Energy is the largest operating cost to a wastewater treatment plant with the energy consumed in running blowers for aeration often cited as the largest of all the energy consumers. With electricity prices continuing to rise, reviewing the energy efficiency of a blower is imperative in selecting the correct blower for any given application - especially when you consider that the energy costs of a blower can account for up to eighty percent of its total lifecycle costs. The type of system and equipment an operator chooses is therefore by no means inconsequential.
Various solutions are available for low pressure systems and the right solution will depend on the specific application. The most common and widely used solutions are rotary blowers and screw blowers - each with their own unique strengths that are ideal under certain conditions.
Two different compression methods exist in principle:
Isochoric compression refers to the process whereby compressed air is delivered without having been compressed inside the blower block. The volume of air inside the block remains constant. This well-known method is the one used by rotary blowers.
The rotors inside the block have a continuous straight-line profile. Rotary blowers draw a certain volume of air into the working chamber, then rotate further to close this chamber and deliver the unchanged volume of air to the outlet side for discharge. The only reason pressure increases to a maximum of 1000 mbar is because the compressed air flows back.
Rotary blowers can deliver air at up to 1000 mbar gauge pressure and have displacements of between 200 and 9000 m3/h.
Screw blowers on the other hand work on the principle of internal compression. Here the volume of air is reduced while it is inside the blower airend.
They have been available for a number of years and it has now become possible to apply the compression technology used for compressors - which normally covers higher pressures - to blowers.
Screw blowers typically deliver pressures of up to 1100 mbar. Because screw blowers normally operate more efficiently, their life cycle costs can be up to thirty percent less than rotary blowers since power costs are lower.
What makes this possible is the aforementioned internal compression in the screw airend. Unlike those in rotary blowers, screw blower rotors are twisted and continuously reduce their air volume enclosed in the airend. In addition, screw blower rotors can turn at higher speeds, which improves efficiency.