Water Treatment/Compressors A New Compressor Becomes a Fresh Breath for an Water Treatment Old Plant

Author / Editor: Cristina Cavazzini* / Dominik Stephan

Even in water treatment, the make it or break it factor might be in the air supply. And compressors can make the difference — To much of anything can make you sick: Oversized plants are a common problem in water treatment applications. Working hand in hand with technology experts and supplying companies can be the key for an efficient re-design process.

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Keep an eye on air supply - an oversized setup and inefficient compressors should be taken care of.
Keep an eye on air supply - an oversized setup and inefficient compressors should be taken care of.
(Picture: Loris Canovi)

An air production system that's oversized in relation to the treated load cannot be efficient from the cost and energy consumption viewpoint — In that case, reviewing the plant set-up might be the way to go. With that consideration in mind, the Iren Group, a multi-utility energy company, set its sights in the restructuring of its own water treatment system for urban sewage. The goal was the revision of a waste water plant serving the municipalities of Rubiera and Scandiano in Italy with a population of 45,000 – and Iren’s partner of choice were the technology experts Robuschi.

Overdimensioning: A Common Problem With Water Treatment

The water line of the Rubiera system is formed of four parallel lines, each initially supplied by its own compressor for generating process air in the oxidisation/nitrification compartment. The thorough renovation of this part of the system highlighted some discrepancies.

“The original set-up”, explains Loris Canovi, head of waste water treatment in the Emilia area at Ireti, a company of the Iren Group, “was discovered to be oversized for the actual demands for oxygen in the tank, necessary for supplying the respiration process for the biomass and for the oxidation of the organic components and the ammoniac nitrogen.” During the checks, it was observed that there were very large variations in the use of air during the day, in relation to production. This meant high residue and wasted energy. Basically, the line set-up didn't allow the machines to lower their production below a certain threshold and, as a result, the amount of oxygen supplied was excessive for the requests of the lines themselves for long periods of the day.

Step by Step Integration

The Iren Group designed and built a system for controlling air production, combined with Ro­buschi technology that, with an innovative compressor never before installed, made it possible to improve system performance.

“The first step was to change the set-up, linking all the machines together. It was seen, in fact, that it would have been sufficient to use only one compressor for generating the process air during the period of less demand, but that compressor had to be very versatile and offer a wide range of capacity variations.” This was a fundamental condition as, in the Rubiera system, the variations can cover a wide spectrum from 600 m3/h up to 3000 m3/h during the period of maximum demand. This is where Robuschi technology, with the new permanent magnet screw Robox Energy WS 85, came into its own.

The Flexibility Edge

Iren and Robuschi technicians worked side by side during the project to refurbish the Emilia wastewater treatment system. “We began with a prototype, the WS 65, and then moved on to a solution with dimensions more in keeping with the system requirements. As a result, we chose select the size WS 85” explains Canovi. The Robuschi technology showed straight away that it possesses the operating flexibility necessary for the requirements of the sewer plant, as it allows the compressor to be switched on and off as needed without creating any problems connected to start-up; this is a feature that other technologies don't have. “This flexibility, which supports the process and know-how without invading them, is a great advantage and a unique feature that can be considered advanced in terms of energy savings.”

The goal was to reach the ideal solution that permits the system not to waste electricity, and it was reached by adopting a control system with a logic implemented by the Iren technicians. Robuschi then improved the solution, adapting it to the specific context. As Canovi explains, the next step will be to combine the new logic with air production division. “To supply the system in moments of higher demand, we'll probably need another unit with a power rating lower than the WS 85 to meet and guarantee the demand with the utmost flexibility in all load situations.” The Rubiera system has been operating with the final layout (the new structure combined with Robox Energy WS 85) for nearly six months and, even if it's still too soon to verify the effective advantages of this new configuration, the initial data can already be assessed.

Energy Consumption Halved

“Thanks to the electricity measurement units that were already installed to measure the energy consumption of the compartment with the old system configuration, we've been able to monitor the electricity consumption as the project proceeded. As a result, we've seen that the new logic resulting from the Iren control system (making it possible to switch off the machines when not in use) meant a 30 % reduction in the electric consumption of the compartments compared with the original configuration, and by installing the size WS 85 we've obtained a further reduction of 20 % in air generation alone, for total energy savings of 50 % for the compartment”, Canovi adds.

This level of reduction in consumption for such a significant cost item as energy is, in itself, a praiseworthy achievement. It can still be improved however, the expert thinks: “The excellent level already reached can be increased by a few percentage points more if we improve some system components, such as the size and efficiency of the permeable mat for the air supply. These are just simple operational measures, but they can raise even further the already high level that we've reached with the refurbishment.”

* * The author is Marketing Specialist at Robuschi/Gardner Denver.