Application of frequency converter in sewage treatment
I. Overview
Water resources are an important factor in economic development and social sustainable development. The urban sewage treatment rate has become an important symbol of regional civilization. Sewage treatment has evolved from the original natural treatment, a simple primary treatment to the use of advanced technologies, advanced treatment of wastewater, and reuse. The treatment process has also evolved from the traditional activated sludge process and oxidation ditch process to a variety of processes nowadays to achieve different effluent requirements.
Second, the sewage treatment process
The general sewage treatment mainly adopts the secondary treatment method: the first level is the mechanical treatment, generally uses the grille and other mechanical equipment to filter the floating material or the larger particles in the sewage; the second level is the biochemical treatment, and is processed according to different treatment requirements. Sulfur contained in the various super silicon or metal elements, so that the treated water can meet the requirements of follow-up water equipment, such as pure water for domestic use, industrial boiler softening and desalinated water, etc.
Third, on-site conditions
Sewage in the sewage collection tank is sent to the sedimentation tank by two sewage pump 1# sewage pump 2#. To prevent accidents from overflowing in the sedimentation tank, a water level detection device is set in the sedimentation tank. When the actual water level exceeds the alarm level, the control system The electric butterfly valve in front of the grille is automatically closed to prevent overflow accidents. The sewage in the sedimentation tank is then sent to the biochemical treatment tank by a biochemical pump. The biochemical treatment tank is also provided with an upper limit detection of the water level, and the biochemical pump controls the water level of the biochemical treatment tank.
Fourth, transformation program
1. Two pumps in sedimentation tank are controlled by one inverter with one drag and two controls;
2, using a more reliable PLC + inverter;
The sedimentation tank is provided 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 signal will be sent to the PLC, the PLC starts the inverter and the frequency up signal is output to the inverter. When the frequency of the inverter reaches 50Hz, if the water level is still at the lower limit position, the PLC sends The switching signal switches the sewage pump 1# to the power frequency operation, and the inverter starts the sewage pump 2# after a delay. On the contrary, when the water level reaches the upper limit position, the sewage pump 1 is stopped, and the PLC issues a frequency reduction signal of the frequency converter. If the water level is lower than the lower limit or upper limit water level alarm due to a water pump or other reasons, the water level detector sends an alarm signal to the PLC. The PLC output activates the alarm circuit (alarm lights and ringing) to prompt the operator to check the cause.
Aerators and submersible pumps are the core equipment for wastewater treatment. Frequency converters are used to control the aerator blower (Roots blower) and submersible pump speed. Frequency control of the blower: Sewage treatment aerobic partial dissolved oxygen concentration Large influence, the dissolved oxygen concentration is too low, the sewage can not reach the standard; too high dissolved concentration, not only waste electricity but also may make the activated sludge floating so that the water can not reach the standard, blower plus frequency converter is to control the concentration of dissolved oxygen in the CASS pool is stable at a constant value.
V. Conclusion:
After frequency conversion, the sewage treatment plant not only improved the degree of automation and control accuracy, but also greatly benefited from energy conservation and consumption reduction. The comprehensive energy-saving rate reached 35%, and the company's profits and social benefits were greatly improved simultaneously.