Pinch analysis of a model mill: Economic and environmental gains from thermal process-integration in a state-of-the-art magazine paper mill

Artikel i vetenskaplig tidskrift, 2005

A model of a modern magazine paper mill has been investigated from an energy perspective. The mill’s refining process has a power demand of 100 MW (3050 kWh/ADt pulp), and 86 MW of this is recovered as steam. Since the steam demand of the mill is low, there is a steam surplus of 21.5 MW. The steam surplus could be increased by 41 % through thermal process-integration. Simultaneously the cooling demand decreased by 13.2 MW or 49 %, resulting in reduced cooling costs and decreased thermal pollution. The financial evaluation, for which a grass-root situation was assumed, shows promising economy if the mill can sell the surplus heat (e.g. to a district heating system): the marginal payback period for increasing the steam surplus would be less than a year, even with low energy prices. If the surplus steam has to be used on site, power generation in a condensing steam turbine is an option. The financials for increasing the power generation are very dependent on the power price, but with current Swedish power prices the marginal payback period would be 3 to 4 years. Energy exports, whether heat or power, would presumably replace fossil fuel. Consequently, the greenhouse gas emissions in society would decrease by thousands of tons per year. In the future it might be possible to decrease the power consumption in the refining process, resulting in a decrease of the steam surplus. With process integration, the power input can be decreased by 30 % before there is a steam deficit. This option offers a good opportunity for profit as well as decreased environmental impact.