Aeration Blowers

When a facility plans for a wastewater treatment plants, they typically design based on population and industry growth twenty to thirty years into the future. Regulatory requirements often dictate designing the activated sludge process equipment based on future-state influent flow and loading conditions, resulting in decades of constrained, inefficient, and suboptimal operation. 

Supplying air to process equipment necessitates a system approach. Selecting the blowers is a critical design step, but far from the final one. The layout of the blower room and ancillary equipment is just as critical to project success as the blowers themselves.

Single-stage centrifugal blowers are a proven technology that have been around for many years and will probably be here for many years to come. A well maintained machine can last for decades and will likely outlast its original control system. Even if the control system is still in good working order the components might already be end of life and hard to replace if any of them fail. If you are thinking about modernizing the hardware (PLC / HMI / Instruments) this is also a great opportunity to make the system a little smarter and user friendly. 

Positive Displacement (PD) blowers have been a workhorse for wastewater treatment for over 150 years. They are robust and simple to operate. They are often the first choice for small facilities and for applications with wide variations in discharge pressure. When combined with variable frequency drives (VFDs) they provide operational flexibility in flowrate across a wide range of discharge pressures.

One definition of “calibrate” is “to determine, rectify, or mark the graduations of something”. An ammeter is an instrument for measuring electric current. Therefore the simple definition of a calibrated ammeter is a current measuring device marked with units of measure, presumably amperes. In the blower industry, however, the term has developed a specific meaning. A calibrated ammeter is an instrument that measures a blower motor’s current draw and converts the measurement to a display of blower airflow rate. 
 

The American Society of Mechanical Engineers (ASME) released their Wire-to-Air Performance Test Code for Blower Systems in 2018. Designated PTC 13-2018, it has rapidly become a standard for inclusion in blower specifications.

The EXPO & Conference focuses on “Optimizing On-site Utilities Powering Automation.” Experts from all over the world convened to discuss compressed air, pneumatics, motors and drives, vacuum, aeration blower and chiller/cooling and water treatment systems.

Held November 2-4, 2021, this 3rd installment of the event continued to provide continuing education, certification and networking opportunities to equipment sales engineers, engineering firm and manufacturing plant personnel.

Most control systems use Proportional-Integral-Derivative (PID) algorithms for controlling DO, basin air flow distribution, and blower pressure or flow. These algorithms are prone to hunting - the cyclic fluctuation of the controlled variable. Fluctuations that oscillate the DO several mg/L above and below the target DO concentration are common.

This article aims to discuss the various technologies of equipment that could be presented to a wastewater operator faced with a temporary need for blower air and to help the operator understand the impact (both monetarily through a “Total Cost of Rental” approach and environmentally) of their decisions.

Real world blower applications rarely operate at steady state design conditions. There are a variety of reasons for this. Designs usually include a margin of safety to accommodate unforeseen conditions. Typically, the process demand itself is variable, requiring a corresponding ability to modulate the blower flowrate.