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Energy – How to achieve more with less

One of today’s most important goals for all papermakers is to produce paper with the greatest economical and ecological efficiency. Part of this process in many paper machines is a shoe press, which has proven to provide energy conservation benefits to the papermaking process for more than 25 years.

While felts with their conditioning system, as well as roll covers, are part of the total dewatering system in a press, this article concentrates on the vital and important role of the shoe press sleeve as a very important contributor to energy savings during papermaking.

As far as shoe press sleeves are concerned, one could state that it is not only important to have the most suitable open area and void volume available to reach the highest dryness levels but also to maintain the same level over the entire sleeve life. It is also crucial not to jeopardize other important paper properties, such as moisture profiles or marking. For a constant high level of performance, several characteristics in a press sleeve need to be considered and optimized.

Certainly one of the most important sleeve properties is wear resistance, making sure that the nominal open area/void volume stays the same over the entire sleeve life. Recent material developments for QualiFlex™ QX and QRV show significantly lower abrasion loss (fig.1 and 2) compared to previous standard materials and competitor materials. Field results and investigation of returned samples did show that abrasion is almost eliminated even under the most difficult conditions. Loss of void volume due to abrasion over the sleeve life very often leads to decreased dryness content after the press, which means higher energy consumption or lower machine speed.

QualiFlex fig 1
Another factor influencing the dewatering capability of a press sleeve is the behavior of a polyurethane matrix under load, which is resulting in more or less groove closure. Over a number of years it was obvious that the groove design clearly defined the reduction of void volume and open area of a sleeve. This was valid with previous materials, but the new QualiFlex materials QX and QRV were developed to reduce this effect. Laboratory tests and, more importantly, documented field results revealed that the sleeve material is now influencing groove closure under load much more than the groove design. In fact, with these new materials it does not make a difference which groove type is used.

A comparison of QualiFlex QX material to previously used standard material and competitor materials shows significantly less groove closure, with a difference of up to more than 20% (fig.3)

QualiFlex fig3

Furthermore, the most suitable surface design for a particular shoe press position can improve or deteriorate specific energy consumption. With QualiFlex, Voith Paper can select sleeve surfaces from the widest range of all press sleeve suppliers and then provide highly tailored solutions for any paper or board machine in the world.

Extensive research and field experience enables the application of the most efficient press sleeve for a shoe press. Everyone can understand that a move from a plain to a vented surface will provide advantages in dryness, but even a change from one groove design to another can result in a dryness deviation of 1 - 2%.

To prove this is valid, not only in theory but also in practice, several case studies were performed. For example, on a board machine running at a slow speed, a vented surface was used after a plain sleeve. With the same specific steam consumption, the machine speed was increased by 10% or 30 m/min. This machine is now running at higher production rates than ever before, and the mill has reduced specific steam consumption at the same time. In this case, the energy saving was approximately 4 % and is equivalent to a gain in profit of € 500.000/year.

On a high-speed machine producing Copy paper at 1.600 m/min the mill experienced from groove closure and reduced dewatering a significant speed reduction and on top of that a dryness loss of 2-3 % at the same time. In this case the paper mill calculated a loss in production of ~ € 58.000 per day.

QualiFlex – developed with Voith Paper’s research and development capability, papermaking knowledge as part of a full-scale supplier, and broad experience from more than 5,000 operated press sleeves – can help significantly reduce energy costs and improve profitability for papermakers.

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