Application of Sunwoele VFD (Variable-frequency Drive) in sewage treatment

I. Overview  

Water resources are an important factor for economic development and sustainable social development, and the urban sewage treatment rate has become an important symbol of a region's civilization. Sewage treatment has developed from the original natural treatment, simple primary treatment to the use of various advanced technologies, advanced treatment of sewage, and reuse. The treatment process has also developed from the traditional activated sludge process and the oxidation ditch process to the current multiple processes to meet different water discharge requirements.

2. Sewage treatment process

General sewage treatment mainly adopts two-stage treatment methods: the first stage is mechanical treatment, generally using mechanical equipment such as grilles to filter floating objects or large particles in sewage; the second stage is biochemical treatment, according to different treatment requirements, treatment Various silicon substances or metal elements that exceed the standard contained in the sewage make the treated water meet the requirements of subsequent water equipment, such as pure water for domestic use, industrial boiler softening and demineralized water, etc.

3. On-site conditions

The sewage in the sewage collection tank is sent to the sedimentation tank by two sewage pumps 1# sewage pump 2#. In order to prevent accidents caused by water overflow in the sedimentation tank, a water level detection device is installed in the sedimentation tank. When the actual water level exceeds the alarm water level, the control system Automatically close the electric butterfly valve in front of the grill to prevent water overflow accidents. The sewage in the sedimentation tank is sent to the biochemical treatment tank by the biochemical water pump, and the biochemical treatment tank is also equipped with a water level upper limit detection, and the water level of the biochemical treatment tank is controlled by controlling the biochemical water pump.

4. Transformation plan

1. The two water pumps in the sedimentation tank are controlled by one VFD (Variable-frequency Drive) with one dragging two;

2. Adopt the method of PLC+VFD (Variable-frequency Drive) with high reliability;

The sedimentation tank is equipped with upper limit, lower limit water level and upper and lower limit alarm water level detection. The control process is that when the water level reaches the lower limit, the water level detection sends a signal to the PLC, and the PLC starts the VFD (Variable-frequency Drive) and outputs the frequency rising signal to the VFD (Variable-frequency Drive). When the VFD (Variable-frequency Drive) When the frequency reaches 50Hz, if the water level is still at the lower limit, the PLC sends a switching signal to switch the sewage pump 1# to power frequency operation, and after a period of delay, the VFD (Variable-frequency Drive) starts the sewage pump 2#. On the contrary, when the water level reaches the upper limit position, the sewage pump 1 will be stopped, and the PLC will send a VFD (Variable-frequency Drive) frequency drop signal. It is sent to the PLC, and the alarm circuit (alarm indicator light and ringing) is activated by the PLC output to prompt the operator to check the reason.

Aerators and submersible pumps are the core equipment for sewage treatment. VFD (Variable-frequency Drive) is required to control the speed of the blower (Roots blower) and submersible pump of the aerator, and the frequency conversion control of the blower: the concentration of dissolved oxygen in the aerobic part of sewage treatment It has a great impact on the treatment results. If the dissolved oxygen concentration is too low, the sewage cannot meet the standard; if the dissolved oxygen concentration is too high, it will not only waste electricity, but also may cause the activated sludge to float up and make the effluent fail to meet the standard. The blower plus VFD (Variable-frequency Drive) is for Control the concentration of dissolved oxygen in the CASS pool to stabilize at a constant value.

V. Conclusion:

The sewage treatment plant has not only improved the degree of automation and control precision after the frequency conversion transformation, but also greatly benefited from energy saving and consumption reduction. The comprehensive power saving rate has reached 35%, and the corporate and social benefits have been greatly improved simultaneously.