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

• For increased production in pulp mills, the recoveryboiler is often a bottleneck. Two different approaches todebottleneck the recovery boiler have been investigated in twomodel mills that represent typical Scandinavian pulp mills. As areference approach, the recovery boiler was upgraded. Inconnection with this, the turbine system was also upgraded toenable increased electricity production. As an alternative to thisconventional approach, the load of the boiler was kept constantby extracting lignin from the black liquor in proportion to theproduction increase. To keep the steam balance, the specificsteam consumption at the mill was reduced through steamsavingmeasures to such an extent that the amount of steamproduced from burning the lignin-lean black liquor was sufficient.Consequently, the extracted lignin was not needed in-houseand could be sold as a biofuel. The net profit of implementinglignin separation was calculated for different conditions. Theresult was that, depending on the conditions, the lignin pricehad to be 2-17 /MWh for lignin separation to be equallyprofitable as boiler upgrade. With an assumed lignin price ofabout 15 /MWh, the conclusion is that lignin separationshould be an economically attractive alternative for debottleneckingthe recovery boiler. With a high power price and along-term investment strategy, however, upgrading the recoveryboiler and the turbine system can be more profitable.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Pappers-, massa- och fiberteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Paper, Pulp and Fiber Technology (hsv//eng)

Nyckelord

Lignin separation

Capacity increase

Power generation

Kraft pulp mill

Biofuel export

Recovery boiler upgrade

Debottlenecking

Steam savings

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