Learn the key differences between positive displacement (PD) and centrifugal blowers and how advances in blower technology, variable-speed controls and lifecycle cost analysis are reshaping equipment selection. This article explains blower operating principles, performance characteristics and application considerations to help engineers optimize energy efficiency, reliability and long-term operating costs in wastewater, industrial and process air systems.
Historically, the most common dual point control has been combining inlet guide vanes and variable discharge diffuser vanes. These are both mechanical systems and predate the availability of economical variable speed control. Recent advances in power electronics technology and improved VFD economics have led to implementing other combinations for dual point control. These include combining VFD control with either VDVs or IGVs.
The ideal blower control matches the blower airflow to the process demand. The process demand, in turn, must be established by the aeration control system. This control strategy has become standard practice in most treatment facilities because of its proven effectiveness in reducing energy consumption and improving process stability.
In order to properly identify the performance requirements of a blower it is necessary to identify the inlet and discharge pressures. The friction losses in the inlet and discharge piping must be calculated to determine the total pressure requirement. This article details a simplified procedure for calculating piping losses.
Many designers and operators believe that multistage centrifugal blowers are not suitable for variable speed control. They also feel that multistage centrifugal blowers are an inefficient option for wastewater aeration. Implementing VFD control of their aeration blowers allowed the plant to improve energy efficiency. The reduction in energy expense paid for the system upgrade in less than two years.
High levels of reliability can be achieved in two ways. First, by design – employing quality materials, proven components, and simplified mechanisms. Second, by incorporating advanced monitoring techniques that identify abnormal operating conditions, provide notification to operators, and initiate equipment shutdown before catastrophic failure occurs. Modern positive displacement (PD) blower packages use both techniques to improve system reliability.
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.
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.
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.
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.
Most electric utilities offer customer incentives for implementing energy conservation measures (ECMs) Incentive programs pay customers to use less energy. In some cases they are mandated by legislation and in others the incentives are driven by the utility’s desire to avoid building new generating capacity. Some incentives are based on reduced energy use (kWh) and some are based on lower peak demand (kW).
KC Water encompasses six wastewater plants and 43 flood and sanitary stations. There are 15 flood stations along the Missouri River that keep Kansas City dry. Then we have 1,350 acres of land for biosolids application. Industrial pre-treatment is the responsibility of the Regulatory Compliance Division. We all work closely together.
Aeration blower upgrades may be part of a total plant upgrade and minimizing energy consumption is a critical consideration. Blower replacements are also a common Energy Conservation Measure (ECM) in cost-reduction programs.
Julie Gass, P.E., is a Lead Mechanical Process Engineer at Black & Veatch and an industry veteran with extensive experience in mechanical equipment in wastewater treatment plants. She also served on the American Society of Mechanical Engineers (ASME) Committee responsible for ASME PTC 13, Wire-to-Air Performance Test Code for Blower Systems, which is the performance test code published in October 2019 for all blower technologies. Blower & Vacuum Best Practices Magazine interviewed Gass to gain her views on aeration blowers, PTC 13, and the firm’s rigorous specification process to ensure treatment plants get the blower best suited for their application.
In the first of this two-part series on the basics of aeration control valves we examined valve fundamentals and basic equations for analysis. Here, we look at interactions between valves and discuss new flow control technologies.
Sizing, selection, and adjusting control valves often causes confusion for process and control system designers. Improper valve application can cause operating problems for plant staff and waste blower power. Basing the airflow control system design on fundamental principles will improve valve and control system performance.
Efficiency compares the inputs used by a system to the outputs produced. It is a commonly used concept, but one which is prone to a great deal of misuse in many industries. This article provides insight into the parameter known as “efficiency,” how it’s calculated, and importantly, it’s uses and limitations in predicting blower energy consumption and comparing alternate system designs.
Turndown designates the operating range of an aeration blower or a blower system – and it can often be the most important factor in determining the ability of a system to match process demand. It is also critical to the system’s energy optimization. Unfortunately, in designing blower systems and controls turndown is not always given the attention that its importance merits. Here’s a look at the critical nature of turndown in wastewater treatment plants and recommendations for ensuring adequate turndown when utilizing Positive Displacement (PD) and centrifugal blowers.
Most blower applications for wastewater treatment are for conventional activated sludge aeration. The water level is typically constant, and pressure variations are usually less than one psi. There are other applications, however, that undergo significant variations in water level. These processes present challenges, but they can be accommodated with proper blower system design.
Most-Open-Valve (MOV) can be a cost-effective way to optimize aeration energy. It can also be a confusing and troublesome addition to a process automation project. In my experience MOV is the least understood aspect of aeration control. This article will shed light on MOV, the process and energy impacts and why it’s worth the trouble.
Blower manufacturers are the source for the most accurate information on aeration blower power consumption. This includes the impact of various control technologies on the many types of blowers used for aeration. However, system designers often need to analyze several alternatives, making reliance on input from suppliers inconvenient. An understanding of the principles of operation will also enhance the designer’s ability to assess the data received from various sources.
The capacity and pressure requirements of blowers in a Water Resource Recovery Facility (WRRF) are determined by the aeration system. When systems are manually controlled blowers often operate at constant flow and pressure day in, day out. When the aeration system is automatically controlled to maintain a set dissolved oxygen (DO), however, the blower’s flow and system pressure vary constantly. Understanding these variations will help designers and suppliers optimize blower performance.
Blower efficiency is a justifiable concern during the design and selection of aeration equipment. However, efficiency may not be the most important consideration in aeration blower applications. In many cases the blower with the highest efficiency will not provide the lowest energy consumption! Blower turndown is a parameter that is generally more important than efficiency in optimizing energy use.
