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Application 2. money for something that won't get you the results you need. But performance isn't the only consideration. Operations and maintenance (O&M;) issues must factor into your decision. Will your operators be confident handling the complex instrumentation on a single-stage centrifugal system, or would something simpler be better, even if it's less efficient? How difficult are the blower components to maintain? Will you want to maintain components such as the air bearings yourself, or add a maintenance contract to the blower purchase? What level of noise from the blowers will be acceptable for your facility, and can noise issues be efficiently mitigated by other measures? Answering these questions, and a few others, will help narrow your choice and get you closer to making the right blower choice for your facility. Four Things You Can Do To Make A Better Blower Decision 1. Correctly determine the process air requirements for your system and desired blower efficiency and capacity turndown. The table below lists the blower types already discussed and their nominal blower efficiency and turndown rates. While higher efficiencies always look more attractive, remember that this is just one consideration. A lower efficiency blower might have O&M; offsets that still save you money and effort in the 4. Increasing blower efficiencies while reducing power costs is important for every wastewater treatment plant, but understanding how a specific blower will perform for your Nominal Turndown plant is even more important. Matching your needs (percent of rated flow) with the right technology might not get you the new50 est, shiniest product in the marketplace, but it will help you achieve the ultimate goal of improved plant 60 reliability, efficiency, and peace of mind. Blower Type Nominal Blower Efficiency (percent) Positive Displacement 45-65 Multi-Stage Centrifugal (inlet throttled) 50-70 Multi-Stage Centrifugal (variable speed) 60-70 50 Single-Stage Centrifugal, Integrally Geared (with inlet guide vanes and variable diffuser vanes) 70-80 45 Single-Stage High Speed Turbo 14 3. long run, making it a better value. Clearly define and specify a pressure rise to the surge point across the entire blower operating range, from the design point to the minimum airflow capacity. Blower surge, a form of unstable operation that involves reversal of flow, is a condition that occurs frequently with blowers in WWTP facilities, and can result in blower shutdowns or damage. Centrifugal blowers are more efficient when they operate close to the surge point, which is why there is a tendency to design blowers to operate at that range. Yet every blower manufacturer has its own criteria on how close it designs to the surge point. Therefore, by specifying a pressure rise to the surge point that you are comfortable with, all manufacturers can design their blowers for you using the same criteria. Indicate your site-specific operating conditions. We are frequently presented with blower performance numbers that are not based on the project location conditions or actual system operations. This is kind of like buying customized snow skis in Hawaii. Sure, you can get them, but will they do what you need them to do? Blower performance numbers need to be calculated using the project location temperature and atmospheric pressure, and the specified guaranteed performance points should be based on your treatment plant's actual operating conditions. Otherwise, you'll receive performance numbers based on conditions that are more favorable for that particular blower, which may not be accurate for your purposes. Do your research. In Carollo Engineers' experience, we have found that testing methods are not consistent among manufacturers. When talking to blower representatives, it's important to qualify their performance and O&M; claims. Ask specific questions about the equipment, its intended operation, its optimal operation, what kind of standard maintenance is involved, and so on. Don't just accept their numbers at face value. 70-82 50 - wateronline.com ■ Juan Loera is a company-wide expert with Carollo Engineers on blower designs. He has worked on a number of wastewater projects in various aspects of analysis, design, and construction of aeration blowers and aeration air system projects, with installations in facilities ranging in capacity from 2,000 to 29,000 standard cubic feet per minute (scfm) per blower. Water Online The Magazine