Increased capacity in kraft pulp mills: Lignin separation and reduced steam demand compared with recovery boiler upgrade

For increased production in pulp mills, the recovery is often a bottleneck. Two different approaches to the recovery boiler have been investigated in two mills that represent typical Scandinavian pulp mills. As a approach, the recovery boiler was upgraded. In with this, the turbine system was also upgraded to increased electricity production. As an alternative to this approach, the load of the boiler was kept constant extracting lignin from the black liquor in proportion to the increase. To keep the steam balance, the specific consumption at the mill was reduced through steamsaving to such an extent that the amount of steam from burning the lignin-lean black liquor was sufficient., the extracted lignin was not needed in-house could be sold as a biofuel. The net profit of implementing separation was calculated for different conditions. The was that, depending on the conditions, the lignin price to be 2-17 €/MWh for lignin separation to be equally as boiler upgrade. With an assumed lignin price of 15 €/MWh, the conclusion is that lignin separation be an economically attractive alternative for debottlenecking recovery boiler. With a high power price and a-term investment strategy, however, upgrading the recovery and the turbine system can be more profitable.