How Is Frequency Conversion Technology Used in Sewage Treatment Projects

Information, electronics, environmental protection, energy conservation, biology and other projects are the pillar industries of contemporary society. With the development of the economy, various types of enterprises have emerged, the expansion of cities and the increase in water consumption of newly built residents have made the purification and treatment of industrial wastewater and domestic sewage become an issue worthy of our attention. To do this, we should pay attention to two aspects:

(1) The discharge of wastewater and sewage must meet standards and must not pollute water sources in rivers, lakes, and oceans;
(2) Wastewater and sewage should be reused as much as possible after purification and treatment;

At present, most domestic sewage treatment uses aeration, which is essentially microbial treatment and is widely used in industries such as cotton spinning, wool spinning, linen spinning, printing and dyeing, detergents, food, light chemical industry, metallurgy, and oil refining. In short, where water is needed, sewage must be discharged and treated before it can be discharged or recycled to avoid environmental pollution. Sewage treatment involves all walks of life, production and life, and has a wide impact. It is a major event that cannot be ignored.

Aeration treatment is wasteful.

(1) Generally there are at least two aeration tanks, and the equipment capacity is configured according to the development of the enterprise. Generally, they are too big and the actual usage is small, so it is common to have big horses and carts, wasting electric energy.

(2) Many unit aeration tanks supply too much oxygen, and the number of blowers is manually closed or universal and cannot be adjusted effectively in a timely manner, which wastes electric energy;

(3) The amount of oxygen supply should be related to the drainage volume and sewage treatment quality, and the temperature changes throughout the year and day and night. When automatic speed adjustment is not possible, there is a waste of electrical energy;

(4) Excessive oxygen supply often affects the quality of sewage treatment, leading to the reduction of microorganisms, worsening of treatment effects, and waste of electricity;

(5) As long as the sewage discharge reaches the standard or is slightly higher than the standard, it is not economical because the aeration supplies excessive oxygen and wastes electricity. Therefore, there is an urgent need for automatic control based on set parameters;

(6)Roots blower is the main equipment for oxygen supply in the aeration tank and adopts constant pressure and variable flow control. When excessive air flow is not needed, the flow rate can be reduced by simply reducing the rotational speed. In other words, this purpose can only be achieved by using variable frequency speed regulation, and sewage can be treated economically and reasonably, and considerable power saving effects can be achieved. Generally, it can save more than 30% of electricity. Roots blower is a constant torque load, the flow rate q is proportional to the rotation speed n, and the power saving rate is proportional to the rotation speed. However, the centrifugal fan is a secondary torque reduction load, the flow rate Q is proportional to the rotation speed N, and the output power P is proportional to n3, so the power saving rate is high, but the pressure H is proportional to n2, which is different from the Roots blower. In short, no matter whether you use a Roots blower or a blower, as long as you use variable frequency speed regulation, there will be obvious energy saving effects.

Closed-loop control method

• (1) Single value PH control method – simple and wire-saving, obvious effect, easy to debug.

The PH value directly reflects the water quality, and the PH sensor is installed at the drain outlet. Detect the change of PH value online, output an analog signal to remove the PH value, and after calculation by the PID regulator, output a 4 ~ 20 mA standard signal to control the frequency output of the frequency converter, adjust the speed of the Roots blower, and change the oxygen supply of the aeration tank.

• (2) Use a dual-value control method, that is, oxygen content, COD value and PH value – complex and expensive, * troublesome to debug,

Different from the above solution, it not only detects the pH value of the water outlet, but also detects the oxygen content in the water online. If the oxygen content in the discharge water is high, it means that the air supply volume of the aeration tank is too large, otherwise it means that the air supply volume is too small. Compared with the above-mentioned single-value control of PH value, this double-value control has higher control accuracy and better control effect, but it is complicated to debug. Due to the addition of PLC and oxygen content tester, the system investment is large.

At present, many cities have online sewage discharge detection network systems that can monitor in real time 24 hours a day. All units will give warning and alarm displays whenever there is an unqualified discharge. This ensures that sewage is discharged in accordance with the standard requirements. The computer management and monitoring system can prompt each unit to manage the normal discharge of sewage at any time and deal with fines for units that discharge below the standard.

Whether it is single-value PH control or dual-value control, that is, oxygen content, COD value and PH value, it can achieve certain economic and social benefits and is worthy of promotion.