Papermaking is an extremely energy-intensive process, because huge amounts of water have to be extracted from the fibre as the slurry is turned into a web and dried. In a series of steps mechanical and physical methods are used to turn a 0.2 % suspension of fibre in water into paper with 93 % dry matter. These steps are primarily responsible for energy consumption in papermaking.
To improve energy efficiency significantly, innovative technologies are needed to improve the water removal and drying steps. As part of the project “Integrated Ecopaper” the papermaker Mondi Frantschach GmbH is now developing a new energy-efficient process to make high-grade packaging papers using local renewable raw materials. Manufacturing a tonne of sack paper consumes 0.9 MWh of electricity and 1.7 MWh of thermal energy, all of which Mondi Frantschach is already providing from biomass. The pioneering process relies on intelligent sensors and new system approaches, and is expected to yield substantial energy savings.
Improving the water removal process
The energy-intensive process of removing water is spread over three sections (“wet end”, “press section” and “dryer section”). Starting from new research-based insights, the aim is to make the individual process stages more energy-efficient and match the three sections to each other better, using a holistic approach.
The project partners are the Institute of Paper, Pulp and Fibre Technology at Graz University of Technology and Wood K plus, a competence centre. The main thrust: applying new techniques to shift the process limits such that the water content at the end of each stage is lower than previously achieved. Shifting water removal toward the “wet end” and the “press section”, which consume comparatively little energy, is intended to reduce energy consumption overall.
Savings are achieved in terms both of electricity and of thermal energy. Total electricity savings in the sectors wire drive, press drive and vacuum pumps are planned to add up to more than 1600 MWh/year; measures taken in the sectors process air, steam, wire and press (where more water is to be removed) are planned to save more than 4000 MWh/year of thermal energy.
Improvements in 3 process stages
Using dry strength agents and flocculants to improve water removal in the “wet end” can result in significant energy savings. This approach, already tried and tested for other types of paper, is to be tried out and adapted for sack papers as part of the project. In the press section an improved design of felts increases the amount of water removed in the press, while reducing energy consumption for drives and suction boxes. In the drying section improved control of steam pressure by means of model-predictive control (MPC) is expected to result in energy savings.
