“Yes, the power withdraw of your mixer is about 1.25 HP!”, the operator confirmed after he took the readings from the mixer VFD HMI.
1.25 HP, it means more than 80% energy saving comparing to the products on the market including one who claimed the most energy efficient.
This is an application to a sludge mixing tank receiving primary sludge and DAF sludge in a WWTP. Previously, a 5 kW submersible mixer was installed. Because the primary sludge (from primary clarifiers) contain some sand/grit, there was serious solids settlement in the tank ( it was once observed about 5~6 ft high sludge settlement along the wall). The tank has been taken out of service for a long time ( at least 4 years).
To solve the problem, the same mixer supplier proposed a large product with 17 kW motor. The client also got proposals from two other suppliers providing different type of mixers. Both mixers require install baffles to the tank, otherwise the mixers only create vortex with little mixing.
After detailed Life Cycle Cost analysis, High Performance Centrifugal Disperseing Impeller (HPCDI) from Revolmix Processing ltd. was selected.
The HPCDI has superior solids suspension capability. It has been almost operated for a whole year, and no solids settlement in the tank was observed!
Energy saving is just part of the value provided to the plant. There is also a significant Operation and Maintenance saving for the mixer. The client normally pull out the submersible mixer annually doing the cleaning and maintenance. In addition, the plant has to rebuild their submersible mixers every a few years.
The HPCDI is a top entry mixer so the maintenance is change the oil annually, spending about 30 minutes.
The client right now use this sludge mixing tank as a fermenter to produce volatile fatty acid (VFA) for biological nutrient removal. It is estimated about 40~100 kg VFA produced daily.