Application of mixer in sewage treatment field

Today, sewage disposal has been widely used in many fields such as environmental protection, urban landscape, and medical care. With the acceleration of industrial development and urbanization, the amount of wastewater discharge has also increased sharply. How to treat wastewater with low consumption and high efficiency has always been a topic of constant discussion and research in the industry. Choosing appropriate and reliable mixers and mixing equipment is an extremely critical link in water and wastewater water treatment.

Mixers have unique applications in the water treatment industry and fields.

The processes involved include rapid mixing, flocculation, chemical preparation and storage, neutralization, homogenization, anaerobic mixing and sludge mixing.

The role of the mixer in sewage disposal treatment projects mainly includes the following four aspects: performing hydraulic circulation, improving oxygen transfer efficiency, facilitating grid and segmented treatment, and improving water quality.

There are no strict and clear standards for the classification of sewage treatment mixers. The characteristics and technical indicators of the product itself determine its application conditions and usage classification.

1. High speed, small impeller type. Its function focuses on mixing. It is characterized by high flow zones, strong turbulence, large velocity gradient in the flow field, and small scope of action. It is suitable for processing units that mainly focus on mixing and stirring, where the space at the bottom of the pool is small or there are certain requirements for GT value. Such as reaction pools and mixing pools in physical and chemical treatment processes, as well as selection pools and anaerobic pools in biological treatment systems. 

2. Low speed, large impeller type. Its role is highlighted in the hydraulic cycle. It is characterized by low flow speed, relatively uniform flow field distribution, and large range of action. It is suitable for treatment structures with large bottom space, no special requirements for GT value, and the purpose of hydraulic circulation and maintaining flow rate.

The function of the quick mix tank mixer is to quickly and evenly mix the added chemicals with the raw water.

From the perspective of stirring, the fast mixing process is a flow control process. Therefore, it is best to choose an axial flow blade with medium and high flow. For a long time, a traditional design method for fast mixing mixers is based on G value or GT value. 

The correlation expression of G value is: GT value is the product of G value and the average residence time (T) of the material. Whether it is the G value or the GT value, only the water treatment capacity, the volume of the rapid mixing tank, the mixer shaft power and the viscosity of the liquid are taken into consideration, and the efficiency of the mixing blade itself is not considered. The mixer selected based on this will greatly exceed the mixing requirements required for the rapid mixing process, both in terms of power and liquid displacement produced by the mixer.

With the development of mixing technology, G value and GT value are now only used as a reference value for mixer selection. The design of the high-efficiency axial flow blade fast mixing mixer is based on the liquid discharge volume of the mixer. The ratio (n) of the liquid discharge volume produced by the mixer during the average residence time to the effective volume of the fast mixing tank is used as the design and Basis for selection. Due to the influence of other factors such as the amount of medicine added, the size and shape of the mixing tank, etc., the ratio will change, but it is generally required that n>1.5. When the same type of paddle achieves the same mixing effect (that is, the same ratio n), the mixing power It will decrease with the increase of D/T (T is the tank diameter or equivalent diameter) value. That is to say, there is more than one mixer suitable for a mixing process, and it can be a combination of multiple mixing powers, mixing speeds and blade diameters.

During the flocculation process, the role of stirring is reflected in the following two points:

One is mixing, which promotes the collision between fine particles and causes the particles to gradually grow; the other is solid suspension, which prevents the stirring particles from settling in the flocculation tank so that they can be uniformly The ground is suspended in the liquid. There is an important constraint in flocculation and mixing, that is, the shear stress generated by the shear rate will break the particles. Therefore, the calculation of the blade tip speed should be considered when designing the flocculation and mixing.