Industrial Utility Efficiency
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.
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.
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).
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.
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 design of wastewater treatment plants is changing, and it has something to do with LEGO® bricks. More specifically, it has to do with how large and complex LEGO structures are built. If you follow the instructions carefully, you build module after module, eventually piecing them together to create a fully functional and cohesive unit.
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.
A replacement strategy for air compressors and blowers integrated into a system-level approach towards energy efficiency can deliver significant energy savings and optimize equipment performance. At the Victor Valley Wastewater Reclamation Authority, a blower replacement project yielded annual energy savings of more than 928,000 kWh and $98,000 in energy costs, while improving the reliability of its secondary treatment process. In addition, the agency qualified for important incentives from its electric utility — significantly improving the project economics and resulting in a 2.94-year payback.
The overall wastewater treatment process is complex, and each step is integral to ensuring water is properly purified. Effluent ends up in the plants, containing substances that must be removed before the water can be properly cleaned and returned for use. The range of potential contaminants is almost endless and can include food, pulp, waste, or other substances. Afterwards, the water requires further scrubbing, with the aid of bacteria. It is in this part of the process that compressed air (ideally provided by energy-efficient rotary lobe blowers) plays a vital role.
A facility audit examined the plant electrical energy consumption to find ideas to reduce plant energy use while meeting the process demand. Based on discussions with plant staff and a brief review of the process, it was decided to focus the effort on reducing the electrical energy required to provide aeration air to the secondary activated sludge process. The aeration air blowers were the largest consumers of electrical power in the plant and significantly less efficient than the newer blowers that have been introduced to the market place in the recent years.
This guide explains three blower technologies and,using examples from actual wastewater plants, describes the most effective technology for particular applications and why. Of course there is no substitute for a consultation specific to your application; however, the guide can help raise the right questions and ensure a productive vendor and technology evaluation process.
