Effect of Lignin Separation to Black Liquor and Recovery Boiler Operation, 2009 TAPPI Engineering, Pulping, Environmental Conference

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Many kraft pulp mills have a desire to increase their production capacity. Often in such cases the recovery boiler is one of the bottlenecks. Recently lignin recovery from black liquor technology has become available that promises increased pulp mill capacity and can help to achieve a completely fossil-fuel free mill.

The separation of lignin is an option that is considered by the pulp mills for several reasons. Firstly, the heat transfer capacity of the recovery boiler is often a bottleneck that limits pulp production. Removing part of the lignin from the black liquor decreases the heat load on the recovery boiler and more pulp can be produced. The separated lignin could be used to replace e.g. fuel oil or natural gas in the lime kilns or be combusted in a power boiler if the energy is required. Upgrading lignin to specialty chemicals for materials applicable for e.g. composites, adhesives and barriers is necessary to make lignin recovery as such profitable. Lignin value in upgraded form would be approximately three times the energy value.