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.
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.
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.
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!
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.
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.
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.
Aeration tanks use bubble diffusers to distribute oxygen within the wastewater. Fine bubble diffusers, or those that produce a large amount of very small air bubbles, first began to become popular in the 1980s, as they had a much higher efficiency than coarse bubble diffusers. Fine bubble diffusers generally feature a membrane that allows airflow to pass from the piping system on the floor of the tank through the body of the diffuser and the membrane, providing oxygen into the wastewater for treatment.