in the sedimentation tank. As the sediment accumulated, it is discharged into an underground sludge tank via bottom venting. After the sludge settled in the underground tank, the supernatant is pumped back to the phosphorus removal unit. The concentrated sludge is delivered by the vacuum pump to the screw press for dewatering, then conveyed via a conveyor to a vacuum dryer for final sludge discharge.

Batch drying of sludge suffers from problems such as low automation, complex processes, high operational intensity, high equipment failure rate, difficulty in pumping sludge from underground tanks, and strong odor from dried sludge.

Horizontal decanter centrifuge offers excellent solid-liquid separation and dewatering performance. The moisture content of dewatered sludge can be reduced to below 80% at ambient temperature, effectively eliminating strong odors caused by vacuum thermal drying. Featuring continuous feeding, stable operation and easy subsequent maintenance. It has been widely applied in solid-liquid separation processes for municipal domestic wastewater, food, pharmaceutical and other industries.

Taking the practical renovation project from batch sludge discharge to continuous sludge discharge as the research case, this paper elaborates on the working principle, model selection, installation and commissioning process of horizontal decanter centrifuge, and summarizes the experience for realizing stable operation and optimal separation performance.

The traditional batch sludge discharge process with stacked spiral dewatering machine is as follows:

Sedimentation tank of phosphorus removal equipment (batch emptying) → Underground sludge tank → Sludge pump → Stacked spiral dewatering machine → Conveyor → Vacuum dryer → Hazardous waste sludge.

The continuous sludge discharge process adopting horizontal decanter centrifuge is as follows:

Sedimentation tank of phosphorus removal equipment (continuous bottom discharging) → Sludge feed pump → Horizontal decanter centrifuge → Hazardous waste sludge.

2. Working Principle of Horizontal Decanter Centrifuge

Horizontal decanter centrifuge consists of an eddy current brake (or auxiliary motor and torque limiting protection device), differential gear, screw, drum, main bearings, base, housing, transmission device and drive motors.

Its working principle is as follows: The suspension liquid enters the drum through the feed pipe. Under the centrifugal force generated by high-speed rotation, solid particles with higher specific gravity settle on the inner wall of the drum. The screw blades moving relatively to the drum continuously scrape off the settled solid particles and discharge them from the slag outlet. The separated clear liquid flows out of the drum through the opening of the liquid level adjusting plate.

The relative movement between the screw and the drum is realized by the differential, and its speed difference is controlled by the eddy current brake (or auxiliary motor and torque limiting protection device). The shell of the differential is connected to the drum, the output shaft is connected to the screw, and the input shaft is connected to the eddy current brake (or auxiliary motor and torque limiting protection device). While the main motor drives the drum to rotate, it also drives the differential to rotate. The eddy current brake (or auxiliary motor and torque limiting protection device) controls the rotating speed of the differential input shaft via the coupling, enabling the differential to transmit torque to the screw at a fixed speed ratio, so as to realize continuous solid-liquid separation.