Across 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 wide 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 within the process operations of a variety of industries such as food manufacturing and the production of pharmaceuticals, textiles, glass, cement, paper, and pulp. They play an essential role too in the output of tanneries, 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.
TYPES OF BLOWERS
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 low-pressure applications that require higher flow rates of over 5,000 m3/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 9,100 m³/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 rotor elements.
Choosing a blower starts with a thorough analysis of an installation and recognition that application characteristics are key to selecting the right technology. In the decisionmaking process, there will undoubtedly be one or more aspects that might take precedence over others. 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-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 significant 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 a far more significant factor 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 biological processes. They supply the right amount of oxygen to microorganisms and maintaining their constant, balanced performance within the plant. 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 available space for a blower installation might dictate the choice of a technology offering 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, as there is no need for the provision of noise-insulated rooms and doors.
- Service and lifetime support. When it comes to routine maintenance and service support, some older blower technologies may require units to be serviced, repaired or refurbished offsite. Advanced design developments in the latest oil-free, low-pressure blowers now sees the inclusion of low-maintenance components, extended on-site service intervals, and the benefits of lifetime customer support plans.
- Comparative performance. It pays to check the vital statistics. As an example, the tri-lobe rotors incorporated into the latest generation of blowers are capable of sweeping nearly six times the volume of air in a single revolution compared to their belt-driven, twin-lobe predecessors. On average, this older technology experiences 5%-7% more transmission losses.
An important advantage of the direct-drive, oil-free, rotary screw blowers is wide turndown, especially on models with integrated inverter drives. This allows the units to match the airflows to the daily and seasonal variations in the effluent inflow, resulting in additional energy savings. In order to cope with fluctuations in air demand, screw blower technology can operate from 100% capacity to 25% with very little change in specific power requirement.
As a practical example of the rotary screw blower’s superior performance in industry, Frito Lay, an affiliate of PepsiCo Foods in Turkey, achieved an average of 30% energy efficiency, lower operating costs and minimum noise levels by installing Atlas Copco’s ZS screw blower technology within its water treatment facility in 2010.
Since then, there have been no unexpected shutdowns due to failure since the first operation of the blowers which operate for a minimum of 18 hours per day, seven days a week, depending on the need of the facility. Currently, no protection is necessary inside the treatment facility’s blower room, where once wearing protective ear defenders was required. Now, noise level at one metre is measured to be from 70 dB(A).
ZS+ blowers are controlled by the Elektronikon operating system. Dissolved oxygen (DO) meter feedback-based blower control helps supports the effective biological process in ETP and also saves energy.
In conclusion, the best blower solution will be one that ticks all the boxes 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 they are designed for oil-free operation, minimum maintenance, and extended service intervals.