The best use of steam - Metso Paper's technology for mechanical steam separation is designed to give environmental and energy benefits

February 2008
By Ulf Eriksson

Considerable volumes of steam are produced in the making of mechanical pulp. The moisture content of the chips is one generator of steam; the amount of energy applied when refining the chips to pulp another.

Harnessing the energy content of the steam is very important. This is achieved by separating the pulp from the steam in a separator. The steam is then carried to a steam reclaiming system to be used elsewhere in the pulp or paper mill.

The traditional method for separating pulp and steam has been via pressure cyclones. A new approach has been introduced that instead of using cyclones uses mechanical separators for different positions in the process.

PeriFeeder installed at Norske Skog Skogn, Norway

Why change?

A mechanical separator offers considerably better separation efficiency, according to manufacturer, Metso Paper. Since a negligible amount of fiber accompanies the steam, the problem of operating stops for cleaning the heat exchange system is minimized. A dirty heat exchange system results in a large amount of energy being discharged directly into the air and wastewater together with accompanying fiber. With a cleaner system, energy consumption is reduced and the environmental impact lessened.

The mechanical separator is much smaller than a pressure cyclone. It can be positioned at the stage between the refiners to replace several pieces of equipment such as the pressure cyclone, cyclone discharger and the refiner feeder. Metso Paper has found that a refiner being fed by a mechanical separator can be run with more stable disc clearance leading to longer refiner segment service life.

Pulp loses brightness at high temperatures. To compensate, chemicals must be added at the subsequent bleaching stage. Since retention time in the separator can now be cut by approximately 30 seconds, results indicate that this loss of brightness has been virtually eliminated and chemical use reduced.

PeriSplitter at Papier Masson, Gatineau, Canada

Installations

Metso Paper has installed its PeriFeeder and PeriSplitter mechanical steam separators at several mills and in various positions (Table 1).

Ulf Eriksson is marketing manager, Metso Paper. For more information email: ulf.eriksson@metso.com

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