At a paper mill in Sweden, about 200 km west of Stockholm, an energy efficient pulp drying system was crucial.
The system chosen uses a pressurized superheated steam dryer to dry the pulp. The internal steam cycle of this dryer is superheated by a heat exchanger.
Exhaust steam from the dried pulp is used as a heat source to produce clean steam in a so called “Reboiler”. This steam is now compressed with two Spilling steam compressors to supply the heat source for the dryer. Overall, the dryer/ steam compressor combination is a self-suppling system, no additional steam from an external source is required. The only heat source input into the drying process is the electrical power demand to drive the two compressors.
The described solution with the pressurised dryer and steam compressor for steam recycling is ideal for the mill. Not only is it very energy efficient, the electricity is also comparably cheap and fossil free, since they are using large-scale hydropower.
In practice, the steam compressors have a better delivery rate than expected, and consume 10% less electricity than anticipated.
This, and the recycling of the steam, lead to CO2-savings of around 14,000 tonnes per /year.
