Atlas Copco’s ZS VSD+ rotary screw blowers deliver 100% oil-free, pulsation-free air for industrial effluent treatment plants.
Atlas Copco’s ZS VSD+ rotary screw blowers deliver 100% oil-free, pulsation-free air for industrial effluent treatment plants.
Filter backwashing at a wastewater treatment plant.
Filter backwashing at a wastewater treatment plant.
A sequence batch reactor at a wastewater treatment plant.
A sequence batch reactor at a wastewater treatment plant.

Requirements for water diffused aeration and filter backwashing in industrial effluent treatment plants are particularly stringent. The cleaning of process waste or contaminated water to make it reusable and recyclable means that selecting the right low-pressure blower technology is a critical decision.

Effluent treatment plant (ETP) installations are to be found within the process operations of a wide variety of industries such as food manufacturing and the production of pharmaceuticals, textiles, glass, cement, paper, and pulp. They also play an essential role 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.

Different types
There are a number of 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 an integrated VSD inverter and intelligent control. However, 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.

Blower technology
The starting point is a thorough analysis of an installation and recognition that application characteristics are key to selecting the right technology. In the decision 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 to support the biological processes. They supply the right amount of oxygen to micro-organisms to maintain 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 space availability 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 re-furbished offsite. Advanced design developments in the latest oil-free, low-pressure blowers now see the inclusion of low maintenance components, extended on-site service intervals, and the benefits of lifetime customer support plans.

Comparative performances: It pays to check the vital statistics. As an example, the tri-lobe rotors incorporated into the latest generation of low-noise, low-vibration, low-pulsation 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. 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.

Lower energy costs
As a practical example of the rotary screw blower’s superior performance in industry, Frito Lay, an affiliate of PepsiCo Foods in Turkey, reinforced its leader position in environmental awareness by achieving 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. 

Installed back in 2010, 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 it was once required to wear protective ear defenders. Noise level at 1 m is as low as 70 dB(A).

At the heart of the Atlas Copco ZS rotary screw blower system, the latest, close-tolerance screw elements incorporate years of experience and development to deliver 100% oil-free, pulsation-free air and carry a five-year warranty of reliability.

As an additional benefit, all ZS+ blowers are complete with an Elektronikon operating system to provide control and enable smart remote monitoring of the overall system performance status, and to increase the blowers’ efficiency and reliability. Furthermore, dissolved oxygen (DO) meter feedback-based blower control not only supports the effective biological process in ETPs but also saves energy.

Conclusion
The full picture of blower technology is a catalogue of comparative technical features and benefits that merit earnest consideration at the point of equipment replacement or site expansion decisions.

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.  The ultimate aim is for a blower system that provides total reliability, guaranteed continuity of process operations, and combines optimum performance with protection of the process, the environment and operational energy costs.

About the author
This article was supplied and written by Mark Ranger, business line manager, Oil-free Air at Atlas Copco.