COMPRESSORS & COMPRESSED AIR SELECTING THE RIGHT BLOWER


Atlas Copco explains how to select the right blower technology for industrial effluent treatment plants


A


cross the nation’s manufacturing industries, there is a universal dependence on the reliable supply of


low-pressure air within a 0.3 to 3bar range to meet the demands of a variety of process applications. Probably none are more stringent than those for water diffused aeration and filter backwashing duties within industrial effluent treatment plant (ETP) installations. And it is in this cleaning of process waste or contaminated water to make it reusable and recyclable, where selecting the right low-pressure blower technology for the job is an essential consideration. ETP installations are to be found in a variety


of industries such as food manufacturing and the production of pharmaceuticals, glass, cement, and paper. They play an essential role too in the chemical industries, and general manufacturing activities. Blower efficiency and operating


characteristics are important factors in the performance of effluent treatment. Not only are these processes required to conform to regulatory and environmental standards, but compliance with strict regulations concerning ETP operations helps to reduce water pollution and encourage water conservation. There are different types of low-pressure


blower technologies available to the industrial plant operator, categorised as lobe, screw, centrifugal, and multistage options. The centrifugal technologies (high-speed turbo blowers, multistage blowers and multistage centrifugal blowers) are primarily designed for


24 FEBRUARY 2021 | PROCESS & CONTROL


low-pressure applications that require higher flow rates of over 5,000m3


/hr, and are best


suited for larger and specialised applications. In contrast, the majority of ETP blower


applications favour the positive displacement options of fixed-speed and VSD driven versions of tri-lobe technology or the direct drive, oil- free, rotary screw blowers delivering a low-pressure flow rate of up to 9,100m³/h. In the case of lobe blowers, manufacturers


such as Atlas Copco offer the option of pure mechanical basic units employing dial gauges for pressure reading or high-end solutions with integrated VSD inverter and intelligent control. But for ETP applications involving back pressures greater than 0.5 bar(g), rotary screw blowers lead the field with an average 30% greater energy efficiency compared to traditional technologies. They demand less energy because the internal compression concept offers higher efficiency derived from the design of its rotor elements. When choosing the right blower technology,


the start point is a thorough analysis of an installation and recognition that application characteristics are key to selecting the right technology. Apart from finding a blower technology that matches the airflow and pressure needs of a specific ETP process, other factors such as initial investment cost or return on investment will also affect the search for the right air blower technology. Key factors that should be taken into


consideration include: Flow and Pressure: A correctly sized blower installation will help to achieve a more energy-


The best solution will be one that ticks all the boxes on questions of the type of blower technology, its physical size and capacity, its level of energy efficiency, and total cost of ownership. There should be positive feedback too on issues such as whether it is designed for oil-free operation, minimum maintenance, and extended service intervals


efficient process. For instance, in a situation where compressor turndown is employed as the low-pressure source, replacing the compressor with an air blower to deliver 0.3 and 1.5 bar(g) air will result in savings. For every 1 bar(g) the air is compressed above the actual demand, 7% of energy is wasted. Operational costs and TCO: The capital cost


of a low-pressure aeration lobe blower may represent less than 5% of a total ETP’s investment. This may appear to be an attractive proposition, but blower running costs are more significant and are likely to constitute up to 80% of the energy costs for an entire ETP. This is because the aeration blowers need energy to run 24 hours a day in supporting the biological processes. It follows that, when considering the total cost of ownership of a blower installation, the need to seek an energy-efficient solution should be at the top of the list. Application conditions: Site characteristics


have a bearing on blower choice. For example, limited space availability for a blower installation might mean choosing technology that offers a smaller footprint and lower noise levels. On the other hand, the application criterion of lower energy costs may be best met by a more energy-efficient technology that comes with a higher capital cost. Operating noise levels: A feature of the


latest generation of low-pressure blowers is intelligent baffle and canopy design that provides reduced sound levels down to 72dB(a) for an improved working environment. Consequently, installation costs are reduced


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