Future CO2 removal from pulp mills – Process integration consequences

Earlier work has shown that capturing the CO2 from flue gases in the recovery boiler at a pulp mill can be a cost-effective way of reducing mill CO2 emissions. However, the CO2 capture cost is very dependent on the fuel price. In this paper, the potential for reducing the need for external fuel and thereby the possibility to reduce the cost for capturing the CO2 are investigated. The reduction is achieved by using thermal process integration. In alternative 1, the mill processes are integrated and a steam surplus made available for CO2 capture, but still there is a need for external fuel. In alternative 2, the integration is taken one step further, the reboiler is fed with MP steam, and the heat of absorption from the absorption unit is used for generation of LP steam needed at the mill. The avoidance costs are in both cases lower than before the process integration. The avoidance cost in alternative 1 varies between 25.4 and 30.7 EUR/tonne CO2 depending on the energy market parameters. For alternative 2, the cost varies between 22.5 and 27.2 EUR/tonne CO2. With tough CO2 reduction targets and correspondingly high CO2 emission costs, the annual earnings can be substantial, 18.6 MEUR with alternative 1 and 21.2 MEUR with alternative 2.