Increased capacity in kraft pulp mills: Lignin separation and reduced steam demand compared with recovery boiler upgrade
Artikel i vetenskaplig tidskrift, 2006
For increased production in pulp mills, the recovery
boiler is often a bottleneck. Two different approaches to
debottleneck the recovery boiler have been investigated in two
model mills that represent typical Scandinavian pulp mills. As a
reference approach, the recovery boiler was upgraded. In
connection with this, the turbine system was also upgraded to
enable increased electricity production. As an alternative to this
conventional approach, the load of the boiler was kept constant
by extracting lignin from the black liquor in proportion to the
production increase. To keep the steam balance, the specific
steam consumption at the mill was reduced through steamsaving
measures to such an extent that the amount of steam
produced from burning the lignin-lean black liquor was sufficient.
Consequently, the extracted lignin was not needed in-house
and could be sold as a biofuel. The net profit of implementing
lignin separation was calculated for different conditions. The
result was that, depending on the conditions, the lignin price
had to be 2-17 /MWh for lignin separation to be equally
profitable as boiler upgrade. With an assumed lignin price of
about 15 /MWh, the conclusion is that lignin separation
should be an economically attractive alternative for debottlenecking
the recovery boiler. With a high power price and a
long-term investment strategy, however, upgrading the recovery
boiler and the turbine system can be more profitable.
Lignin separation
Capacity increase
Power generation
Kraft pulp mill
Biofuel export
Recovery boiler upgrade
Debottlenecking
Steam savings