Are you using the right technology?
Screw vs. roots blower
While the screw and Roots blower are not as widely recognized as medium-pressure compressor systems, this low-pressure equipment is essential for several industries. These include aquaculture, cement plants, flue gas desulfurization, food and beverage, non-woven textiles, and pneumatic conveying.
Several facilities use typical medium-pressure air compressor systems that produce 7 to 8 bars, while only needing up to 2 bars for low pressure applications. This results in excessive energy consumption and costs.
With this in mind, a low-pressure screw or lobe (roots) blower typically produces pressure between 0.3 and 1 bar. As a result, they are an excellent fit for low-pressure applications. Lobe (roots) technology has been around since Francis and Philander Roots first developed it in 1854, and has not evolved much since then.
In this article, we discuss lobe (Roots) and screw technology in low-pressure blowers and highlight why screw blowers are a better solution for low-pressure applications. Read on below to learn more.
How does a lobe or roots blower work?
A lobe or roots blower is a low-pressure blower that uses isochoric compression. This means that the air volume in the compression chamber remains constant. The lobe rotors in the chamber rotate, which decreases the volume of the chamber and causes compression.
This compression occurs externally against full counter-pressure because of incoming air from a connected pipeline. External compression results in low efficiency and high noise levels.
As a result, the use of lobe technology is limited to low-pressure applications in a single stage. Two-stage and three-stage versions are available. However, they are not as common because of their low efficiency and high noise levels.
A lobe or roots blower is made for low-pressure use. However, it is not the best choice because of the reasons stated above. Today's industrial sector calls for equipment that is efficient and keeps costs as low as possible.
Pressure/Volume diagram of a lobe blower
4-1: Air intake – volume increase to Vs
1-2: Compression by back-flow from receiver to blower
2-3: Air delivery from blower to receiver
Rectangle area 1-2-3-4 represents the compression work Wt.
Power consumption is proportional with blue area 1-2-3-4
Pressure/Volume diagram of a screw blower
4 -1: Suction – air enters the compression chamber
1-2: Internal compression – as the rotors move towards each other, the air volume decreases
2-3: Discharge – air is pushed out into the pipeline, deliver to receiver
How does a screw blower work?
Why screw blowers are a better choice than a roots blower
Up to 80% of operating an air compressor is its energy costs.
That said, it’s worth pointing out that the internal compression mechanism of a screw blower is inherently efficient. This is because screw blowers consume less energy and generate less heat due to their design.
Let us explain this with an example:
35 °C Ambient temperature, 2000 m3/hr Rated flow, 0.7 bar(g) Pressure
Considering the above values, the energy consumed by the roots type blower would be 61 kW with an air discharge temperature of 125 °C. With a screw blower, 43 kW of energy is consumed with an air discharge temperature of 94 °C.
On average, screw blowers contribute to 35 to 40% energy savings per year.
This makes them better for low-pressure industrial applications. Their total cost of ownership is usually lower than a roots type blower.
In addition, rotary screw air blowers can benefit from variable speed drive (VSD) technology.
This is because VSD equipment matches its motor speed to the air demand instead of always operating at maximum speed. As a result, energy consumption and cost are reduced.
In a nutshell, screw blowers are great energy savers. They produce less heat, making them both cost and energy efficient. This means they are a great choice for low-pressure industrial applications.