The dramatic rise in energy costs, emissions trading as well as pressure to increase profitability, have pushed energy efficiency to the forefront for tissue makers.
Tools for reaching energy targets
At Metso, Best Available Technology (BAT) and Best Operational Practices (BOP) are ongoing processes for helping tissue makers clearly define their product range and for assisting them in designing optimal, energy efficient production systems.
BAT models are important tools for determining the potential of energy reduction in the various process areas in a tissue line. At Metso such a model involves a state-of-the-art high-speed Advantage DCT 200 tissue machine, running at 2000 m/min. The target for this machine concept, when running at 100% energy efficiency, is to operate below 2000 kWh/ton or at about 30 to 35% less than most machines operates today.
Energy reductions since the Tissue World Conference 2007
By using new process solutions and energy efficient equipment described below, Metso has reduced the total energy consumption in tissue lines by 20% from 2 850 kWh/ton to 2 280 kWh/ton.
Smart design in stock preparation, an optimized layout of the building and an alternate process solution with reduced number of pumps plus reduction of chest sizes have cut energy consumption. Eliminating gear boxes for refiners and a new type of refiner segment also contribute to energy reduction in this area.
The elimination of secondary screening and an improved headbox design are the main reasons for reduced energy consumption in short circulation. Increasing of after press dryness, Yankee head insulation and increased exhaust humidity has trimmed energy consumption in drying.
New drive systems and reduced drag load have diminished consumption in drives. Replacing conventional water-ring pumps with turbo blowers has reduced consumption in the vacuum system.
In spite of these advances, Metso continues to develop and implement new technology to move beyond these current energy consumption reductions.
New forefront technologies
NTT press technology designed to improve solids content to as much as 47%, which gives an additional 12-14% reduction in drying energy consumption. A turbine positioned in the forming section can reduce electric power consumption by about 10%, when at least 50% of the energy from the slice jet flow is recovered to produce electricity. Positioning a steam generator directly after the hood, but before the air/air heat exchanger enhances the overall efficiency of the heat recovery system.
“At Metso our target is to reduce energy consumption without sacrificing productivity or quality,” says Borje Sandgren, Product Manager Energy, Tissue Business Line.
