A fit-for-purpose vacuum system and efficient doctoring and dewatering solutions for forming and drying sections are the fundamental base for enabling high energy efficiencies coupled with low cost pulp, paper, board and tissue production.
By Jukka Lehto, CEO & Managing Director, Jussi Lahtinen, Sales Director & Patrik Högl, Technical Sales Manager, Runtech Systems Oy
Vacuum usage in a paper machine is used for a variety of reasons. Dewatering the paper sheet is the obvious usage; holding and controlling the route the sheet takes through the press section and conditioning the press felts are other uses of vacuum in a paper machine. Vacuum is also used to hold and control the water jet at a suction roll.
Early paper machine designs did not use vacuum at all, but relied on gravity and press nips to dewater paper. This we refer to as nip-dewatering. Machine speeds were historically much slower than they are today. It is hard to imagine a modern paper machine without a vacuum system, and felt-dewatering is still the most common way to dewater the paper in the press section.
The vacuum levels in a paper machine are typically between 5 and 70 kPa – a relatively low figure when compared to other vacuum applications in, for instance, the chemical industry. The air flows, though, are very high due to the large open areas found in a paper machine.
Vacuum usage, which is a result of air being pulled through a restriction, is an expensive tool; it is one of the top three energy consumers in a paper mill. Historically it has been made available in abundance, and often used in excess. With today’s increasing cost of energy, paper mills are demanding reduced operational costs to help with their competitiveness. Therefore, it makes sense to review air flow demands and, where suitable, apply old school thinking, i.e. nip-dewatering rather than felt dewatering.
High speed motors, developmentdriven by frequency converters, allows a typical RunEco blower to provide paper machine vacuum levels between 30 and 70 kPa. A wider range of impeller designs allows highly efficient levels across the operating range. This means that the amount and the usage of throttling valves can be reduced to a minimum. The result is energy savings of 30 to 70% when compared with traditional vacuum systems.
furthermore, Ecopump turbo blowers operate without the need for sealant liquid (water), thus contributing to water savings in a paper mill.