Choosing The Right Blower For Your Wastewater Treatment
In any wastewater treatment plant, about 60% of the energy
needs are for aeration. Blowers provide this aeration, keep
bacteria suspended, and allow solids to be separated from liquids
(flocculation) - essential for proper wastewater treatment.
Types of blowers:
Hybrid blowers and rotary lobe blowers:
Hybrid blowers (also known as screw blowers) and positive displacement blowers (rotary lobe blowers) are normally used for small or medium flows. Positive displacement blowers are known as rotary lobe blowers because they use straight or twisted lobe rotors without internal compression. Meanwhile, hybrid blowers are known as screw blowers because they use a low-pressure screw rotor. To avoid confusion, we will use the terms hybrid blowers and rotary lobe blowers.
Rotary lobe blowers perform well despite changing conditions, with output and pressure governed by the speed you run them at. They cost less than turbo and hybrid blowers, but often consume more energy - this can be due to efficiency losses through their transmission, motors, gears, and variable frequency drives.
Both hybrid and rotary lobe blowers also lose efficiency due to increased pressure. Hybrids are usually more efficient than rotary lobe blowers, which have no internal compression during a 360-degree rotation. In applications with large variations in flow and pressure, hybrid blowers can achieve rates as little as 25 percent of the original design point.
Both rotary lobe and hybrid blowers are renowned for their reliable turn-down facilities, considering maximum and minimum blower or system flow rates. However, they must be sized correctly due to their simplicity. Although they only require moderate repair over time, high levels of vibration mean that screw coatings can wear away and need replacing.
All in all, both hybrid and rotary lobe blowers are robust machines that are easy to operate and maintain by plant personnel. Hybrid blowers have lower initial and repair costs than special purpose centrifugal blowers while their cost is similar to that of standard turbo blowers. Rotary lobe blowers have lower initial costs and lower repair costs than a turbo blower.
Turbo blowers provide high levels of efficiency because the turbo impeller is connected to the shaft, which makes it possible to eliminate transmission losses. They are most efficient when operating at or close to design point, performing cost-effectively in applications with narrow swings in turndown.
Controls may be needed to protect against surging as they must be able to handle conditions at the extremes. Although they don't take up a lot of space, they are very sensitive to contamination and sudden pressure swings. For applications with low variation in operating conditions, they use less energy than rotary lobe blowers, despite higher initial costs.
High speed single-stage centrifugal blowers
Centrifugal blowers are often used for medium or large flows at a wastewater treatment plant. Typical vane-style blowers usually run at a constant speed, but you can vary the airflow by throttling the inlet valve. They achieve their highest efficiency when operating in the design range. While they are robust machines that don't take up a lot of space, controls are needed to protect against surging.
Although they employ proven technology that's been in use since the 1980s, centrifugal blowers require a high initial investment and can require costly repair. However, with proper maintenance, they can last longer than other blowers. Under typical conditions encountered in municipal wastewater treatment plants, a turndown at constant pressure of 55% can be achieved without any loss in efficiency.
For large wastewater treatment plants, it can be advisable to use a combination of blower technologies at different points in the treatment process. This can help improve overall energy efficiency and reduce initial and long-term operating costs. In fact, the overall turndown range can be extended to 6:1 or more.
For instance, turbo blowers are best suited for applications where they can run at the same speed all day and are less efficient when used in applications with regular fluctuations. The best way to optimize a system is to combine a turbo (for a base load) with a hybrid blower (for peak load and low flow conditions). However, it is essential that the turbo and hybrid can work together without surging. An idling feature and inverter control can help ensure the success of this combination. It should also be noted that the hybrid blower is equipped with pulsation attenuation which minimizes disturbances in the system when operating the turbo.
Selecting the proper blower, or combination of blowers, should
increase your plant's efficiency and reduce operational costs.
If you'd like advice on the correct blower for your wastewater
treatment plant, please call our toll-free number 1-800- 367-4180.
We have experts on hand to help you choose, install, and maintain
a variety of equipment.