Introduction
Aeration blowers receive a plenty of consideration from design engineers, suppliers, and end users. Given that blowers consume more than 50% of the energy in a typical wastewater treatment plant, this is understandable. (WWTP). They serve as "low hanging fruit" for energy-saving wastewater treatment techniques!
In some sectors, the design flow and discharge pressure are specified as a single operating point for blower applications. On the other hand, municipal wastewater treatment applications typically call for blower systems that offer a range of flows and output pressures. This reflects variation in the treatment procedure, despite the fact that it can be frustrating for suppliers. Optimizing the performance of the blowers requires an understanding of the varied process demands on the system.
How to choose the right blower technology for STP?
It is extremely typical for STPs to have an aeration tank with a water column between 5 and 6 meters, which generates a back pressure of 0.5 to 0.6 bar(g) on the aeration blowers. Additionally, as the water column level rises, the Oxygen Transfer Efficiency (OTE) in the aeration tank rises as well.
Up to the water level in the aeration tank is less than 4 meters, the conventional Tri-Lobe Blowers are effective. Only 0.45 bar(g) or less of back-pressure resistance is provided by this. However, the twin lobe and tri-lobe blowers start using high power and raise the energy expenses for the STPs soon the pressure surpasses 0.5 bar(g).
Therefore, for pressures more than 0.5 bar, it is strongly advised to employ the rotary screw blower technology. In terms of energy efficiency, screw blowers perform on average 30% better than roots blowers that use classic Lobe Technology. The screw blowers are created using cutting-edge technology that can potentially save your money on energy costs and have a smaller negative impact on the environment.
Screw blowers are more efficient than conventional belt-driven blowers because they are direct-coupled/gear-driven equipment. This increase in efficiency is the result of the fact that gear-driven machines like oil-free screw blowers often have transmission losses of 5% to 7% less than belt-driven machines.
The wide turndown of gear-driven oil-free screw blowers is a significant additional benefit. It will be very helpful if the influent capacity varies significantly throughout the day or throughout the seasons.
Additionally, using the dissolved oxygen (DO) metre feedback-based blower control is strongly advised because it not only supports the efficient biological process in the ETP but also reduces energy costs.
Additionally, compared to fixed speed blowers, variable speed drive (VSD) or variable frequency drive (VFD) blowers that operate based on dissolved oxygen (DO) metre feedback save more energy. Screw blowers also benefit from remote monitoring, IoT, and noise reduction.
Types of blowers:
Although there are many different kinds of blowers, just a few are frequently employed due to their toughness, dependability, and capacity to adapt to a range of situations. They enable the efficient, dependable, rapid, and successful completion of large-scale industrial activities.
1. Positive Displacement Industrial Blowers
2. Centrifugal Industrial Blower
3. Multi Stage Centrifugal Blowers
4. Regenerative
5. High Speed Industrial Blower
How to design air blowers
Step 1: Determining the air flow rate: The air flow rate required for aeration depends on how much organic matter is present in the effluent. The air flow rate is commonly calculated using the formula below:
Q = K x V x S
Where:
Q = air flow rate (m3/min)
K = oxygen transfer rate (kgO2/kWh)
V = volume of wastewater (m3)
S = oxygen demand (kgO2/ m3)
Step 2: Selecting the blower: Once you are aware of the required air flow rate, you can select the appropriate blower. Blowers are categorized based on their ability to produce pressure and flow. Select a blower that can deliver the required air flow rate and pressure and has an efficiency of at least 70%.
Step 3: Checking the rating of motor: The motor rating should be checked to ensure the blower can generate the required power. The required power can be calculated using the formula below:
P = (Q x P) / η
Where:
P = power required (kW)
Q = air flow rate (m3/min)
P = pressure required (Pa)
η = blower efficiency
Step 4: Checking the noise level: Assessing the blower's noise level will ensure that it complies with local regulations. The noise level can be reduced by selecting a blower with a lower speed, installing a muffler or silencer, or moving the blower to a different location.
Conclusion:
Blowers for wastewater aeration are an essential component of a complex treatment system. The need for air during the procedure is ever-changing. The system needs are unlikely to be satisfied by supplying a single blower that operates at a single flow rate and discharge pressure.
Variable process demand, present and prospective loadings, and the effect of ambient conditions on performance will all be taken into account in a good design. The range of operation that the blower system must support should be specified as a consequence.
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