In the complex system engineering of sewage treatment, the mixer plays a crucial role as it can thoroughly mix sewage, sludge, and various chemicals, resulting in better treatment efficiency. Today, let's talk about the common types of mixers in sewage treatment and how to choose the right mixer.
Common types of mixers
agitators
1. Mixing and Stirring Series: Suitable for stirring liquids containing suspended solids in municipal and industrial wastewater treatment processes. Generally, multi-stage electrodes are used with a direct connection structure, which has low energy consumption and high efficiency, like an energy-saving expert. The impeller is formed by precision casting or stamping, with high precision, high thrust, and compact structure. For example, in some small sewage treatment plants' primary sedimentation tanks, this mixing and stirring series of submersible mixers can be used to fully mix sewage and settled sludge, avoiding sludge settling at the bottom of the tank and affecting the treatment effect.
2. Low speed push flow series: suitable for aeration tanks and anaerobic tanks in municipal and industrial sewage treatment plants, mainly used for water circulation and effective flow and aeration of water during nitrification, denitrification, and phosphorus removal stages in sewage tanks. It adopts a helical gear reducer, equipped with a low-power and low-speed motor, a large impeller diameter of the mixer, made of polyurethane material and aluminum alloy, with high strength and strong corrosion resistance. In the aeration tank of a large sewage treatment plant, a low-speed push flow submersible mixer can make the aeration more uniform and improve the efficiency of sewage treatment.
Paddle stirrer
There are two types: flat propeller and inclined propeller. The flat blade agitator consists of two straight blades, with a blade diameter to height ratio of 4-10 and a circumferential velocity of 1.5-3m/s. The resulting radial flow velocity is relatively low. The two blades of the inclined blade agitator are folded 45 ° or 60 ° in opposite directions, resulting in axial liquid flow. The paddle agitator has a simple structure and is commonly used for mixing low viscosity liquids and dissolving and suspending solid particles. In the dosing process of sewage treatment, if the agent is a low viscosity liquid, a paddle stirrer can be used to quickly mix the agent with the sewage and promote chemical reactions.
turbine agitator
Composed of 2-4 flat or curved blades installed on a horizontal disc. The ratio of the outer diameter, width, and height of the blade is generally 20:5:4, and the circumferential velocity is generally 3-8m/s. Turbine generates highly turbulent radial flow during rotation, suitable for the dispersion of gases and immiscible liquids, as well as liquid-liquid phase reaction processes. The viscosity of the stirred liquid generally does not exceed 25 Pa · s. In the process of wastewater treatment involving gas-liquid reactions, such as introducing oxygen into the wastewater for aeration treatment, a turbine agitator can effectively disperse the gas in the liquid and improve the utilization rate of oxygen.
anchor stirrer
The shape of the outer edge of the blade should be consistent with the inner wall of the mixing tank, with only a small gap between them, which can remove viscous reaction products attached to the tank wall or solid matter accumulated at the bottom of the tank, and maintain good heat transfer effect. The peripheral velocity of the blade edge is 0.5-1.5m/s, which can be used to stir Newtonian and quasi plastic fluids with viscosity up to 200Pa · s. When dealing with wastewater containing viscous substances or in the sludge treatment stage, anchor agitators can play a significant role in preventing viscous substances from adhering to the inner walls of the equipment and ensuring the mixing effect.
Spiral belt mixer
The outer diameter of the ribbon is equal to the pitch, and it is specifically used for stirring high viscosity liquids (200-500 Pa · s) and quasi plastic fluids, usually operating in laminar flow. In sewage treatment, if high concentration sludge or high viscosity sewage is encountered, the screw belt agitator can play its advantage and stir these high viscosity substances evenly.
Key points for selecting a blender
1. Consider sewage treatment processes: Different sewage treatment processes have different requirements for the mixer. In biological treatment processes, such as activated sludge process, a mixer is required to mix sewage and activated sludge, allowing microorganisms to fully contact with sewage, and providing a certain amount of dissolved oxygen. In this case, a submersible mixer or a turbine mixer can be selected; Chemical treatment processes, such as coagulation and sedimentation, mainly involve the rapid mixing and reaction of coagulants and wastewater, and paddle agitators are more suitable.
2. Understand the properties of wastewater: The viscosity, density, corrosiveness, and suspended solids content of wastewater can all affect the selection of a mixer. If the viscosity of the sewage is high, it is necessary to choose equipment suitable for mixing high viscosity liquids such as anchor mixers and screw mixers; If the sewage is highly corrosive, the material of the mixer must be selected from corrosion-resistant materials such as stainless steel; Wastewater with high suspended solids content should consider the anti clogging performance of the mixer, such as the self-cleaning function of the impeller of a submersible mixer, which is very practical.
3. Pay attention to the performance of mixing equipment: mixing intensity, mixing efficiency, power consumption, reliability, and other performance indicators should be considered. The mixing intensity should meet the requirements for sufficient mixing of sewage, chemicals, sludge, etc; High mixing efficiency can save processing time; Low power consumption reduces operating costs; High reliability can reduce equipment failures and ensure the continuity of sewage treatment. For example, in large-scale sewage treatment plants, it is necessary to choose mixers with high power, high mixing efficiency, and strong reliability.
4. Considering the situation of the water tank: The shape, depth, and volume of the water tank also have an impact on the selection of the mixer. The types of mixers suitable for rectangular and circular pools may be different; For deep water pools, it is necessary to consider the diving depth of the mixer and whether the mixing effect can cover the entire pool; If the volume of the pool is large, multiple mixers or high-power mixers may be needed to meet the mixing requirements.
Application scenarios of mixers
1. Dosing device: When dissolving or diluting drugs, small stirring devices such as paddle mixers or small submersible mixers are generally used to quickly dissolve and evenly mix the drugs, ensuring the dosing effect.
2. Coagulation tank: used for mixing chemicals and sewage to accelerate the reaction rate. Usually, slurry mixers and reaction stirring equipment are used to allow the coagulant and sewage to fully contact and form floc precipitation.
3. Anaerobic tank/anoxic tank: It is necessary to achieve mixing of returning sludge and sewage, mixing of mud and water, and ensuring biochemical effects. Push flow submersible mixers and submersible mixing thrusters are used to circulate sewage in the tank and provide a good living environment for microorganisms.
4. Sludge temporary storage tank: In order to prevent sludge sedimentation, sludge agitation can be carried out, and submersible mixers or other suitable mixing equipment can also be used to maintain the fluidity of sludge and facilitate subsequent processing.
The selection and application of mixers in sewage treatment is a meticulous task that requires comprehensive consideration of various factors to choose the most suitable mixer, in order to ensure efficient and stable sewage treatment work and contribute to environmental protection.
