In recent years, with the increasing attention of the country to environmental protection, various countries have established their own sewage treatment plants. These sewage treatment stations are relatively small in scale and have a small treatment capacity. At the same time, in order to save treatment costs, many of them use biochemical treatment. As is well known, in the biochemical treatment system, Roots blowers consume a lot of energy, generally accounting for about 40% of the total energy consumption of the entire sewage plant, and some even more. However, in recent years, energy consumption costs, mainly based on electricity bills, have continued to rise. Many sewage treatment plants cannot operate normally due to high operating costs, causing the heavily invested sewage treatment plants to fail to realize their benefits. Some have started to illegally discharge sewage, leading to the deterioration of China's water environment. Therefore, optimizing the operation and management of sewage treatment plants, saving costs, and reducing treatment costs are important means to ensure the normal operation of sewage treatment plants.
I think the sewage treatment plant should start with the Roots blower first. Firstly, let's analyze the working principle of the Roots blower.
The Roots blower is a positive displacement fan that delivers air in proportion to its rotational speed. The three bladed impeller performs three suction and exhaust operations with two impellers per rotation. Compared to the two bladed fan, the Roots blower has less gas pulsation, less load variation, and higher mechanical strength. There are two three bladed impellers on two parallel axes, and a small gap is always maintained between the impellers and the inner hole surface of the elliptical casing. Due to the constant rotation of the impellers in opposite directions, a certain amount of gas surrounded by the casing and impellers is transported from the suction side to the discharge side. Each impeller is always maintained in the correct phase by synchronous gears, and there is no mutual contact phenomenon, so it can be driven at high speed without internal lubrication. Moreover, the structure is simple, the operation is stable, the performance is stable, and it is suitable for various purposes. It has been applied in a wide range of fields.
Usually, Roots blowers and water pumps in sewage treatment systems are operated by motors at a constant speed, and the air volume is adjusted by changing the valve opening at the fan outlet or the water supply volume is adjusted by changing the valve opening on the water pump outlet pipeline. The biggest feature of fans and pumps is that the load torque is proportional to the square of the speed, while the shaft power is proportional to the cube of the speed. Therefore, if the constant speed operation of the motor is changed to adjust the motor speed according to the required flow rate, a lot of electricity can be saved. In the sewage treatment system, the main function of the Roots blower is to inject oxygen into the biochemical system, so that the biochemical system has sufficient oxygen. We put an online dissolved oxygen meter in the biochemical tank, set the required oxygen content in the water on the dissolved oxygen meter, and send the data of the online dissolved oxygen meter to the PLC. The PLC controls the frequency converter, and then the Roots blower is controlled by the frequency converter, which has a significant effect.
We know that the wind pressure of a Roots blower is not limited by the fan speed, and its wind pressure can remain constant regardless of changes in speed. And the air volume is directly proportional to the fan speed, that is, Q=KN
Q: Representing air volume N: represents fan speed K: is a coefficient
From the formula, it can be seen that air volume regulation is completely achieved by changing the motor frequency through a frequency converter to achieve stepless speed change, which has the effect of regulating air volume. According to the on-site application process, the lowest frequency of the fan is 15HZ, usually around 35HZ, and there are occasional times when it operates at full airflow of 50HZ. Since the biochemical system process is basically the same, the air volume adjustment is basically the same in different biochemical systems. Therefore, the application of frequency conversion technology can achieve an energy-saving effect of about 40%.
The Roots blower is a constant torque load, and its power saving rate is proportional to the speed drop, that is, N%=△ N%. Although it has a higher power saving rate than general fans and water pumps, its power is larger. As long as the aeration system in the biochemical tank is not damaged, it works continuously and has a long operating time, so it has great potential for power saving and high cost.
After the technical transformation of the Roots blower, the production method of adjusting the air pressure or volume by adjusting the size of the outlet valve in the past has been changed. The labor intensity has been reduced, the timeliness of adjustment has been improved, and the energy consumption of a single machine has significantly decreased.
The frequency converter has the following advantages after energy-saving transformation of the fan:
1. Improve power factor and reduce reactive power loss;
2. The use of a frequency converter control has automatic energy-saving control function, which can automatically adjust the voltage and frequency according to the load situation, so that the motor can operate at the highest efficiency state;
3. The frequency converter has advanced magnetic flux vector control, low-frequency output rated torque, and can effectively control the Roots blower;
4. Save and reduce operating costs;
5. Realize soft start and no high current surge during startup;
6. Extend the service life of the Roots blower.
In the sewage treatment system, various water pumps also need to be energy-efficient. We can use frequency converters to control them according to the needs of the process to achieve energy-saving goals. At the same time, when installing water pumps, we should also pay attention to the following points to achieve energy-saving goals.
1、 Choose a reasonable installation location, reduce bends, and have the water outlet facing the pool.
2、 Shorten the pipeline.
3、 Expand the outlet pipe diameter.
4、 It can be removed when the inlet water can maintain cleanliness.
5、 Adjust the axial clearance to prevent inappropriate clearance between the impeller mouth ring and the axial clearance. When using, adjust according to the factory instructions of the water pump.
6、 Timely eliminate pipeline blockages. Foreign objects left in the inlet pipe, impeller or guide shell flow channel will reduce the amount of water discharged.
7、 Prevent the water pump from entering the air. The water pump has air intake, and the water output will significantly decrease. It is necessary to inspect and maintain the sealing parts.
8、 Using a coupling for direct transmission instead of a flat belt can improve transmission efficiency.
9、 In some places, try not to use bottom valves if possible.
