Energy Export Opportunities from Kraft Pulp and Paper Mills and Resulting Reductions in Global CO2 Emissions

Doktorsavhandling, 2008

With increasing energy prices and increasing demand for CO2-lean energy sources, energy savings in the pulp and paper industry become ever more relevant. Significant energy savings in kraft mills can be made by e.g. improved heat integration and installation of an energy-efficient evaporation plant. The heat integration can be improved by solving pinch violations or by extracting high-temperature excess heat that can be used in a specially designed evaporation plant. In this study, these two approaches were applied to different model mills: a market pulp mill and an integrated fine paper mill (both with a pulp production of 1000 ADt/day). In the market pulp mill, both approaches for heat integration resulted in steam savings of about 4.5 GJ/ADt (26% of the steam demand) for an investment cost of about 10 M€. Owing to inherent process differences, the steam savings were about 15% lower for about 20% higher investment cost in the integrated mill. The methods and basic results have also been verified in a case study of a real market pulp mill. The energy savings enable an increase of the electricity production by about 120 GWh/year (about 50%) in both the market pulp mill and the integrated mill. As an alternative to increased electricity production, the use of internal biofuel can be decreased, enabling export of about 450 GWh/year of lignin from the market pulp mill (requiring that lignin is separated from the black liquor) or about 415 GWh/year of bark from the integrated mill. The economy for electricity and biofuel export depends mainly on the energy prices and investment costs. With expected future energy prices, both approaches can be profitable in the integrated mill. In the market pulp mill, electricity production seems to be the most robust alternative due to the investment and operating costs related to a lignin separation plant. However, lignin separation decreases the load of the recovery boiler and can thus be a cost-effective alternative for debottlenecking the recovery boiler in a case of increased pulp production. Since no fossil fuel is used in any of these mills, the energy export does not change the net CO2 emissions from the mills. Instead, the reductions in CO2 emissions will be off-site, where fossil fuel or fossil-fuel-based electricity is substituted. The potential for reductions in global CO2 emissions for a future situation were assessed by using four energy market scenarios. The total potential, if applied to all kraft pulp and paper mills in Sweden, is comparable with the Swedish goal for reducing the CO2 emissions by 2.9 million tonnes during 2008-2012 (based on the emissions in 1990).