Flexible and efficient: Nash supplies a vacuum system for the new PM2 paper machine at Zellstoff Pöls

Zellstoff Pöls, in Austria, is the largest manufacturer of high quality, chlorine-free bleached long-fibre sulphate pulp in Central and South Eastern Europe. For the new PM2 paper machine, Nash is supplying the vacuum system for dewatering in the wire section and the press section.

PM2 was a turnkey project, with the vacuum system and implemented technology specified by the paper machine manufacturer. Nash was in continuous contact with the paper machine manufacturer during the tender phase. Together, they developed the optimal solution for this challenging task, and the flexibility of the Nash solution and its energy efficiency eventually impressed and won over the customer.

Flexibility for the vacuum

Many paper machines produce only a single paper weight (e.g. 80 g/m2 , similar to copy paper) or weights within a very tight range. In such cases, only minor modifications to vacuum requirements are needed as production conditions, and thus the vacuum levels themselves, are kept relatively constant.

In contrast, the Zellstoff Pöls PM2 focuses on "MG" or "machine glazed" papers (a paper with very high strength), and incorporates the production of paper basis weights between 28 and 120 g/m2 . This wide product spectrum places high demands on the flexibility of the vacuum system, as the method of drying has to adapt to each paper grade.

For Gardner Denver Nash, the project represented an ideal opportunity to prove its high level of expertise in vacuum systems for paper machines. The major challenge was adapting the vacuum at the various suction points for each specified paper weight and the required drying needs. This was accomplished through the use of frequency converters that allowed for "fine adjustment" of the speed and the vacuum level to meet the specific requirements of the paper grade produced. The customer provided the list of vacuum requirements, but the specification of suitable pumps, the determination of the number of pumps and their assignments to the various suction points were the responsibility of the Nash team in Nuremberg.

In a first step, the required number and capacity of the liquid ring vacuum pumps were calculated for ensuring the requisite operational flexibility of the vacuum system. It had to be taken into consideration that strongly fluctuating vacuum levels are often applied at the various suction points in accordance with the grammage to be produced. All Nash pumps are driven with a frequency converter for "fine adjustment" purposes. In this way, the motor and pump speed - and thus the vacuum level of the pump - can be exactly controlled and precisely adapted to the specific requirement.

Efficient use of energy

An important reason that the Nash concept was accepted was the energy efficiency of the machines implemented. Optimal dewatering of the paper in the Forming and Press sections (where Nash vacuum pumps are used) reduces energy (steam) consumption in the Dryer section.

The customer’s specification was clear; focus on energy efficiency. Efficient operation of both the paper machine and the vacuum system result in lower energy consumption and lower operating costs. The alternative concept (low purchase costs that result in high energy costs over the operating life) was not deemed interesting by the customer.

The project covers a scope of supply of five 2BE4 pumps of various sizes, all operated with frequency converters. The pumps will be provided in standard cast iron material construction with polyisoprene coating.

Finally, the decision that Nash was the superior vacuum supplier for their new paper machine was due to convincing arguments from about the product’s flexibility, energy efficiency and insensitivity to water.

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