Roots blower in sewage treatment station

With the national attention to environmental protection, each has set up its own sewage treatment station. These sewage treatment stations are relatively small in scale and small in treatment capacity. At the same time, in order to save the treatment cost, more biochemical treatment is adopted. As we all know, roots blower consumes a lot of energy in biochemical treatment system, which accounts for about 40% of the total energy consumption of the whole sewage treatment station, some even more.

Sewage treatment station, I think we should start with roots blower. First of all, let’s analyze the working principle of Roots blower.

Roots blower is a positive displacement fan, the delivered air volume is proportional to the rotating speed, and the three blade impeller sucks and exhausts three times each time the three blade impeller rotates. Compared with the two blade type, the gas pulsation is less, the load change is small, and the mechanical strength is high. There are two trilobal impellers on the two parallel shafts. There is always a small gap between the wheel and the hole surface of the elliptical case and the impellers. As the impellers rotate in the opposite direction, a certain amount of gas surrounded by the box and impeller is transported from the suction side to the discharge side. Each impeller is always kept in the correct phase by the synchronous gear, so it can be high-speed, without internal lubrication, and has simple structure, stable operation and stable performance. It has been used in a wide range of fields.

Generally, roots blower and water pump on the sewage treatment system operate at a constant speed, and then adjust the air volume by changing the valve opening at the outlet of the fan or regulating the water supply by changing the opening of the regulating valve on the outlet pipeline of the water pump. The biggest characteristic of fans and pumps is that the load torque is directly proportional to the square of the speed, and the shaft power is proportional to the cubic of the speed. Therefore, if the constant speed operation of the motor is changed to adjust the speed of the motor according to the required flow, a lot of electric energy can be saved. In the sewage treatment system, the main function of Roots blower is to flush oxygen to the biochemical system, so that the biochemical system has sufficient oxygen. We put an on-line dissolved oxygen meter in the biochemical tank, set the oxygen content required in the water on the dissolved oxygen meter, send the data of the online dissolved oxygen instrument to PLC, and then control the frequency converter to the roots blower, which has obvious effect.

We know that the air pressure of Roots blower is not limited by the speed of the fan, no matter how the speed changes, the air pressure can remain unchanged. The air volume is proportional to the fan speed, i.e. q = kn

Q: Represents the air volume n: represents the fan speed K: is the coefficient

It can be seen from the formula that the frequency of motor can be changed completely by frequency converter to achieve stepless speed change for air volume regulation. According to the field application process, the lowest frequency of the fan is 15Hz, which is usually about 35Hz, and there are some moments when the air volume is 50 Hz. Because the biochemical system process is basically the same, the air volume regulation in different biochemical systems is basically the same, so the application of frequency conversion technology can achieve about 40% energy saving effect.

Roots blower is a constant torque load, and its power saving rate is directly proportional to the speed drop, that is, n% = △ n%. Although it is different from the general fans and pumps, the power saving rate is higher, but because of its large power, and as long as the aeration system in the biochemical tank is not bad, it works continuously, and the start-up time is also very long, so the power saving potential is large and the cost of power saving is high.

After the technical transformation of Roots blower, the production mode of adjusting air pressure or air volume by adjusting the size of outlet valve is changed. The labor intensity is reduced, the regulation is timely, and the energy consumption of single machine is obviously reduced.

The inverter has the following advantages after energy-saving transformation of fan:

1. Improve power factor and reduce reactive power loss;

2. The inverter control has the function of automatic energy saving control, which can automatically adjust the voltage and frequency according to the load condition, so that the motor can run in the highest efficiency state;

3. The frequency converter has advanced flux vector control, low frequency output rated torque, can implement strong control to roots blower;

4. Saving and reducing operation cost;

5. Realize soft start and no large current impact when starting;

6. The service life of screw fan is prolonged.

In the sewage treatment system, all kinds of water pumps also need to save energy. According to the needs of the process, we can use frequency converter control to achieve the purpose of energy saving. At the same time, when the water pump is installed, we should also pay attention to the following points to achieve the purpose of energy saving.

1、 Choose a reasonable installation position, reduce elbows and make the outlet face the pool.

2、 Shorten the line.

3、 Expand the outlet pipe diameter.

4、 It can be removed when the water can be kept clean.

5、 Adjust the axial clearance to prevent improper impeller ring and axial clearance. Adjust according to the instructions of the pump.

6、 Remove the blockage in the pipeline in time. If foreign matters remain in the inlet pipe, impeller or guide shell channel, the water yield will be reduced.

7、 Prevent air from entering the water pump. Water pump into the air, water output will be significantly reduced, the sealing parts should be inspected and maintained.

8、 The transmission efficiency can be improved by using the coupling direct transmission instead of the flat belt.

9、 In some places, the bottom valve can not be used as much as possible.