Energy saving with existing vacuum systems using liquid ring pumps

The right condition and correct operation of vacuum systems is a key to the overall paper machine productivity – in terms of reliability as well as in terms of efficiency and energy costs. 50% of energy saving are possible, with a mosaic of optimization measures. We will eventually reduce the rotating speed of the liquid ring vacuum pump by 30% (x 0.7) and consequentially reduce the power absorbed by 50% (as 0.7 x 0.7 = 0.49). We take advantage of leverage: the suction capacity is proportional to the rotating speed, but the power absorbed increases (or decreases) exponentially. It is not new: in the 90s replacing 25 year-old liquid ring pumps through new one, we could reduce the specific consumption and save 50% of energy but this issue became nowadays more and more important.

Some relevant topics

A bunch of relevant questions leads to good practices, energy saving and improved reliability: how much vacuum do we really need? How to produce it? It is about materials of constructions, about water recycling and fiber recovery, etc. for this we have selected a few frequently asked questions.

VAKUO focuses on demanding applications, like paper manufacturing, where a reliable technology is required

When to repair, restore or rebuild a vacuum pump?

We recommend measuring the performances of each vacuum pump on a regular basis, ideally once a year and offer surveys including capacity test and endoscopy. Measuring and collecting data is our first step (and priority) to be able to analyze and optimize.

Repair or replace the vacuum pump? Is it the right pump for this service?

An 100 KW-pump can often save or waste 30 KW. They cost 30 KW x 12.5 Ct/KWh x 8,000 h/a = 30,000 euro/year, which is the price for a new pump. The price for repair or for a new pump is negligible compared to the potential energy saving.

Why does the efficiency of LRVPs decrease?

Wear of critical areas, because corrosion or abrasion, will affect the critical clearances. The worst solution is to increase the rotating speed to compensate the loss of capacity.Deposits of fiber, fillers, scale, etc. will clog the internal paths creating a backpressure leading to an increased power draw.

What is a good efficiency for a vacuum system?

1 KW/m³ min is our target, with pumps that are in good condition and are properly selected for the services. The liquid ring pumps, cooling and condensing at the inlet, take advantage of the “condensation effect” and will handle an effectively reduced volumic flow.

Central vacuum or dedicated pumps?

A system with dedicated pumps for each service (each vacuum) is more efficient as we avoid an expansion, which creates an additional volumic flow: 100 m³/min at -40 Kpa become 150 m³/min if they have to be expanded to -60 Kpa.

Do we need preseparators?

Yes. Because vacuum pumps are compressors, they are designed to handle air and vapors, not to pump liquids. Liquid ring pumps are robust, they can handle water, but in a very inefficient manner: a pre-separator will improve the efficiency as well as the maintenance intervals.

Energy saving using water at a lower temperature?

Yes, but not directly. Using water at a lower temperature, we would just increase the suction capacity of the pump. We will save energy as soon as we reduce the rotating speed (by replacing the small motor pulley or installing a frequency converter).

“Flat sided” (axial) or “conical design” (radial)?

Both designs have advantages, VAKUO offers both. Pumps with “cones” are more robust and more efficient, if we take advantage of the larger ports to recycle more water. The “flat sided” pumps are more versatile and can adapt to different vacua.

Are LRVP’s suitable for variable speed operation?

Yes, especially liquid ring vacuum pumps will take advantage of the above mentioned leverage: adjusting the suction capacity we get an exponential energy saving. We will adapt capacity and vacuum along the lifecycle of the felts.