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.
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.
Originally built in 1958, the CMA wastewater treatment plant serves 14,000 residents, as well as businesses, in Clearfield Borough and surrounding portions of Lawrence Township, Clearfield County, PA. From the start, the plant consistently met water quality and effluent parameters as specified in its National Pollutant Discharge Elimination System (NPDES) permit throughout. However, new mandates in 2010 and the need for ongoing improvements drove the need for plant upgrades.
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.
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 Wastewater Association of Rheinfelden-Schwörstadt operates the wastewater treatment facilities in Schwoerstadt and Rheinfelden-Herten, Germany, as well as several rainwater overflow basins. This wastewater treatment facility now satisfies the highest requirements, and with a population of about 47,000, has reached a size that also guarantees sufficient disposal capacity for future generations.
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.
Aeration blowers receive a lot of attention from design engineers, suppliers, and end users. That is understandable since blowers account for more than 50 percent of the energy used in a typical wastewater treatment plant (WWTP). They represent “low hanging fruit” for energy conservation measures in wastewater treatment!
Yeast fermentation is a vital process in the production of many food and beverage products. It is a common application within breweries, bakeries, and wineries, along with other facilities where biogas and ethanol are produced. In these facilities, fermentation tanks filled with a reaction liquid are often supplied with air from blowers. Recently, there has been a trend in the adoption of high-speed turbo blowers for yeast fermentation applications, as the blower technology can yield large energy savings if properly installed and controlled.
The Ilmajoki sewage treatment plant (STP) located in southern Finland was built in the mid-1970s during a boom of infrastructure construction. Over time, industrial presence in the Ilmajoki area grew, and the plant saw an increase in flow of industrial effluent—or liquid waste and sewage. As the amount of influent increased, the plant was no longer able to meet required performance criteria suffered from a severe lack of oxygen—particularly during peak loading times.
Hoffman & Lamson has been manufacturing multi-stage centrifugal blowers for a long time. Lamson was founded in 1880, and Hoffman was established in 1905. Now a single entity under the Gardner Denver Nash Division, the company has some serious resources to complement its 100-plus years of blower expertise.