MATERIAL & ENERGY FLOWS – A SERIES OF BY-PRODUCT SYNERGY PROJECTS.

It is important to understand initially that water is a scarce resource in this part of Denmark and is therefore systematically valorised. As we mentioned above, in order to reduce consumption of ground water, Lake Tissø has become the main source of water for the industrial partners in Kalundborg. The reduction in the use of ground water has been estimated at close to 2 million cubic metres per year (Christensen, 1999). However, in order to reduce overall water consumption by the partners, the Statoil refinery supplies its purified wastewater as well as its used cooling water to Asnæs power station, thereby allowing this water to be "used twice" and saving additionally 1 million cubic metres of water per year. Asnæs power station supplies steam both to Statoil and Novo Nordisk for heating of their processes. By functioning in a co-generation mode, the power station is able to increase its efficiency. Excess gas from the operations at the Statoil refinery is treated to remove sulfur, which is sold as a raw material for the manufacture of sulfuric acid, and the clean gas is then supplied to Asnæs power station and to Gyproc as an energy source. In 1993 Asnæs power station installed a desulfurisation unit to remove sulfur from its flue gases, which allows it to produce calcium sulfate (gypsum). This is the main raw material in the manufacture of plasterboard at Gyproc. By purchasing synthetic "waste" gypsum from Asnæs power station, Gyproc has been able to replace the natural gypsum that it used to buy from Spain. In 1998 approximately 190,000 tons per year of synthetic gypsum were available from the power station. Novo Nordisk creates a large quantity of used bio-mass coming from its synthetic processes and the company has realised that this can be used as a fertiliser since it contains nitrogen, phosphorus and potassium. The local farming communities use more than 800,000 cubic metres of this liquid fertiliser each year as well as over 60,000 tons of a solid form of the fertiliser. Finally, residual heat is also provided by Asnæs power station to the district heating system of the town. The system functions via heat ex-changers so that the industrial water and the district heating water are kept separate.