What kind of fans can the water treatment industry choose?

In the water treatment industry, the core function of fan is to provide stable airflow for process links (such as aeration, stirring, gas stripping, etc.), and its selection needs to be comprehensively judged in combination with specific application scenarios (such as sewage treatment, drinking water treatment, industrial wastewater treatment), process requirements (air volume, wind pressure, aeration efficiency) and operating costs. The following are commonly used fan types, applicable scenarios and key selection in the industry to help accurately match the demand:

I. Types of core fans in water treatment industry and applicable scenarios

The working principle of different fans determines their wind pressure and air volume characteristics, which need to correspond to different process links of water treatment (such as municipal sewage aeration, sludge treatment, air flotation process, etc.). The specific comparison is as follows:

Fan Type Core Principle Wind Pressure Range Air Volume Range Applicable to Water Treatment Scenes Core Advantages Potential Points for Attention

The impeller of centrifugal fan rotates to produce centrifugal force, which throws the gas out of the pressurized medium and low wind pressure (< 50kpa) and large flow (usually > 100m/min). 1. Large municipal sewage treatment plant (oxidation ditch, AAO process aeration);

2. High-volume aeration in industrial wastewater treatment;

3. Aeration of ozone contact tank for drinking water treatment 1. Stable flow and small pressure fluctuation;

2. Suitable for long-term continuous operation;

3. Low maintenance cost (no wearing parts) 1. Large floor space;

2. Low energy efficiency during low load operation;

3. Control cabinet (soft start/frequency conversion) is required for startup.

Roots blower is engaged with two rotors, which forcibly conveys gas (positive displacement) with medium and high wind pressure (30-100 kPa) and small and medium flow rate (< 80m/min). 1. Small and medium-sized sewage treatment plants (SBR process, biological contact oxidation pond);

2. Aerobic digestion and aeration of sludge;

3. Air flotation process (air supply for dissolved air flotation) 1. The wind pressure is stable and is not affected by the inlet pressure;

2. Simple structure and low failure rate;

3. Adapting frequency conversion adjustment (some models) 1. High noise (muffler/sound insulation cover is required);

2. The flow adjustment range is limited (excessive throttling is easy to overheat);

3. The lubricating oil needs to be changed regularly.

The eccentric rotor of the rotary fan rotates in the cylinder, and the volume changes. The intake/exhaust air pressure is low (< 20kPa) and the flow rate is small (< 20m/min). 1. Small sewage treatment equipment (decentralized sewage treatment in family/community);

2. Landscape water/black and odorous water treatment (micro aeration);

3. Laboratory wastewater treatment 1. Very low noise (no additional noise reduction);

2. Small size and flexible installation;

3. Less oil mist and low gas pollution. 1. The upper limit of wind pressure is low, which is not suitable for high resistance systems;

2. Long-term high-load operation is easy to wear;

3. The flow regulation accuracy is low.

The magnetic bearing of the magnetic suspension centrifugal fan supports the impeller, and rotates without contact, with medium and high wind pressure (30-80 kPa) and large flow (> 150 m/min). 1. Large municipal sewage treatment plant (aeration system above 10,000 tons);

2. High concentration organic wastewater treatment (high oxygen demand scenario);

3. Projects with high requirements for energy consumption and noise 1. Extremely high energy efficiency (20%-30% less than traditional centrifugal fans);

2. No mechanical wear and long service life (15-20 years);

3. Low noise (below 80dB) 1. High initial investment cost (about 2-3 times that of traditional fans);

2. High maintenance technical requirements (professional team required);

3. Not applicable to frequent start-stop scenes

The aerodynamic principle of air suspension centrifugal fan makes the impeller suspend, and the medium and high wind pressure (20-70 kPa) and medium flow rate (50-150 m/min) in non-contact operation 1. Medium-sized sewage treatment plant (5,000-10,000 tons/day);

2. Industrial wastewater treatment (such as chemical and printing and dyeing wastewater aeration);

3. Projects requiring high maintenance convenience 1. No lubricating oil and no secondary pollution (suitable for drinking water treatment);

2. Flexible start and stop, adapting to variable load conditions;

3. Simple maintenance (no bearing, gear box) 1. The stability of wind pressure is slightly lower than that of magnetic suspension fan;

2. High temperature and high humidity environment need extra protection;

3. The performance-to-price ratio of large-flow scenes is lower than that of magnetic levitation.

Second, the key factors of selection (avoiding mismatch)

Clear process requirements: air volume and air pressure are the basis.

Air volume: it should be calculated according to "treated water × oxygen demand (such as 0.5-1.2 mo/m water for biological aeration)", and 10%-20% margin should be reserved (to cope with load fluctuation);

Wind pressure: pipeline resistance and aerator resistance should be considered (for example, the resistance of microporous aerator is about 15-25kPa, and that of rotary aerator is about 10-15kPa), and the total wind pressure = sum of resistance+safety margin (5-10kPa).

Example: AAO process for municipal sewage, the treatment capacity is 10,000 tons/day, the oxygen demand is about 80kgO₂/ day, and the converted air volume is about 400 m/min (air oxygen content is 21%). If microporous aerator is used, the total air pressure should be ≥40kPa, and centrifugal or magnetic suspension fans are preferred.

Operating cost: Energy consumption accounts for over 70%, so priority should be given.

The water treatment fan is a "24-hour continuous operation equipment", and its energy consumption cost accounts for more than 70% of its whole life cycle cost, so it is necessary to compare the specific power (energy consumption per unit air volume, kW/(m/min)):

Magnetic suspension/air suspension fan: the specific power is about 0.03-0.05 kW/(m/min), which is suitable for long-term high load;

Traditional centrifugal fan: the specific power is about 0.06-0.08 kW/(m/min), which is suitable for load stability scenarios;

Roots blower: The specific power is about 0.08-0.12 kW/(m/min), which is suitable for small and medium flow and high wind pressure scenes.

Installation and maintenance: match the site conditions

Space: Centrifugal and magnetic levitation fans occupy a large area (the machine room needs to be reserved), and rotary and small roots fans can be mounted on the wall/vertically;

Noise: Low-noise models (such as rotary and magnetic levitation, with noise ≤85dB) should be selected for projects near residential areas, otherwise, additional noise enclosures should be installed (increasing costs);

Maintenance: Oil-free models (air suspension, magnetic levitation) are suitable for remote projects (reducing oil change frequency), and oil-free models (Roots, traditional centrifugal) need to check the oil level and filter element regularly.

Water quality characteristics: avoid equipment corrosion or blockage.

Corrosive wastewater (such as chemical and electroplating wastewater): the fan casing and impeller made of stainless steel (304/316L) shall be selected to avoid corrosion of carbon steel;

Dust-bearing wastewater (such as mine and building materials wastewater): pretreatment (precipitation/filtration) is needed before aeration to prevent dust from entering the fan, wearing the impeller or blocking the air inlet.

Three, different scale water treatment project selection suggestions

Core considerations of recommended fan type for typical handling capacity of project scale

Rotary fans and small roots fans with small dispersed projects < 500 tons/day are small in size, flexible in installation, meet the requirements of micro-aeration and have low noise.

Roots blower and air suspension centrifugal blower for medium-sized projects with a capacity of 500-10,000 tons/day balance energy consumption and investment, and adapt to variable load (such as intermittent aeration in SBR process).

Large-scale municipal projects > 10,000 tons/day magnetic levitation centrifugal fans and large-scale centrifugal fans have high flow and high energy efficiency, which reduce long-term operating costs and are suitable for continuous operation.

summary

The core logic of water treatment fan selection is "scene matching+cost balance";

Low flow, low wind pressure and low noise requirements → rotary fans are preferred;

Small and medium flow, medium and high wind pressure, limited budget → roots blower;

Large flow, high energy consumption sensitivity, long-term operation → magnetic suspension/air suspension centrifugal fan;

Ultra-large flow, stable load and low maintenance requirements → choose traditional centrifugal fan.

It is suggested that detailed process parameters (capacity, oxygen demand, aeration mode) should be provided to the fan manufacturer before type selection, and professional technicians should conduct fluid simulation calculation to avoid excessive energy consumption or process failure due to parameter mismatch.